title: A new post-treatment process for attaining Ca2+, Mg2+, SO42- and alkalinity criteria in desalinated water.
abstract: A novel post-treatment approach for desalinated water, aimed at supplying a balanced concentration of alkalinity, Ca(2+), Mg(2+) and SO(4)(2-), is introduced. The process is based on replacing excess Ca(2+) ions generated in the common H(2)SO(4)-based calcite dissolution post-treatment process with Mg(2+) ions originating from seawater. In the first step, Mg(2+) ions are separated from seawater by means of a specific ion exchange resin that has high affinity toward divalent cations (Mg(2+) and Ca(2+)) and an extremely low affinity toward monovalent cations (namely Na(+) and K(+)). In the second step, the Mg(2+)-loaded resin is contacted with the effluent of the calcite dissolution reactor and Mg(2+) and Ca(2+) are exchanged. Consequently, the excess Ca(2+) concentration in the water decreases while the Mg(2+) concentration increases. The process is stopped at a predetermined Ca(2+) to Mg(2+) 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 Mg(2+) ions, while at the same time enables the application of the cheap H(2)SO(4)-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 Mg(2+) concentration of 12mg/L using the process is estimated at $0.004/m(3) product water.
authors.affiliation: Faculty of Civil and Environmental Engineering, Technion, Haifa 32000, Israel.
authors.forename: Liat
authors.initials: L
authors.lastname: Birnhack
authors.forename: Ori
authors.initials: O
authors.lastname: Lahav
mesh_terms: D002118:Calcium / Q000737:chemistry*; D002119:Calcium Carbonate / Q000737:chemistry; D003198:Computer Simulation; D003362:Cost-Benefit Analysis; D004553:Electric Conductivity; D007474:Ion Exchange; D007557:Israel; D008274:Magnesium / Q000737:chemistry*; D009995:Osmosis; D012117:Resins, Synthetic / Q000737:chemistry; D012965:Sodium Chloride / Q000302:isolation & purification*; D012995:Solubility; D012996:Solutions; D013431:Sulfates / Q000737:chemistry*; D013464:Sulfuric Acids / Q000737:chemistry; D018508:Water Purification / Q000191:economics / Q000379:methods*
chemical_list: D012117:Resins, Synthetic; D012996:Solutions; D013431:Sulfates; D013464:Sulfuric Acids; D012965:Sodium Chloride; D002119:Calcium Carbonate; D008274:Magnesium; C033158:sulfuric acid; D002118:Calcium