Pit-lake remediation by chemically activated Chlorocardium rodiei: Simultaneous metal ion removal from acidic waters

Abstract

The current study investigates the valorization of waste wood from a tropical hardwood found in Guyana (Greenheart – Chlorocardium rodiei) to high surface area activated carbons (AC). We subsequently deployed these adsorbents to sequester Mn 2+, Fe3+, and Al3+ from the acidic waters of a recreational bauxite pit-lake. We studied the impact of activation parameters such as temperature, impregnation ratio and acid concentration on the texture and surface chemistry of ACs and demonstrate that optimized low pH at point-of-zero charge (pHpzc) ACs are efficient adsorbents for the target ions. A mesoporous AC with specific surface area of 2208 m2/g, 11 % surface oxygen and pHpzc of 1.98 was produced under optimized conditions. ACs removed 93–100 % of target ions from pit-lake waters at a native pH of 3.1. Al3+ exerted an antagonistic effect on Mn2+ adsorption in synthetic binary ion systems reducing adsorption by as much as 56 %. The Sips Model fitted the adsorption data best predicting maximum adsorption capacities for Mn2+, Fe3+ and Al3+ of 17.8 mg/g, 23.7 mg/g, and 6.12 mg/g for these low pHpzc optimized materials. These materials show great promise in removing heavy metals from acidic waters.