Salt Lake Bischofite Preparation Of Ultrafine Flame Retardant Magnesium Hydroxide

Magnesium hydroxide is one of the most promising flame retardant among polyolefine flame retardants without halogen. The preparation of ultra-fine magnesium hydroxide was investigated under the condition of normal pressure from the saline bischofite, and then the fire retardant effect of modified magnesium hydroxide on linear polyethylene with low density was examined. Furthermore, the study concerning the reclamation and utilization of ammonia in mother liquor of the deposition reactor was performed.Firstly the paper discussed the preparation technique of the fire retardant magnesium hydroxide from the saline bischofite.And it discussed the feasibility of the preparation of ultra-fine magnesium hydroxide under normal pressure so as to alter traditional synthesis techniques under high temperature and pressure. The thermodynamics study indicated the negatively absolute value changes of Gibbs free energy is more 63kJ/mol as for the reaction of the saline bischofite ammonia under normal pressure, the trend of the reaction is big. In the other hand, the reaction is also belonged to ion-deposited reaction ,getting a high velocity, and the technological flow of ultras-hydroxide magnesium was decided according to the principal.Secondly the technics condition of ultra-fine magnesium hydroxide from the saline bischofite was discussed through lots of experimentations. The optimum experimental conditions during the preparation of ultra-fine magnesium hydroxide under normal pressure were explored. The result indicated that the recovery ratio is 80.5 % when the bittern and ammonia was added simultaneously, and the concentration of bittern is 4.3mol/L, the concentration of ammonia is 28%, the reaction temperature is 55C, the joining velocity of saline bischofite is 3.3 ml/minute, the pH of substrate liquid is about 11. Under ultrasonic dispersing with alcohol solvent, the result showed that the mean particle size of the magnesium hydroxide was 200~300nm and the specific surface area was 48.1+0.5m2/g, among which whose volume percentage with particle sizeless than 1um is more 98%. The samples assume the shape of platelet and belongs to the hexagonal crystalline system. The purity of the samples was more 98 %.Then the magnesium hydroxide after preparation was modified with stearic acid salt. The retarded experimental results demonstrate that the optimum experiment condition is as follows: the modifying additive is sodium stearate, the modification time is 4 hours, the dosage of sodium stearate is 5%, and the modification temperature is 70C. The study discover the angle of contact is 132.6 degree after surface modification,and indicate the magnesium hydroxide of polarity is changed from hydrophilicity to hydrophobicity, and the result is good. Then the samples of linear polyethylene with low density were prepared by liquation method. The oxygen index of the linear polyethylene with low density was 30.5 % when 140 shares of modified magnesium hydroxide was added(usually polymer with an oxygen index more than 27 was called retarded materials).It can satisfy the requirement for the flame retardant of magnesium hydroxide.Finally it also studied the ammonia recovery and reclamation in mother liquor of deposit magnesium hydroxide experiment. The once evaporation method by adding calcium oxide was adopted. The recovered ammonia was returned into experimental process. It indicated that the once conversion is about 98% .So it can considerably reduce production cost and boost economic benefit.