Salt‐free softening by thermo‐reversible ion‐adsorbing hydrogels

Abstract

In this article, we demonstrate the properties of a hydrogel capable of adsorbing calcium cations from aqueous streams at ambient temperatures (10-25 C) and showing almost complete desorption of the bound calcium ions at slightly elevated temperatures (40-50 C). Successful breakthrough experiments in a fixed bed column set-up show the potential of the hydrogel in softening water streams from 150 ppm toward <10 ppm hardness levels. The regeneration ability is based on the thermo-reversible internal ion pair-formation mechanism of the hydrogel. Additionally, it was shown that the thermo-reversible adsorption mechanism was successful for magnesium and copper ions too. The exploration of the properties of hydrogel CS-1B14 is the first step in the development of sustainable water-softening processes, both at industrial scale as well as for household applications, using low-grade residual heat to regenerate these gels. In this way, the use of concentrated brine streams, acid/caustic treatment, or high regeneration temperatures is avoided.

Aluminum-Cycle Ion Exchange Process for Hardness Removal: A New Approach for Sustainable Softening

“…In the mid-1960s, the Sirotherm process was introduced as a novel ion exchange process that relied on thermal regeneration, , but the commercial scale-up was a failure. Similar thermal regeneration processes using hydrogels have been investigated, but currently have limited capacity compared to commercial resins . Weak-acid cation (WAC) exchange resin can be a possible alternative to minimize Na-laden spent regenerant, but efficient regeneration of WAC requires mineral acids.…”