Theory of Copper-Electrolyte Slimes Decoppering in the Presence of Hydrogen Peroxide

The problem of copper leaching from copper-electrolyte slimes is discussed. To intensify the long and costly process, it is proposed to use a leaching system containing sulfuric acid and hydrogen peroxide as an oxidizing agent. The chemical transformations possible variants at the treatment of slime under the specified conditions and the thermodynamic parameters of the predicted reactions are considered. Solution composition effect on the copper dissolution rate at room temperature was studied in the presence of hydrogen peroxide using the rotating disc technique. It is found that dissolution rate constant at using hydrogen peroxide slightly inferior to dissolution rate constant under autoclaved conditions in an oxygen atmosphere.

Dilute nitric or nitrous acid solution containing halide ions as effective media for pure gold dissolution

Bromide salts are more effective than chloride salts in gaining the ability of dissolving gold in dilute aqueous nitric acid solution. At 60 °C, a piece of gold-wire (ca. 20 mg) is dissolved in 20 mL of as low as 0.10 mol L−1 HNO3 solution containing 1.0–5.0 mol L−1 NaBr and the dissolution rate constant, log(k/s−1), increases linearly with increasing NaBr concentration.

Ultrasonic-Assisted Dissolution of Polystyrene in Decahydronaphthalene for the Preparation of Poly(Cyclohexylethylene)

Dissolution process of polystyrene in decahydronaphthalene solution was conducted and compared under different conditions. The effects of dissolution time and temperature on the dissolution ratio of polystyrene were performed with the assistance of ultrasonic and mechanical agitation, respectively. The dissolution ratio of polystyrene increased with the increment of dissolution time and dissolution temperature, polystyrene dissolved faster under ultrasonic-assisted process. The polystyrene dissolution kinetic model was developed and used to calculate the dissolution rate constant. The kinetic model showed good agreement with the experimental data, and the dissolution rate constant indicated that ultrasonic can obviously enhance the dissolution process of polystyrene in decahydronaphthalene solution.

Dissolution measurement free from mass transport

Standard dissolution experiments are carried out in stirred liquid. Therefore, the measured dissolution rate contains also diffusive and convective contributions, besides the desired surface reaction contribution. We present here a methodology, based on the hydrodynamical analysis of classical dissolution experiments, enabling us to extract the pure dissolution rate constant from the set of the already measured dissolution rates. The application of this analysis to the case of gypsum shows that the removal of the mass transport contribution from the dissolution rates of this mineral found in the literature brings, despite their apparent inconsistency, a coherent description of its dissolution kinetics and a well-defined value of its rate constant.

Mechanisms and Kinetics of Silica-Rich Binary Na2O-SiO2 Glass Corrosion in 100°C Water at pH=7

Sodium-rich glasses of the system Na2O-SiO2 are well known to be easily soluble in water. This is not true for silica-rich compositions. We have manufactured quenched glasses with silica contents between 65 and 80 wt.% SiO2 and followed the water interaction at 100°C by measuring mass and sample dimensions in intervals. Comparing the path of edge length, mass and volume to a general shrinking core model for cuboids we conclude that only compositions between 65 and 70 wt% SiO2 can be described well by a simple dissolution process. The logarithm of the dissolution rate constant varies linearly with the SiO2 content. At higher silica contents the mechanism changes towards leaching of sodium. We propose changing glass structures to be responsible for the change in mechanism.