Biosorption of manganese onto chitin and associated proteins during the treatment of mine impacted water

The manganese removal capacity of two purities of crab-shell chitin was evaluated under different pH conditions by means of kinetic tests and sorption isotherms. Demineralized (DM-SC20) and demineralized/deproteinized (DMP-SC20) crab-shell chitin were tested and compared to evaluate the contribution of chitin and its associated proteins to biosorption. The kinetics of manganese adsorption onto both types of solids was well described by the pseudo-second order model. The adsorption rates depended on the pH of system and the type of solid, with faster changes occurring under alkaline conditions and with DMP-SC20 (k2 = 0.411–0.535 g/mg min) than with DM-SC20 (k2 = 0.125–0.197 g/mg min). The adsorption equilibrium isotherms were best fit by the Langmuir, rather than Freundlich, model. The maximum sorption capacity (qm, mg/g) was found to depend greatly on the pH of the solution, with minimal or no sorption observed at pH <5. At higher pH regimes, qm values ranged from 0.165 (at pH 5.4) to 0.981 (at pH 8.7) for “pure” chitin (DMP-SC20) and increased from 0.878 (at pH 5.2) to 5.437 (at pH 8.6) when both chitin and protein were present (DM-SC20). Results clearly suggest that the chitin-associated proteins offer additional sorption sites for manganese.