Key influencing factors for magnesium hydroxide microparticle “nucleation-crystallization-growth” using saline-lake hydromagnesite

The effects of different precipitants, magnesium source concentration, precipitant concentration, feed rate and precipitation temperature on the particle size of MH were compared with the chemical precipitation method and the hydrothermal method. Under the optimum conditions, the particle size and D 50 of MH were 0.47 um and 0.41 um, which is equivalent to the MC-1-2 standard of magnesium hydroxide for flame retardants. The test results show that the dosage ratio of Mg 2+ /OH − has the greatest influence on the crystallization nucleation process of MH. When ammonia water is used as precipitant, the reaction is smoother and there is more water of crystallization in the MH core, which helps to improve the flame retardant effect of MH. In addition, the hydrothermal conditions can effectively control the structure of the crystal surface, thus improving the phenomenon of agglomeration. Theoretical studies show that the reason for the high surface energy and strong polarity of MH surface is due to the insufficient formation of (001) crystal plane and the increase of work function after the adsorption of hydroxyl (OH − ) by MH. A large number of hydroxyl groups on the surface imparts “hydrophilicity” to MH. Therefore, one of the strategies to improve the aggregation of MH surface may be to promote the formation of (001) crystal plane and avoid the adsorption of OH − in the process of MH “nucleation and crystallization growth” . This study provides an improved idea for the synthesis strategy of “seed crystallization growth” of magnesium hydroxide.