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.
Influence of deposit morphology on the kinetics of copper cementation on pure iron
Abstract The kinetics of copper cementation on pure iron substrates were studied using a rotating disc geometry. The effect of rotational speed of the iron disc, copper ion concentration, hydrogen ion concentration, and temperature on the kinetic response was investigated. The range of each parameter studied was selected with some consideration for commercial operations for copper recovery using iron as the precipitant metal. The optimum values of each parameter for maximum cementation rate were determined. At low temperatures (10–30°C), an experimental activation energy of 22.89 kcal mol −1 was calculated indicating that the system is strongly controlled by a surface reaction mechanism or pore diffusion process. At high temperatures (30–60°C), an experimental activation energy of 7.94 kcal mol −1 was obtained which shows that the system may be controlled by both diffusion and surface reaction mechanisms. The deposits obtained were pure copper and not a copper-iron alloy. The total iron consumption, presented as can factor, was around 1.0. The structural characteristics of the resultant deposits were studied with the help of a scanning electron microscope. The structure and morphology of the deposits were analyzed in conjunction with their respective specific rate constants. A change in the surface roughness of the rotating disc and hence in the effective deposition surface area as a result of modification to the deposit morphology obtained for different experimental conditions was found to be the major reason for variations in the reaction rate. For the experimental conditions employed in this study, most of the deposits seen were bulbous or botryoidal crystal masses of different degrees of texture and size.
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.