JOURNAL PAPERS

 

Acid leaching of heavy metals from bentonite clay, used in the cleaning of acid mine drainage

 

 

F. Enslin; L. van der Mey; F. Waanders

School of Chemical and Minerals Engineering, North-West University, Potchefstroom, South Africa

 

 

---

SYNOPSIS

Heavy metals and sulphates in acid mine drainage (AMD) can be adsorbed onto bentonite clay, leaving clean water and a heavy metal loaded clay precipitate as products. Due to the toxicity of heavy metals, the clay could not be disposed of safely in the past. A method was thus required to remove the heavy metal content from the clay. Acid leaching was proposed to liberate the heavy metals from the loaded clay. Sulphuric, nitric and hydrochloric acid were considered as lixiviants. Loaded clay samples were leached over a range of pH values from 1 to 3.5 to identify an optimum leaching condition. From the results it was found that metals can be recovered from loaded bentonite clay by means of acid leaching and the optimum pH for heavy metal liberation was found to be 2.5, with uranium as an exception, being optimally leached at a pH of 3. This allows for the possibility of selective leaching. Furthermore, X-ray diffraction analyses indicated that the clay structure did not deteriorate significantly during acid leaching, suggesting that the bentonite could be reused. The treatment of AMD with bentonite clay, and subsequent acid leaching of the clay, is a sustainable solution, and current outcomes could possibly lead to industrial implementation of the process during water purifying and metal recovery from waste streams.

Keywords: Acid mine drainage, bentonite, heavy metals

---

 

 

“Full text available only in PDF format”

 

 

References

Agnello, V. N. Bentonite, pyrophyllite and talc in the Republic of South Africa. Department of Minerals and Energy. Directorate: Mineral Economics, Pretoria. 2005.         [ Links ]

Brink, M.C. Purification of water. Patent applied for. No. 2008/06195. Registered on 2008/07/16. 2007.         [ Links ]

Brink, M.C., Waanders, F.B., and Erasmus, C. 2008. The elimination of toxic heavy metals from acid mine drainage (AMD). Unpublished. Sent to Mine Water and the Environment in 2009.         [ Links ]

Burgess, J.E. and Stuetz, R.M. Activated sludge for the treatment of sulphur-rich waste waters. Minerals Engineering, vol. 15, 2002. pp. 839-846.         [ Links ]

Oelofse, S. Emerging issues report: Mine water pollution. Department of Environmental Affairs and Tourism. Directorate: Information management. 2008.         [ Links ]

Rameback, H., Albinsson, Y., Skálberg, M., Eklund, U.B., Kjellberg, L., and Werme, L. 1999. Transport and leaching of technetium and uranium from spent U0₂ fuels in compacted bentonite clay. Journal of Nuclear Materials, vol. 227. 1999. pp. 208-214.         [ Links ]

Waanders, F.B. Environmental Management Programme Report for Proposed clay quarry prospects on the farm Mara 'A' 854, Kroonstad District, Free State Province. For: Tradeworx 25 (Pty) Ltd. Potchefstroom. 2003.         [ Links ]

Waanders, F.B., Brink, M.C., and Dreyer, C.J.B. A viable solution to the problem of the elimination of acidic mining effluents. Unpublished. For: Clear Water Effluent and Pollution Control. Randburg. 2008.         [ Links ]

 

 

Paper written on project work carried out in partial fulfilment of B.Eng. (Chem. Eng.)