Preparation Of Iron Phosphate By Ammoniated Slurry Of Wet Process Phosphoric Acid

Industrial-grade monoammonium phosphate(MAP)is often used to produce flame retardants and fire extinguishing agents because of its good thermal stability.In agricultural production,industrial-grade MAP is a high purity nitrogen and phosphorus compound fertilizer,and it also the main raw material for preparing high-grade water-soluble fertilizer.With the development of water-soluble fertilizers in China,the demand for industrial-grade monoammonium phosphate is also increasing with each passing day.In the process of modern agricultural development,industrial-grade monoammonium phosphate will in an important position.The neutralized slurry concentration process developed independently in China not only solves the problem that it is difficult to produce ammonium phosphate from most middle and low-grade glutinous phosphate rocks in China,but also reduces the material requirements of reaction equipment,which makes the development of ammonium phosphate industry in China rapidly.But everything has two sides.Many metal ion impurities contained in Wet process phosphoric acid will produce a large amount of water-insoluble ammoniated slurry slag during neutralization with ammonia.A large number of ammoniated slurry slag can not be digested during the production process of industrial-grade monoammonium phosphate.As a result,the industrial-grade monoammonium phosphate device often stops at full tank,which restricts the continuous production of industrial-grade monoammonium phosphate.Therefore,how to deal with the ammoniated slurry slag produced in the production of ammonium phosphate has become a difficult problem faced by major phosphorus chemical enterprises.In this thesis,we use the slurry of ammonium phosphate produced in the process of preparing monoammonium phosphate by slurry process of wet-process phosphoric acid as a raw material to prepare iron phosphate material with high value.The main research contents include three parts: Firstly,with sulfuric acid as leaching agent,theeffect of sulfuric acid on phosphorus leaching from slurry slag under different acid dosage,reaction temperature and reaction time was studied,and the optimum leaching conditions were determined.Then,the purified solution was obtained by using cooling crystallization and chemical precipitation to remove magnesium and fluorine impurities from the leaching solution.The effects of different temperatures on the removal rate of magnesium in the process of cooling crystallization has been researched.The effects of the dosage of different defluorinating agents,reaction temperature and reaction time on the removal efficiency of fluorine impurities in the leaching solution were studied.And the optimun impurity removal conditions were determined.Finally,the purified solution was used as phosphorus source to react with ferrous sulfate heptahydrate,and the effects of different phosphor、iron material ratio,reaction pH,reaction temperature and the amount of surfactant on the content of phosphorus,iron and the molar ratio of iron to phosphorus were studied.XRD,SEM,IR,TG-DTA,EDS and particle size analysis were used to characterize the crystal form,micro-morphology,containing groups,crystalline water content,containing elements and median particle size of the samples.The main conclusions are as follows:(1)The phosphorus in the slurry of wet phosphoric acid ammoniation was leached with sulfuric acid as leaching agent.The optimum leaching conditions were as follows: the dosage of sulfuric acid was 0.9(the mass ratio of sulfuric acid to dry basis of slurry),the reaction temperature was 90℃,and the reaction time was 60 min.When the dosage of sulfuric acid is 0.9(the mass ratio of sulfuric acid to dry basis of slurry),most of the phosphorus-containing non-water-soluble substances in the slurry of wet-process phosphoric acid ammoniation are dissolved,and the digestion is89.04%.(2)Magnesium impurities in sulphuric acid leaching solution were removed by cooling crystallization method.The optimum cooling crystallization temperature was8℃.Under this condition,the removal rate of magnesium impurities(expressed as the content of magnesium oxide)in the leaching solution is 61.83%.Fluorine impurities in sulfuric acid leaching solution after cooling crystallization and filtration were removed by chemical precipitation method with sodium sulfate as precipitant.Theoptimum defluorination process was as follows: the dosage of sodium sulfate was 1.2times of the theoretical value,the reaction time was 60 min,and the reaction temperature was 60℃.Under this condition,the removal rate of fluorine impurity is59.07%.(3)The optimum technological conditions for preparing iron phosphate powder by oxidation liquid precipitation method using purified solution as phosphorus source are as follows: molar ratio of phosphate to iron is 1:1,reaction pH is 2,reaction temperature is 80℃,and the dosage of surfactant PEG is 3% of the mass of iron salt.Under this condition,the iron and phosphorus molar ratio of the synthesized iron phosphate is the nearest to 1.(4)Under the optimum process conditions,the iron phosphate powder which prepared by oxidation liquid precipitation method is amorphous.The content of crystalline water was 19.27%.The phase of iron phosphate powder calcined at 700 degree temperature changed from amorphous to three square crystal.The median particle size(D50)of iron phosphate sample is 760 nm.The particle distribution is uniform,the dispersion is good,and the particle size range is narrow.