The CESL Cu-As Process has achieved greater than 99% deportment of arsenic to leach residues (the by-product of the metallurgical process). Arsenic components in the residue have been identified, with the use of advanced mineralogical methods, as basic ferric arsenate (BFAS) and scorodite – both of which are considered the most stable forms for arsenic fixation. Furthermore, air quality monitoring during pilot operations confirmed concentrations well below the government occupational exposure levels.
Short- and long-term testing was conducted to assess the stability of arsenic in residues that were generated in continuous pilot plant trials. Short-term testing was conducted on 59 pilot samples containing arsenic up to 9.7% using the Environmental Protection Agency’s (EPA) standard hazardous material characterization procedure (Toxicity Characteristic Leaching Procedure, TCLP). The testing consistently demonstrated that the residue was non-hazardous, with leached arsenic more than an order of magnitude below the EPA classification limit.
To confirm long-term stability, a more rigorous testing program was developed. This ongoing test program has demonstrated excellent residue stability, with arsenic concentrations well below the 5 milligrams per litre EPA limit after over 800 days plus of testing.