TOXICITY AND STABILITY OF IRON-ARSENIC ALLOY

Iron-arsenic alloy is a waste-form of a novel gold recovery technology from gold-arsenicbearing concentrates. This study investigates toxicity and solubility of Fe-As alloy in aqueous solutions. Results of the TCLP-like test, to evaluate the potential toxicity of a solid Fe-As alloy, suggest that the alloy is not stable in acidic conditions (pH 2.88), and releases As in concentrations exceeding the TC threshold level by more than four times. Calcium arsenate dust toxicity has been also evaluated for comparison. It was found to release 40 times more As than iron-arsenic alloy. Concentrations of As in the SPLP-like test leachates were well within the regulatory limit, thus demonstrating the relative stability of the Fe-As alloy in normal meteoric waters (pH 5). Long-term leaching tests in the environmentally-relevant pH range of 5 to 9 at 22°С demonstrate that FeAs alloy is very susceptible to acidic pH conditions. Arsenic solubilization was high under acidic conditions (at pH5 and pH6), which suggests that in the long term it can be mobilized within the environment if exposed to meteoric waters, and certainly to acid rain. However, at the neutral and alkaline pH conditions typical of monofills it appears to be stable over the long term.

1. Magalhaes M. Arsenic. An environmental problem limited by solubility / M. Magalhaes // Pure and Applied Chemistry. – 2002. –10. – P. 1843-1850.

2. WHO. Guedelines for drinking-water quality. Second edition. Volume 1: Recommendations. World Health Organization, Geneva, 1998.

3. Seitkan A. Processing double refractory gold-arsenic-bearing concentrates by direct reductive melting / A. Seitkan, S.A.T. Redfern // Minerals Engineering. – 2016. – Vol. 98. – P. 286-302. DOI: https://doi.org/10.1016/j.mineng.2016.08.017.

4. Patent KZ N 2015/0394.1 Method of processing gold arsenic-bearing sulfide concentrates / Seitkan A., Redfern S.A.T., March 2016.

5. Thermal Behavior of Iron Arsenides Under Non-Oxidizing Conditions / А. Seitkan et al // ACS Omega. – 2020. – 5(12). – P. 6423-6428. DOI: 10.1021/acsomega.9b03928.

6. Kozmin Yu.A. Sposob pererabotki mysh’yaksoderzhashchikh materialov (in rus) / Yu.A. Kozmin, N.G. Serba, A.S. Kulenov – IC N1082849, 1984.

7. Mehta A.K. Investigation of new techniques for control of smelter arsenic bearing wastes. EPA-600/S2-81-049. U.S. Environmental Protection Agency, Industrial Environmental Research Laboratory, 1981.

8. Izvlechenie zolota iz upornyh rud kombinirovannym sposobom / N.G. Serba et al // Sbornik nauchnyh trudov VNIITSVETmeta / VNIITSVETmet. – 2000. – P. 285-288.

9. USEPA. Method 1311: Toxicity Characteristic Leaching Procedure, 1992. Available from: http://www.epa.gov/hw-sw846/sw-846-test-method-1311-toxicity-characteristic-leaching-procedure.

10. USEPA. Method 1312: Synthetic Precipitation Leaching Procedure, 1992. Available from: https://www.epa.gov/hw-sw846/sw-846-test-method-1312-synthetic-precipitation-leachingprocedure.

11. Department of the Environment. Arsenic-bearing wastes. Waste Management Paper, (20), 1980.

12. Swash P.M. Synthesis, characterisation and solubility testing of solids in the Ca-Fe-AsO4 system / P.M. Swash, A.J. Monhemius // In Sudbury 95 – Mining and the environment / CANMET. – Ottawa, Canada, 1995. – P.17-28.

13. Leist M. Evaluation of leaching tests for cement-based immobilization of hazardous compounds / M. Leist, R.J. Casey, D. Caridi // Journal of Environmental Engineering Asce. – 2003. – P. 129:637-641.

14. Hopkin W. The problem of arsenic disposal in non-ferrous metals production / W. Hopkin // Environmental Geochemistry and Health. – 1989. – № 3-4. – P. 101-112.

15. USEPA. 40 CFR Part 261. Federal Register, March 29, 1990.

16. Wusaty A. Bakyrchik mining venture. Kyzyl Gold Project. Environmental Feasibility Study / A. Wusaty, D. Douglas // Sustainability Pty Ltd., 2011.

17. Harris G.B. The disposal of arsenical solid residues / G.B. Harris, S. Monette // Productivity and Technology in the Metallurgical Industries / TMS-AIME/GDMB Joint Symposium. Cologne, Germany. –1989. – P. 545-559.

18. Schwertmann U. Iron oxides in the laboratory: Preparation and characterization / U. Schwertmann, R.M. Cornell // Weiheim, New York, Basel and Cambridge, 1991.

19. Emmet M. Environmental stability of As-iron hydroxides / M. Emmet, G. Khoe // Proceeding EPD Congress. – 1994. – P. 153-166.

20. Swash P.M. Hydrothermal precipitation from aqueous solutions containing iron (III), arsenate and sulphate / P.M. Swash, A.J. Monhemius // Hydrometallurgy. – 1994. – 94. – P. 177-190.

21. NEN 7345, 1995. Leaching characteristics of solid earthy and stony building and waste materials.