Thesis for the Degree of Master of Science


Year 2003
Ville Suontaka

Copper solvent extraction - electrowinning process monitoring system

During the last two decades, copper leaching, solvent extraction and the electrowinning process have become an important process option for producing copper from low-grade oxidized ore. The process is relatively young and intrinsically quite stable and therefore previous development has mainly focused on the process equipment. This has led to a low level of automation compared to other mineral processing operations. Improvements in plant control would make it possible to keep process variables near their optimal values, which would increase the amount of copper produced, reduce the amount of chemicals and energy used, and improve copper quality. These improvements would lead to remarkable economic benefits.

The aim of this Master\'s thesis was to study possibilities to apply model-based control in copper leaching, solvent extraction and the electrowinning process.

In the literature part of the thesis, copper leaching, solvent extraction and the electrowinning process were described and the current status of modeling, simulation and control of the process was studied. Published models and their application to process control were studied. It was found that implementations of advanced process control in copper leaching, solvent extraction and the electrowinning process have not been reported so far. Usually only low-level regulatory control, where controller set points are set manually, is implemented. However, model-based control has been successfully applied to other solvent extraction and electrowinning processes.

In the experimental part of the thesis, a prototype of a process monitoring application based on copper solvent extraction - electrowinning steady state mass balances was designed and implemented. The purpose of the application is to assist process operators in process control and to function as a basis for a control application to be developed in the future. Flow measurements and on-line analyzer assays are used to calculate amounts of copper transferred in different stages of the process. These values are compared to theoretical values calculated on the basis of solvent extraction isotherm data to monitor performance of the process. Process measurements always contain random errors and therefore a mass balance reconciliation algorithm is used to adjust measurement data to obey mass conservation laws. At first, the theory concerning the operation of the application was explained. Next, the structure and operational principle of the application were designed. After that, the application was tested with plant history data and it was found that the operational principle of the application is functional and it probably works at the plant with only small plant-specific modifications. With the help of the application, process operators would be able to control the process in such a way that process variable variations are reduced and, thus, copper production and copper cathode quality are improved.

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