Kinetic and thermodynamic analysis of adsorption of arsenic (III) with waste crab shells

Recently, pollution incidents in surface water occurred frequently all over the world, which normally caused the surface water to have lower concentrations of heavy metals. A low cost waste crab shell (WCS) has been studied for the removal of arsenic from the contaminated surface water. The adsorption kinetics of WCS for low concentration (<1 mg/L) of arsenic (III) in a controlled batch system was studied. The effects of initial arsenic (III) concentrations, temperature, pH, and WCS biomass dose on the adsorption were investigated. Under the conditions set in this research, the maximum adsorption capacity for arsenic (III) was 165.78 mg/kg at 0.928 mg/L of initial arsenic (III) concentrations, pH 7.0, 40 °C, and 2.0 g/L of WCS biomass. The kinetics fitted the pseudo-second-order model better than models, such as pseudo-first-order model, Elovich kinetic model, and intra-particle diffusion model, etc. An examination of thermodynamic parameters showed that the adsorption of arsenic (III) with WCS was non-spontaneous and endothermic, as well as a physical process. The results suggested that WCS adsorption may be a useful option for arsenic removal from slightly arsenic-contaminated surface water.