A two-step electrochemical method for separating Mg(OH)2 and CaCO3: Application to RO reject and polluted groundwater

Manikandan Santhanam, Rajeswari Selvaraj, Maruthamuthu Sundaram

Research output: Contribution to journalArticlepeer-review

Abstract

The process of removing Ca2+ and Mg2+ ions typically results in the co-precipitation of Ca2+ and Mg2+ along with other salt waste. To improve water treatment efficiency towards a zero-waste goal, it is crucial to separate Ca2+ and Mg2+, and recover them in their purified form. This study proposes a two-step electrochemical approach that separately recovers Ca2+ as CaCO3 and Mg2+ as Mg(OH)2. The first step uses an undivided cell with 3D electrodes and controlled flow directions to selectively precipitate CaCO3 on the electrode, keeping the cell removal efficiency. The second step employs a two-compartment cell with a cationic exchange membrane to recover Mg(OH)2. This approach was evaluated on RO reject water with high Ca2+ to Mg2+ ratio and industrial effluent-polluted groundwater with a low ratio. Treatment of domestic RO reject water using undivided cell specifically recovered 64% of CaCO3, although the low conductivity of the RO reject water limited further Mg2+ recovery. Conversely, treating industrial effluent-polluted groundwater with this two-step process successfully recovered 80% of CaCO3 and 94% of Mg(OH)2. SEM, EDAX, and XRD analysis confirmed the quality of the recovered products.

Original languageEnglish
Article number142212
JournalChemosphere
Volume358
DOIs
StatePublished - 1 Jun 2024
Externally publishedYes

Keywords

  • Calcium
  • Groundwater
  • Hardness
  • Magnesium
  • Pollution
  • Salt waste

ASJC Scopus subject areas

  • General Chemistry
  • Public Health, Environmental and Occupational Health
  • Pollution
  • Health, Toxicology and Mutagenesis
  • Environmental Engineering
  • Environmental Chemistry

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