Effect of modified biochar on the immobilization of Pb2+ and CrO42− in cement-based materials

Abstract

Cement-based solidification/stabilization (S/S) is widely used for the treatment of hazardous waste because it is a low-cost and straightforward process. However, the immobilization efficiency of traditional cement systems for amphoteric and anionic heavy metals is insufficient. Therefore, improving the immobilization ability of cement-based materials for amphoteric and anionic heavy metal pollutants is the key focus of current research. Herein, we innovatively increased the adsorption capacity of anions using quaternary ammonium group-functionalized modified biochar and systematically investigated the adsorption mechanism of modified biochar for Pb²⁺ and CrO₄²⁻ under the alkaline conditions. Modified biochar was further incorporated into the cement matrix to evaluate its immobilization efficiency for Pb²⁺ and CrO₄²⁻ and its effect on the properties of cement-based materials. Results showed that the substitution of quaternized biochar reduced the leaching concentrations of Pb²⁺ and CrO₄²⁻ due to the positive charge of quaternized biochar under strong alkaline conditions, which reduced the electrostatic repulsion between anions and facilitated the adsorption of more heavy metal ions. Furthermore, due to the microfilling, internal curing, and hydration nucleation effects of biochar, biochar substitution improved the compressive strength of cement and the formation of hydration products. This study proposes a new strategy for preparing biochar–cement composite immobilization materials to address the bottleneck in cement-based S/S technology.