水溶液中硅酸溶解和胶结的实验研究

本研究了几种不酸ＰＨ值对硅酸胶结的影响。结果表明，草酸浓度增大时，硅酸胶结速度变缓，至ＰＨ３－４时，硅酸不再胶结；而ＨＣＬ浓度增大，虽然胶结速度变缓，但最终仍胶结。     

Photocurrents and degradation rates on particulate TiO2 layers: Effect of layer thickness, concentration of oxidizable substance and illumination direction

Different routes for immobilization of TiO₂ on conducting substrates were compared to find active and stable photocatalysts, which could either be operated in open circuit (photocatalysis) or with applied electric potential (photoelectrocatalysis). The advantage of applying an electric potential was investigated. Polarization curves and photoelectrochemical degradation reactions served to characterize catalysts and to find a way of predicting the optimum synthesis conditions. The difference between front side (EE) and back side (SE) illumination is discussed as a function of layer thickness, as well as the influence of oxidizable substance concentration on photocurrents. Stability of catalysts was investigated in repetitive degradation experiments.     

ClO2的制备方法及其储存条件的研究

本文采用了以还原性有机酸—草酸代替无机酸和无机还原剂还原氯酸钠制备二氧化氯的工艺,来研究生产二氧化氯的最佳方法以及二氧化氯溶液的储存条件。结果表明,该法工艺简单,成本低,无设备腐蚀,而且产品纯度高,产率可达90%以上。生产出的二氧化氯采用低温(1℃～2℃)蒸馏水吸收,效果较好,其溶液在密闭、低温、暗处等条件下,保存较好。     

Activation flotation and mechanism of lime-depressed pyrite with oxalic acid

Flotation tests,contact angle measurements,infrared spectrum analyses,X-ray analyses and computer simulation were carried out in order to study the activation mechanism of lime-depressed pyrite with ox...     

Separation and recovery of vanadium from leached solution of spent residuehydrodesulfurization (RHDS) catalyst using solvent extraction

Leached solution, generated by oxalic acid washing of spent residue hydrodesulfurization (RHDS) catalyst, was used for separation and recovery of vanadium. First of all, solvent extraction, using mixture of 20% (v/v) Alamine-336 and 5% (v/v) tri-butyl phosphate (TBP) as a phase modifier, was conducted to extract molybdenum completely at pH 0.50. Then molybdenum-free solution was used for vanadium extraction at pH 1.25 with 20% Alamine-336 and 5% TBP. Stripping of vanadium from loaded organic solution was performed with 1.5 M H₂SO₄ at O/A phase ratio of 5:1 where more than 99% of vanadium was stripped in two stages. The stripped vanadium solution was further processed by precipitating with ammonium hydroxide to recover ammonium-meta-vanadate which was calcined to obtain vanadium pentoxide. Finally a conceptual process was established for recovery of high purity vanadium pentoxide from oxalic acid leached solution of spent residue hydrodesulfurization (RHDS) catalyst.     

High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process.In this study,a new method for leaching NdFeB waste with oxalic acid was developed.The high-efficiency,simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit.Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90℃ for 6 h in the aqueous solution of oxalic acid(2 mol/L) with a liquid-solid ratio of60 mL/g,the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%,respectively.Rare earth oxalate and Fe(C₂O₄)3^3- were left in the residue and the leaching solution,respectively.The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction(XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDS).Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model,and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction.The leaching residue was calcined at 850℃ for 3 h and then decomposed into rare earth oxide,which can be directly used to prepare rare earth alloy via molten salt electrolysis.For the leaching solution,ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate(FeC₂O₄-2H₂O).     

Effect of oxalic acid on control of postharvest browning of litchi fruit

Litchi (Litchi chinensis Sonn.) fruit, cv. Huaizhi, was treated with 2 and 4 mM oxalic acid and stored at room temperature to investigate the effect of oxalic acid on pericarp browning. The results showed that the pericarp browning indices of the fruit, treated with both oxalic acid concentrations, were significantly lower than that of the control, due to increase of membrane integrity, inhibition of anthocyanin degradation, decline of oxidation, and maintanance of relatively low peroxidase activity in the fruit during storage. It appears that application of oxalic acid can effectively control the pericarp browning of litchi fruit during postharvest storage.     

Recovery of oxalate from scrubbing solution containing rare earths and iron produced during uranium recovery from phosphoric acid

A solution containing oxalate complexes of rare earths, yttrium and iron (III) is obtained during the processing of wet process phosphoric acid for uranium recovery by solvent extraction. A process is described to recover oxalic acid from such a solution. The process is based on the conversion of iron (III) oxalate into calcium oxalate by calcium chloride followed by the metathesis of calcium oxalate with sulphuric acid to produce calcium sulphate and free oxalic acid. Data is presented to illustrate the influence of various parameters such as pH, temperature, digestion time and amount of calcium chloride on effective conversion of calcium oxalate. Under optimized conditions of pH 1, digestion time 2 h, twice the stoichiometric ratio of calcium chloride at ambient temperature (30±1°C) the recovery of calcium oxalate was found to be >94%. An overall schematic material balance flow -sheet for treating the oxalate solution of rare earths, yttrium and iron (III) to oxalic acid recovery has been presented. An improvement in the second cycle of patented process flow-sheet based on 1.5 M D2EHPA + 0.2 M TBP incorporating oxalic acid scrubbing / recycle for uranium recovery from phosphoric acid has been tested and found to be simple in terms of operations and capable of meeting product specifications..     

Use of Polyaminocarboxylic Acids as Hydrophilic Masking Agents for Fission Products in Actinide Partitioning Processes

During the partitioning of trivalent actinides from High Active Raffinate (HAR) solutions, most processes have to cope with an undesirable co-extraction of some of the fission products. Four hydrophilic complexing agents of the group of polyaminocarboxylic acids, namely EDTA, HEDTA, DTPA, and CTDA were tested and compared for their ability to complex fission products in a simulated PUREX raffinate solution, thereby preventing their extraction into an organic solvent. Several solvents, based on TODGA and the DIAMEX reference molecule DMDOHEMA, that are commonly known to show quite high Zr and Pd co-extraction, were studied. Our investigations ultimately resulted in a substitution of oxalic acid and HEDTA by cyclohexanediaminetetraacetic acid (CDTA). A small addition of this hydrophilic complexing agent to the feed decreased the distribution ratios of Zr from 100 to <0.01. The suppression of Pd was also very effective, resulting in >90% of the metal retained in the feed solution. The extraction of trivalent actinides and lanthanides was not negatively affected by the presence of CDTA. Furthermore, experiments with high concentrations of Zr proved the applicability of this new masking agent. The suppression of Zr and Pd extraction was also verified at a high Pu loading which makes CDTA as a masking agent attractive for grouped actinide extraction processes (GANEX) as well as DIAMEX-SANEX type separations.     

Electrochemical polishing of ITO films

Oxalic acid and tartaric acid were used to electrochemically treat the surface of indium tin oxide (ITO) films. To improve the surface of ITO films, the applied voltage was found via potentiodynamic technique. By controlling the concentration of oxalic acid and tartaric acid, the surface can be effectively planarized via the formation of a passive layer. The composition of this passive layer might be SnO₂ according to XPS analysis and potential-pH diagrams. The best treatment with root-mean-squared roughness less than 1.0 nm can be obtained by electropolishing at 0.65 V in 3 wt% tartaric acid.