【作者】 吴鹏；

【导师】 刘桂华；

【作者基本信息】 中南大学 ， 材料冶金， 2022， 博士

【摘要】 有机物对全球氧化铝生产的负面影响已达数十年之久。铝土矿中的腐殖酸、纤维素和木质素等高分子量有机物在高温（323～553 K）、高压（1.0～4.5 MPa）、浓碱(Na₂O>2.10 mol·L^-1)、高离子强度(I>1.8mol·L^-1)和母液长期循环等条件下会不断分解,并在溶液中积累了成百上千种不同类型的有机物。在过去的二十年里,有机物对工业生产氧化铝的危害,如苛性碱和氢氧化铝的损失、大量泡沫的生成、晶种分解被抑制等,已经变得愈来愈显著。由于工业铝酸钠溶液具有温度高、碱性强、离子强度高和有机物浓度高等特点,吸附法、母液焙烧法和石灰苛化法等已有的有机物脱除方法目前难以克服成本高、效率低和工艺复杂等问题。本文针对有机物在铝酸钠溶液中的赋存状态和界面行为不明确等问题,采用表面张力法、荧光探针法和热力学计算等方法,并结合Langmuir-Blodgett（LB）膜技术,阐明了有机物在铝酸钠溶液中的界面排列、胶束化行为以及有机物分子间的相互作用规律。在此基础上,提出了泡沫浮选分离的方法,实现了铝酸钠溶液中多种有机物的高效富集和经济脱除,揭示了有机物在不同条件下的浮选脱除规律。此外,基于工业铝酸钠溶液中总有机碳浓度高、泡沫丰富的事实,在无需使用任何添加剂的情况下,验证了泡沫浮选法在工业铝酸钠溶液中高效经济脱除有机物的技术可行性并开发了原则流程。主要研究内容和结论如下:（1）明确了单一有机物在合成铝酸钠溶液中的界面行为。通过测定有机物在合成铝酸钠溶液中的表面张力-浓度（γ-lgC）曲线,明确了草酸钠和苯甲酸钠等有机物在铝酸钠溶液中具有良好的表面活性,并揭示了温度和碱浓度等因素对其表面活性的影响。在相同条件下,有机物在合成铝酸钠溶液(C_Na2O=2.42 mol·L^-1,α_k=1.45)中的临界胶束浓度的大小顺序为:酒石酸钠>草酸钠>柠檬酸钠>苯甲酸钠>月桂酸钠>硬脂酸钠。通过芘荧光探针法验证了有机物胶束的形成过程,结果显示月桂酸钠和硬脂酸钠的临界胶束浓度分别为1×10^-3.4mol·L^-1和1×10^-3.6 mol·L^-1,与表面张力法所得结果相吻合。有机物在铝酸钠溶液中胶束形成过程的热力学计算结果表明该过程趋向于无序状态的自发进行。在298 K下,有机物最大表面吸附量的大小顺序为:草酸钠>苯甲酸钠>月桂酸钠>柠檬酸钠>硬脂酸钠。此外,有机物的最小平均分子截面积与吸附层厚度随其碳链的增长而增大;温度升高会导致有机物的最小平均分子截面积和吸附层厚度增大,而最大表面吸附量减小。（2）阐明了混合有机物在合成铝酸钠溶液中的复杂界面行为。以草酸钠/苯甲酸钠和柠檬酸钠/月桂酸钠等有机物的二元混合体系为研究对象,确定了其在合成铝酸钠溶液中不同温度下的临界胶束浓度。通过与单一体系的结果对比,证明了草酸钠会抑制共混体系在铝酸钠溶液中胶束的形成,而硬脂酸钠等长链有机物会促进这一过程。共混体系在铝酸钠溶液中形成胶束的能力随着温度的升高而减弱。草酸钠和柠檬酸钠在铝酸钠溶液中对其他有机物的表面吸附量和平均分子截面积有着不同的作用。在Gibbs吸附公式和Clint模型的基础上,以表面活性剂非理想混合模型计算了有机物混合体系在铝酸钠溶液中的分子间相互作用参数和临界胶束浓度,结果显示计算结果与实验测定值较为吻合。此外,三元有机物混合体系的界面行为较复杂,还有待进一步的研究。（3）发现了合成铝酸钠溶液中的多层吸附现象。在不同铺展浓度等条件下,分析了苯甲酸钠等低分子量有机物和月桂酸钠等中等分子量有机物及其混合体系在空气/铝酸钠溶液界面上的聚集行为和界面结构。有机物Langmuir单层的π-A等温线和LB膜的微观形貌显示,随着有机物铺展浓度的增加,铝酸钠溶液亚相的崩溃压增大,π-A等温线向左平移,有机物的最小平均分子面积减小;硬脂酸钠和月桂酸钠在界面上的胶束尺寸随铺展浓度的增加而增大。此外,棕榈酸钠和油酸钠在混合体系中的引入改变了硬脂酸钠LB膜的高度和形貌。（4）开发了泡沫浮选脱除铝酸钠溶液中有机物的技术原型。相比于合成铝酸钠溶液,工业铝酸钠溶液的起泡能力更强,气泡的尺寸（分布）小,稳定性好。选用十二烷基硫酸钠（Sodium dodecyl sulfate）作为起泡剂和捕收剂,研究了苯甲酸钠等有机物在合成铝酸钠溶液中的泡沫富集分离过程,结果显示有机物的脱除率和富集比值均随有机物浓度和温度的升高而增大。同时,有机物在铝酸钠溶液表面形成的紧密的多层吸附结构促进了泡沫浮选法对有机物在气/液界面的高效富集。在333 K时,泡沫浮选法对硬脂酸钠的脱除率达到了29%以上,富集比值为2.42～3.02。此外,选用两种不同的工业铝酸钠溶液验证了泡沫浮选法在实际生产中的可行性。在没有使用任何添加剂的情况下,Zunyi（ZY）拜耳液中有机物的富集比值超过了2.71,而Nanshan（NS）拜耳液中达到了3.46。对泡沫浓缩液进行分离和干燥处理后,固体样品中总有机碳含量超过了20%。最后,开发了泡沫浮选脱除铝酸钠溶液中有机物的原则流程。图67幅,表26个,参考文献259篇更多还原

【Abstract】 The negative effect of organics on the global alumina production process has been for decades.Under the conditions of high temperature（323～553 K）,high pressure（1.0～4.5 MPa）,high concentration of alkali(Na₂O>2.10 mol·L^-1),high ionic strength(I>1.8mol·L^-1)and long-term circulation of liquor,high molecular weight organics such as humic acid and lignin in bauxite degrade continuously and generate hundreds of different types of organics in the solution.In the past two decades,the harm of organics to industrial alumina production,such as loss of caustic soda and aluminum hydroxide,formation of rich foam,inhibition of seed decomposition and other problems,has become more and more obvious.Due to the high temperature,strong alkalinity,high ionic strength,and high organic concentration in the Bayer liquor,the existing organic removal methods such as adsorption method,solution roasting method and lime causticizing method are difficult to overcome the problems of high cost,low efficiency,and complex process.In this thesis,the interfacial structure,micellarization behavior,and the interaction law between organic molecules of organics were studied by surface tension method,fluorescence probe method,and thermodynamic calculation combined with Langmuir-Blodgett（LB）film balance technique,in response to the problems of unclear occurance and interfacial behavior of organics in the sodium aluminate solution.On this basis,a froth flotation method was proposed to realize the efficient enrichment and economic removal of various organics in the sodium aluminate solution.At the same time,the flotation removal law of different organics under different conditions was discussed.In addition,based on the fact of high total organic carbon concentration and rich foams in industrial sodium aluminate solutions,the technical feasibility of the froth flotation method for the efficient and economic removal of organics from the industrial sodium aluminate solution was verified without the use of any additives,and the basic flow was proposed.The main conclusions are as follows:（1）The interfacial behavior of single organic matter was clarified in the synthetic sodium aluminate solution.The surface tension-concentration（γ-lgC）curves of organics in the synthetic sodium aluminate solution were determined and it was clear that organics such as sodium oxalate and sodium benzoate had good surface activity in the sodium aluminate solution.The effects of factors such as temperature and alkali concentration on their surface activity were revealed.Under the same conditions,the order of the critical micelle concentrations of the organics in the synthetic sodium aluminate solution(C_Na2O=2.42 mol·L^-1,α_k=1.45)was:sodium tartrate>sodium oxalate>sodium citrate>sodium benzoate>sodium laurate>sodium stearate.The formation of micelles was verified by pyrene fluorescence probe method and the results showed that the critical micelle concentrations of sodium laurate and sodium stearate were respectively 1×10^-3.4 mol·L^-1 and 1×10^-3.6mol·L^-1,which were consistent with the results obtained by surface tension method.The thermodynamic calculations of the micelle formation of organics in the sodium aluminate solution showed that the process tended to proceed spontaneously in a disordered state.At 298 K,the order of the maximum surface adsorption of organics was:sodium oxalate>sodium benzoate>sodium laurate>sodium citrate>sodium stearate.The minimum average molecular cross-sectional area and the thickness of the adsorption layer of organics increased with the increase of their carbon chain.The increase of temperature led to the increase of the minimum average molecular cross-sectional area and the thickness of the adsorption layer of organics,while the maximum surface adsorption decreased.（2）The interfacial behavior of the mixture of organics was elucidated in the synthetic sodium aluminate solution.Binary organic mixtures such as sodium oxalate/sodium benzoate and sodium citrate/sodium laurate were studied to determine their critical micellar concentrations at different temperatures in the synthetic sodium aluminate solution.By comparing the results with those of single system,it was demonstrated that sodium oxalate inhibits the formation of micelles in sodium aluminate solution for the mixtures,while long-chain organics such as sodium stearate promote this process.The micelle formation ability of the organic mixtures in the sodium aluminate solution diminishes with increasing temperature.Sodium oxalate and sodium citrate have different effects on the surface adsorption and average molecular cross-sectional area of other organics in sodium aluminate solutions.The intermolecular interaction parameters and critical micelle concentrations of the mixed system of organics in sodium aluminate solution were calculated based on the Gibbs adsorption equation and Clint model with a non-ideal mixing model of surfactants,and the results showed that the calculated results were in good agreement with the experimentally values.In addition,the interfacial behavior of the ternary organic mixture system is more complicated and requires further study.（3）Multilayer adsorption was found in the synthetic sodium aluminate solution.The aggregation behavior and interfacial structure of low molecular weight organics such as sodium benzoate and medium molecular weight organics such as sodium laurate and their mixtures at the interface of air/sodium aluminate solution were analyzed under different spreading concentrations and other conditions.Theπ-A isotherm of the Langmuir monolayer and the microscopic morphology of LB film showed that the collapse pressure of the subphase of sodium aluminate solution increased with the increase of the organic spreading concentration.Theπ-A isotherm shifted to the left and the minimum average molecular area of the organics decreased.The micellar sizes of sodium stearate and sodium laurate at the air/solution interface increased with the increase of the spreading concentration.In addition,the introduction of sodium palmitate and sodium oleate in the mixtures changed the height and morphology of the LB film of sodium stearate.（4）Technical prototype of froth flotation for organic removal was presented in sodium aluminate solutions.Compared with the synthetic sodium aluminate solution,the industrial sodium aluminate solution has stronger foaming ability,smaller size（distribution）of bubbles and better stability.Sodium dodecyl sulfate（SDS）was selected as the foaming agent and collector,and the foam enrichment separation process of organics such as sodium benzoate in the synthetic sodium aluminate solution was studied.The results showed that the removal efficiency and enrichment ratio of organics increased with the increase of organic concentration and temperature.Meanwhile,the tight multilayer adsorption structure formed by the organics on the surface of sodium aluminate solution promoted the efficient enrichment of organics at the air/solution interface by froth flotation.The removal efficiency of sodium stearate by froth flotation reached higher than 29%at 333 K,with an enrichment ratio ranging from 2.42 to 3.02.In addition,two different industrial sodium aluminate solutions were chosen to verify the feasibility of froth flotation in practical production.Without use of any additives,the enrichment ratio of organics in Zunyi（ZY）Bayer liquor exceeded 2.71,while it reached 3.46 in Nanshan（NS）Bayer liquor.After solid-liquid separation and drying of the concentrated foam,the total organic carbon content in the solid sample exceeded 20%.Finally,the basic flow of organic removal from sodium aluminate solutions by froth flotation was proposed.更多还原