高分子絮凝剂作用下的拜耳法赤泥沉降行为研究

【作者】 张琨瑜；

【导师】 胡慧萍；

【作者基本信息】 中南大学 ， 冶金物理化学， 2008， 硕士

【摘要】 我国一水硬铝石型铝土矿高压溶出后的赤泥沉降性能差，需添加高效絮凝剂以促进赤泥沉降。目前，国内使用的此类絮凝剂大多是进口产品。而且，对赤泥分离用高分子絮凝剂的设计和选型还没有有效的理论指导。本文对拜耳法赤泥在不同絮凝剂作用下的沉降行为进行研究，旨在探索赤泥与絮凝剂的相互作用机理。采用酸碱电位滴定研究了赤泥的表面电性。结果表明，聚丙烯酸钠（SPA）的吸附使赤泥表面羟基增多，零电点（PZC）下降；聚丙烯酰胺（PAM）的吸附使赤泥表面羟基减少，PZC升高。絮凝剂添加量增加，赤泥表面羟基的变化量增加。硅矿物（尤其是方钠石）含量越高，赤泥的表面羟基越多，PZC越低。通过赤泥沉降实验研究了赤泥沉降效果的影响因素。结果表明，过量的表面负电荷或正电荷使赤泥膨胀而难于下沉；絮凝剂添加量过多或过少都不利于赤泥沉降；SPA对赤泥沉降的促进作用不如PAM，对赤泥矿浆的澄清效果比PAM好；赤泥沉降速度随PAM的水解度增大明显降低；聚丙烯酰胺基甲基三甲基氯化铵（PATAC）对赤泥的沉降效果远不如SPA。采用电导／pH滴定和稀溶液粘度法分别测得PAM经NaOH溶液溶解后的水解度和特性粘度。结果表明，随着溶解PAM所用的NaOH浓度增大，PAM的水解度增大，生成的分子内氢键使PAM的特性粘度先增大后减小。热重和红外光谱分析表明，PATAC在高温高碱度溶液中不稳定，分解产物HPATAH中含有的-CH₂-OH和-CONH₂两种官能团形成-CH₂-OH～-CONH₂分子内氢键。对高分子絮凝剂与赤泥的相互作用机理作了一些探讨。SPA或PAM通过氢键或Ca²⁺等阳离子的“架桥”作用与赤泥表面发生吸附，不能有效降低赤泥矿浆的上清液浊度；水杨酸基团与赤泥表面的铁离子形成六元环螯合物，明显提高了赤泥矿浆的澄清度；高分子链上分子内氢键的形成使絮凝剂对赤泥的絮凝性能严重下降。更多还原

【Abstract】 Red mud generated from Chinese diaspore bauxite has a poor settling performance, so that red mud settlement requires excellent polymeric flocculants. However, most of these excellent polymeric flocculants are imported products. In the view of a lack of theoretical basis for the design and selection of polymeric flocculants used in red mud separation, the settling behaviour of red mud treated by different flocculants was studied in this paper to investigate the interaction mechanism between red mud and flocculants.Red mud surface charge properties were investigated using acid/basic potentiometric titration. The results show that the adsorption of sodium polyacrylate （SPA） causes the increase of red mud surface hydroxyl groups and the decrease of the red mud point of zero charge （PZC）. However, the adsorption of polyacrylamide （PAM） causes the reverse result. The changed amount of red mud surface hydroxyl groups increases with the dosage increase of flocculants. The more the silica-containing compounds in red mud, especially in the case of sodalite, the more the red mud surface hydroxyl groups and the lower the PZC.The factors to affect red mud settlement were studied by red mud settling tests. The results show that excessive negative or positive surface charges result in a failed red mud settlement. Neither excessive nor insufficient flocculants are helpful for red mud settlement. Red mud treated by SPA has a lower settling rate than by PAM, but has a higher supernatant clarity degree. Red mud settling rate decreases obviously with the increase of the PAM hydrolysis degree. Red mud settling results from polyacrylamidomethyltrimethyl ammonium chloride （PATAC） are much worse than those from SPA.The hydrolysis degree and intrinsic viscosity of PAM dissolved in NaOH were measured by conductivity/pH titration and Ubbelodhe viscosimetric measurement, respectively. The results indicate that the hydrolysis degree of PAM dissolved in NaOH solution increases with the increase of NaOH concentration and the intrinsic viscosity increases at first and then decreases due to the formation of intramolecular hydrogen bonds. The results from thermogravimetric analysis and infrared spectral analysis show that PATAC is unstable in caustic solution at a higher temperature and its decomposition product HPATAH has two functional groups of -CH₂-OH and -CONH₂ to form a -CH₂-OH～-CONH₂ intramolecular hydrogen bond.Some interaction mechanisms between polymeric flocculants and red mud were discussed. SPA and PAM interact with red mud surface by hydrogen bond or Ca²⁺ bridge, which cannot effectively reduce the supernatant turbidity of red mud slurry. And the salicylate group forms a stable six-membered ring complex with Fe³⁺ from red mud surface to greatly improve the supernatant clarity degree. The formation of intramolecular hydrogen bonds in polymer chains results in the flocculants having a poor flocculation performance for red mud.更多还原