Lime dosing in a high-density sludge (LD-HDS) process is amongst the most widely applied acid
mine drainage (AMD) treatment processes worldwide. It is effective and reliable, however, an
intrinsic issue for metalliferous mining derived AMD is the formation of an ecotoxic metal(loid)-
bearing (e.g. As, Pb, Ni, Cd and Sb) ochre waste ...
Lime dosing in a high-density sludge (LD-HDS) process is amongst the most widely applied acid
mine drainage (AMD) treatment processes worldwide. It is effective and reliable, however, an
intrinsic issue for metalliferous mining derived AMD is the formation of an ecotoxic metal(loid)-
bearing (e.g. As, Pb, Ni, Cd and Sb) ochre waste product. Herein the efficacy and selectivity of
AMD (pH 3.5; 1-500 g/L), citric and oxalic acid (0.01-1M) for ecotoxic metal(loid) dissolution from
such ochre has been investigated. When AMD is applied at a low solid-liquid ratio (namely 1 g/L)
or citric and oxalic acids are at low concentrations (namely ≤0.1M) such lixiviants are selective for
certain ecotoxic metals which have been designated by BCR 4-step sequential extraction as
“exchangeable” (namely: Sb, Cd, Cu and Ni) in preference to Fe. This suggests that they could
potentially be integrated into the LD-HDS process in order to lower the ecotoxicity of the final ochre
product and thereby valorise it for use in a wide range of commercial applications. Conversely
when AMD is applied at a higher solid-liquid ratio (namely ≥100 g/L) ecotoxic metal precipitation
occurred (due to the alkaline pH of the ochre). This suggests that the ochre could also be reused
for AMD remediation.