Study on the mechanism of removing fluoride from wastewater by oxalic acid modified aluminum ash-carbon slag-carbon black doped composite

In this study, SAA@CS-CB(aluminum-ash carbide slag carbon black doped composite) was prepared by sintering method and modified by impregnation with oxalic acid to obtain SAA@CS-CB_oa. Fluoride adsorption experiments were carried out using this composite as adsorbent. With increasing pH values, the adsorption amount of fluoride decreases in the range of 2–11. The pseudo second order equation and Langmuir model were fit to the experimental data, and the adsorption of fluoride by SAA@CS-CB_oa exhibited spontaneous and endothermic characteristics. When PO₄^3-, CO₃^2–, SO₄^2-, Cl^-, NO₃^–, Br^- and HCO₃^– anions were individually or combined in solution, the adsorbents exhibited higher fluoride selectivity and sensitivity, while PO₄^3-and CO₃^2– weakened the adsorption of fluoride in solution in the same way regardless of the presence of the other 5 anions. The results of SEM, EDS, XRD and FTIR characterizations showed that the mechanism of fluoride adsorption and removal by SAA@CS-CB_oa included the combined effects of electrostatic attraction, surface coordination precipitation and ion exchange. SAA@CS-CB_oa is an effective composite material for water adsorption of fluoride, and still has an excellent performance of cyclic regeneration after 10 times adsorption desorption. This study provides a new approach for the utilization of fluoride removal resources for industrial solid waste resource recycling.