The contrasting role of minerals in biochars in bisphenol A and sulfamethoxazole sorption.

Biochars are one of carbon-rich substances that have attracted enormous attention because of its values in energy storage, carbon sequestration, and environment remediation. Apart from the carbon structure, biochars also contain inherent mineral component and polar functional groups. However, the importance of the inherent minerals to the stability of biochars as well as the sorption of organic compounds remains unclear. In this work, the demineralized treatment by the hydrofluoric acid was employed to remove the inorganic minerals from biochars produced at 300 and 500 °C. The inorganic minerals in biochars were identified and quantified by XRD, XPS and SEM-EDS techniques. Approximately 75% of biochar minerals belonged to the Si- and Al-containing minerals, which connected with carbon skeletons. The impact of these minerals to bisphenol A (BPA) and sulfamethoxazole (SMX) sorption was investigated. The mineral removal decreased BPA sorption but increased SMX sorption. Moreover, the relative contributions of surface adsorption and partition processes were quantified for both compounds through isotherm modeling. The BPA sorption was regulated by the joint effect of adsorption and partition, while more than 82% of the SMX sorption was dominated by the partition process. Such understanding of biochar minerals and carbon structure to the migration of organic contaminants will benefit biochar production and application.