Effective Removal of Calcium and Magnesium Ions from Water by a Novel Alginate–Citrate Composite Aerogel

In this work, a novel alginate/citrate composite aerogel (CA–SC) was synthesized by chemical grafting technology combined with vacuum freeze-drying method, and CA–SC was used for removing calcium (Ca(2+)) and magnesium (Mg(2+)) ions from water. The experimental results indicate that the as-prepared CA–SC has a high affinity for Ca(2+) and Mg(2+) and can remove 96.5% of Ca(2+) (or 96.8% of Mg(2+)) from the corresponding solution. The maximum adsorption capacities of CA–SC for Ca(2+) and Mg(2+) are 62.38 and 36.23 mg/g, respectively. These values are higher than those of the most reported Ca(2+)-sorbents and Mg(2+)-sorbents. The CA–SC adsorbent can be regenerated through a simple pickling step, and its adsorption performance keeps stable after repeated use. Analysis of the adsorption mechanism shows that the CA–SC combines Ca(2+) and Mg(2+) in water mainly through coordination effect.