15 / 2021-06-22 23:53:49

Adsorption properties and mechanism of Pb(II) by acid modified ceramsite

Municipal sludge,phosphogypsum,modified ceramsite,adsorption,heavy metal

Municipal sewage sludge, phosphogypsum and red mud are typical solid waste of wastewater treatment, phosphoric acid and aluminum production industry. A ceramsite was prepared by sludge, phosphogypsum and red mud with the mass ratio of 5:3:2. And it was sintered at 950℃ for 25min before modifying by a series of hydrochloric acid, nitric acid and citric acid. Pb(II) solution was used as adsorption object of modified ceramsite. And the adsorption mechanism of Pb(II) on ceramsite was analyzed by Boehm titration, pH_pzc, FTIR and specific surface area data. The results show that maximum adsorption rates were observed on ceramsite modified with hydrochloric acid and nitric acid at concentration of 1mol/L, which were 90.38% and 88.57% respectively. For citric acid modified ceramsite, the best adsorption rate was 57.85% at acid concentration of 0.5mol/L, which was lower than that of unmodified ceramsite (66.86%). The pH_pzc value of modified ceramsites were significantly lower than unmodified ones. When pH was lower than pH_pzc, modified ceramsite could overcome the electrostatic repulsion to adsorb Pb(II) at pH of 5. FTIR and BET analysis showed that -OH, C-O and other groups involved in the adsorption. The modified ceramsites had large specific surface area and developed pores, which was conducive to the adsorption. Compared with unmodified ceramsite, acidic groups of ceramsite modified by hydrochloric acid, nitric acid and citric acid increased by 72%, 75% and 69%, respectively. Acidic groups of all ceramsites decreased after Pb(II) adsorption, especially carboxyl and hydroxyl groups. It indicated that carboxyl and hydroxyl groups were the main participant in the adsorption of Pb(II).