轻烧粉酸溶法制备氢氧化镁及热分解机理研究

Preparation of Magnesium Hydroxide by Acid Dissolution and Its Thermal Decomposition Mechanism by Light Burning Powder

以菱镁矿轻烧粉和盐酸为原料,经过酸溶反应得到酸溶精制液,再以氨气为沉淀剂制备氢氧化镁.研究酸溶过程中Mg^(2+)浸出率随酸矿比(HCl与MgO物质的量的比,以下同)、酸溶时间和盐酸浓度的变化规律;沉镁过程中反应温度、氯化镁初始浓度和氨镁比(氨气与氯化镁中Mg^(2+)物质的量的比,以下同)对Mg^(2+)转化率的影响.采用SEM和XRD对产品表征,利用热重分析对氢氧化镁在不同升温速率下热分解动力学和机理进行研究.结果表明:酸矿比1.9∶1、盐酸浓度2.0 mol/L、酸溶2 h时,镁离子浸出率达到89.4%;氯化镁浓度1.0 mol/L、80℃、氨镁比4∶1时,镁离子转化率达到91.8%.通过Doyle法和Kissinger法计算氢氧化镁热分解活化能,其平均热分解活化能为153.73 kJ·mol^(-1).对热重分析数据进行处理和拟合,判断氢氧化镁热分解反应机理函数为Avrami-Erfeev(n=1.5)的随机成核和随后生长机理.

Magnesium hydroxide was prepared from magnesite powder and hydrochloric acid through acid dissolution reaction,and then ammonia was used as precipitant.The variation of Mg^(2+) leaching rate with acid ore ratio(the amount ratio of HCl to MgO),acid dissolution time and hydrochloric acid concentration were studied.The effects of reaction temperature,initial concentration of magnesium chloride and ammonia magnesium ratio(the amount ratio of NH_(3) to Mg^(2+))on Mg^(2+) conversion rate during magnesium precipitation.The product was characterized by scanning electron microscope and X-ray diffraction.Thermal decomposition kinetics and mechanism of magnesium hydroxide under different heating rate were studied by thermogravimetric analysis.The results showed that acid ore ratio 1.9∶1,hydrochloric acid concentration 2.0 mol/L,acid dissolution 2 h,magnesium ion leaching rate reached 89.4%.When the concentration of magnesium chloride was 1.0 mol/L and the ratio of ammonia to magnesium was 4∶1 at 80℃,magnesium ion precipitation rate reached 91.8%.The thermal decomposition activation energy of magnesium hydroxide was calculated by Doyle method and Kissinger method,and its average thermal decomposition activation energy was 153.73 kJ·mol^(-1).The thermogravimetric analysis data were processed and fitted to determine that the thermal decomposition reaction mechanism function of magnesium hydroxide was the random nucleation and subsequent growth mechanism of avrami-erofeev(n=1.5).