Thermal conductivity of copper smelting mattes and slags

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Kemian tekniikan korkeakoulu | Master's thesis
Sustainable Metals Processing
Degree programme
Master's Programme in Chemical, Biochemical and Materials Engineering
67 + 5
Current cooling system in copper flash smelting furnace has been developed to have a capability of predicting condition of refractory inside an operating furnace. This system requires thermal conductivity of copper matte and fayalite slag, which have never been analyzed in any research. Since flash smelting furnaces process raw material from solid to liquid, the aim of thesis is to measure thermal conductivity of copper mattes and fayalite slag at low to high temperature. The analysis must be able to explain causes of the measured values, their behavior at elevated temperatures, and their connections to characteristics of the samples. Characterization of samples, e.g. using SEM-EDS and XRD, was done prior to thermal conductivity measurement. The method of thermal conductivity measurement, laser flash analysis, was predetermined from the start of thesis. Five matte samples and three slag samples were prepared. Among the five matte samples, two were doped with arsenic to observe its effect to thermal conductivity of copper matte. The measurement temperature points were 300 °C, 600 °C, and 900 °C, which resemble raw material’s temperature inside flash smelting furnace. To observe thermal conductivity of molten slag, one slag sample was measured as well at 1000 to 1200 °C. Thermal conductivity analysis is executed by NETZSCH company, using NETZSCH 467 HT HyperFlash®. The thermal conductivity measurement results for copper matte were 1.2 to 1.5 W m-1 K-1 at 300 °C and around 2.1 W m-1 K-1 at 900 °C. Meanwhile, arsenic containing matte samples had lowered thermal conductivity, between 0.5 and 1.3 W m-1 K-1 at 300 to 900 °C. The observation of experimental data concluded that thermal conductivity of copper mattes increases linearly with temperature. Its dependence on temperature was weak since the margin was barely 1 W m-1 K-1. Low values of thermal conductivity were within expectation as copper sulfide has low thermal conductivity based on prior research. Positive relation between thermal conductivity and temperature, however, was outside expectation because it indicated non-conductor material. Thermal conductivity of observed slags are between 1.6 and 1.9 W m-1 K-1. These values were close to prior research in silicate slag. The three slag samples had more than 30 wt-% SiO2 content and they behaved as glassy slag. Glassy structure of slag samples probably because the basic oxides were only Al2O3 and a minor amount of FeO, meanwhile the iron content in all slag samples were not enough for complete fayalite formation. Experimental data of the three slag samples were not conclusive as well because one slag sample had thermal conductivity which was lower than expected. In addition, experimental data of molten slag did not match the references. Its thermal conductivity increased with temperature, although it was supposed to decrease.
Jokilaakso, Ari
Thesis advisor
Luomala, Matti
copper matte, fayalite slag, thermal conductivity, laser flash analysis, glassy slag
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