Dia-nanofiltration-electrodialysis hybrid process for selective removal of monovalent ions from Mg2+ rich brines

Paz Nativ; Noga Fridman-Bishop; Oded Nir; Ori Lahav

doi:10.1016/j.desal.2020.114357

Dia-nanofiltration-electrodialysis hybrid process for selective removal of monovalent ions from Mg²⁺ rich brines

Paz Nativ^*, Noga Fridman-Bishop, Oded Nir, Ori Lahav

^*Corresponding author for this work

Environmental Science and Engineering

Research output: Contribution to journal › Article › peer-review

5 Scopus citations

Abstract

A hybrid nanofiltration-electrodialysis process was developed and tested for highly-selective separation of MgSO₄ from seawater. The magnesium-rich solution was produced primarily for replenishing Mg²⁺ into desalinated water within the post-treatment step in seawater desalination plants. The new three-step process consists of: (1) seawater nanofiltration (NF) for generation of a magnesium-rich retentate; (2) a Dia-NF step in which the NF retentate is used as feed, which is aimed at minimizing unwanted solutes (primarily B, Na⁺ and Cl⁻); and (3) a selective electrodialysis (ED) step on the retentate from step 2, aimed at further lowering the Cl⁻:Mg²⁺ mass ratio to below 0.2, to produce a high-purity MgSO₄-rich product solution. Results are presented with an emphasis on the ED step, for which the effects of flow velocity, current density and two operation modes (constant-current and constant-potential) were assessed. The results show a highly-dependent selectivity of the monovalent-selective ion-exchange membrane to the cell potential, suggesting that it can serve as a fine-tuning tool for selective ED processes. The cost of adding 20 mgMg/L to one m³ of desalinated water was estimated at ~$0.014/m³, which is competitive compared to other separation techniques, and certainly versus the alternative of direct dosage of food-grade magnesium salts.

Original language	English
Article number	114357
Journal	Desalination
Volume	481
DOIs	https://doi.org/10.1016/j.desal.2020.114357
State	Published - 1 May 2020

Keywords

Desalinated water
Electrodialysis
Ion exchange membranes
Mg replenishment

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title = "Dia-nanofiltration-electrodialysis hybrid process for selective removal of monovalent ions from Mg2+ rich brines",

abstract = "A hybrid nanofiltration-electrodialysis process was developed and tested for highly-selective separation of MgSO4 from seawater. The magnesium-rich solution was produced primarily for replenishing Mg2+ into desalinated water within the post-treatment step in seawater desalination plants. The new three-step process consists of: (1) seawater nanofiltration (NF) for generation of a magnesium-rich retentate; (2) a Dia-NF step in which the NF retentate is used as feed, which is aimed at minimizing unwanted solutes (primarily B, Na+ and Cl−); and (3) a selective electrodialysis (ED) step on the retentate from step 2, aimed at further lowering the Cl−:Mg2+ mass ratio to below 0.2, to produce a high-purity MgSO4-rich product solution. Results are presented with an emphasis on the ED step, for which the effects of flow velocity, current density and two operation modes (constant-current and constant-potential) were assessed. The results show a highly-dependent selectivity of the monovalent-selective ion-exchange membrane to the cell potential, suggesting that it can serve as a fine-tuning tool for selective ED processes. The cost of adding 20 mgMg/L to one m3 of desalinated water was estimated at ~$0.014/m3, which is competitive compared to other separation techniques, and certainly versus the alternative of direct dosage of food-grade magnesium salts.",

keywords = "Desalinated water, Electrodialysis, Ion exchange membranes, Mg replenishment",

author = "Paz Nativ and Noga Fridman-Bishop and Oded Nir and Ori Lahav",

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year = "2020",

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AU - Lahav, Ori

PY - 2020/5/1

Y1 - 2020/5/1

N2 - A hybrid nanofiltration-electrodialysis process was developed and tested for highly-selective separation of MgSO4 from seawater. The magnesium-rich solution was produced primarily for replenishing Mg2+ into desalinated water within the post-treatment step in seawater desalination plants. The new three-step process consists of: (1) seawater nanofiltration (NF) for generation of a magnesium-rich retentate; (2) a Dia-NF step in which the NF retentate is used as feed, which is aimed at minimizing unwanted solutes (primarily B, Na+ and Cl−); and (3) a selective electrodialysis (ED) step on the retentate from step 2, aimed at further lowering the Cl−:Mg2+ mass ratio to below 0.2, to produce a high-purity MgSO4-rich product solution. Results are presented with an emphasis on the ED step, for which the effects of flow velocity, current density and two operation modes (constant-current and constant-potential) were assessed. The results show a highly-dependent selectivity of the monovalent-selective ion-exchange membrane to the cell potential, suggesting that it can serve as a fine-tuning tool for selective ED processes. The cost of adding 20 mgMg/L to one m3 of desalinated water was estimated at ~$0.014/m3, which is competitive compared to other separation techniques, and certainly versus the alternative of direct dosage of food-grade magnesium salts.

AB - A hybrid nanofiltration-electrodialysis process was developed and tested for highly-selective separation of MgSO4 from seawater. The magnesium-rich solution was produced primarily for replenishing Mg2+ into desalinated water within the post-treatment step in seawater desalination plants. The new three-step process consists of: (1) seawater nanofiltration (NF) for generation of a magnesium-rich retentate; (2) a Dia-NF step in which the NF retentate is used as feed, which is aimed at minimizing unwanted solutes (primarily B, Na+ and Cl−); and (3) a selective electrodialysis (ED) step on the retentate from step 2, aimed at further lowering the Cl−:Mg2+ mass ratio to below 0.2, to produce a high-purity MgSO4-rich product solution. Results are presented with an emphasis on the ED step, for which the effects of flow velocity, current density and two operation modes (constant-current and constant-potential) were assessed. The results show a highly-dependent selectivity of the monovalent-selective ion-exchange membrane to the cell potential, suggesting that it can serve as a fine-tuning tool for selective ED processes. The cost of adding 20 mgMg/L to one m3 of desalinated water was estimated at ~$0.014/m3, which is competitive compared to other separation techniques, and certainly versus the alternative of direct dosage of food-grade magnesium salts.

KW - Desalinated water

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KW - Ion exchange membranes

KW - Mg replenishment

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Dia-nanofiltration-electrodialysis hybrid process for selective removal of monovalent ions from Mg²⁺ rich brines

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Keywords

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