Rice Straw-Derived Biochar Properties and Functions as Cu（II） and Cyromazine Sorbents as Influenced by Pyrolysis Temperature

In this study, biochars from rice straw （Oryza sativa L.） were prepared at 200-600 ℃ by oxygen-limited pyrolysis to investigate the changes in properties of rice straw biochars produced at different temperatures, and to examine the adsorption capacities of the biochars for a heavy metal, copper（II） （Cu（II））, and an organic insecticide of cyromazine, as well as to further reveal the adsorption mechanisms. The results obtained with batch experiments showed that the amount of Cu（II） adsorbed varied with the pyrolysis temperatures of rice straw biochar. The biochar produced at 400 ~C had the largest adsorption capacity for Cu（II） （0.37 mol kg-1） among the biochars, with the non-electrostatic adsorption as the main adsorption mechanism. The highest adsorption capacity for cyromazine （156.42 g kg-1） was found in the rice straw biochar produced at 600 ℃, and cyromazine adsorption was exclusively predominated by surface adsorption. An obvious competitive adsorption was found between 5 mmol L-1 Cu（II） and 2 g L-1 cyromazine when they were in the binary solute system. Biochar may be used to remediate heavy metal- and organic insecticide-contaminated water, while the pyrolysis temperature of feedstocks for producing biochar should be considered for the restoration of multi-contamination.