Research On The Preparation Of Flame-retardant Magnesium Hydroxide With Ammonium As Precipitant

Magnesium hydroxide as a flame retardant has attracted great concern owing to its non-toxic, smoking-free, thermally stable and neutralizing with acid gas to reduce environmental pollution. Magnesium hydroxide decomposes into magnesium oxide and water. Magnesium hydroxide absorbs large amounts of heat in the process of decomposition to lower the temperature around the burning material. Magnesium oxide can prevent further combustion. Rich magnesite resource in our country provides sufficient guarantee for the development of magnesium hydroxide. In this paper, magnesium hydroxide was synthesized through ammonium hydroxide as precipitation agent. In order to get better technological conditions, We studied the different processing conditions of magnesium hydroxide in the preparation process, including the concentration of ammonium hydroxide, feed rate, mixing rate, and tested filtration rate and the natural sedimentation rate. The filtrate after precipitation of MgCl2·6HaO with NH3·H2O was tested. Filtrate contains magnesium chloride, ammonium hydroxide and ammonium chloride, and the concentration of each component in the filtrate was relatively thin. Large amounts of energy were consumed in the way of direct evaporation or salting out crystallization. In this paper, we used calcium hydroxide to deal with the filtrate.1. Synthesis of Magnesium hydroxide by Ammonium hydroxideIn this part, Magnesium hydroxide was synthesized through MgCl2·6H2O and NH3·H2O at ambient temperament, and then transferred to the autoclave. We study the different influences of synthesis parameters on the morphological characteristics and size distribution in the preparation process, including the concentration of ammonium hydroxide, feed rate, mixing rate. The results show that the mean particle size of the magnesium hydroxide is about 700-900 run with hexagonal structure and the specific surface area is about 19.7 m2/g when the concentration of ammonia hydroxide is 4 mol/l, feed rate is 2 ml/min, mixing rate 200 rpm and the temperature is 180 ℃for 4 h during the reaction process.2. Calcium hydroxide method to deal with the filtrate.In this paper, we used calcium hydroxide to deal with the filtrate. A series of synthesis parameters were studied on the purity and the yield of magnesium hydroxide, including the amount of calcium hydroxide, reaction temperature and time. The results show that the yield of magnesium hydroxide is about 96%, the purity of magnesium hydroxide is about 83%, when the ratio of practical and theoretical is 1:1, the reaction time is 15 min in each temperature of 90 ℃ and 100 ℃.