Cost effective biochar gels with super capabilities for heavy metal removal

Abstract

A novel material, the biochar of a konjac-based material (KGMB), was prepared conveniently and economically with chemical activation of hydrothermally synthesized carbon nanospheres. Those carbon nanospheres have small sizes and high surface areas due to the high temperature sintering, which could be used for efficient adsorption of heavy metal ions such as Pb²⁺ and Cd²⁺. Detailed adsorption behaviors of the optimized biochar including adsorption isotherms and adsorption kinetics were investigated. The results indicated that the adsorption process is spontaneous, exothermic and pseudo-second-order chemisorption. When the temperature was 298 K, the KGMB dose was 5 mg, the initial concentration of Pb²⁺ and Cd²⁺ was both 50 mg L⁻¹, the contact time was 24 h and pH of the ion solution was 5.5, the adsorption capacity reached up to 186.56 mg g⁻¹ for Pb²⁺ and 129.67 mg g⁻¹ for Cd²⁺, respectively. What's more, the adsorption capacities of Pb²⁺ and Cd²⁺ were 69.34 and 71.06 mg g⁻¹, respectively, after adsorption–desorption process happened three times. Comparisons of the adsorption capacity of various adsorbents for Pb²⁺ and Cd²⁺, showed that this biochar is superior to many other adsorbents in terms of adsorption capacity and it is a cheap, efficient and accessible biochar. Thus, KGMB is a promising candidate for wastewater treatment.