超微细改性氢氧化铝的工艺研究

采用改进的精制拜尔法制备超微细改性氢氧化铝,在种分过程中加入分散改性剂,解决了粒子团聚问题,提高了产品质量,实现粒子的表面改性,使晶种能多次循环使用,有效地降低了成本。优惠工艺条件为:αk=1.4、晶种系数1.5、分解温度40℃、分解时间为4h时,分解率53.68%,产品的平均粒径0.50μm。     

Effect of Ultrasound Frequency on the Precipitation Process of Supersaturated Sodium Aluminate Solution

The effects of frequency of ultrasound on the precipitation process of prepared supersaturated sodium aluminate solutions of practical concentration were studied experimentally under seeded, isothermal, batch crystallization conditions at various temperatures and initial ak(mole ratio of Na2O/Al2O3). The decomposition and the particle number percentage for size below 2 mm at time of 15 h were compared, particle size distribution and SEM photos of the product aluminum hydroxide were also analyzed. The results indicate that the ultrasonic treatment at 16 kHz can enhance the decomposition rate of sodium aluminate solutions, and also has effects on particle morphology and particle size distribution of aluminum hydroxide precipitated.     

ANFIS-Based Prediction of the Decomposition of Sodium Aluminate Solutions in the Bayer Process

This article presents the results of nonlinear statistical modeling of the decomposition process of sodium aluminate solution, as part of the Bayer technology for the production of alumina. Based on the data collected in 2011 and 2012 from industrial production in the Bira? Alumina Factory, Zvornik (Bosnia and Herzegovina), nonlinear statistical modeling of the industrial processes was derived. The model was developed as an attempt to define the dependence of the degree of decomposition of sodium aluminate solution as a function of the input parameters of the leaching process: caustic ratio (α_k) of the solution; ratio of the crystallization; content of Na₂O_(caustic) in the solution; the initial temperature of the solution; the final temperature of the solution; average diameter of the crystallized seeds; and duration of the crystallization process. As a tool for statistical modeling, Adaptive Network Based Fuzzy Inference System (ANFIS) was applied. The defined model using ANFIS methodology expressed a high level of fitting, and could be used to effectively predict the degree of decomposition of the sodium aluminate solution as a function of the input process under industrial conditions.     

Alumina trihydrate crystallization. Part 2. A model of agglomeration

In the second part of this paper on the kinetics of crystallization of aluminum trihydroxide from caustic aluminate solutions, interest is specially focused on the analysis of crystal size distribution as a function of time, in an isothermal batch crystallizer. Breakdown and agglomeration are shown to affect these curves simultaneously. While only qualitative information on breakdown was obtained, agglomeration could be isolated experimentally. Its rate was measured and fitted to a kinetic model which pictures agglomeration as the result of binary collisions between particles.     

烧碱法生产液体铝酸钠的工艺研究

将颗粒状(为了混料均匀,如果选用片状的氢氧化钠,需要粉碎后进入配料工段使用)氢氧化钠与铝钒土按一定比例混合均匀,经450～500℃煅烧0.5h,再经溶解、过滤、洗涤、精制得到合格液体铝酸钠。本工艺采用低温煅烧,常压溶解的方法生产液体铝酸钠,具有生产工艺简单,易于操作,设备简单,损耗低,减少环境污染等特点,并且避免了液体烧碱法生产铝酸钠时的炉内粘接现象;采用自制高效脱硅剂对铝酸钠进行脱硅,可得到高质量的铝酸钠。经精制后的低硅铝酸钠可以进入结晶工序制得氢氧化铝,或用于"氢氟酸—铝酸钠法"和"氟硅酸钠法生产冰晶石"工艺的生产原料,具有较强的环境效益和经济效益。     

Selective electrochemical reactions of an alumina hydrate crystallization inhibitor

Selective reactions of catechol have been studied in regard to its inhibition properties towards alumina hydrate crystallization. Electrochemical reactions of the inhibitor leading to products without inhibition behaviour have been obtained using different conditions. First, a pure sodium hydroxide solution (1.0 M NaOH) was used to electrochemically react the catechol. The inhibitor reactions were then carried out in both saturated and supersaturated sodium aluminate solutions (NaAl(OH)₄). Electrocatalytic hydrogenation (ECH) of the aromatic ring over rhodium-based catalysts leads to the saturated non-inhibiting molecule, 1,2-cyclohexanediol. Temperature shows no significant influence on the ECH process within the temperature range where the alumina hydrate crystallization is normally carried out. The presence of aluminate ions in solution has, however, a detrimental effect on the current efficiency. Electro-oxidation of the catechol produces muconic acid by cleavage of the carbon-carbon bound. It also produces other oxidation products and, eventually, may lead to total mineralization of catechol into carbonate, which is a less inhibiting molecule. A detrimental effect of the presence of aluminate on the electro-oxidation is also observed. Electrochemical techniques are proposed as new pathways for organic control in caustic medium.     

甲醇溶析铝酸钠制备氢氧化铝

以甲醇水溶液分解铝酸钠晶体,采用溶析法制备了超细氢氧化铝. 考察了30℃下氧化铝、氧化钠溶解度随甲醇质量分数的变化规律,研究了甲醇质量分数和反应温度对水合铝酸钠晶体分解工艺的影响,用XRD, IR, SEM及粒度分析、纯度分析等手段对制备的氢氧化铝产品进行了表征. 结果表明,随着溶剂中甲醇质量分数的增加,氧化铝和氧化钠溶解度均下降,但氧化铝下降幅度更大;铝酸钠溶液分子比(氧化钠/氧化铝摩尔比)先增加后减小,到甲醇质量分数为0.8左右时达到最大值. 30℃下水合铝酸钠晶体与甲醇质量分数为0.5~0.8的甲醇-水混合溶剂反应1~3 h,铝酸钠分解率可达到80%~90%,温度升高,分解率略有下降. 甲醇溶析得到的氢氧化铝30℃下为拜耳石型,温度升高逐渐变为三水铝石型,红外光谱完整. 产品形貌规则,为高纯薄片状超细氢氧化铝,平均厚度100 nm,平均粒径1.05 mm.     

Separation of NaOH by Solvent Extraction Using Weak Hydroxy Acids

Abstract

Separation of sodium hydroxide from aqueous salt solutions at elevated pH may be accomplished by use of solvent extraction with weak hydroxy acids. A series of lipophilic weak hydroxy acids, including alkyl phenols and fluorinated alcohols, has been characterized with regard to their ability to extract sodium into 1‐octanol as a function of temperature and extractant concentration. Isotherms are presented at 10, 25, and 60°C, employing extractant concentrations up to 1 M and aqueous NaOH concentrations up to 7 M. Near stoichiometric loading of all compounds tested may be achieved in a process postulated to be simple cation exchange. Extraction strength increases with the expected acidity of the hydroxy acids. Strongest extraction was observed with two alkyl phenols and 4‐n‐octyl‐α,α‐bis(trifluoromethyl)benzyl alcohol. Essentially complete removal of free hydroxide from a solution containing sodium hydroxide, nitrate, and aluminate was accomplished using 1 M 4‐tert‐octylphenol in 1‐octanol at 60°C. Consequently, as the pH of the solution was lowered, aluminum was observed to precipitate as the Bayerite form of Al(OH)₃. Contacting the loaded solvent with water released NaOH into the strip solution, and good selectivity for hydroxide vs. nitrate and aluminate was obtained. Since hydroxide equivalents rather than the hydroxide ion itself are believed to be extracted by the weak hydroxy acids, the process is referred to as pseudo‐hydroxide extraction. Application of this concept to sodium removal and caustic recycle in the treatment of alkaline nuclear waste appears feasible.     

Crystallization of aluminium hydroxide from the reactive NaAl(OH)4–NaHCO3 solution: Experiment and modeling

The crystallization kinetics of aluminium hydroxide from the sodium aluminate solution reacted with sodium bicarbonate were systematically investigated in a steady-state MSMPR (mixed-suspension mixed-product removal) crystallizer for the first time, and the expressions of the nucleation rate, growth rate and the agglomeration kernel of aluminium hydroxide were successfully regressed. The aluminium hydroxide particles precipitated from the reactive system are identified as gibbsite by XRD and SEM examinations. The volume growth rate order of gibbsite with respect to the relative supersaturation of the solution is above the linear growth rate order, and the spiral growth mechanism for the growth of the basal face of gibbsite in the reactive system was further identified by the growth rate, morphology analysis as well as the calculated surface entropy factor. The secondary nucleation rate of gibbsite from the reactive system is three to four orders of magnitude larger than that from seeded process reported in the only available literature reference. The agglomeration kernel of gibbsite in the reactive system increases linearly with growth rate and residence time, and the positive order about 0.55 of magma density is thoroughly different from the negative order of magma density for gibbsite agglomeration in seeded process presented in the literature.     

从高苛性比铝酸钠溶液中制取氢氧化铝的实验研究

霞石经高压水化学法处理,得到高苛性比铝酸钠溶液加入CaO,生成水合铝酸三钙,溶解于碳酸氢钠溶液中,得到低苛性比铝酸钠溶液,经除杂碳分后,可制得符合国家二级标准(GB/T4294—1997)的氢氧化铝制品。实验结果表明,在水合铝酸三钙形成过程中,影响因素大小的顺序为:CaO/Al2O3>温度>时间;在氧化铝溶出过程中,影响因素大小的顺序为:温度>时间>碳酸氢钠加入量。实验所采用的工艺路线,对于解决从高硅原料中提取氧化铝的问题,具有重要的意义和实际应用价值。     

熔盐法活化处理含铬红土镍矿浸出液的铬铝分离及碱液循环

基于Na2CO3, Na2CrO4, NaAlO2在NaOH溶液中的溶解度及NaAlO2的性质,采用蒸发结晶、碳化沉铝、苛化等方法对浸出液中铬、铝进行了分离,并实现了碱液循环. 结果表明,采用分步结晶,一次蒸发排盐终点控制碱液浓度在40%(w),结晶相中为大量NaAlO2和少量Na2CrO4;二次蒸发碱液浓度控制在50%(w),结晶相中为大量Na2CrO4和少量Na2CO3. 一次排盐结晶相溶解后通过碳化方式将铝分离,深度碳酸化后NaAlO2分解率达90.8%;二次排盐结晶相溶解后在90℃、苛化1 h、加钙量为理论量的1.2倍时,苛化率达79.2%,苛化液蒸发后过滤得到较纯的Na2CrO4晶体.     

碳分法制取药用氢氧化铝

以铝酸钠为原料采用碳分工艺，通过控制碳分工艺条件及洗涤、烘干条件，制得了符合中华人民共和国药典要求的药用氢氧化铝     

Modeling of Boehmite Leaching from Actual Hanford High‐Level Waste Samples

Abstract

The Department of Energy plans to vitrify approximately 60,000 metric tons of high level waste sludge from underground storage tanks at the Hanford Nuclear Reservation. To reduce the volume of high level waste requiring treatment, a goal has been set to remove about 90 percent of the aluminum, which comprises nearly 70 percent of the sludge. Aluminum in the form of gibbsite and sodium aluminate can be easily dissolved by washing the waste stream with caustic, but boehmite, which comprises nearly half of the total aluminum, is more resistant to caustic dissolution, and requires higher treatment temperatures and hydroxide concentrations. In this work, the dissolution kinetics of aluminum species during caustic leaching of actual Hanford high level waste samples is examined. The experimental results are used to develop a shrinking platelet model that provides a basis for the prediction of dissolution dynamics from a known process temperature and hydroxide concentration. This model is further developed to include the effects of particle size polydispersity, which is found to strongly influence the rate of dissolution. Two identical parameters for this model are used to describe leaching data from two sets of leaching results. When compared to other common monodisperse shrinking particle models, this result suggests a more physically meaningful model.     

Tailoring the reaction mixture composition for preparing zeolite coatings on aluminum supports in alkaline environments

Various alkaline reaction mixture compositions were tested for determining their suitability to be used in the direct crystallization of zeolites on aluminum supports. No organic materials, such as templates, complexing agents, and corrosion inhibitors were included in the reaction mixtures. It was observed that aluminum supports remained quite stable in alkaline synthesis mixtures when suitable reaction mixture compositions with relatively high silica content were used. These favorable compositions might be recognized from their sodium silicate/(sodium hydroxide?+?sodium aluminate) mass ratios, as depicted in this study. Coatings were prepared on aluminum by using some of these compositions. It was determined that aluminum hydroxide phases commonly forming on the support could be eliminated to a great extent and consequently, crystalline coatings of zeolites P and Y were obtained on aluminum surfaces. The coatings exhibited trivial mass loss in the mechanical stability tests applied.     

Filtration characteristics of aluminium hydroxide mixtures (alumina hydrates)

The specific cake resistance of the alumina hydrates obtained from sodium aluminate solutions was investigated against the caustic ratio, ageing and filtration pressure using a laboratory test filter at constant pressure filtration conditions. The alumina hydrate product was produced from sodium aluminate solutions by seeding the aluminium hydroxide crystals of definite size distribution at constant solution temperature. The specific cake resistance was found to increase with the caustic ratio and filtration pressure and to decrease with the ageing of alumina hydrates in aluminate solutions.     

Electrochemical production of aluminum hydroxide from kaolins

It has been shown that an electric spark discharge in saturated alkaline solution acts as a catalyst of ionization during the decomposition of kaolinite into aluminate and silicate components. The production of aluminum hydroxide from KM-1-grad kaolin (Chalgansk deposit) is 24.8–37.2% of the estimated value.     

新法铝热炼镁还原渣提取高白氢氧化铝

新法铝热炼镁工艺以白云石和菱镁石为原料、以铝粉为还原剂,在真空还原获得金属镁的同时得到富含CaO·2Al₂O₃的还原渣,该还原渣可通过氢氧化钠和碳酸钠的混合碱液溶出得到铝酸钠溶液,并通过碳酸化分解制备氢氧化铝。以该工艺所得还原渣为原料,系统地研究各溶出条件对氧化铝溶出率的影响,并对碳分所得氢氧化铝进行性能检测。结果表明,在氢氧化钠浓度80 g·L^-1、碳碱浓度110 g·L^-1、溶出时间120 min、溶出温度95℃、液固比为6的条件下,炼镁还原渣中氧化铝的溶出率在85%以上。氢氧化铝产品白度均大于98,平均粒径为26.98 μm,能够达到高白氢氧化铝的要求。     

偶联剂对聚丁烯–1/碳酸钙复合材料性能的影响

采用硅烷、铝酸酯和钛酸酯偶联剂对碳酸钙进行表面处理,并以聚丁烯–1为基体制备了聚丁烯–1/碳酸钙复合材料,研究了这3种偶联剂对复合材料性能的影响。结果表明,钛酸酯和铝酸酯偶联剂对碳酸钙改性的效果最好,其中铝酸酯偶联剂改性的碳酸钙接触角最大,对复合材料的增韧效果最明显,当铝酸酯偶联剂改性的用量为碳酸钙的1.5%时,改性后的碳酸钙接触角可达162.4°,相应的复合材料缺口冲击强度由未改性时的21.5 k J/m2提高至31.7 k J/m2。对铝酸酯偶联剂改性碳酸钙填充的复合材料的结晶性能及微观结构进行了分析与表征,发现铝酸酯偶联剂改性碳酸钙能够提高聚丁烯–1的结晶度,在基体内形成紧密堆积的细小球晶;铝酸酯偶联剂改性碳酸钙在聚丁烯–1中的分散性较佳,无明显团聚现象,与聚丁烯–1界面结合能力强,能够吸收形变功,提高复合材料的韧性。     

铝酸钠溶液中有机物排除试验研究

在拜耳法氧化铝生产中,有机物常会伴随铝土矿进入到铝酸钠溶液中。随着生产的进行,有机物含量会逐渐增加,严重的影响着氧化铝的正常生产。本文研究了浓缩结晶法对铝酸钠溶液中有机物排除率的影响规律,结果显示,有机物的排除率与苛性碱浓度密切相关,当苛性碱浓度约为360 g/L时,有机物的排除率最高,可达80%以上。     

Alumina trihydrate crystallization. Part 1. Secondary nucleation and growth rate kinetics

The kinetics of crystallization of alumina trihydroxide (hydrargillite) from caustic aluminate solutions of industrial composition (second stage BAYER process) were studied in a laboratory batch isothermal crystallizer. The yield and crystal size distribution of precipitate with time were obtained by varying the initial seed concentration. In this paper, the mass balance was used to determine nucleation and growth rate kinetics. First, from among the laws available in the literature, those which applied to alumina trihydrate crystallization were defined (model A). Kinetic constants of this model were calculated from experimental results. Then, a model based on a secondary nucleation mechanism was proposed (model B) that fits experimental data, and explains the induction periods found in the decomposition of aluminate solutions, even when seeds are present.