【作者】 吕保林；

【导师】 陈启元；

【作者基本信息】 中南大学 ， 冶金物理化学， 2010， 博士

【摘要】 氧化铝生产过程中过饱和铝酸钠溶液种分过程是重要工序之一。种分分解速率过低,氢氧化铝产品粒度分布不均等问题严重制约着氧化铝工业的发展。众多强化方法中,结晶助剂强化法具有明显的优越性。但目前对结晶助剂的遴选一直处于经验水平。本文采用分子拆分法、QSPR模型构建法,结合量子化学计算、PSD、FT-IR、27Al-NMR、Raman、SEM等分析测试手段,分别研究了丙氨酸、Na4EDTA及EDTA、单羧基芳香族羧酸、21种L型氨基酸等多种有代表性的含羧基结晶助剂对铝酸钠溶液种分过程的影响及其作用机理,总结了含羧基结晶助剂分子设计的一般性规则,可望为工业结晶助剂的分子设计及遴选提供理论基础。具体结论如下：1.系统研究了丙氨酸及其拆分分子对铝酸钠溶液种分过程的影响。发现α-丙氨酸的抑制作用源于其分子中氨基或羧基对氢氧化铝表面“活性点”的封闭；促进作用源于其分子中氨基和羧基的共同作用。α-丙氨酸使铝酸钠溶液种分分解率改变的本质可能源于溶液中铝酸根离子之间平衡的打破,也可能源于溶液中新的含铝组元的产生。丙氨酸对种分分解率大小、氢氧化铝附聚大小及附聚周期的影响与其分子中氨基和羧基的相对位置有关；丙氨酸对种分分解率及氢氧化铝附聚随种分时间变化趋势、氢氧化铝附聚随丙氨酸浓度变化趋势的影响则与其分子中氨基和羧基的相对位置无关。α-丙氨酸的吸附改变了氢氧化铝(001)面及(100)面的电子结构,表现为“电子给体”。2.系统研究了Na4EDr队和EDTA对铝酸钠溶液种分过程的影响。对比研究发现EDTA阴离子或者直接作用于铝酸根离子,或者通过水分子间接作用于铝酸根离子,或者通过两种方式同时作用于铝酸根离子,促进了新的含铝组元的生成,改变了铝酸钠溶液结构,强化了种分分解；H+通过中和反应促进了种分分解；Na+可能通过其与铝酸根离子形成Na(H2O)4+·Al(OH)4-离子中间体促进了种分分解。Na4EDTA和EDTA对氢氧化铝附聚随结晶助剂浓度变化趋势及氢氧化铝附聚周期影响的不同与Na+和H+有关。3.系统研究了单羧基芳香族羧酸对铝酸钠溶液种分过程的影响。发现单羧基芳香族羧酸对铝酸钠溶液种分分解的抑制作用源于其对氢氧化铝表面“活性点”的封闭,抑制顺序与其分子中氧原子所带净电荷数呈对应关系；对氢氧化铝附聚的抑制作用可能与其偶极矩及附加偶极矩有关；对氢氧化铝长大方式的影响与苯环上烷基和结晶助剂浓度有关。单羧基芳香族羧酸的吸附改变了氢氧化铝(001)面和(100)面的电子结构,’表现为“电子给体”。4.构建了氢氧化铝中位粒径变化与21种L型氨基酸结晶助剂分子描述符之间的QSPR模型,最佳模型表达式如下：△d50=0.4188(R3p)+2.1181(C-006)-0.8283(Mor04v)+2.4709(Mor07u) +1.0809(Mor10e)-1.3492 (n=21,RMSECV=1.6558,q2=0.6908,R2=0.7654)5.总结了结晶助剂分子设计的一般性规则,即：(1)氨基和羧基相距较近的的脂肪族类结晶助剂有利于强化铝酸钠溶液种分分解；氨基和羧基相距较远的脂肪族类结晶助剂有利于强化氢氧化铝附聚。(2)分子中同时含有多个羧基和氨基的脂肪族类结晶助剂有利于强化铝酸钠溶液种分分解。(3)分子中含有单羧基的芳香族类结晶助剂不利于强化铝酸钠溶液种分分解和氢氧化铝附聚。(4)分子中原子间距较小且含有较多的同时连有烷基和杂原子的亚甲基的L型氨基酸类结晶助剂,有利于强化氢氧化铝附聚。更多还原

【Abstract】 The crystallization of Al(OH)3 from seeded supersaturated sodium aluminate solutions is one of the most important processes in alumina production. But the development of alumina industry is seriously restricted by many problems such as the slow seeded precipitation rate and too broad distribution of the particle size of Al(OH)3 product. Among all the enhancing methods, the advantage of crystallization additive is obvious. But the selection of crystallization additive keeps on the empirical level at present.The effects of many representative crystallization additives with carboxyl group on the seeded precipitation process of sodium aluminate solutions and the interaction mechanisms in sodium aluminate solutions were investigated by the molecular separation and a QSPR model in combined with the quantum chemistry calculation, PSD, FT-IR, 27Al-NMR, Raman, SEM, et al, respectively. These crystallization additives involve alanine, Na4EDTA, EDTA, monosubstituted aromatic carboxylic acid, and twenty one kinds of L-amino acids. The general rules of the molecular design of the crystallization additive with carboxyl group were obtained, which could offer a theoretical basis for the molecular design and the selection of the crystallization additive in alumina industry. The inclusions were drawn as follows:1. Effects of alanine and its separation molecular on the seeded precipitation process of sodium aluminate solutions were investigated systematically. It was found that the inhibitory effect of a-alanine was derived from the occupied active sites on the surface of Al(OH)3 by amino group or carboxyl group in a-alanine; the positive effect resulted from the combined action between amino group and carboxyl group in a-alanine. The essence of the change of the seeded precipitation ratio of sodium aluminate solution caused by a-alanine could originate from the imbalance among aluminate ions present in solution, and might also be derived from the formation of the new component containing Al element in solution. The effects of a-alanine on the amount of the seeded precipitation ratio, the amount of the agglomeration of Al(OH)3 and the agglomeration period of Al(OH)3 were correlative with the relative position of amino group and carboxyl group in a-alanine. The effects of a-alanine on the tendency of the change of the seeded precipitation ratio and the agglomeration of Al(OH)3 with the seeded time, and on the tendency of the change of the agglomeration of Al(OH)3 with the concentration of alanine were independent on the relative position of amino group and carboxyl group in a-alanine. The change of the electron structure of (001) and (100) surface of Al(OH)3 took place in the existence of a-alanine. a-alanine was shown as "electron donor".2. Effects of Na4EDTA, EDTA on the seeded precipitation process of sodium aluminate solutions were investigated systematically. It was comparatively found that the generation of the new component containing Al element was derived from the direct interaction or the indirect interaction via water molecular or both of the two interactions between EDTA anion and aluminate ion, which alters the structure of sodium aluminate solution and enhances the seeded precipitation. The seeded precipitation process of sodium aluminate solutions was accelerated by H+ with neutralization reaction. The seeded precipitation process of sodium aluminate solutions was accelerated by Na+, which could possibly result from the formation of Na(H2O)4+·Al(OH)4-. The effects of Na4EDTA on the tendency of the change of the agglomeration of Al(OH)3 with the concentration of the crystallization additive and the agglomeration period of Al(OH)3 were different from that of EDTA, which was related with the existence of Na+and H+.3. Effects of monosubstituted aromatic carboxylic acid on the seeded precipitation process of sodium aluminate solutions were investigated systematically. It was found that the inhibitory effect on the seeded precipitation of sodium aluminate solution was originated from the occupied active sites on the surface of Al(OH)3 caused by monosubstituted aromatic carboxylic acid, the inhibitory order was corresponding with the net charges of oxygen atoms in monosubstituted aromatic carboxylic acid. The inhibitory effect of monosubstituted aromatic carboxylic acid on the agglomeration of Al(OH)3 was possibly related with the dipole moment and the additional dipole moment of the crystallization additive. The growth style of Al(OH)3 affected by monosubstituted aromatic carboxylic acid was connected with alkyl in benzene ring and the concentration of crystallization additive. Monosubstituted aromatic carboxylic acid could change the electron structure of (001) and (100) surface of Al(OH)3 change and was shown as "electron donor".4. The QSPR model between the change of the median particle size of Al(OH)3 and the molecule descriptors of twenty one kinds of L-amino acids was established. The best QSPR model was established as follows:△d50＝0.4188(R3p)+2.1181(C-006)-0.8283(Mor04v)+2.4709(Mor07u) +1.0809(Mor10e)-1.3492 (n=21, RMSECV=1.6558, q2=0.6908, R2=0.7654, F=9.8402)5. The general rules of the molecular design of the crystallization additive were summarized as follows:(1) Aliphatic crystallization additive containing amino group and carboxyl group which has short distance and long distance could enhance the seeded precipitation of sodium aluminate solutions and the agglomeration of Al(OH)3, respectively.(2) Aliphatic crystallization additive simultaneously containing multiple carboxyl groups and amino groups could enhance the agglomeration of Al(OH)3.(3) Aromatic carboxylic additive crystallization aid containing single carboxyl group could not enhance the seeded precipitation of sodium aluminate solutions and the agglomeration of Al(OH)3.(4) L-amino acid where the distance of atoms is smaller and there has multiple methylenes simultaneously connected with alkyl and heteroatom could enhance the agglomeration of Al(OH)3.更多还原