Pressure Oxidative Leaching Research Articles

Extracting valuable metals from zinc sulfide concentrate: A comprehensive simulation-based life cycle assessment study of oxidative pressure leaching

Considering the increasing environmental consciousness and the imperative for sustainable development, conventional zinc smelting operations employing the roast-leaching-electrowinning process face growing environmental pressures. Consequently, the oxidative pressure leaching process has emerged as an alternative processing route. This study focuses on recovery of major metals from ZnS concentrate, building a comprehensive model to simulate the oxidative pressure leaching process. The process model built demonstrated that zinc, sulfur, indium, gallium, cadmium, cobalt, germanium, and copper could be recovered effectively, the main chemical inputs being sulfuric acid, oxygen, and lime, while zinc electrowinning constituting over 90 % of the total electricity consumption. The results were used to compile a life cycle inventory, culminating in a gate-to-gate assessment of the environmental impacts of the process. The global warming potential for the treatment of 1 t of ZnS concentrate is approximately 2,000 kg CO2 eq. The primary environmental impacts in the process are from chemical inputs and electricity consumption. Based on these findings, recommendations for sustainable production practices are proposed. These include systematic recovery and reuse of electrolytic off-gas and roasting heat, greater utilization of renewable energy, enhanced iron removal processes, and exploration of alternative chemicals for Ga and Ge recovery.

Kinetics analysis of copper extraction from copper smelting slag by sulfuric acid oxidation leaching

Copper smelting slag (CSS) is generally produced from the pyrometallurgy of copper sulfide concentrate, the current storage disposal methods of CSS not only occupy precious land and pollute the environment, but also waste resources. To recover copper from the CSS and explore the atmospheric pressure oxidative leaching kinetics of copper extraction from CSS with sulfuric acid was investigated intensively. In this study, the effect of particle size, sulfuric acid concentration, temperature, liquid-to-solid ratio, and hydrogen peroxide added amount were investigated comprehensively. The results indicated that the decrease of particle size and increase of other parameters can significantly promote the leaching of copper. Under the optimum conditions, 90.7 % of the copper in the CSS was effectively leached, other copper in the leaching slag mainly existed in the form of fine-grained embedded copper sulfide. The dominant phase of the leaching slag is magnetite, which could be further recovered by conventional magnetic separation. Moreover, the kinetics of copper atmospheric pressure oxidative leaching in CSS were further expounded. The results indicated that the copper leaching kinetic conforms to the shrinking core model, and the overall leaching reaction was controlled by the internal diffusion control with an activation energy of 11.22 KJ/mol. The apparent reaction order of sulfuric acid and particle size are determined to be 0.965 and 0.478 respectively. Finally, the kinetics model equation is established for copper at normal pressure as:1-23η-1-η2/3=0.032·CH2SO40.965·r0-0.956·t. This research could provide an alternative solution for the efficient utilization of CSS.

Comprehensive recovery of arsenic and valuable metals from lead smelting flue dust: Process optimization and mechanism investigation

The comprehensive recovery of arsenic and valuable metals from lead smelting flue dust have received widespread attention due to its extremely high toxicity and economic value. In this research, a clean process which consisted of pressure oxidation leaching, preferential separation of Zn and Cd, reduction of As(Ⅴ) and recovery of indium was proposed. Thermodynamic calculation of leaching process suggested that the increasing of temperature reduces the redox potential required for the oxidation of As3+ to As5+, and the optimal conditions were found to be at acid concentration of 100 g/L, oxygen pressure of 2.0 MPa, temperature of 170 °C, L/S of 10 mL/g, leaching time of 2.5 h and agitating speed of 500 r/min. Under the selected conditions, the leaching extents of As, Cd, In, Sb and Zn are 99.17 %, 98.96 %, 92.68 %, 40.23 % and 96.63 %, respectively, while lead remained in the leaching residue. The separation of arsenic and other valuable metals in leachate is the most difficult and critical section of the process, where As2S3 was particularly added to the acid solution in certain manner to preferentially precipitate Zn and Cd in the forms of ZnS and CdS, subsequently reduce As(Ⅴ) to As(Ⅲ). Experiments by adding arsenic filter cake furtherly confirmed the reducibility of As2S3 and realized simultaneous extraction of arsenic in arsenic cake and acid leaching solution. Eventually, arsenic was recovered as As2O3 with a high purity of 98.56 % and the total extraction extent of indium is 93.76 %.

Ultrasonic pretreatment for enhancing flotation separation of elemental sulfur and silver-bearing lead minerals from an oxidative pressure leaching residue of zinc sulfide

Ultrasonic pretreatment was introduced to enhance the flotation separation of elemental sulfur and silver-bearing lead minerals from an ultrafine residue produced by oxidative pressure leaching of zinc sulfide. The particle size analysis of residue shows that ultrasonic pretreatment increases the number of particles with high sulfur content in the −19 μm fraction. This resulted from the associated sulfur was effectively liberated from other minerals. The complete liberation proportions of elemental sulfur and plumbojarosite in residue are respectively increased by 20.91 % and 38.53 % after ultrasonic treatment, in terms of mineral liberation analysis (MLA). Time-of-flight secondary ion mass spectrometry (ToF-SIMS) investigation implies that the surface structure difference between elemental sulfur and silver-bearing lead minerals is expanded by ultrasonic pretreatment. As a result, the separation of sulfur and silver-bearing lead minerals is significantly improved by ultrasonic pretreatment. Under optimized conditions of ultrasonic power, ultrasonic treatment time and solid weight, pilot-scale flotation produced a concentrate that the sulfur grade and recovery of concentrate increased by 11.63 % and 9.10 %, respectively, and the lead and silver recoveries of tailings increased by 8.72 % and 9.50 %, respectively, compared with those obtained by using the flotation without pretreatment. This work may provide an important reference for effectively recycling complex secondary resources and reducing the difficulty of subsequent values extraction.

Preparation of chromium oxide by hydrothermal reduction of sodium chromate aqueous solution with hydrogen and application to chromite ore processing

Chromium oxide (Cr2O3) has wide application in various industries. Its traditional production process, uses sodium carbonate (Na2CO3), which is converted into cheaper byproducts, including sodium sulfate (Na2SO4) and sodium bisulfate (NaHSO4). These byproducts contain hexavalent chromium (Cr(VI)), which can lead to serious environmental pollution. In this work, a cleaner production process for Cr2O3 through the hydrothermal reduction of a sodium chromate (Na2CrO4) aqueous solution with hydrogen (H2) was studied. Nearly single-phase chromium oxide hydroxide (CrOOH) formed as a solid product after the hydrothermal reduction. Then, Cr2O3 was obtained by the thermal decomposition of CrOOH. The advantages of the new process are remarkable. First, the raw material, the Na2CrO4 aqueous solution, was the direct intermediate product in the pressure oxidative leaching of chromite ore with sodium hydroxide (NaOH). Second, the reduction efficiency of Cr(VI) increased up to 97.6%, and the total yield of chromium from Na2CrO4 to Cr2O3 was as high as 94.2%. Finally, 96.6% of sodium could be converted into NaOH, so the aqueous solution in the hydrothermal hydrogen reduction process could be recycled as the leaching agent for the pressure oxidative leaching process of chromite ore. Consequently, a complete cleaner and shorter preparation route from chromite ore to Cr2O3 was achieved by integrating three processes: the pressure oxidative leaching of chromite ore, the hydrothermal reduction of the Na2CrO4 aqueous solution, and the thermal decomposition of CrOOH. The new method achieves the high-efficiency use of chromium resources, cyclic utilization of material, and extremely low environmental pollution of Cr(VI), and well exemplifies the principle of the 3Rs (Reduce, Recycle, Reuse).

Research on the distribution of S species in the pressure oxidation leaching process of SrS solution

Strontium compounds apply extensively in a variety of domains. Commonly, strontium compounds are made by carbonization of SrS solution. H2S is readily generated in this process. To avoid H2S byproducing, a novel strategy for the pressure oxidation leaching process of SrS solution was used. The overoxidation of sulfides was restrained, and a higher separation efficiency of Sr and S was obtained, which was beneficial for synthesizing other strontium compounds. The effects of the oxidation pH environment, reaction temperature, initial total sulfide concentration and reaction time on the conversion ratio of S species were investigated. The results showed that S0 was preferably generated in a near-neutral, low-temperature and low initial total sulfide concentration oxidation environment. The optimum oxidation conditions were summarized experimentally: 48 mL/L HCl (pH = 7.11), 25 °C reaction temperature, 8.2 g/L initial total sulfide concentration and 60 min reaction time. The optimum conversion ratios were obtained under optimum oxidation conditions as follows: χsulfide 2.3%, χH2S 0.5%, χS0 81.5%, χinter 10.0% and χS - Sr 5.7%. SrCl2 crystal was recovered finally from the leachate. At last, the pressure oxidation mechanism of SrS was discussed.

Thermodynamic analysis and in situ powder X-ray diffraction investigation of the formation and transformation of mineral phases during pressure oxidation of pyrite

Acid oxidative pressure leaching is a cost-effective way for recovering gold from refractory gold ores such as gold-bearing pyrite, yet our knowledge of the dissolution, crystallization, and phase transformation during pressure leaching is still controversial. This is partially due to the lack of thermodynamic data and in situ studies of the leaching process. Here, we combine thermodynamic modelling and in situ powder X-ray diffraction (PXRD) to investigate mineralogical phase changes during oxidation of pyrite. The polyhedron method has been utilised to estimate the standard Gibbs free energy of formation (∆Gfo) and enthalpy of formation (∆Hfo) of 31 sulphate minerals from 25 °C to 300 °C. The calculated thermodynamic data for the sulphate minerals agree well with the literature, with an average relative error of 0.23% for both ∆Gfo and ∆Hfo demonstrating the reliability of the polyhedron method. Some new thermodynamic data for the mineral phases at elevated temperature was calculated and used to construct the Eh-pH diagrams for the Fe-S-H2O system at 225 °C, which were used to predict phase transformations and chemical reactions during oxidation of pyrite. Based on the analysis of thermodynamic diagrams, the formation of basic ferric sulphate (BFS: Fe(OH)SO4) is favoured at stronger acidic and higher solution redox potential conditions, while hematite and FeSO4∙H2O occur at low solution redox potential conditions. These predictions agreed with the results from laboratory-based in situ PXRD experiments, in which the mineralogical phase transformations were studied during acid pressure treatment of pyrite in a capillary. The influence of initial concentration of ferric ions on the change of mineral phase was revealed. The results confirmed the formation of FeSO4∙H2O and Fe(OH)SO4 phases during the heating (24–225 °C) and annealing stages. These phases may passivate pyrite surface and hence slow down further pyrite oxidation but were re-dissolved during the annealing and/or cooling stages, depending on the initial concentration of ferric ions.

Acid pressure oxidation leaching of arsenopyrite in the presence of pyrite: Oxygen consumption kinetics

In the process of extraction of gold from refractory sulphide ores, arsenopyrite and pyrite represent two of the major hosts for gold in solid solution. In this study, the pressure oxidation of arsenopyrite and arsenopyrite-pyrite mixtures in a H2SO4–O2 system have been investigated, with the aim of using the oxygen consumption kinetics to probe the oxidation mechanisms. The effects of temperature (180–220 °C), acidity (pH 0.5–2.5), dissolved iron concentration (10 and 30 g/L) and molar ratios (0:1–3:1) of pyrite-to-arsenopyrite (Py/Aspy) were evaluated. Kinetic analysis of arsenopyrite dissolution at 180–220 °C via a shrinking core model indicated an activation energy (Ea) of 48.46 kJ/mol, suggesting a mixed interface reaction and diffusion control. The order of the reaction to acidity was 0.16 at 200 °C, suggesting that [H+] is likely not the rate-limiting factor under typical reaction conditions. The addition of Fe(II) ions to the feed enhanced arsenopyrite oxidation, due to the formation of Fe(III) as a surrogate oxidant to drive the reaction.The Ea for Py/Aspy of 1:1 exhibited two behaviours, calculated to be 77.32 kJ/mol below 200 °C and decreasing to 34.59 kJ/mol above 200 °C. The former was attributed to surface control due to the oxidation of elemental sulphur, followed by a switch to mixed control at elevated temperatures. As Py/Aspy was increased to 2:1 and 3:1, a single behaviour was observed, with Ea values of 56.01 kJ/mol and 43.35 kJ/mol respectively. These values imply a mixed control and begin to approximate literature values for pyrite oxidation. A time-to-a-given-fraction method was also used to examine changes in Ea with reaction extent. Arsenopyrite was found to be under mixed control for most of the reaction extent. At increasing pyrite fractions, oxidation was observed to be reaction-limited at the initial stage of reaction, potentially reflecting the kinetics of sulphur oxidation.

Rhenium extraction from pressure oxidative leaching solution of molybdenite concentrate using hydrophobic deep eutectic solvents

This research is one of the early studies to evaluate the capability of hydrophobic deep eutectic solvents (DESs) as an eco-friendly solvent for precious and strategic metal extraction, rhenium (Re). In this study, the selective transfer of Re from aqueous solution and pressure oxidative leaching solution of molybdenite concentrate was investigated by mixing fatty acid (Decanoic acid) and quaternary ammonium salt (Aliquat 336). To evaluate the extraction potential of hydrophobic-DES in the ratio of Decanoic acid (Deca):Aliquat 336 = 2:1, FTIR, 1H NMR, thermal gravimetric analysis was used. For finding an optimum condition for Re separation, various extraction conditions were initially investigated in synthetic aqueous solution. In this area, the maximum extraction percentage was obtained at a concentration of Re = 100 mg/L, ratio of organic to aqueous phase (O:A) = 1 to 25, contact time = 10min, pH = −0.5, and temperature = 25°C. In the stripping step, the recovery of >90% Re at selected O:A = 5:1 showed that significant reduction of water consumption. After that, the complex situation for selective Re extraction from molybdenite leaching solutions with different cations and anions was studied. For increasing the extraction and separation factor of Re in comparison to the other ionic specious (e.g., Cu, Fe, Mo and S), the neutralization process was also applied. To understand the extraction mechanism for Re, anion exchange constant (KOE) and ion pair constant (KIP) were determined. In this area, the ion pair formation was chosen as the main reaction mechanism; however, anion exchange reaction was not negligible role in Re extraction. Toxicity study on hydrophobic-DES was investigated by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method. The obtained results according to IC50 and viability of cells culture represented the low toxicity of hydrophobic-DES.

Eco-friendly extraction of arsenic and tungsten from hazardous tungsten residue waste by pressure oxidation leaching in alkaline solutions: Mechanism and kinetic model

Tungsten residue waste (TRW), considered an environmental burden due to high content and excessive leaching toxicity of arsenic (As), are also secondary tungsten (W) resources. A novel method for simultaneous extraction of arsenic and tungsten from TRW via alkaline pressure oxidative leaching was proposed. The results show that As in the TRW mainly exists in the form of As coprecipitated with Mn(Ⅱ) oxides and FeAsS. In addition, As coprecipitated with Mn(Ⅱ) oxides and W are encapsulated in Fe, Mn oxides. The structure of Fe, Mn oxides with dense surface can be destroyed and the chemically stable arsenopyrite can be efficiently oxidized by oxygen in alkaline solutions. The leaching efficiency of As and S reached 97% and 99% at 80 min, respectively, while that of W reached 82% at 10 min. The leaching rate of As and S is controlled by diffusion with the apparent activation energies of 16.67 kJ/mol and 15.66 kJ/mol, respectively. Compared with TRW, the leaching toxicity of As in the leach residue decreased from 10.2 mg/L to only 0.071 mg/L. The new process suggests new possibilities for removal and recovery of As and W from TRW that will contribute to circular economy and environmental protection.

Influence of rheology in the filtration of leach slurry generated by alkaline pressure leaching of a limestone ore

The Nuclear Power Plant, which uses uranium as a fuel, is considered as a clean source of energy with low carbon footprint and less environmental damage. In processing the uranium ore, the filtration of alkaline leach slurry generated by oxidative pressure leaching is a challenge due to very fine grind size coupled with high total dissolved solutes (TDS). The present study aimed at improving and understanding the filtration of the leach slurry with the help of slurry rheology. The effect of solid concentration, temperature, particle size, and dosages of dewatering aids on the rheological behavior of the slurry and the filtration performance was investigated. The slurry rheology was delineated by the Herschel–Bulkley model, temperature effects were incorporated using the Arrhenius type model, and particle size distribution (PSD) was represented by the Rosin–Rammler PSD model. The dosages of dewatering aids were compared using rheological parameters. It was found that the filtration rate decreases as solid concentration increases (10 to 75%, w/w) due to an increase in the shear stress (9.93 to 757 Pa at 1400 s−1). The leach slurry showed shear thickening at ≤ 60% solids (w/w) and shear thinning at ≥ 70% solids. The maximum solid packing volume fraction was found to be 0.59 and 0.54 at 1300 and 441 s−1, respectively. Increase in filtration rate was observed at elevated temperatures as the apparent viscosity (at 1300 s−1) decreased from 0.0195 Pa.s at 20 °C to 0.0135 Pa.s at 70 °C. The fluid flow activation energy was determined to be 5.5 and 7.1 kJ/mol at 1110 s−1 for 50 and 73% solid concentration (w/w), respectively. When the particle size (d90) was changed from 66 to 42 µm, a decrease in filtration rate was observed due to an increase in apparent viscosity from 0.0120 to 0.0163 Pa.s at 1400 s−1. The high molecular weight polyacrylamide based non-ionic synthetic flocculant N 100 and non-ionic biodegradable polysaccharide surfactant guar gum formed flocs through the bridging mechanism and gave best flocculation results, and therefore selected. The present work helps the researchers in better understanding and improving the filtration process of ore slurries.

A feasible strategy for deep arsenic removal and efficient tungsten recovery from hazardous tungsten residue waste with the concept of weathering process strengthening

Tungsten residue waste (TRW), generated by tungsten hydrometallurgy, is classified as a hazardous solid waste by Chinese government due to its high content and leaching toxicity of arsenic, but is also a typical critical metal secondary resource of tungsten. Deep arsenic removal and tungsten recovery of TRW are beneficial to waste harmless treatment and circular economy. However, the occurrence state and weathering mechanism of arsenic in TRW have not been investigated and reported, which is the fundamental reason why the harmless treatment of TRW has become a bottleneck problem. In this paper, a feasible and novel strategy for deep arsenic removal and efficient tungsten recovery from TRW was proposed based on the concept of weathering process strengthening. The results show that arsenic in TRW mainly exists in the form of arsenopyrite, and ionically bound arsenic (V) generated by weathering of arsenopyrite directly leads to leaching toxicity of arsenic in TRW exceeding 5 mg/L. The environmental risk of arsenic in TRW can be completely eliminated by strengthening the uncontrollable and slow weathering process of TRW into a controllable and efficient process. Over 98 % of arsenic and 84 % of tungsten were simultaneously leached from TRW under optimal conditions via an enhanced pressure oxidation leaching process in alkaline solutions based on the leaching thermodynamic and kinetic, resulting in only 0.07 mg/L of arsenic leaching toxicity in the secondary leach residue. Hydrated ferric oxide (HFO) generated by the leaching process provides the possibility for the diffusion of reactants and products, so that arsenic and tungsten can be high-efficiently leached. The harmless secondary leach residue can be used as a raw material for the production of building materials, cement, and glass. Taking into account the reduction of alkali consumption and recovery of tungsten and arsenic, the leach solution was recycled. The closed-loop strategy shows great promise for the harmless treatment and tungsten recovery of TRW on an industrial scale to promote circular economy and environmental protection.

Comparation on the methods of removing impurity metals from copper powder of waste printed circuit boards

Copper powder of waste printed circuit boards (WPCBs), an important secondary metal resource, is usually processed by copper concentrate pyrometallurgy system to recover valuable metals. However, metals such as Pb, Sn, Zn and Al in copper powder of WPCBs are harmful to copper smelting system. Therefore, a two-stage leaching process was proposed to remove impurity metals from copper powder, and different routes were screened. Copper powder was firstly leached in the hydrochloric acid to remove Al, and then the Al-removed residue was treated to recover Sn and Pb by two routes, i.e., acid oxidation leaching or alkaline pressure oxidation leaching, respectively. The results showed that more than 97.15% of Al in copper powder was removed by the hydrochloric acid leaching. In HCl system adding H2O2, the leaching ratios of Pb and Sn reached 91.07% and 94.67%, respectively. In the alkaline pressure oxidation leaching system, the leaching ratios of Pb and Sn were 86.63% and 93.80%, respectively. In general, the separation and recovery of valuable metal resources in the WPCB copper powder were realized, and Cu was further enriched, providing high-quality raw materials for copper pyrometallurgy.

Metallurgical byproducts application aimed at improving ore concentration efficiency at Talnakh Concentrator

Talnakh Concentrator processes the mixture of high-grade and cupriferous ores to produce copper and nickel-pyrrhotite concentrates via the process implemented in 2016. Since 2018, pursuing a comprehensive use of raw materials, Talnakh Concentrator proceeded with reconcentration of low-nickel pyrrhotite product to produce low-grade reflotation concentrate (0.8–1.2% of nickel) sent to Nadezhda Metallurgical Plant named after B.I. Kolesnikov (hereinafter, NMP) for hydrometallurgical processing. Testing of Copper Plant’s byproducts application was aimed at increasing nickel recovery as a result of the nickeliferous pyrrhotite surface activation by copper ions. It is impractical to apply blue vitriol, traditionally used for this purpose, as it leads to a significant decrease in technical and economic performance due to an increase in operating costs for reconcentration. The Copper Plant products, such as decopperized electrolyte and a coppernickel solution from PGM Concentrator were tested as activators. These products contain not only residual amount of copper ions, but also a substantial quantity of sulphuric acid. The study showed that Copper Plant’s solution application increased the amount of nickel recovered to the product of reconcentration and improved the product pyrrhotite content that favorably effected its subsequent pressure oxidation leaching. Application of the copper-nickel solution from PGM Concentrator is considered to be the best option due to a higher ratio of copper ions to sulphuric acid. Solutions applied during nickel-pyrrhotite flotation at Talnakh Concentrator were also studied. The authors simulated the initial composition alteration of Talnakh Concentrator’s feed with an increase in a share of cupriferous ore, containing much less pyrrhotite than high-grade ore. It was found out that if the feed contained critical amount of cupriferous ore, application of Copper Plant’s solutions contributed to maintenance of sulphur content in the nickel-pyrrhotite concentrate of Talnakh Concentrator that provided energy potential required for the appropriate thermal conditions of NMP’s smelting vessels.

Eco-Friendly Extraction of Arsenic and Tungsten from Hazardous Tungsten Residue Wastes by Pressure Oxidation Leaching in Alkaline Solutions: Mechanism and Kinetic Model

Eco-Friendly Extraction of Arsenic and Tungsten from Hazardous Tungsten Residue Wastes by Pressure Oxidation Leaching in Alkaline Solutions: Mechanism and Kinetic Model

Separation and Stabilization of Arsenic from Lead Slime by the Combination of Acid Leaching and Forming Scorodite

In this paper, a scheme is proposed for the treatment of arsenic-containing lead slime by the combination of acid pressure oxidation leaching and forming scorodite. On the basis of thermodynamic calculations, the effects of six factors including acid concentration, oxygen partial pressure (pO2), liquid to solid ratio (L/S), agitating speed, leaching time and temperature for the removal of arsenic were studied in an acid pressure oxidation leaching process, then the optimum leaching conditions were established: L/S of 10 mL/g, leaching time of 2.5 h, pO2 of 2.0 MPa, leaching temperature of 170 °C, acid concentration of 100 g/L and stirring speed of 300 r/min. Under the optimal conditions, the leaching rate of arsenic from lead slime reached 99.10% and the arsenic content of the leaching residue was about 0.80%. After a decontamination procedure, the total arsenic concentration in the acid solution obtained from leaching experiments was 37.18 g/L, and the initial pH was 0.50. Finally, as high as 98.5% of arsenic extracted from the lead slime was stabilized in the form of scorodite (FeAsO4·2H2O) by the precipitation process under the following conditions: initial pH value of 1.0, Fe(II)/As molar ratio of 1.3, pO2 of 2.5 MPa, temperature of 160 °C and precipitation time of 2.0 h.

A Study on the Selective Leaching of Valuable Metals and the Configuration of Iron Silicon Phases in Copper Smelting Slag by Oxidative Pressure Leaching

A Study on the Selective Leaching of Valuable Metals and the Configuration of Iron Silicon Phases in Copper Smelting Slag by Oxidative Pressure Leaching

Application of FTA Analysis for Calculation of the Probability of the Failure of the Pressure Leaching Process

European Union legislation requires organizations to assess their processes in the context of risk management. The main task of risk management is to manage all risks that can significantly affect the outcome of processes. The article is focused on risk evaluation in pressure leaching at elevated temperature using the method Fault Tree Analysis (FTA). The effectivity of pyrite and arsenic pyrite decomposition by oxidative pressure leaching is influenced by the duration of the process, by the temperature, concentration of the leaching solution and by a density of the slurry. It was found that, under equitable conditions, the arsenic pyrite decomposes more intensely than pyrite. Under laboratory conditions, leaching is performed in an autoclave. Due to the aggressive environment, increased pressure and temperature, process failure is possible. Its probability was calculated by FTA. It has been found that the probability of the top event in the examined process was disproportionately high (0.057) and represents an invitation to take corrective actions. The Monte Carlo method was used for the simulation of the effect the probability of basic events on the probability of the top event—the failure of the leaching process.

Intensification of solid–liquid separation by thermal sedimentation in pressure oxidative leaching process of chromite

In the leaching process of chromite, how to quickly separate sodium chromate from leaching slurry is a key issue. In this paper, a simple method, named thermal sedimentation, was firstly introduced into the solid–liquid separation of sodium chromate. The results shown that the thermal sedimentation can respectively shorten the separation time (h) by 71.9% and 53.9% when compared to dilution filtration and centrifugation separation. In terms of processing unit volume of leaching slurry, the power consumption of thermal sedimentation was 6.48 × 103 J, which was the lowest in the investigated separation methods. Meanwhile, the alkali solution after the separation of thermal sedimentation can be directly reused. When sedimentation temperature was 150 °C, sedimentation efficiency was higher. In addition, the relationship between slurry viscosity and sedimentation velocity was consistent with Coe-Clevenger method and Stokes formula. The thermal sedimentation can be regarded as an effective solid–liquid separation method for liquid phase oxidative leaching system of chromite.

Removal and reuse of arsenic from arsenic-bearing purified residue by alkaline pressure oxidative leaching and reduction of As (V)

Arsenic removal from arsenic-bearing purified residue by alkaline pressure oxidative leaching (APOL) and reduction of arsenate in solution to arsenite by sulfur dioxide gas was studied. The effects of different parameters including NaOH concentration, oxygen partial pressure, temperature, liquid/solid ratio, and leaching time for the extraction of arsenic were investigated based on thermodynamic calculation. The optimum leaching conditions have been established as: 2.5 mol/L of NaOH concentration, 0.5 MPa of oxygen partial pressure, 120 °C of temperature, 4 mL/g of liquid/solid ratio and 3.0 h of time. Under these conditions, the leaching rates of arsenic, zinc and nickel respectively reached 94.47%, 19.90% and 12.66%, while copper and cobalt were hardly leached out, achieving the selective removal of arsenic from the arsenic-bearing purified residue. The reduction of As(V) in solution was optimized by orthogonal experimental design method, and the effects of experimental parameters including initial pH, reduction temperature (T), flow rate of SO2 (F), and reduction time (t) on reduction of As(V) were investigated. The results show that the optimum reduction parameters were 4 of initial pH, 30 °C of temperature, 60 mL/min of SO2 flow rate and 2.5 h of time. Based on these conditions, the reduction rate of As(V) reached 92.95%.