Measurements of zinc oxide solubility in sodium hydroxide solution from 25 to 100 °C

The solubility of zinc oxide in sodium hydroxide solution was measured in a closed polytetrafluoroethylene vessel from 25 to 100 ℃. The ZnO solubility was determined by employing the method of isothermal solution saturation. The results show that only ZnO solid exists in the equilibrium state in the low concentration alkali regions, and the solubility of zinc oxide is almost invariable with temperature. With the increase of alkali concentration, equilibrium solid turns from ZnO to NaZn（OH）3 suddenly, this mutation is called invariant point. The alkali concentration of the invariant points increases with increasing temperature, but the solubility of NaZn（OH）3 decreases with increasing alkali concentration at the same temperature. At the same Na2O concentration, the higher the temperature is, the higher the solubility of NaZn（OH）3 is.

Leaching kinetics of scheelite concentrate with sodium hydroxide in the presence of phosphate

The reaction kinetics for the leaching of low-grade scheelite concentrate was investigated in an autoclave with sodium hydroxide in the presence of phosphate. The effects of stirring speed (300-600 r/min), reaction temperature (353-383 K), sodium hydroxide concentration (1.69-6.76 mol/L) and phosphate concentration (0.68-1.69 mol/L) on the WO3 dissolution ratio were studied. The results showed that the WO3 dissolution ratio was practically independent of stirring speed, while it increased with increasing the reaction temperature, and the concentrations of sodium hydroxide and phosphate. The experimental data were consistent with the shrinking core model, with a surface chemical reaction as the leaching rate-determining step. The apparent activation energy was calculated as 49.56 kJ/mol, and the reaction orders with respect to the concentrations of sodium hydroxide and phosphate were determined as 0.27 and 0.67, respectively. The kinetics equation of the leaching process was established.

Desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system

A novel process was proposed for treating nickeliferous laterite ores with molten sodium hydroxide.The effect on silicon extraction caused by the factors,such as stirring speed,reaction temperature,particle size and NaOH-to-ore mass ratio,was investigated.The results show that increasing stirring speed,reaction temperature and NaOH-to-ore mass ratio while decreasing particle size increases silicon extraction rate.The desiliconization kinetics of nickeliferous laterite ores in molten sodium hydroxide system was described successfully by chemical reaction control model.The activation energy of the desiliconization process was found to be 44.01 kJ/mol,and the reaction rate based on a chemical reaction-controlled process can be expressed as:1-(1-α) 1/3 = 27.67exp[-44 010/(RT)]t.

Cementing properties of steel slag activated by sodium silicates and sodium hydroxide

Steel slag which is mainly composed of γ-Ca2SiO4 and other silicates or alumino-silicates is activated by sodium sificates and sodium hydroxide. The powders of such steel slag are usually inert to hydrate and subsequently have very low ability of cementing. But when sodium silicates and sodium hydroxide are used as activators the steel slag shows very good properties of cementing. When activated with NaOH solution the hardened slurry of the steel slag has a compressive strength of 11.13 MPa after being cured for 28 days. When activated with Na2SiO3 solution the samples after being cured for 28 days have an average compres- sive strength of 40.23 MPa. While the steel slag slurry which is only mixed with water has a compressive of 0.88 MPa after being cured for 28 days.

Kinetics and leaching behaviors of aluminum from pharmaceutical blisters in sodium hydroxide solution

A hydrometallurgical process was developed for recycling pharmaceutical blisters.Leaching aluminum from pharmaceutical blisters using sodium hydroxide(NaOH) solutions was investigated with respect to leaching behaviors and kinetics.AL9(34) orthogonal design of experiments suggests that the most significant factor is NaOH concentration followed by temperature and leaching time.Factorial experiments demonstrate that the leaching rate of aluminum increases with increasing of the factors.The optimum conditions are temperature of 70 °C,leaching time of 20 min,NaOH concentration of 1.25 mol/L,liquid-to-solid mass ratio of 15:1 and agitation speed of 400 r/min.Under optimum conditions,the leaching rate is up to 100%,implying that aluminum and polyvinyl chloride(PVC) plastic in pharmaceutical blisters are separated completely.Kinetics of leaching aluminum is best described by the product layer diffusion control model,and the activation energy is calculated to be 19.26 kJ/mol.

Effect of Sodium Hydroxide on the Properties of Phosphogypsum based Cement

The effect of sodium hydroxide （NaOH） amount on phosphogypsum based cement was investigated. The mechanical performances and hydration mechanism of the phosphogypsum-based cement with different proportions of NaOH and steel slag were analyzed based on setting time, volume stability, strength test, XRD and SEM analyses. The experimental results show that, NaOH as an alkali activator significantly reduces the cement setting time and improves the cement early strength. But the acceleration of hydration proces produces coarse crystalline hydration products and the osteoporosis structure of hardened paste, which has a negative effect on later age strength. The combination of 1% NaOH and 5% steel slag as alkali activating agents is optimal with respect to early and later age strengths. Overdose of NaOH not only decreases the cement strength at later age, but also may cause problem of volume stability.

Role of hydrazine and hydrogen peroxide in aluminium hydroxide precipitation from sodium aluminate solution

Aluminium hydroxide precipitation from synthetic sodium aluminate solution was studied in the presence of hydrazine or hydrogen peroxide. The addition of low concentration of hydrazine is found to be effective, while higher amount of hydrogen peroxide is required to generate similar effect. XRD data confirm the product phase to be gibbsitic by nature. The scanning electron micrographs （SEM） show that agglomerated products form in the presence of hydrazine while fine discrete particles are produced with hydrogen peroxide. The probable mechanism of precipitation in the presence of hydrazine and hydrogen peroxide is also discussed.

Desilication kinetics of calcined boron mud in molten sodium hydroxide media

Desilication kinetics of calcined boron mud(CBM) occurring in molten sodium hydroxide media was investigated. The effects of factors such as reaction temperature and Na OH-to-CBM mass ratio on silicon extraction efficiency were studied. The results show that silicon extraction efficiency increases with increasing the reaction time and Na OH-to-CBM mass ratio. There are two stages for the desilication process of the calcined boron mud. The overall desilication process follows the shrinking-core model, and the first and second stages of the process were determined to obey the shrinking-core model for surface chemical reaction and the diffusion through the product layer, respectively. The activation energies of the first and second stages were calculated to be 44.78 k J/mol and 15.94 k J/mol, respectively.

Preparation of Spherical Silica-supported Biosorbent for Copper Ions Removal in Wastewater Based on Sol-gel Reaction and Simple Treatment with Sodium Hydroxide

A new and effective strategy was proposed for preparing new organic-inorganic composite biosorbent with spherical silica as supporting core and chitosan（CS）-based hybrid layer as shell based on sol-gel reaction and simple treatment with sodium hydroxide（NaOH）. The coating layer was covalently bound on the supporting silica through polysaccharide incorporated sol-gel process starting from CS and inorganic precursor γ-glycidoxypropyltrimethoxysiloxane（GPTMS）. GPTMS had epoxide groups and cross-linked amine groups of CS to avoid its acidic solubilization. The composite biosorbent had coarse surface due to the wet phase-inversion by treating in NaOH solution. The prepared biosorbent could be used in treating electric plating wastewater.

Preparation of sodium molybdate from molybdenum concentrate by microwave roasting and alkali leaching

The preparation process of sodium molybdate has the disadvantages of high energy consumption,low thermal efficiency,and high raw material requirement of molybdenum trioxide,in order to realize the green and efficient development of molybdenum concentrate resources,this paper proposes a new process for efficient recovery of molybdenum from molybdenum concentrate and preparation of sodium molybdate by microwave-enhanced roasting and alkali leaching.Thermodynamic analysis indicated the feasibility of oxidation roasting of molybdenum concentrate.The effects of roasting temperature,holding time,and power-to-mass ratio on the oxidation product and leaching product sodium molybdate (Na_(2)MoO_(4)·2H_(2)O) were investigated.Under the optimal process conditions:roasting temperature of 700℃,holding time of 110 min,and power-to-mass ratio of 110 W/g,the molybdenum state of existence was converted from MoS_(2) to Mo O3.The process of preparing sodium molybdate by alkali leaching of molybdenum calcine was investigated,the optimal leaching conditions include a solution concentration of 2.5 mol/L,a liquid-to-solid ratio of 2 mL/g,a leaching temperature of 60℃,and leaching solution termination at pH 8.The optimum conditions result in a leaching rate of sodium molybdate of 96.24%.Meanwhile,the content of sodium molybdate reaches 94.08wt%after leaching and removing impurities.Iron and aluminum impurities can be effectively separated by adjusting the pH of the leaching solution with sodium carbonate solution.This research avoids the shortcomings of the traditional process and utilizes the advantages of microwave metallurgy to prepare high-quality sodium molybdate,which provides a new idea for the highvalue utilization of molybdenum concentrate.

Corundum dissolution in concentrated sodium hydroxide solution

The corundum(α-alumina) core has been considered as a suitable candidate for investment casting of hollow, high pressure turbine engine airfoils due to its excellent properties. However, the efficiency of removing alumina cores in concentrated caustic solution cannot meet the needs of industrial production. In this paper, the effects of temperature and initial solution concentration on dissolution of α-alumina were studied by the classical weight-loss method. The fractal kinetic model was developed in order to describe α-alumina dissolution, assuming that the nonporous particles shrank during reaction process. The results show that the dissolution rate increases with increasing reaction temperature and initial solution concentration. Especially, the initial solution concentration has a significant influence on α-alumina dissolution rate at a higher reaction temperature. The activation energies decrease with increasing initial solution concentration, and the chemical reaction is the rate-controlling step.

Properties of Geopolymers Made from Fired Clay Bricks Wastes and Rice Husk Ash (RHA)-Sodium Hydroxide (NaOH) Activator

High cost has been pointed among factors that limit the promotion of geopolymers. To contribute to the reduction of the use of costly industrial sodium silicate in activators for geopolymers, a gel obtained with RHA and concentrated sodium hydroxide was used in the present study to develop an alkaline activator with 8 M NaOH and to produce geopolymers with crushed fired clay bricks wastes (FCBW). Characteristics of the gel were compared to that of commercial sodium silicate which was also mixed with 8 M NaOH in the ratio 1:1 to produce geopolymers. Chemical and mineralogical analyses were done on raw materials. Fourier Transformed Infrared Spectroscopy (FTIR) was done on the gel, commercial sodium silicate and products. Biaxial four point flexural strength, bulk density, water absorption and scanning electron microscopy (SEM) tests were also done on products. Results showed that RHA-NaOH alkaline activator has good potential in consolidating FCBW powder through geopolymerization process which gave products that had characteristics not far from that when the commercial sodium silicate was used. The gel obtained by mixing RHA and NaOH can contribute to the reduction of the use of costly commercial sodium silicate in the production process of geopolymers. However, appropriate filtration process is needed for the RHA-NaOH gel to reduce its impurities as undissolved entities, which will consequently contribute to improve the flexural strength, the density and the microstructure of its products which were low compared to when commercial sodium silicate was used.

Influence of Sodium Carbonate Amount on Crystalline Phase and Structure Stability for Doping Nickel Hydroxide

Alpha nickel hydroxide has better performances than commercial beta nickel hydroxide. However, the main defect is that α-phase is difficult to synthesize and easily transformed to β-phase Ni（OH）2 upon aging in a strong alkaline solution. In this study, the Al-Co, Al-Yb, Yb-Co and Al-Yb-Co multiple doping was used respectively. By controlling the amount of sodium carbonate, the α-Ni（OH）2 was prepared by ultrasonic-assisted precipitation. And the influence of sodium carbonate on the crystalline phase and structure stability for alpha nickel hydroxide was studied. The results demonstrate that, with increasing amount, the biphase nickel hydroxide transforms to pure alpha nickel hydroxide gradually, and the structure stability is also improved. When the amount of sodium carbonate is 2 g, the sample still keeps α-Ni（OH）2 after being aged for 30 days, for Al-Yb-Co-Ni（OH）2. And when the amount is less than 2 g, the phase transformations exist in the samples with different extents. These results demonstrated that the amount of sodium carbonate is a critical factor to maintain the structural stability of α-Ni（OH）2.

STUDIES ON THE REACTION OF SULFUR,SELENIUM AND TELLURIUM WITH SODIUM HYDROXIDE UNDER PHASE TRANSFER CATALYSIS(Ⅱ).A CONVENIENT METHOD FOR THE SYNTHESIS OF BI(ACYL)DISULFIDES

A simple and general method for the synthesis of bi(acyl)disulfides is reported.Sulfur is allowed to react with sodium hydroxide to give sodium disulfide at 65℃ under PTC,which can react with acyl halides to afford bi(acyl)disulfides in good to excellent isolated yields.The effects of solvents and phase transfer catalysts are discussed.

Secondary Crystallization of Na_2CO_3-Modified HZSM-5 Zeolites with Tetrapropylammonium Hydroxide and Their Catalytic Performance in Thiophene Alkylation Reaction

The Na2CO3-modified HZSM-5 zeolites were further treated by tetrapropylammonium hydroxide(TPAOH) solution. The effect of TPAOH concentration on the secondary crystallization process was investigated. The resulting samples were characterized by a complementary combination of X-ray diffraction, N2 adsorption/desorption, scanning electron microscopy, X-ray fluorescence spectroscopy, XPS, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, BET and temperature-programmed desorption techniques. The results showed that the secondary crystallization of the HZSM-5 zeolite could result in migration of non-framework species from the internal channels to the zeolite surface and their transformation into framework species. The catalytic activity of these modified samples for thiophene alkylation was evaluated. Both the activity and stability of the catalysts were improved after secondary crystallization.

Synthesis and Characterization of Proton-conducting Polymer Electrolytes Based on Acrylonitrile-Styrene Sulfonic Acid Copolymer/Layered Double Hydroxides Nanocomposltes

Acrylonitrile-sodium styrene sulfonate copolymer/layered double hydroxides nanocomposites were prepared by in situ aqueous precipitation copolymerization of acrylonitrile （AN） and sodium styrene sulfonate （SSS） in the presence of 4-vinylbenzene sulfonate intercalated layered double hydroxides （MgA1-VBS LDHs） and transferred to acrylonitrile-styrene sulfonic acid （AN-SSA） copolymer/LDHs nanocomposites as a proton-conducting polymer electrolyte. MgA1-VBS LDHs were prepared by a coprecipitation method, and the structure and composition of MgAl-VBS LDHs were determined by X-ray diffraction （XRD）, infrared spectroscopy, and elemental analysis. X-ray diffraction result of AN-SSS copolymer/LDHs nanocomposites indicated that the LDHs layers were well dispersed in the AN-SSS copolymer matrix. All the AN-SSS copolymer/LDHs nanocomposites showed significant enhancement of the decomposition temperatures compared with the pristine AN-SSS copolymer, as identified by the thermogravimetric analysis. The methanol crossover was decreased and the proton conductivity was highly enhanced for the AN-SSA copolymer/LDHs nanocomposite electrolyte systems. In the case of the nanocomposite electrolyte containing 2% （by mass） LDHs, the proton conductivity of 2.60×10^- 3 S·m^-1 was achieved for the polymer electrolyte.

氢氧化钠分子结构原位漫反射一维及二维漫反射中红外光谱研究

通过原位一维漫反射中红外(MIR)光谱开展了氢氧化钠分子结构研究。实验发现,氢氧化钠分子结构主要红外吸收模式包括OH基团伸缩振动模式(νOH-NaOH-_(一维))和OH基团面内摇摆振动模式(ρOH-NaOH-_(一维))。进一步开展了氢氧化钠分子结构的原位二维漫反射MIR光谱研究。采用原位漫反射一维及二维漫反射MIR光谱开展氢氧化钠结构研究,对氯碱工业具有重要意义。

制备氢氧化锆及其氧化锆含量和氧化钠含量的影响因素探究

将氧氯化锆和氢氧化钠作为原料采用直接沉淀法制备40%氢氧化锆,其中氢氧化锆氧化锆含量与氢氧化钠溶液浓度、氧氯化锆投料时间、氢氧化钠溶液温度、反应温度、反应时间密切相关。氢氧化锆中氧化钠含量与m_(氢氧化钠/氧氯化锆、洗涤情况)、反应温度密切相关,与反应时间无明显相关性。制备40%氢氧化锆氧化锆含量最佳条件为:氢氧化钠溶液浓度为32%,m_(氢氧化钠/氧氯化锆)为1.6倍,氧氯化锆投料时间为1min,氢氧化钠溶液温度为10℃,反应温度为60℃,反应时间为20min。

两种方法对于氢氧化钠溶液标定不确定度影响的比较

利用《化学试剂标准溶液的制备》和《测量不确定度评定与表示》对两种方法中产生的标准不确定度进行计算,对两种不同配制邻苯二甲酸氢钾基准溶液方法(固体称量法和液体移取法)对于氢氧化钠溶液浓度标定产生的不确定度进行了比较。结果表明:固体称量法和液体移取法的合成标准不确定度分别为2.343×10^(-3)和3.750×10^(-3),在氢氧化钠标定的方法中,用固体称量法,直接称量一定质量邻苯二甲酸氢钾加蒸馏水溶解配制溶液所产生的最后滴定误差更小。

镓精矿氢氧化钠浸出过程镓的浸出行为

从湿法炼锌工艺中得到的镓精矿是制备金属镓重要的中间产品,氢氧化钠浸出镓精矿制备电积前液是制备高品质金属镓的生产关键环节。通过研究氢氧化钠浸出镓精矿过程中添加剂的种类、添加剂用量、氢氧化钠浓度、浸出液固比、反应温度和浸出时间等工艺参数,分析了各工艺参数在镓精矿浸出过程中对Ga、Al的浸出率及浸出滤液过滤性能的影响。结果表明,在添加剂CaO 15%、NaOH浓度3 mol/L、液固比L/S=10、反应温度80℃、浸出时间120 min的最优条件下,Ga的浸出率为98.15%,Al的浸出率为53.01%,浸出滤液过滤速度为108.88 mL/min,添加剂CaO在反应过程中生成的铝酸钙作为滤饼支撑骨架,有效改善了浸出滤液的过滤性能。