分光光度法测定油田水样中的硫酸根离子

建立了油田水中SO42-的分光光度测定法。在稀盐酸介质中BaCrO4与SO42-反应生成BaSO4沉淀,并定量置换出CrO42-。溶液经煮沸,并调节至碱性,以沉淀过量的BaCrO4,离心分离后,于420 nm处以试剂空白作参比,测定上清液中CrO42-的吸光度。硫酸根浓度在8.0~120μg/mL范围内符合比耳定律,检出限为4.0μg/mL,相对标准偏差为2.84%(n=8),回收率在97.0%~103%。     

浅谈镀铬液中硫酸的质量浓度

从故障分析入手,阐述了镀铬液中硫酸的质量浓度主要根据ρ(CrO3)与ρ(SO42-)比值,其大小直接影响着镀铬质量.当镀液中金属杂质的积累并超过一定数值时,会造成镀层产生缺陷.采用增加硫酸质量浓度提高ρ(SO42-)与ρ(CrO3)比值的方法,可以改善镀液性能、排除故障.     

浓缩湿法磷酸中硫酸根的脱除研究

对50％P2O5湿法磷酸中硫酸根的脱除行为进行了研究,考察了脱硫剂、脱硫剂用量及反应时间对硫酸根脱除率的影响。结果表明,用磷矿和碳酸钡作脱硫剂,在70℃下经3 h反应可使磷酸中的SO42-脱除率达到98％以上,再结合溶剂萃取,可使净化酸中的SO42-含量低于100×10-6,达到工业级磷酸标准。     

增塑剂三甘醇二异辛酸酯的合成

研究了在实验室条件下,以硫酸、磷酸为催化剂合成三甘醇二异辛酸酯的最佳工艺条件,并初步探讨了SO42-/TiO2和SO42-/Fe2O3固体超强酸催化剂的催化效果.结果表明,硫酸催化的最佳反应条件为:m(硫酸)/m(三甘醇)=1.2%,n(异辛酸)/n(三甘醇)=2.15,反应温度220℃,反应时间6 h,酯化率达到96.3%;磷酸催化的最佳反应条件为:m(磷酸)/m(三甘醇)=3.0%,n(异辛酸)/n(三甘醇)=2.15,反应温度220℃,反应时间7h,酯化率达到95.2%;SO42-/TiO2和SO42-/Fe2O3固体超强酸催化剂也具有较好的催化效果,进一步研究后有望应用于实际工业生产.     

铬酸钠在氨和二氧化碳介质中的转化与相平衡

研究了铬酸钠在氨和二氧化碳介质中脱钠转化反应时氨盐比、铬酸钠溶液初始浓度、温度等对反应转化率的影响，测定了25℃和35℃下Na+，NH4+CrO42-－H2O体系的溶解度和相图，并以此分析了反应过程中CrO42-的析出形式及铬酸铵的分离方法，发现在反应过程中生成铬酸铵钠复盐，以N42CrO4为盐析剂能够使反应后溶液中绝大部分CrO42-以NaNH4CrO4·2H2O复盐结晶形式析出，铵盐中间体具有易分解的特性，为开发铬盐转化的新途径提供了依据．     

延缓镀铬槽液使用期限的措施

提出了镀铬槽液维护的措施:注重原材料的选择、控制铁杂质的积累、增加铬酐与硫酸根的比值等.分析了镀铬液中金属杂质离子存在状态的CrO3与SO42-比值及pH的相关性.实践证明,采用适当措施可有效延长槽液的使用期限.     

SO42-对复合水泥固化处理Cr(Ⅵ)的影响

由于CrO4^2-和SO4^2-的化学性质很相近,在利用含石膏的水泥固化处理Cr（Ⅵ）时．SO4^2-会极大地干扰水泥水化物与Cr（Ⅵ）之间的化学作用,进而影响到水泥对Cr（Ⅵ）的固化效果。合成含铬钙矾石的实验表明：在SO4^2-充足的情况下,CrO4^2-无法进入钙矾石晶格。用合成的水化硅酸钙（C-S-H）对CrO4^2-进行吸附的实验表明：混凝土中的C-S-H对CrO4^2-的吸附量不大,说明在水泥固化Cr（Ⅵ）时,C-S-H对Cr（Ⅵ）的同化不起主要作用。用毒性浸提程序和固化体无侧限抗压实验检测复合型水泥对Cr（Ⅵ）的固化效果。结果发现：在搅拌水中Cr（Ⅵ）的掺入浓度高达4.000g／L,不含石膏复合水泥的胶砂试件28d龄期的粉碎样浸提出的Cr（Ⅵ）的浓度已低达0．2mg／L,在添加Na2CrO4后,胶砂的抗压强度明显提高。掺10％石膏的复合水泥对Cr（Ⅵ）的固化效果不如未掺石膏的复合水泥。     

半水物法磷酸生产影响因素分析

以南化设计院设计的三槽半水物法磷酸生产工艺实践,概述原料、液相SO42-浓度、反应温度、磷酸浓度、反应时间、料浆液固质量比等因素对半水物法磷酸生产的影响,结合公司在半水物法磷酸生产过程中的经验,列出主要控制条件。     

共存阴离子对氢氧化铌吸附磷酸根的影响

以氢氟酸法制备的氢氧化铌为吸附剂,以水溶液中磷酸根为吸附对象,考察了Cl-、SO42-、NO3-3种阴离子对吸附效果影响。结果表明,在温度为25℃,磷酸根质量浓度50mg/L、体积200mL,吸附剂用量0.1g,pH=2条件下,氢氧化铌对磷酸根的最大吸附量可达43.31mg/g。当3种共存阴离子质量浓度分别为50、100、150mg/L时,氢氧化铌对各阴离子吸附顺序依次如下:PO43->>SO42->NO3->Cl-;PO43->>SO24->NO3->Cl-;PO43->>Cl-≈SO42->NO3-。共存阴离子Cl-、SO42-、NO3-存在与PO34-形成吸附竞争,均使氢氧化铌对PO34-吸附量减少。采用质量分数为25%的氨水(10mL)洗去氢氧化铌表面吸附的PO43-,并用蒸馏水进行冲洗,将所得滤液用蒸馏水稀释定容到50mL,其解吸率为53.1%。吸附前后及解吸后的氢氧化铌红外光谱分析结果表明,氢氧化铌表面吸附的磷酸根并没有被完全解吸下来。     

磷钼酸在酯化反应体系中对316不锈钢的腐蚀抑制机理

采用扫描电子显微镜(SEM)和X射线光电子能谱(XPS)研究了模拟醋酸丁酯反应(CH3COOH、H2SO4、H3PMo12O40,105℃)条件下316不锈钢(316SS)的表面形貌和元素组成。结果表明,磷钼酸经物理吸附在不锈钢表面形成保护层,并发生氧化还原反应,生成的水合物、氧化物、难溶盐类沉积在不锈钢表面,形成致密的钝化膜,从而抑制316SS的局部腐蚀,阻止点蚀的扩散和蔓延,PMo12O430-、MoO42-和CrO42-使钝化膜表层具有阳离子选择性,能阻挡SO24-通过该膜到达金属表面,膜内层结晶态氧化物具有阴离子选择性,阻止基体金属离子穿过钝化膜而溶解,从而抑制局部腐蚀的进一步扩展。     

Membrane Characteristics and Fouling Study in MEUF for the Removal of Chromate Anions from Aqueous Streams

Abstract

Micellar‐Enhanced Ultrafiltration (MEUF) of the chromate anions from aqueous solutions has been studied at room temperature (28±2°C) using cationic surfactants, cetyltrimethylammonium bromide (CTAB), and cetylpyridinium chloride (CPC), micelles of which adsorb the chromate ions by electrostatic interactions. The solution is processed by ultrafiltration, using a membrane with a pore size small enough to block the passage of the micelles and the adsorbed ions. The process is highly efficient in removing the chromate ions. In the absence of other electrolytes, chromate ion rejections up to 99% were observed at optimal conditions of pH, pressure, temperature, feed chromate, and surfactant concentrations. The presence of added NaCl reduces the chromate rejection, but it was still considerable (up to 82%), even in the presence of 100 mM NaCl. The rejection rate of chromate was found to be highly dependent on the pH of the feed solution. The influence of membrane characteristics on the chromate ion removal was also studied. Various resistances like fouling resistance, concentration polarization resistance, and membrane resistance were also estimated to quantify their effects on the removal efficiency and on the flux behavior.     

Electrochemical membrane reactor: In situ separation and recovery of chromic acid and metal ions

An electrochemical membrane reactor with three compartments (anolyte, catholyte and central compartment) based on in-house-prepared cation- and anion-exchange membrane was developed to achieve in situ separation and recovery of chromic acid and metal ions. The physicochemical and electrochemical properties of the ion-exchange membrane under standard operating conditions reveal its suitability for the proposed reactor. Experiments using synthetic solutions of chromate and dichromate of different concentrations were carried out to study the feasibility of the process. Electrochemical reactions occurring at the cathode and anode under operating conditions are proposed. It was observed that metal ion migrated through the cation-exchange membrane from central compartment to catholyte and OH⁻ formation at the cathode leads to the formation of metal hydroxide. Simultaneously, chromate ion migrated through the anion-exchange membrane from central compartment to the anolyte and formed chromic acid by combining H⁺ produced their by oxidative water splitting. Thus a continuous decay in the concentration of chromate and metal ion was observed in the central compartment, which was recovered separately in the anolyte and catholyte, respectively, from their mixed solution. This process was completely optimized in terms of operating conditions such as initial concentration of chromate and metal ions in the central compartment, the applied cell voltage, chromate and metal ion flux, recovery percentage, energy consumption, and current efficiency. It was concluded that chromic acid and metal ions can be recovered efficiently from their mixed solution leaving behind the uncharged organics and can be reused as their corresponding acid and base apart from the purifying water for further applications.     

SOLVENT EXTRACTION OF CHROMIUM(Vl) BY 3-(4-PYRIDYL)-l,5-DIPHENYL PENTANE

The distribution equilibrium of Cr(VI) between an aqueous sulfuric acid solution of potassium bichromate and a nitrobenzene solution of 3-(4-pyridyl)-l,5-diphenyl pentane (PDPP or B) has been studied. Hydrogen chromate ion among several ionic species of Cr(VI) in the aqueous solution is extractable in the present system. The chromium concentration in the organic phase is correlated with the concentrations of hydrogen chromate and hydrogen ion in the aqueous phase with PDPP in the organic phase. The interfacial reaction rate is also obtained and it gives the equilibrium relation by equating the extraction rate with the stripping rate. Results of the freezing point depression of the organic solution and the interfacial tension, obtained for the present system, indicate that the Cr(VT)-PDPP complex in the organic phase might be the aggregation of several molecules of chromate acid and PDPP, and that the complex is surface active. A Cr(VI)-PDPP complex adsorbed at the liquid-liquid interface reacts with hydrogen chromate ion in the aqueous phase consecutively.     

The role of hexafluorozirconate in the formation of chromate conversion coatings on aluminum alloys

Aluminum based surfaces are routinely coated with a chromate based layer that provides unparalleled corrosion protection. Widely used conversion coating treatment formulations contain hexafluorozirconate as a major constituent besides chromate, ferricyanide, fluoride, and fluoborate. The function of hexafluorozirconate is the subject of this study as its function is still largely unknown. Hydrophobicity, surface morphology, and the chemistry of the surface, resulting from treatment with hexafluorozirconate, were studied using contact angle measurements, scanning electron microscopy, and energy dispersive spectroscopy, respectively. X-ray photoelectron spectroscopy was extensively utilized to determine the chemistry of the surface resulting from the hexafluorozirconate pretreatment. Our results indicate that fluoride ion containing hexafluorozirconate complex does not attack the oxide film in a manner that uncomplexed simple fluoride ion does. Hexafluorozirconate is involved in the formation of an Al-Zr-O-F based hydrated layer that increases the hydrophilicity of the surface, activates the surface, and lowers the corrosion resistance. These factors enhance the interaction of chromate with the alloy surface to result in the formation of a uniform conversion coating. Based on these results, a new model has been proposed for the formation of chromate conversion coatings.     

由铬酸钾制备铬酸钠结晶分离过程研究

以铬酸钾中间体为原料,系统地研究了采用结晶分离等常规手段制备铬酸钠产品的清洁制备方法。应用等温法分别测定了KNO3在Na2CrO4水溶液中和Na2CrO4在KNO3水溶液中的相平衡数据,绘制了溶解度曲线,确定采用先冷却结晶后蒸发结晶的方法制备铬酸钠晶体产品。考察了冷却结晶终点温度和物料配比,分析了分步蒸发结晶产品,确定了结晶最佳操作条件:K2CrO4与NaNO3的质量比在1∶(0.9～1.2),冷却结晶的终点温度控制在4℃。提出铬酸钾通过结晶方式转化为铬酸钠的整体工艺流程,并进行了全流程循环实验。采用重结晶法对铬酸钠产品进行精制,获得高纯度的铬酸钠晶体,质量分数由81.4%提高到92.2%,且粒径较大,粒度均匀。     

Effect of chromate ion on zinc electrowinning from acid sulphate electrolyte

The effect of chromate ion and its interaction with antimony and glue on zinc electrowinning from acid sulphate electrolyte were studied. During electrolysis at 430 A m^–2 and 45°C, the chromate ion was found to polarize the cathodic reaction resulting in a refined zinc deposit having a morphology featuring a vertical orientation of the zinc platelets. Although chromium did not codeposit, the current efficiency for zinc deposition was dramatically decreased in the presence of > 1000 mg dm^–3. This effect became more pronounced when the electrolyte also contained additives such as antimony and glue.     

重铬酸钠溶液分解碳酸钙制取铬酸钙

介绍了一种制取铬酸钙的新方法,利用重铬酸钠溶液分解碳酸钙,可以得到高纯度的铬酸钙. 实验表明,温度和浓度是影响碳酸钙分解的关键因素,当重铬酸钠浓度大于60%、重铬酸钠与碳酸钙摩尔比大于1.05:1时,常压沸腾条件下即可完全分解碳酸钙,制得纯度99.5%的铬酸钙,收率接近100%. 分解过程中产生的二氧化碳气体可用于碳化分离铬酸钙后的铬酸钠溶液再生重铬酸钠,循环利用. 新方法工艺简单、产品纯度和收率都较高,无环境污染.     

两种方法测定赤泥中可溶性硫酸根

赤泥中含有硫酸根离子,其含量对赤泥的回收利用过程带来麻烦,也对回收产品的质量有影响.本文用2种方法测定赤泥中的硫酸根并进行对比,希望找到简便、快捷、准确、精密度高的实验方法.铬酸钡分光光度法:在410nm硫酸根在0～6.00mg·(50mL)-1范围内与铬酸根吸光度呈线性关系,线性回归方程:y=0.1747x-0.00...     

Sorption rules of chromium(VI) ions by wood-based polyampholytes

The sorption laws of chromium(VI) on highly porous wood ionites in dependence on the pH of the medium, the metal ion concentration in the solution, and the duration of the phase contact have been investigated. It was found that the magnitude of the exchange capacity of the sorbents is defined by the ion state of the functional groups of polyamfolytes and chromate ions in the solution.