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

Selective separation of metals from wastewater using sulfide precipitation: A critical review in agents, operational factors and particle aggregation

Extensive research has been conducted on the separation and recovery of heavy metals from wastewater through the targeted precipitation of metal sulfides. It is necessary to integrate various factors to establish the internal correlation between sulfide precipitation and selective separation. This study provides a comprehensive review of the selective precipitation of metal sulfides, considering sulfur source types, operating factors, and particle aggregation. The controllable release of H2S from insoluble metal sulfides has garnered research interest due to its potential for development. The pH value and sulfide ion supersaturation are identified as key operational factors influencing selectivity precipitation. Effective adjustment of sulfide concentration and feeding rate can reduce local supersaturation and improve separation accuracy. The particle surface potential and hydrophilic/hydrophobic properties are crucial factors affecting particle aggregation, and methods to enhance particle settling and filtration performance are summarized. The regulation of pH and sulfur ion saturation also controls the zeta potential and hydrophilic/hydrophobic properties on the particles surface, thereby affecting particle aggregation. Insoluble sulfides can decrease sulfur ion supersaturation and improve separation accuracy, but they can also promote particle nucleation and growth by acting as growth platforms and reducing energy barriers. The combined influence of sulfur source and regulation factors is vital for achieving precise separation of metal ions and particle aggregation. Finally, suggestions and prospects are proposed for the development of agents, kinetic optimization, and product utilization to promote the industrial application of selective precipitation of metal sulfides in a better, safer, and more efficient way.

Chemical Treatment of Highly Toxic Acid Mine Drainage at A Gold Mining Site in Southwestern Siberia, Russia

The critical environmental situation in the region of southwestern Siberia (Komsomolsk settlement, Kemerovo region) is the result of the intentional displacement of mine tailings with high sulfide concentrations. During storage, ponds of acidic water with incredibly high arsenic (up to 4 g/L) and metals formed on the tailings. The application of chemical methods to treat these extremely toxic waters is implemented: milk of lime Ca(OH)2, sodium sulfide Na2S, and sodium hydroxide NaOH. Field experiments were carried out by sequential adding pre-weighed reagents to the solutions with control of the physicochemical parameters and element concentrations for each solution/reagent ratio. In the experiment with Ca(OH)2, the pH increased to neutral values most slowly, which is contrary to the results from the experiment with NaOH. When neutralizing solutions with NaOH, arsenic-containing phases are formed most actively, arsenate chalcophyllite Cu18Al2(AsO4)4(SO4)3(OH)24·36H2O, a hydrated iron arsenate scorodite, kaatialaite FeAs3O9·8H2O and Mg(H2AsO4)2. A common specificity of the neutralization processes is the rapid precipitation of Fe hydroxides and gypsum, then the reverse release of pollutants under alkaline conditions. The chemistry of the processes is described using thermodynamic modeling. The main species of arsenic in the solutions are iron-arsenate complexes; at the end of the experiments with Ca(OH)2, Na2S, and NaOH, the main species of arsenic is CaAsO4−, the most toxic acid H3AsO3 and AsO43−, respectively. It is recommended that full-scale experiments should use NaOH in the first stages and then Ca(OH)2 for the subsequent neutralization.

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.

Recent trends in removal and recovery of heavy metals from wastewater by electrochemical technologies

Heavy metal-laden water and wastewater pose a threat to biodiversity, including human health. Contaminated wastewater can be treated with several separation and purification methods. Among them, electrochemical treatment is a notable clean technology, versatile and environmentally compatible for the removal and recovery of inorganic pollutants from water and wastewater. Electrochemical technology provides solution for the recovery of metals in their most valuable state. This paper analyses the most recent electrochemical approaches for the removal and recovery of metal ions. Various current works involving cell design and electrode development were addressed in distinguished electrochemical processes, namely, electrodeposition, electrocoagulation, electroflotation, and electrosorption. Cathodic reduction of metal ions has been proven in result to metal deposit on the metal, metal oxide, stainless steel, and graphite electrode. However, little progress has been made toward electrode modification, particularly the cathode for the purpose of cathodic reduction and deposition. Meanwhile, emerging advanced materials, such as ionic liquids, have been presented to be prominent to the technological advancement of electrode modifications. It has been projected that by integrating different priorities into the design approach for electrochemical reactors and recent electrode developments, several insights can be obtained that will contribute toward the enhancement of the electrochemical process performance for the effective removal and recovery of heavy metals from water and wastewater in the near future.