Characteristics and mechanism of Ni2+ and Cd2+ adsorption by recovered perlite from agar extraction residue

Abstract

Ni2+ and Cd2+ in wastewater accumulated through the ecological chain and could jeopardize human health. Adsorption of Ni2+ and Cd2+ from wastewater using recovered perlite was an important way to solve the problem of resource utilization of solid waste from agar production. Our previous study confirmed that recovered perlite from agar extraction residue had better pore size and specific surface area than commercial perlite. However, the adsorption efficiency and adsorption mechanism of recovered perlite were the main factors limiting its adsorption application. The adsorption process of Ni2+ and Cd2+ by recovered perlite in aqueous solution was described by the pseudo-second-order kinetic equation, and the relevant adsorption mechanism was mainly chemisorption. Compared with commercial perlite, the adsorption removal rate of Ni2+ and Cd2+ by enzymatic recovered perlite could reach 92.9% and 89.2%, respectively, and were improved by 12.63% and 13.03%. Langmuir isothermal adsorption model could better describe isothermal adsorption process of recovered perlite on heavy metal Ni2+ and Cd2+, and the relevant adsorption mechanism was mainly monolayer adsorption. The XPS results indicated that the decrease of Si-O Si2+ hydroxyl coordination bond and the increase of C-Si bond might make the binding effect of recovered perlite with heavy metals stronger. The competitive adsorption of Ni2+ and Cd2+ by recovered perlite was still dominated by chemisorption and monolayer adsorption. This study was expected to provide theoretical basis and technical support for the removal of Ni2+ and Cd2+ from wastewater using recovered perlite from seaweed residue.