Alkaline-reductive pretreatment proposal for the removal of economically burdened semimetals from silver sulfosalts
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abstract
Arsenic contamination in aquifers can occur naturally when an arsenopyrite vein comes into contact with water flow. However, this is not the only mineral species whose arsenic and other semimetals content is environmentally significant. The largest release of these potentially toxic elements into the environment originates from anthropogenic activity. An example of this is the Fresnillo mining district in Zacatecas, Mexico, where silver content is associated with complex mineral species, the semimetal content of which complicates the efficient dissolution of silver and forces the industry to seek extractive alternatives that allow for the concentration and removal of these elements through controlled unit operations that move away from the pyrometallurgical route, where semimetals are released into the environment as gaseous waste. Furthermore, the presence of these semimetals implies an economic loss in the commercialized value of these mining by-products. This study addresses the use of alkaline-reductive solutions as pretreatment stages, where arsenic and antimony can be removed from the complex structure of sulfosalt, resulting in secondary minerals such as acanthite, whose leaching with alternative complexing agents proves to be more efficient. The comparison among the regulating agents of the medium (NaOH, Na2S, and KOH) confirmed the formation of acanthite at high concentrations (3 mol/L) after 12 h of treatment in any of these media. However, the medium regulated by KOH showed the highest dissolution rate of arsenic (92.03 %25) and antimony (63.37 %25), while maintaining the precious metal content in the residual solids selectively. These residues were characterized using SEM-EDS mapping and XRD techniques, and were subsequently subjected to leaching tests with thiosulfate, demonstrating the effectiveness of the KOH medium as a pretreatment stage for the formation of acanthite after the majority concentration of arsenic and antimony in the chemical processing liquors.
