A new post-treatment process for attaining Ca²⁺, Mg²⁺, SO₄²⁻ and alkalinity criteria in desalinated water

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• 作者：Liat Birnhack ; Ori Lahav
• 关键词：Post-treatment ; Mg²⁺ ; Ion exchange ; Desalination ; Cost analysis
• 刊名：Water Research
• 出版年：2007
• 出版时间：September 2007
• 年：2007
• 卷：41
• 期：17
• 页码：3989-3997
• 全文大小：458 K

文摘

A novel post-treatment approach for desalinated water, aimed at supplying a balanced concentration of alkalinity, Ca²⁺, Mg²⁺ and SO₄²⁻, is introduced.

The process is based on replacing excess Ca²⁺ ions generated in the common H₂SO₄-based calcite dissolution post-treatment process with Mg²⁺ ions originating from seawater. In the first step, Mg²⁺ ions are separated from seawater by means of a specific ion exchange resin that has high affinity toward divalent cations (Mg²⁺ and Ca²⁺) and an extremely low affinity toward monovalent cations (namely Na⁺ and K⁺). In the second step, the Mg²⁺-loaded resin is contacted with the effluent of the calcite dissolution reactor and Mg²⁺ and Ca²⁺ are exchanged. Consequently, the excess Ca²⁺ concentration in the water decreases while the Mg²⁺ concentration increases. The process is stopped at a predetermined Ca²⁺ to Mg²⁺ ratio. All water streams used in the process are internal and form a part of the desalination plant sequence, regardless of the additional ion exchange component. The proposed process allows for the supply of cheap Mg²⁺ ions, while at the same time enables the application of the cheap H₂SO₄-based calcite dissolution process, thus resulting in higher quality water at a cost-effective price. A case study is presented in which additional cost of supplying a Mg²⁺ concentration of 12 mg/L using the process is estimated at $0.004/m³ product water.