Kinetic and Thermodynamic Studies on Lead-Rich Slag Reduction at Various CaO/SiO2 Ratios

A bath smelting furnace is a clean technology replacing sinter machines to simultaneously produce lead-rich slag and lead metal. Lead-rich slag can be used as a feedstock for blast furnaces or smelting reduction furnaces to produce lead metal. Understanding the reduction mechanism of lead-rich slag by carbon provides useful information for the complete reduction of the lead oxide. Kinetic studies on the reduction of lead-rich slags with CaO/SiO 2 ratios of 0.38, 0.56, and 0.80 were carried out in the temperature range 1073–1473 K. The volume of the product gas was measured continuously to represent the extent of lead-rich slag reduction. It was found that the reduction was initially chemically controlled and then diffusion controlled. At the chemically-controlled stage, the activation energy of the reduction was higher at lower CaO/SiO 2 ratios. An increase of the CaO/SiO 2 ratio from 0.38 to 0.56 can decrease the activation energy from 273 kJ/mol to 95 kJ/mol. At the diffusion-controlled stage, the activation energy was determined to be 392 kJ/mol, 294 kJ/mol, and 280 kJ/mol for the slags with CaO/SiO 2 ratios of 0.38, 0.56, and 0.80, respectively. Formation of liquid plays an important role in the reduction of the lead-rich slag. The reduction mechanism has been analyzed by experimental results and thermodynamic calculations.