A study of factors influencing the kinetics of copper cementation during atmospheric leaching of converter matte
The kinetics of copper cementation during atmosphere leaching of a Ni-Cu matte in CuSO4-H2SO4 solution was studied as a function of initial copper ion concentration, initial acid concentration, temperature, stirring rate, particle size distribution and pulp density. It was found that all these process variables influenced the rate of cementation. A two-stage rate of reaction was observed in most of the experiments, with the rate of cementation in the initial stage being slower than that of the subsequent second stage. The increased rate of cementation in the second stage was attributed to the enhancing effect of the surface deposit. The cementation process was found to take place by two different rate-controlling mechanisms. At a temperature range of 50i?½70i?½C, an activation energy of 74.6 kJ/mol was obtained, indicating a surface reaction controlled process. At higher temperatures (70i?½80i?½C) a lower value of activation energy was observed (18.2 kJ/mol), indicative of a process controlled by diffusion through surface layers. The structural characteristics of the cemented deposit could not be determined in the investigated system where the deposit was mixed with the leach solid residue.
Kinetics of Cu(II) cementation on a pure aluminum disc in acidic sulphate solutions
Abstract The rates of copper cementation on pure aluminum discs were studied as a function of (a) initial copper ion concentration, (b) temperature, (c) initial hydrogen ion concentration, and (d) the effect of the peripheral velocity of the Al disc.At low initial copper ion concentration (1 × 10−4M), there are two rate-controlling processes: ionic diffusion control at temperatures. above 40°C, and surface reaction control at temperatures below 40° C. At higher initial copper ion concentrations (5 × 10−3 M), the rate is controlled by a chemical (surface) reaction.When the-hydrogen ion concentration is increased to 0.7 M, the cementation rate increases. The pH remains constant during the reaction.The cemented deposit is pure copper. The structure. of the deposit is dependent on both temperature and the initial copper ion concentration. At high initial copper ion concentration (5 × 10-3 M) and at high temperatures (75° C), the rate, which was constant initially, increases with increasing deposition. Resume ...
Flash calcination of a magnesite ore in a free-fall reactor and leaching of magnesia
Abstract Flash calcination of a magnesite ore in a free-fall reactor and leaching of calcined magnesite with aqueous carbon dioxide were investigated. The effect of temperature and particle size on the weight loss were observed in the calcination experiments. The maximum weight loss was obtained as 43.2% for the particles of −100 + 140 mesh at the calcination temperature of 850°C. In leaching experiments; leaching temperature and time, particle size, stirring speed, and solid/liquid ratio were selected as variables. The dissolution fraction of magnesium increases with the increase in the leaching time, temperature and to a lesser degree stirring speed. The dissolution also increases with decreasing solid/liquid ratio and particle size. A thermal gravimetric method was used to measure activation energy, preexponential factor and rate constants for the thermal decompositon of the magnesite ore. The activation energy and preexponential factor were calculated as 39.4 kcal mol−1 and 3.5×106 s−1, respectively. The rate constants were found to vary between 1.2×104 and 1.3×10−2 s−1 in the temperature range of 823 to 1023 K.