Extraction of Platinum from Silicate Melt in a Direct Current Ore-Thermal Furnace

Pyrometallurgical extraction of platinum from an oxide system based on SiO₂, Al₂O₃, and CaO, which is unclaimed waste of the glass industry with a platinum content of 0.03%, is experimentally studied. Reducing smelting was carried out in a laboratory DC ore-thermal furnace equipped with a 10 dm³ graphite crucible with an axially installed graphite electrode. The crucible had a magnesite lining and was located in a steel casing. A negative potential was applied to the electrode, and a positive potential was applied to the crucible. Melting was carried out at a current of 300 A and a voltage of 100 V. The material was loaded during the melting process as it melted. The temperature of the melt was 1850 K. A charge of 41.6 kg was remelted in 6.5 h with an intermediate drain of melt. Draining was partially carried out by tilting the crucible, leaving the metallic phase at the bottom. The metal phase obtained was 322 g, which was ferrosilicon and contained ≈20% Si and 1.44% Pt. The energy and material balances of melting were considered. The microstructure of the starting material and melting products was investigated. In the starting material, the platinum is contained in the form of inclusions about 10 μm in size, which, when the material is melted, settle to the bottom of the crucible and dissolve in ferrosilicon formed as a result of carbothermic reduction. It is shown that Stokes’ law is applicable to determine the sedimentation rate under electric melting conditions. When ferrosilicon solidifies, the platinum and copper form separate phases in which the platinum content is about 50%.