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Magnesium hydroxide is an environmentally friendly and efficient material for the removal of harmful constituents from water by adsorption. The crystal facets and morphology have an important influence on the adsorption performance, thus the controllable growth of Mg(OH)2 and modification of its adsorption capacity has been a research focus. Herein, we report a solvent control method for synthesizing Mg(OH)2 with different polarities. By introducing ethanol and ethylene glycol in the crystallization solvent, the growth of crystal facets can be selectively promoted or inhibited. Besides, the adsorption of Congo red increases with the increase in the proportion of the (101) crystal facet, and Mg(OH)2 with large polarity and adsorption capacity can be obtained. Adsorption thermodynamics and kinetics show that the adsorption process is more consistent with the Langmuir isothermal adsorption model and quasi-second-order kinetic model. The removal rate of Congo red could reach 96%, and the maximum adsorption capacity reached 116.414 mg g−1. [ABSTRACT FROM AUTHOR]

In this paper, the effect of Na+ concentration on the crystalline phase, morphology, and content of vaterite in a system with different Ca2+ and CO32− ratios using steamed ammonia liquid waste as the calcium source was investigated, and the effect of Na+ on the yield of vaterite was studied systematically for the first time. The obtained products were characterized by powder X-ray diffraction (XRPD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, laser particle size analysis (LPSA), and so on. The results show that the variation of Na+ concentration in different Ca2+ and CO32− ratio systems has an effect on the particle size, morphology, content, and CaCO3 yield of vaterite. Thermogravimetric (TG) analysis indicates that Na+ is involved in forming CaCO3 but does not enter the interior of the vaterite crystals. Mechanistic analysis shows that changes in Na+ concentration can alter the initial pH of the reaction system and the conductivity of the solution, thus changing the processes such as early nucleation and crystal growth of vaterite as well as inhibiting the vaterite phase transition, which determines the particle size of the vaterite obtained. This study reveals to a certain extent the influence of Na+ on the early nucleation and crystal growth of vaterite and provides theoretical support for the realization of large-scale industrial production of vaterite. [ABSTRACT FROM AUTHOR]

Magnesium hydroxide (Mg(OH) 2 ), as a green halogen-free flame retardant, has attracted significant attention in the field of flame retardant composite materials. In addition to conventional indicators such as purity and whiteness, Mg(OH) 2 is required to take the form of regular hexagonal sheets to ensure the dispersion of composite materials. We use irregular large particles of Mg(OH) 2 prepared by the magnesium factory in western Qinghai as raw materials to study the influence of alkali metal ions K + and Na + mainly present in salt lakes on the physicochemical properties of Mg(OH) 2 . The products were characterized via X-ray diffraction, scanning electron microscopy, automatic nitrogen physical adsorption apparatus, and other modern characterization techniques. Results show that alkali metal ions K + and Na + considerably influence the crystal surface polarity, particle size, and morphology of the prepared Mg(OH) 2 . The mechanism analysis shows that the presence of K + and Na + alters the dissolution, recrystallization, and growth characteristics of Mg(OH) 2 . This study provides theoretical support for the realization of high-performance Mg(OH) 2 using salt lake resources and demonstrates the value for promoting the large-scale industrial application of the salt lake industry., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)