Method for producing wet-process phosphoric acid from low-grade phosphate rock

Abstract

The invention discloses a method for producing wet-process phosphoric acid by utilizing low-grade phosphorite. The method is characterized by adopting a two-step reaction and backwashing method and specifically comprises the steps of: in first-step reaction, decomposing phosphorite with phosphoric acid in an extraction tank, and removing residues through solid-liquid separation to obtain clear liquid; and in the second-step reaction, reacting the extracted clear liquid with sulfuric acid in a reactor to generate calcium sulphate dihydrate crystal (ardealite) and phosphoric acid solution, and performing solid-liquid separation to obtain the phosphoric acid solution and the ardealite, returning a part of phosphoric acid solution to be used for decomposing phosphorite and a part of phosphoric acid solution to be used for outputting finished products. High-concentration high-quality wet-process phosphoric acid can be produced by utilizing the low-grade phosphorite; the phosphoric acid yield is high; and in addition, the white gypsum side product capable of being widely applied directly can be obtained. The method has wide industrial application prospects.

Description

technical field [0001] The invention relates to a method for producing wet-process phosphoric acid by using low-grade phosphate rock, belonging to the field of wet-process phosphoric acid production. Background technique [0002] Wet-process phosphoric acid is one of the important methods for preparing phosphoric acid, and it is also the basic product of the phosphorus chemical industry. It is widely used in the phosphate industry and the phosphorus compound fertilizer industry, and has a large demand. The production process of wet-process phosphoric acid is mainly to produce phosphoric acid by decomposing phosphate rock with inorganic acid (mainly sulfuric acid). The total amount of phosphate rock resources in my country is close to 50 billion tons, and P in phosphate rock 2 o 5 The rich ore with a content of more than 30% only accounts for about 8% of the reserves, and most of them are low-grade ores. 2 o 5 The average grade is only 16.85%, and most of them are colloph...

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Problems solved by technology

[0004] One of the main characteristics of low-grade phosphate rock is that the content of acid-insoluble impurities is particularly high. When phosphoric acid is produced by traditional phosphoric acid production methods, almost all of it enters phosphogypsum, which greatly reduces the quality of phosphogypsum and makes its comprehensive utilization difficult.

Moreover, due to the high content of impurities in low-grade phosphate rock, phosphate rock often has low decomposition rate and low washing rate. The calcium sulfate package generated by the reaction inactivates the reaction, and the formation of calcium hydrogen phosphate crystals increases the P 2 o 5 The loss of calcium sulfate crystals is difficult to separate, resulting in problems such as poor quality of finished phosphoric acid, resulting in abnormally high production costs and extremely unstable production, so that it is impossible to produce agricultural diammonium phosphate and high-grade agricultural monoammonium phosphate

[0005] Chinese patent CN9110859.7 "Tower Type Wet Process Phosphoric Acid Production Method and Equipment" mentions that medium and low-grade phosphate rock can be used as raw material to produce wet process phosphoric acid, but the grade of phosphate rock used is P 2 o 5 ≧25%, the range of available medium and low-grade phosphate rock is narrow; this method directly enters the mixed slurry of phosphate rock powder and circulating phosphoric acid into the extraction tower to react with sulfuric acid, and does not separate the impurities in phosphate rock from phosphogypsum come; and use concentrated sulfuric acid as the extractant, resulting in local SO 4 2- High concentration makes the reaction incomplete

[0006] Chinese patent 200510022547.2 "Method for producing wet-process phosphoric acid by using medium and low-grade phosphate rock" also mentions that its method can use medium- and low-grade phosphate rock as raw material to produce wet-process phosphoric acid, but the grade of phosphate rock used is P 2 o 5 %: 18~26%, and require MgO≦2.0wt%, Fe 2 o 3 +Al 2 o 3 ≦3.5wt%; it has strict requirements on the impurity content of phosphate rock, and at the same time, the process is complicated, the reaction is complicated, and the two-stage multi-stage reaction makes the cost high and does not have industrial universality; the method adopts multi-stage countercurrent extraction, and the operation The process is long and the requirements for production equipment are high; at the same time, there is no washing of residue and gypsum and the use of washing water, and the industrialization of resource technology has not been realized.

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