Adsorption of Calcium Ion in Cooling Water Using Ion-Imprinted Adsorbents for Scale Inhibition

Calcium is the main ion that causes scaling in circulating cooling water, but current works mainly focus on developing scale inhibitors, lacking reports on the softening of hard water and efficient recovery of economic ions. In this study, calcium ion-imprinted polymers (Ca2+-IIP) were developed with the bulk polymerization method for the adsorption and recovery of calcium ions (Ca2+) from cooling water, aiming to mitigate scaling and achieve resource utilization. The Ca2+-IIP could effectively capture Ca2+ with a maximum adsorption capacity of 61.2 mg/g, and it only decreased by about 8% after six adsorption/desorption cycles. In addition, Ca2+-IIP could selectively adsorb Ca2+, with selectivity coefficients of up to 5.9, 2.8 and 3.7 for Na+, K+ and Mg2+, respectively. The adsorption mechanism was explored with Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, and the carboxyl and hydroxyl groups were involved in the adsorption, where the O atoms provided lone pair electrons to interact with Ca2+. Moreover, Ca2+-IIP could obviously inhibit scaling in cooling water with different cycle times. This work develops a potentially effective adsorbent for Ca2+ recycling and scale inhibition in circulating cooling water.