A system for preparing feed-grade phosphoric acid by wet-process phosphoric acid and its preparation method

Abstract

The invention discloses a system and a preparation method for preparing feed-grade phosphoric acid from wet-process phosphoric acid, and relates to the technical field of phosphoric acid production. The preparation method is composed of processes such as wet-process phosphoric acid desulfate radical removal, heavy metal removal, graded concentration defluorination, air stripping defluorination, steam defluorination and the like. Using wet-process phosphoric acid as raw material to remove sulfate and heavy metal ions in phosphoric acid under different phosphoric acid concentration conditions, the feed grade is completed by using steps such as fractional concentration defluorination section, multi-stage series gas defluorination section and steam defluorination section. Purify phosphoric acid to obtain high-quality feed-grade phosphoric acid. The method for preparing feed-grade phosphoric acid by wet-process phosphoric acid does not require phosphoric acid filtration or pressure filtration, and no slag phosphoric acid and solid waste are generated during the process, with high phosphorus yield, high defluorination efficiency, good recovery of fluorine resources, and P in the product phosphoric acid. 2 o 5 The / F can reach more than 300, the process continuity is good, the device capacity is large, and it also has the characteristics of low comprehensive energy consumption and excellent investment. The maximum can reach 300,000 tons P 2 o 5 / year.

Description

technical field [0001] The invention relates to the technical field of phosphoric acid production, in particular to a system for preparing feed-grade phosphoric acid from wet-process phosphoric acid and a preparation method thereof. Background technique [0002] Feed-grade phosphoric acid is prepared by wet-process phosphoric acid. The key technology of the purification process is defluorination. At present, the domestic feed-grade phosphoric acid purification process has the following problems: (1) Large loss of phosphorus: At present, domestic feed-grade wet-process phosphoric acid purification uses chemical precipitation to defluorinate more, Chemical defluorination is the use of alkaline Na 2 CO 3 The formation of sodium fluorosilicate with fluorosilicate is achieved by utilizing the low solubility of sodium fluorosilicate in phosphoric acid. In phosphoric acid P 2 o 5 Under the condition of concentration of 40-47%, harmful impurities such as sulfate radicals, heavy m...

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Problems solved by technology

[0002] Feed-grade phosphoric acid is prepared by wet-process phosphoric acid. The key technology of the purification process is defluorination. At present, the domestic feed-grade phosphoric acid purification process has the following problems: (1) Large loss of phosphorus: At present, domestic feed-grade wet-process phosphoric acid purification uses chemical precipitation to defluorinate more, Chemical defluorination is the use of alkaline Na 2 CO 3 The formation of sodium fluorosilicate with fluorosilicate is achieved by utilizing the low solubility of sodium fluorosilicate in phosphoric acid. In phosphoric acid P 2 o 5 Under the condition of concentration of 40-47%, harmful impurities such as sulfate radicals, heavy metal ions and fluoride ions in phosphoric acid will form solid phase precipitates, and liquid-solid separation methods such as vacuum filtration or mechanical pressure filtration are used to realize phosphoric acid purification, but the solid phase contains walk a lot of P 2 o 5 , high phosphorus loss, high cost of liquid-solid separation; (2) low defluorination efficiency: gas stripping defluorination process, concentrated phosphoric acid is defluorinated by gas after removing sulfate and heavy metal ions, and the final product phosphoric acid P 2 o 5 / F reaches 300 to meet the quality requirements of feed-grade phosphoric acid. The gas stripping defluorination process is mostly single-stage defluorination, intermittent production, and the defluorination efficiency is low, especially when the Fe, Al, and Mg impurities in phosphoric acid are high ((Fe 2 o 3 +Al 2 o 3 +MgO) / P 2 o 5 >0.08) The defluorination efficiency is greatly reduced; (3) In the air stripping defluorination phosphoric acid purification process, in order to improve the air stripping defluorination efficiency, the general process is to concentrate dilute phosphoric acid to obtain P 2 o 5 Concentrated phosphoric acid with a concentration of 48-50%. During the aging process of concentrated phosphoric acid, impurities such as Fe and Al in phosphoric acid will form iron and aluminum phosphate precipitates. At the same time, F in phosphoric acid will also form some fluoride salts with fine crystal particles. For aging and sedimentation separation, it is necessary to recover phosphoric acid with higher solid content in the lower part of the sedimentation tank, that is, slag acid (the proportion of slag acid is generally 30%), and a filter press is generally used, but the cost of phosphoric acid filter press operation is high and the loss of phosphorus is large; Before the acid cleaning in the upper part of the cleaning tank is sent to the air stripping defluorination, a phosphoric acid filtration process is generally set up to further reduce the solid phase in the concentrated phosphoric acid (this solid phase is mostly fluorine salt with fine crystal particles). At present, phosphoric acid filtration is also a difficult problem , some slag acid will also be produced during the operation, and the cost is relatively high

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