Metal adsorption capabilities of clinoptilolite and selected strains of bacteria from mine water

Small-scale mining has socio-economic advantages such as the reduction of unemployment and the general improvement of the economy. However, these operations if not properly managed or controlled have a potential to cause environmental damage, particularly with respect to the contamination of groundwater and water supplies that are not distant from where these mining activities take place. This paper focuses on metal removal from water contaminated by heavy metals emanating from small-scale mining operations using clinoptilolite and bacteria. Removal of As, Ni, Mn, Au, Co, Cu and Fe was carried out on mine water samples using original and HCl-activated (in 0.02 M and 0.04 M) natural clinoptilolite and bacterial strains (a mixed consortia of Bacillus strains (Bacillus subtilis, Bacillus cereus, Bacillus firmus, Bacillus fusiformis, Bacillus macroides and Bacillus licheniformis), Pseudomonas spp., Shewanella spp. and a mixed consortia of Acidithiobcillus caldus, Leptospirillum spp., Ferroplasma spp. and Sulphobacillus spp.). The purpose of the study was to compare the removal efficiencies of the bacterial strains versus natural clinoptilolite adsorbents for metal cations. The Bacillus consortia removed most of the metals up to 98% metal removal efficiency with the exception of nickel where clinoptilolite showed good removal efficiency. The 0.02 M HCl-activated clinoptilolite also demonstrated excellent removal capabilities with Cu, Co and Fe removal efficiency of up to 98%. Both clinoptilolite and bacteria demonstrated capabilities of removing Cu²⁺, Co²⁺, Fe²⁺, Mn²⁺, As³⁺ and Au from solution which augurs well for metal recovery from mining and mineral processing solutions, as well as in water decontamination.