Understanding and enhancing the stability of arsenic by-product from sulphidization process for arsenic removal in metallurgical waste streams

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Pyrometallurgical processes, such as roasting, smelting and converting, are a major part of metal extraction from sulfide ores. Off-gases from these processes contain high quantities of toxic gases such as sulphur dioxide and heavy metals. Flue gas desulphurization is a necessary step in which sulphur dioxide is converted to sulphuric acid as the product in the sulphuric acid plant. Meanwhile, a weakly acidic waste stream loaded with metals and contaminants scrubbed from the off-gases is generated as the waste by-product. Of particular importance among these contaminants is arsenic (As) from processing of arsenic-bearing ores, with arsenic concentrations typically on the order of g/L. This is a very large quantity of arsenic and far exceeds the global demand for the element. Therefore, acid plant effluent treatment is primarily a matter of waste management where two crucial factors should be considered: mass to volume ratio and stability of the waste by-product. To address the arsenic management challenge, a sulphidization process is proposed that generates the least volume of arsenical waste by-product compared to existing alternatives. This process removes arsenic by precipitating it in the form of arsenic trisulphide with arsenic content as high as 60%. However, the stability of arsenic trisulphide is a concern because the release and mobilization of arsenic from this waste by-product poses environmental risks to the surrounding waters and soil. The objective of this research is to examine the stability of arsenic trisulphide under a variety of conditions specifically those relevant to safe storage in the field. This information will assist in developing the sulphidization process to manage arsenic-bearing metallurgical waste streams.**