Initial Sulfuric Acid Concentration Research Articles

Evaluation of hydrometallurgical black mass recycling with simulation-based life cycle assessment

Abstract Purpose The recycling of lithium-ion batteries is an emerging field faced with the challenge of recovering more than the most valuable elements from the batteries. While the literature presents many innovative approaches to the problem, an overview of the technical and environmental prospects of hydrometallurgical black mass recycling remains crucial. The goal was to analyze the impacts of a black mass process flowsheet and suggest ways to further reduce the impacts of battery recycling. Methods The flowsheet was drafted from the literature by combining both state-of-the-art and experimentally demonstrated unit processes by starting with the leaching system, where reductive leaching is performed using only the copper and iron impurities already present in the black mass. The process targeted copper, manganese, cobalt, nickel, and lithium recovery, and three scenarios for manganese recovery were investigated. The flowsheet was simulated using HSC Sim software, and the mass and energy balances were adapted into internally consistent life cycle inventories. The scope was “gate-to-gate” in Europe and CML methodology was used for impact assessment. Results and discussion Assuming that mechanical pre-treatment carries more environmental benefits than burdens, the results indicated that hydrometallurgical black mass recycling had a tentatively lower environmental footprint compared to virgin raw materials in all impact categories except ozone depletion, the results indicated that hydrometallurgical black mass recycling had a tentatively lower environmental footprint compared to virgin raw materials in all impact categories except ozone depletion. Sulfuric acid and neutralizing chemicals were among the most significant contributors to the impacts, and therefore further analysis was conducted based on an experimental study on low acid leaching with a low (< 0.5 M) initial sulfuric acid concentration instead of the baseline 2 M. This reduced the impacts by approximately 30–40% in all categories by decreasing downstream chemical consumption, and more significantly decreased ozone depletion. The challenges and opportunities for further process improvement were also considered. Conclusions The study highlights the importance of process optimization to improve the environmental sustainability of battery chemical production, but also revealed critical research gaps in the experimental literature. Rather than focusing on a single unit process, experimental black mass recycling research should aim at finding solutions that are optimal for the up- and downstream units, such as minimization of aluminum in the black mass and acid consumption.

Study on the treatment of pyrolysis products from the nitric acid pressure leach liquor of laterite

As the demand for nickel increases sharply, it is of great significance to extract valuable metals such as nickel and cobalt from lateritic nickel ore with huge reserves. Based on the nitric acid pressure leaching process (NAPL) of laterite nickel ore, a clean process of laterite nickel ore treatment is proposed. The process includes concentration and crystallization of pressure leaching solution of nitric acid, pyrolysis of mixed nitrate crystal, alkaline leaching of mixed oxides and acid leaching of alkaline leaching residue. Based on previous work, the high-pressure alkaline leaching process of pyrolysis products (mixed oxides) and atmospheric pressure sulfuric acid leaching process of alkaline leaching residue were studied in this paper. First, the Eh-pH diagrams of metal-water system of common elements in laterite nickel ore was summarized according to the reaction equations of different substances in aqueous solution, and the subsequent wet leaching process was guided. The following alkaline leaching experiments showed that under the conditions of 300 g/L NaOH concentration, 3.5 mL/g liquid–solid ratio, 160 °C leaching temperature and 1 h leaching temperature, 85.0 % of aluminum in mixed oxides can be leached and scandium can be enriched by 13 times. Finally, under the conditions of initial sulfuric acid concentration of 4 M, temperature of 100 °C, leaching time of 30 min and liquid–solid ratio of 4 mL/g, the leaching rates of Al, Ni, Mg, Co, Mn, Fe and Sc in alkaline leaching residue were 92.0 %, 97.5 %, 98.4 %, 92.3 %, 62.7 % and 68, respectively. A new procedure for treating lateritic nickel ore is proposed, allowing for thorough recovery and usage of important components. The technique is green and environmentally benign, resulting in closed-loop production of laterite-nickel ore treatment with numerous application possibilities.

Sulfuric acid leaching of a complex zinc sulfide concentrate with high copper and lead concentrations under oxygen pressure

ABSTRACT This paper presents the use of an oxygen pressure-based acid leaching process for the selective extraction of basic metals from a complex zinc ore containing high concentrations of lead (6.00%) and copper (2.47%). The effects of leaching temperature, ore particle size distribution, leaching time, liquid-to-solid ratio, and oxygen partial pressure on the leaching efficiencies of zinc and copper were investigated, and the phase transformation behaviour of lead compounds was studied. Under the optimal conditions that is, a particle size of −48/+40 μm, initial sulfuric acid concentration of 150 g/L, liquid-to-solid ratio of 6:1, leaching time of 150 min, leaching temperature of 150°C, and oxygen partial pressure of 0.8 MPa – the leaching efficiencies of zinc, copper, and iron were 98.85%, 82.69%, and 33%, respectively. The leaching residue showed that almost all of the zinc sulfide was dissolved as ZnSO4, and most of the negatively charged bivalent sulfur was converted to zero-valent element sulfur. Through the pressure leaching reaction, galena in the concentrate was converted to lead jarosite (PbFe6(SO4)4(OH)12) and elemental sulfur. The formation of lead jarosite facilitated the removal of a significant portion of iron during leaching, reducing the subsequent purification burden.

A Study on the Treatment and Recovery of Sodium Sulfate (Na<sub>2</sub>SO<sub>4</sub>) Generated When Recovering Valuable Metals (Ni, Co, Mn, Li) from Waste Lithium Ion Batteries(LIBs)

Concerns have arisen regarding the high concentrations of sodium sulfate in wastewater resulting from the waste Li-ion battery wet recycling process. In addressing this issue, Bipolar electrodialysis was employed to desalinate high-concentration sodium sulfate and recover it as sulfuric acid and sodium hydroxide. The investigation encompassed various experimental variables, such as applied voltage (maintained at a constant level), feed solution concentration, the initial concentrations of sulfuric acid and sodium hydroxide, and volume ratio (F/A/B). Optimal conditions were determined by assessing water migration (%), the recovery rates (%) of sulfuric acid and sodium hydroxide, concentration of the recovered substances, process time, and energy consumption. A higher applied voltage was found to reduce process time while increasing energy consumption, with the 25 V condition considered preferable. When utilizing a high-concentration feed solution, energy consumption rises; however, it decreases per unit of processed solution, rendering a 1.30 M Na<sub>2</sub>SO<sub>4</sub> feed solution preferable. Increasing initial concentrations of sulfuric acid and sodium hydroxide substantially prolonged process time and increased energy consumption, emphasizing the advantage of commencing with low initial concentrations. Adjusting the volume ratio facilitated the concentration and recovery of sulfuric acid and sodium hydroxide with minimal impact on process time or energy consumption. Under the identified optimal conditions, the recovery of 1.70 M sulfuric acid and 2.44 M sodium hydroxide was achieved.

Evolution of the Bromate Electrolyte Composition in the Course of Its Electroreduction inside a Membrane-Electrode Assembly with a Proton-Exchange Membrane.

The passage of cathodic current through the acidized aqueous bromate solution (catholyte) leads to a negative shift of the average oxidation degree of Br atoms. It means a distribution of Br-containing species in various oxidation states between -1 and +5, which are mutually transformed via numerous protonation/deprotonation, chemical, and redox/electrochemical steps. This process is also accompanied by the change in the proton (H+) concentration, both due to the participation of H+ ions in these steps and due to the H+ flux through the cation-exchange membrane separating the cathodic and anodic compartments. Variations of the composition of the catholyte concentrations of all these components has been analyzed for various initial concentrations of sulfuric acid, cA0 (0.015-0.3 M), and two values of the total concentrations of Br atoms inside the system, ctot (0.1 or 1.0 M of Br atoms), as functions of the average Br-atom oxidation degree, x, under the condition of the thermodynamic equilibrium of the above transformations. It is shown that during the exhaustion of the redox capacity of the catholyte (x pass from 5 to -1), the pH value passes through a maximum. Its height and the corresponding average oxidation state of bromine atoms depend on the initial bromate/acid ratio. The constructed algorithm can be used to select the initial acid content in the bromate catholyte, which is optimal from the point of view of preventing the formation of liquid bromine at the maximum content of electroactive compounds.

A Comparison Between Trioctylamine (TOA) and Tris(2-Ethylhexyl) Amine (TEHA) in Solvent Extraction of Sulfuric Acid*

ABSTRACT The study investigated the behavior of two amines, Trioctylamine (TOA) and Tris(2-Ethylhexyl) amine (TEHA), in the sulfuric acid extraction system, with varying concentrations of extractants and modifiers, as well as the temperature of the sulfuric acid extraction. The study found that TOA had a higher ability in the extraction of sulfuric acid and was less dependent on temperature. However, an increase in the initial sulfuric acid concentration resulted in a drop in acid extraction percentage when TOA was employed, while such a drop was not observed in the case of TEHA. The study also illustrated the necessity of using Octanol as a modifier, with different minimum levels required for TOA and TEHA. Additionally, Octanol showed a positive effect on the extraction level of sulfuric acid in the TEHA – H2SO4 extraction system, which can be considered an advantage in the facile stripping of the loaded organic phase. The slope analysis method revealed that more than 1 mol of TOA is necessary to extract 1 mol of sulfuric acid, while 1 mol of TEHA can absorb 2 mol of sulfuric acid. FTIR spectra analysis confirmed TOA's participation in the extraction of sulfuric acid and provided insights into the chemical bonds formed. Overall, the study provides a comprehensive understanding of the solvent extraction of sulfuric acid and can be useful in optimizing the extraction process for industrial applications.

Optimization and kinetic analysis of direct acid leaching of vanadium from converter vanadium slag under atmospheric pressure

Converter vanadium slag is an important kind of raw material for the production of vanadium products. Not only does the atmospheric acid leaching of vanadium from vanadium slag without roasting avoid the pollution of exhaust gas generated from roasting, but also it reduces the threat of Cr(VI) and V(V) and is conducive to the vanadium products preparation with low valence state. In this paper, the optimization of leaching conditions by response surface methodology and the direct sulfuric acid leaching kinetics of vanadium from converter vanadium slag were investigated. In the consequence of experiments, the optimum atmospheric sulfuric acid direct leaching conditions were initial sulfuric acid concentration of 4 mol/L, reaction temperature of 90 °C, reaction duration of 8 h and liquid to solid ratio of 8 mL/g with the particle size of vanadium slag below 20 μm. Under the optimum conditions, the vanadium leaching efficiency was 86.09%. The kinetics analysis demonstrated both the chemical reaction and inner diffusion were the control steps of the leaching process. The calculated apparent activation energy of the leaching process was 17.63 kJ/mol and the reaction order of sulfuric acid was 0.78.

Innovative application of two-stage sulfuric acid leaching for efficient recovery of Ti from titanium-bearing electric furnace slag

A two-stage sulfuric acid leaching process was developed to efficiently recover Ti from a titanium-bearing electric furnace slag (TEFS) made from V-Ti magnetite, which has a high content of impurities and low Ti content. The efficiency of the recovery mechanism was investigated. Anosovite and gangue minerals in the TEFS reacted with sulfuric acid and generated several solid substances such as TiOSO4, CaSO4, sulfates of Mg and Al, and silicate in the first-stage of the acidolysis, which formed the product layer and hindered the diffusion of sulfuric acid. Moreover, a high content of the impurities caused the gangue minerals to closely wrap around the anosovite, which hindered the acidolysis. By adopting a two-stage acid-leaching process, soluble sulfates, which are the most abundant product of acidolysis, were dissolved in water during the first-stage of the water leaching, which exposed the unreacted anosovite, diopside, and spinel. Accordingly, sulfuric acid completely reacted with the unreacted minerals during the second-stage acidolysis. The Si- and Ca-containing products of the acidolysis mainly existed in the form of silicate and CaSO4 and were later converted to silica gel and gypsum, respectively, after the second-stage water leaching. With this innovative process, the leaching rate of Ti improved significantly, achieving a 99.33% total leaching rate. Moreover, lowering the initial sulfuric acid concentration to 48% still yielded a total leaching rate of 98.04%, with the Ti grade of the final residue dropped to 3.14%.

Statics simulation of the sulphate iron-containing wastewater neutralization process

At the present stage of technical progress, all industries face an extremely complex problem of creating reliable barriers that prevent the penetration of industrial emissions into the environment. Currently, the issues of stabilizing the quality of wastewater treatment have become especially important in connection with the task of developing wastewater-free industrial complexes. Among the complex scientific and technical problems associated with this task, the problem of stable and reliable maintenance of water quality parameters at the outlet of technological systems is crucial, as leakage of pollutants immediately affects the state of basic production, disrupting its technology and infecting ecosystems.
 The focus of industry on a sharp reduction in emissions and on the creation of industrial cycles with circulating water supply requires intensive efforts to improve the wastewater treatment technology, the introduction of high-performance processes and devices, as well as the synthesis of control systems for typical wastewater treatment processes. 
 For the performance of automated control systems for typical cleaning processes, it is necessary to develop a software package on the basis of appropriate mathematical models of typical processes. To obtain them, methods of mathematical and simulation modeling and variance analysis were used.
 In order to assess the quality of modeling, the presented mathematical model describing the statics of the neutralization process for ferrous sulfate water was tested for compliance. To do this, two experiments were performed (the first at an initial concentration of sulfuric acid of 800 [mg/l] and ferrous sulfate of 4000 [mg/l] and the second at an initial concentration of sulfuric acid of 800 [mg/l] and ferrous sulfate of 2000 [mg/l]). First of all, a precondition for the reproducibility of experimental results was verified using the Cochrane test. The mathematical model was verified for adequacy on the basis of Fisher's criterion for the significance level q = 0.05 with degrees of freedom j1 = 16 and j2 = 17.
 For the first experiment, Grozr = 0.50557 and Gmab = 0.73; i.e., Grozr < Gmab and dispersions are homogeneous. Frozr = 1.0225 and Fmab = 2.4 and thus Frozr < Fmab, and there is no reason to say that the model is inadequate.
 For the second experiment, Grozr = 0.50308 and Gmab = 0.73; i.e., Grozr < Gmab and dispersions are also homogeneous. Frozr = 1.0005 and Fmab = 2.4 and thus Frozr < Fmab, which also indicates that the model is adequate.
 The issue related to the performance of technological systems for wastewater treatment in non-stationary modes is directly dictated by the specific operating conditions of treatment facilities, which are expressed by the instability of parameters at their inlet. The inability to apply the necessary technological action to the flow in time is a serious obstacle to the implementation of the cleaning depth, which is guaranteed by the physicochemical basis of the methods incorporated in technological systems and requiring cleaning standards. The operator cannot handle this complex task manually. On the basis of the proposed mathematical model, a structural-parametric diagram of the automated process control system has been developed, which makes it possible to proceed to the elaboration of algorithms and software for the control system necessary for automated control of the wastewater treatment process.

Study on preparation and properties of zinc ferrite product by leaching from zinc calcine

In this paper, zinc ferrite was prepared from zinc calcine by sulfuric acid leaching, and its properties were studied by the methods of XRD, XRF and SEM/EDS. The results show that sulfuric acid leaching of zinc ferrite from zinc calcine is mainly affected by the initial concentration of sulfuric acid and leaching temperature. If the initial concentration of sulfuric acid and leaching temperature are too low, the soluble oxides in zinc calcine can not be completely dissolved. The prepared zinc ferrite was not suitable for application for too many impurities. However, the higher initial concentration of sulfuric acid and leaching temperature are, the lower recovery of zinc ferrite is. The suitable conditions for preparation of zinc ferrite from zinc calcine by sulfuric acid leaching are liquid-solid ratio 7:1, stirring speed 400rpm, sulfuric acid concentration 160g/L, leaching temperature 85°C, leaching time 120min. The particle size of zinc ferrite is fine, most of them is between 2~5μm. The impurity content of zinc ferrite is less. Zinc ferrite particles are composed of spherical and irregular shape, and they are agglomerate and encase each other.

Selection of sorption materials for the extraction of nickel and cobalt from the ore of the Gornostaevskoye deposit

Oxidized nickel ores account for the majority of industrial ores suitable for nickel production. The processing of such ores using traditional pyrometallurgical technology is not economically viable due to the low nickel content. One of the most cost-effective methods of processing oxidized nickel ores is sulfuric acid leaching technology followed by sorption extraction. The aim of this work is to establish the kinetic and thermodynamic parameters of the sorption extraction of nickel and cobalt using iminodiacetate chelating ion-exchange sorbents from various manufacturers, to select a desorbing solution and to determine the degree of desorption. The sorption of nickel and cobalt was carried out in a weakly acidic medium from a model solution containing impurities of other metals in static and dynamic modes. The limiting sorption capacity for the studied sorbents is 18-26 mg/g for nickel and 1-2 mg/g for cobalt in the static mode. The sorption capacity in the dynamic mode for nickel is equal to 25.5 g/L for Purolite S 930, 29.2 g/L for Lewatit TP 207, 1.4 g/L, and 1.8 g/L for cobalt, respectively. The best desorption parameters are achieved when using a 2 M sulfuric acid solution. The degree of desorption for sorbents Purolite S 930 and Lewatit TP 207 exceeds 90%. The use of the Lewatit TP 207 sorbent for the extraction of nickel from the leaching solution of nickel ore of the Gornostaevskoye deposit in 5 cycles made it possible to obtain a commercial desorbate with a nickel content of 18 g/L. The use of a part of the commercial desorbate obtained in the previous cycle, further strengthened to the initial concentration of sulfuric acid, for re-extracting nickel from the saturated sorbent during a cyclic process leads to a deterioration in desorption characteristics. It is recommended to remove the commercial desorbate from the process after several cycles of desorption and supply new solution of sulfuric acid for desorption to restore the sorption parameters.

Mechanism and kinetics of synergistic decopperization from copper anode slime by ultrasound and ozone

Copper anode slime is a typical hazardous waste that is rich in precious metals, rare metals and other valuable metals. Decopperization is the first step to recycle rare and precious metals from copper anode slime. In this work, the synergistic effect of ultrasound and ozone on copper leaching from copper anode slime was studied to develop an efficient and clean decopperization process. The effects of the reaction time, temperature, initial sulfuric acid concentration, ultrasound power and ozone flow rate were investigated. The results show that the dissolution fraction of copper can reach 98.46% under the optimum ultrasound and ozone reaction conditions. However, the leaching efficiency of copper under ozone is only 50.99% at 30 min. The kinetics analysis shows that the leaching reaction follows the classical unreacted-core shrinking model. The apparent Ea value and reaction orders were estimated to be 10.37 kJ/mol and 0.34, respectively. Meanwhile, the leaching kinetic equation under ultrasound and ozone was established using quadratic regression. Surface analyses indicated that the copper compound leached under ultrasound and ozone exposure. The higher leaching efficiency of copper results because copper and its compounds are transformed into soluble copper sulfate under the combination of ozone and ultrasound. The concentration of precious metals in the leaching residue under ultrasound and ozone is the highest, indicating that the synergistic effect of ultrasound and ozone can effectively enrich valuable precious metals. Synergistic decopperization from copper anode slime by ultrasound and ozone offers wide application prospects in transforming harmful anode slime waste into valuable materials.

The influence of sulfur addition on the hazard-type reaction of ilmenite ores with sulfuric acid

Abstract The paper presents results of thermokinetic investigation of the hazard-type reaction of Norwegian and Australian ilmenite ores with sulfuric acid, modified by the addition of elemental sulfur, to increase the process safety in industrial conditions. In the reactions of both ilmenite ores the addition of sulfur caused a reduction of the thermal power generated in the reaction and a decrease in the value of the thermokinetic parameter ΔTmax/Δτ for almost the whole range of initial concentrations of sulfuric acid. It was also found that the addition of sulfur to the reaction did not negatively affect the degree of ilmenite leaching. The interpretation of the obtained thermokinetic curves allowed to determine safe process conditions for both types of titanium raw materials.

Thermodynamic Analysis of Zinc Sulfide Dissolution Stoichiometry in Sulfuric Acid Solution with Oxygen Participation

In this work, a thermodynamic study of zinc sulfide high temperature oxidative leaching was carried out. At the metals sulfides dissolution under oxidants action in acidic solutions several simultaneously proceeding reactions are possible. With the aim finding the proportion of potential reactions, a thermodynamic calculation was carried out using stoichiometric equations with equal oxidant consumption. Moreover, stoichiometric coefficients were chosen in such a way that reagents could exchange 1 mole of electric charge. Such an approach allows one to ensure a comparison of different oxidants’ usage effectiveness for sulfide leaching. Thermodynamic analysis results are in accordance with experimental data, which confirm that reactions with the formation of sulfur and sulfate-ions are uppermost at zinc sulfide dissolution in sulfuric acid solutions under oxygen action. Oxygen consumption and initial sulfuric acid concentration influence on proportion of this reactions and zinc equilibrium concentration in solution were investigated. Thermodynamic analysis showed that at insufficient acid concentration, which limits the maximum degree of zinc sulfide oxidation reaction advancements with sulfur formation, oxygen is consumed on oxidation reaction with the formation of sulfate-ions, which spend oxygen less effectively, due to four times smaller zinc dissolution. Thermodynamic calculations carried out allowed us to find out optimal proportions of oxygen consumption and initial sulfuric acid concentration, which provide achievement of a maximal zinc equilibrium concentration in solution at a higher effectiveness of oxidant consumption without labor-intensive experiments. At optimal acid consumption, a zinc equilibrium concentration is directly proportional to initial acid concentration. Directly proportional dependence of zinc cations’ formation on acid consumption was also detected at acid concentration optimal values.

Thermodynamic analysis of zinc sulfide dissolution stoichiometry in sulfuric acid solution with oxygen

A thermodynamic study of zinc sulfide high temperature oxidation leaching was conducted. Several processes can run simultaneously while metal sulfides are dissolved by oxidants in acidic solutions. Thermodynamic calculations were made using stoichiometric equations with equal oxidant consumption in order to identify the proportion of potential reactions. Moreover, stoichiometric coefficients were chosen in such a way as to reagents could exchange 1 mole of electric charge. This approach ensures a comparison of different oxidants in terms of their effectiveness in sulfides leaching. Thermodynamic analysis results obtained agree with experimental data confirming that oxidizing reactions with the formation of sulfur and sulfate ions prevail in zinc sulfide dissolution in sulfuric acid solutions under the oxygen effect. The effect of oxygen consumption and initial sulfuric acid concentration on the proportion of these reactions and equilibrium concentration of zinc cations in the solution was studied. Thermodynamic analysis showed that if the acid concentration is insufficient and limits the maximum progress of zinc sulfide oxidation with sulfur formation, oxygen is also consumed for the oxidation reaction with the formation of sulfate ions spending oxygen less effective due to 4 times less zinc cations passing to the solution. Thermodynamic calculations made it possible to find out the optimal proportions of oxygen consumption and initial sulfuric acid concentration to achieve the maximum zinc equilibrium concentration in the solution with more effective oxidant consumption without any labor-intensive experiments. The equilibrium concentration of zinc cations in the solution is in direct proportion to the initial acid concentration, and zinc cation formation is in direct proportion to oxygen consumption at the optimal acid concentration.

Kinetics of nickel leaching from low-nickel matte in sulfuric acid solution under atmospheric pressure

In the conventional metal extraction process, copper-nickel sulfide ores are generally treated by pyrometallurgical processes, including smelting and converting operation. The purpose of the smelting process is to eliminate most of the iron and to concentrate the valuable metals, such as nickel, copper and platinum group metals, into a low-nickel matte. Then, the remaining iron is oxidized and fluxed for removal as silicate slag in the converting process, and the low-nickel matte is converted into a high-nickel matte. However, a substantial portion of cobalt is also oxidized and converted into the slag phase. Additionally, the subsequent treatment of the high-nickel matte after the grinding and flotation processes is complicated, and leads to the dispersion of noble metals. Usually, the loss of noble metals is about 10% ~ 20%. Direct treatment of low-nickel matte by hydrometallurgical methods instead of the converting process may be a good choice, which will prevent the loss of associated elements, such as cobalt and noble metals. Since copper has a very strong affinity for sulfur, the sulfides of iron, cobalt and nickel may dissolve into the liquid phase (leach liquor) under controlled the acidity of the solution, whereas the cuprous sulfide should remain in the residue. The inert noble metals should concentrate in the cuprous sulfide. However, a large amount of toxic hydrogen sulfide will be released in the leaching process, which can be converted to elemental sulfur by the Claus process. Based on the above considerations, it is possible to develop a method for extracting valuable metals from low-nickel matte and recovering the associated cobalt and noble metals. In this study, the kinetics of the acid leaching process of low-nickel matte under atmospheric pressure was studied. In addition, the effects of the stirring speed, initial sulfuric acid concentration, reaction temperature and particle size on the leaching of nickel were investigated. The kinetic analysis of the leaching data for various experimental conditions indicated that the reaction was controlled by diffusion through an inert porous layer. It was determined that the reaction order was 0.54 with respect to sulfuric acid with an activation energy of 58.3 kJ mol−1.

Technology of Gold Extraction from Mature Dumps by Thiourea Leaching

Tajikistan has a large volume of gold-containing dumps, which on conversion to gold equals ~18 t. These dumps are products of amalgamation and cyanidation processes, resulting from treating the ores from Tarorskoe, one of the largest deposits in Tajikistan, and from a few other nearby deposits: Dzhilau, Khirskhon, and Olimpiiskoe. The mineralogical composition of the dumps is represented primarily by quartz, feldspar, and clay minerals. Their average content of gold is rather high, 2.4 g/t. Therefore, it is expedient to treat the dumps on the premises of JV Zerafshan plant (in the city of Pendzhikent, Tajikistan), which processes ores of the Tarorskoe deposit and has an unloaded technological cycle. The treatment of these dumps does not require an ore pretreatment stage, since, for the actual grain-size class (–0.074 mm, 58.11%), the content of cyanided gold is 89.7%. This work presents the results of studying the extraction of gold from the dumps by thiourea leaching. The purpose of this work is to find ways to decrease the consumption of expensive reagent thiourea. It is found that the sample of the dumps contains sorption-active minerals, which lead to the loss of gold with tails. Therefore, it is suggested that raw material should undergo a preliminary acid treatment to reduce the consumption of thiourea and sodium sulfite should be added to the pulp during carbon in thiourea leach. A high degree of extraction (~89%) is achieved when thiourea is loaded in the amount of 2 kg/t, ferric sulfate 7 kg/t, sodium sulfite 12 kg/t, and the initial concentration of sulfuric acid of 0.5% (at the stage of acid treatment). In this case, the consumption of thiourea is 0.8 kg/t. A process flow diagram for the dump treatment is proposed, which includes the following operations: preliminary acid treatment, carbon in thiourea leach, desorption, reactivation, electrolysis, and melting.

Recovery of gold from mature dumps by thiourea leaching

Tajikistan has a large amount of gold-bearing dumps making up - 18 tons in gold equivalent. These dumps are tails of amalgamation and cyanidation processes obtained in the processing of ores from the largest deposit in Tajikistan - Tarorskoe and a number of adjacent deposits - Jilau, Khirskhon, Olimpiyskoe. In terms of their mineralogical composition, dumps consist primarily of quartz, feldspar, and clay minerals. Average gold content in them is quite high - 2.4 g/t. Therefore, it is feasible to involve them in processing based on the existing Joint Venture «Zarafshon» plant (Penjikent, Tajikistan) processing ores from the Tarorskoe deposit and having underutilized process capacity. These dumps require no ore preparation for processing as the cyanided gold content is 89.7 % at the existing grain size class (-0.074 mm, 58.11 %). This article presents the results of studies on gold extraction from dumps by thiourea leaching. The paper is aimed at searching for ways to reduce the consumption of an expensive component - thiourea. It was found that dump samples contain sorption-active minerals that lead to the loss of gold with tails. In this regard, it is proposed to conduct gold sorption leaching. It was established that thiourea consumption can be reduced by acid pretreatment of raw materials with Na 2 SO 4 added to pulp during the thiourea leaching process. A high degree of extraction (-89 %) is achieved when loading 2 kg/t of thiourea, 7 kg/t of ferrous sulfate (III), 12 kg/t Na 2 SO 4 and the initial concentration of sulfuric acid of 0.5 % (at the stage of acid pretreatment). Thus, the thiourea consumption is 0.8 kg/t. A dump processing flow chart is presented that includes the following operations: acid pretreatment, thiourea sorption leaching, desorption, reactivation, electrolysis, and melting.

Leaching Behaviors of Impurities in Titanium-Bearing Electric Furnace Slag in Sulfuric Acid

Titanium-bearing electric furnace slag (TEFS) was prepared from vanadium titanomagnetite and leached with sulfuric acid. The Ti leaching rate of vanadium titanomagnetite TEFS is significantly lower than that of ilmenite TEFS. The impurity content in vanadium titanomagnetite TEFS is higher than that in ilmenite TEFS. This might be one of the main factors resulting in the low leaching rate of Ti, so the leaching behaviors of various impurities under different conditions (temperature, acid/solid weight ratio, particle size, and initial sulfuric acid concentration) were investigated. The following trends were observed under different leaching conditions: The leaching rate of Fe increased rapidly and reached equilibrium quickly, that of Si increased quickly in the early stage and then decreased in the later stage, that of Ca increased initially and reached equilibrium later, and the leaching rates of Mg and Al increased gradually until the equilibrium was reached. The leaching rate of Fe was too rapid to be able to investigate its leaching kinetics, and the insoluble leached products of Si and Ca interfered with their leaching. The effects of leaching parameters on the leaching of impurities were further analyzed by X-ray diffraction (XRD) and scanning electron microscopy analysis. XRD data indicated that spinel is the major Mg- and Al-bearing mineral in TEFS. Mg and Al showed similar leaching behaviors, and their leaching conformed to a new model based on interface transfer and diffusion across the product layer, both of which affect the leaching rate.

Mechanism and kinetics study of sulfuric acid leaching of titanium from titanium-bearing electric furnace slag

Titanium(Ti)-bearing electric furnace slag (TEFS) was leached with sulfuric acid in this study. The influence of temperature, acid/solid ratio, particle size, and initial sulfuric acid concentration on the Ti extraction was evaluated. The leaching kinetics indicate that diffusion across the product layer and the interface transfer both affected the decomposition of the TEFS, and the apparent activation energy was24.01kJ/mol. Reaction temperature was the most important factor that influenced the extraction of Ti, followed by the acid/solid ratio, sulfuric acid concentration, and particle size. The Ti leaching rate reached up to 89.46 % under the conditions of an average particle size of 31.5μm, acid/solid ratio of 2.0:1, initial acid concentration of 88.0wt%, reaction temperature of 513.15K, and water leaching temperature of 333.15K for 120min. Fe was almost completely dissolved in the acid, whereas MgO (22.73wt%) and Al2O3 (44.57wt%) in spinel were retained in the leach residue, and SiO2 (45.94wt%) and CaO (34.96wt%) occurred in the form of diopside in the leach residue. During the leaching process, substantial TiOSO4 and CaSO4·2H2O were produced and coated the TEFS particles, which hindered the leaching of Ti.