Modified zeolite adsorbents for the remediation of potash brine-impacted groundwater: Built-in dual functions for desalination and pH neutralization

Abstract

Clinoptilolite zeolites were modified through acid treatment followed by Ca(OH)2 conditioning. The modified zeolite adsorbent (H-Zeo-CaOH) has built-in dual functions for desalination and pH neutralization. The modified zeolites were evaluated using synthetic saline water and groundwater spiked with brine produced during potash mining, and characterized using multiple instrumental techniques. Batch adsorption experiments were conducted for (1) zeolites treated with acids of varying strengths, (2) Ca(OH)2-conditioned acid-treated zeolites, and (3) natural zeolites. Acid-treated zeolites, with or without Ca(OH)2 conditioning, exhibited dramatically improved Na+ removal. Na+ removal from saline water (1000–5000mg Na+/L) using the modified zeolites ranged from 45 to 88%, whereas natural zeolites achieved approximately 25%. The modified zeolites desalinated the brine-impacted groundwater (73–87% Na+ removal), despite abundant K+ ions in the groundwater, which are highly competitive for adsorption sites. The acid treatment caused dealumination within the zeolites, generating acidified zeolites with a high affinity for Na+ and a large porosity. Sodium adsorption sites, visualized by synchrotron-based scanning transmission X-ray microscopy, correlated with alumina (>Al-O-Na) in the modified zeolites. The effluent, which is normally highly acidic due to protonic exchanges in acid-treated zeolites, was neutralized by the concomitant release of hydroxyl ions only when using the H-Zeo-CaOH adsorbent.