Phytoremediation of Cyanide-Laden Mine Tailings by Phaseolus Lunatus: A Sustainable Solution for Greenstone Mining Limited, Uganda.

Cyanide contamination from gold mine tailings presents ecological and human health risks, particularly in the artisanal mining and small-scale mining regions in Uganda. This study evaluated the phytoremediation potential of Phaseolus lunatus (lima beans) for cyanide-contaminated tailings from Greenstone Mining Limited. Field-based pedon experiments were conducted at planting densities of 0, 5, 10, and 15 plants/m² over an 84-day growth period. Cyanide concentrations in soils and plant tissues were quantified using titrimetric method. Soil cyanide reduction increased with plant density, reaching maximum values of 42.6 ± 1.8, 54.7 ± 1.4, and 59 ± 0.8%, respectively, compared to 3.4 ± 1.2% in the unplanted control pedon. Cyanide uptake and rate of detoxification were most pronounced during the vegetative stage, coinciding with rapid root development. Cyanide distribution in tissues followed the order of roots > stems > leaves > seeds, indicating dominant in-situ phytodegradation and limited translocation to edible tissues facilitated by the β-cyanoalanine synthase pathway. First-order kinetics best fitted the data (R² = 0.841 - 0.921), with rate constants rising with density and projected time to reach the permissible limit decreasing from 250 to 116 days. These results demonstrate that P. lunatus is an effective, low-cost phytoremediation option for cyanide-contaminated mine tailings in tropical environments.