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.