Preparation Of Pellets From Phosphate Rock Powder And Its Performance Evaluation

The raw material of yellow phosphorus production by electric furnace method is mainly high-grade massive phosphorus ore.With the continuous consumption of high-grade phosphorus ore resources,fewer massive raw materials that meet the requirements of entering the furnace.In order to effectively solve the problem of raw material source in yellow phosphorus production,the rational application of the phosphorus ore powder produced in the mining or crushing process has also attracted researchers’attention.The preparation of phosphorus ore powder pellets provides a feasible technical idea for the preparation of furnace raw materials.To further study the preparation and properties of phosphate rock powder pellets,three types of phosphate rock powder materials（includes raw ore powder,concentrate powder and the mixture powder）were taken as the objects.In this paper,the optimal preparation process of each powder pellet was studied,and then the mechanical properties and high-temperature reduction performance of the prepared pellets were systematically evaluated.Finally,the reaction mechanism in the pellet reduction process were clarified by using the X-ray powder diffraction analyzer（XRD）and scanning electron microscope（SEM）analysis of the slags.The main research contents and conclusions are as follows:The content of P₂O₅in the raw ore powder is 18.45%,and the molar ratio of silicon to calcium is 1.29.The content of P₂O₅in the raw ore powder is 30.74%,and the molar ratio of silicon to calcium is 0.27;The melting characteristic temperature value of the concentrate powder was higher than that of raw ore powder,and that in the mixture powder was rather intermediary between the above two.When the dosage of DS binder is 0.5%and the roasting temperature is 1000℃,the average compressive strength of raw ore powder,concentrate powder and mixed sample cooked pellets are 1235.6N/piece,1265.3N/piece and 1367.2N/piece respectively,and the compressive strength of cooked pellets is more than 1000N/piece,which meets the requirements of industrial production.The addition of coal powder will greatly reduce the compressive strength of pellets,and the greater the amount,the more obvious the decrease of compressive strength of pellets.The results of pellet reduction tests show that the main factors affecting pellet reduction rate are reaction time,reaction temperature and coal ratio.The reduction rate can reach 95.31%under the conditions of 1400℃temperature,2h reaction time and 20%coal ratio.The reduction rate of concentrate powder pellet can reach 95.39%under the conditions of temperature 1450℃,reaction time 2h,coal ratio 20%and silicon calcium molar ratio 1.0.When the ratio of raw ore powder to concentrate powder is 2:1（silicon calcium molar ratio 0.84）,the reduction rate can reach 94.56%under the conditions of 1450℃,2h reaction time and 20%coal ratio.The XRD and SEM methods were used to analyze the phase composition and micro morphology of the pellet reduction slag.The results showed that the defluorination reaction of apatite mainly occurs at 1300℃,and a small amount of phosphate was reduced by carbon.When the temperature rose to 1400℃～1450℃,the reduction reaction between phosphate and carbon was enhanced which might be the increase of liquid phase in the reduction system.