Characterisation of a Rehabilitated Tailings Dam Mine Water as a Potential Acid Mine Drainage and Removal of Heavy Metals Using Locally Produced Activated Carbon*

Abstract

Mine waters can be acidic or circumneutral and may often contain concentrations of heavy metals, which are produced from mining base and precious metals. In this work, reddish-brown mine water from an old, rehabilitated tailings storage facility (OTSF) of a mine in Ghana was investigated in terms of physical and chemical characteristics. GARD guide and Hill geochemical classification frameworks (GCF) were also used to ascertain the characteristics of the OTSF mine water in terms of acid mine drainage (AMD). The potential for using locally produced Palm Kernel Shell (PKS) activated carbon for heavy metal adsorption in OTSF mine water was also investigated. The kinetics of the adsorption process were tested using pseudo-first-order (PFO) and second-order (PSO) kinetic models. The results showed that the physicochemical parameters of the OTSF mine water measured were all below the Ghana Standard Authority (GSA) effluent discharge limit for general mining except pH = 5.00-5.40. In terms of heavy metals, except As and Cd, Mn (0.75 > 0.2 mg/L GSA), Fe (25.2 > 10 mg/L GSA), and Pb (0.31 > 0.1 mg/L GSA) were all above GSA effluent discharge limit. The OTSF mine water had low chloride but a high sulphate concentration (395 > 250 mg/L GSA). The drainage, which measured Eh of 460 mV, showed a moderate oxidising environment of OTSF mine water. The GCF revealed that the OTSF mine water is between partially oxidised to low neutralised AMD with potentially less toxic constituents. Locally produced PKS-activated carbon reduced the concentration of As, Pb, Fe, and Mn of the OTSF mine water below the GSA effluent discharge limit. The adsorption kinetics of potential constituents like Fe and Mn fitted well to PFO and PSO, indicating adsorption as diffusion controlled and chemisorption, respectively. This work has demonstrated the potential of using locally produced PKS-activated carbon as an excellent and cost-effective adsorbent for the treatment of heavy metals from the OTSF mine water.