Application of ion exchange resins to reduce hardness and scaling of drinking water: Experimental and modeling

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In this research, the performance of strong cationic Purolite C-100 Na+, Ambersep IR252 H+, Amberlite IR120 H+ ion exchange resins and an IRA402 OH- anionic resin have investigated to the reduction of hardness and TDS of drinking water in Bushehr, Iran. Also, to demonstrate the efficiency of these resins, the experimental variables affecting the ion exchange process such as contact time and adsorbent consumption were investigated. The results showed that the maximum adsorption capacity in the best operating condition was 48.01, 45 and 36.01 mg.g-1 for Purolite, Ambersep, and Amberlite resins, respectively. The maximum percentage of total hardness reduction parameters, calcium and magnesium ions reduction at best operating condition was 90.086%, 93.085%, 77.27% for Purolite ion exchange resins, 83.84%, 86.70%, 71.59% for Ambersep ion exchange resins and 69.83, 69.41, 69.32 for Amberlite ion exchange resins, respectively. Also, in the compound stage (the combination of cationic and anionic resins), at the best condition, 3 g/L of cationic resin and 12 g/L of anionic resin had the best efficiency in adjusting pH and reducing TDS. To study the adsorption kinetic process of calcium and magnesium ions by three strong cationic ion exchange resins, three pseudo-first-order, pseudo-second-order, and Morris-Weber models were employed. Among these models, the pseudo-second-order kinetic model had the best agreement with the experimental data. The models of Langmuir, Freundlich, Temkin, and Dobinin-Radskvich were utilized for the equilibrium study of hardened ions adsorption (calcium and magnesium). From the equilibrium study of the absorption process, it was founded that this process involves both chemical and physical absorption and the Langmuir model has the best agreement with the experimental data.