Selective leaching kinetics of calcareous phosphate rock in lactic acid

Lactic acid was used to investigate the selective leaching kinetics of calcareous phosphate rock. The influence of acid concentration, liquid/solid ratio, particle size and temperature was studied in order to expound the dissolution kinetics of calcareous material in the rock. It was found that the leaching rate of calcareous material increased with increasing the acid concentration, liquid/solid ratio and temperature and decreasing particle size. A semi-empirical model was suggested to illustrate the selective leaching of calcareous material analyzing the experimental data. The selective leaching curves were evaluated in order to test the validity of kinetic models for liquid–solid systems. The kinetic data were analyzed by graphical and statistical methods and it was found that the leaching of calcareous material in the rock was controlled by chemical reaction, i.e., 1 − (1 − α)1/3 = 19.1C1.753(L/S)1.627D−0.737e−42954.62/RTt. The apparent activation energy of the leaching process was 42954.62 J mol−1 over the reaction temperature range from 298 to 338 K.