Potassium(K)is a fundamental macronutrient for plant growth.With the fast development of world agriculture,the attainable K levels in soils have dropped gradually because of crop removal,water runoff and soil leakage.Therefore,a large amount of soluble potassium fertilizers is required to sustain an adequate supply of soluble K for plant growth per year.Recently,it is reported that the Khorat Plateau in the northeast of Thailand has rich potassium ore with vast reserve,so it would be very significant to develop the advanced technology for the production of soluble potassium fertilizer from the underground potash salt mine in Thailand.In this work,the reserve of the underground potash salt mine in Thailand was estimated,and the production process of potassium chloride from this potash ore was developed in order to provide the fundamental information for industrial application.The research contents include the following several aspects.　　The potassium-bearing salt ore is found in Maha Sarakham Formation at the depth of150to300meters,and the average thickness of the potassium-bearing section is 20 meters.A total of 29 drill-holes,spacing from 500 to1,200 meters,were drilled to obtain samples from underground.Then,the collected samples were analyzed,and it was found that the potassium content had an average value of 8.18％(K2O)and the average density of the mineral sample was 2.05±0.06 g/cm3.The amount of potassium salt in the underground resources was estimated to be about35million tons.　　The potash ore samples were characterized by XRD and XRF,it was found that the ore samples consisted of carnallite,sylvinite and halite with KCl average content of 16.23％.The cold decomposition and positive flotation process was selected to recover KCl from the potash ore,and the operation conditions of the process were optimized based on the laboratory testing.The optimum process conditions for cold decomposition and positive flotation were 25℃ and 30％ solid content,and the purity of refined potassium chloride reached 95.48％ with recovery rate of 85.70％.　　In the end,the engineering design for the 100,000 tons per year production process of the potassium chloride was carried out.The mineral processing involved 3 different processes to produce 3 different outputs,without waste discharge from any of the processes.For processing of 10％ K2O ore feed grade,the first output is NaCl with 98％ concentration at 27.5 ton/hour,which is an industrial grade salt.The second output is fine grade KCl with 95％concentration(K2O 60％)at 12.5 ton/hour.The third output is waste brine MgCl2 at 85 ton/hour,which would be backfilled underground.The overall KCl product recovery rate from this process was about 83.4％.