Background, Aim and Scope:
Acid mine drainage (AMD) is due to the exposure of sulfides to the atmospheric water and oxygen. In addition to AMD, oxidation of arsenopyrite and other As bearing sulfides can release arsenic (As) in the environment. In view of the risks to living organisms due to contamination of ground and surface water sources with As, this work was performed in order evaluate the effectiveness of lime (CaCO3) to control the dispersion of this metalloid in the environment.
Materials and Methods:
Partially oxidized samples of sulfide bearing materials from gold mines in Brazil were used to evaluate the arsenic mobilization by leaching tests. Columns containing ground samples, with and without liming treatments, were leached with distilled water every two weeks over a 156-day period.
Results:
The acid-base accounting (ABA) static tests classified the samples as potential acid forming materials. In the treatments without liming, As, Fe and S concentrations in the leachates were higher than in treatments with carbonate. Nevertheless, the effectiveness of liming to decrease As mobilization was less in the sample containing goethite.
Discussion:
High correlation between Fe and As concentrations in the leachates (r=0,749) suggests that iron (hydr)oxides are retaining arsenic in the solid phase. Oxidation rates of As bearing sulfides were increased at low pH, probably due to the enhanced activity of bacteria (Acidithiobacillus) and decreased rate of Fe precipitation, thus reinforcing generation of acid water, and consequently releasing As.
Conclusions:
Our results corroborate the use of carbonates to control the dispersion of As in acid mine drainage affected environments. However the effectiveness of the liming treatment seems to be dependent on the presence of iron (hydr)oxides in the sample.
Recommendations and
Perspectives:
These findings can be useful to remediate areas affected by acid mine drainage and arsenic mobilization in partially oxidized sulfide materials
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