Leaching optimization and dissolution behavior of alkaline anions in bauxite residue

Bauxite residue is a highly alkaline waste containing soluble alkaline anions, which can cause environmental concerns. The optimal leaching conditions, distribution of alkaline anions, types of pivotal alkaline anions and their dissolution behaviors were investigated based on the combination of single factors-orthogonal experiments and leaching stage experiment. Using a two-stage leaching, 86% of the soluble alkaline anions $\left({\text{CO}}_3^{2?},{\text{HCO}}_3^{?},\text{Al}{\left(\text{OH}\right)}_4^{?},{\text{OH}}^{?}\right)$ were leached with a L/S ratio of 2 mL/g, at 30 °C, over 23 h. During the first stage of leaching, approximately 88% of alkaline anions were leached from the dissolution of free alkali (NaOH, carbonate, bicarbonate, NaAl(OH)₄) with the rest originating from the dissolution of alkaline minerals (calcite, cancrinite and hydrogarnet). Supernatant alkalinity was 69.78 mmol/L with ${\text{CO}}_3^{2?}$ accounting for 75%. Furthermore, carbonate leaching was controlled by solid film diffusion using the Stumm Model with an apparent activation energy of 10.24 kJ/mol.     

Removal of arsenic from water: Effects of competing anions on As(III) removal in KMnO4–Fe(II) process

Effects of sulfate, phosphate, silicate and humic acid (HA) on the removal of As(III) in the KMnO₄–Fe(II) process were investigated in the pH range of 4–9 with permanganate and ferrous sulfate applied at selected dosage. Sulfate decreased the removal of arsenic by 6.5–36.0% at pH 6–9 and the decrease in adsorption did not increase with increasing concentration of sulfate from 50 to 100 mg/L. In the presence of 1 mg/L phosphate, arsenic removal decreased gradually as pH increased from 4 to 6, and a sharp drop occurred at pH 7–9. The presence of 10 mg/L silicate had negligible effect on arsenic removal at pH 4–5 whereas decreased the arsenic removal at pH 6–9 and the decrease was more significant at higher pH. The presence of HA dramatically decreased the arsenic removal over the pH range of 6–9 and HA of higher concentration resulted in greater drop in arsenic removal. The effects of the competing anions on arsenic removal in the KMnO₄–Fe(II) process were highly dependent on pH and the degree of these four anions influencing As(III) removal decreased in the following order, phosphate > humic acid > silicate > sulfate. Sulfate differed from the other three anions because sulfate decreased the removal of arsenic mainly by competitive adsorption while phosphate, silicate and HA decreased the removal of As(III) by competitive adsorption and sequestering the formation of ferric hydroxide derived from Fe(II).     

Factors affecting the anodic behaviour of zinc electrode in borate solutions

The anodic behaviour of Zn electrode in 1 × 10⁻² M Na₂B₄O₇ solutions in the absence and presence of various concentrations of Na₂SO₄, Na₂S₂O₃ or Na₂S as aggressive agent was studied by galvanostatic polarization technique. In the absence of sulphur-containing anions in solution, the polarization curves are characterized by one distinct arrest corresponding to Zn(OH)₂ and/or ZnO, after which the potential increases linearly with time due to the formation of barrier oxide film before reaching the oxygen evolution reaction. The duration time of the arrest decreases with increasing current density while the rate of oxide film formation increases. On the other hand, the duration time of the arrest increases with the number of anodic cyclization while the rate of oxide film formation decreases. Additions of low concentration of the aggressive anions have no effect on the passive film formed on the metal surface. The potential starts to oscillate within the oxygen evolution region with increases in the concentration of these aggressive anions. Further increases in the concentration of these aggressive anions are associated with impaired Zn passivity that might indicate pitting attack. The aggressiveness of the sulphur species decreases in the order: . The effect of raising pH of the solution on the anodic behaviour of Zn electrode in the presence of anions was also investigated. It was found that the raising the pH of the solution affecting on the rate of oxide film formation and the breakdown potential value.     

Solvation of protons and the strength of superacids

Analysis of literature indicates that the strength of superacids is mainly determined by unusual chemical properties of weakly solvated protons while the extent of dissociation of superacids is rather low and is less important. A higher chemical activity of protons in very concentrated acids and in such water-free superacids as liquid HF or 100% H₂SO₄ results from a weaker solvation of these species with the molecules of superacids which are less basic than water. In contrast, solvation by superacids of the negatively charged anions is stronger than in water solutions. These conclusions are illustrated by the ab initio quantum chemical calculations performed for self-dissociation of anhydrous liquid hydrofluoric acid. This revised version was published online in August 2006 with corrections to the Cover Date.     

Sorption behaviors of aromatic anions on loess soil modified with cationic surfactant

Modification of soils with hydrophobic cationic surfactants is an effective approach for enhancing the sorptive capabilities of soil in the vadose zone for the purpose of retaining organic contaminants prior to cleanup. The objective of this study was to examine the sorptive behavior of the cationic surfactant-modified loess soil for aromatic anions in the aqueous phase in an attempt to define the sorptive mechanisms. Some dominant factors governing the sorption, such as ionic strength and divalent heavy metal cation, were investigated. The sorption isotherms of 2,4-dinitrophenol (DNP) and benzoic acid (BA) in the modified soil samples were obtained using the batch equilibration method. Under the laboratory conditions, the modified loess soil utilized in this study was prepared by replacing the cations of loess soil with a cationic surfactant—hexadecyltrimethylammonium (HDTMA) bromide. The acidic aromatic compounds, DNP and BA existing as aromatic anions in the natural mixture of loess soil and aqueous phase, were selected as indicator compounds to measured the sorption behaviors of aromatic anions on the HDTMA-modified loess soil. The results confirmed that the sorptive capabilities of aromatic anions in loess soil were greatly enhanced by modification with HDTMA. The increase of ionic strength and the addition of divalent heavy metal cation Zn²⁺ significantly increased the sorption of aromatic anions on the HDTMA-modified loess soil. In binary solute systems, the sorbed amounts either of DNP or BA on the HDTMA-modified loess soil were reduced if two compounds existed simultaneously in the soil. This results indicated that competitive adsorption between the two aromatic anions occurred in soil matrix.     

BX_4~-(X=H,F,Cl,Br,I)的相对论赝势从头算研究(Ⅲ)

本文应用相对论赝势ab initio的方法,系统地研究了三卤化硼与卤素负离子反应生成的四卤化硼负离子的几何结构,并预测了BX_4~-(X=cl,Br,I)的键长。计算了该系列的稳定化能,得出稳定性顺序为BH_4~->>BF_4~->>BCl_4~->BBr_4~->BI_4~-。分析其电子结构得出,该系列分子的成键主要通过硼和卤素的σ轨道作用。     

MIEX对水中溴离子的去除效能及其影响因素

利用烧杯试验研究了一种新型磁性离子交换树脂(MIEX)对水中溴离子的去除效能,并考察了水中常见阴离子及有机物对其去除效果的影响.试验结果表明,MIEX可以有效去除纯水中的溴离子,投加量为10 mL/L和20 mL/L时其对溴离子去除率均在90％以上,且达到交换平衡时间分别为5 min和3 min.水中常见的其它带负电物质会在一定程度上影响溴离子的去除效果,在常见的含量条件下10 mL/L的MIEX对溴离子的去除率一般在50％以上.阴离子含量以及MIEX的选择性是影响其对溴离子去除效果的主要因素.有机物的存在使MIEX对溴离子的去除率明显下降,去除率在70％左右.MIEX对有机物、阴离子的去除过程存在差异:10 mL/L的MIEX去除阴离子的反应平衡时间在5 min左右,而去除有机物的平衡时间则较长,其对2种表征有机物含量的指标(UV254、DOC)的去除稳定时间均在20 min以上.     

PPY掺杂离子对电催化脱氯Pd/PPY/Ni电极的影响

为制备高效稳定的用于电催化去除氯代有机物的电极,采用扫描电子显微镜和电催化脱氯实验考察不同聚吡咯掺杂离子对Pd/PPY/Ni复合电极的形貌和电催化加氢脱氯性能的影响.将制备的电极在强吸附性阴离子存在情况下,考察其电催化性能的变化.结果表明,掺杂离子对复合电极的形貌和电催化性能有显著的影响,对甲苯磺酸掺杂的聚吡咯对应的Pd/PPY(PTS)/Ni电极有最高的电催化加氢脱氯效率(高达91.1％),高氯酸钠掺杂的聚吡咯对应的电极电催化性能最差.电催化体系中强吸附离子(ClO4-,Cl-)的存在对电极性能有微弱影响,表明电极具有良好的稳定性,可高效去除水中的氯酚类氯代有机物.     

On the pitting corrosion currents of zinc by chloride anions

The changes in the pitting corrosion current density with time on zinc electrode concerning the concentration of both the passivating borate and the aggressive chloride anions were followed using a simple electrolytic cell. The pitting corrosion currents started to flow after an induction period, τ. This period is found to be a function of the concentration of Cl⁻ anion, according to the relation logτ=β−γlogC_Cl⁻. The pitting corrosion currents finally reached a steady-state value, which depended on the concentration of both B₄O₇²⁻ and Cl⁻ anions. At a constant B₄O₇²⁻ anion concentration, the pitting corrosion current varied with the concentration of Cl⁻ anion according to the relation logi_pit=a₁+b₁logC_Cl⁻. It also varies at constant Cl⁻ anion concentration and various B₄O₇²⁻ anion concentration according to the relation logi_pit=a₂−b₂logC_B4O7²⁻. The susceptibility of the passivating zinc to pitting corrosion was found to be increasing as the temperature and pH of the solution increases. Results are discussed on the basis of adsorption of the aggressive anion on the passivating film, followed by penetration through the film and incorporation in it. This undermines the oxide film and causes pitting corrosion.     

电化学方法合成铅、钛金属醇盐

通过改变电极距离、电解温度、导电盐浓度以及电极电位与电解次序,考察了铅、钛电极溶解时电流密度与电流效率的变化;用红外、拉曼光谱等测试技术对纳米PbTiO3 前驱体进行了表征。结果表明,在c〔(Bu4N)Br〕=0 03mol/L的乙醇溶液中,保持电极距离0 8cm、电位12V、温度50℃电解钛片4h, 40℃电解铅片2h,每隔30min加入0 1mL乙酰丙酮,可制得铅、钛金属醇盐PbTi(OCH2CH3 )(6 y) (acac)y,前驱体中含有乙酰丙酮基团(acac- ),电流效率超过92%。