Metal Sulfide Precipitation: Recent Breakthroughs and Future Outlooks

The interest in metal sulfide precipitation has recently increased given its capacity to efficiently recover several metals and metalloids from different aqueous sources, including wastewaters and hydrometallurgical solutions. This article reviews recent studies about metal sulfide precipitation, considering that the most relevant review article on the topic was published in 2010. Thus, our review emphasizes and focuses on the overall process and its main unit operations. This study follows the flow diagram definition, discussing the recent progress in the application of this process on different aqueous matrices to recover/remove diverse metals/metalloids from them, in addition to kinetic reaction and reactor types, different sulfide sources, precipitate behavior, improvements in solid–liquid separation, and future perspectives. The features included in this review are: operational conditions in terms of pH and Eh to perform a selective recovery of different metals contained in an aqueous source, the aggregation/colloidal behavior of precipitates, new materials for controlling sulfide release, and novel solid–liquid separation processes based on membrane filtration. It is therefore relevant that the direct production of nanoparticles (Nps) from this method could potentially become a future research approach with important implications on unit operations, which could possibly expand to several applications.

Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator

<p>The timing and degree of immiscible sulfide precipitation in a magma effectively controls the formation of magmatic sulfide deposits and the budget of degassing sulfur species in volcanic systems. Besides the absolute sulfur (S) content, sulfide precipitation is strongly affected by the sulfur content at sulfide saturation (SCSS) in the host silicate melt. Assimilation of S-rich wall-rocks, such as black shales, effectively increases the S content in the magma, while simultaneously lowering the SCSS. Accordingly, assimilation has been identified as the most important process in the formation of many economically significant magmatic base metal sulfide deposit, especially in continental tectonic settings. Detailed understanding of the relation between wall-rock assimilation and sulfide saturation requires accurate thermodynamic models for open magmatic systems experiencing assimilation-fractional crystallization (AFC).</p><p>The Magma Chamber Simulator (MCS) is currently the only geochemical modeling software that considers the thermodynamic phase equilibria in open magmatic systems involving magma and wall-rock (and recharge) subsystems. We utilized the MCS to explore how assimilation affects the SCSS and S content of the magma. With the current lack of thermodynamic data for sulfides, we tentatively modeled S as a trace element and varied its compatibility to wall-rock in the different models. For a case study, we chose the mafic layered intrusions of Duluth Complex, Minnesota, which host some of the largest Cu-Ni sulfide deposits in the world. Assimilation of the adjacent black shale has been established as the main source for S in the deposits.</p><p>Our MCS models show in detail how continuous assimilation of the black shale lowers the SCSS of the melt. Partial melt from the black shale enriches the magma in SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, K<sub>2</sub>O, and H<sub>2</sub>O, while depleting FeO, MgO, CaO, and Na<sub>2</sub>O, which causes a first order decrease in the SCSS. The compositional change also replaces troctolitic cumulates (plagioclase, olivine ± clinopyroxene) with norite (plagioclase and orthopyroxene), which leads to more pronounced FeO depletion in the melt, further lowering the SCSS. On the other hand, the assimilated partial melt also increases the melt mass in the magma subsystem, which counteracts the S enrichment. Accordingly, in the model where S is compatible to the wall-rock residual, the degree of sulfide saturation only slightly increases relative to the same magma experiencing FC without assimilation.</p><p>More than half of the wall-rock S must partition to the assimilated partial melt in order to meet the S isotopic criteria of the modeled Cu-Ni-deposits. The main stage of sulfide precipitation is associated with ~30 wt.% crystallization of the assimilating host magma. The proportion of sulfides relative to silicates in these models is smaller than observed in the Duluth Complex deposits, which underlines the role of dynamic processes in concentrating sulfides from the silicate magma.</p>

Precipitation Reaction Mechanisms of Mineral Deposits Simulated with a Fluid Mixing Model

Nonmagmatic, carbonate-hosted epigenetic hydrothermal Pb–Zn deposits similar to those at the Huize Pb–Zn Mine are widespread across the Sichuan–Yunnan–Guizhou (SYG) polymetallic province. The precipitation mechanisms of these geologically intriguing deposits are an area of interest for many researchers. To simulate the underlying precipitation reaction mechanisms and dynamics of each aspect, a fluid mixing model for metal sulfide precipitation was used in a series of experiments, where solutions that contain Pb/Zn chloride complexes and sulfide were subjected to pH changes, water-rock reactions, and dilutions. Based on the results of these experiments, thermodynamic phase diagrams, and other experimental findings, a fluid mixing genetic model was developed for SYG Pb–Zn deposits, and this model was used to analyze the mechanisms of metal sulfide precipitation. The results indicate that acidic fluids in the form of chloride complexes transported Pb and Zn, whereas sulfide exists in the form of H2S within these fluids. The precipitation of metal sulfides occurs when these fluids undergo changes in pH, water-rock reactions, or isothermal dilution. The pH changes were found to be the most effective method for the induction of sulfide precipitation, followed by dilution and then water-rock reactions. The formation of sulfide precipitates due to pH changes, water-rock reactions, and dilution can be attributed to a single mechanism, i.e., changes in the pH of the fluid. Therefore, changes in pH are the primary mechanism of sulfide precipitation.

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

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.