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EFFECT OF CaO/MgO RATIO AND BASICITY DURING TIN SMELTING ON THE METAL AND SLAG FORMATION (II)

M. Collen Seema

Abstract

The current demand of some specific metals (alloys) in the HiTech industry has pushed researchers to increase the number of investigations to improve the quality of products on the market. Generally, coltan is a byproduct of tin metallurgy and is collected in the slag. The formation of phases in the slag needs to be investigated in order to optimize the collection of coltan in specific phases by trying different ratios in fluxes. Also, cassiterite is associated with iron ores and during smelting the iron get reduced together with tin and ends up contaminating the metal. The basicity is always a useful parameter that govern the behavior of the slag. Basicity was varied through addition of CaO and MgO. The CaO/MgO was varied by changing CaO and keeping MgO constant as opposed to previous study where CaO/MgO was varied by changing MgO and keeping CaO constant. Different basicities of 0.8, 1, 1.2, 1.3 and 1.4 were used. A cassiterite ore from the Kibara belt was used in this study. A tube furnace was used for the reduction of the samples at 14000C for an hour after the desired temperature was reached. A graphite crucible was used for the experiments. The ore and the fluxes were milled together for 15 minutes to homogenize the feed. Carbon monoxide was blown into the furnace to act as a reducing agent. The feed and the products were analyzed using an X-ray Fluorescence, X-ray Diffraction, Scanning electron macroscopy and Energy Dispersive Spectroscopy. Previous works have kept CaO constant. The correlation between the CaO/MgO ratio and the quality of the metal as well as the slag was established. Further, the influence of the basicity, based the fact that MgO was kept constant at 0.8, the correlation between the basicity and the quality of the slag and metal was established. The phases that formed and preferentially collected Nb and Ta were identified. A comparison with previous study where CaO was kept constant revealed that the phases that formed in the slag were similar. Results showed, the tin grade increases from 81.2% (head grade) to 98.5% at a basicity of 0.8 while recovery drops from 85.8% at basicity 0.8 to 76.9% at basicity 1.4. The tin content in the metal is inverse proportional to the basicity. The basicity of 0.8 yields a high Sn recovery and grade while high Nb/Ta are achieved at basicity 1.2.

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DOI resolver: doi.org/10.5593/sgem2019/1.3/s04.100

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