Biosorption of heavy metals from mining influenced water onto chitin products

Abstract

Mining influenced water (MIW) emanating from mine sites poses a major environmental concern due to its impact on water contamination caused by low pH and the presence of high concentrations of toxic metals. Chitorem SC-20® (raw crushed crab shells containing 40% (w/w) CaCO3, 30% protein, 20% chitin, 7% moisture, and 3% ash) and Chitorem SC-80® (the chitin polymer containing 88% chitin and 12% moisture) were used to evaluate heavy metals removal from MIW. It was found that SC-20 was very effective at neutralizing the strong acidity of MIW, even at loads as low as 1g/L the equilibrium pH was neutral. At a load of 2g/L, SC-20 showed a final pH of 7.94 with almost complete (>99.8%) removal of iron (120mg/L), lead (1.1mg/L) and zinc (79mg/L), along with partial removal of cadmium (96% of 1.3mg/L), cobalt (54% of 0.78mg/L), copper (42% of 72mg/L), and manganese (64% of 52mg/L) from MIW. Metal removal was achieved primarily by neutralization and precipitation mainly due to the dissolution of the CaCO3 from the SC-20. SC-80 was used to differentiate the effect of alkalinity and the amount of metal adsorption achievable by the chitin polymer. Lead (up to 1.24mg/g), cadmium (up to 1.81mg/g), and cobalt (up to 0.93mg/g) from single-metal solutions were adsorbed onto the chitin polymer (SC-80). Metal adsorption onto the chitin polymer seemed to have a minor role as a mechanism of metal removal from MIW. Overall, this study demonstrated that crab-shell products can be an important alternative for MIW remediation.