Effect Of Iron - Aluminum - Magnesium Impurity On The Production Of Diammonium Phosphate (DAP) In Phosphoric Acid

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 Yuntianhua international chemical co., LTD.(hereinafter referred to as:Yuntianhua International) is now producing DAP with clarifying concentrated acid. The MER of clarifying concentrated acid is more than0.105on average. It’s too high for the64%total nutrient content of DAP production. Although the N content of the DAP product can barely meet the requirement, but it can not meet the quality requirements of high-class products or export products. Combining with the production situation, the impact of iron, aluminum and magnesium content of DAP production is studied. The method of purifying wet process phosphoric acid is explored as well, in order to produce high quality DAP. Firstly, the impact of iron,aluminum and magnesium content on DAP production is studied in several aspects:In the process of ammoniation, the relation between DAP slurry viscosity and iron, magnesium and aluminum content of phosphate is studied.Combined with the actual phosphoric acid impurity range, Fe2O3,Al2O3and MgO is added into phosphoric acid respectively and quantitatively. By using these different impurities contented phosphoric acid, the influence on phosphate slurry viscosity is studied while producing DAP. Different impurities contented DAP is produced by using these different impurities contented phosphoric acid. By certain detection, the influence on the quality of the products (mainly refers to N/P and soluble P content) is studied.Secondly, as (Fe、Al)3KH14(PO4)8·4H2O, NaxMgxAl2-x(F、OH)6H2O would be generated during the aging process of concentrated phosphoric acid, and K、Na contributes to the formation of these compound sediments, some sylvite and sodium salt are added into the concentrated acid to prompt the generation of the sediment, so as to achieve purier concentrated phosphoric acid without Fe, Al and Mg. The experimental results show that after purification process, the purified phosphoric acid has reached the requirement of production of high-classe DAP. The iron removal rate of concentrated phosphoric acid could reach30%, the optimum process conditions are as follows:The dosage of K2SO4is5%o weight of the concentrated acid;The duration of aging process is above48h;The temperature of aging process is60℃The removal rate of aluminum and magnesium of concentrated phosphoric acid could reach31%and18%respectively. Producing DAP sample with the clarified phosphoric acid (MER0.090) as the raw material, and then the samples were analysised. The optimum technological conditions as follows:The dosage of NH4F is1%weight of the concentrated acid;The duration of aging process is above24h;The temperature of aging process is60℃. The results shows that total nitrogen content of DAP is vastly improved comparing with blank sample (about0.4%).