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6CCVD Research

Electrodeposition of Calcium Carbonate and Magnesium Carbonate from Hard Water on Stainless-Steel Electrode to Prevent Natural Scaling Phenomenon

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-10-05
JournalWater
AuthorsFaléstine Souiad, Yasmina Bendaoud-Boulahlib, Ana Sofia Rodrigues, Annabel Fernandes, Lurdes Ciríaco
InstitutionsUniversité Constantine 2, University of Beira Interior
Citations11
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This study validates a controlled electrodeposition method for preventing natural scaling in hard water by selectively removing calcium (Ca2+) and magnesium (Mg2+) ions onto a stainless-steel cathode.

  • Core Value Proposition: Scale formation is inhibited by recovering scale-forming ions as solid deposits (magnesian calcite and magnesium oxide carbonate) via galvanostatic electrolysis, avoiding the use of chemical inhibitors.
  • Optimal Operating Point: The best balance between removal efficiency and energy cost was achieved at an applied current intensity of 0.1 A (corresponding to 100 A m-2 current density).
  • Process Enhancement: Removal rates for Inorganic Carbon (IC), Ca2+, and Mg2+ increased significantly with higher stirring speed (1000 rpm) and larger cathode area (20 cm2), confirming mass transfer limitations.
  • Scaling Inhibition Performance: Accelerated scaling tests (chronoamperometry) showed that water treated at 0.1 A exhibited the lowest current reduction over time, indicating superior scale inhibition properties.
  • Anode Material Comparison: While Ti/Pt/PbO2 achieved higher raw removal percentages for IC and Ca2+, the BDD anode provided better performance in the critical accelerated scaling tests.
  • Robustness and Scale-Up: The solid deposit formed on the cathode did not impede subsequent deposition. IC removal remained constant over eight consecutive assays without cleaning, suggesting the process is robust and suitable for delayed maintenance cycles.
  • Chemical Composition Influence: Carbonate removal efficiency is strongly dependent on the initial water composition, increasing when the Ca/Mg molar ratio is greater than 1.

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Optimal Current Intensity (I)0.1ABest overall performance (removal and scaling inhibition).
Optimal Current Density100A m-2Based on 0.1 A applied to 10 cm2 cathode area.
Optimal Stirring Speed1000rpmUsed to increase mass transfer.
Cathode MaterialStainless Steel (SS)-Working electrode for deposition.
Cathode Area Tested10 and 20cm220 cm2 provided higher removal rates.
Anode Materials TestedBDD, Ti/Pt/PbO2-BDD showed better scaling test results at 0.1 A.
IC Removal (0.1 A, 4h)70-80%Using BDD anode, SS 20 cm2 cathode.
Ca2+ Removal (0.1 A, 4h)50-60%Using BDD anode, SS 20 cm2 cathode.
SEC (IC removal, 0.1 A)85.0kWh kg-1Specific Energy Consumption (BDD anode, SS 20 cm2).
SEC (Ca2+ removal, 0.1 A)47.05kWh kg-1Specific Energy Consumption (BDD anode, SS 20 cm2).
Initial pH (Solution S)7.9 ± 0.2-Simulated Bounouara hard water.
Initial Conductivity1.7 ± 0.2mS cm-1Solution S.
Deposit CompositionMagnesian Calcite, Magnesium Oxide Carbonate-Crystalline phases identified by XRD.
Accelerated Scaling Potential-0.96V vs. Ag/AgClApplied potential for chronoamperometric tests.

Key Methodologies

Section titled “Key Methodologies”
  1. Model Water Simulation: Aqueous solutions were prepared simulating Bounouara (Algeria) hard water (Solution S: [HCO3-] 350 mg L-1, [Mg2+] 40 mg L-1, [Ca2+] 170 mg L-1). Solutions A-E were used to vary the Ca/Mg molar ratio.
  2. Electrochemical Cell Setup: Experiments were performed in undivided cylindrical glass cells (200 or 500 mL working volume) in batch mode at room temperature.
  3. Galvanostatic Electrolysis: A Direct Current (DC) power supply was used to maintain constant anodic current intensities ranging from 0.025 A to 0.5 A for 4 or 8 hours.
  4. Electrode Configuration: Anodes included commercial Si/BDD (20 cm2) and lab-prepared Ti/Pt/PbO2 (10 cm2). Cathodes were stainless steel (SS) plates (10 or 20 cm2), centered parallel to the anode.
  5. Mass Transfer Control: Solutions were continuously stirred at 300, 500, or 1000 rpm to investigate the influence of turbulence and boundary layer thickness.
  6. Analytical Monitoring: Samples were collected periodically (60 or 120 minutes) to measure IC (TOC analyzer), Ca2+ and Mg2+ (Ion Chromatography), pH, and conductivity.
  7. Scaling Inhibition Assessment: Accelerated scaling tests utilized chronoamperometry on treated solutions, applying a fixed potential (-0.96 V vs. Ag/AgCl) to a 1 cm2 SS working electrode for 60 minutes, measuring current decay due to scale formation.
  8. Solid Deposit Analysis: The recovered deposits were characterized using X-ray Diffractometry (XRD) for crystalline phases, Energy Dispersive Spectroscopy (EDS) for elemental composition, and Scanning Electron Microscopy (SEM) for morphology.

Commercial Applications

Section titled “Commercial Applications”
  • Wastewater Treatment and Desalination: Pretreatment of brackish water or industrial concentrates (e.g., reverse osmosis reject streams) to remove scaling ions (Ca2+, Mg2+) before membrane filtration, extending membrane life and efficiency.
  • Municipal Water Softening: Providing a chemical-free method for reducing water hardness in drinking water distribution systems, avoiding the addition of salts or chemical inhibitors.
  • Industrial Cooling Systems: Preventing scale buildup in cooling towers, heat exchangers, and boilers, significantly reducing maintenance downtime and improving thermal efficiency.
  • Infrastructure Protection: Utilizing the process to maintain the internal diameter and flow rate of metallic pipes in water distribution networks by preventing spontaneous scale accumulation.
  • Resource Recovery: The recovered solid deposit (magnesian calcite/magnesium oxide carbonate) can be valorized for use in construction materials or other industrial applications.
View Original Abstract

This study focuses on preventing scale formation in hard waters by controlled electrode-position of Ca2+ and Mg2+ on a stainless-steel cathode at constant applied current intensity. The influence of the anode material, BDD or Ti/Pt/PbO2, cathode active area, stirring speed, and applied anodic current intensity on the inorganic carbon (IC), Ca2+, and Mg2+ removal was investigated. Assays were performed with model hard water solutions, simulating Bounouara (Algeria) water. The scaling inhibiting properties of the treated water were followed by measuring IC, calcium, and magnesium concentrations and chronoamperometric characterization of the treated solutions. The influence of the Ca/Mg molar ratio on the inorganic carbon removal by electrolysis was also evaluated, utilizing model solutions with different compositions. It was found that an increase in stirring speed or cathode geometric area favors IC and Ca2+ and Mg2+ removal rates. The applied current intensity was varied from 0.025 to 0.5 A, and the best results were obtained for 0.1 A, either in IC and Ca2+ and Mg2+ removals or by the accelerated scaling tests. However, energy costs increase with applied current. The deposit formed over the cathode does not seem to influence posterior deposition rate, and after eight consecutive assays, the solid deposition rate was kept constant. Ca/Mg ratio influences IC removal rate that increases with it. The results showed that hard-water scaling phenomena can be prevented by solid electrodeposition on the cathode at applied constant current.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1985 - DĂ©termination du caractĂšre incrustant d’une eau par un essai d’entartrage accĂ©lĂ©rĂ©
  2. 1996 - Estimation of the deposition rate of thermal calcareous scaling by the electrochemical impedance technique [Crossref]
  3. 1990 - CaractĂ©risation du pouvoir incrustant d’une eau par chronoampĂ©romĂ©trie au potentiel optimal d’entartrage
  4. 2010 - Characterization of natural scale deposits formed in southern Algeria groundwater. Effect of its major ions on calcium carbonate precipitation [Crossref]
  5. 2020 - Geochemical characterization and thermodynamic study of water scaling phenomenon at Tiznit region in Southern Morocco [Crossref]
  6. 2013 - Research progress of brackish water desalination by reverse osmosis [Crossref]
  7. 2019 - Selection of pretreatment technologies for seawater reverse osmosis plants: A review [Crossref]
  8. 2019 - Intermediate concentrate demineralization techniques for enhanced brackish water reverse osmosis water recovery—A review [Crossref]
  9. 2019 - Reverse osmosis pretreatment technologies and future trends: A comprehensive review [Crossref]
  10. 2019 - Scaling of reverse osmosis membranes used in water desalination: Phenomena, impact, and control; future directions [Crossref]

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