Type-wide biochars loaded with Mg/Al layered double hydroxide as adsorbent for phosphate and mixed heavy metal ions in water
Wei-Hao Huang, Ying-Ju Chang, Rome-Ming Wu, Jo‐Shu Chang, Xiang-Ying Chuang, Duu‐Jong Lee
Abstract
This study discussed the adsorption of mixed heavy metal ions (Cu 2+ , Co 2+ , Pb 2+ ) and phosphate ions by ten pristine biochars and those with precipitated Mg/Al layered double hydroxide (LDH). The pristine biochars have adsorption capacities of 6.9–13.4 mg/g for Cu 2+ , 1.1−9.7 mg/g for Co 2+ , 7.8−20.7 mg/g for Pb 2+ , and 0.8−4.9 mg/g for PO 4 3− . The LDH-biochars have markedly increased adsorption capacities of 20.4–25.8 mg/g for Cu 2+ , 8.6−15.0 mg/g for Co 2+ , 26.5−40.4 mg/g for Pb 2+ with mixed metal ions, and 13.0−21.8 mg/g for PO 4 3− . Part of the Mg ions but Al ions are released from the LDH-biochars during adsorption, counting less than 7.2% of the adsorbed ions. The pristine biochars have specific adsorption sites for Cu 2+ and Co 2+ , separate Pb 2+ sites related to ether groups on biochar, and areal-dependent sites for PO 4 3− . There is no universal adsorption mechanism corresponding to mixed metal ion adsorption for individual pristine biochar involving different contributions of C–O–C, C–O–H, and C O groups and graphitic-N, pyrrolic-N, and pyridine-N groups. The LDH complexes with hydroxyl and carbonyl groups of biochar, and the LDH interacts with biochar's ether groups, which contributes to metal adsorption, against the conception that the biochar is merely a carrier of LDH as adsorbents.