The Effect of CaCl2 and Basicity of PAC on Fluoride Removal by PAC-PDMDAAC Coagulation.

Fluoride contamination in water sources poses significant risks to human health and ecosystems, necessitating effective treatment strategies. This study investigates the influence of calcium chloride (CaCl2) and the basicity of polyaluminum chloride (PAC) on fluoride removal using PAC-PDMDAAC coagulation. Through systematic jar tests, the effects of varying PAC basicity (0.5, 1.0, and 2.0) and CaCl2 addition sequences were examined under different fluoride concentrations (1.0, 3.0, and 10.0 mg/L). Results indicate that PAC with lower basicity (B = 0.5) exhibits superior fluoride removal efficiency, showing an increase of 20%-40% compared to PAC (B = 2.0), primarily due to the electro-neutralization mechanism of monomeric aluminum species (Ala). The introduction of PDMDAAC reduced the coagulation performance of PAC, especially at an initial fluoride concentration of 1 mg/L. The fluoride removal rate decreased from 80% to 57% at B = 0.5, from 91% to 62% at B = 1.0, and from 72% to 25% at B = 2.0. The order of adding CaCl2 affects the removal rate of fluoride, with the CaCl2 + PAC sequence outperforming the reverse sequence. The study highlights the importance of optimizing coagulant basicity and CaCl2 dosing order to enhance fluoride removal efficiency, providing valuable insights for water treatment processes. These findings contribute to the development of more efficient and cost-effective coagulation strategies for fluoride removal in water treatment plants.