Geochemical behavior and stabilization of spent sulfate-reducing biofilter mixtures for treatment of acid mine drainage.

Sulfate-reducing biofilters operated in semi-passive or passive modes constitute an approach of choice for treatment of acidic mining effluents. The aim of the present study involved examining the behavior of biofilters after use based on two modes of management, namely in unsaturated and saturated media. Two acidophilic biofilters were investigated following their mixing with different alkaline industrial residues (i.e., 25% fly ash biomass or 30% aluminum red mud, or 10% kiln dust). Percolation column tests for a 330-d period indicated that aluminum red mud and lime kiln dust (to a lesser extent) are efficient materials for maintaining the pH neutrality of biofilter leachate and to reduce release of metals (i.e., Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in spent biofilters. The storage of biofilters in saturated mode also makes it possible to preserve the reducing conditions of the environment and neutrality of the pH and to limit the dissolution of the solution of cadmium, nickel and zinc. Conversely, increased iron release is noted under saturated conditions. Finally, the results indicated that a mixture of biofilters and lime kiln dust is preferable to surface addition of these to reduce the loss of metals in leachates.

Toxicity assessment of garden soils in the vicinity of mining areas in Southern Morocco.

The aim of the present work is the assessment of the concentration, toxicity and phytoavailability of heavy metals in garden soils in the vicinity of three mines (A, B and C) in South of Morocco by using concurrently selective chemical extractions, MetPLATE a toxicity bioassay and plant growth experiments. The tailings materials containing very high concentrations of Mn, Cu and Co in mine A, Co, Mn, Cr and Ni in mine B and Cu and Zn in mine C. The high toxicity of tailings from mine C (86.7% inhibition) and moderate toxicity of tailings from mine B (51.0% inhibition) were mainly due to the relative high concentrations of soluble Cu and Zn. Nevertheless, the low metal toxicity observed in most garden soils was confirmed by the low metal concentrations in the soil water extracts. In all garden soils, Lactuca sativa L. and Lolium multiflorum L. contained in their shoots Cd, Co, Cr, Cu and Ni below toxic concentrations while Zn (in all soils) and Mn in two soils from mine A were accumulated at concentrations high enough to be considered phytotoxic. The low biomass produced on garden soils in the vicinity of mines B and C is explained by the relative low toxicity compared to mine A. Transfer factor values for Zn were higher than those found for Mn for both plant species, confirming that this element is present at lower bioavailable fraction in soil than Zn.