Zhiying Ding

Predominance diagrams for Zn(II)–NH3–Cl−−H2O system

Abstract The thermodynamics in zinc hydrometallurgical process was studied using a chemical equilibrium modeling code (GEMS) to predict the zinc solubility and construct the species distribution and predominance diagrams for the Zn(II)–NH3–H2O and Zn(II)–NH3–Cl−−H2O system. The zinc solubilities in ammoniacal solutions were also measured with equilibrium experiments, which agree well with the predicted values. The distribution and predominance diagrams show that ammine and hydroxyl ammine complexes are the main aqueous Zn species, Zn(NH3)42+ is predominant in weak alkaline solution for both Zn(II)–NH3–H2O and Zn(II)–NH3–Cl−−H2O systems. In Zn(II)–NH3–Cl−−H2O system, the ternary complexes containing ammonia and chloride increase the zinc solubility in neutral solution. There are three zinc compounds, Zn(OH)2, Zn(OH)1.6Cl0.4 and Zn(NH3)2Cl2, on which the zinc solubility depends, according to the total ammonia, chloride and zinc concentration. These thermodynamic diagrams show the effects of ammonia, chloride and zinc concentration on the zinc solubility, which can provide thermodynamic references for the zinc hydrometallurgy.

Preparation of metal zinc from hemimorphite by vacuum carbothermic reduction with CaF2 as catalyst

Abstract Zn reduction was investigated by the vacuum carbothermic reduction of hemimorphite with or without CaF 2 as catalyst. Results indicate that CaF 2 can catalyze the carbothermic reduction of zinc silicate, decrease the reaction temperature and time. The lower the reaction temperature and the more the amount of CaF 2 , the better the catalytic effect. The optimal process condition is obtained as follows: the addition of about 10% CaF 2 , the reaction temperature of 1373 K, the molar ratio of C to Zn Total of 2.5, the pressure of system lower than 20 kPa, the reaction time of about 40 min. Under the optimal process condition, the zinc reduction rate is about 93% from hemimorphite.

Study on the Structure and Generation Mechanism of Intermediate (6AlO–OH) in Decomposition Process of Sodium Aluminate Solutions

The intermediate (6AlO–OH) from decomposition of sodium aluminate solutions was verified with Raman and UV-Vis spectrometry. The generation mechanism of intermediate was explored. The molecular structure and spectroscopic property (Raman and UV-Vis spectra) of intermediate (6AlO–OH) were calculated by the quantum computational chemistry method based on DFT method employing B3LYP level with 6-311+G (d, p) basis set. By analyzing the experimental and calculated spectra results, it was confirmed that the intermediate is 6AlO–OH during the decomposition process of sodium aluminate solutions. The molecular electrostatic potential of intermediate (6AlO–OH) was also determined.

Effects of additives on zinc electrodeposition from alkaline zincate solution

Abstract The effects of additives on the surface and cross-sectional morphologies of zinc deposits on iron substrate from alkaline zincate solution were characterized by scanning electron microscope (SEM). The cathodic reaction mechanisms under various concentrations of additives were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. It is found that with increasing the additive A content in the bath solution, the nucleation overpotential (NOP) value is obviously increased and the inhibition effect is strengthened. This may be mainly due to the adsorption of additive A on the cathodic electrode surface, which can cover the active sites and block the discharge reduction. The results of EIS analysis indicate that the rate-determining step of zinc electrodeposition process is changed from mixed control step into electrochemical reduction step in the presence of additive A. However, any quantity of additive B has little effect on the NOP value and the inhibition effect is not obvious. Furthermore, addition of additive A and additive B at the same time displays the strongest inhibition effect and shows a strong synergism because of their co-adsorption on the cathodic electrode surface.