Sulfide Precipitation Process Research Articles

Process and kinetics of ammonium sulfide removal of zinc, nickel and cobalt from manganous sulfate electrolyte

In producing electrolytic manganese and manganese-based lithium batteries, Manganous sulfate solution serves as a crucial intermediate material. During the preparation of manganese sulfate solution by acid leaching, the removal of impurities such as zinc, nickel, and cobalt ions by sulfide precipitation is essential for obtaining high-quality metallic manganese and high-purity manganese sulfate. The results show that when the temperature is 45 °C, the pH is 5.60, the ammonium sulfide dosage is 40 %, the time is 5 min, and the rotation speed is 650 rpm, the sulfidation rates of zinc, nickel and cobalt are 99.07 %, 89.30 %, and 87.70 % respectively. At this time, the loss rate of manganese in the solution after sulfide impurity removal is 11.45 %, and the manganese-impurity ratio is 80.00. Response surface methodology analysis revealed that temperature, pH, and ammonium sulfide concentration significantly affected the manganese loss rate. After process optimization, at a temperature of 32.70 °C, a pH of 5.20, and an ammonium sulfide concentration of 32.73 %, the manganese loss rate decreased to 6.05 %, while the removal rates of Ni, Co, and Zn were 75.35 %, 60.80 %, and 99.51 %, respectively. In the Manganous sulfate electrolyte with or without ammonium sulfate, the sulfide precipitation processes of zinc, nickel and cobalt ion are all first-order reactions, and the reaction order is zinc > nickel > cobalt. More importantly, the density functional theory (DFT) calculation results also confirmed the formation sequence of zinc sulfide > nickel sulfide > cobaltous sulfide, which supported the experimental results well. This study will lay the foundation for process optimization and mechanism elucidation of impurity ions in ammonium sulfate electrolyte precipitated by ammonium sulfate.

Iron, boron, and sulfur isotope constraints on the ore-forming process of subseafloor replacement-style volcanogenic massive sulfide systems

The well-preserved Ashele subseafloor replacement-style volcanogenic massive sulfide (VMS) deposit in the Central Asian Orogenic Belt comprises two stages of Cu mineralization, i.e., early massive sulfides dominated by colloform and euhedral pyrite intergrown with chalcopyrite and sphalerite, which were replaced by late vein-dominated chlorite-chalcopyrite assemblages. In this study, a combined systematic Fe, B, and S isotope investigation was first applied to investigate the sulfide precipitation processes and the relative proportion of fluid sources in different alteration and mineralization stages of the Ashele deposit. Boron isotopes of Mg-rich tourmaline (δ11B from −5.57‰ to −2.73‰, average (avg.) −4.23‰) indicate significant seawater (∼19%) participated during the formation of massive sulfides. A two-component mixing model is used to estimate the contribution of seawater and igneous sulfur to the total sulfur budget, and the results show the increasing contribution of magmatic sulfur from the early (35%) to late (76%) stages. In addition, δ56Fe values of pyrite gradually increase from the massive ore (−0.46‰ to −0.02‰, avg. −0.24‰), quartz-pyrite (−0.09‰ to 0.07‰, avg. −0.01‰), chlorite-chalcopyrite-quartz-pyrite (0‰ to 0.21‰, avg. 0.08‰) to the quartz-sericite zone (−0.02‰ to 0.29‰, avg. 0.14‰), which is likely related to the different extent of isotopic exchange and formation temperature, and could be used in the exploration of VMS systems. The new two-stage ore-forming model shows that in the early stage, rapid mixing of hydrothermal fluid from underlying magma chamber with abundant cold seawater led to rapid deposition of pyrite and associated Cu mineralization under relatively oxidized condition, and long-term hydrothermal activities in relatively closed systems would promote the formation of upper massive ores, which resulted in an equilibrium system between pyrite, chalcopyrite, and associated fluid with wide ranges of δ56Fe in pyrite (−0.46‰ to −0.02‰) and chalcopyrite (−1.56‰ to −0.49‰). The late hydrothermal activities in relatively open system would contribute to stringer sulfides or stockworks underlying the massive ore in relatively reduced conditions with heavier Fe isotope compositions in pyrite (−0.09‰ to 0.29‰) and chalcopyrite (−0.60‰ to −0.04‰). Overall, our study demonstrates that the coupling of B, Fe, and S isotopes could be a useful tool to indicate long-term subseafloor infilling and replacement processes for subseafloor replacement-type VMS deposits, which are the prerequisite to form large-tonnage VMS deposits.

Fe-Cu-Zn Isotopic Compositions in Polymetallic Sulfides from Hydrothermal Fields in the Ultraslow-Spreading Southwest Indian Ridge and Geological Inferences

Submarine hydrothermal sulfides from the ultraslow-spreading Southwest Indian Ridge (SWIR) were sampled from three hydrothermal fields, and the Fe-Cu-Zn isotopic compositions were analyzed in this study. The Fe isotopes ranged from −0.011‰ to −1.333‰. We believe the processes controlling the Fe isotope variability in the hydrothermal systems include the sulfide precipitation process, the initial isotopic composition of the hydrothermal fluid, and the temperature during precipitation. Among these factors, the sulfide precipitation process is the dominant one. The Cu isotope compositions of the sulfides varied from −0.364‰ to 0.892‰, indicating that the hydrothermal fluid preferentially leached 65Cu in the early stages and that hydrothermal reworking led to decreases in the Cu isotopes in the later stages. In addition, because mass fractionation occurred during sulfide precipitation, the Zn isotope variations ranged from −0.060‰ to 0.422‰. Combined with the S isotopic compositions, these results also implied that different Fe-Cu-Zn isotopic fractionation mechanisms prevailed for the different sample types. Based on these results, we are sure that the metallic elements, including Fe, Cu, and Zn, were derived from the mantle in the SWIR hydrothermal field, and the Fe-Cu isotope results indicated that these metallic elements were provided by fluid leaching processes. Using the isotopic fractionation and sulfide results, we calculated that the Fe-Cu-Zn isotopic compositions of the hydrothermal fluid in this field were δ56Fe(fluid): −0.8~0.0‰; δ65Cu(fluid): 0.3~1.3‰; and δ66Zn(fluid): 0~0.48‰.

Heat treatment-enhanced bioleaching of new electroplating sludge containing high concentration of CuS and its mechanisms

Electroplating sludge by CaO/Ca(OH)2 precipitation craft represents a typical toxic heavy metals-bearing hazardous waste worldwide. Recently, sulfide electroplating sludge is growingly produced as a substitute for Ca(OH)2-based hydroxides sludge since sulfide precipitation process sharply reduces the production of sludge, posing an urgent challenge to the traditional treatment ways suitable for hydroxides sludge. In this work, bioleaching was firstly utilized to extract Cu from the new sulfide electroplating sludge containing high concentration of CuS, and a thermal pre-treatment was used to promote the bioleaching performance. The results showed that a low Cu dissolution of 53% from the original sulfide sludge by bioleaching was gained because of the refractory nature of sulfides. However, a thermal treatment evidently enhanced the bioleaching efficiency of sulfide electroplating sludge. The Cu release efficiency sharply rose from 59% to 100% when the roast temperature lifted from 200 °C to 600 °C. However, a higher temperature of 800 °C strongly injured the bioleaching, gaining the lowest Cu release of 46%. A full conversion of refractory CuS into highly water soluble CuSO4 occurred with the 600℃-roast, concomitant with the formation of a finer particle which witnessed a great rise in the specific surface area from 3.64 to 12.06 m2/g, accounting for 100% Cu liberation by bioleaching. In contrast, the calcination at 800 °C prompted the decomposition of CuSO4 to form CaSO4 which not only covered the sludge as coating layer but also induced sludge aggregation to form a larger particle with a smaller specific surface area of 1.22 m2/g, inhibiting the bioleaching. This present works revealed the internal mechanisms for a perfect combined process of the thermal treatment and bioleaching for tackling the sulfide electroplating sludge.

A novel approach for removing cadmium from synthetic wet phosphoric acid using sulfide precipitation process operating in batch and continuous modes

The removal of heavy metals, especially cadmium, from wet phosphoric acid is still a challenging stage during the manufacturing of phosphate fertilizers. In this work, a novel approach was developed to improve the performance of the sulfide precipitation process as a purification technique. This is based on NaHS rather than Na2S as a precipitating agent in both batch and continuous modes for cadmium removal from synthetic wet phosphoric acid. First, the respective performance of Na2S and NaHS was compared in the batch mode. NaHS was shown to improve decadmiation in comparison to Na2S even though the same trends were observed for both precipitating agents as a function of operating conditions. An increase in Sulfur/Cd2+ molar ratio improved cadmium sulfide precipitation. Conversely, increasing temperature and phosphoric acid concentration impaired the effectiveness of cadmium removal efficiency. An apparent kinetic model was developed taking into consideration the reaction mechanisms and supersaturation to predict the residual cadmium concentration in phosphoric acid solutions. The feasibility of the continuous process based on NaHS was also assessed. The results showed that a residence time of 40 min was needed to achieve 85.6 % of Cd2+ elimination at 25 °C. As aggregation seemed to be the main mechanism governing particle size, this increased with the Sulfur/Cd2+ ratio, which could improve downstream solid separation. Eventually, these findings of this study provide useful insights into the feasibility of chemical precipitation using NaHS as a technology of phosphoric acid decadmiation in the industry.

Enhanced desorption of cationic and anionic metals/metalloids from co-contaminated soil by tetrapolyphosphate washing and followed by ferrous sulfide treatment

In this study, a novel approach was employed for the remediation of cationic and anionic metals/metalloids co-contaminated soil by tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment. Tetrapolyphosphate could simultaneously enhance the desorption of cationic metals (Pb and Zn) and anionic metal/metalloid (Cr and As) from the contaminated soil in the whole tested pH range of 2–10. With addition of 0.15 mol/L tetrapolyphosphate at pH 7.0, the removal ratio of Pb, Zn, As and Cr could achieve 83.1%, 70.4%, 75.7% and 66.4% respectively. The fractionation analysis of heavy metals/metalloids demonstrated the release of exchangeable and Fe/Mn bound forms contributed to most desorption of Pb and Zn. The decreases of non-specifically sorbed form and amorphous and poorly-crystalline hydrous oxides of Fe and Al bound form were responsible for most removal of As. The comparison with other common washing agents (EDTA, oxalate and phosphate) under their respective optimal dosage could confirm that tetrapolyphosphate was superior to simultaneously desorb the cationic and anionic metals/metalloids with higher efficiency. After 12 h, applying 150 mg/L FeS at pH 3.5 could totally remove Pb, Zn, As and Cr from the washing effluent by sulfide precipitation, reduction and adsorption processes. Higher pH would inhibit the removal of As and Cr by FeS. Meanwhile, the residual of tetrapolyphosphate could be totally recovered from the washing effluent by employing anion exchange resin. This study suggests tetrapolyphosphate enhanced soil washing coupled with ferrous sulfide treatment is a promising approach for remediation of cationic and anionic metals/metalloids co-contaminated soil in view of its high efficiency and simple operation.

Changing the conventional clarification method in metal sulfide precipitation by a membrane-based filtration process

The metal sulfide precipitation process is a widely studied technology used to recover metals or remove pollutants from different aqueous sources. However, the conventional clarification stage used to separate the generated precipitates cannot effectively remove them from recovered solutions. Taking this into account, the current study focuses on developing a new separation method applied in metal sulfide precipitates, based on a membrane filtration process. Different operating conditions and metal concentration in the feed solution were evaluated for the separation of copper sulfide precipitates formed from synthetic cyanide solutions in ceramic microfiltration membranes. Results showed attractive values of flux and copper recovery. Flux results ranged between 0.9 L/m2s and 1.2 L/m2s for copper concentrations above 500 mg/L, and copper recoveries resulted closer to 100% at the determined optimal operating conditions (4.5 pH, 120% NaHS stoichiometric dosage, and 2 bar feed pressure). These flux values decreased up to one order of magnitude for diluted copper concentrations, due to a change of aggregation capacity of precipitates. This study has demonstrated that the membrane filtration process can be a suitable alternative for the conventional gravitational clarification, promoting better performance results in terms of equipment capacity, metal recovery, and process safety.

Hydrophilicity/hydrophobicity of metal sulfide particles as a determinator of aggregation performance in wastewater

Differences in aggregation performance of metal sulfide particles generated in wastewater during sulfide precipitation processes cannot be adequately explained by their zeta potentials. Herein, different aggregation performances among CuS, CdS and As2S3 particles produced by sulfide precipitation in strongly acidic wastewater were found to depend on the different hydrophilicity/hydrophobicity of these particles. Density functional theory (DFT) calculation revealed the mechanism of hydrophobicity/hydrophilicity of the metal sulfide particles, which verified the hydrophobic particles preferred to self-aggregate, whereas the hydrophilic particles were more likely to bind to H2O molecules and disperse in wastewater. Metal sulfide particles generated under different conditions also have different hydrophilicity/hydrophobicity and on which the aggregation performances of the particles depend. It was confirmed that the different aggregation performances among CuS, CdS and ZnS particles generated in low-pH wastewater were also determined by their different hydrophilicity/hydrophobicity rather than their zeta potentials. This study explains the reason of different aggregation performances among precipitates produced by sulfide precipitation in wastewater. Additionally, this study has revealed that, in strongly acidic wastewater, the tiny and hydrophilic metal sulfide particles were difficult to be separated by settling and coagulation method, which provides an instruction to further study for the downstream separation process of the metal sulfide particles formed by sulfide precipitation.

Novel photo-activated method for removal of mercury from industrial wastewater

Mercury-laden wastewaters need new treatment options to meet current and pending regulations. Some facilities employ a sulfide precipitation process to lower the concentrations of Hg in their discharge through chelation and filtration. However, this process still results in mercury concentrations higher than the imposed limits for discharge by upcoming U.S. EPA regulations. This paper focuses on a simple approach, Ultraviolet Activated Chelation (UVAC), which has resulted in mercury concentrations as low as 10 ppt when applied to wastewaters from three industrial facilities. An investigation into the effect(s) of certain variables on the treatment process, such as pH and residence time, was carried out through batch experiments using plant wastewater. A discussion on UVAC effectiveness is based on results from the completion of a pilot-scale UVAC system that was designed, fabricated, and operated based on bench-scale experimental data. Concentrations as low as 12 ppt were obtained for the majority of the four-month pilot study.

Removal of nickel through sulfide precipitation and characterization of electroplating wastewater sludge

Abstract This work consists of the removal of nickel by sulfide precipitation from industrial electroplating wastewater and characterization of the produced sludge. Tests are carried out in a perfectly stirred batch reactor on electroplating industrial solution and synthetic solution prepared in the laboratory. The aim is to evaluate the impact of complexing agents formed during precipitation of metal ions in the industrial effluent. The concentration of nickel in both solutions is 100 mg/L. The operating conditions for the sulfide precipitation process are optimized: pH, molar ratio [S=]/[Ni2+] and dosage of S= ions. For an initial pH of 5 and an equimolar ratio of [S=]/[Ni2+]:1/1, the results show that the removal efficiency of Ni2+ ions is approaching 91 and 94% for industrial and synthetic solutions, respectively. Otherwise, for the same pH value in supersaturation conditions ([S=]/[Ni2+]:1.5/1), the removal efficiency is approaching 62 and 92% for industrial and synthetic solutions, respectively. For an effective metal removal, the optimal dosage of sulfide ions was evaluated. For 33 mg/L of S=, the removal efficiency of Ni2+ is approximately 90%. The resulting sludge has been characterized by X-ray diffractometry, scanning electron microscopy, infrared spectroscopy and thermal analysis. It consists essentially of millerite and nickel oxide.

Experimental and simulation studies of metal sulfide precipitates separation in copper smelting waste acid using a gravitation field-flow fractionation method

Sulfide precipitation method has been widely used in the removal of arsenic and heavy metals from copper smelting waste acid. Nevertheless, tiny metal sulfide particles are generated during the process, making it difficult to achieve solid-liquid separation as well as solid-solid separation. This study designed an innovative gravitational field-flow fractionation (GFFF) tank to effectively separate fine sulfide precipitate particles of different heavy metals, relying on the difference in particle sizes. To achieve better tank performance, the effects of process conditions on the size variation of precipitate particles produced in metal sulfide precipitation process (Cu(Ⅱ), Zn(Ⅱ), or As(Ⅲ)) were firstly investigated. The results show that supersaturation level, sulfide to metal molar ratio, and pH have significant effects on the precipitate particle size, while reaction time affects slightly. The optimum conditions were identified to achieve the greatest possible differences in particle sizes of the three metal sulfide precipitates. To further analyze its performance, a 3D model of the GFFF tank was built, with the fluid flow field and precipitate particle movement simulated under the optimum conditions. The simulation results demonstrate that the designed GFFF tank can realize efficient separation of fine metal sulfide precipitates for the recovery of valuable metals.

Design and analysis of continuous-flow reactors for copper sulfide precipitation process by a computational method.

Sulfide precipitation method has been widely applied in heavy metal-polluted wastewater treatment, due to the low solubility of most metal sulfide precipitates. Nevertheless, the relevant hydrodynamics studies on the metal sulfide precipitation process are rarely found in the literature. In this study, three continuous-flow sulfide precipitation reactors (CFSPRs) were designed and evaluated by a computational method. To characterize the process efficiency of copper sulfide precipitation in different reactors, fluid velocity field, species concentration distribution, and reaction rate distribution maps were acquired as simulation results. A two-factor designed set of boundary conditions was used to determine their effects on processing efficiency. The model results indicate that the inflow rate and reactor layout have significant effects on the copper sulfide precipitation process. The layout of reactor no. 3 and the inflow rate of 0.75 m/s prove to have higher treatment efficiencies than those at other conditions. Possible explanations for the simulation results were proposed. The model data of effluent concentration were compared and statistically analyzed with the measured concentrations of copper ion and sulfur ion in the outlet stream, and the results demonstrate a strong correlation between them, which suggests the model is reasonably accurate.

Impact of precipitate characteristics and precipitation conditions on the settling performance of a sulfide precipitation process: An exhaustive characterization of the aggregation behavior

The sulfide precipitation process is currently the most successful technology for recovering cyanide and copper in cyanidation gold plants. The application of this chemical process has been implemented in the SART (Sulfidization, Acidification, Recycling, and Thickening) process. This process includes thickening and filtering unit operations to separate the solids precipitated in the sulfidization reactor. Nevertheless, solid-liquid separation in the thickener has not been optimized, resulting in the loss of copper precipitates in the overflow and, consequently, inducing a reduction in copper recovery in the overall process. This performance could be influenced by the colloidal characteristics of the particles formed in the reaction, but only a few studies have found quantifiable evidence in this regard. Moreover, the impact of the main variables of the process (e.g., pH, sulfide content, and reaction time) on the aggregation behavior has not been studied. Thus, this work attempts to reduce the current lack of scientific understanding of the SART process with respect to the industrial practice. In this context, the goal of this work was to carry out a chemical characterization, particle electrical charge (zeta potential) assessment, chemical computational simulation and settling tests of precipitates obtained from sulfide precipitation assays, in order to create a deep characterization of copper and zinc precipitates. The main results attend to understand the aggregation behavior of the precipitates, the relevance of reaction parameters (pH and sulfide addition) in the aggregation characteristics and its impact in settling results. This study is the first research focused on the characterization of sulfide metal precipitates in cyanide media and its impact in the process.

UV light irradiation improves the aggregation and settling performance of metal sulfide particles in strongly acidic wastewater

Tiny metal sulfide particles are usually generated in the metal sulfide precipitation process, and residual dissolved sulfide (H2S, HS− and S2−) generally makes the aggregation and settling performance of these particles worse. In this work, under strongly acidic conditions with 0.102 M H2SO4, the characteristics of CuS, CdS and mixed metal sulfide particles (CuS and CdS) produced in strongly acidic wastewater by H2S were initially studied. Then, UV light irradiation was employed to improve the aggregation and settling performance of the metal sulfide particles, and relevant mechanisms were investigated. The results showed that the residual H2S in suspension can deteriorate the settling performance of metal sulfide particles. After H2S was removed, CuS particles exhibited good settling performance, but the settling performance of CdS and mixed sulfide particles remained poor. Subsequent studies showed that UV light irradiation effectively improved the aggregation and settling performance of CdS and mixed metal sulfide particles in the presence of H2S. After 30 min of UV irradiation, the average hydrodynamic diameter of CdS particles increased approximately 166-fold in the presence of 131.40 mg/L H2S, and that of mixed sulfide particles increased approximately 105-fold with the existence of 129.30 mg/L H2S. Further study revealed that H2S in suspensions played an important role in the aggregation of metal sulfide particles under UV irradiation. HS• generated by the photolysis of H2S oxidized a portion of S2− on the surface of CdS particles and a portion of S2− and Sn2− on the surface of mixed sulfide particles to S22− and S0, which resulted in a decrease of negative charge and an enhanced aggregation of these particles. Finally, this study showed that the settling performance of CdS and mixed sulfide particles was effectively improved at high initial H2S concentrations under UV irradiation. This study provides a clean and effective method to improve the metal sulfide precipitation process for strongly acidic wastewater treatment.

A Novel Process for the Treatment of Copper-Smelting Waste Acid with a High Arsenic Concentration

A novel process was proposed for the separation of Cu and As from Cu-smelting waste acid (CSWA). This process includes three steps, namely, the oxidization of As via the addition of H2O2, the selective separation of Cu through the use of Na2S, and the removal of As via the synthesis of scorodite. The CSWA was initially oxidized using H2O2 where the As(III) transformed into As(V). The oxidization of As(III) is believed to be the decisive step with regard to the selective separation of Cu and As via the sulfide precipitation process. The results showed that 99.4% of the Cu and 1.8% of the As were precipitated via the sulfidization process and that 98.8% of the As in the Cu-removed CSWA was removed in the form of scorodite (FeAsO4·2H2O). This novel process exhibits promising application prospects for the treatment of CSWA.

Isotopic footprints of the giant Precambrian Caixiashan Zn-Pb mineralization system

Carbonate-replacement Zn-Pb deposits are formed through fluid circulation within carbonate rocks and are an important global source of Zn and Pb. The Caixiashan carbonate-replacement deposit is one of the largest Zn-Pb systems in China. The Mesoproterozoic syn-sedimentary stage (I) of the Caixiashan deposit is characterized by sulfides with negative δ34S values (−25.3 to −8.6‰) generated by organic sulfate reduction, which co-precipitated with the host rocks. The Neoproterozoic main sulfide precipitation stage (II) was caused by thermo sulfide reduction resulting in positive δ34S values (7.9–12.3‰). Carbonates from stage I have δ13CPDB of −1.2 to 2.8‰ and δ18OSMOW of 17.1–24.0‰, similar to those of marine carbonate rocks. Dolomite and calcite from stage II have δ13CPDB ranging from −5.1 to −0.2‰ and δ18OSMOW of 14.1–19.7‰, consistent with dissolution of carbonate rock. In contrast dolomite and calcite from stage III have mantle C-O signatures with the δ13CPDB ranging from −7.5 to 0.4‰ and δ18OSMOW from 5.8 to 13.2‰. C-O isotopic signatures suggest that the original carbonates were dissolved by the acid generated from sulfide precipitation consistent with the sulfide precipitation process. Subsequent precipitation of carbonates created large volumes of dolomite alteration that coated the sulfides and possibly contributed to the preservation of the ore, as dolomite would dissolve more slowly than calcite. Carboniferous magmatism (stage III) resulted in a magmatic overprint on the stage II sulfide. The metal sources of these sulfide ore packets are mainly derived from the Mesoproterozoic carbonate rocks as indicated by the lead isotopes of sulfides and also C-O isotopes of carbonates. The deposit is characterized by a complex paragenesis with multiple overprinting sources of hydrothermal fluids and sulfide over 700 m.y. The syn-sedimentary stage (∼1019 Ma) and main mineralization stage (859–837 Ma) at Caixiashan are chronologically and tectonically associated with the assembly and break-up of the Rodinia supercontinent, whereas the magmatic-hydrothermal modification stage (∼353 Ma) is associated with the closure of the Paleo Asian Ocean during the Early Carboniferous.

Variability of Fe isotope compositions of hydrothermal sulfides and oxidation products at mid-ocean ridges

Abstract Significant Fe isotopic fractionation occurs during the precipitation and oxidative weathering of modern seafloor hydrothermal sulfides, which has an important impact on the cycling of Fe isotopes in the ocean. This study reports the Fe-isotope compositions of whole-rock sulfides and single-mineral pyrite collected from hydrothermal fields at the South Mid-Atlantic Ridge (SMAR) and the East Pacific Rise (EPR) and discusses the impacts of precipitation and late-stage oxidative weathering of sulfide minerals on Fe isotopic fractionation. The results show large variation in the Fe-isotope compositions of the sulfides from the different hydrothermal fields on the mid-oceanic ridges, indicating that relatively significant isotope fractionation occurs during the sulfide precipitation and oxidative weathering processes. The Fe-isotope compositions of the sulfides from the study area at the SMAR vary across a relatively small range, with an average value of 0.01‰. This Fe-isotope composition is similar to the Fe-isotope composition of mid-oceanic ridge basalt, which suggests that Fe was mainly leached from basalt. In contrast, the Fe-isotope composition of the sulfides from the study area at the EPR are significantly enriched in light Fe isotopes (average value − 1.63‰), mainly due to the kinetic fractionation during the rapid precipitation process of hydrothermal sulfide. In addition, the pyrite from different hydrothermal fields is enriched in light Fe isotopes, which is consistent with the phenomenon in which light Fe isotopes are preferentially enriched during the precipitation of pyrite. The red oxides have the heaviest Fe-isotope compositions (up to 0.80‰), indicating that heavy Fe isotopes are preferentially enriched in the oxidation product during the late-stage oxidation process. The data obtained from this study and previous studies show a significant difference between the Fe-isotope compositions of the sulfides from the SMAR and EPR. The relatively heavy Fe isotopes compositions of the sulfides from the SMAR may suggest the equilibrium fractionation process under high temperature conditions. The red Fe oxides are enriched in heavy Fe isotopes, indicating that the oxidative weathering processes result in the occurrence of significant Fe-isotope fractionation and the preferential enrichment of heavy Fe isotopes in the oxidation product.

Separation of Cu from dilute Cu–Ni–Co bearing bioleach solutions using solvent extraction with Chemorex CP-150

ABSTRACTSolvent extraction of Cu from simulated and real bioleaching solutions obtained from a complex Cu–Ni–Co bearing tailing was investigated using Chemorex CP-150 extractant. The effects of several critical parameters, namely pH, contact time, extractant concentration, metal ion concentration, and organic/aqueous phase ratio on Cu extraction were evaluated. Isotherm studies showed that more than 99.9% Cu was transferred with a single stage for each of the extraction and stripping steps. A mixed Ni–Co sulfide was produced from the extraction effluent. A developed flow sheet was proposed to treat Cu–Ni–Co bearing sulfidic tailings by bioleaching, jarosite precipitation, solvent extraction, and sulfide precipitation processes.

Leaching and selective copper recovery from acidic leachates of Três Marias zinc plant (MG, Brazil) metallurgical purification residues

Zinc plant purification residue (ZPR), a typical Zn-hydrometallurgical waste, was collected from the Três Marias Zn plant (MG, Brazil). ZPR was characterized for its metal content and fractionation, mineralogy, toxicity and leachability. Toxicity characteristics leaching procedure (TCLP) and European Community Bureau of Reference (BCR) sequential extraction results revealed that this ZPR displays high percentages of metals (Cd, Cu, Zn and Pb) in the highly mobilizable fractions, increasing its hazardous potential. Bulk chemical analysis, pH dependent leaching and acid (H2SO4) leaching studies confirm that the ZPR is polymetallic, rich in Cd, Cu and Zn. The sulfuric acid concentration (1 M), agitation speed (450 rpm), temperature (40 °C) and pulp density (20 g L−1) were optimized to leach the maximum amount of heavy metals (Cd, Cu and Zn). Under optimum conditions, more than 50%, 70% and 60% of the total Cd, Cu and Zn present in the ZPR can be leached, respectively. The metals in the acid leachates were investigated for metal sulfide precipitation with an emphasis on selective Cu recovery. Metal sulfide precipitation process parameters such as initial pH and Cu to sulfide ratio were optimized as pH 1.5 and 1:0.5 (Cu:sulfide) mass ratio, respectively. Under optimum conditions, more than 95% of Cu can be selectively recovered from the polymetallic ZPR leachates. The Cu precipitates characterization studies reveal that they are approximately 0.1 μm in diameter and mainly consist of Cu and S. XRD analysis showed covellite (CuS), chalcanthite (CuSO4·5H2O) and natrochalcite (NaCu2(SO4)2(OH)·H2O) as the mineral phases. ZPRs can thus be considered as an alternative resource for copper production.

Application of sodium- and biogenic sulfide to the precipitation of nickel in a continuous reactor

Attention has been focused in recent decades upon the precipitation of metal sulfides from acid mine drainage (AMD) and pregnant leach solutions, due to the advantages of the sulfide precipitation process over traditional methods employing hydroxides. The aim of this work was thus to explore technologies for the precipitation of valuable metals, such as nickel using such sulfides (as either Na2S or biogenic sulfide). The recovery of nickel sulfide was improved when the initial pH of the solution containing each metal was set to 7. In such a condition the removal efficiency of nickel was 99.9%, corresponding to a residual level of 0.13mgL−1 for nickel in solution. Kinetic parameters for precipitation were determined from the particle size distributions (produced in an MSMPR reactor) using the method of moments, where the growth and nucleation rates, as well the agglomeration kernel, were calculated. The precipitation of nickel at an initial pH of 7 showed a nucleation rate value of 8.16×1018#m−3s−1, the highest volumetric growth rate (1.03×101μm−3s−1) and agglomeration kernel of 9.71×10−23m3#−1s−1. The biogenic sulfide was a suitable alternative to sodium sulfide for nickel removal. Both sodium sulfide and biogenic sulfide can be utilized to precipitate nickel as millerite (NiS), allowing the effluent compliant with environmental legislation.