Technical Note

Feasibility of Cyanide Elimination using Plants

S. Trapp*, M. Larsen, A. Pirandello, J. Danquah-Boakye

Environment & Resources DTU Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark

Received 27 May 2002; accepted 15 January 2003


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.

Keywords: Cyanide; elimination; mining; gold; silver; mine effluents; heavy metals; phytotreatment; plants; Sorghum; phytotoxicity

* Corresponding author
   E-mail : stt@er.dtu.dk