Density and Surface Tension of the Molten Slags of Germanium Concentrate Production

The pyrometallurgical production of germanium concentrates from the raw materials (coal, argillite, siltstone) of brown coal fields is accompanied by the formation of molten silicate slags. The mineral component of the raw materials concentrates in slags, reaching 60 wt %. It is obvious that the process indices are mainly determined by the physicochemical properties of the molten slags, such as density rho and surface tension sigma, reflecting the structure of molten silicates. The compositions of the slags after processing of carbonaceous raw materials differ significantly from those of the slags of nonferrous and ferrous metallurgy: they contain higher contents of SiO2 (up to 50-55%), Al2O3 (up to 20-22%), K2O, and Na2O (up to 5-6%). In addition, the slags contain significant contents of sulfide sulfur (up to 3%) and trace amounts of nonferrous metals and rare elements (up to 5%). The differences between the compositions of the molten slags of germanium production and the slags of main metallurgy influence their properties and require special studies. Industrial cyclone melting and electric smelting slag samples are studied. Semi-synthetic samples are analyzed; these samples are produced from industrial ones by the addition of SiO2 and CaO in order to determine the influence of composition on rho and sigma. The measurements are based on the maximum pressure in an inert gas bubble blown in a melt, more specifically, on the differential version to improve the accuracy. The cell consists of the melt to be studied in an alundum crucible with an immersed alundum capillary and a reference capillary immersed into distilled water. The melt temperature is measured in the range 1100-1400 degrees C. rho and sigma of the melts are found to fall in the ranges from 2.20 to 4.3 t/m(3) and from 218 to 531 mN/m, respectively. The values of rho and sigma significantly depend on the basicity (ratio of the sum of the CaO and MgO contents to SiO2) and the Al2O3 content. The temperature dependences of rho and sigma are found to be linear with negative temperature coefficients. In the general case, rho and sigma of the melts significantly differ from, for instance, the blast furnace slags at the same basicity. The obtained results are valuable for predicting the structures of melts and their behavior under real conditions.