Metal oxide loaded biochars derived from Chinese bai jiu distillers' grains used for the adsorption and controlled release of phosphate

The resource utilization of distillers' grains (DGs) is an essential issue for the sustainable development of Chinese bai jiu industry. In this study, metal oxide (MxOy, M=Mg, Al and Fe) loaded biochar (MBC) was prepared by using DGs for the production of novel adsorption/release materials for phosphate (P). The results indicated that the P adsorption capacity of Mg-BC, Al-BC and Fe-BC were as high as 14.74, 8.06 and 14.51 mg P/g, respectively. XPS and FTIR analysis demonstrated that the adsorption mechanism of MBC for P included electrostatic attraction, hydrogen bonding, ion exchange, precipitation and ligand exchange. The release of P from M-BC+P could be controlled by low molecular weight organic acids (LMWOAs), which were affected by the loaded metal oxides on the biochar. The release of P from Mg-BC+P was higher than 70 % after 7 days, which was about 60 % if Al-BC+P was used. Thus, M-BC+P can be used as a high-performance controlled release phosphate fertilizer, providing a promising value-added application approach for the bai jiu distillers' grains.