Stabilization and solidification of brine water containing selenium, chromium, copper, and mercury utilizing a microwave enabled sol-gel process

• Published in: Environmental science water research & technology 2021-05, Vol.7 (5), p.94-912
• Main Authors: Kearns, Alex, Bansal, Meenakshi, Kalbfleisch, Theodore, Keller, Aaron, Ellison, Kirk, Chauhan, Rajat, Ghorbanian, Mahyar, Gupta, Gautam
• Format: Article
• Language: English
• Subjects: Bituminous coal; Brines; Chromium; Coal; Coal-fired power plants; Contaminants; Effluent treatment; Effluents; Electric power generation; Encapsulation; Fly ash; Fossil fueled power plants; Gels; Information processing; Leaching; Mercury; Power plants; Selenium; Silica; Silicon dioxide; Sol-gel processes; Solidification; Stabilization; Vitrification; Wastewater; Wastewater treatment
• ISSN: 2053-1400; 2053-1419
• DOI: 10.1039/d1ew00081k

To comply with the new regulations on coal-fired power plants, many treatment scenarios are inclining towards zero-liquid discharge (ZLD) technologies. Therefore, there has been a dramatic shift in the treatment approaches for managing effluents at coal-fired plants within the past decade. Traditionally, stabilization/solidification (S/S) ZLD technologies fall into two categories: cementitious and vitrification. However, neither approach offers the ideal solution for coal-fired power plants needing ZLD by S/S methods. Here, we report a novel proof-of-concept of a sol-gel encapsulation - chemical and physical - method using only one chemical: tetramethyl orthosilicate and the resulting materials are evaluated as an alternative S/S effluent treatment. We demonstrate that the concept of sol-gel encapsulation is an efficient method to solidify and chemically stabilize various brine waters and wastewater effluents from a midwestern coal-fired power plant that burns both bituminous and sub-bituminous coals. The encapsulated solids successfully retained positively charged contaminants during leaching analyses, while struggling to retain negatively charged contaminants. Based on the results shown, it is proposed that the negatively charged silicon dioxide network chemically fixates positively charged contaminants, leading to the retention of those contaminants. These results demonstrate that sol-gel encapsulation has the potential to be developed as an alternative S/S technique to meet the challenges of ZLD technologies. It is anticipated that the work presented will be a starting point for further development of S/S treatment with sol-gels derived from fly ash. Solidification/stabilization of wastewater from a coal-fired power plant, burning bituminous and sub-bituminous coals via sol-gel synthesized from tetramethyl orthosilicate (TMOS) (top) and demonstration of TMOS chemical fixation mechanism (below).