Synergistic desalination of potash brine-impacted groundwater using a dual adsorbent

The impact of saline mining effluent has been a significant environmental concern. Natural and modified clay-mineral adsorbents have been receiving increasing attention for salinity reduction of brine-impacted water, especially for natural resource extraction sites and surrounding environments. In this study, a dual-adsorbent treatment based on the sequential application of calcined layered double hydroxide (CLDH) and acid-treated zeolite was developed, evaluated and characterized for the desalination of potash brine-impacted groundwater. Potash brine produced by conventional potash mining in Saskatchewan (Canada) contains a large amount of Na⁺, K⁺ and Cl⁻. The CLDH and acid-treated clinoptilolite zeolites were combined to sequentially remove Cl⁻ and Na⁺. A series of batch adsorption experiments were conducted for synthetic saline water and potash brine-spiked groundwater using various combinations of adsorbents: natural zeolites (NZ) or acid-treated zeolites (AZ) with or without the CLDH pretreatment. The experiment revealed that the Na⁺ removal percentage was synergistically increased by the dechlorination pretreatment using CLDH, and further improved by AZ. The CLDH-AZ dual adsorbent achieved a Langmuir Na⁺ adsorption capacity of 24.4 mg/g, a significant improvement over conventional approaches to zeolite-based desalination. Using the brine-impacted groundwater with a high sodium adsorption ratio (SAR) of 13.3 ± 0.1, the CLDH-AZ dual adsorbent decreased the concentrations of Na⁺, K⁺, and Cl⁻ by 87, 97, and 87%, respectively (below drinking water standards). It also exhibited the additional advantages of neutralizing the effluent pH and decreasing the hardness, SAR, and total dissolved sulfur concentration. This study addresses the removal mechanisms, which are associated with the structural memory effect, dealumination, protonic exchanges, and zeolite porosity changes. Synchrotron-based scanning transmission X-ray microscopy analyses provided visual evidence of sodium adsorption sites (Si−O−Na and Al−O−Na) associated with dealumination in the acid-treated zeolites. This study is the first report that demonstrates the synergy of the CLDH-AZ dual adsorbent treatment for potash brine-impacted water. - Highlights: • CLDH and acid-treated zeolites were sequentially applied for desalination. • Adsorption experiments were performed with NaCl solutions and saline groundwater. • Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻, and S were removed and the effluent pH was neutral. • Memory effect, dealumination, proton exchange, and zeolite porosity were addressed. • STXM visualized Na⁺ adsorption related to silanol groups in acid-treated zeolite.