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The structural changes and phase transition of kaolinite during thermal treatment were investigated by thermogravimetric analysis, differential thermal analysis, infrared spectroscopy, X-ray diffraction (XRD) and solid-state 29 Si magic angle spinning nuclear magnetic resonance in this paper. It was found that kaolinite experiences solid phase chemical transformation on heating, during which silicon in kaolinite-layered structure is activated. The thermal treatment of kaolinite at a temperature of above 980°C results in the formation of amorphous SiO 2 . The recrystallization of mullite occurred when the temperature exceeded 1100°C. Quartz keeps unchanged below 1200°C. The thermochemical (TC) process provides an avenue for the removal of silicon in kaolinite. The appropriate conditions for kaolinite activation were found to be 1050-1100°C and 90-60 min. The XRD patterns of solid leached residue revealed that amorphous SiO 2 could be efficiently removed by alkali leaching. The TC process was applied to desilication of kaolinite type bauxite ores. Above 50% silica total removal and 9-10 A/S ratio of desilication product were obtained at the heat conditions of 1050-1100°C and 90-60 min for an ore sample bearing 19.4% kaolinite and 4.6% quartz and with the 4.4 A/S ratio.

An organic binder, Funa, has been developed and used in the production of iron ore pellets for direct reduction in China. This paper mainly describes the effects of the binder on balling behaviors of magnetite concentrates as compared to bentonite binder. Natural ballability and dynamic ballability of concentrates as well as the mechanical strengths of the balls have been included in the assessment. Results show that the organic binder markedly improved the natural ballability and the mechanical strengths but reduce the balling rate compared to bentonite. Investigation shows that the improvement in natural ballability by the binder is attributed to its increasing effect on the wettability on the surface of concentrates. Due to its effects of increasing liquid viscosity, however, the binder clearly reduced the balling rate of the concentrates. The binder clearly improved wet ball strength also due to its viscosity increasing effects, as well as its chemical bonding to the iron ore surface. High-strength solid bridging of the binder and chemical bonding are the main reasons for much greater strengths of dry balls.

Abstract: Kinetics of silver leaching from a manganese-silver associated ore in sulfuric acid solution in the presence of H2O2 has been investigated in this article. It is found that sulfuric acid and hydrogen peroxide have significant effects on the leaching rate of silver. The reaction orders of H2SO4 and H2O2 were determined as 0.80 and 0.68, respectively. It is found that the effects of temperature on the leaching rate are not marked, the apparent activation energy is attained to be 8.05 kJ/mol within the temperature range of 30 C to 60 C in the presence of H2O2. Silver leaching is found to be diffusion-controlled and follows the kinetic model: 1−2x/3−(1−x)2/3=Kt. It is also found that particle size presents a clear effect on silver leaching rate, and the rate constant (k) is proportional to d −20 .