The adsorption characteristics of Pb²⁺ and Cd²⁺ by straw based biochars generated at medium-high pyrolysis temperatures

This paper is the result of environmental geological survey engineering.

Objective Effect of pyrolysis temperature and raw materials on adsorption of heavy metals by straw-based biochar.

Methods Corn straw and rice straw were used as raw materials to prepare straw based biochars (i.e. S450, S600, Y450, Y600) under anoxic conditions at 450℃ and 600℃. And the differences in their surface characteristics and their adsorption capacity for Pb²⁺ and Cd²⁺ in solutions were studied.

Results The results showed that the pyrolysis temperature had a significant effect on the physicochemical properties of different biochars. With the increase of pyrolysis temperature, the C contents of biochars increased, but N, H, O contents decreased. Besides, their specific surface area, total pore volume and average pore diameter all showed a decreased tendency. As the result of the increase of pyrolysis temperature, the adsorption capacity and rate of Pb²⁺ and Cd²⁺ increased. Meanwhile, the adsorption capacity of Pb²⁺ and Cd²⁺ of corn straw biochar was significantly higher than that of rice straw biochar. The adsorption of Pb²⁺ and Cd²⁺ by the four biochars was dominated by chemical precipitation.

Conclusions The adsorption of Pb²⁺ and Cd²⁺ was mainly multilayer and monolayer adsorption, respectively. Straw based biochars with higher pyrolysis temperature had higher adsorption capacity for Pb²⁺ and Cd²⁺. This study is useful for straw resource utilization and heavy metal pollution remediation.