Characterisation of a Rehabilitated Tailings Storage Facility Drainage for Potential Acid Mine Drainage and Removal of Heavy Metals Using Locally Produced Activated Carbon

Abstract

Acid mine waters often contain concentrations of heavy metals, which are produced from mining base and precious metals. In this work, reddish-brown mine drainage 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 drainage in terms of acid mine drainage (AMD). The potential for using locally produced palm kernel shells activated carbon for heavy metal adsorption in OTSF drainage 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 drainage measured were all below the Ghana Standard Authority Effluent Discharge Limit (GSAEDL) for general mining except (pH = 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 GSAEDL. The OTSF drainage had low chloride but high sulphate concentration (390 > 250 mg/L GSAEDL). The drainage measured Eh of 460 mV showed a moderate oxidising environment of OTSF drainage. The GCF revealed that the OTSF drainage is between partially oxidised to low neutralised to warrant any serious AMD characteristics. Locally produced Palm-Kernel Shell (PKS) activated carbon reduced the concentration of As, Pb, Fe, and Mn of the OTSF drainage below the GSAEDL limit. The adsorption kinetics of Fe and Mn fitted well to PFO and PSO indicating adsorption as diffusion control 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 removal of heavy metals from the OTSF drainage.