Abstract
High purity magnesium hydroxide has been synthesised from seawater with the addition of dolomite lime as reagent. High intensity ultrasound-assisted crystallization of magnesium hydroxide was carried out during precipitation with the intention to obtain fine particles of Mg(OH)2 as well as to prevent their agglomeration. Investigations were conducted on magnesium hydroxide samples in the form of sludge and voluminous powder. The composition, morphology, and properties of the product were determined by chemical, XRD, FTIR, and SEM/EDS analysis. The particle size distribution was detected by the laser light scattering method. The results showed that the mean particle size of magnesium hydroxide sludge was 5.75 µm, while voluminous powder was 7.58 µm. The morphology of magnesium hydroxide voluminous powder was in the form of aggregated filamentous (up to 300 nm in size) or flake structures.
Highlights
Magnesium hydroxide is used in a wide range of applications, such as antibacterial agent, neutraliser of acidic water pollutants, liquid wastes and gases, filler in the paper industry, neutralising agent in pharmaceuticals, fertiliser additive, precursor for the production of magnesium oxide, as refractory material and flame retardant.[1,2,3,4] The method of synthesis and the process conditions affect the physicochemical properties of magnesium hydroxide, which are defined by shape, size, and degree of diversity of the particles.[4]
The results showed that the mean particle size of magnesium hydroxide sludge was 5.75 μm, while voluminous powder was 7.58 μm
The addition of a smaller amount of dolomite lime in the process of precipitation of magnesium hydroxide from seawater decreases the coagulation stability of the colloidal system by decreasing the electrokinetic potential, achieving an isoelectric point faster (ζ = 0), the results of which cause an increase in the rate of sedimentation and an increase in the capacity of the thickener
Summary
Magnesium hydroxide is used in a wide range of applications, such as antibacterial agent, neutraliser of acidic water pollutants, liquid wastes and gases, filler in the paper industry, neutralising agent in pharmaceuticals, fertiliser additive, precursor for the production of magnesium oxide, as refractory material and flame retardant.[1,2,3,4] The method of synthesis and the process conditions affect the physicochemical properties of magnesium hydroxide, which are defined by shape, size, and degree of diversity of the particles.[4]. Morphology of the synthesised particles can be in different forms: as needles, tubes, fibres, platelets, rods, and flowers.[4,5,6,7,8] Magnesium hydroxide can be obtained by various methods of synthesis from mineral resources such as magnesite, serpentinite, dolomite, carnallite, mineral salt and seawater.[9,10,11] Synthesis methods are sol-gel, chemical precipitation, electrochemical, solvothermal and hydrothermal, methods based on microemulsion, chemical vapour deposition, microwave, sonochemistry, and combustion.[4,8,12,13,14,15,16,17] Sonochemistry is the method in which molecules undergo a chemical reaction due to the application of powerful ultrasound radiation (20 kHz–10 MHz).[18] The observed chemical transformations generated through ultrasonic irradiation are not due to the interaction between the ultrasound and the substance, but a consequence of the effect of cavitation which the propagating ultrasound waves generate in a medium. Cavitation generates microbubbles with vapour in the liquid, accompanied by an inward collapse when the size of the bubble is no longer tenable
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