Evaluation of Cd2+, Cu2+, Pb2+, and Zn2+ Removal by Cow Manure and Corn Stover Biochar with the Emphasis on the Solubility-Normalized Dubinin–Radushkevich Approach for the Computation of the Adsorption Potential (ε).

A study on the adsorption capacity and mechanisms on cow manure (CM400-5) and corn stover (CS700-2) biochar to remove typical heavy ions from water has been performed. The Cd2+ , Cu2+ , Pb2+ , and Zn2+ , commonly found in the first flush of the urban/industrial stormwater runoff, were tested under controlled conditions. The obtained experimental data were modeled with the Freundlich, Langmuir, and Harkins–Jura isotherms to describe the adsorption pathways. The novel solubility-normalized Dubinin–Radushkevich (D-R) approach is introduced for the determination of the adsorption mechanisms. The solubility-normalized mode emphasizes the importance of the solubility concentration in calculating the mean free energies of adsorption used to identify removal mechanisms. The proposed model was experimentally validated for the carbon-based (biochar) adsorbers and inorganic (heavy metals) ions. Comparison of obtained results with the commonly used nonnormalized D-R model shows a likely underestimation of the mean free energy values, which could misrepresent the dominant mechanism of adsorption. [ABSTRACT FROM AUTHOR]