【作者】 章宣；

【导师】 李小斌；

【作者基本信息】 中南大学 ， 有色金属冶金， 2011， 硕士

【摘要】 在拜耳法生产氧化铝工艺中,种分过程是决定产品化学纯度和物理性能的关键步骤。尽管对种分过程已有大量研究,但我国氧化铝生产中晶种分解过程还是普遍存在分解率低、分解时间长、种子比大和设备产能低等问题。为了提高设备利用率,论文研究了溶液诱导方式和引发剂种类对铝酸钠溶液诱导成核制备晶种的分解过程的影响,并讨论了温度对少量溶液慢速诱导成核所制得晶种粒度的影响。结果表明：1)直接添加固体引发剂诱导成核的分解过程仅在低苛性比溶液和低分解初温的条件下才能进行,其产品粒度较细；少量溶液快速诱导成核的分解过程由于晶种制备段条件难以控制,故难以得到粗颗粒氢氧化铝；相比之下,少量溶液慢速诱导成核的分解过程控制较高的晶种制备段温度,却可得到粒度较粗的氢氧化铝产品；2)引发剂种类对铝酸钠溶液诱导成核制备晶种的分解过程有较大影响,其中引发剂A效果最佳；3)对于在少量溶液中慢速诱导成核制备晶种过程,温度越高,分解率越低,所得晶种粒度越大。在此基础上,为了控制所得氢氧化铝产品的粒度,本文研究了该分解过程中细颗粒的行为,并讨论影响细颗粒长大行为的因素和抑制细颗粒附聚的条件。结果表明：1)对于少量溶液慢速诱导成核制备晶种的分解过程,控制较高的晶种制备段温度(80℃)可制得粗晶种,可制得粒度约为50μm的氢氧化铝产品；2)对于铝酸钠溶液诱导成核制备晶种的分解过程,较低的分解温度(45-50℃)可抑制细颗粒的附聚,最终得到平均粒度为1-2μm的超细氢氧化铝产品,而有机添加剂B可强化分解过程,细化产品粒度,完善产品形貌；3)引发剂A的添加量增加促进分解过程的进行,但对细颗粒的长大无影响；晶种制备段较慢的诱导速度、溶液分段添加和有机添加剂E均可促进细颗粒的长大；铝酸钠溶液中碳酸钠和硫酸钠抑制分解过程,但可促进晶体长大；4)对于低温下大量活性晶种循环或高温下溶液中添加大量活性晶种的分解过程,细颗粒的行为以长大为主；对于高温下溶液中添加少量活性晶种的分解过程,细颗粒的行为以附聚为主；5)分解过程中添加适量工业粗晶种可减少产品中细颗粒的含量,粗晶种添加量越大,产品中细颗粒越少,但并未彻底粗化产品。更多还原

【Abstract】 The seeded precipitation of sodium aluminate solution is the key process to control the chemical purities and physical properties of products in the Bayer process of alumina production. Though numerous investigations on seeded precipitation have been undertaken, the low precipitation rate, the big ratio of seeds, long precipitation time and low equipment productivity are still the severe problems in the gibbsite (Al(OH)3) precipitation process. In order to improve the utilization efficiency of equipment, this paper investigated the influence of inducing methods and species of initiators on the precipitation process with seeds prepared by inducing nucleation in sodium aluminate solution. Furthermore, the effect of temperature on the particle size of seeds prepared by slowly inducing nucleation in a small amount of solution was also discussed. Conclusions are as follows:1) The precipitation process of inducing nucleation by directly adding solid initiator occurred only under conditions of low precipitation temperature and low caustic ratio of the sodium aluminate solution, and super-fine products can be achieved. The coarse aluminum hydroxide cannot be prepared in precipitation process of rapid inducing nucleation in a small amount of solution due to the difficulty in controlling the conditions in the stage of preparing seeds. In contrast, coarse aluminum hydroxide particles were achieved under high temperature in the stage of preparing seeds during the precipitation process with seeds prepared by slowly inducing nucleation in a small amount of solution.2) Initiator species had great influence on the precipitation process, and initiator A was the best one among them.3) The precipitation rate was low and the particle size of seeds obtained was large under the high temperature in the process of preparing seeds by slowly induced nucleation from a small amount of solution. And then, in order to control the particle size of products, this paper has investigated the behavior of fine particles in the precipitation process. The influences on the growing of fine particles and the conditions of inhibiting the agglomeration have also been discussed in this paper. Conclusions are as follows:1) Coarse products with mean particle size of 50μm were obtained in the precipitation process with coarse seeds prepared by slowly inducing nucleation in a small amount of solution under high temperature (80℃).2) Fine products with mean particle size of 1-2μm were obtained in the precipitation process with seeds prepared by inducing nucleation under low temperature (45-50℃) while the agglomeration was inhibited. Moreover, organic additive B can facilitate the precipitation process, refine the particle size of products and improve the morphology of products.3) When the amount of initiator A was increased, the precipitation rate raised, but the particle size of products remained the same. Meanwhile, the slow inducing rate in the process of preparing seeds, the fractionated addition of sodium aluminate solution and organic additive E can increase the particle size of products. In addition, the sodium carbonate and sodium sulfate in sodium aluminate solution inhibited precipitation, but facilitated the growth of particles.4) Grow-up was the dominant behavior of particles in solution when a great amount of seeds recycled under low temperature or a large amount of active seeds were added into solution under high temperature. Agglomeration was the dominant behavior of particles in solution when a small amount of active seeds were added into solution under high temperature.5) The appropriate addition of coarse seeds during the precipitation can reduce the amount of fine particles in the products. The more the addition amount, the less fine particles in the products, but the fine particles still existed in products.更多还原