Discussion about extraction rate

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Our company's 120,000 tons/year phosphoric acid plant adopts the dihydrate process, supporting 150,000 tons of ammonium phosphate. The phosphoric acid reaction uses a double-tank single propeller (the size of the reaction tank is: Φ 11000×6900, the effective volume of each reaction tank is: 522m3, and the motor power of the stirring paddle is 185kW). The air cooling process, the phosphoric acid filtration adopts a double-series domestic flip-plate filter, and the surface cooler cooling process. The ball mill adopts a diameter of 3.6* 6m overflow ball mill, average grinding fineness -100 mesh 70%. Due to poor cooling effect, the temperature of the extraction tank is as high as 95-100°C. In order to increase the phosphorus yield and reduce the extraction temperature, the cooling method of the extraction tank was modified in 2015. Affected by the site conditions, the 1# extraction tank adopts low-level flash cooling and the temperature is maintained at 91°C-93°C. The 2# extraction tank adopts surface cooling and the temperature is maintained at 100°C. System operation indicator liquid-to-solid ratio: 1# 2.0-2.5 ； 2# 1.8-2.2 Sulfur trioxide: 1# 0.02-0.035 ； 2# 0.02-0.025 (remarks: In order to produce 60% granular ammonium phosphate, control the extraction rate of phosphoric acid residual sulfur): 97.5%. Washing rate 99.5%, phosphoric acid concentration: 22.5-23%, the system capacity is 480 tons/day. In order to reduce the company's production costs and release the company's production capacity, it was decided to activate the original 60,000 tons of ammonium phosphate system (200 tons/day) and 100,000 tons of ammonium phosphate compound fertilizer (300 tons/day) in January 2017, which led to an increase in the production pressure of the phosphoric acid system. The average daily processing standard ore (30%) was 1,350-1,500 tons/day. The system was started on the 1.1st, and the system operation indicator liquid-to-solid ratio in the first half month: 1# 2.0-2.5 ； 2# 1.8-2.2 Sulfur trioxide: 1# 0.02-0.035 ； 2# 0.02-0.025 (remarks: In order to produce 60% granular ammonium phosphate, control the extraction rate of phosphoric acid residual sulfur): 96.5%. Washing rate 98.5%, phosphoric acid concentration: 22.5-23%, the average grinding fineness is -100 mesh 70%, and the ore blending adopts Hubei ore/Guizhou ore 2:1. Due to the serious structure of the production system in winter, after adjusting the mine, the Hubei ore/Guizhou ore 1:1, coupled with the ball mill failure, the grinding fineness is reduced to about 65%, and the system extraction rate is reduced to 90 below, the lowest is 85%, the washing rate is normal. Because the activity of Guizhou ore is suspected to be poor, the ore mix of Hubei ore/Guizhou ore is adjusted to 2:1. The extraction rate begins to rise to 95%, but it fluctuates in multiple shifts, and the fluctuation range is 90-95%. I would like to ask you for help, analyze the reasons, and please enlighten me. Attached is the pulp fineness analysis.: Grinding fineness 69.0 74.0 73.8 66.4 62.6 60.2 72.5 77.2