Optimization of the Counterion Enhances Selective Cu ²⁺ Recovery by Standard Cation‐Exchange Resin

ABSTRACT

This study systematically investigated the potential effects of mobile counterions (Ca ²⁺ or Na ⁺ ) on standard cation‐exchange resin (CER)‐based selective Cu ²⁺ recovery from water. When Na ⁺ (or Ca ²⁺ ) served as the mobile counterion, zero net Ca ²⁺ (or Na ⁺ ) removal from feedwater during exhaustion was observed after a standard CER column was activated by a Ca ²⁺ –Na ⁺ binary brine with a critical Ca ²⁺ (or Na ⁺ ) equivalent fraction of 0.70 (or 0.08). By contrast, Ca ²⁺ counterion use was associated with a lower Cu ²⁺ level (0.12 vs. 0.71 mg/L) in product water, increased the Cu ²⁺ breakthrough volume by >10%, and shortened (by 80%) the time required for Ca ²⁺ and Na ⁺ to achieve ion‐exchange equilibrium. When a critical Ca ²⁺ –Na ⁺ binary brine with Ca ²⁺ as the mobile counterion was used, a standard CER column consistently exhibited zero net Na ⁺ removal from feedwater, >90% Cu ²⁺ removal and recovery, and stable Ca ²⁺ substitution for Cu ²⁺ during six exhaustion–regeneration cycles.