In recent years, with China's phosphate rock resources exploitation scale expanding gradually, the poor qualitative of phosphorus resource is becoming more and more serious. A mass of iron impurities such as iron(Fe), magnesium(Mg) and aluminum(Al) are dissoved into phosphate, causing MER of concentrated acid getting higher. The high MER concentrated phosphoric acid is negatively effected on the viscosity of diammonium phosphate slurry and the quality of the DAP products. The Third Ring Branch of Yunnan Yun...