【作者】 张海宝；

【导师】 彭志宏；

【作者基本信息】 中南大学 ， 材料冶金， 2010， 硕士

【摘要】 在碱法生产氧化铝过程中,水合铝酸钙是一种重要的化合物,很容易广泛生成于生产的各个阶段,造成氧化铝的损失。3CaO·Al203·6H20是众多水合铝酸钙中最主要的一种,与水化石榴石化学性质相似。所以研究从水合铝酸钙中回收氧化铝不仅可以提高水合铝酸钙中氧化铝的回收率,而且对于从钠硅渣脱碱后渣(主要含水化石榴石)中回收氧化铝有重要的指导意义,另外对其他工业中产生的固体铝酸钙的处理同样有参考价值。本文在常压、较低温度条件下对从C3AH6中回收氧化铝进行了研究,并对相关反应机理进行了探讨；研究分为两步,首先在水中用CO2对C3AH6进行分解处理,使之分解为Al(OH)3和CaCO3,然后再用碱液从分解渣中浸出氧化铝。主要研究内容和结论如下：(1)对铝酸钙分解和分解渣溶铝过程进行了热力学分析。计算结果表明,用CO2分解处理C3AH6和用碱液从分解渣中回收氧化铝是可行的,为本文的实验研究提供了理论指导。(2)研究了温度、CO2浓度、时间、液固比和水合铝酸三钙生成条件对铝酸钙分解过程的影响,并对分解机理进行了探讨。结果表明,在空气和乙醇介质中,C3AH6与CO2间的反应十分缓慢；而在水中时,C3AH6的水化与HCO3-的生成使C3AH6与CO2之间分子与分子的作用变为水溶液中众多离子之间的作用,促进了C3AH6与CO2的反应速率,生成CaCO3、结晶不完善的Al(OH)3和H2O。提高反应温度、CO2浓度及延长反应时间均能提高C3AH6在水中与CO2的反应速率。C3AH6在水中与CO2反应存在两种主要的反应方式,即在反应初期主要取决于C3AH6的水化作用,反应中后期则以HCO3-分解C3AH6为主。(3)研究了起始苛性碱浓度、液固比,温度、时间和铝酸钠溶液组成等对分解渣溶铝过程的影响,并对溶铝过程机理进行了探讨。结果表明溶铝过程中氧化铝溶出率随起始苛性碱浓度的升高先升高后降低,随温度的升高而升高；溶铝过程中Al(OH)3的溶解反应与CaCO3的反苛化反应同时进行,明确了Al(OH)4对反苛化的促进作用；增加起始碳碱浓度、提高温度能有效抑制反苛化反应,提高氧化铝的溶出率,而添加草酸钠不能有效提高氧化铝溶出率。更多还原

【Abstract】 Hydrated calcium aluminates are important compounds in the alumina refining process by alkali method, which can be generated easily in various stages of production, resulting in the loss of alumina.3CaO·Al2O3·6H2O (C3AH6) is the foremost one among the numerous hydrated calcium aluminates, whose chemical property is similar with hydrogarnet. So to study the recovery of alumina from the hydrated calcium aluminates not only can raise alumina recovery rate, but also can be an important guideline for recovering alumina from dealkalization residue (mainly containing hydrogarnet); in addition, it can make reference to deal with the solid calcium aluminate produced by other industries.In this paper a novel method by which alumina is recovered from hydrated calcium aluminates at normal pressure and low temperature has been studied, and the related reaction mechanism has been discussed. The research consists of two steps, firstly hydrated calcium aluminates were decomposed into Al (OH) 3 and CaCO3 by using CO2 as the reagent in water medium, then alumina was dissolved from the residue by using alkali liquor. Main contents and conclusions are as follows:(1) Using C3AH6 as research object. Thermodynamic analysis of the process of decomposition and dissolving alumina were done. Results show that the decomposition by using CO2 as the reagent and the dissolving alumina by using alkali liquor are feasible, which provided a theoretical guidance for experimental research in this paper.(2) The influencing factors such as temperature, the concentration of CO2 in the mixture of CO2 and air, and reaction medium, the mechanism of decomposition were studied. Results show that the reaction rate of C3AH6 with CO2 is extremely slow both in the air and in the ethanol medium. However, in the medium of water, the reaction occurs quickly with the products of Al (OH) 3, CaCO3 and H2O, because the reaction of molecules between C3AH6 and CO2 has been changed into the reaction among the ions in aqueous solution as a result of the solvation of C3AH6 and the formation of HCO3. The reaction rate increases with the increase of the reaction temperature, CO2 concentration and reaction time. The mechanism of decomposition, that the reaction rate is determined mainly by the solvation of C3AH6 in the initial stage of the reaction and by the formation of HCO3 in the late reaction stage, is proposed by combining with the change of pH value in the reaction process.(3) The influencing factors such as initial concentration of Na2OK, L/S radio, reaction temperature, reaction time, CaCO3 and composition of aluminate solution and the mechanism of dissolving alumina were studied. Results show that the dissolution rate of alumina increases with temperature increment; it also increases with the elevation of initial concentration of Na2OK firstly, but decreases later. During the progress of dissolving alumina, the dissolution reaction of Al(OH)3 and the anti-causticization reaction of CaCO3 occur at the same time. Obviously the promotion of Al(OH)4- to the reaction of anti-causticization is confirmed. Increasing the initial concentration of Na2Oc and the reaction temperature can effectively inhibit the anti-causticization reaction, but the addition of sodium oxalate on the inhibition of anti-causticization is not obvious.更多还原