Interaction of H2O with (CuS)n, (Cu2S)n, and (ZnS)n small clusters (n = 1-4, 6): relation to the aggregation characteristics of metal sulfides at aqueous solutions

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.

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.

Determination of Size Distribution of Precipitation Aggregates Using Non-Invasive Microscopy and Semiautomated Image Processing and Analysis

Particle size distribution (PSD) determination is a typical practice for the characterization of the slurries generated in a precipitation plant. Furthermore, the precipitates generated in these processes form colloidal or aggregated suspensions. Nevertheless, the conventional methods used to estimate PSD (e.g., laser diffraction and/or a cyclosizer) have not been designed to measure particles that tend to aggregate or disaggregate, since they include external forces (e.g., centrifugal, agitation, pumping and sonication). These forces affect the true size of the aggregates formed in a unit operation, thereby losing representativeness in terms of aggregates particle size. This study presents an alternative method of measuring the size distribution of particles with aggregation behavior, particularly, by using non-invasive microscopy and image processing and analysis. The samples used were obtained from an experimental precipitation process by applying sulfidization to treat the cyanide-copper complexes contained in a cyanidation solution. This method has been validated with statistical tools and compared with a conventional analysis based on laser diffraction (Mastersizer). The PSD results obtained with optical microscopy show a bi-modal behavior of the precipitates. However this behavior could be not determined when using the laser diffraction technique. The PSD obtained for the sample tested by microscopy had a mean of 119.7 μm, a median of 147 μm and a 90% distribution reached a particle size of 312.5 μm. These values differ with those obtained by the laser diffraction technique. Our results show significant differences between the methods analyzed, demonstrating that the image processing and analysis obtained by optical microscopy is an excellent and non-invasive alternative to obtain size distributions of aggregates in precipitation processes.