Biologically produced sulfur as a novel adsorbent to remove Cd from aqueous solutions.

Biological desulfurization processes of landfill gas yield an enormous amount of biologically produced S (BPS) as a byproduct. Capability of BPS to remove Cd from aqueous solutions was tested and its removal efficiency was compared to that of granular activated carbon (GAC). Kinetics of Cd removal by BPS was a two-stage process with an initial rapid adsorption showing 45% of initial Cd was removed within 5 min, followed by a slower adsorption. Cadmium adsorption onto the BPS fitted the Langmuir isotherm model and maximum adsorption capacity of the BPS (63.3 mg g) was 1.8 times higher than that of GAC (36.1 mg g). Thermodynamic parameters showed that Cd adsorption by BPS was favorable and endothermic. Data from XPS proved the main adsorption mechanism to be complexation of Cd with sulfides in the BPS. Results demonstrated that BPS can be recycled as a novel adsorbent for Cd removal from wastewater.