Extraction Of Valuable Metals Research Articles

Modeling of Thermal Effect of Chemical Reactions in Heap Bioleaching of Chalcopyrite

Heap bioleaching is regarded as an environmental-friendly technology to extract valuable metals, such as gold, silver, copper, etc., from low grade or waste ores. The chemical reactions accelerated by microorganisms are usually complex. Microbial activity is ascribed to the physiochemical factors such as temperature. Due to the variety of ore components, the thermal effect is difficult to elaborate. In this study, typical ores used for heap bioleaching of chalcopyrite are theoretically analyzed to explore the mechanism involving the thermal effect of chemical reactions. The thermal distribution is compared between different proportional combinations. The results show that biotite is the dominant contributor and should be verified carefully in the heap bioleaching of chalcopyrite.

Extraction of Valuable Metals From Spent Hydrodesulfurization Catalyst By Two Stage Leaching Method

Spent hydrodesulfurization (Co-Mo/γ-Al2O3) catalyst generally contains valuable metals like molybdenum (Mo), cobalt (Co), aluminium (Al) on a supporting material, such as γ-Al2O3. In the present study, a two stages alkali/acid leaching process was conducted to study leaching of cobalt, molybdenum and aluminium from Co-Mo/γ-Al2O3 catalyst. The acid leaching of spent catalyst, previously treated by alkali solution to remove molybdenum, yielded a solution rich in cobalt and aluminium.

Recovery of Valuable Metals from Zinc Plant Residues by Two-Stage Selective Atmospheric Leaching Process

A hydrometallurgical process was used for selectively extraction of valuable metals from zinc plant residues. The process includes the following two steps. (1) The zinc plant residue is treated by sulfuric acid atmospheric leaching process with KMnO4 as oxidatant to selectively dissolve zinc while leaving most (above 98 pct) of indium and germandium in the iron residues. (2) The iron residues are treated by acidic atmospheric leaching process with NaClO3 as oxidant to dissolve indium and germanium. The valuable metals of indium and germanium in the second leaching solution can be reclaimed by further treatment. The optimum operating parameters of the first stage and the second stage were established by conditional tests. The experimental data indicated that under the conditions employed the zinc extraction in the first stage was above 95%, and the leaching percentage of indium and germanium in the second stage reached 91.6% and 90.7%, respectively.

High blood lead levels in e-waste recyclers

ObjectivesThere is a huge informal sector of electronic and electrical waste recycling in India. Domestic as well as imported e-waste is being recycled to extract valuable heavy metals like lead,...

Waste Catalyst Utilization: Extraction of Valuable Metals from Spent Hydroprocessing Catalysts by Ultrasonic-Assisted Leaching with Acids

Every year large quantities of spent hydroprocessing catalysts containing high concentrations of metals such as Mo, V, Ni, and Co are discarded as solid wastes from the petroleum refining industries. The metals present in the spent catalysts can be leached by water and pollute the environment. As these catalysts are hazardous wastes, landfills or other treatment methods for disposal are not preferable when all costs and liabilities are taken into account. Intensive efforts have been made in recent years on the development of processes for recycling and utilization of the waste catalyst materials as much as possible. Recovery of the valuable metals from the spent catalysts is an attractive option for their recycling and utilization. In the present work, the influence of ultrasonic agitation in enhancing the extraction of valuable metals such as Mo, V, and Ni from spent hydroprocessing catalysts by acid leaching was investigated. Two acids, one inorganic (H2SO4) and the other organic (citric acid), were use...

Gelation of aqueous clay mineral dispersions leaching at low pH: Effect of mineral/pulp composition and temperature

Presence of gangue aluminosilicate clay (e.g., muscovite) minerals plays an important role in controlling mineral ore processability and extraction of valuable metals (e.g., copper, gold). Hydrometallurgical processing of clay containing minerals at low pH (~1) and elevated temperature (e.g., 70°C) sometimes leads to deleterious viscous gel formation nominally ascribed to leached Si(IV) polycondensation. In this study, the leaching and gelation behaviour of 30–57wt.% solid muscovite dispersions was investigated at pH 1 with a particular focus on the role of mineral chemistry (low-Fe vs. high-Fe substituted muscovite), temperature (25 and 70°C) and supernatant Si(IV) and Al(III) concentration (0.1–1.5M). The temporal particle interactions, reflecting the extent of gelation was characterized by pulp shear rheology. At 25°C, low yield stress was initially displayed by low-Fe muscovite dispersion whilst the high-Fe muscovite dispersion formed a gel. At 70°C, however, both dispersions initially displayed lower yield stress. In all cases, the magnitude of yield stress systematically attenuated in the course of 4h aging. The lower shear yield stresses observed at 70°C correlated with significantly lower concentration (<0.1M) of leached Si(IV). Whilst the increase of the solution Si(IV) concentration of 0.25–1M had no impact on rheology of dispersions at 25°C, strong gelation occurred within 2h in the presence of 1M Si(IV) at 70°C. The gelation induction time decreased with increasing solution Al(III) concentration or dispersion solid content, whilst it was completely absent at lower Si(IV) concentrations. Results demonstrated that the proliferation and polycondensation of Si(IV) species alone is necessary but not sufficient cause of gelation which occur at lower Si(IV) concentrations (e.g., 0.25M) under plant conditions, albeit other species (e.g., Al(III) and Fe(III)) prevail. Both intense heating and higher Si(IV) concentration are shown to be conducive to gelation.

Leaching of roast-reduced manganese nodules in NH 3–(NH 4) 2CO 3 medium

Reduction roast–ammonia leach process developed at NML for extraction of valuable metals from manganese nodules yielded low cobalt recovery (56%), although copper and nickel recoveries were > 90% (Jana et al., 1999b). With an aim to increase the cobalt recovery, a modified NH 3–(NH 4) 2CO 3 leaching flow-sheet have been developed for treatment of reduced manganese nodules. The major steps of this flow sheet are: (i) wet grinding cum preconditioning of reduced nodules in concentrated ammoniacal liquor in presence of surfactant, (ii) precipitation of Fe and Mn from the preconditioned liquor by air purging, and (iii) leaching of the residue from the preconditioning stage. This paper describes the optimization studies of each of the above steps in bench scale for maximum metal recoveries. The role of surfactant (during preconditioning) and the need for S/L separation after the preconditioning stage for better Co recovery are highlighted. Bench scale trials under optimized conditions yield about 95% Cu, 94% Ni and 80% Co recovery. Based on the bench scale results, large scale leaching campaigns (10 kg/batch) under lock-cycle mode were also carried out, which gave quite encouraging results with average metal recoveries Cu 92.5%, Ni 91.5% and Co 71.3% in seven cycles.

Salt extraction process–novel route for metal extraction Part 3–electrochemical behaviours of metal ions(Cr, Cu, Fe, Mg, Mn) in molten (CaCl2–)NaCl–KCl salt system

The present work is Part 3 of a novel salt extraction process towards the extraction of metal values from slag, low-grade ores, etc. The electrochemical behaviour of different metal ions, Cr(III), Cr(II), Cu(II), Fe(III), Mg(II) and Mn(II) was studied using cyclic voltammetry (CV) at 827°C in (CaCl2–)NaCl–KCl system with a tungsten or glassy carbon electrode. The deposition process of Cr(III) species was found to be consisted of two electrochemical steps, while, in the case of other species, the deposition only involves one step. The deposition potentials and diffusion coefficients were determined from the cyclic voltammetrys. Electrodeposition of chromium was performed using a two-electrode cell under constant voltage, and pure dendrite and nodular-like crystals of chromium were obtained. The present study provides a good understanding of the electrochemical behaviour of these metal ions in molten salts, and thus is helpful to this novel salt process for the recovery of metal values from slag or other materials.

Extraction of valuable metals from low-grade nickeliferous laterite ore by reduction roasting-ammonia leaching method

Nickel and cobalt were extracted from low-grade nickeliferous laterite ore using a reduction roasting-ammonia leaching method. The reduction roasting-ammonia leaching experimental tests were chiefly introduced, by which fine coal was used as a reductant. The results show that the optimum process conditions are confirmed as follows: in reduction roasting process, the mass fraction of reductant in the ore is 10%, roasting time is 120 min, roasting temperature is 1 023–1 073 K; in ammonia leaching process, the liquid-to-solid ratio is 4:1(mL/g), leaching temperature is 313 K, leaching time is 120 min, and concentration ratio of NH3 to CO2 is 90 g/L:60 g/L. Under the optimum conditions, leaching efficiencies of nickel and cobalt are 86.25% and 60.84%, respectively. Therefore, nickel and cobalt can be effectively reclaimed, and the leaching agent can be also recycled at room temperature and normal pressure.

The salt extraction process – a novel route for metal extraction Part 2 – Cu/Fe extraction from copper oxide and sulphides

The present work is Part 2 of a novel salt extraction process towards the extraction of metal values from slag, low grade ores, etc. The authors describe the extraction of copper/iron from CuO, Cu2S and CuFeS2, which provides a green process route to treat the copper ore including both oxides and sulphides. The dissolution properties were investigated with respect to process parameters such as weight ratio of flux/copper ore and temperature. The highest extraction ratio is found at 92% in dissolution of Cu2S, and residue of salt melt was confirmed to be mainly Al2O3. A cell voltage between 1·6 and 2·2 V is introduced for electrolysis, and the cathode products are proved to be pure Cu for electrolysis of CuO/Cu2S, and Cu/Fe mixture for CuFeS2 by X-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy analysis. Some sulphur and iron chloride were found to volatilise and were deposited in the low temperature zone. Yield of copper has been estimated to be 52·3% during electrolysis of Cu2S.

The salt extraction process: a novel route for metal extraction Part I – Cr, Fe recovery from EAF slags and low grade chromite ores

The present work is part of an investigation towards the development of a process route for the extraction of metal values from slag, low grade ores and other oxidic materials such as spent refractories using molten salts in the temperature range 800–950°C. The present paper focuses on the recovery of metal values, primarily Cr and Fe, from electric arc furnace slag and chromite ore. The impact of different factors to the dissolution of slag, such as temperature, holding time, flux content and weight ratio of flux/slag was studied. Based on the optimised experimental factors, the salt bath containing metal values extracted from the slag/ore was electrolysed under an applied voltage of 2·8 V. The cathode deposit was subjected to SEM/EDS and XRD analyses, which confirmed the formation of CrFe alloy. The process was also extended towards the production of CrFe alloy directly from chromite ore. The results show that the molten salt extraction process offers a promising route towards the recovery of metal values from slags and low grade ores.

Some kinetics aspects of chlorine-solids reactions

The present paper describes detailed kinetics investigations on some selected chlorine-solid reactions through thermogravimetric measurements. The solids studied in this article include chemical pure oxides and sulfides as well as their natural bearing materials. The chlorinating agents employed are gaseous mixtures of Cl 2 +N 2 (chlorination), Cl 2 +O 2 (oxychlorination), and Cl 2 +CO (carbochlorination). Results are presented as effects of various parameters on the reaction rate of these solids with these chlorinating agents. It was observed that the reactivity of these solids towards different chlorinating agents varied widely. Sulfides could be chlorinated at room temperature, while carbochlorination of chromium (III) oxide was possible only above 500 °C. The variation of the chlorination rate of these complex materials with respect to gas velocity, composition and temperature enabled us to focus some light on the plausible reaction mechanisms and stoichiometries. The obtained results were used for selective removal of iron from chromite concentrates, extraction of valuable metals from sulfide materials, purification of MgO samples, etc.

Extraction of valuable metals from new type of cathodic active material scrap for lithium ion battery using Supercritical CO2

Extraction of valuable metals from new type of cathodic active material scrap for lithium ion battery using Supercritical CO2

A High Temperature Process for Extracting Valuable Metals from Waste Electric and Electronic Scraps (WEES)

In the view points of resource recycling and environment protection it is necessary to extract the valuable metals from waste electric and electronic scraps (WEES) which contain considerable amounts of valuable metals such as copper, tin, gold, and silver. In present work, a novel process to extract valuable metals such as copper and tin from WEES by smelting with the addition of waste copper slag as a slag formative has been developed. The process uses only waste copper slag without using any additional flux components as slag formatives. In each set of experiment, crushed WEES were melted with waste copper slag for 30 min at 1623 K in air atmosphere. Based on proposed process flow-sheet, up to 90% of copper and 80% of tin contained in the raw materials were extracted as a Cu-Fe-Sn alloy phase at the input ratio of 50 : 50 of WEES and waste copper slag. [doi:10.2320/matertrans.M2009062]

Possibilities to use oxidic by-products for precipitation of Fe/As from leaching solutions for subsequent base metal recovery

In acidic biological and chemical leaching processes for base metal recovery, iron is dissolved in addition to the desired metal values. Prior to valuable metal extraction iron has to be removed. This is usually achieved through hydroxide precipitation of ferric iron by the addition of lime or limestone to a pH of approximately 3 whereby ferric hydroxide is formed. The aim of this work has been to investigate the possibility to substitute lime or limestone with oxidic industrial by-products for neutralisation and precipitation of iron from leaching solutions. The neutralisation potential for 10 selected oxidic by-products like slags, ashes and dusts were examined and compared with slaked lime. Experiments were performed by decreasing pH to 3 by additions of H 2SO 4 to slurry of respective by-product at an S/L ratio of 1/10 at 25 °C and continued till no changes in pH were observed during 10 days. Original samples, residues and solutions were analysed by ICP-MS and XRD in order to identify potential harmful elements for the subsequent metal recovery steps. Characterisation of the by-products revealed high concentrations of oxides such as lime, calcite and metal oxides as well as different forms of silicates in the materials which all dissolved at pH 3. The neutralising potential was found to be high for most of the by-products investigated and in the case of Ladle slag it was even higher than for slaked lime. Slags generally had higher neutralisation potential and long-term effects while the ashes had high initial reactivity which is important for continuous neutralisation in stirred tanks with limited retention times. The most reactive materials were Bioash and Mesa lime which both contained considerable amounts of calcite. Replacement of the conventional lime and limestone with oxidic by-products for neutralisation of acidic leaching solutions has the potential to save costs, environmental resources, reduce CO 2 emissions and to recycle metal values like zinc contained in the by-products.

Surface chemical and flotation behaviour of chalcopyrite and pyrite in the presence of Acidithiobacillus thiooxidans

Extraction of valuable metals and removal of sulfide minerals from abandoned mines holds the key for environmental protection. This paper discusses the utility of Acidithiobacillus thiooxidans for the selective removal of pyrite from chalcopyrite for the economic extraction of valuable copper. Interaction of bacterial cells with the sulfide minerals altered the surface chemistry of both the minerals and cells. The isoelectric point of both pyrite and chalcopyrite shifted to higher pH after interaction with cells. Adhesion kinetics of the bacterial cells to both the minerals was similar, however, the adsorption density on pyrite was higher compared to that on chalcopyrite. Interaction with cells rendered both the minerals hydrophilic. Flotation of minerals, preconditioned with cells, with potassium isopropyl xanthate as collector resulted in depression of pyrite and good flotation of chalcopyrite. The observed behaviour is discussed in detail. Poor selectivity achieved when the minerals were floated together was overcome by conditioning the collector interacted minerals with the bacterial cells prior to flotation. Thus it was possible to selectively depress pyrite from chalcopyrite at both acidic and neutral pH conditions.

Processing of copper anodic-slimes for extraction of valuable metals

This work focuses on processing of anodic slimes obtained from an Egyptian copper electrorefining plant. The anodic slimes are characterized by high concentrations of copper, lead, tin and silver. The proposed hydrometallurgical process consists of two leaching stages for the extraction of copper (H 2SO 4–O 2) and silver (thiourea–Fe 3+), and pyrometallurgical treatment of the remaining slimes for production of Pb–Sn soldering alloy. Factors affecting both the leaching and smelting stages were studied.

Effects of O2 on aqueous SO2 leaching of Co, Cu and Ni from discard smelter slag

AbstractIn the leaching of non‐ferrous smelter slag with a dissolved gas mixture of SO2 and O2, the behaviour of Co, Cu, Ni, Zn and Fe was studied in a 1‐L batch reactor. The parameters investigated include PSO2, PO2, temperature, particle size and pH. Co, Zn and Fe behaved similarly while Ni and Cu displayed distinguishable characters. The addition of O2 prevented the precipitation of Cu after dissolution, and increased acidity of the leaching solution. The increase in acid strength resulted in an increase in the extraction of Co, Zn and Fe. The effect of acidity on Cu and Ni extraction was however much weaker. The combination of SO2 and O2 was found to be a more effective oxidant of Fe(II) to Fe(III) than O2 alone. Simultaneous extraction of valuable metals and removal of Fe could be achieved by leaching at pH of 3 to 4. Maximum selectivities obtained for Co, Ni and Cu over Fe were 300, 2000 and 4000, respectively.

Electrochemical aspects in some of the hydrometallurgical processes

Hydrometallurgy deals with extraction of metal values from ore minerals through aqueous processing by solubilizing the specific metal value into the aqueous phase and subsequently taking it out of the solution. These steps may be chemical or electrochemical in nature. The electrochemical phenomena depends on the electrical properties of the solid material and the redox characteristics of the solution. The present paper discusses electrochemical aspects of some hydrometallurgical operations involving the following phenomena: (i) corrosion coupling, (ii) galvanic coupling, (iii) dissolution via cyclic action of a redox couple, (iv) displacement or cementation reaction, (v) precipitation under reducing conditions, (vi) dissolution under high pressure, and (vii) dissolution influenced by hole transfer.

Extraction of Metal Values from Manganese Nodules in the Ocean Environment Using Zinc Matte as a Reductant

The leaching process of manganese nodules in the marine environment is significant in the recovery of several metal values. In this experiment, reduction leaching of manganese nodules was carried out using zinc matte as a reductant in dilute HCl solution. The leaching characteristics of Mn, Co, Ni, and Cu from manganese nodules depended on the leaching temperature and initial HCl concentration. A temperature of approximately 70°C was suitable for the present reduction leaching, and the extraction rate increased with increase in the initial HCl concentration. More than 97% of Mn, 92% of Co, and 88% of Ni were easily extracted. The dissolution of Mn, Co, Ni, and Cu depended upon the amount of zinc matte added. The ratio of liquid and solid was also an important factor in the extraction of manganese nodules. As the liquid/solid (L/S, lixiviant/manganese nodule) ratio was increased, the extraction rate increased. The extraction rate was independent of stirring speed.