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 acid-oxygen leaching of low-sulfur Ni-Cu matte at atmospheric pressure
Abstract The leaching of low-sulfur Ni-Cu matte in acid-oxygen (CuSO 4 -H 2 SO 4 -O 2 ) solution at atmospheric pressure was researched. This matte was obtained from high grade Ni-Cu matte by magnetic separation, which mainly contained Ni-Cu alloy and a small quantity of sulfides. The effects of temperature, agitation speed, oxygen flow rate, particle size, acid concentration and concentration of copper ion were studied. It is found that the matte particles are leached by shrinking core mechanism and the leaching process is electrochemically controlled. In a temperature range of 30–60 °C, the surface reaction is rate-limiting step, with an apparent activation energy of 41.9 kJ/mol. But at higher temperature (70–85°C), the rate process is controlled by diffusion through the product layer, with an apparent activation energy of 7.3 kJ/mol.
Measuring Functional Service Quality Using SERVQUAL in a High-Dependence Health Service Relationship
Although there is a growing concern about health care quality, little research has focused on how to measure quality in long-term care settings. In this article, we make the following observations: (1) most users of the SERVQUAL instrument reassess customers' expectations each time they measure quality perceptions; (2) long-term care relationships are likely to be ongoing, dependent relationships; (3) because of this dependence, customers in the long-term care setting are likely to reduce their expectations when faced with poor service quality; (4) by using this "settled" expectations level, service providers may make biased conclusions of quality improvements. We recommend various methods for overcoming or minimizing this "settling" effect and propose modifications to the SERVQUAL gap 5 measure to assess quality in a long-term care setting.