Detoxification of E-waste polluted site using cashew nut shell-based activated carbon

Abstract

This study considered the potential use of activated carbon (AC) produced from cashew nuts for remediation of electronic waste (E-waste) polluted soil sites at Agbogbloshie, Accra, Ghana. The AC supplied by Climate-Environmental Research and Technology (CLERET) Laboratory, one of the research and development (R&D) umbrellas of Explore Scientific Innovations Ltd., Ghana. It was prepared by a two-stage process involving wood-fired reactor for thermal pyrolysis at temperature ranging from 800–1000 oC, followed with activation with oxidizing gas generated by wood-fired steam boiler at 160 oC and 7.5 atm pressure for 30 minutes. The product was characterized based on bulk density, particle size, iodine number, electrical conductivity (EC), porosity, and pH. Three replicates of soil samples were scooped from at a depth of 0–15 cm using a soil auger from two randomly selected sites. The samples were digested with 10 ml of ternary solution (20 ml of HClO4; 500 ml of HNO3; 50 ml of H2SO4) on a hot plate at 90°C for 30 minutes to an hour and analyzed for selected heavy metals (Pb, Fe, Cu, Cr and Cd) using Atomic Absorption Spectrophotometer (AAS). The cashew nut shell-based AC significantly removed the heavy metal contents of the E-waste polluted soil with removal efficiency in the order: Cd (100%) > Pb (93%) > Fe (87%) > Cu (87%) > Cr (76%) for granular and Cd (100%) > Pb (98%) > Fe (96%) > Cu (94%) > Cr (87%) for powdered activated carbons. The slopes of the linear graph of the adsorption isotherms of the tested metals which is indicative of the quality of adsorption of the metals were in the order: Pb (0.9754) > Fe (0.9093) > Cr (0.8799) > Cu (0.8176) > Cd (0.7511). These agro-based waste materials therefore have great potential for effective detoxification of E-waste polluted sites.