The immobilisation and retention of soluble arsenic, cadmium and zinc by biochar

Water-soluble inorganic pollutants may constitute an environmental toxicity problem if their movement through soils and potential transfer to plants or groundwater is not arrested. The capability of biochar to immobilise and retain arsenic (As), cadmium (Cd) and zinc (Zn) from a multi-element contaminated sediment-derived soil was explored by a column leaching experiment and scanning electron microanalysis (SEM/EDX). Sorption of Cd and Zn to biochar’s surfaces assisted a 300 and 45-fold reduction in their leachate concentrations, respectively. Retention of both metals was not affected by considerable leaching of water-soluble carbon from biochar, and could not be reversed following subsequent leaching of the sorbant biochar with water at pH 5.5. Weakly water-soluble As was also retained on biochar’s surface but leachate concentrations did not duly decline. It is concluded that biochar can rapidly reduce the mobility of selected contaminants in this polluted soil system, with especially encouraging results for Cd. ► The capability of biochar to immobilise and retain arsenic (As), cadmium (Cd) and zinc (Zn) from a multi-element contaminated sediment-derived soil was explored by a column leaching experiment and scanning electron microanalysis (SEM/EDX). We highlight the following results from this study: ► Large surface area and surface sorption of Cd and Zn to biochar reduces the concentrations of these metals in leachates from a contaminated soil 300 and 45-fold respectively. ► Metal retention was not reversible by continued leaching of the sorbant biochar. ► Biochar increased leachate pH and water-soluble carbon but this did not appear to be detrimental to its effects and may aid retention of Cd. ► Although some arsenic was sorbed to biochar, leachate concentrations were not duly reduced. ► Developments in micro-analyses techniques will allow more detailed exploration of the encouraging results seen here with regards to interior surfaces of biochar’s vast porous structure. Biochar retains readily soluble cadmium and zinc from a contaminated soil, significantly reducing their potential mobility, but has limited effects on arsenic.