The Precipitation of Calcium and Magnesium From Sea Water by Sodium Hydroxide

Kapp, Eleanor M.

doi:10.2307/1536800

Cited by 27 publications

(23 citation statements)

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“…Local pH increases near the cathode during seawater (not artificially buffered) electrolysis can lead to precipitation of magnesium hydroxide (Mg(OH)2), which occurs when pH ≥ ~9.5(ref. 18 ), blocking the cathode 14,19 . Stabilization of pH fluctuations may require the addition of supporting electrolytes 20,21 .…”

Section: Acidicmentioning

confidence: 99%

Electrolysis of low-grade and saline surface water

et al. 2020

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Powered by renewable energy sources such as solar, marine, geothermal and wind, generation of storable hydrogen fuel through water electrolysis provides a promising path towards energy sustainability. However, state-of-the-art electrolysis requires support from associated processes such as desalination of water sources, further purification of desalinated water, and transportation of water, which often contribute financial and energy costs. One strategy to avoid these operations is to develop electrolysers that are capable of operating with impure water feeds directly. Here we review recent developments in electrode materials/catalysts for water electrolysis using low-grade and saline water, a significantly more abundant resource worldwide compared to potable water. We address the associated challenges in design of electrolysers, and discuss future potential approaches that may yield highly active and selective materials for water electrolysis in the presence of common impurities such as metal ions, chloride and bio-organisms. Freshwater is likely to become a scarce resource for many communities, with more than 80% of the world's population exposed to high risk levels of water security 1. This has been recognized within the Sustainable Development Goal 6 (SDG 6) on Clean Water and Sanitation 2. At the same time, low-grade and saline water is a largely abundant resource which, used properly, can address SDG 7 on Affordable and Clean Energy as well as SDG 13 on Climate Action. Hydrogen, a storable fuel, can be generated through water electrolysis and it may provide headway towards combating climate change and reaching zero emissions 3 , since the cycle of generation, consumption and regeneration of hydrogen can achieve carbon neutrality. In addition to providing a suitable energy store, hydrogen can be easily distributed and used in industry, households and transport. Hydrogen, and the related fuel cell industry, has the potential to bring positive economic and social impacts to local communities in terms of energy efficiency and job markets; globally the hydrogen market is expected to grow 33% to US$155 billion in 2022 4. However, there are remaining challenges related to the minimization of the cost and integration of hydrogen into daily life, as well as meeting the ultimate hydrogen cost targets of

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Section: Acidicmentioning

confidence: 99%

Electrolysis of low-grade and saline surface water

et al. 2020

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“…The amount of sodium hydroxide used (g/L) to raise the pH of seawater, quartz pulp and kaolin pulp, normalised by the amount required to obtain pH 12.2, is shown in Figure 5. A marked buffer effect was observed for pure seawater and quartz slurry between pH 10 and 11, which coincided with the formation of magnesium precipitates, where carbonate precipitation started at pH 9.3 and ended at pH 10, while hydroxide deposition started at pH 10.3 and completed at pH 11 [39][40][41]. This effect was not clear in the kaolin pulp, indicating a lower formation of magnesium precipitates, which is compatible with the loss of magnesium in solution (from 1380 to 659 mg/L).…”

Section: Formation Of Magnesium Precipitatesmentioning

confidence: 90%

“…For that matter, the pulp began to flow depending on both the applied stress and the time of stress application (Figure 9). Otherwise, for pulps in which there were no solid precipitates, the yield stress was a precise value: quartz pH 8, 55 Pa; kaolin pH 8, 38 Pa; and kaolin pH 10.7, 42 Pa. An exceptional contrast of the system that held precipitates (quartz at pH 10.7) with respect to the rest of the slurries is that the yield stress was displayed in a range of stress (40)(41)(42)(43)(44)(45)(46) Pa) instead of a single point. For that matter, the pulp began to flow depending on both the applied stress and the time of stress application (Figure 9).…”

Section: Creep Testsmentioning

confidence: 99%

Viscoelasticity of Quartz and Kaolin Slurries in Seawater: Importance of Magnesium Precipitates

Jeldres

Fuentes

Robles

et al. 2019

Metals

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In this study, the viscoelastic properties of quartz and kaolin suspensions in seawater were analysed considering two distinct conditions: pH 8 and 10.7. Creep and oscillatory sweep tests provided the rheological parameters. An Anton Paar MCR 102 rheometer (ANAMIN Group, Santiago, Chile) was used with a vane-in-cup configuration, and the data were processed with RheoCompassTM Light software (ANAMIN Group, Santiago, Chile). The outcomes were associated with the formation of solid species principally composed of magnesium precipitates. The magnesium in solution reduced in the presence of quartz (68 wt %), from 1380 to 1280 mg/L. Since the difference was not large regarding the solid-free seawater, the disposition of solid complexes at pH 10.7 was expected to be similar. The jump in pH caused both yield stress and viscoelastic moduli to drop, suggesting that the solid precipitates diminished the strength of the particle networks that made up the suspension. For the kaolin slurries (37 wt %), the yield stress raised when the pH increased, but unlike quartz, there was significant adsorption of magnesium cations. In fact, the concentration of magnesium in solution fell from 1380 to 658 mg/L. Dynamic oscillatory assays revealed structural changes in both pulps; in particular, the phase angle was greater at pH 8 than at pH 10.7, which indicates that at more alkaline conditions, the suspension exhibits a more solid-like character.

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“…These compounds are highly insoluble, and constitute precipitates at the anode and in the chamber. For this reason, it is necessary to previously remove the precipitable ions by adding sodium carbonate or sodium hydroxide [18].…”

Section: Test Sitementioning

confidence: 99%

Hypochlorite Generation from a Water Softener Spent Brine

Sánchez-Aldana

Ortega-Corral²,

Rocha-Gutiérrez

et al. 2018

Water

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Industries that require water with low hardness consume large amounts of NaCl for water softening. In this work, water softener spent brines were recovered and used as raw material in an electrolysis cell with cationic exchange membrane (CEM) to yield both sodium hypochlorite and sodium hydroxide amounts, which are the most common disinfectants used to sanitize production areas. Spent brines contained mainly an average of 4.5% NaCl, 650 mg L−1 Ca2+, and 110 mg L−1 Mg2+, the last two cations adversely affect the CEM and must be treated prior to the electrolytic process. Two hardness removal methods were evaluated separately—lime-soda ash and sodium hydroxide-soda ash softening—the last one being the most effective as total hardness was decreased by 99.98%. This pretreated spent brine was then introduced into the electrolysis cell. Experimental design comprised five level variations for current intensity, % NaCl, and time. The best operation conditions yielded 2800 mg L−1 NaOCl for a 5% NaCl solution. By incorporating chlorine gas trap to increase OCl− concentration a maximum of 7400 mg L−1 NaOCl was achieved. Finally, biocidal activity was tested following sanitation protocols (NaOCl dilution level) on workbenches and a decrease in bacterial count of at least 5 logs under laboratory-controlled conditions.

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The Precipitation of Calcium and Magnesium From Sea Water by Sodium Hydroxide

Cited by 27 publications

References 0 publications

Electrolysis of low-grade and saline surface water

Electrolysis of low-grade and saline surface water

Viscoelasticity of Quartz and Kaolin Slurries in Seawater: Importance of Magnesium Precipitates

Hypochlorite Generation from a Water Softener Spent Brine

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