Selenium recovery by sulfuric acid leaching
Selenium is a trace element that is essential for normal physiological functioning of all living organisms, but an excessive intake of Selenium can be hazardous to human health. As such, the safe recovery and management of Selenium from various sources is of great importance. Currently, Selenium is mainly recovered by hydrometallurgical processes, such as leaching with sulfuric acid. This process is often used for the recovery of Selenium from ore deposits, contaminated soils and wastewaters.
The sulfuric acid leaching process of Selenium is carried out by first crushing, grinding and sieving the sample material to a certain particle size. This allows for increased surface area and a more efficient leaching. The sample material is then mixed with sulfuric acid and heated in a reactor, typically at temperatures of 80–95 °C. The sulfuric acid solution leachable Selenium into the solution, which contains both free and dissolved Selenium. This solution is then neutralized and the resulting slurry is separated into a solid and liquid phase.
The liquid phase is then further processed by precipitation, filtration and other methods. For example, Selenium can be removed from the solution by precipitation with sulfide reagents, such as ammonium sulfide, sodium sulfide and ferric sulfide in order to form insoluble Selenium sulfide. The resulting precipitate is filtered off and the filtrate is treated to remove residual sulfide reagents.
The solid residue from the liquid-solid separation can also be further processed. It is possible to extract additional Selenium from the solid residue by treating it with sodium sulfide. The extracted Selenium is then precipitated as Selenium sulfide and subsequently separated by filtration.
The recovered Selenium can be further processed in order to obtain high purity Selenium products. This can involve purification steps such as acid washing, precipitation and crystallization. The precipitated Selenium sulfide is then calcined to form Selenium dioxide and filtered prior to crystallization. The crystals are then separated and washed before being vacuum dried and packaged.
In conclusion, sulfuric acid leaching is an effective method for the recovery of Selenium from ores, soils and wastewaters. It is a relatively simple and cost-effective process with the potential for recovering significant amounts of Selenium. Furthermore, further purification steps can be employed in order to produce a high purity Selenium product for specific applications.
