US EPA

1438424 

Journal Article 

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

Enslin, F; van Der Mey, L; Waanders, F 

2010 

Yes 

Journal of South African Institute of Mining and Mineralogy
ISSN: 0038-223X 

110 

4 

187-191 

WOS:000279187700006 

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. 

Acid mine drainage; bentonite; heavy metals