The Effect and Potential Mechanism of Cement-Based Pellets for Fluoride Removal from Surface Water

Fluoride contamination in water is a global health concern. While many studies have used simulated fluoride-containing solutions in labs, few have conducted defluorination experiment on natural fluoride-contaminated water. In this study, we prepare three defluorination pellets (P1, P2, P3) using cement, sludge, and rice husk powder with mass percentages of 75%: 20%: 5%, 70%: 20%: 10%, and 65%: 20%: 15%, respectively, and tested their defluorination efficiency in water samples taken from the South Jiaolai River in Shandong Province, China. An outdoor experiment was conducted in May and June in Jiaozhou, Shandong Province, which lasted for 24 days. For each treatment, 10 g/L of pellets were added to 50 L of natural water samples with 3 replicates. The initial fluoride concentration of the water samples was 1.90 mg/L, and the fluoride concentration and pH value were measured every 3 days. SEM, EDS, XRD, and FTIR were used for analyzing potential defluorination mechanisms. The results showed that 3 types of pellets were effective in fluoride removal. On the 24th day, the fluoride concentrations in the water samples treated with pellets were significantly lower than that of the control group. The fluoride concentration in water samples treated with P1, P2, and P3 decreased to 0.74, 0.75, and 0.99 mg/L, respectively. AlF 3 and MgF 2 could be found in the composition of the pellets after the treatment of water samples, and hydroxylated metal oxides and CaCO 3 both contributed to the defluorination process. The prepared pellets have potential for application in defluorination of fluoride-contaminated surface water.