Comparative study of simple and modified rice husk biochar for cadmium removal: adsorption performance and possible mechanisms

In the present study, the simple and chemically modified forms of biochar (KMnO4 and HNO3; 0.01 M) obtained from rice husks were used to study the possible mechanism behind the process of cadmium (Cd) adsorption from the synthetic solution having Cd2+ ranged from 10 to 50 ppm. At 50 ppm, the maximum adsorption has been observed and it showed 93% removal by the KMnO4 modification and 86% by HNO3 modification, whereas simple biochar led to 82% removal only. The adsorption pattern follows the Langmuir and pseudo-second-order model. With characterization techniques, it has been confirmed that the KMnO4-modified forms of biochar showed more adsorption capacity than HNO3-modified and simple biochar. Furthermore, to check its practical applicability, the modified forms of biochar have been applied to the wastewater collected from Banaras locomotive works, Bhagwanpur, and Lohta sites of Varanasi city, UP, India. Again, the maximum adsorption of Cd2+ has been observed with KMnO4 modification (92–95%) at all the sites. This result also confirmed that KMnO4 was the best modifying agent over HNO3. Therefore, its application could be promoted in metal-contaminated water and soil to decrease the availability of toxic metals.