Optimization of the Counterion Enhances Selective Cu2+ Recovery from Water Using a Standard Cation-Exchange Resin-Packed Column

Abstract

This study systematically investigated the potential effects of mobile counterions (Ca2+ or Na+, exhibiting moderate or minimal selectivity) on standard ion-exchange resin (IER)-based selective Cu2+ recovery during Ca2+-Cu2+-Na+ ternary feedwater treatment. When Na+ (or Ca2+) served as the mobile counterion, zero net Ca2+ (or Na+, as the competing ion) removal from ternary feedwater was apparent during exhaustion after circular activation of a standard IER column by an optimized Ca2+-Na+ binary brine with a critical Ca2+ (or Na+) equivalent fraction of 0.70 (or 0.08), enabling complete self-inhibition of Ca2+ (or Na+) during exhaustion. Under such conditions, Ca2+ (compared with Na+) counterion use was associated with a lower Cu2+ level (0.12 vs. 0.71 mg/L) in product water, increased the Cu2+ breakthrough volume by > 10%, and shortened (by 80%) the time required for Ca2+ and Na+ to achieve ion exchange equilibrium. When an optimized Ca2+-Na+ binary brine with Ca2+ as the mobile counterion was used, a standard IER column consistently exhibited zero net removal and recovery of Na+ (the competing ion), > 90% Cu2+ removal and recovery, and stable Ca2+ substitution for Cu2+ during six exhaustion/regeneration cycles.

Keywords: Heavy metal Selective ion removal Ion exchange resin Self-inhibition mechanism of competitive ions Mobile counterion