Environmentally Sustainable Mining: Reusable Zeolite for Sodium Mitigation from Potash Brine Impacted Groundwater

Abstract

Potash mining creates highly saline waste products. Current industry standards include storage and contamination prevention measures; however, the risk to surrounding soil and groundwater from the highly saline waste solution is a significant concern.

Zeolites, specifically clinoptilolite-rich zeolites, have drawn significant attention as a viable and cost-effective treatment method for contaminated solutions. Zeolite has been successful in the reclamation of saline coalbed natural gas co-produced solutions; however, zeolites have thus far not been specifically examined for desalination of potash brine impacted solutions. The desalination capabilities of three natural zeolites from mines located in North America, were examined using synthetic saline solutions and groundwater spiked with potash brine from a local Saskatchewan mine. Bear River zeolite (Idaho, USA) was the most effective, achieving a Na+ removal percentage of approximately 70%. A selectivity sequence of K+>Na+>Ca2+≈Mg2+ was determined through batch adsorption experiments with potash brine spiked groundwater.

Pre-treatment strategies were evaluated during this study to optimize the adsorption capacity of the natural zeolites. Acid treatment (1M H2SO4) was used to promote protonation of the zeolite exchange sites, resulting in an increase Na+ sorption capacity of approximately 10%. However, the sorption solution was strongly acidic and problematic for practical applications. Cations such as sodium and calcium have commonly been used to pre-treat zeolites to increase the sorption capacity. As sodium removal was the primary objective, thus, pre-treatment techniques using calcium and magnesium ions were examined. A hard water solution was simulated using CaCl2 and MgCl2 to remove the Na+ ions from zeolite exchange sites. This technique increased the Na+ removal percentage for the Canadian zeolite by approximately 77%.

Sodium sorption experiments created zeolite with sodium saturated exchange sites. To minimize the waste products produced, this study examined sodium removal and water softening cycles. The significant Na+ sorption improvement suggested initially using the Canadian zeolite to soften simulated hard water, producing Ca- and Mg-rich zeolites and recycling the zeolite for Na+ adsorption experiments. The dual treatment of saline and hard water solutions was studied for five complete cycles with a stable functioning exchange system being achieved. The regeneration increased sorption capacity while extending the life cycle of the zeolite adsorbent.