Adsorption characteristics of modified rice straw biochar for Zn and in-situ remediation of Zn contaminated soil

Abstract

Remediation of heavy metal pollution in farmland soil is very important to protect human health and ecological security, and biochar has a certain adsorption and fixation effect on soil heavy metals. In this paper, three kinds of biochar (unmodified biochar, acid modified biochar and biochar from pyrolysis of alkali modified rice straw, abbreviated as RBC, HRBC and KRBC, respectively) were prepared from rice straw, the surface morphology characteristics of RBC, HRBC and KRBC were characterized with SEM scanning, BET specific surface area measurement and porosity measurement and the adsorption characteristics of Zn in/on the three kinds of biochar and the in-situ immobilization effect for the soil Zn were investigated through the laboratory simulation. The results showed that KRBC had larger specific surface area, richer porosity, more oxygen-containing functional groups on the surface, as well as higher aromaticity and carbonization degree than that of RBC and HRBC; the adsorption kinetic characteristics of Zn in RBC, HRBC and KRBC were fitted well with the quasi second-order kinetic model and the adsorption thermodynamic characteristics of Zn in RBC, HRBC and KRBC could be described well with both the models of Langmuir and Freundlich, the maximum adsorption capacity of Zn was the order of KRBC>RBC>HRBC; KRBC had the strongest immobilization ability for Zn in soil, which was related to the strongest ability of KRBC to improve soil pH and soil organic carbon. Therefore, biochar from pyrolysis of alkali modified rice straw (KRBC) was being of the significant immobilization remediation effect on soil Zn pollution. This study can provide theoretical and technical support basis for remediation of Zn contaminated soil. • KRBC had larger specific surface area, richer porosity, more oxygen-containing functional groups on the surface, as well as higher aromaticity and carbonization degree. • KRBC has the largest adsorption capacity for Zn than that of RBC and HRBC. • KRBC had the stronger immobilization ability for Zn in soil, and stronger ability to improve soil pH and soil organic carbon.