The dissolution kinetics of colemanite in phosphoric acid solutions was studied. The effects of particle size, temperature, acid concentration, solid-to-liquid ratio, and stirring speed on the dissolution rate were determined. It was observed that the dissolution rate increased with decreasing particle size and solid-to-liquid ratio and with increasing temperature, but stirring speed had no effect on it. The dissolution rate increased up to an acid concentration of 19.52% (by wt) and then decreased with increasing acid concentration. The dissolution kinetics of colemanite were examined according to the heterogeneous and homogeneous reaction models for the acid concentration range of 1.43−19.52% (by wt) of acid concentration, and it was found that the dissolution rate was controlled by surface chemical reaction. The activation energy of this process was determined to be 53.91 kJ mol-1.

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In this study, some physical properties of biodiesel obtained from different mixtures of sunflower oil and beef tallow are investigated. The biodiesel cold-flow specifications, such as viscosity, pour point, cloud point, and cold-filter plugging point, were tested for the different sunflower oil/beef tallow (SO/BT) ratios. Also, the sulfur content and heat value of the biodiesel samples have been determined. It was observed that the examined physical properties of the methyl esters changed negatively as the beef tallow ratio in the mixture increased. However, until the ratio of 40% beef tallow and 60% sunflower oil, there was no important deterioration in the properties of methyl esters. When beef tallow contents were higher than 40%, some specifications of methyl esters were beyond the biodiesel standards of ASTM D 6751 and EN 1424.