Djouani Razika

Advanced study on the extraction of Nickel from its ores

Keywords: Nickel extraction, laterite ores, sulfide ores, Ni secondary sources, leaching

Introduction 2. Nickel production process 2.1.Laterite processing 2.2.sulfide processing 2.3.Ni Secondary resources 3. Disadvantages and alternative technologies 4. Strategies to improve nickel extraction 5. Conclusion and recommendation

Introduction

Nickel is a normally happening metallic component with a gleaming white sparkly appearance. It is the fifth most basic component on earth that happens broadly in its outside layer and center with a wide appropriation in nature as it tends to be found in air, water, and soil under different mineral structures. Nickel is mined from two sorts of minerals: laterites and sulfides. Albeit about 70% of the mineral stores are found in laterite metals, just about 40% of the nickel generation is from laterites. Laterites are for the most part used to create ferronickel, which is utilized straightforwardly in steelmaking. Some laterite metals are utilized to make softening evaluation nickel and nickel matte while sulfides are refined to deliver highgrade nickel. It is a characteristic asset that can't be expended like numerous different metals; it is completely recyclable where it very well may be reused over and over without loss of value, adding to the round economy model (CE).

The world is getting progressively reliant on nickel, as it has numerous mechanical and business employments. Most nickel is utilized for the creation of hardened steel and other nickel composites with high consumption and temperature opposition. Nickel metal and its compounds are utilized generally in the metallurgical, substance and nourishment handling ventures, particularly as impetuses and shades. (McCllveen and Negusanti, 1994), these requests have outpaced the worldwide pace of monetary development which prompts a deficiency of Nickel and numerous basic minerals wares.

So to defeat it just as to verify long haul reasonable supplies for its eager financial improvement technique; numerous nations governments over the world entitled various research projects to productively create, use nickel assets just as grow proficiently, green nickel generation innovation and began to build their attention on the preparing of the colossal stores of nickel rich laterite minerals due to declining worldwide stores of nickel sulfides. There are 2 main hydrometallurgical processes: high-pressure leaching (HPAL) and atmospheric acid leaching.

Nickel laterite processing

A majority of pyrometallurgical processes (ferronickel and matte smelting) use standard flowsheet involving drying, smelting, calcining/reduction, and electric furnace.

The 2 principal hydrometallurgical methods presently practiced are the Caron method and the HPAL process. Generalized block flow diagrams for the processes are shown in figure 3.

Pyrometallurgical process

A review for pyrometallurgical processes for laterite ores has been done by Bergman In conventional pyrometallurgical processing, the ore is dried, calcined (and sometimes reduced) in a rotary kiln and smelted in an electric furnace in the presence of carbon. If matte is the desired product, then sulfur is added to the kiln. The crude metal/matte is further processed/refined to produce the final product.

Pyrometallurgical processes are energy-intensive since all of the free moisture and combined water has o be removed in the process and all of the material has to be first calcined and then melted to form a slag at about 1600°C. This requires both hydrocarbon fuels (coal, oil or naphtha) and electric power.

Hydrometallurgical Processes

A review of hydrometallurgical processes for laterites has been done by Reid and

Barnett (2002). A general description is provided by Simons (1998)

a) Caron Process

The Caron process could be used for limonitic ores or a mixture of limonite and saprolite. The ore is dried and nickel is selectively reduced (together with cobalt and some iron) to metallic nickel at ~ 700°C. The metallics are extracted by leaching in an ammoniacal solution. Recovery of nickel and cobalt decreases with the increasing amount of saprolite since nickel and cobalt are locked in a silicate matrix and are difficult to reduce at this temperature.

The Caron process suffers from several disadvantages: The front-end of the Caron process is pyrometallurgical involving drying, calcining and reduction. These steps are energy-intensive. The back-end is hydrometallurgical requiring various reagents. The nickel and cobalt recoveries are lower than for the smelting processes or the HPAL process.

b) HPAL process

The chemistry of the HPAL process has been reviewed by Whittington and Muir (2000). Mixed ore is briefly slurred and heated at 250-225 C in a titanium-clad autoclave by steam and sulphuric acid injection, and nickel and cobalt are extracted into an acidic solution together with iron and aluminum. At such high temperatures, iron and aluminum hydrolyze and precipitate as hematite and a range of mixed alunite / jarosite phases, depending on the leaching conditions. This hydrolysis generates acid and reduces the overall acid consumption of the HPAL process, leaving approximately 50-60 g / l of free acid in the leaching solution.

The leach slurry is " flashed " from the autoclave, the solids are separated from the liquor by counter-current decantation (CCD), the liquor neutralized to remove iron (III), aluminum and chromium (III) and the soluble nickel and cobalt are subsequently

processed. (McDonald and Whittington 2007)

The pressure leaching is carried out either in Pachuca tanks (Moa Bay) or titanium lined autoclaves (all modern plants). Leach temperatures vary in the range of 245 to 270°C. Solid-liquid separation is carried out by Counter-Current Decantation (CCD).

There are various ways of purifying the nickel-containing solution and separating nickel and cobalt. In modern plants, such separation is carried out by solvent extraction (SX). Final products produced are electro-nickel, nickel oxide or nickel briquettes. Some plants produce intermediate materials (mixed sulfides or mixed hydroxides) that are refined elsewhere.

Other hydrometallurgical processes

Several newer processes are currently being piloted and evaluated. These include: c) AL: Atmospheric Leaching-Similar to the leaching step described above for saprolite. Atmospheric leaching (AL) at a lower temperature (~ 90 C) and in open vessels avoids the need for expensive HPAL autoclaves. The difference between HPAL and AL is the last one on atmospheric pressure. The caron process is both pyrometallurgical and hydrometallurgical and can be applied to limonite and transition layers. This process involves first drying and calcinating / reduction (pyrometallurgy) and then a leaching process using an ammonia solution. The ion exchange technique may be used in the next step when a purification process is HPAL processes require predominantly limonitic ores; in the case of the dry laterites, they contain nontronite and/or smectite. Generally speaking the ores:

• contain some saprolite

• have lower Mg-usually limited to <4 % (At higher Mg acid consumption is higher)

• require lower Al content (clays are high acid consumers; therefore the Al content should not be too high)

The case for AL vs. HPAL has been under discussion for many years and gives rise to a substantial list of relative strengths and weaknesses as summarized in Table 3.

Considering that the choice between AL and HPAL is an economic one relating to the cost of acid supply, mineralogy of the ore body and recovery trade may not represent a shift in the development of the quantum process and other factors, particularly those related to infrastructure, may require significant improvement. It is clear from Table 3 that several considerations must be examined when determining whether AL is a viable processing option.

d) EPAL Process:

This includes an additional leaching step for saprolite using residual acid from the HPAL step (+ added acid). Saprolite is leached at atmospheric pressure and is a high acid consumer (believed to be up to 1 t acid/t ore). This process can consume more saprolite than the conventional HPAL process. This is currently being piloted by BHP-B for Ravens Thorpe. e) Acid Heap Leaching (for saprolitic ores) Heap leaching is a low-cost technology used in industrial mining to recover precious metals such as gold and uranium, along with several other highly sought-after metals such as copper, from their primary resources (ores and minerals). There has been a growing demand for heap leaching for many decades due to its environmental benefits.

Heap leaching provides a benign, effective and economical solution for the environment to mining operators and produces only minor emissions from furnaces. The cost of the heap leaching process is low, making it an attractive option from a financial point of view.

Although early in maturation, heap leaching appears to offer the most cost-effective method for the extraction of nickel from low-grade nickel laterites.

Several companies, including the Yunnan Tin Group, CVRD Inco, and Mirabela Nickel, have examined heap leaching for the treatment of laterite minerals.

In Australia, Metallica Minerals is looking to develop its Lucky Break, Nornico Normally, the case against the hydrochloric acid leaching of nickel laterites focused on the need to use highly corrosion-resistant materials and to control the emission of hydrogen chloride gas. However, there is substantial literature examining the use of hydrochloric acid and many new processes proposed in recent years based on novel chemistry that has only been achieved in strong chloride liquors. (Table 4)

Nickel sulfides processing

Nickel sulfide ores are generally rich in copper, and both copper and nickel are present in the form of sulfides, which are densely embedd ed with each other, and it is difficult to directly separate copper and nickel by beneficiation methods. Most companies currently use Copper Nickel mixed flotation -copper nickel smelting -high ice nickel crushing process. The main pyrometallurgical processes include flash smelting and molten pool smelting. Flash smelting is a high-temperature (1 450 ~ 1 550 ° C) reaction tower that sprays deeply dehydrated powder concentrate from the top of the reaction tower at high speed.

Within the range of 2 to 3 s, the decomposition, oxidation, and melting of the sulfide are substantially completed. The molten pool smelting is through an intermediate process of osmosis, the sulfide concentrate, partially oxidized roasting calcine, return material and appropriate flux and other materials, at a certain temperature (1 200 ~Melting at 1 300 ° C), through a series of chemical reactions, smelting and dissolution processes to form metal sulfides (nickel ruthenium) and oxides (slag). Low nickel bismuth produced by flash smelting and molten pool smelting cannot meet the processing requirements of the refining process, it is necessary to produce high nickel niobium by further blowing. Then, the high nickel niobium is subjected to grindingcopper-nickel flotation separation to obtain copper and nickel concentrate; so that the copper-nickel is initially separated. The obtained nickel concentrate is then smelted and blown by fire. A nickel sulfide electrode is prepared, and finally, electrowinning is performed to obtain an electrowinning nickel. For high-grade copper-nickel sulfide ore, this treatment method is mature and has high production efficiency. Figure 3 shows the process flow for the production of high nickel bismuth from a typical nickel sulfide ore (China Jinchuan Company)

Hydrometallurgical Process

The hydrometallurgical process of nickel sulfide ore was developed in the 1970s. There are two kinds:

1. Soluble anodic electrolytic refining, crude nickel anodic electrolysis and nickel sulfide anodic electrolysis.

Selective leaching -clean liquid -electrowinning.

The second process develops rapidly, and depending on the electrolyte system, the selective leaching-cleaning-electrowinning process can be divided into a chlorinationcleaning-electrowinning process and a sulphuric acid cleaning-electrowinning system.

(Sahu 2008, Yang et al.2012)

In the process of producing refined nickel by chlorination-cleaning-electrowinning, due to the high chemical activity of chlorine and chloride, the generated chloride has a large solubility and strong complexing ability for impurities, so at normal temperature and pressure, high nickel, cobalt, and copper in the crucible can enter the solution.

By adjusting the relative addition rates of chlorine and feedstock, the redox potential of the leaching can be controlled and a continuous leaching process can be achieved. Within the range of 2 to 3 s, the decomposition, oxidation, and melting of the sulfide are substantially completed. The molten pool smelting is through an intermediate process of osmosis, the sulfide concentrate, partially oxidized roasting calcine, return material and appropriate flux and other materials, at a certain temperature (1 200 ~Melting at 1 300 ° C), through a series of chemical reactions, melting and dissolution processes to form metal sulfides (nickel ruthenium) and oxides (slag). Low nickel bismuth produced by flash smelting and molten pool smelting cannot. To meet the processing requirements of the refining process, it is necessary to produce high nickel niobium by further blowing. Then, the high nickel niobium is subjected to grindingcopper-nickel flotation separation to obtain copper and nickel concentrate; so that the copper-nickel is initially separated. The obtained nickel concentrate is then smelted and blown by fire. A nickel sulfide electrode is prepared, and finally, electrowinning is performed to obtain an electrowinning nickel. For high-grade coppernickel sulfide ore, this treatment method is mature and has high production efficiency.

Ni secondary resources

There are not many significant nickel mineral resources.

Nickel recovery from spent batteries

Glencore, 2017, estimated that more than 10 M electric vehicles will be sold annually in 2025, generating net additional primary nickel requirements of more than 400Kt Ni. This is one of the reasons why the recycling of spent batteries appears to be an attractive option to meet the demand for a nickel while avoiding environmental risks.

Ni extraction from spent catalysts

The extraction of Ni can be carried out efficiently from spent catalysts. The recycling of spent catalysts has become an unavoidable task, not only to reduce their costs but also to reduce waste catalysts to prevent environmental pollution. Although pyro-based processes have been used earlier, recent developments in the processing of such materials have mostly involved hydrometallurgical processes.

The initial composition of nickel catalysts depends on the reaction involved. For example catalyst for hydroalkylation reaction contains other metals such as tungsten, besides nickel. The spent HDS catalysts generally consist of 10-30% Mo, 1-12% V, 0.5-6% Ni, 1-6% Co, 8-12% S, 10-12% C and rest as alumina

Disadvantages and alternative technologies

Overall, each approach has significant issues, some of which are in common with the other processes as well as their process. Specific issues such as high capital costs (PAL, EPAL), high energy consumption (Caron), high acid consumption with certain types of ore (PAL), high corrosion and maintenance costs (PAL, EPAL) and process complexity (PAL, EPAL). Other processes have been tested and, in some cases, implemented for projects. These include high-pressure acid leaching combined with atmospheric pressure agitated leaching (PAL + AL) in the case of EPAL in Ravens Thorpe, and stand-alone atmospheric pressure agitated tank leaching (AL) in Weda Bay, Indonesia, along with heap leaching (AL) in Çalda, Turkey. Other processes using chloride leaching have been tested but have not been applied to the commercial recovery of laterites.

Microbial leaching

Microbial leaching began in the 1950s as a hydrometallurgical process for the dissolution of metals in ore by the catalysis of certain microorganisms. Microbial leaching metal is suitable for the treatment of low-grade and other difficult mineral resources in the metallurgical industry because of its low investment, low cost, simple process, and environmental friendliness. understanding of the underlying mechanisms is needed to improve the efficiency of these processes. In the bioprocessing of minerals, microbes act as catalysts for the leaching of metals from complex minerals or act as pre-treatment agents to alter the mineral structure, making them susceptible to lixiviant or leaching agents.

Microorganisms that play a pivotal role in the bioprocessing of minerals are broadly classified as heterotrophic and autotrophic according to their nutritional behavior.

Heterotrophic microbes are non-photosynthetic; they derive energy from organic carbon sources for their metabolism. These microorganisms secrete metabolites such as hydroxycarboxylic acids, exo-polysaccharides, and these microbial metabolites are metal complexing and chelating agents that help dissolve metals by lowering the pH of the medium (Tzeferis 1992). Autotrophic microorganisms, on the other hand, are photosynthetic; they use atmospheric CO2 as a carbon source. However, the chemolithotrophic group of microbes belongs to autotrophic microorganisms that rely on reduced inorganic iron and sulfur compounds for their nutrition.

Strategies to improve mining and moving towards commercialization

Mining activities have the potential to have a significant impact on people and ecosystems. Exploration, mining, processing, and related activities include measures to prevent, minimize and mitigate environmental impacts. They also expect land once used for mining to be restored to a more natural state. Responding to these expectations builds public trust and promotes a sustainable, competitive industry.

Strong environmental and economic performance requires ongoing and expanded efforts and resources to minimize the industry's dependence on water, reduce the potential for harmful discharges, improve tailings management, improve waterprocessing technologies and reduce habitat and biodiversity loss. The mining industry is looking for ways to improve energy efficiency and reduce greenhouse gas

2018)

Comminution is a process of crushing and grinding rock to release valuable minerals. This process accounts for more than 505% of the energy consumption of the mine site and up to 3% of all the electricity generated in the world. Air ventilation is essential for the safety of workers in underground mining. This is also an energyintensive process. Improving energy efficiency in these and other areas is an important environmental and economic opportunity for the industry. (The Deloitte, 2017)

Energy management programs with renewables as a major component can reduce energy costs by 25% in existing mines and 50 % in new mines.

Renewable energy sources can reduce or eliminate the dependence on diesel. Examples exist, such as Glencore's two three-megawatt turbines and storage facilities at its Raglan nickel mine in Northern Quebec. However, issues related to year-round access to sunlight and the intermittent nature of wind today limit the use of such technologies.

Mining value from waste can also reduce environmental costs, particularly in older operations. For example, sulfide minerals that cause acid mine drainage can be extracted from tailings to reduce the potential harm to the environment and the associated costs of liability for companies.

Conclusion and recommendation

The global mining sector is under pressure. In the short term, falling commodity prices are squeezing cash flows. Looking ahead, many existing mines are ripening, resulting in the extraction of lower ore grades and longer distances from the face of the mine; ore-body-replacement rates are declining, and new-mine-development times are increasing. On top of that, global mining operations are as much as 28% less productive today than they were 10 years ago-and that's after adjusting for declining ore grades (Ajay Lala et al. 2015). The industry has shifted its focus to improving productivity by "sweating" existing assets, but this strategy will only go so far. Despite the booms and busts of the industry, the nature of mining has remained the same for decades.

Achieving a breakthrough in productivity performance requires rethinking how mining works. The potential for such a breakthrough is now coming within the reach of the industry through digital and technological innovations that could transform key aspects of mining. In this article, we describe some digital technologies that have been in operation for a long time and are now available and affordable enough to operate on a scale across the mining industry. Their applications include building a more comprehensive understanding of the resource base, optimizing the flow of materials and equipment, improving anticipation of failures, increasing mechanization through automation, and monitoring of performance in real-time. Each of these opportunities alone has real potential; together, they represent a fundamental shift in both potential safety outcomes and how value can be captured in the mining sector.

Research on the mineral phase transition during mineral remodeling is of great importance. On this basis, the technical difficulties in combining pyrometallurgical and hydrometallurgical processes will be resolved and the development of new, clean and efficient metallurgical methods and technologies will lead to the future development of nickel production alongside the recycling of metals that have already created a win-win scenario for both the environment and industry. Treating spent Raney nickel catalyst by sulfuric acid leaching and soda ash precipitation.

Appendix Table 1 Nickel bearing minerals

A simple leaching process to recover over 99% Ni by sulfuric acid was proposed.

The diffusion-controlled model to represent the kinetics was proposed.

Investigating the dissolution kinetics of nickel from the spent catalyst in nitric acid medium.

The study of kinetics and statistical analysis of nickel

(

  Acharya et al. 1999(a), 2010(b))

  This exploration article is a diagram of the procedures utilized in the partition of Ni from its metals and the second asset. It gives likewise an understanding into how conceivably we may improve Ni extraction later on. The nickel mined originates from two kinds of mineral stores: Magmatic sulfide stores where the essential metal mineral is pentlandite [(Ni, Fe)9S9] Laterites where the central metal minerals are nickeliferous limonite [(Fe, Ni) O(OH)] and garnierite (a hydrous nickel silicate). Regardless of lateritic metals establishing 60% of the land-based Ni assets, ~ 60% of essential generation originates from sulfide mineral (Superiadi, 2007). Laterite nickel minerals regularly happening in tropical or subtropical districts comprise of weathered ultramafic rocks containing high levels of press and magnesium. These deposits usually exhibit different layers due to weathering conditions such as a silica-rich layer, a limonite layer dominated by goethite [FeO(OH)] and hematite (Fe2O3) and a saprolite [(Ni, Mg) SiO3.nH2O] layer rich in magnesium and basal elements. Between the saprolite and limonite layer, there is a magnesium-rich transition layer (10-20% Mg) with iron, called serpentine [Mg3Si2O5(OH)4]. The limonitic layer is not very suited for upgrading while upgrading the magnesium-rich saprolitic layer is also limited to concentrate the nickel. The mined ores (1-4% Ni) are processed to upgrade the metal content with 10-20% Ni in the concentrates. Thus, the preconcentration of nickel ores is an important unit operation to upgrade the nickel before commencing any extraction steps. Ni is mined from sulfide ores, Nickel ferrolaterite and serpentine. Although the sulfide ores are the preferred source of this metal more than 40% of the world's supply of Nickel comes from laterites and serpenties. (McCutcheon 2003, Blainey 1994, Dakvi 2004) (Figures 1 and 2). The production of Ni from sulfide ores is obtained mostly by a pyro-metallurgical process (Crundwell et al. 2011). Laterite ores can be divided into 3 main layers: limonite, transition, and saprolite. Limonite and transition are processed by hydrometallurgical processes and saprolite by the pyro-metallurgical process due to the low iron content (Crundwell et al.2011, Oxley and Barcza 2013).

(

  2003). Other reviews include those by Simons (1998), Taylor (2000), Diaz et al. (1998) and Ozberk et al. (1986). Pyrometallurgical processes are suited for ore containing predominantly saprolite. These ores contain proportionately lower cobalt and iron compared to the limonitic ores. The Ni/Co ratio in the smelter feed is generally ~ 40. These ores are smelted to produce either ferronickel or matte.

  Other reviews include those by Taylor (2000), Berezowsky et al. (1991), Berezowsky (1997), Motteram et al. (1996), Urbain et. al (1986) and O'Kane (1979).

  required. (Whittington and Muir (2000), Motteram et al. (1996), Mudd (2010), Oxley and Barcza(2013), Mohammad Reza F et al. (2014), Norgate et al. (2011), Dalvi et al. (2004)).

  projects, and Heron Resources ' Jump up Dam project into production status. Nickel juniors including GME Resources and Cortona Resources are also considering heap leaching to process their deposits. f) Chloride Leaching (for mixed limonitic and saprolitic ores) The use of hydrochloric acid was proposed to have several advantages as compared with sulphuric acid (Gibson and Rice, 1997), namely: ✓ The leach liquor is amenable to purification by direct solvent extraction (DSX) with Versatic 10 and to a lesser extent Cynex 301 particularly concerning Ni/Co/Mn/Mg separation and stripping of the extract. ✓ Concentrated chloride liquors produced from solvent extraction (SX) containing nickel, iron or magnesium can be spray roasted to produce pure nickel oxide or hematite or magnesia, respectively, together with hydrochloric acid.

  During the hydrometallurgical development of nickel sulfide, Canada Eagle Bridge Nickel, France Nickel, Finland Outokumpu, and South Africa Impala And so on made a huge contribution. The hydrometallurgy of nickel sulfide is generally based on high nickel niobium, and the extraction process can be divided. (Sahu 2008, Yang et al.2012)

  The hydrometallurgical process of nickel sulfide ore in China mainly adopts a selective sulfuric acid leaching-cleaning-electrowinning process. In 1993, China's Xinjiang Fukang smelter used copper-nickel high-nickel bismuth sulfuric acid to selectively leaching the metallurgical process, becoming the first domestic manufacturer of nickel metallurgy wet process. (Sahu 2008, Yang et al. 2012) 2.2.2. Pyrometallurgical process Nickel sulfide ores are generally rich in copper, and both copper and nickel are present in the form of sulfides, which are densely embedded with each other, and it is difficult to directly separate copper and nickel by beneficiation methods. Most companies currently use Copper Nickel mixed flotation -copper nickel smelting -high ice nickel crushing process. The main pyrometallurgical processes include flash smelting and molten pool smelting. Flash smelting is a high-temperature (1 450 ~ 1 550 ° C) reaction tower that sprays deeply dehydrated powder concentrate from the top of the reaction tower at high speed.

  It is therefore essential to consider the secondary sources of Ni from various industrial wastes. It exists in different sources, such as spent batteries. (Yang et al. (2016), Joulié et al. (2014) ), catalysts (Akcil et al. (2015)), wastewater (Benvenuti (2014), Shen et al. ( 2015)) and electronic wastes(Hadi et al. (2013), Robotin et al. (2011)). Two routes can be employed for Ni recovery from wastes: (i) leaching of wastes and subsequently recovering Ni solution (hydrometallurgical process); (ii) thermally treating wastes (pyrometallurgical process) Coman et al. (2013) 2.3.1. Nickel recovery from spent solution Existing methods used to remove nickel from industrial effluent, including chemical precipitation, chemical reduction, flocculation, filtration, evaporation, solvent extraction, biosorption, activated carbon adsorption, ion exchange, reverse osmosis, electrodialysis, membrane separation processes, etc. Spent plating baths are another source of high amounts of dissolved Ni (Tanaka et al. 2008). Methods used to treat such waste include electrodialysis (Li et al. 1999), electrowinning (Vegliò et al. 2003) and continuous extraction of solvents (Tanaka et al. 2008). Widyarani et al. (2017) evaluated the performance of a double chamber electrodeposition cell (DCEC) using water hyacinth as a cell separator for the removal of nickel ion. Benvenuti et al. (2014) extracted 97.9 percent Ni in a lab-scale electrodialysis system to treat a solution simulating the nickel plating of the rinse water. The process saved 120 kg/month of Ni on a large scale with the complete reuse of the rinse water. Dube et al. (2016) used < 50 μm magnetite powder (Cermag 10.1) to extract 98% Ni from the rinse water (29.8 ppm) of the plating plant in Zimbabwe.

  In nickel-based rechargeable batteries, the active material used is Ni(III) oxy-hydroxide (NiOOH), which is converted to Ni(OH)2 during discharge and reformed during recharge (Beck and Rüetschi 2000). Cadmium, a highly toxic metal, can be replaced by a hydrogen-absorbing alloy in NiMH batteries that is less benign and increases the performance of such batteries (Beck and Rüetschi 2000; Fetcenko et al. 2007). Nickel is present in LIBs as Li0.85Ni0.05 (NiO2) in + 2 states in the nickel oxide layered structure (Meshram et al. 2015b) a. Recovery of Ni from spent Li batteries Li-ion batteries are commonly used as phone power sources, but their continued use will degrade their capabilities. (Armaroli and Balzani. 2011). In 2020, the quantity and weight of Li ions may exceed 25 billion units and 500 thousand tons (Zeng et al. 2014). By using Li-ion batteries, their capabilities will continue to deteriorate and the battery needs to be replaced. As a result, the increased consumption of Li batteries can produce waste to the environment, a recovery process to obtain Ni is therefore necessary. Spent Li batteries containing lithium and other metals are mainly treated with hydrometallurgical processes and are also treated in combination with pyrometallurgical treatment. This may involve integrated pre-treatment steps such as pyrolysis or mechanical processing. To investigate the extraction of cobalt, nickel, manganese, etc. from LIBs, different acids such as HCl, H2SO4, HNO3 and a few organic acids such as DL-malic acid, citric acid, etc. have been leached (Meshram et al. 2014). Most of the work using LiCoO2-based batteries reported very low levels of nickel; however, quite recently, many researchers have used LIBs of mixed chemistry, which contain substantially nickel, as an important element for sustainable processing. Recovery of Ni from Ni-Cd batteries Batteries such as Ni-Cd have been part of the most widely used systems; therefore numerous studies have been carried out in recent years on the treatment and recycling of batteries and hydrometallurgical processes. Bartolozzi et al. (1995) described the hydrometallurgical process for the recovery of nickel and cadmium from spent Ni-Cd batteries. After primary treatment (grinding, drying, mechanical separation), the leaching of the powder obtained from primary treatment was performed with H2SO4 and H2O2 at pH= 0.3 for 60 min at 60 ° C. As a result, 98% of nickel was recovered in this process. Nogueira and Margarido (2004) investigated the leaching behavior of electrode materials from spent nickel-cadmium batteries in sulfuric acid media. Sulfuric acid leaching was the first chemical step in their process. The hydroxide phases of Ni, Cd, and Co were readily soluble at a low acid concentration (e.g. pH~1) for 30 min at room temperature. Electrode metallic nickel was reported to have completely leached at high temperatures (95 ° C) and mild acid concentrations (2.5 mol H2SO4) after 4 h. Kim et al. (2009) investigated the recovery of nickel, copper, tin and lead from waste multi-layer ceramic capacitors (MLCC) through a hydrometallurgical process. The nickel extraction was reported to be 97% with 1 mol HNO3 at 90 ° C for 90 min and 5 gL -1 pulp densities. Currently, spent Ni-Cd batteries are industrially treated pyrometallurgical, e.g. in Inmetco (USA), Accurec (Germany), SabNife (Sweden) or Snam-Svam (France). Hydro methods are also used in Batenus (Germany) or TNO (Holland) processes. These are primarily based on solvent extraction followed by electroplating, ion exchange or membrane technology (Rudnik and Nikiel 2007). Cadmium distillation is performed either to recover CdO in an open furnace or metallic Cd and high Ni-containing alloy in a closed furnace under controlled atmosphere (Espinosa et al. 2004a, 2004b). Espinosa and Tenório (2006) optimized the process of distillation of cadmium using coal as a reductive agent. The recovery of Cd metal was too slow below 900°C with Zn as the main impurity. Yang has also used a potentiostat electrodeposition technique to recover heavy metals from spent Ni-Cd batteries (Yang 2003). The best results have been achieved with the complete recovery of Cd and Ni in 4 M HCl at 60 ° C. However, the high leaching efficiency of 9 M HCl at 120 ° C was achieved by Stefănut et al.2008. The electrodeposition of both metals was carried out from the solution of leaching (pH 4.9) in the range of potential applications -200 to -1300 mV. The deposit was 10.12% Cd and 7.67 % Ni at a scanning rate of 50 mV / s, while the deposit was 23.05 % Cd and 14.44 % Ni at 10 mV / s. Peng et al. 2012 studied the extraction of cadmium from acidic solutions into paraffin wax using different extractors at temperatures between 55 and 65 ° C. Cd and Ni are the main components of the leach liquor in Ni-Cd batteries (Reddy et al. 2005). Using the Cyanex 923 solvent, more than 99.9% of cadmium was extracted from the leach liquor (Reddy et al. 2005; Reddy and Priya 2006). However, Babakhani et al. (2013) used a 5:1 ratio of Cyanex 302 to D2EHPA to completely extract cadmium at pH 2 with < 5 percent of Ni extraction. Earlier Nogueira and Delmas (1999), proposed a flow sheet for the recovery of metals in pure form from sulfate solutions.

(

  Zeng and Cheng 2009). Since disposal is the last option with great liability, several processing methodologies are reported including those industrially used (Marafi and Stanislaus 2008a, 2008b). (Table 5) 2.3.4. Recovery of Ni from polymetallic sea nodules Ocean nodules are the potential source of Ni and other metals, although the economic potential for the recovery of Ni, Cu, and Co from nodules has long been recognized, it was only in the last two decades or so that experiments on extracting methods were conducted. Ocean nodules and low-grade nickel sulfide ore are important, but less viable, mineral resources of Ni, Cu, and Co. In low-grade nickel sulfide ore, nickel minerals appear as fine particles closely associated with copper, cobalt, iron and other minerals, resulting in a low recovery of valuable metals from traditional ore enrichment (Wegorzewski et al. 2018). Ni, Cu, Co, and other metals fill the interstitial sites of manganese oxide mineral lattice in ionic form, leading to the necessary destruction of the high-valence manganese mineral lattice for the extraction of metals from polymetallic nodules (Padhan et al. 2014) Table 6

  (Wang et al. 1993, Liu et al. 1995, Zhai et al. 1997, Wang et al. 2011) A variety of metals were involved in the application. Of these, copper, uranium, and gold have been industrialized from their ores. The bioleaching process of metals such as nickel, cobalt, lead, and cadmium is still undergoing experimental research. Microbial leaching is generally considered to be the direct extraction of metals and the replacement of conventional smelters. (Wang et al. 1993, Liu et al. 1995, Zhai et al. 1997, Wang et al. 2011) Microbial mineral processing is an interdisciplinary process involving the application of microorganisms for the extraction of metal values under ambient conditions. Application of microbes for mineral processing has been extensively studied in the recovery of copper, gold, cobalt and uranium metals (Rawlings et al. 2002(a), 2003(b), Olson et al.2003). Microbial processing offers many advantages over conventional metallurgical mineral processing methods for the recovery of metals from low-grade ores and minerals due to its simple operation, low energy and reduced capital investment and eco-friendly nature (Acevedo 2000, Castro et al. 2000). Although microbial mineral processing has attracted a great deal of attention in recent decades, a thorough

  (GHG) emissions to reduce its environmental footprint. (The Mining Association of Canada, 2016) Activities such as processing ore, discharging effluent and managing tailings are based on the use of water. If not properly managed, mining activities can cause water pollution due to acid mine drainage, metal contamination, and erosion and sedimentation. Climate change brings with it further challenges related to the availability of freshwater, droughts, floods, snowmelt patterns, changes in water temperatures and other issues. (Natural Resources Canada, 2016, Impact.canada.ca,

FasterTable 4 ••••••••••Table 5

 45 process water Heap leaching far less complex than HPAL or AL (eg. No CCD, ratio; downstream processing more challenging (e.g. solid-liquid separation) Lower nickel and cobalt extractions ( esp. from neutralizing ores) a, b, c, d, e, gCenterfold ( 1979), b. Chander ( 1982), c. Reid and Barnett (2002), d. Griffin et al. ( 2002), e. Wedderburn (2005), f. Neudorf and Huggins ( 2006), g. Smit and Steyl ( 2006); h. Neudrof ( 2007), i. Santos de Pontes Pereira and De Araujo Gobbo ( 2007). Advantages and disadvantages of atmospheric chloride leaching as compared to Faster extraction kinetics [j] Recovery of acid and magnesia by pyrohydrolysis eliminating final effluent [j] Precipitation of hematite allows high recovery of hydrochloric acid [j] • Reduced capital requirements [k] • Suitable for treating limonite and saprolite • Maintaining magnesium concentration of acidic brine and water balance a challenge [j] Not suitable for treating high magnesium saprolites [j] Not suitable for treating high magnesium saprolites [j] • Chloride medium requires special corrosion fractions [k] Reduced reagent requirements [k] Good settling and filtration characteristics of iron-containing precipitates [k] Environmentally stable iron hydrolysis products like hematite can be formed [k] Recovery of magnesium as kieserite reduces discharge to the environment [k] precautions [k] Water balance difficult to maintain [k] [J] Harris et al., ( 2003, 2006 b), [k] Smit and Steyl (2006) Nickel extraction from spent catalysts Highlights Ref Testing the spent catalysts for recycling of critical metals An HCl leaching process to leach nickel (~ 73%) at 80°C and recovery NiO from a spent catalyst sample (17.7% Ni) was reported. ~ 99% Ni leaching from a spent catalyst of steam reforming plant with 50% sulfuric acid at 100°C in > 5 h time was reported. High Ni extraction(~ 98%) with sulfuric acid from a spent fertilizer catalyst was achieved. Combining acids (HNO3/H2SO4/HCl to treat the spent Simens et al. . (2008) hydride sulfurization catalyst showing similar leach efficiency (99% Ni and V, and ~ 90% Mo).

leaching in nitric acid solutions subjecting spent catalysts ( 3 .MonhemiusFigure 1 Figure 4

 314 Figure 1 Flowsheet summarizing typical processing of magmatic sulfide ores

Table 2 World primary nickel usage and production (INSG, 2018)

 2

	World Primary Nickel	2016	2017	2018f
	Usage	2.033Mt	2.192Mt	2.344Mt
	Production	1.991Mt	2.07Mt	2.224Mt

Table 3 Advantage and disadvantage of atmospheric leaching (stirred tank or heap) as compared to pressure acid leaching Expected advantages Refs Expected disadvantages Refs

 3

	Lower CAPEX
	Conventional	equipment
	technology
	Cheaper (less exotic) materials of
	construction
	Lower maintenance costs
	Higher plant availability


Ahmet Faruk Aysan
email: aaysan@hbku.edu.qa

Ali Yavuz

Polat Abdullah

Hasan Tekin
email: hasantekin@karabuk.edu.tr

Ahmet Semih Tunalı
email: tunali.ahmet@metu.edu.tr

The Ascent of Geopolitics: Scientometric Analysis and Ramifications of Geopolitical Risk

Keywords: Bibliometric analysis, Defence and peace economics, Geopolitical risk, Scopus JEL codes: C22, G12, G18, G41

In recent years, geopolitical risk (GPR) has been a crucial factor in investment decisions and stock markets. Therefore, we explore the research on the GPR by employing bibliometric and scientometric analytical techniques. We find 366 scientific contributions in December 2021 from the Scopus database by searching "Geopolitical risk" in abstracts, keywords, and titles.

Our findings show that GPR research has gained momentum in the last three years.

Specifically, the journal Defence and Peace Economics has one of the highest numbers of research and citation on GPR.

Introduction

Geopolitical risk (GPR) is a critical ingredient for financial markets and investment choices by central bank executives, entrepreneurs, and market contributors. GPR, as a vital factor, shapes financial cycles and macroeconomic policies. As [START_REF] Caldara | Measuring Geopolitical Risk[END_REF] recently show its importance, GPR negatively impacts economic activities and stock returns; that is why the liquidity flows from unstable markets to stable markets.

GPR has become a growing scientific subject due to its relevance in the global world in the last decade. Caldara and Iacoviello present the worldwide impact events between 1985 and 2018 (2018, 35) Source: Caldara and Iacoviello (2018, 35).

This study employs the bibliometric analytical technique by investigating the GPR research. Utilizing the Scopus database and the bibliometric analysis, we aim to assess the development in GPR research by describing quantitatively and evaluating all information in the dataset. Hence, this study contributes to the literature by presenting the existing research that may give new insights for prospective studies in GPR.

We retrieved 366 scientific contributions in December 2021 from the Scopus database by searching "Geopolitical risk" in abstracts, keywords, and titles. The findings mention that the GPR research has gained momentum in the last three years. Especially, Defence and Peace Economics leads the GPR research in economics with one of the highest numbers of research and citation.

One of the primary findings of this paper is that geopolitical risk is becoming more popular in recent years. The number of publications in this field increases rapidly after 2016 due to the rise in incidents that increase geopolitical risks. Similarly, authors in countries that are involved in international conflicts and have relatively higher geopolitical risks, such as Turkey, Russia, China, South Africa, contribute more to this field. Hence, authors from high geopolitical risk countries tend to be academically interested in geopolitical risk research. In addition, the creation of the GPR index by Caldara and Iacoviello in February 2018 allows the researchers to measure the geopolitical risk. This appears to be another reason for the parabolic increase of geopolitical risk studies in recent years. Another finding of this paper is that geopolitical risk studies can be clustered as in social science, financial, and energy studies when abstracts are analyzed with co-occurrence. Besides, it can be seen from the journals that Defence and Peace Economics leads economics journals while energy journals are not at the center.

The rest of the article proceeds as follows: the next section overviews the GPR papers in journals that published the highest number of documents and reviews some highly cited documents more in detail. The following section presents the data and methodology. Then, the subsequent sections analyze the overview of the geopolitical risk and authors, respectively. The last section concludes.

Geopolitical Risk in the Literature

Regarding the GPR literature, we select the papers in five journals, which published the highest number of documents: Resources Policy, Defence and Peace Economics, Finance Research Letters, Energy, and Energy Economics.

First, the papers in Resources Policy mainly focus on the resources like oil [START_REF] Plakandaras | Point and density forecasts of oil returns: The role of geopolitical risks[END_REF][START_REF] Godil | How oil prices, gold prices, uncertainty and risk impact Islamic and conventional stocks? Empirical evidence from QARDL technique[END_REF][START_REF] Olanipekun | Crude oil production in the Persian Gulf amidst geopolitical risk, cost of damage and resources rents: Is there asymmetric inference?[END_REF][START_REF] Drachal | Forecasting crude oil real prices with averaging time-varying VAR models[END_REF][START_REF] Kisswani | A symmetric time-varying effects of uncertainty fluctuations on oil price volatility: A nonlinear ARDL investigation[END_REF][START_REF] Kumar | Does geopolitical risk improve the directional predictability from oil to stock returns? Evidence from oil-exporting and oilimporting countries[END_REF]Li et al., 2021;[START_REF] Razek | Saudi Arabia's currency misalignment and international competitiveness, accounting for geopolitical risks and the super-contango oil market[END_REF], precious metals [START_REF] Zhou | The effects of geopolitical risks on the stock dynamics of China's rare metals: A TVP-VAR analysis[END_REF][START_REF] Yilanci | The role of economic policy uncertainty and geopolitical risk in predicting prices of precious metals: Evidence from a time-varying bootstrap causality test[END_REF], and gold [START_REF] Godil | How oil prices, gold prices, uncertainty and risk impact Islamic and conventional stocks? Empirical evidence from QARDL technique[END_REF][START_REF] Li | Dynamic spillovers of geopolitical risks and gold prices: New evidence from 18 emerging economies[END_REF]Li et al., 2021;[START_REF] Triki | The GOLD market as a safe haven against the stock market uncertainty: Evidence from geopolitical risk[END_REF].

Papers in Resources Policy are more concerned with gold, oil, precious metals, resources.

Next, papers related to energy are [START_REF] Muñoz | Quantifying the geopolitical dimension of energy risks: A tool for energy modelling and planning[END_REF] in Energy, and [START_REF] Qin | Asymmetric effects of geopolitical risks on energy returns and volatility under different market conditions[END_REF] and [START_REF] Shen | Does geopolitical risk promote mergers and acquisitions of listed companies in energy and electric power industries[END_REF] in Energy Economics. The GPR literature in Energy [START_REF] Mohsin | Assessing oil supply security of South Asia[END_REF]Su et al., 2019b;[START_REF] Alqahtani | Oil price changes, uncertainty, and geopolitical risks: On the resilience of GCC countries to global tensions[END_REF][START_REF] Dutta | News-based equity market uncertainty and crude oil volatility[END_REF][START_REF] Salisu | Geopolitical risk and forecastability of tail risk in the oil market: Evidence from over a century of monthly data[END_REF][START_REF] Tiwari | Structure dependence between oil and agricultural commodities returns: The role of geopolitical risks[END_REF][START_REF] Wang | Geopolitical risk and crude oil security: A Chinese perspective[END_REF] and Energy Economics [START_REF] Bouoiyour | What are the categories of geopolitical risks that could drive oil prices higher? Acts or threats?[END_REF][START_REF] Liu | Geopolitical risk and oil volatility: A new insight[END_REF][START_REF] Abdel-Latif | Financial liquidity, geopolitics, and oil prices[END_REF][START_REF] Mei | Geopolitical risk uncertainty and oil future volatility: Evidence from MIDAS models[END_REF][START_REF] Storhas | Multiscale lead-lag relationships in oil and refined product return dynamics: A symbolic wavelet transfer entropy approach[END_REF][START_REF] Tiwari | Gold-oil dependence dynamics and the role of geopolitical risks: Evidence from a Markov-switching time-varying copula model[END_REF][START_REF] Gu | The macro effects of GPR and EPU indexes over the global oil market-Are the two types of uncertainty shock alike?[END_REF] mainly examine the relationship between GPR and oil market. Recent research in Energy Economics [START_REF] Liu | Geopolitical risk and oil volatility: A new insight[END_REF][START_REF] Mei | Geopolitical risk uncertainty and oil future volatility: Evidence from MIDAS models[END_REF][START_REF] Qin | Asymmetric effects of geopolitical risks on energy returns and volatility under different market conditions[END_REF] evaluates the impact of GPR on volatility. Papers in Energy and Energy Economics are more concerned with energy, oil, and energy, oil, volatility respectively.

The documents in Finance Research Letters analyze the relationship between GPR and cryptocurrencies [START_REF] Aloui | Are Islamic gold-backed cryptocurrencies different?[END_REF][START_REF] Colon | The effect of political and economic uncertainty on the cryptocurrency market[END_REF], oil [START_REF] Antonakakis | Geopolitical risks and the oil-stock nexus over 1899-2016[END_REF], stock markets [START_REF] Kannadhasan | Do Asian emerging stock markets react to international economic policy uncertainty and geopolitical risk alike? A quantile regression approach[END_REF][START_REF] Abakah | Re-examination of risk-return dynamics in international equity markets and the role of policy uncertainty, geopolitical risk and VIX: Evidence using Markov-switching copulas[END_REF][START_REF] Choi | Evidence from a multiple and partial wavelet analysis on the impact of geopolitical concerns on stock markets in North-East Asian countries[END_REF][START_REF] Nguyenhuu | The impacts of rare disasters on asset returns and risk premiums in advanced economies 1870-2015[END_REF][START_REF] Phan | Geopolitical risk and bank stability[END_REF], and volatility [START_REF] Gkillas | Volatility jumps: The role of geopolitical risks[END_REF][START_REF] Gkillas | Forecasting realized gold volatility: Is there a role of geopolitical risks?[END_REF][START_REF] Nonejad | Forecasting crude oil price volatility out-of-sample using news-based geopolitical risk index: What forms of nonlinearity help improve forecast accuracy the most?[END_REF]. Table 1 summarizes the literature overview above. Paper in the Finance Research Letters mainly focuses on the cryptocurrency, oil, stocks, volatility issues.

The papers in Defence and Peace Economics examine the effect of GPR on financial markets [START_REF] Aslam | How Different Terrorist Attacks Affect Stock Markets[END_REF][START_REF] Apergis | Does Geopolitical Risks Predict Stock Returns and Volatility of Leading Defense Companies? Evidence from A Nonparametric Approach[END_REF][START_REF] Kim | Can Big Data Forecast North Korean Military Aggression?[END_REF][START_REF] Bouri | Geopolitical Risks and Movements in Islamic bond and Equity Markets: A Note[END_REF][START_REF] Bilgin | How Do Geopolitical Risks Affect Government Investment? An Empirical Investigation[END_REF][START_REF] Bouri | Jumps in Geopolitical Risk and the Cryptocurrency Market: The Singularity of Bitcoin[END_REF][START_REF] Khan | Guns and Blood: A Review of Geopolitical Risk and Defence Expenditures[END_REF][START_REF] Lee | Geopolitical Risks in the Post-Cold War Era: Make America Great Again Can Be Make the World Great Again[END_REF][START_REF] Kyriazis | The Impacts of Geopolitical Uncertainty on Turkish Lira during the Erdoğan Administration[END_REF][START_REF] Pyo | Does Geopolitical Risk Matter? Evidence from South Korea[END_REF], gold [START_REF] Huang | Effects of Geopolitical Risks on Gold Market Return Dynamics: Evidence from a Nonparametric Causality-in-quantiles Approach[END_REF] and oil markets (Su et al., 2019b;[START_REF] Cunado | Time-varying Impact of Geopolitical Risks on Oil Prices[END_REF][START_REF] Aloui | Are Islamic gold-backed cryptocurrencies different?[END_REF]Khan, Su, and Tao, 2021). The main keywords for the Defence and Peace Economics stand as defence, gold, oil, stocks, terrorism (Table 1) (2021), more recently assesses whether the GPR is a matter for the South Korean stock markets and finds that while positive geopolitical events positively affect stock prices, adverse geopolitical events have restricted impacts. [START_REF] Lee | Geopolitical Risks in the Post-Cold War Era: Make America Great Again Can Be Make the World Great Again[END_REF] examines GPR from the Middle East to Korea and indicates that while the cases associated with GPR increase in China, Korea, Russia, and Korea, those related to GPR decrease in Israel, Saudi Arabia, and Turkey.

Since oil markets are directly related to the GPR, DPE contributes to the relationship between the GPR and oil markets with the following four papers. [START_REF] Aloui | Oil-stock Nexus in an Oil-rich Country: Does Geopolitical Risk Matter in Terms of Investment Horizons?[END_REF] indicate that news of geopolitical tensions influences the stock market in Saudi Arabia, which has high GPR and is a rich oil-exporting country with high-frequency bands. Also, [START_REF] Khan | Does Oil Prices Cause Financial Liquidity Crunch? Perspective from Geopolitical Risk[END_REF] demonstrate a positive association between oil prices and financial liquidity in Saudi Arabia in the medium run. Su et al. (2019b) utilize [START_REF] Caldara | Measuring Geopolitical Risk[END_REF] GPR index comprising 11 national and international newspapers. They examine the association between the GPR and oil prices worldwide and reveal a positive relationship between wars and oil prices. Still, the GPR does not influence a sudden decrease in oil prices.

Last, [START_REF] Cunado | Time-varying Impact of Geopolitical Risks on Oil Prices[END_REF] explore how oil supply shocks affect GPR and oil prices. They

show that the geopolitical tensions in the Middle East drive the relationship between the GPR and oil supply shocks; that is why higher GPR means higher oil prices.

Next, [START_REF] Apergis | Does Geopolitical Risks Predict Stock Returns and Volatility of Leading Defense Companies? Evidence from A Nonparametric Approach[END_REF] examine 24 global defense companies whether the GPR may forecast actions in stock markets and volatility. They find that international geopolitical events are apt to influence the risk profile of defense companies, but these events are less likely to predict stock returns. [START_REF] Bouri | Geopolitical Risks and Movements in Islamic bond and Equity Markets: A Note[END_REF] analyze the GPR and movements in Islamic bond and equity markets and indicate that GPR affects both Islamic equity market volatility and returns. [START_REF] Bouri | Jumps in Geopolitical Risk and the Cryptocurrency Market: The Singularity of Bitcoin[END_REF] investigate the jumps in the cryptocurrency market and GPR in the context of Bitcoin. They show that jumps in GPR only impact Bitcoin in all cryptocurrencies; hence, this makes "Bitcoin is a hedge against GPR" (2020, 1). More recently, [START_REF] Kyriazis | The Impacts of Geopolitical Uncertainty on Turkish Lira during the Erdoğan Administration[END_REF] assess the association between GPR and the Turkish lira. They find that the uncertainty that arises from the GPR reduces the value of the Turkish lira against other currencies such as the Euro and the US dollar. Huang, Suleman, and Zhang (2021) explore whether GPR influences the returns in the gold market employing highfrequency data. They indicate that GPR impacts volatility more depending on the type and content of geopolitical events. [START_REF] Bilgin | How Do Geopolitical Risks Affect Government Investment? An Empirical Investigation[END_REF], on the other hand, analyze the association between government investment and GPR by using panel data for 18 countries. They find that the GPR drives government investment. [START_REF] Khan | Guns and Blood: A Review of Geopolitical Risk and Defence Expenditures[END_REF] assess defense expenditures and GPR. They mention that the relationship between defense expenditure and GPR is positive in China, India, and Saudi Arabia, but it is negative in South Korea and Turkey. However, they do not find any causality between defense expenditures and GPR in Brazil, Israel, and Russia, in which the internal political system determines defense expenditures.

Data and Methodology

We use the Scopus database by searching "Geopolitical risk" in abstracts, keywords, and titles in December 2021 since Scopus provides a high quality, well-organized and indexed database for bibliometric/scientometric studies [START_REF] Cobo | An Approach for Detecting, Quantifying, and Visualizing the Evolution of a Research Field: A Practical Application to the Fuzzy Sets Theory Field[END_REF][START_REF] Baas | Scopus as a Curated, High-Quality Bibliometric Data Source for Academic Research in Quantitative Science Studies[END_REF]. There are 366 scientific publications until the time we downloaded the data. Scopus provides data such as citation numbers, publication date, authors, countries, institutions. Science mapping is crucial for bibliometric studies and in this paper, we use VOSviewer created by [START_REF] Van Eck | VOSviewer manual[END_REF][START_REF] Powell | Mapping knowledge and innovation research themes: Using bibliometrics for classification, evolution, proliferation and determinism[END_REF]. VOSviewer is often used in other studies on bibliometric analyses [START_REF] Liao | A Bibliometric Analysis and Visualization of Medical Big Data Research[END_REF][START_REF] Shah | Prosumption: bibliometric analysis using HistCite and VOSviewer[END_REF][START_REF] Hamidah | A Bibliometric Analysis of Covid-19 Research Using VOSviewer[END_REF]. VOSviewer allows analysis like co-authorship, co-occurrence, citation, bibliographic coupling, and co-citation. In co-authorship analysis, the relatedness of items is based on the authors' number of co-authored documents. In citation analysis, the relatedness of items is based on the number of times they cite each other. In co-occurrence, the relatedness of items is determined based on the number of documents in which they occur together. In bibliographic coupling, the relatedness of items is based on the number of references they share. In co-citation, the relatedness of items is based on the number of times the papers are cited together [START_REF] Van Eck | VOSviewer manual[END_REF][START_REF] Bi | New research trends in unconventional oil and gas environmental issue: A bibliometric analysis[END_REF][START_REF] Mourao | Forest Entrepreneurship: A Bibliometric Analysis and A Discussion about the Co-Authorship Networks of An Emerging Scientific Field[END_REF][START_REF] Aysan | The Ascent of Bitcoin: Bibliometric Analysis of Bitcoin Research[END_REF].

Overview of the Geopolitical Risk

In this section, we discuss the overview of the GPR. Significant peaks of GPR are around Gulf War, 9/11, the invasion of Iraq by the US, the Russia-Ukraine War, and the Paris terrorist attacks in 2015 [START_REF] Caldara | Measuring Geopolitical Risk[END_REF]. Although the number of publications on GPR increases during or after the GPR index spikes, there is a continuous and parabolic increase in the number of publications after 2016 (see Figure 1 and Figure 2). to create their own GPR index for subjects like [START_REF] Aslam | How Different Terrorist Attacks Affect Stock Markets[END_REF]. Hence, it was difficult and time-consuming to conduct empirical research on GPR, or studies on this subject were not practical like [START_REF] Suder | Terrorism and the International Business Environment: The Security-Business Nexus[END_REF], [START_REF] Karasalihovic | Strategy Guidelines for the Croatian Petroleum[END_REF][START_REF] Wei | Political-Economic Relations with China: Comparative Survey of Japan and Western Europe's Economic Relations with China (1949-2002)[END_REF]. Hence, Caldara and Iacoviello's GPR index help other researchers to study GPR without a need to measure the GPR.

The other significant reason for the increase in GPR papers could be the election of US Authors affiliated in China, South Africa, Turkey, the United Kingdom (UK), and the US have the greatest total link strength (see Figure 5), and those in Russia can be added to these countries in terms of the number of the publication (see Figure 6). The authors in the US, France, and Greece are in the center of the map in the blue cluster. The authors in other countries in the blue cluster have small link strength and link to these three countries. The authors in China form the biggest red cluster which mostly consists of East Asian countries like Australia, Hong Kong, Japan, New Zealand, South Korea, and Taiwan. Consequently, we can claim that geopolitical proximity is an important factor for citation networks. The Green Cluster is also significant since leaders of this cluster in terms of total link strength are India, Pakistan, Russia, and Turkey which have high geopolitical risks. If we focus on a country in this cluster, it would be Turkey since it has one of the greatest total link strengths even though the influence of Turkish academy to the world is limited in other fields and Turkey has no or few universities in the top 500 lists2 . This can be explained by Turkey's involvement in international political issues in the last years, such as Arab Spring, Syrian War, Libyan Crisis, Eastern Mediterranean Crisis. Additionally, Turkey's GPR generally is higher than the global average [START_REF] Caldara | Measuring Geopolitical Risk[END_REF]. Hence, interest and inquisitiveness towards GPR could be higher in Turkey. Turkey is a part of international political disputes or neighbor of conflicts that could increase the GPR of Turkey, such as ISIS, the US-Iran Tension, the Ukraine-Russia War. As a result, Turkish academic outputs can be seen as the crucial source by the world.

The authors affiliated in Russia, France, Greece have also published a substantial number of documents on GPR (see Figure 6). Like Turkey, these countries are also involved in many political disputes. Hence, it can be concluded that the authors affiliated with countries that are implicated in international conflicts or tensions are more likely to study GPR and have greater link strength in the GPR field. Notes: The words that used more than one document are taken for the network map.

Source: Scopus.

Titles are one the most striking part of the studies. Hence, we analyzed the network map of titles of the studies in the GPR field in Figure 7. As expected, GPR is at the center, link with most of the words, and its node's size is prominently greater than any other node, which represents the occurrence of the words in the titles. Uncertainty also has a notable size and is in the same cluster as GPR since they are related and uncertainty links with various clusters like GPR.

There are also clusters worth mentioning like blue, purple, red, and green. On the lower side, there is a red cluster that includes energy-related concepts like natural gas, energy security, Russia. The green cluster is on the upper end, and it comprises more econometric analysis of different fields since analysis, approach, economic policy uncertainty has the greatest size and include different fields like growth, tourism, and Bitcoin price. Blue and Notes: The words that are used more than five times are taken for the co-occurrence map of the abstracts. Structured abstract labels and copyright statements are ignored. Source: Scopus.

Since abstracts give the summary and the objectives of the studies, we also analyzed the abstract of the articles. Figure 8 shows that there is a clear distinction between the three clusters, which demonstrates that there are mainly three different main subjects in this field.

Firstly, the blue cluster evidently represents studies related to energy since it includes nodes like natural gas, gas supply, Middle East, North Africa, production. The green cluster mainly represents research on social sciences since concepts like security, power, state, nation, border, global risk are in the green cluster. Lastly, the red cluster shows financial studies because concepts like portfolio, return, volatility, relationship, investor, and gold are in the red cluster.

Moreover, the location of the nodes is also significant. The oil market is at the closest point of the blue cluster to the red cluster in the network map. This result is maybe due to oil market prices often being compared to gold and other assets in econometric studies. Therefore, the oil market frequently takes place in portfolio studies.

On the other hand, there is some exception in these clusters. For instance, the oil market is not in the red cluster, while it may be expected to be in the energy cluster. This result is due to oil market prices often being compared to gold and other assets in econometric studies, therefore, the oil market frequently takes place in portfolio studies. However, the oil market is at the closest point of the red cluster to the blue cluster in the network map. Hence, the location of the nodes is also significant to analyze studies in the GPR field.

Analysis of Authors

It is insightful to analyze the authors of the papers to understand the GPR field more comprehensively. Figure 9 represents the ten most productive authors of the area. By far, Gupta is the leader of the field in terms of the number of publications. Some of the characteristics of these authors are common. For instance, most of the authors in Figure 9 are applied econometricians. Hence, it can be concluded that econometric analysis is essential in this field, and it is suitable for econometric studies. Especially with the GPR index created by [START_REF] Caldara | Measuring Geopolitical Risk[END_REF], econometric studies increased in the field. Co-authorship analysis helps us to understand which authors work together. The size of the nodes represents the total link strength of the authors. In Figure 11, clusters are generally well distributed, and there are few connections between clusters. In other words, the collaboration between authors is not diverse. Gupta is the most apparent exception for the collaboration since he has links with authors from almost all clusters, and he is at the center of the map. Also, his node is significantly bigger than the others. Hence, his total link strength may be explained by his co-authorship with different clusters. Note: Authors that cited more than 20 times are taken since there are more than 10,000 cited authors when there is no threshold. Source: Scopus.

In Figure 14 In Figure 13, we claim that countries of authors matter. However, Figure 14 shows that the subjects of the documents are essential. For instance, some papers focus on energy [START_REF] Mohsin | Assessing oil supply security of South Asia[END_REF][START_REF] Vakulchuk | Renewable Energy and Geopolitics: A Review[END_REF] and cryptocurrencies [START_REF] Al-Yahyaee | Can Uncertainty Indices Predict Bitcoin Prices? A Revisited Analysis Using Partial and Multivariate Wavelet Approaches[END_REF][START_REF] Aysan | Effects of the Geopolitical Risks on Bitcoin Returns and Volatility[END_REF][START_REF] Colon | The Effect of Political and Economic Uncertainty on the Cryptocurrency Market[END_REF]. Hence, documents with similar subjects are located closely and linked to each other.

Another interesting fact is that all documents are recently published. In Figure 2, the increase of the overall GPR papers is related to the GPR index. Hence, recent studies have more citations since the size of the nodes represents citation in Figure 14. The citation analyses by various markets can offer better insights into the literature. We classify the various markets such as oil, bond, foreign exchange, and the stock market by searching documents' titles, abstracts, and keywords. There are substantially more articles related to the oil market (125) than the stock market (47). Papers 3 focusing on bond and foreign exchange markets is negligible in terms of the number of documents (nine and two, respectively).

3 Bond articles are mainly about the US bond market. Foreign exchange market articles are about countries with FX issues like Turkey (Mansour-Ichrakieh and Zeaiter, 2019) and some ASEAN countries [START_REF] Hui | The long-run effects of geopolitical risk on foreign exchange markets: evidence from some ASEAN countries[END_REF]. We focus on stock and oil markets since they have many publications. Regarding the oil market citation analysis, there are interesting results as the size of nodes for France and Germany, Turkey, and the US are among the smallest in terms of total link strength.

However, they are the most significant nodes considering all topics. Similarly, the node of Saudi Arabia is one of the greatest when we restrict the oil market. Hence, we can conclude that the authors' affiliated country characteristic is an essential factor for studies. Relatively, there are more equal nodes on the stock market analysis, similar to general analysis. Since most countries have stock exchanges, the papers focusing on the relationship between the stock market and GPR are more evenly distributed, unlike those related to the oil market.

Concluding Remarks

This article investigates a bibliometric analysis of GPR research by employing the Scopus data. The results show that the GPR research has gained momentum in recent years.

Fundamental reasons for this rise could be the adverse political atmosphere and international conflicts like the Syrian Civil War, ISIS, Trade War, Russia-Ukraine War. Also, geopolitical risk studies are popular and at the center of the analysis in the countries that involved those conflicts like Russia, Turkey, and China. In addition, unlike other fields, the majority of the most cited authors are from China, Turkey, or South Africa. Furthermore, there is an uptrend in the number of geopolitical risk studies after 2016, the numbers soar in 2018 since Caldara and Iacoviello created a geopolitical risk index at the beginning of the year. Hence, accessibility to prepared geopolitical risk index may facilitate and accelerate studies in geopolitical risk. According to our co-occurrence analysis on abstracts, there are three main clusters in this field which are finance, social science, and energy although there are some negligible exceptions and interdisciplinary studies. These clusters are observed in the journals as well. The journal Defence and Peace Economics leads the GPR research with one of the highest numbers of research and citation. Furthermore, its node is in the center of the citation analysis map and has strong links with social science and finance journals. Besides, there are various energy journals, while they mostly link to each other.

In sum, this study contributes to the literature by presenting the existing research that may give new insights for future works in GPR. Moreover, the GPR research may be extended by interacting with various institutional determinants. For further research, in the coming years, data may be expanded to ensure that momentum in the geopolitical risk continues since parabolic increase exist an only couple of years and it may be a temporal and misleading period.

  , as in Figure 1. These events are as follows: United States (US) bombs Libya, US invasion of Panama, Kuwait invasion, Gulf war, Iraq disarmament crisis, 9/11, Iraq invasion, London bombings, Iran nuclear tensions, Arab spring, the Syrian war, Russia annexes Crimea, Islamic State in Iraq and Syria (ISIS) escalation, Paris attacks and North Korea. Mainly, all these events trigger the attention to the GPR research.

Figure 1 .

 1 Figure 1. Geopolitical Risk by Year.

Figure 2 .

 2 Figure 2. Document Numbers by Year. Notes: This figure presents the document counts from 1992 to 2021. Source: Scopus.

Figure 3 .

 3 Figure 3. Citation Analysis of Sources. Source: Scopus.

Figure 4

 4 Figure 4 presents the documents by subject area defined by the Scopus database.

Figure 4 .

 4 Figure 4. Network Map of Documents by Subject Area. Source: Scopus.

Figure 5 .

 5 Figure 5. Country-based Citation Analysis.Notes: The countries where more than two documents were published are taken for the network map. Source: Scopus.

Figure 6 .

 6 Figure 6. Number of Documents by Authors' Country. Source:Scopus.

Figure 7 .

 7 Figure 7. Co-occurrence Map of Titles.

  purple clusters are close to each other and in the middle. The purple cluster includes the stock market, oil price, and exchange rate. The stock market is close to the upper side and the oil price is close to the lower side.

Figure 8 .

 8 Figure 8. Co-occurrence Map of Abstract.

Figure 9 .

 9 Figure 9. Document Numbers by Authors. Notes: This figure compares the document counts for up to 10 authors. Source: Scopus.

Figure 10 .

 10 Figure 10. Co-authorship Analysis of Countries. Source: Scopus.

Figure 11 .

 11 Figure 11. Co-authorship Analysis of Authors. Source: Scopus. Citation analysis of authors shows the citations among the authors, and the size of the

Figure 12 .

 12 Figure 12. Citation Analysis of Authors.Notes: Authors with more than ten citations are taken for the network map. Source: Scopus.

Figure 13 .

 13 Figure 13. Co-citation Analysis of Authors.

  , citation analysis of documents is more distributed, and there is no single central article, as in Figure 12. Antonakakis et al. (2017), Balcilar et al. (2018), Mohsin et al. (2018), Aysan et al. (2019), and Su et al. (2019a) stand out from other documents. However,[START_REF] Sharif | COVID-19 pandemic, oil prices, stock market, geopolitical risk and policy uncertainty nexus in the US economy: Fresh evidence from the wavelet-based approach[END_REF] stand out from all of the papers since they focus on the COVID-19 pandemic. Therefore, most articles about COVID-19 and GPR cited[START_REF] Sharif | COVID-19 pandemic, oil prices, stock market, geopolitical risk and policy uncertainty nexus in the US economy: Fresh evidence from the wavelet-based approach[END_REF].

Figure 14 .

 14 Figure 14. Citation Analysis of Documents. Source: Scopus.

Figure 15 .

 15 Figure 15. Citation Analysis of Authors' Affiliated Country for Oil Market. Sources: Scopus.

Figure 16 .

 16 Figure 16. Citation Analysis of Authors' Affiliated Country for Stock Market. Sources: Scopus.

Table 1 . Selected journals in GPR: A literature overview

 1

	Journals	# of GPR papers Focused keywords
	Resources Policy	19	gold, oil, precious metals, resources
	Defence and Peace Economics	15	defence, gold, oil, stocks, terrorism
	Finance Research Letters	11	cryptocurrency, oil, stocks, volatility
	Energy	9	energy, oil
	Energy Economics	9	energy, oil, volatility
	Source: Scopus & Authors' compilation
	Considering its importance, the journal of Defence and Peace Economics (DPE) leads the
	GPR to the earliest literature in economics by having one of the highest numbers of
	documents in this bibliometric analysis. We also give more information about some of the
	highly cited articles in this journal. First, Aslam and Kang (2015), as the earliest paper of
	DPE, examine terrorist attacks and stock markets in Pakistan and find that the Karachi stock
	market gives different responses to various terrorist attacks. Then, as another growing
	literature, Kim, Kang, and Lee (2018) use big data to predict the military aggression of North

Korea. They show that news articles published by the United Kingdom media have significant predictive power for North Korean military attacks. Another Korean case-based paper, Pyo

  President Donald Trump and his policies, which increased GPR in the world, especially in China due to the Trade War and in Muslim countries because of the Muslim Ban(Shen et al., 2021, 1). Although spikes are shorter in Trump's era, there is a general upward trend after 2016 compared to the previous years. As a result, this increase in tension possibly encouraged

	GPR research.

Figure 3 shows the citation analysis of sources. Resources Policy is linked to energy journals like Energy Policy, Energy, International Journal of Energy Sector Management, or International Journal of Energy Economics and Policy. Additionally, fields like sustainability link to the Resources Policy. On the other hand, Defence and Peace Economics focuses more on general issues and government policies. Hence, it is linked to the Economic Analysis and Policy, International Economics, Journal of Public Affairs. Economic Modeling is in the middle of Resources Policy and Defence and Peace Economics. Apart from them, the Asia-Pacific Journal of Financial Studies is an outlier since its research is based on a particular region of the world.

See the ranking at https://www.timeshighereducation.com/student/where-to-study/study-in-turkey.

Co-citation analysis of authors shows the network based on the papers cited in the same study. As shown in Figure 13, the network map of the authors' co-citation analysis is different from other maps, and it is like a circle. Besides, links between nodes are superabundant.

Based on these results, we conclude that most authors are cited in the same articles. However, there are clear clusters that might result from the authors' affiliated countries. The orange and brown clusters predominantly consist of Chinese authors such as Tao, Su, We, Chang, Lee, and Wang. The pink, blue and yellow clusters are primarily formed by the Middle Eastern and Indian authors such as Adewale, Al Mamun, Uddin, Bekun, Akadiri, Uddin, Bouri, Shahbaz, Dutta. The green cluster includes several Turkish authors, Demir, Balcilar, Gozgor, Aysan.