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Technical
Note Feasibility of Cyanide Elimination using
Plants Cyanide
is the reagent of choice for gold and silver extraction, but also a toxic chemical that
may cause severe environmental pollution problems. Vascular plants possess an enzyme
system that detoxifies cyanide by converting it to the amino acid asparagine. The
phytotoxicity of cyanide is indirectly connected to the efficiency of this enzyme system:
Plants only survive cyanide exposure up to a dosage they can metabolize. Cyanide
phyto-toxicity was measured for the subtropical grass Sorghum bicolor. Potassium
cyanide was not toxic when added to the irrigation water at up to 125 mg KCN/L (50 mg
CN/L). In a degradation test, cyanide was efficiently degraded by sorghum roots and
leaves. Cyanide elimination using plants seems to be a feasible option for gold and silver
mine waste and wastewater. Theoretical estimates indicate that a large area of land is
needed. But the process is cost effective, sustainable, and has less critical emissions
than any competing technology. Until now, phytotreatment of gold mining wastewater has
only been tested on a lab scale. With the current knowledge, a pilot-scale demonstration
could be implemented immediately. |
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