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Grinding is an indispensable process in many industrial plants. Nonetheless, the ground products may pass through the surface and/or undergo structural changes that may affect subsequent processes. In this study, the changes in the oil shale surface during its dry grinding in a ball mill were followed by Fourier-transform infrared (FTIR) analysis under different grinding conditions such as grinding time, ball type (i.e. ceramic or steel), and number of balls. Moreover, the generated heat limits during grinding were revealed by correlating the change in surface function groups of the ground products with those of conventionally heated oil shale samples in a furnace. The results indicated that the more intense the grinding action, in terms of the number or size of grinding balls and the grinding time, the higher the variations in the ground products' FTIR spectra, indicating the higher the surface oxidation of oil shale. More interestingly, correlating the FTIR spectra of the heated samples with those of the ground products indicated that the temperature inside the mill does not exceed 150 °C. [ABSTRACT FROM AUTHOR]

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Calcite is considered a semi-soluble mineral in flotation. Its solubility in acids plays a major role in its floatability. In this study, micro-flotation experiments are conducted to investigate the interaction of calcite particles with potassium oleate (KOl). Potassium oxalate is used as a depressant in the presence of HC1 or H2SO4as pH modifiers. Flotation experiments indicated that calcite behaves differently in the presence of HCl and H2SO4. The calcite floatability is higher in the case of HCl. The different behavior is more obvious in the presence of oxalate. The depressing effect of oxalate is more pronounced in the case of using H2SO4as a pH modifier. In addition, the sensitivity of calcite flotation to pH goes back to the amount of free Ca-ions in the solution. Ionic equilibrium of the dissolved ionic species is proved to play a crucial role in either enhancing or reducing the oleate adsorption, which in turn affects the calcite floatability. [ABSTRACT FROM AUTHOR]