Ultrasound-Assisted Leaching Kinetics Of Potassium From Potash Ores

The soluble hoevellite resources are severely scarce in China.However,the insoluble potash ores,such as K-feldspar and phosphorus-potassium associated ore are very abundant.The extraction of soluble potassium from these insoluble potassium resources to produce potassium fertilizer and compound fertilizer has important significance.The use of acid for decomposition of K-feldspar and extraction of potassium has attracted widespread attention because of the characteristics of extensive applicability,simple process and comprehensive utilization of resources.However,the acid decomposition process still exists the drawbacks of large consumption of acid and additive.Therefore,how to strengthen the acid leaching process of potassium feldspar so as to overcome these drawbacks is an important research topic.In this paper,ultrasound was employed to strengthen acid leaching process,and the leaching kinetics of potassium from potassium feldspar and phosphorus-potassium associated ore was studied.The main contents and conclusions are as follows:(1)The extraction of potassium from K-feldspar in the calcium fluoride-sulfuric acid system at low temperature with the aid of ultrasound was studied.Leaching parameters affecting the leaching rate of potassium,such as sulfuric acid concentration,liquid/solid ratio,material ratio,and reaction temperature were investigated.The results show that the leaching rate of potassium increases by 3%~8% in the presence of ultrasound.Under the optimum reaction conditions of ultrasonic power of 100 W,reaction temperature of 90°C,liquid/solid ratio of 4,material ratio of 0.1,sulfuric acid concentration of 40% and leaching time of 7h,the leaching rate of potassium can reach 83.23%.(2)The reaction mechanism was discussed and the leaching kinetics model was established for K-feldspar-calcium fluoride system.The structures of K-feldspar and residues obtained with and without ultrasound were characterized by XRD and SEM.The results show that the acid leaching process mainly results from the decomposition of K-feldspar by HF,and the strengthening effect resulting from ultrasound can be explained by its "cavitation" effect.The leaching processes of K-feldspar with and without ultrasound follow the classical unreacted core-shrinking model with chemical reaction being the rate-limiting step.The apparent activation energies with and without ultrasound are 45.7and 40.5 kJ/mol,respectively.The apparent frequency factor in the Arrhenius equation with ultrasound is 12.5 times of that without ultrasound.The strengthening effect of ultrasound is the result of kinetic compensation effect resulting from the coupling of slightly increased activation energy and increased frequency factor.(3)Potassium from phosphorus-potassium associated ore exists mainly in the form of K-feldspar,and the mineral structure and composition of phosphorus-potassium associated ore are more complex than pure K-feldspar,hence,the extraction of potassium should be more complex.Based on the acid leaching result of pure K-feldspar,the extraction of potassium from phosphorus-potassium associated ore in the calcium fluoride-sulfuric acid system at low temperature with the assistant of ultrasound was further studied.Meanwhile,the leaching kinetics model with ultrasound was established.The results show that the leaching rate of potassium can reach 94.02% under the optimum reaction conditions ofultrasonic power of 100 W,reaction temperature of 90°C,liquid/solid ratio of 4,material ratio of 0.1,sulfuric acid concentration of 60% and leaching time of 7h.The kinetics analysis shows that the leaching process follows the classical unreacted core-shrinking model with internal diffusion being the rate-limiting step.The apparent activation energy is20.25 kJ/mol,and the semi-empirical kinetic equation coupling the parametric cumulative effect is as follows:This paper can provide basic data and theoretical support for the extraction of soluble potassium from insoluble potash ores.