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Nickel is a strategic element whose production and consumption in over a decade has increased to over 39% and 71%, respectively. Generally, due to their complex mineralogy, laterites, the current attractive source of Ni, are subjected to hydrometallurgy and pyrometallurgy techniques without enrichment in order to extract Ni. Therefore, numerous investigations in vogue on laterite enrichment performed spanning from 1964 to date were reviewed in this article, and the future directions were proposed through critical synthesis. The possibilities of obtaining both higher recoveries and increase in grade for Ni were noticed using selective comminution-classification method followed by flocculation-flotation strategy. Hence, in order to improve on the reported Ni yields from selective comminution-classification process, one of the ways could be to subject the ore to a multi-stage selective comminution-classification method followed by subjecting the obtained concentrate to flocculation-flotation technique. Therefore, the findings of this investigation would aid in upscaling the production to meet the demand. Properties of goethite and serpentine were explored. Physical and flotation methods for laterite enrichment were reviewed. Future directions for laterite beneficiation were proposed. [ABSTRACT FROM AUTHOR]

Rare metal gallium is classified as a strategic material because of continued high demand, uncertain supply, and low reserves. Corundum flue dust (CFD) is generated during bauxite smelting to produce brown corundum. Gallium (Ga), Zinc (Zn), and potassium in the bauxite could be enriched with CFD through this process, so CFD is regarded as one of the potential sources of Ga and Zn. A novel that utilizes ultrasound to enhance the H2SO4 leaching efficiency of Ga and Zn from CFD was developed from CFD. The effects of ultrasound power, leaching time, sulfuric acid concentration, and leaching temperature on the leaching behavior of Ga and Zn were studied, and the corresponding kinetics model was established. It was found that the maximum Ga and Zn leaching efficiencies of 81.22% and 96.72% were obtained at optimum leaching conditions: the leaching temperature of 90°C, the leaching time of 60 min, 3 M H2SO4, the solid-to-liquid ratio of 1:5 (g/mL), and the ultrasound power of 750 W. In all cases, the leaching effect of Zn is not significantly improved by ultrasonic treatment, but the leaching efficiency of Ga has a positive effect (more than an 18% increase). Kinetic analysis shows that the leaching process of Ga and Zn were controlled by chemical reaction and diffusion, respectively. The apparent activation energy values are 20.39 kJ/mol for Ga and 13.44 kJ/mol for Zn. The characterization of the leaching residues reveals that the ultrasound effected to enable the whole block to be fractured or dispersed into fragments, accelerating the penetration of H2SO4 into the pores and cracks at the solid, which further prompts the dissolution of the encapsulated gallium and achieves the conspicuous improvement to Ga leaching efficiency. [ABSTRACT FROM AUTHOR]

The aim of lithium-ion battery (LiB) recyclers is to create a closed-loop process to recover and reuse all the material as secondary sources of material to manufacture new batteries. Global LiB recycling companies apply pyrometallurgy, hydrometallurgy, or direct recycling to meet this goal. Pyrometallurgy is very energy intensive, but hydrometallurgy requires a pretreatment process and a new version of direct recycling that shows more promise for automation would also require pretreatment. Currently, recycling companies appear to favor hydrometallurgy. This review summarizes the current state of development of the pretreatment process involving battery discharging and mechanical treatment series from the literature and its application in the industry, with particular attention on Asia Pacific recyclers. The key pretreatment steps of battery discharging and mechanical treatment are the focus of this review, but pretreatment of the black mass containing cathode material prior to leaching is also included. Discharging is important to reduce the risk of fire during mechanical treatment. An interesting finding is that despite promising laboratory results, there has been no reported commercial application of battery discharging using the submersion method in an electrolyte solution. An efficient mechanical treatment of discharged batteries is essential to remove the impurities which could adversely impact the subsequent LiB processing. Research into mechanical treatment should also include a method to evaluate the liberation of material. This review has highlighted a new potential flowchart for recycling of various cathode types of LiBs. [ABSTRACT FROM AUTHOR]

Recovery of nickel and cobalt from laterite ores is important to meet the demand for these metals. In this work, a process was developed for the separation of metal ions from synthetic sulfate leach liquor of laterite ores containing Fe(III), Al(III), Ni(II), Co(II), Ca(II), Mg(II), and Mn(II). First, Fe(III) and Al(III) were removed by precipitation of their hydroxides by adjusting solution pH and then Mn(II) was removed from the filtrate by oxidative precipitation with NaClO. Sequentially, Co(II) and Ni(II) from the filtrate containing Mg(II) and Ca(II) were separated by selective precipitation of CoS and NiS by adding Na2S solution, leaving Ca(II) and Mg(II) in the filtrate. The mixed precipitates of CoS and NiS were completely dissolved by 0.1 M HCl solution containing NaClO. Co(II) can be separated from Ni(II) present in the HCl solution by either oxidative precipitation with NaClO or selective extraction with saponified Cyanex 272. Optimum conditions for these procedures were obtained. Continuous experiments indicated that the purity of Co(II) and Ni(II) solutions was higher than 99%. [ABSTRACT FROM AUTHOR]

Presented universal recommendations for the reduction of crud formation, reviewing various aspects affecting the loss of diluent and extractant due to the formation of a third phase (crud), encountered in many hydrometallurgical plants using copper solvent extraction. In this paper introduce the reasons of the crud formation , description of the stable emulsions containing solid particles and choice of technological scheme. An analysis of operations to be considered in the operation of copper solvent extraction plants is presented, due to the deterioration of copper grade below 0.5% in ore and the increase in aluminum content up to 20–25%. Results of use of extraction properties of modified extractants of ACCORGA series and unmodified extractant Lix984N on pregnant leached solution of the most important deposits (Almaly and Aktogay) are given. It is established that for solutions of Almaly deposit, ACCORGA5640 and unmodified Lix984 extractants have high selectivity to copper. Distribution of iron, silica, and copper ions during extraction was studied, and it was found that high selectivity to copper/iron and copper/silica is possessed by extractant Lix 984N, ACCORGA5640. It was found that for solutions of the Aktogay deposit, the ratio of interphase suspension in both extractants is the same, and phase separation in experiments with the use of extractant Lix 984N was 10 s shorter with the use of extractant ACCORGA5640. It was found that the addition of ACCORGACR60 reagent in the amount of 5-10 ppm also leads to a decrease in the volume of crud by 13%, for a stronger suppression of crud. [ABSTRACT FROM AUTHOR]

In general, separating osmium and ruthenium metals via hydrometallurgical methods poses significant challenges. This study presents a novel approach to separate osmium from a metallic mixture with ruthenium through selective dissolution using a two phase system. The system comprises an aqueous phase containing sulfuric acid solution with sodium chlorate and an organic phase consisting of pure tributyl phosphate. Among the several variables investigated in this work, sulfuric acid concentration and stirring speed showed most significant effect on the dissolution of osmium metal. Based on the potential-pH diagram of osmium metal, an oxidation reaction of osmium metal by the sulfuric acid and sodium chlorate mixture was proposed. The role of tributyl phosphate was to prevent the evaporation of the dissolved osmium tetroxide species by extracting into organic phase. The separation of the two metals was accomplished by selective dissolution of osmium at the following conditions: 3 M sulfuric acid, 0.7 M sodium chlorate, pure tributyl phosphate, pulp density of 2 g/L, 20°C, 60 minutes and stirring speed of 200 rpm. Use of a mixture of thiourea and hydrochloric acid solution containing ascorbic acid completely stripped the osmium from the loaded tributyl phosphate. Comparison of dissolution efficiency of osmium metal between two phase system and one phase system of sulfuric acid-sodium chlorate-water indicated that the employment of tributyl phosphate in two phase system was of importance in the recovery of the dissolved osmium species. Our results demonstrated that osmium can be separated from ruthenium by selective dissolution with the two phase system. [ABSTRACT FROM AUTHOR]

The following review is Part III of a series concerned with the direct hydrometallurgical processing of nickel sulfide flotation concentrates. In the first part of this series, piloted leaching processes and commercial nickel sulfide operations that employed direct hydrometallurgical processing were comprehensively reviewed. In the second part of this series, laboratory investigations into pressure leaching of nickel sulfide concentrates were critically analyzed. In Part III of this series, laboratory investigations into the leaching of nickeliferous sulfide concentrates at ambient pressure are reviewed, and the challenges and research opportunities in the direct leaching of nickel sulfide flotation concentrates are summarized. The majority of the published studies on atmospheric leaching of nickel sulfide flotation concentrates have focused on leaching in chloride media due to the faster leaching kinetics in chloride lixiviants relative to sulfate media; bioleaching due to the perceived environmental advantages over other leaching systems; and pyrometallurgical pre-treatments to render refractory sulfide minerals more amenable to subsequent leaching. [ABSTRACT FROM AUTHOR]

The following review is the second part of a series concerned with the direct hydrometallurgical processing of nickel sulfide flotation concentrates. In the first part of this series, piloted leaching processes and commercial nickel sulfide operations which employed direct hydrometallurgical processing were comprehensively reviewed. In Part II of this series, laboratory investigations into the pressure leaching of nickeliferous sulfide concentrates are critically analyzed. From this review, it is apparent that sulfuric acid pressure leaching processes have received the most attention relative to other lixiviant systems such as ammonia/ammonium, chloride, and nitric acid. This is likely due to the numerous technical advantages sulfate-based leaching systems offers relative to other lixiviants. Laboratory investigations into atmospheric concentrate leaching processes are explored in Part III of this series. [ABSTRACT FROM AUTHOR]

Increasing demand for low carbon technologies and renewable energy sources requires our resources and economies to be circular. Many countries agree that the responsible consumption, production, and recycling of rare-earth-containing products is essential as a way to achieve the sustainable development goals also set out in the European Green Deal. Sustainable sourcing is targeted with carefully designed roadmap for cost efficient REE production from end-of-life products (EoLs) in addition to mining activities as providing primary sources. Hydrometallurgical methods, such as roasting, leaching, precipitation, crystallization, solvent extraction, and ion exchange includes fast developing, selective, eco-friendly, and cost-effective technologies especially for the extraction of REEs. This article provides an overview of primary and secondary resources and summarizes presents case scenario of studies carried out on the use of some promising methods, which could serve as an economical means for recovering REEs. [ABSTRACT FROM AUTHOR]

The extraction of nickel (Ni) from sulfide resources commences with flotation to produce a concentrate which is then smelted to produce a nickel-enriched phase called matte, and further refined to produce pure Ni products as well as by-products, such as cobalt (Co), copper (Cu) and precious metals. However, the traditional concentrate smelting-matte refining process, whilst technologically robust, is capital intensive and suffers from several environmental and technical issues such as sulfur dioxide emissions, poor recovery of cobalt and difficulty processing concentrates high in magnesia and arsenic without appropriate blending with high grade concentrates to dilute the concentration of these species. The direct hydrometallurgical processing of nickel sulfide concentrates and whole ores may be a remedy to these issues and hydrometallurgy offers several advantages over pyrometallurgy such as potentially lower capital costs, the ability to process lower grade materials and produce marketable metals or compounds directly from ore/concentrate. Despite the advantages of hydrometallurgy over traditional base metal sulfide smelting, the hydrometallurgical processing of nickel concentrates has been limited to a small handful of commercial operations, some of which only produce an upgraded intermediate for pyrometallurgical processing. In Part I of this three-part series, a comprehensive review of piloted processes for direct hydrometallurgical processing of nickel sulfide concentrates is presented, followed by a survey of industrial operations which have carried out direct leaching of nickel sulfide concentrates. A review of research activities and challenges/opportunities in the direct hydrometallurgical processing of nickel sulfide concentrates are presented in Part II and Part III of this series. [ABSTRACT FROM AUTHOR]

Bauxite Residue (BR) is an industrial waste generated by the extraction of alumina through the Bayer process. It is usually stored in specially constructed sedimentation ponds. Long-term storage notoriously leads to severe environmental issues due to its high alkalinity which affects neighboring communities. It contaminates phreatic and surface waters through the infiltration of metal laden caustic solution and radionuclides. The air also gets polluted through dispersion of particles which threatens surrounding biodiversity. To manage these environmental concerns, it is necessary to engineer the waste residue into value added products. This paper systematically reviews the mineralogical and chemical characterization of the waste and techniques developed for its recycling. [ABSTRACT FROM AUTHOR]

At the end of their efficient functionality in energy production/storage applications, spent lithium-ion batteries need to be recycled. Recycling remains the most preferred economic option with benefits such as prevention/reduction of environmental issues due to landfilling and more efficient use of natural resources. In this paper, characteristics of lithium-ion battery components before and after being spent are presented, together with highlights of various extractive options suitable for recycling. The main emphasis of this review is on the direct recycling approach, which employs the physical separation of anode and cathode materials. Since flotation is the most common processing method successfully applied to the physical separation of minerals in the mining industry, researchers have given a lot of attention to this area. The success of recycling by flotation is mainly dependent on wettability differences between the anode (hydrophobic) and cathode (hydrophilic) components. However, such components are subjected to surface modifications due to the intimate organic coating introduced in battery production. As such, the hydrophobic entities of the solid electrolyte in battery assembly, which are so essential for the electrochemical functionality of the battery during its life cycle, present main challenges on the selectivity of flotation as a recycling option. Thus, the restoration of the original hydrophobicity/hydrophilicity level of each electrode has been the main focus area for many investigations. This paper also provides an up-to-date review of proposed pretreatment options. [ABSTRACT FROM AUTHOR]

Cobalt is a key element of the lithium-ion batteries that supply energy and continuous power to several electronic equipments such as cellphones, computers, and electric vehicles. Due to the depletion of primary sources of metal extraction and limited supply, countries are now focusing on recycling secondary resources for economic and sustainable management. Though the majority of the technologies involved are focused on industrial-scale development, they lack eco-friendliness and efficiency. The dead lithium-ion batteries containing several valuable metals such as cobalt, lithium, manganese and nickel are regarded as an appealing secondary resource. Battery recycling is required not only to reduce energy consumption but also to alleviate the scarcity of rare resources and eliminate pollution from hazardous components, as the world moves toward more sustainable industries such as consumer electronics and electric vehicles. The significance of cobalt recovery from secondary resources is emphasized in this paper. From the research, it is found that the amount of cobalt is more in the spent LIBs. Hence, focus is given on the green method of leaching of the spent Lithium-ion batteries (LIB) and extracting the valuable metals such as cobalt, nickel and lithium using organic acids. The method of using organic acids as leachant is environmentally friendly, cost-effective, and has the potential to provide sustainable development in the battery industry. This initiative is aimed to stimulate people's interest in wasted LIBs recycling with organic acids and raise awareness of the benefits. [ABSTRACT FROM AUTHOR]

Copper ores, end-of-life electric and electronic equipment and car electronics can contain, besides Cu, substantial amounts of geochemically scarce companion elements. Geochemically scarce elements have an upper crustal abundance of <0.025 (weight)%. In view of resource conservation and reduction of pollution there is a case for near-zero waste processing. Improving the generation of ore concentrates and use of kinetic and thermodynamic data regarding smelting and converting can increase the production of geochemically scarce elements in the pyrometallurgical processing of copper ores. Reprocessing of copper ore processing residues can serve the generation of geochemically scare elements and the clean-up of matrix materials. Modularization of products, closed-loop take-back, including deposit-refund, systems for end-of -life products, and changes in the pre-processing thereof can be conducive to improved recovery of geochemically scarce elements from end-of-life electric and electronic equipment and car electronics. A comparatively large variety of geochemically scarce elements originating in end-of-life products can be recovered when in smelting lead and copper serve as collectors. Substantial research and development work is needed to optimize the co-production of geochemically scarce elements by hydrotechnology from copper ores and (mined) end-of-life products and to assess the potential of solvochemistry. There is technical scope for significant progress in the direction of near-zero waste processing in processing copper ores and (mined) end-of-life products, but for the realization of near-zero waste processing there are hurdles to be overcome related to marketability of outputs, safe handling of hazardous elements and company behavior. Also, the techno-economic potential of hydrotechnology and solvochemistry in extracting copper ores, copper ore processing residues and end-of-life products is uncertain. In view thereof, the feasibility near-zero waste production of copper and its geochemically scarce companion elements from copper ores and end-of-life electric and electronic equipment and car electronics is uncertain. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries (LIBs) are employed in various electronic devices and industries. The recovery of valuable metals from spent LIBs has attracted much interest due to potential environmental issues and economic values. Metallic alloys can be obtained from the UHT process of spent LIBs. In this study, a hydrometallurgical process was developed for the recovery of metal compounds from synthetic metallic alloys containing Co, Ni, and Cu. This process consisted of leaching, solvent extraction, stripping and precipitation. First, the metallic mixtures were completely leached by the mixture of 2.0 moL·L−1 HCl and 10%(v/v) H2O2 solutions at 60°C. Metal ions in the leachate were sequentially separated by solvent extraction with 0.7 moL·L−1 Cyanex301 and 1.0 moL·L−1 Aliquat 336 for Cu(II) and 1.0 moL·L−1 ALi-SCN for Co(II), whereas Ni(II) was remained in the final raffinate. The compounds of Cu(II) and Co(II) were recovered from the respective loaded organics by precipitation stripping method, while Ni(II) compounds were recovered by precipitation from the final raffinate without changing its acidity. Mass balance of the whole process indicated that the recovery percentage of metal compounds such as CuC2O4, CoCO3, and NiC2O4 · 2 H2O was 98.6, 99.4, 99.8% from the leaching solution and the purity of the compounds was higher than 99.9%. A process was proposed for the recovery of pure metal compounds from spent LIBs. The advantages of this process are the possibility that metal compounds with high purity can effectively be synthesized and the aqueous raffinates and the stripped organic solutions after each step can be recycled. [ABSTRACT FROM AUTHOR]

This study presents an up-to-date review on the methods and technologies applied for the recovery of Co from end-of-life Li-ion batteries. Considering the upcoming world demand for electric vehicles, it has been demonstrated that Co recycling from such batteries is technically feasible and vital in an attempt to provide a global supply of the metal. In this study, a number of recovery methods (including thermal, mechanical, and manual preprocessing, along with pyro- and hydrometallurgical methods) with distinct efficiency levels was described, several of which may be combined and associated between them in order to improve the overall Co separation and recovery performances. [ABSTRACT FROM AUTHOR]

Spodumene is the main source of lithium among the lithium-containing minerals. A number of studies have been done on the extraction of lithium from naturally occurring α-spodumene as well as pre-treated β-spodumene and the effect of key factors that influence extraction and optimum processing conditions have been discussed. Some of these methods have remained at a laboratory scale because they were not economically and operationally feasible, while some have been developed further. The increasing demand for lithium justifies efforts for the development of new methods as well as improving the existing commercial extraction processes. A comprehensive and detailed study of the available literature on lithium extraction studies is a useful starting point for this research. The present article is a review of the extraction methods of lithium from spodumene concentrate, after beneficiation, which have been studied to date. [ABSTRACT FROM AUTHOR]

Waste electrical and electronic equipments (WEEE or e-waste) are an important source for rare earth elements (REEs). Among various type of WEEE, NdFeB magnets are known for their high content of neodymium (Nd) and dysprosium (Dy). Recovery of REEs from NdFeB magnets is of prime interest for the industry to meet the ever-growing demand for REEs. In this study, some physical and hydrometallurgical approaches including demagnetization, grinding, screening, leaching, precipitation and extraction have been adopted to study the Nd and Dy recovery from spent NdFeB magnets. Various inorganic (HCl, HNO₃, H₂SO₄ and aqua regia) and organic reagents (acetic acid and oxalic acid) were tested as lixiviants for leaching of the magnets. As a new approach, the recovery of Nd and Dy in the leaching solution was tested by eliminating the iron by a solution purification process involving precipitation of ferric iron in solution as hydroxide and solvent extraction with ionic liquids (ILs). The comparative studies demonstrated that the extraction efficiency of di-2-ethylhexyl phosphoric acid (D2EHPA) was higher than trihexyltetradecylphosphonium chloride (CYPHOS® IL101) after leaching stage. Nd and Dy were successfully extracted with complete recovery from the optimized system. [ABSTRACT FROM AUTHOR]

Gold and copper thiosulfate adsorption from an alkaline gold ore leachate was investigated by using polyethylenimine-coated iron oxide magnetic nanoparticles (NPs). The ore, sourced from a mine in Nevada, USA, was leached with calcium thiosulfate for 48 h in the presence of Cu(II) at a pH of 8 and a temperature of 50°C. A response surface methodology was used to analyze the effect of adsorbent dosage, adsorption time and solution temperature on the recovery of gold and copper from the solution. The results showed that the gold adsorption was nonlinearly dependent on the adsorbent dosage only. In contrast, the recovery of the copper depended on all three predictors, including interaction between the temperature and adsorbent dosage. The optimal conditions for maximal gold adsorption was 35 g/L adsorbent dosage, 55 min time and a temperature of 23°C. The selective elution of loaded metals on the NPs was also successfully achieved. [ABSTRACT FROM AUTHOR]

Pretreatment of ilmenite are required to enhance leaching efficiency of ilmenite. Strong acid leaching is promising in terms of the purity of the produced TiO2, low energy consumption and waste management. The effect of several factors on the acid leaching kinetics in reported processes was reviewed. Temperature, time and acid concentration significantly affect the dissolution of titanium and impurities in ilmenite. The addition of either iron powder or chloride/sulfate salts affects significantly the leaching rate of ilmenite. Either HCl leaching followed by solvent extraction or alkaline leaching followed by hydrolysis-calcination is recommended for the production of pure TiO2 from ilmenite. [ABSTRACT FROM AUTHOR]

The price of cobalt has increased by some 450% in the past two years, mainly due to increasing demand for lithium–ion batteries. With an official 2017 production of 64 kt, the Democratic Republic of Congo produces more than half of the world's cobalt. African Copperbelt operations have traditionally focused on copper production; however, it has now become imperative to also consider cobalt recovery from these ores. A plethora of processing routes is possible. Most hydrometallurgical flowsheets recover cobalt from the raffinate of the low-grade copper solvent-extraction circuit. Downstream purification processes include sequential precipitation with a variety of reagents, solvent extraction, and ion exchange. Product choices include hydroxide, carbonate, sulfate, and metal cathode. This study assesses technical and economic advantages and limitations of various approaches to the hydrometallurgical processing of cobalt in an African context. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive review of polymeric resins used for metal separation in hydrometallurgy and water/wastewater treatments. The adsorption selectivity of a resin depends on the characteristics of the functional group and solution pH. The resins are reviewed and categorized with respect to the principal acting atoms in functional groups (i.e., nitrogen, sulfur, phosphorous, oxygen) and ion-exchange properties. General selectivity trends, metal ion preferences, and applications reported in the scientific literature are summarized for each functional group. This review is intended as a reference for the selection of ion-exchange resins for metal separation and recovery. The selection criteria also depend on the type of process and metal ion concentration. [ABSTRACT FROM AUTHOR]

The by-products of zinc refineries are used as the primary mineral resources for the commercial production of indium. The discarded LCDs containing adequate amount of indium is rather worth as its secondary resources compared to the by-products of zinc refineries. Mining and recycling rates of indium, respectively from minerals and waste LCDs are in progress to meet its huge demand. Recycling of the LCDs has been dominating over mining, as presently 480t of indium are produced annually from mining, however, that of 650t annually from recycling. Different aspects of the extractive metallurgy of indium are summarized in this review paper. [ABSTRACT FROM AUTHOR]

Porphyry copper and mixed copper-gold sulfide deposits contain varying amounts of precious (gold and silver) and platinum group metals (PGMs). Currently, milling and froth flotation is the most common processing route for the treatment of high-grade base metal sulfide ores. During this process, the precious metals and PGMs are also concentrated and represent a possible opportunity for the beneficiation of these metals to increase the overall economic value of the ore. Although not yet commercialized, the high temperature pressure oxidation (POX) of copper concentrates provides an alternative processing route to traditional smelting technology. With increasingly aggressive air quality standards and rising upstream processing costs for smelting, hydrometallurgical processing options become progressively attractive. The treatment of POX residues for the recovery of precious metals has seen significant attention and multiple processing routes have been developed on various scales. Extraction and beneficiation of PGMs from copper concentrate POX residue has garnered significantly less attention and mechanistic questions remain to be answered. Based on a review of the processing options for PGM ores and concentrates, hydrometallurgical processing routes for the extraction of PGMs from copper concentrate POX residues are envisioned. [ABSTRACT FROM PUBLISHER]

The bottom ashes, produced by the industrial incinerators, are an essential secondary raw material resource that has been drawing attention to recover economically important metals. In the present study, a hydrometallurgical process (chemical leaching) has been discussed to recover some economically important metals using lab scale reactors (600 mL and 2L capacity). Prior to the leaching tests, the material was characterized for chemical composition and mineralogical phase analysis through XRD. In addition, the conventional process of magnetic separation was applied before leaching tests to remove some easily separable parts. Two acidic reagents (HCl and H2SO4) and an alkali reagent (NaOH) have been used to compare the recovery of metal values from the pre-treated bottom ash samples at varying concentrations. Process parameters such as acid/alkali concentration, working volume and temperature have been optimized and the recoveries of metal values under optimum conditions were recorded. The studies showed that 3M H2SO4,1.5 L working volume and 80°C were sufficient to leach 88% Mo, 82% V, 37% Ni, 37% Fe, and 28% Cu. Acid leaching tests using H2SO4were found to be an economical and appropriate solvent for metal recovery from bottom ash. [ABSTRACT FROM PUBLISHER]

Leaching is a hydrometallurgical activity widely used in mineral processing, both for metallic and non-metallic ores, and in soil remediation. The dissolution of valuable species by heap leaching is strongly dependent on the design and operating variables, so the study of the influence of these variables on recovery and their optimization for the best performance are attractive tasks for the development of the mining industry. In this work, a methodology is developed that enables the planning and design of leaching systems. This methodology uses a proposed superstructure and a mathematical model to analyze the system behavior and determine the optimal design and operating conditions. The model was generated with a Mixed Integer Nonlinear Programming (MINLP) approach and solved by different solvers under GAMS® software (General Algebraic Modelling System). The Spatial Branch-and-Bound (SBB) solver obtained the global optimum in the shortest times. Based on a case of study for copper leaching, it is demonstrated that the procedure allows achieving optimal design and operational conditions. [ABSTRACT FROM PUBLISHER]

This study demonstrates an efficient synthesis of highly reactive silica using hydrometallurgical processing of serpentinite tailings. Proposed process uses two-stage (acid and alkaline) leaching of serpentinite tailings and precipitation of silica from the sodium metasilicate solution using hydrochloric acid. The alkaline leaching and the effect of impurities on the precipitation of amorphous silica under the conditions of maximum sol stability were examined in detail. The proposed route is technologically advantageous because the product did not contain residues of the original raw serpentinite and was characterized by high purity (99.4 wt. % SiO2), large specific area (541 m2g–1), and consistent quality. Moreover, less sensitivity to the presence of impurities and longer gelation times, offering a longer time period for manipulating the product in the final stages of the process, were achieved. The total yield of silicon in the overall process was 90–91%. [ABSTRACT FROM PUBLISHER]

Mixers are widely used in chemical and hydrometallurgical processes. For instance, one of the greatest challenges in the field of hydrometallurgy process is agitation made by impeller inside mixers. Solvent extraction is a process for separating components in solution by their distribution between two immiscible liquids. Dynamic mixers are qualified as efficient vessels for mixing in processes accompanied by mass, momentum and heat transfer and chemical reaction. One of the advantages of this type of receptacles is their high productivity. In this study, recent conceptual and technological innovations in various dynamic mixers are reviewed. For this purpose, geometrical, operational, and physical effective parameters in the most important research are investigated. In addition, optimal parameters, drop size measurement, and distribution are discussed. Current industrial applications and efficiency are discussed from a process perspective, focusing on mixing. Considering the development of flow equipment in various flow regimes, advances in this field will play a crucial role in scientific and industrial communities. For design and optimization of the dynamic mixers, some models are used. The model structure is selected based on its good compromise between accuracy and complexity. Validation of the computational fluid dynamics models with experimental data by using progressive methods resulted in realistic simulations. In recent researches, there has been an increasing interest in the development of alternative designs for improvements of key elements, such as geometry of baffles, mixer vessels, impellers, operational parameters of mixers and impellers, etc. [ABSTRACT FROM PUBLISHER]

Heap leaching is a well-established extractive metallurgical technology enabling the economical processing of various kinds of low-grade ores, which could not otherwise be exploited. However, despite much progress since it was first applied in recent times, the process remains limited by low recoveries and long extraction times. It is becoming increasingly clear that the choice of heap leaching as a suitable technology to process a particular mineral resource, which is both environmentally sound and economically viable, very much depends on having a comprehensive understanding of the underlying fundamental mechanisms of the processes and how they interact with the particular mineralogy of the ore body under consideration. This paper provides an introduction to the theoretical background of various heap leach processes, offers a scientific and patent literature overview on technology developments in commercial heap leaching operations around the world, identifies factors that drive the selection of heap leaching as a processing technology, describes challenges to exploiting these innovations, and concludes with a discussion on the future of heap leaching. [ABSTRACT FROM AUTHOR]

Coal combustion results in wastes such as fly ash, slag, and flue gases. In Turkey, approximately 45 million tons of coals are fired annually and consequently around 20 million tons of fly ashes are produced. Such large volumes of ash pose a significant problem both for society and the environment. Furthermore, significant amounts of uranium and thorium are often encountered in these ashes. These concentrations are relatively higher for ashes from younger age lignites. Within the scope of this study, a series of characterization tests were performed on samples taken from Soma thermal power plant, one of the largest in Turkey. Characterization studies include particle size analysis, moisture analysis, density determination, pH profile measurements, chemical analyses, and mineralogical analyses. Leach tests with sulfuric acid (H2SO4) were then performed. The leaching of the radioactive minerals (uranium and thorium) with the help of sulfuric acid in the ashes was examined and the optimum leaching parameters were investigated. The recovery opportunities of uranium and thorium metals in the ashes were addressed. The results indicated that under optimum conditions, 94.71% uranium dissolution efficiency and 93.21% thorium dissolution efficiency were obtained. [ABSTRACT FROM AUTHOR]

Gold is one of the most important sources of currency entry in the economics of any state. Besides mining raw materials, fit for effective gold extraction, residues of gold extraction factories are the source of this precious metal. Moreover, the role of industrial wastes, which has a rich source of nonferrous and noble metals, increases. Processing expediency of complicated wastes is determined by their harmful ecological influence on the environment. Involving to processing of gold, the enumerated sources demands the use of high leading technologies, taking into account the variety of their composition. One of the ways of increasing effectiveness of processing the gold-containing materials may be introduction of direct hydrometallurgy processes. Hydrometallurgical methods of processing differ in low power capacity, simplicity of implement process, decreasing pollution of the environment. It is necessary for this not only to sort out selective solvents, but also to elaborate methods of regeneration and recycling of the used solutions and solvents. At present leaching of gold-containing raw materials by cyanide is the main hydrometallurgical process and the main advantage of cyanide is high selectivity with regard to gold. However, leaching by cyanide solutions has a set of substantial drawbacks: process duration, high cost of the reagent, nonadaptability of “stubborn” ores and concentrates, absence of possible regeneration of cyanide solutions and the main thing is high toxicity of cyanide compounds. Therefore elaboration of new hydrometallurgical methods of extracting gold using selective nontoxic reagents, in particular, iodine solutions is important scientific and practical task. [ABSTRACT FROM PUBLISHER]

With the vigorously growing demand of the steel industry, oil and gas industry, corrosion resistance alloys, cast iron, and catalyst industries, high-grade molybdenum ores are being exhausted gradually in the world. Thus, much attention have been drawn to the recovery of molybdenum from low-grade molybdenum ores in recent years. With the increasingly stringent environmental requirements, the shortcomings due to SO2emission in the roasting process of traditional technology becomes obvious. This review outlines metallurgical processes for molybdenum production from various resources, particularly focusing on recent developments in direct hydrometallurgical and recovery processes to identify potential sources of molybdenum products and by-products such as uranium which can be economically produced. Several methods have been extensively reviewed for molybdenum separation and purification from solution which are potentially applicable to leach solutions of molybdenum ores and raw materials. The main methods include solvent extraction, ion exchange, membrane-based separation, and precipitation. Solvent extraction is highly selective for recovery of molybdenum and the most promising method recommended for future research and development. Membrane-based separation is the next preferred method for selective extraction of molybdenum, purification of molybdenum solutions, or co-recovery of other valuable metals. Ion exchange offers useful means for purification and/or co-recovery of other base metal impurities, although the scale of application of ion exchange in the industry is limited. [ABSTRACT FROM PUBLISHER]

Platinum-group metals (PGMs) have become one of the most sought after rare metals in this modern age of science and they will continue to increase in importance as a result of their advantageous use in clean-air technology. Due to the scarcity of these precious metals, the application of ion exchange processes to recover PGM ions from relatively uncontaminated aqueous solutions, such as produced by the leaching of secondary sources including used automotive catalytic converters and electronic scrap, is becoming an increasingly cost-effective option and hence an important topic for the PGM production industry. This paper provides a general overview of the basic principles and theories relevant to the hydrometallurgical recovery of PGMs using ion exchange resins, along with a review and discussion of the most important factors that affect the separation and purification of PGMs present initially in predominantly ionic state in an aqueous hydrochloric acid solution. It is shown that in these acidic chloride solutions, the current system of choice for the leaching of PGMs, the adsorption behavior of the PGM ions onto chelating ion exchange resins is strongly dependent on the anionic PGM chloro-complex species present. In addition, it is revealed that the main factors affecting this complexation are (i) acidity and chloride ion concentration of the contacting aqueous chloride solution, (ii) “ageing” of the solution, and (iii) temperature of the solution. [ABSTRACT FROM PUBLISHER]

An update is presented to the paper “Recent trends in the processing of enargite concentrates” by Safarzadeh, Moats, and Miller (2014). Publications which were not included in the initial review paper, primarily to avoid redundancy, are presented and discussed here. Thus, roasting, atmospheric acidic and alkaline leaching, the dissolution of enargite in low-melting point salts, bioleaching, and pressure leaching are presented. For the first time, the modified phase stability (Kellogg) diagram and the Eh-pH diagram for the Cu-As-S system including sinnerite (Cu6As4S9) have been established. According to the results from different treatment options discussed in our earlier review and also in this paper, it is evident that the most recent research activities for the treatment of enargite concentrates are centered around roasting, alkaline sulfide leaching, and high temperature pressure oxidation. Taking into account the advantages and disadvantages of the mentioned processing options, and the numerous preliminary experiments performed, the acid bake-leach process has been identified and is being studied at the University of Utah. It has been found that enargite transforms to water-soluble copper sulfate, arsenic trioxide and elemental sulfur by sulfuric acid baking of enargite at 200°C, with less than 1% of the arsenic being released to the gas phase. This process strategy provides a new possibility for the treatment of enargite concentrates. [ABSTRACT FROM PUBLISHER]

The copper industry is witnessing great interest in the development and utilization of copper-arsenic deposits. While most plants tend to use traditional processing technologies, the depletion of conventional copper ores has created competition for designing and implementing new process alternatives for the treatment of copper-arsenic ores containing minerals such as enargite, luzonite, and tennantite. Nevertheless, the downstream processing of high-arsenic copper concentrates represents a significant metallurgical challenge in terms of both arsenic separation and also its stabilization in an environmentally benign form that fulfills the current and future environmental policies. Smelters are subject to penalties on high arsenic-bearing copper concentrates. While reductive roasting can drive-off the arsenic from enargite concentrates to an acceptable level suitable for smelting (<0.5 wt.%), this option has generally been viewed as unacceptable due to environmental conflicts and the lack of a market for arsenic trioxide. The lack of a suitable pyrometallurgical option has led to several proposed hydrometallurgical treatments of enargite concentrates. Hydrometallurgical options include either selective arsenic dissolution to produce a clean copper concentrate or collective leaching of copper and arsenic. Both options with various conditions and lixiviants are discussed and evaluated. In this review, alkaline sulfide leach (ASL), sulfate- and chloride-based leach systems, high temperature pressure oxidation (HTPOX), sodium hypochlorite leach, bio-leach/oxidation, nitrogen species catalyzed pressure oxidation, Cominco Engineering Services Limited, Intec, HydroCopper™ and Fluobor® processes are outlined. Pyrometallurgical process strategies have also been briefly reviewed. Among all processing options, ASL, HTPOX, Fluobor® and reductive roasting processes are given special attention with specific flowsheets for enargite concentrates discussed. [ABSTRACT FROM PUBLISHER]

Leaching of iron, either as an impurity to be removed or as a metal to be recovered, requires a different approach than that of the oxidative leaching that dominates biohydrometallurgy of other metals. In particular, the significant increase in solubility that results from reducing Fe3+to Fe2+suggests that a reductive leaching process is most suitable. A wide range of anaerobic iron-reducing bacteria have been demonstrated to exist in the last few decades, which reduce Fe3+to Fe2+as part of their respiration. More of these organisms are continually being discovered, and many of these have promise for reductive bioleaching of iron. This review examines the many types of bacteria that have been demonstrated to reduce and solubilize iron, and the environments where such organisms can be found. The cultivation requirements of these organisms are also discussed, along with descriptions of the work that has been done to apply them to specific applications. These applications include decolorization of kaolin and silica, iron removal from bauxite, recovery of iron from low-grade or difficult-to-process ores, and promoting breakdown of iron-rich rocks to liberate other metals. Reductive iron leaching in these applications has been shown to be most effective for dissolving the more hydrated and amorphous iron oxides, with low dissolution rates for highly crystalline oxides such as hematite. It has also been shown that, the given sufficient adaptation and leaching time, these microorganisms can produce iron-bearing solutions containing as much as 1800 mg of Fe2+per liter. [ABSTRACT FROM PUBLISHER]

This review addresses the detrimental effects of fluoride on the various steps which constitute any hydrometallurgical operation. It focuses on the specific examples of apatite flotation, copper bioleaching, zinc electrowinning, and the manufacture of phosphoric acid. The presence of fluoride modifies the surface characteristics of minerals altering their effective flotation. Toxicity of fluoride to bacteria directly affects the mechanisms of bioleaching. Fluoride can interfere with the adhesion of metals to cathodes and affect deposit morphology during electrodeposition. In phosphoric acid synthesis from phosphate ores, fluoride affects production efficiency by altering the crystal morphology of the gypsum by-product. [ABSTRACT FROM AUTHOR]

Chalcopyrite passivation phenomenon drastically slows the copper extraction rate in hydrometallurgical processes; currently, scientists have reached an apparent consensus about the causes of this phenomenon. A great deal of information on this subject can be found in the literature, but there are also abundant differences in the experimental conditions applied and contradictions in the conclusions reached, making it difficult to obtain a global and structured view of the real advances in the research. This paper comprises an ordered classification of the available information regarding the unresolved and the often-ignored issues addresses by electrochemistry and surface analysis techniques. [ABSTRACT FROM PUBLISHER]

Sulfide minerals are one of the most important sources of metal values. On the other hand, some sulfides such as pyrite are considered as one of the major impurities in solid fossil fuels such as coal. Oxidation of these sulfides has been one route to obtain base metals and to remove sulfur by leaching. This work summarizes the results obtained regarding the use of ozone in the oxidation of sulfide ores containing gold, silver, and copper. Results show that the extraction of gold and silver is increased by at least 15%, with lower cyanide consumption; the extraction of copper increased by 16% and in less time; and in the case of coal, sulfur is removed above 70%. These results indicate that oxidation treatment with ozone could be a promising clean technology to optimize ore processing, which is difficult to treat by current industrial methods. [ABSTRACT FROM AUTHOR]

Present paper focuses on the selective recovery of copper from the enriched ground printed circuit boards (PCBs) using leaching and solvent extraction. The metal-enriched ground sample obtained from the beneficiation of the sized PCBs in a laboratory scale column type air separator contained mainly 49.3% Cu, 3.83% Fe, 1.51% Ni, 5.45% Sn, 4.71% Pb, and 1.85% Zn. The leaching of the enriched sample with 3.5 mol/L nitric acid dissolved 99% copper along with other metals at 323 K temperature and 120 g/L pulp density in 1 h time. The composition of the leach liquor with wash solution was found to be 42.11 g/L Cu, 2.12 g/L Fe, 4.02 g/L Pb, 1.58 g/L Zn, and 0.4 g/L Ni. The McCabe-Thiele plot indicated the requirements of three counter-current stages for maximum extraction of copper from the leach liquor at pH 1.5 using 30, 40, and 50% (v/v) LIX 984 N at the phase ratios (A/O) of 1:3, 1:2, and 1:1.5, respectively. The counter-current simulation studies show the selective extraction of 99.7% copper from the leach liquor feed of 1.5 pH in three stages with 50% LIX 984 N at A/O phase ratio of 1:1.5. The stripping of copper from the loaded organic with sulfuric acid produced copper sulfate solution from which copper metal/powder could be recovered by electrolysis/ hydrogen reduction. [ABSTRACT FROM AUTHOR]

In this study, application of the Response Surface Methodology and the Central Composite Design (CCD) technique for modeling and optimization the influence of some operating variables on gold and silver recovery in a cyanidation process were investigated. Three main cyanidation parameters, namely grinding time, sodium cyanide concentration, and alkalinity of solution, were changed during the concentration tests based on CCD. The range of values of the cyanidation process variables used in the design was as follows: grinding time, 32.61-44.39 min, sodium cyanide concentration, 1989-4511 ppm, and pH, 9.32-12.68. A total of 20 cyanidation tests were designed and carried out in the CCD method according to software-based designed matrix. According to the results, i.e., gold and silver recoveries with these three parameters, empirical model equations, were developed. Second-order equations of responses at the base of parameters were achieved by using statistical software. The model equations were then individually optimized by using quadratic programming to maximize both gold and silver recoveries within the experimental range. The optimum conditions were found to be 41.89 min for grinding time, 3665.28 ppm for cyanide concentration, and pH 9.32, for achieving the maximum gold recovery (96.23%). Similarly, the conditions for maximum silver recovery were 65.62% at 44.39 min for grinding time, 4511.34 ppm for cyanide concentration, and pH 12.68. The predicted values for gold and silver recoveries were found to be in a good agreement with the experimental values, with R2 as correlation factor being 0.91 and 0.94, respectively. [ABSTRACT FROM AUTHOR]

The sorption of gold chloride ([image omitted]) from chloride solution on synthetic and natural magnetite powders was investigated by batch sorption experiments. The effects of different parameters on the recovery were studied. The results showed that Gold (Au) uptake by magnetite was influenced by pH, contact time, chloride concentration, and initial Au concentration. Gold uptake by synthetic and natural magnetite was maximum at pH 6-7 with sorption amounts of 4.4 μmol/g and 5.0 μmol/g, respectively, after 24 hr at an initial Au concentration of 0.05 mol/m3. The Scanning Electron Microscopy-Energy Dispersive X-ray and Back Scattering Electron analyses of the magnetite particles after treatment confirmed the presence of Au precipitates on the magnetite (Fe3O4) surface. [ABSTRACT FROM AUTHOR]

A review of the literature dealing with the effect of cobalt on lead-based anodes for oxygen evolution during electrolysis of sulfuric acid solutions verifies that the presence of cobalt at the anode-electrolyte interface, either as constituent of the anode material or as ions in the electrolyte, catalyzes the evolution of oxygen and reduces the corrosion of the anodes and the contamination by lead of metal cathodes produced during electrowinning. However, due to harmful effects of cobalt ions on the cathodic reaction in some processes, these benefits are limited to the electrowinning of copper. Efforts to develop a way of introducing cobalt at the anode-electrolyte interface without interfering with the cathodic reactions are reviewed in this paper. The use of lead-cobalt alloy anodes has had limited success due to issues arising from the low solubility of cobalt in lead, segregation during casting of the alloys, and nonuniform distribution of cobalt which affects the integrity of the anodes. This has been overcome in part lately by inclusion of cobalt into only the surface layer of a lead or lead alloy substrate, by thermal treatment of a cobalt salt to form a catalytic cobalt oxide surface species, or by electrodeposition of composite lead-cobalt oxide anodes. The last approach in particular has been actively investigated by several groups, but to our knowledge it is yet to find application in the industry. The review also critically examines the likely reaction mechanisms involved. [ABSTRACT FROM AUTHOR]

Several hydrometallurgical processes have been studied for the extraction of metals from lean ores utilizing various flow sheet options. Of particular significance is the grade of the ore being treated, the energy consumed and associated costs, options for byproduct recovery, and the relative price of the products. A process scheme needs to be optimized for simultaneously maximizing metal throughput and minimizing the direct operating costs incurred within constraints set for the operating variables. This leads to a multi-objective optimization problem. The range of input grades for raw material, which a flowsheet can handle, needs to be worked out based on an optimization exercise. A lean manganese-bearing resource such as polymetallic sea nodules has been chosen in this article for the development of an optimization approach based on which the input raw nodules grades are to be treated by a particular flowsheet. Only the chemical consumption costs have been adopted in this article as a measure of direct operating costs. A linear simulation model for the flowsheet has been developed, keeping a set of design parameters constant. The solutions generated by using a sequential modular approach become inputs to an optimization procedure based on a multi-objective genetic algorithm belonging to the differential evolution family. The variables considered in the optimization task are the grade of nodules and reactivity of different species inside the reactor. A nickel equivalent (t/h function) has been suggested as a measure of productivity, as it indirectly enhances the input manganese ore grade through a price ratio effect. This productivity function was maximized with the simultaneous minimization of direct chemical costs. Pareto optimal solutions were generated with grades of nodules and reactivity in the leach reactor as decision variables. The effect of the price ratio on the Pareto optimal solutions was also investigated. The various cases investigated clarifies the methodology for choosing an appropriate ore grade range for a given process flowsheet. Appropriate decisions regarding the nature of raw material to be used for a given flowsheet are then found on the basis of the Pareto optimal solutions. [ABSTRACT FROM AUTHOR]

Electrochemical processes utilizing three-dimensional (3-D) electrodes have significant potential for a variety of applications, particularly for the treatment of dilute effluents. The use of electrons to reduce the metal species from solution can be regarded as “cleaner” technology than the use of a chemical reagent, which would further contaminate the waste stream. Literature detailing the studies of these electrodes has been extensively published. A review of such literature is presented, summarizing the various types of 3-D electrodes and certain design considerations. [ABSTRACT FROM AUTHOR]

The effect of cobalt ions in the electrolyte on the performance of lead alloy anodes used for oxygen evolution during electrolysis of copper/sulfuric acid solutions has been studied extensively over the past 90 years. A review of the literature has confirmed that cobalt both as constituent of the anode material and present as ions in the electrolyte reduces the rate of corrosion of the anodes, lowers the overpotential for the evolution of oxygen, and reduces lead contamination of the copper cathodes. Despite the fact that these effects have been developed into widespread applications in the electrowinning industry, a fundamental understanding of the mechanism of the action of cobalt ions remains a point of debate. A selection of the most relevant literature on this phenomenon has been reviewed and the data and proposed mechanisms critically evaluated. [ABSTRACT FROM AUTHOR]

Titania-rich slags with 80 mass percent TiO 2 are produced in the electric arc furnaces of QIT-Fer & Titane, Inc., by the continuous smelting of hemo-ilmenite ore with anthracite coal. Titania slag represents an important feedstock for the manufacture of titanium dioxide pigment by the sulphate process. Moreover, part of the production of the titania-rich slag is further acid-leached under a high-pressure and moderate-temperature hydrometallurgical process to yield an upgraded titania slag with 94.5 mass percent TiO 2 , which is used in the chloride process. After describing in detail the beneficiation, chemistry, and mineralogy of the hemo-ilmenite ore, this article reviews the unique crystallochemistry and mineralogy of the titanate phases with pseudobrookite-karrooite structure and to a lesser extent silicates and oxides present in these titania-rich feedstocks, focusing on the chemical reactions occurring at each step of the pyro- and hydro-metallurgical processes. The behavior of major elements such as titanium, iron, magnesium, calcium, aluminum, and silicon along with that of minor elements such as vanadium, chromium, and manganese are particularly detailed. A general discussion of the methods specifically developed for the study of the synthetic minerals present in these materials is also presented. [ABSTRACT FROM AUTHOR]

The use of ammonium carbonate for the extraction of metals such as copper and nickel is well known. Less well known is the fact that ammonium carbonate extraction was used for the commercial recovery of zinc decades before its application to either copper or nickel. This article reviews the published data on the Schnabel Process (the hydrometallurgical extraction of zinc by ammonium carbonate) covering the period of 1880–2005. [ABSTRACT FROM AUTHOR]

Modeling the chemical equilibrium in ionic solutions encountered in industrial applications, especially in the field of hydrometallurgy, still remains an unresolved issue. The complicated speciations, as well as the high ionic strengths encountered in these solutions, render the theories of analytical chemistry practically useless. The Debye–Hückel theory is examined in depth, so as to reveal the reasons of its failure. To remedy this problem, over the years, a large number of semi-empirical models have been proposed that are here reviewed, in order to help the reader find a model best suited for a system of interest. The models are classified into three main categories, based on their fundamental logic: ion interaction models describe the system through the physical interactions of the ions; ion association models describe the system through chemical equilibriums; and finally hybrid models use concepts from both previous categories. Focus is given in presenting the idea upon which each model is based rather than simply presenting the equations required for its implementation. [ABSTRACT FROM AUTHOR]

This short communication highlights important biological features of a pyritic refractory gold ore heap-leaching environment. Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans were to be two of only three bacterial species detected on the ore surfaces at ambient temperature. Sulfobacillus was not originally introduced in the inoculum, but was later detected in the column. Only organisms of the Leptospirillum genus were present in the ferric sulfate leaching solution. Ignoring that the ore hosted approximately 500 times more microorganisms than the solution can greatly underestimate the oxidizing potential. One or more of these microorganisms oxidized ferrous ions, leading to a rise in the solution potential. They also oxidized elemental sulfur, resulting in a higher sulfate yield than measured in sterile medium. [ABSTRACT FROM AUTHOR]