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By-Product Recovery from Reclaimed Water Concentrates

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Abstract:

Chemical pretreatment followed by secondary RO and evaporation/crystallization was studied for treatment of reclaimed waters desalination concentrates. The objectives were removal of potential fouling minerals of Ca, Mg, and silica by an optimized lime-soda softening while producing by-products with potential resale value. Three different bench-scale lime-soda processes were evaluated. Traditional method produces low quality Mg(OH)2 and CaCO3. Modified process with preacidification to eliminate carbonate removes 98-99% of Ca and Mg and produces CaCO3 that is >94% pure. To prevent the contamination of by-products with CaSO4 in high-sulfate concentrates, a CaSO4 crystallization step was successfully added to the modified process to precipitate CaSO4 before precipitation of Mg(OH)2 and CaCO3. After removal of Ca and Mg, a model of a seawater system containing Na-K-Cl-SO4 using Pitzer's equations was developed to predict solubility of the Na2SO4 minerals at 25°C. The experimental results verified the accuracy of the model and the obtained solids were 81-88% Na2SO4.

Document Type: Research Article

DOI: https://doi.org/10.2175/193864708788734386

Publication date: 2008-01-01

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