Sorption of cadmium by rice husk char, bamboo char, and coconut shell char in aqueous solutions

Abstract

Cadmium (Cd) is a byproduct of zinc production. It has a high solubility, mobility and biological accumulation leading to a risk of bone and kidney damage after long-term exposure. Sorption is an effective method to treat Cd-contaminated water. As a great potential contaminant sorbent, biochar can be produced from rice husk, coconut shell and bamboo under their respective optimum conditions for the sorption of toxic metal ions were used as representatives. Sorption models of kinetics and isotherms were used to fit the experimental results. Pseudo-first-order models fitted the data better than pseudo-second-order for all types of biochar. The Cd 2+ sorption capacity of coconut shell char and bamboo char was higher than rice husk char (7.3723 mg/g ≈ 7.3835 mg/g > 5.0345 mg/g). Freundlich model fitted the results of coconut shell biochar and bamboo biochar better than Langmuir model, which indicate a strong bond for Cd 2+ sorption. In contrast, for rice husk biochar Langmuir model fitted the results better than Freundlich model indicating monolayer sorption mechanism dominated the sorption.