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The Effect Of Crystallization Additive With Carboxyl Group On The Seeded Precipitation Process Of Supersaturated Sodium Aluminate Solutions

Posted on:2011-01-08Degree:DoctorType:Dissertation
Country:ChinaCandidate:B L LvFull Text:PDF
GTID:1101360305992867Subject:Metallurgical physical chemistry
Abstract/Summary:PDF Full Text Request
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.
Keywords/Search Tags:supersaturated sodium aluminate solutions, process enhancement, molecular design of crystallization additive with carboxyl, mechanism
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