Dissolution Characteristics Of The Sludge In Wet Process Phosphoric Acid

In this paper, the physical and chemical properties of the sludge in wet process phosphoric acid were detected by X-ray fluorescence spectrum and laser particle size analyzer first, elements and valuable content were analyzed. Taking the sludge as the research object, based on the situation that it contains a lot of valuable components, abilities that transform the citrate acid soluble phosphorus in the sludge into water soluble phosphorus by three kinds of inorganic acid:nitric acid, sulfuric acid and hydrochloric acid, were testified. Parameters were optimized through experiments after that. Considering the complexity of the components and instability of effective constituent, in order to establish a proper standard for the detection of phosphorus content, the experiments provided some relevant data on the available phosphorus content extraction, with EDTA, CA and NTA. Finally, according to the results of the inorganic acid experiments, initial experiments were carried out as well.Results showed that in the sludge, main elements are O, P, F, S, Fe, Ca, Al, K, Na, Si, etc. And they were mainly existed in the form as some tiny amorphous micro crystals. Particle size is large, the average size is 120.343μm.In the nitric acid experiments, conversion rate is mainly depended on the reaction temperature and acid amount, good rate can be obtained at higher levels. Reaction time, acid concentration and stirring intensity showed less influence. Concentration and stirring intensity reduced first, then increased the rate along with the rising of the numbers. Reaction time had the least influence.In the sulphuric acid experiments, conversion rate depended mostly on the temperature and acid concentration, those both showed a positive correlation. Reaction time and acid amount were positive in general, bur also negative in a shorter reaction time or higher acid amount. Stirring intensity had the least influence in all five factors.In the hydrochloric acid experiments, the conversion rate was mainly determined acid concentration, acid amount and stirring intensity. The stirring intensity was positive bur negative while it’s too high. Concentration and amount of the acid strengthened the conversion. Reaction time and temperature showed weak influence, and inhibition took place in high temperature.Sulfuric acid showed the best conversion rate and lowest cost among nitric acid, sulfuric acid and hydrochloric acid. It’s suitable for production of commodity phosphate products, such as fertilizer etc. Nitric acid and hydrochloric acid showed lower conversion rate, but still can be used to develop and produce some high value-added products, such as new fertilizers, iron phosphate, etc.The most suitable effective phosphorus extraction among the three kinds of organic complexing agents, EDTA, NTA and CA, was EDTA. In order to make sure the available phosphorus analysis results are accurate, for 1g of sludge or corresponding products, it will take at least 180mL,37.5g/L EDTA-2Na solution to extract all the available phosphorus. And the reaction should take no less than 80rpm stirring intensity, after more than 60 minutes.Based on the results of sulfuric acid experiment, SSP were produced by phosphate after decomposition of sludge with sulfuric acid. The results showed that the product met the national standard, and the method was feasible, both technically and economically.