Effect of ammonium chloride on leaching behavior of alkaline anion and sodium ion in bauxite residue

This study focused on leaching behavior of alkaline anion and sodium in bauxite residue through ammonium chloride treatment. The results showed that the pH of bauxite residue decreased from 10.49 to 8.93, total alkaline anion ( ${\text{HCO}}_3^{?},{\text{CO}}_3^{2?}$, OH^?, $\text{A}1{\text{O}}_2^{?}$) concentration reduced from 38.89 to 25.50 mmol/L, leaching rate of soluble sodium was 80.86% with ammonium chloride addition of 0.75%, liquid/solid (L/S) ratio of 3 (mL/g), temperature of 30 °C and reaction time of 18 h; L/S ratio was the main factor affecting the removal of alkaline anion and the leaching of sodium. Furthermore, ammonium chloride promoted the dissolution of diaspore and changed the micro/morphological characteristics with the increase of massive structure. The findings of this work will contribute to achieve soil-formation of bauxite residue.     

Migration and distribution of saline ions in bauxite residue during water leaching

Bauxite residue, a highly saline solid waste produced from digestion of bauxite for alumina production, is hazardous to the environment and restricts vegetation establishment in bauxite residue disposal areas. A novel water leaching process proposed here was used to investigate the dynamic migration and vertical distribution of saline ions in bauxite residue. The results show that water leaching significantly reduced the salinity of bauxite residue, leaching both saline cations Na⁺, K⁺, Ca²⁺ and anions CO^2?₃, SO^2?₄, HCO^?₃. Na⁺ and K⁺ migrated from 40–50 to 20–30 cm of the column, presenting a high migration capacity. The migration capacity of Ca²⁺ was lower and accumulated at 30–40 cm of the column. CO^2?₃ initially distributed at 20–30 cm of the column, subsequently transported to 30–40 cm of the column, and finally returned to 20–30 cm of the column along with evaporation. SO^2?₄ was originally distributed at 40–50 cm, but finally migrated to 20–30 cm of the column. Nevertheless, HCO^?₃ remained at the bottom of the column, and its migratory was less affected by evaporation.     

热处理温度对铝矾土基喷涂料性能的影响

以铝矾土骨料及细粉为主要原料,铝酸钙水泥为结合系统,研究了不同热处理温度对铝矾土基喷涂料性能的影响。结果表明,随着热处理温度的提高,铝矾土基喷涂料的体积密度减小;线变化率随着热处理温度的提高呈现收缩先增大后减小最终出现膨胀的变化规律。铝矾土基喷涂料的抗折强度和耐压强度随着热处理温度的提高先增大后减小。铝矾土基喷涂料的热膨胀系数在900℃时出现最大值7．05×10^-6／℃。     

消失模铸钢涂料耐火骨料烧结性的研究

以石英粉和铝矾土组成复合耐火骨料,在不同温度下进行烧结,使用BST401抗折弯仪测试烧结试样的抗弯强度,研究不同配比的耐火骨料的烧结性。研究表明,随着复合骨料中铝矾土含量的增加和烧结温度的升高,试样的抗弯强度都有增大的趋势。当铝矾土含量为60%、石英粉含量为40%、试样在1500℃时抗弯强度显著增大。并对烧结试样进行扫描电镜(SEM)分析,试样烧结良好,符合消失模铸钢涂料耐火骨料的要求。     

Dealkalization of Bauxite Residue Through Acid Neutralization and Its Revegetation Potential

Bauxite residue is a highly alkaline industrial solid waste generated through the alumina production process. Its high alkalinity causes serious environmental pollution. In this article, a fast, high-efficiency, low-cost dealkalization process was developed. Bauxite residue was dealkalized by sulfuric acid and CAM, a calcium-containing compound. The revegetation potential of dealkali bauxite residue was also studied. The dealkalization rate reached up to 94.31% when 18.4% sulfuric acid was added, and 2% CAM leaching occurred at room temperature for 10–30 min. The filtration speed increased by about 70 times with the addition of CAM up to 4.5%. The subsequent pot experiment showed that the dealkali bauxite residue met the growth requirements of plants. Scanning electron microscopy analysis showed that the particle size of neutralized bauxite residue was enlarged, thereby accelerating the soil formation process of the bauxite residue. This work provides technical support for ecologic restoration of a bauxite residue disposal area.

     

Effect of exchangeable cations on the physicochemical properties of smectite

The effect of exchange cations (Mⁿ⁺: Li⁺, Na⁺, K⁺, NH ₄ ⁺ , Ca²⁺, Mg²⁺, Fe³⁺, and Al³⁺) and thermal treatment on the physicochemical properties of smectite was investigated. Before thermal treatment, unheated (25°C) Mⁿ⁺-smectite showed increased d ₀₀₁ spacing upon glycol solvation; after heating at 300°C or above (400°C), d ₀₀₁ spacing upon glycol solvation of Al-, Fe-, Mg-, Li-smectite decreased and reached 10 Å. However, an increase in d ₀₀₁ of Ca²⁺-, Na⁺-and NH ₄ ⁺ -smectite upon glycol solvation indicated that d ₀₀₁ varied with the nature of exchangeable cation and the temperature of heating. The results generally suggested the following: d ₀₀₁ of homoionic smectite before and after heating at various temperatures depended upon the nature of exchangeable cation. The cation exchangeable capacities (CECs) and the BET surface areas (S_BETs) were functions of the type of exchangeable cations, since S_BETs drop off in the following order: Na⁺-smect > Ca²⁺-smect > Mg²⁺-smect > NH ₄ ⁺ -smect > Li⁺-smect > K⁺-smect > Fe³⁺-smect > Al³⁺-smect. Finally, we have noted good progress in the exchangeable properties of synthesized clay in comparison with the Na homoionic smectite form, except for K homoionic clay, which have the lowest CECs, S_BETs, and consequently, the lowest exchangeable properties.     

红硅石粉用于熔铜炉衬的试验研究

采用特级矾土熟料、一级矾土熟料、活性α-氧化铝粉及红硅石粉为原料,硼酐为矿化剂,研究分别加入5%、10%、15%、20%、25%和30%红硅石粉对熔铜炉炉衬耐火材料性能的影响。利用X射线衍射仪(XRD)检测了加入红硅石粉前后物相组成的变化,并采用扫描电子显微镜(SEM)观察和分析了试样烧成后的晶体形貌。结果表明:红硅石粉的加入能显著提高炉衬材料内莫来石的生成量,从而提高材料的抗侵蚀性能及其他性能,适宜作熔铜炉炉衬原料,但其加入量有上限,最佳加入量为20%。     

Rapid preparation of ceramic moulds for medium-sized superalloy castings with magnesia-phosphate-bonded bauxite-mullite investments

Phosphate-bonded investments have already been widely utilized in dental restoration and micro-casting of artistic products for its outstanding rapid setting and high strength.However,the rapid setting rate of investment slurry has up to now been a barrier to extend the use of such slurry in preparation of medium-sized ceramic moulds.This paper proposes a new process of rapid fabrication of magnesia-phosphate-bonded investment ceramic moulds for medium-sized superalloy castings utilizing bauxite and mullite as refractory aggregates.In order to determine the properties of magnesia-phosphate-bonded bauxite-mullite investments (MPBBMI),a series of experiments were conducted,including modification of the workable time of slurry by liquid(mL)/powder(g)(L/P) ratio and addition of boric acid as retard agent and sodium tri-polyphosphate (STP) as strengthening agent,and adjustment of bauxite (g)/mullite(g)(B/M) ratio for mechanical strength.Mechanical vibration was applied to improve initial setting time and fluidity when pouring investment slurry;then an intermediate size ceramic mould for superalloy castings was manufactured by means of this rapid preparing process with MPBBMI material.The results showed that the MPBBMI slurry exhibits proper initial setting time and excellent fluidity when the UP ratio is 0.64 and the boric acid content is 0.88wt.%.The fired specimens made from the MPBBMI material demonstrated adequate compression strength to withstand impact force of molten metal when the B/M ratio is 0.89 and the STP content is 0.92wt.%.The experimental results confirmed the feasibility of the proposed rapid fabricating process for medium-sized ceramic moulds with MPBBMI material by appropriate measures.     

用声发射研究集料尺寸对混凝土受压力学性能的影响

声发射作为一种动态无损检测方法，在混凝土材料研究中得到了广泛应用。研究混凝土在受压情况下的声发射特性，对含有不同最大集料粒径的普通混凝土和高强混凝土作了测试，涉及声发射信号、最大集料粒径、抗压强度和压应变。实验结果表明，受压过程中探测到的声发射信号包含的信息可用于判定试件的稳定性；声发射信号与集料粒径有很好的相关性。     

Characterization of ASR damage in concrete using nonlinear impact resonance acoustic spectroscopy technique

This research reports on a successful application of the nonlinear impact resonance acoustic spectroscopy (NIRAS) technique for the characterization of progressive damage in standard concrete specimens. Damage in the specimens is introduced, following ASTM C 1293 testing procedures, through the deleterious alkali–silica reaction (ASR), which leads to the formation of a gel-like reaction product, microcracks, and interfacial debonding between cement and aggregate phases. The microcracks and debonded interfaces act to increase the nonlinearity of concrete. The response of the specimen to impact loading is analyzed to obtain a nonlinearity parameter, which is used as a measure of damage. Measurements are performed on concrete prisms undergoing the ASTM C 1293 expansion test; three aggregates with varying reactivity are examined. The results from the expansion test are compared with those from the NIRAS measurements. For potentially reactive aggregate, the NIRAS technique offers a more definitive assessment of the damage state of the specimen and can be used to distinguish marginally reactive aggregates. The NIRAS results not only demonstrate a clear distinction between nonreactive and reactive aggregates using the nonlinearity parameter, but also the capability to quantitatively track ASR-induced damage in concrete, potentially forming the foundation for field assessment and monitoring.     

Incorporating Nano-silica as a Binder to Improve Corrosion Resistance of High Alumina Refractory Castables

In this study, four types of castables as calcium-aluminate cement (CAC)-bonded and nano-silica (NS)-bonded castables based on tabular-alumina and bauxite aggregates were prepared to investigate the replacement of the calcium-aluminate cement by NS. All samples were allowed to dry at 110 °C then fired at 800 and 1200 °C. Bulk density and apparent porosity of samples were measured. The molten aluminum static corrosion test (cup test) results showed that NS-bonded specimens had higher resistance to corrosion compared to CAC-bonded samples (based on the measured average aluminum penetration depth into the refractory texture). However no penetration was observed in bauxite NS-bonded samples. The results were consistent with dynamic corrosion test in aluminum melt carried out at 800 °C for 100 h. The small pore size in NS-bonded castables was found to be the main cause for high corrosion resistance as micro-pores prevented the melt to penetrate into the refractory.     

Effects of iron-containing phases on transformation of sulfur-bearing ions in sodium aluminate solution

Sulfides in the high-sulfur bauxite lead to serious steel equipment corrosion and alumina product degradation via the Bayer process, owing to the reactions of sulfur and iron-containing phases in the sodium aluminate solution. The effects of iron-containing phases on the transformation of sulfur-bearing ions (S^2–, S₂O₃^2?, SO₃^2? and SO₄^2?) in sodium aluminate solution were investigated. Fe, Fe₂O₃ and Fe₃O₄ barely react with SO₃^2? and SO₄^2?, but all of them, particularly Fe, can promote the conversion of S₂O₃^2? to SO₃^2? and S^2– in sodium aluminate solution. Fe can convert to Fe(OH)₃^? in solution at elevated temperatures, and further react with S^2– to form FeS₂, but Fe₂O₃ and Fe₃O₄ have little influence on the reaction behavior of S^2– in sodium aluminate solution. Increasing temperature, duration, dosage of Fe, mole ratio of Na₂O_k to Al₂O₃ and caustic soda concentration are beneficial to the transformation of S₂O₃^2? to SO₃^2? and S^2–. The results may contribute to the development of technologies for alleviating the equipment corrosion and reducing caustic consumption during the high-sulfur bauxite treatment by the Bayer process.     

铝矾土粉料结构特性对铸型涂料性能的影响

通过涂料配比试验,分析了铝矾土粉料的体积密度、表面酸碱性及多孔结构对铸型涂料性能的影响。结果表明,采用高体积密度的铝矾土粉料可得到涂层致密的砂型醇基涂料;根据铝矾土粉料表面酸碱性合理选择聚合磷酸盐的种类,可使砂型水基涂料具有良好的稳定性;铝矾土粉料的多孔结构有利于改善消失模涂料的透气性。     

Low-cost adsorbents for a dye uptake from contaminated water modeling of adsorption isotherms: The Langmuir,Freundlich and Elovich models

The adsorption of organic molecule to clay minerals has been reported by several investigators. Bentonite, which is made homoionics by mono-, di- and trivalent cations was used to remove the dye, an organic molecule (Quinalizarin) used to dye cotton. Equilibrium data were obtained by the batch technique. The results show the largest adsorption capacity of the homoionic bentonite; the saturation level was reached, the high adsorption capacity (79 meq/100 g), close to the cation exchange capacity of the synthesized bentonite (89 meq/100 g), indicates a strong interaction between the dye molecule and the adsorbent. Adsorption onto the clay was essentially immediate and correlated with the cation exchange-capacity (CEC). The type of exchangeable cations indicate that adsorption was primarily to the negatively charged sites on the clay. The amount of the adsorbed color was found to be a function of the type of exchangeable cations; it drops off in the following order: Bent-Al³⁺ > bent-NH⁴⁺ > bent-Na⁺ > bent-Fe³⁺ > bent-Li⁺ > bent-Ca²⁺ > bent-Mg²⁺ > bent-K⁺. The Langmuir, Freundlich and Elovitch models were employed to examine the equilibrium adsorption data. In all cases, the results show that all adsorption systems could be adequately fitted by these three models. It is seen that the linear fit is fairly good for these three models, the correlation coefficients R ² was found to be equal to 0.9 in approximately all cases. The article is published in the original.     

放粗铝土矿选矿精矿粒度的可行性研究

铝土矿选矿精矿粒度对精矿脱水过滤及拜耳法生产氧化铝具有重大影响。通过对铝土矿选矿精矿铝硅比的要求,一水硬铝石嵌布状态的研究,发现矿石中存在的大量粒度较粗的一水硬铝石富集合分配 ,并测量了其粒度（工艺粒度）。并对磨矿产品的富集合体解离度进行了互分析计算,精矿粒度可放粗至７５％～０．０７５ｍｍ左右。     

Kinetics of simultaneous leaching of Ag and Pb from hydrometallurgical zinc residues by chloride

The leaching kinetics of silver and lead simultaneously from zinc residue by chloride was investigated.The effects of stirring speed,temperature,sodium chloride concentration,particle size and liquid/solid ratio on Ag and Pb dissolution in sodium chloride were studied.It was determined that the dissolution rates increased with increasing sodium chloride concentration,temperature and decreasing particle size.The dissolution kinetics followed a shrinking core model,with inter-diffusion through gangue layer as the rate determining step.This finding is in accordance with the apparent activation energy(Ea)of 26.8 kJ.mol-1(Ag)and 26.5 kJ.mo1-1(Pb),and a linear relationship between the rate constant and the reciprocal of squared particle size.The orders of reaction with respect to sodium chloride concentration,temperature and particle size were also achieved.The rate of reaction based on diffusion-controlled process can be expressed by semi-empirical equations.     

石英粉粒度对涂料性能影响的正交试验

在石英粉粒度对涂料性能影响的试验中,选用不同粒度的石英粉作为耐火骨料,钠基膨润土和CMC联合作为悬浮剂,淀粉水溶液和水玻璃作为粘结剂,以水为载液。首先进行单一变量试验,选出4种较为关键的性能,通过4种不同粒度的骨料搭配,按照4种不同的加入量,进行4因素4水平正交试验。采用极差法来分析各种因素对涂料性能的影响,得出综合性能最好的组合并对该组合进行性能分析。结果表明,当耐火骨料的组分:240、270、300、320号加入量比为80:80:80:20时,石英粉涂料的综合性能最好。     

Proton-conducting sorption-active cyclam-based layers on chemically modified PVC surfaces of cellulose fabric

At different concentrations of hydrochloric, sulfuric, and phosphoric acids, the conductivity of the following electrochemical cell was measured: anode-acid solution-in-air bridge-acid solution-cathode. Cellulose fabric, the fibers of which are encapsulated in polyvinyl chloride, the surface of which is chemically modified with porous layers of aggregates formed by acid molecules and salt groups of ethanol and acetate cyclams, served as the bridge. The range where the logarithmic conductivity is proportional to the acid concentration is found. In this range, the molar contents of acids and water in the layers are estimated, the presence of aggregates composed of acid hydrates and cyclam salt groups is determined, the structure of layer is studied, and the similarity between the H⁺ conductivity of the layers on fabric and the conductivity of membranes based on polymers involving the skeleton ammonia salt groups is followed. For the aggregate layers, the specific surface; the limiting volume of pores; and the adsorption capacities for water, alcohol, benzene, and hexane vapors are measured. The formation of aggregates is shown to produce an insubstantial effect on the adsorption characteristics of the surface. During migration of H⁺ ions in the fabric and on its surface, the following process was carried out in the electrochemical cell: adsorption of NH₃, formation of NH ₄ ⁺ ions, and transfer of NH ₄ ⁺ ions to the catholyte. The migration velocity of H⁺ ions is shown to correspond to the measured current in the circuit, and NH ₄ ⁺ ions formed are found to be accumulated in the catholyte.     

Synthesis and characterization of polyaniline nanoparticles in SDS micellar solutions

Polyaniline (PANI) dispersions consisting of 10–20 nm sized nanoparticles were prepared by oxidation with ammonium peroxydisulfate (APS) in sodium dodecylsulfate (SDS) micellar solutions. Coalescence and coagulation were prevented by electrostatic repulsive interaction between anionic SDS micelles. Particle morphology was dependent on the initial shape of surfactant aggregates (micelles) and the molar ratio of SDS to aniline monomer. Spherical particles were obtained at very low monomer concentration and the shape of particles began to be distorted from the spherical shape as monomer concentration increased at constant 0.2 M SDS concentration. The size of spherical particles was the same order of the micellar size or slightly larger. UV–VIS spectroscopy, compositions of PANI powder, morphology, crystalline structure, thermal stability, molecular weight and conductivity of PANI particles synthesized at various monomer and surfactant concentrations were investigated.     

铝土矿浮选尾矿基本特性与再利用研究

对河南铝土矿正、反浮选脱硅尾矿的组成与基本性质进行了分析检测。根据铝土矿尾矿粒度细、比表面积大、粘度大等特性,提出了利用铝土矿浮选尾矿制备处理废水材料的思路,并针对河南中州铝厂正浮选脱硅尾矿进行了改性和处理含铬废水的探索试验。结果表明,进行酸化处理、低温焙烧后的尾矿对废水中的铬离子去除率可达到95%。说明铝土矿浮选尾矿通过改性制备处理重金属离子废水材料是可行的。