Thermodynamic properties of concentrated zinc bearing solutions

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Linnanmaa, hall IT115

Topic of the dissertation

Thermodynamic properties of concentrated zinc bearing solutions

Doctoral candidate

Master of Science Tuomas Vielma

Faculty and unit

University of Oulu Graduate School, Faculty of Technology, Research Unit of Sustainable Chemistry

Subject of study

Applied Chemistry

Opponent

Professor Michael Steiger, University of Hamburg, Germany

Custos

Professor Ulla Lassi, University of Oulu, Research Unit of Sustainable Chemistry

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Solution chemistry explains the challenges related to zinc refining

The dissertation measured the properties of concentrated zinc-containing aqueous solutions that are essential for zinc production. Based on new measurements and scientific literature, a model describing these properties was created.

Zinc production relies on a three-step RLE process. In the first step, the zinc-containing mineral concentrate is roasted, i.e. oxidized at high temperature, to a more soluble form. In the second step, it is dissolved in sulfuric acid and the resulting solution is purified of other metals and impurities. In the third step, the metallic zinc is recovered electrolytically. Finally, the zinc is smelted and cast for delivery to customers.

The purification of the zinc-containing solution consists of different steps, each with its own specific conditions. A thorough understanding and improvement of the operation of these purification steps requires an in-depth understanding of the behavior of the process solution and, generally, the salt solutions over a wide range of process conditions, temperatures and concentrations. The main challenge is the lack of relevant scientific literature.

The main results of the dissertation are experimental new data for freezing point decreases and densities for concentrated zinc-containing aqueous solutions, and a mathematical model derived from these and literature values. Model calculations and simulations of the various stages of the zinc production process have shown its usefulness in the study of the operation of the process and, in particular, in understanding the prevailing physico-chemical phenomena. The dissertation provides a basis and paves the way for further research into the various properties of concentrated zinc-containing aqueous solutions, and in particular the purification steps.
Last updated: 17.9.2019