Replenishing Mg(II) to desalinated water by seawater nanofiltration followed by magnetic separation of Mg(OH)2(s)Fe3O4 particles

Orly Lehmann*, Or Eckhaus, Ori Lahav, Liat Birnhack

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Magnesium (Mg2+) appears at high concentration in seawater and seawater-reverse-osmosis brines. In contrast, desalinated water is almost completely depleted of Mg2+, a mineral perceived essential for human health and agricultural irrigation. The paper introduces a cost-effective method to enrich desalinated water with an almost pure Mg(II) solution, originating from seawater. The method uses seawater nanofiltration (or nanofiltration of seawater-reverse-osmosis brine) to produce brine characterized by high Mg2+ concentration, accompanied by relatively low B, Cl, and Na+ concentrations. Subsequently, Mg(II) is separated from the produced nanofiltration brine by precipitating Mg(OH)2(s) and adsorbing it onto the surface of micro-magnetite particles. Finally, the solid slurry (Fe3O4 + Mg(OH)2) is magnetically separated from the brine and the Mg(OH)2(s) is re-dissolved into the desalinated water in a separate reactor. Application of the method results in a relatively pure Mg(II) addition to the desalinated water product. For example, for Mg(II) addition of 10 mg/L (as recommended by the World Health Organization), the following negligible concentrations of unwanted species are added to the water (in mg/L units): Na+: 0.04, Cl: 0.18, Ca2+: 0.05, and B: 0.0094. The cost of adding 10 mg Mg/L was estimated at 0.76 cent$/m3 of desalinated water, i.e. competitive with previously suggested processes.

Original languageEnglish
Pages (from-to)19903-19916
Number of pages14
JournalDesalination and Water Treatment
Volume57
Issue number42
DOIs
StatePublished - 7 Sep 2016
Externally publishedYes

Keywords

  • FeO, Mg(OH)
  • Magnesium recovery
  • Magnetic separation
  • SWRO

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