Abstract
This study explored the possibility of using reverse osmosis (RO) reject water as a mixing water for producing cementitious bricks using calcium sulfoaluminate (CSA) cement along with gypsum, and it investigated the changes in the properties of CSA cement pastes when RO reject water was used. The results were compared with those obtained using purified water and seawater. Overall, the use of RO reject water improved the cement paste’s strength. Given that the use of RO reject water very slightly affected ettringite formation but more significantly influenced the Al2O3-Fe2O3-mono (AFm) phases (i.e., monosulfate, kuzelite, and Friedel’s salt) and amorphous aluminum hydroxide (AH3), the strength improvement was likely mainly due to the formation of Friedel’s salt rather than ettringite formation. This study also demonstrated that the use of RO reject water for brick production satisfied the Korean Standards (KS) F 4004 and toxicity characteristic leaching procedure (TCLP); thus, it is recommended to use RO reject water as a mixing water to produce CSA cement bricks for use in construction.
Highlights
Reverse osmosis (RO) is a desalination process that removes salts and minerals from seawater or brackish water with a salinity of total dissolved solids (TDS) of ~1000–60,000 mg/L to produce clean water with less than 500 mg/L TDS [1]
That a stiffer mortar is more advantageous for brick production when considering common production processes of cement bricks
Overall, compared to the use of purified water, the use of reverse osmosis (RO) reject water as a mixing water for calcium sulfoaluminate (CSA) cement was beneficial in improving strength and satisfied the Korean Standards (KS) F 4004 for brick production
Summary
Reverse osmosis (RO) is a desalination process that removes salts and minerals from seawater or brackish water with a salinity of total dissolved solids (TDS) of ~1000–60,000 mg/L to produce clean water with less than 500 mg/L TDS [1]. The RO process currently produces about 50% of the total desalinated water available worldwide [2]; it yields a huge amount of further concentrated brines (or RO reject water) with over ~10,000 mg/L TDS as a waste byproduct. Various technologies designed to minimize or reuse RO reject water have been developed, such as evaporation and crystallization, forward osmosis, membrane distillation, electrodialysis, and zero discharge desalination; all these technologies demand substantial additional costs [2,4,5]. It is necessary to develop a new way of treating
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