【作者】 王伟；

【导师】 戴永年； 翟玉春；

【作者基本信息】 东北大学 ， 冶金物理化学， 2009， 博士

【摘要】 我国有丰富的镁资源,随着国民经济的快速发展,镁资源特别是矿产镁资源的消耗越来越多,优质资源急剧减少,因此对于低品位菱镁矿及其他含镁废弃物的利用研究日益迫切。本文设计了综合利用低品位菱镁矿和硼泥的“硫酸铵焙烧法”绿色新工艺,打通了工艺流程,优化了工艺参数,实现了化学品—硫酸铵的循环利用,研究了反应过程的动力学。制得了硫酸镁、氢氧化镁和氧化镁,并利用自制的MgO和CaO制备了镁钙砂,用纳米Mg(OH)2制备了防火涂料。取得结果如下：(1)采用硫酸铵焙烧法由低品位菱镁矿制备镁的化合物,通过单因素实验和正交实验优化了工艺条件。结果表明：随着焙烧温度的提高,镁的转化率先提高后降低；随着焙烧时间的延长和n((NH4)2SO4):n(MgO)的增大,镁的转化率提高。优化工艺条件为焙烧温度475℃,焙烧时间4 h,n((NH4)2SO4):n(MgO)1.1：1,此时镁的转化率为91.4%。检测表明,产物硫酸镁中Mg含量为9.72%,达到饲料级标准。(2)采用TG-DTA研究了轻烧镁粉与硫酸铵的反应过程,结果表明,该过程有三个放热峰,分别对应三个反应：(3)分别采用Kissinger法和Doyle-Ozawa法计算轻烧镁粉与硫酸铵反应各阶段吸热峰的表观活化能,结果如下三个反应峰的反应速率方程分别为第一个峰：第二个峰：第三个峰：(4)采用硫酸钱焙烧法由硼泥制取镁的化合物,通过单因素实验和正交实验优化了工艺条件。实验结果表明,随着焙烧温度的提高,镁的转化率先提高后降低；随着焙烧时间的延长和n((NH4)2SO4):n(MgO)的增大,镁的转化率提高；优化工艺条件为焙烧温度500℃,焙烧时间4 h,n((NH4)2SO4):n(MgO)1.2：1,此时镁的转化率为84.0%。(5)采用TG-DTA研究了硅酸镁与硫酸铵的反应过程,结果表明,该过程有三个放热峰,分别对应四个反应：(6)分别采用Kissinger法和Doyle-Ozawa法计算硅酸镁与硫酸铵反应阶段第一和第二吸热峰的表观活化能,结果如下两个反应峰的反应速率方程分别为第一个峰：第二个峰：(7)采用氨法由自制硫酸镁溶液制备微米氢氧化镁,研究发现,随着Mg2+初始浓度、反应时间、反应液pH值和陈化时间的增大,镁的沉淀率提高；随着反应温度和陈化温度的提高,镁的沉淀率先提高后降低。通过实验得到优化工艺条件为Mg2+初始浓度2.0 mo1·L-1,反应温度60℃,pH值11,反应时间60 min,此时Mg的沉淀率为90.1%。XRD分析表明产物为氢氧化镁,结晶良好。SEM检测表明,粉体颗粒呈粒径均匀的花状球形,微粒分散度良好,平均粒径约在2.5μm。TG-DTA分析表明Mg(OH)2的分解反应主要发生在310～390℃范围。(8)氨法制备氢氧化镁的晶体生长动力学研究表明,Mg(OH)2的晶体质量(即镁的沉淀率)和晶体平均粒径随着反应时间的延长呈指数增长,随着沉淀反应的进行,晶体的生长速率逐渐降低。m-t和D-t的关系式如下：(9)利用自制的高纯MgO微粉和CaO作原料,采用一步煅烧工艺制备高纯镁钙熟料,体积密度达到3.31 g·cm-3,显气孔率为1.08%。由于自制镁钙砂杂质含量少,其烧结性能和抗水化性能优于市售镁钙砂。添加TiO2微粉可有效促进镁钙砂的烧结,最佳添加量为1%,此时抗水化性能明显改善,超过1%后变化不明显。(10)采用氨水和氢氧化钠组成的复合碱液作为沉淀剂制备高纯纳米氢氧化镁粉体,研究发现随着Mg2+初始浓度的增加和反应温度的提高,粉体平均粒径先降低后增加；随着反应时间和陈化时间的延长,粉体平均粒径增加；随着搅拌强度的增加,平均粒径减小。当反应条件为Mg2+初始浓度2 mol·L1,反应温度50℃,反应时间60 min,搅拌强度900 r-min-1,陈化时间90 min时,所得氢氧化镁粉体为六方片状晶体,粒径在50～140 nm之间,平均粒径为91.4 nn。(11)以自制的Mg(OH)2纳米粉体为阻燃剂制备防火涂料,根据涂层的表观性能、干燥时问和耐燃性能进行检测,确定涂料的最优配方,该涂料达到国家一级技术标准；结合TG-DTA分析,表明自制纳米氢氧化镁有良好的阻燃作用。更多还原

【Abstract】 In our country, there are abundant magnesium resources. With the rapid development of national economy, the consumption of magnesium resources, especial mineral magnesium resources, is great more and more, the reserve of high-quality resources reduses rapidly, so it becomes increasingly urgent in the study for utilization of low-grade magnesite and other waster materials of MgO. In this dissertation, a green new technology, ammonium sulfate calcination method, was designed to realize the comprehensive utilization of low-grade magnisite and boron mud. The process flows were gotten through, the processing parameters were optimized, the chemical, (NH4)2SO4, realized recycling, the reaction kinetics was studied, the products of MgSO4·7H2O, Mg(OH)2 and MgO were prepared. Taking self-made MgO and CaO as raw materials, MgO-CaO clinker was prepared; taking nano-Mg(OH)2 as raw materials, fireproof paint was prepared. The following conclusions were obtained.(1) Compound of magnesium was prepared through ammonium sulfate calcination method from low-grade magnesite. The technological conditions were optimized through single factor experiments and orthogonal experiments. The results indicate that the conversion rate of Mg increases with the increasing of calcination temperature first then decreases, increases with the increasing of calcination time and mol ratio of (NH4)2SO4 and MgO. At the optimum technological conditions of alcination temperature 475℃, calcinations time 4 h, n((NH4)2SO4):n(MgO) 1.1:1, the conversion rate of Mg is 91.4%. The content of Mg in final product of MgSO4·7H2O is 9.72%, which meets feed-grade standard.(2) TG-DTA analysis was used to study the reaction mechanism of light-burned magnesia and ammonium sulfate. The results indicate there are three exothermic peaks, which are corresponding to three reactions (3) The apparent activation energies of three reactions of light-burned magnesia and ammonium sulfate were calculated through Kissinger method and Doyle-Ozawa method. The results are shown in following table.The reaction rate equations are First peak: Second peak: Third peak:(4) Compound of magnesium was prepared through ammonium sulfate calcination method from boron mud. The experiment results indicate that the conversion rate of Mg increases with the increasing of calcination temperature first then decreases, increases with the increasing of calcination time and mol ratio of (NH4)2SO4 and MgO. At the optimum technological conditions of alcination temperature 475℃, calcinations time 4 h, n((NH4)2SO4):n(MgO) 1.1:1, the conversion rate of Mg is 84.0%.(5) TG-DTA analysis was used to study the reaction mechanism of MgSiO3 and ammonium sulfate. The results indicate there are three exothermic peaks, which are corresponding to four reactions (6) The apparent activation energies of first and second reactions of MgSiO3 and ammonium sulfate were calculated through Kissinger method and Doyle-Ozawa method. The results are shown in following table.(7) Micro-Mg(OH)2 was prepared through ammonia precipitation method from self-made MgSO4 solution. The studies show that the precipitation rate of Mg increases with the increasing of initial concentration of Mg2+, reaction time, pH value and ageing time, increases first then decreases with the increasing of reaction temperature and ageing temperature. The optimum technological conditions obtained through experiments are initial concentration of Mg2+ 2.0 mol·L-1, reaction temperature 60℃, pH value 11, reaction time 60 min, at that time, the precipitation rate of Mg is 90.1%. XRD analysis indicates the product is Mg(OH)2 and well crystallized. SEM test indicates the grains are flower-like spherical, the granularity is uniform, the average grain size is about 2.5μm, the dispersivity is good. TG-DTA analysis indicates the decomposition of Mg(OH)2 occures at 310～390℃.(8) The studies of Mg(OH)2 crystal growth kinetics of ammonia precipitation method indicate the mass of Mg(OH)2, i.e. the precipitation rate of Mg, and the average grain size of crystal increase exponentially with the reaction time. With going on of precipitation reaction, the growth rate of crystal decreases gradually. The relations of m-t and D-t are(9) Taking self-made high-purity micro-MgO and CaO powder as raw materials, high-prity MgO-CaO clinker was prepared through one step sintering technics. The bulk density can be up to 3.31 g·cm-3, the apparent porosity is 1.08%. Because the impurities in self-made MgO-CaO clinker are few, the sintering character and hydration resistance are better than those of saled clinker. Adding TiO2 micro-powder in material can promotes the sinter properties of clinker, the optimum added amount is 1%, at that time, the hydration resistance improves greatly, after that the improvement is not significant.(10) Nano-Mg(OH)2 powder was prepared taking the mixed alkaline solution of ammonia and NaOH as precipitator. The studies indicate that the average particle size of powder decreases first then increases with the increasing of initial concentration of Mg2+ and reaction temperature, increases with the prolonging of reaction time and ageing time, decreases with the increasing of stirring rate. When initial concentration of Mg2+ is 2 mol·L-1, reaction temperature is 50℃, reaction time is 60 min, stirring rate is 900 r·min-1, ageing time is 90 min, the morphology of Mg(OH)2 particles is hexagonal flake, the grain size is 50～140 nm, the average diameter is 91.4 nm.(11) Taking self-made nano-Mg(OH)2 powder as fire retardant, fireproof paint was prepared. According to the appearance properties, dehydration times and resistance properties of fireproof coat, the optimum formulation was confirmed. This paint meets national first class technical standard, which and TG-DTA results indicate that self-made nano-Mg(OH)2 powder has good flame retardancy.更多还原