Treatment of calcium in hard water from acid sulfate soil and its utilization in a pre-designed cation exchange resin system for fluoride adsorption in water.

In this study, a pre-designed cation exchange resin (CER) column was first tested to remove calcium in naturally contaminated water from acid sulfate soil for water supply purpose, and it was further used as a novel and natural calcium hydroxide-supported CER composite (NCHO/CER) for the treatment of fluoride in water. Results of SEM, EDX, FTIR, and XRD analyses confirmed the formation of calcium hydroxide nanoparticles in the CER structure. The fluoride adsorption capacity of NCHO/CER was systematically studied by varying the influencing factors, such as the reaction time, pH level, adsorbent mass, initial concentration, and temperature. The adsorption kinetics followed a pseudo-second-order model, while the isotherm curves fitted to the Freundlich model, indicating the occurrence of multilayer adsorption on the adsorbent surface. Moreover, NCHO/CER showed the ability not only to be reused after multiple cycles but also to remove fluoride from actual tap water and groundwater, proving that NCHO/CER is effective for the recovery and reuse of contaminated calcium for fluoride treatment in water.