Methods of decomposing middle- and low-grade phosphate ore with double acids to produce polyphosphoric acid

Abstract

A method of decomposing any phosphate ore with hydrochloric acid and sulfuric acid to produce polyphosphoric acid is provided. The method includes: decomposing the phosphate ore with the hydrochloric acid to produce calcium chlorophosphate, decomposing the calcium chlorophosphate with the sulfuric acid by utilization of a hemihydrate-dihydrate method or a dihydrate method to produce phosphoric acid with a high concentration, desulfurizing, concentrating and polymerizing to obtain industrial polyphosphoric acid. Another method includes purifying the calcium chlorophosphate, decomposing with the sulfuric acid by utilization of a hemihydrate-dihydrate method or a dihydrate method, producing the phosphoric acid with a high concentration, desulfurizing, concentrating and polymerizing to obtain low-arsenic polyphosphoric acid. Calcium chlorophosphate mother liquor is salted out to obtain chloride through feeding HCl, and is returned to the e phosphate ore decomposing step. Rare earth, iodine, uranium, and other useful elements in the phosphate ore is enriched and extracted. The chloride and silicon slag are prepared into a high-activity silicon fertilizer by intermediate-temperature calcination. A byproduct HCl gas is fed into calcium chlorophosphate mother liquor of the next cycle to salt out the chloride, thus forming a closed cycle process. Water is added into phosphogypsum, pulped, and washed to obtain high-quality gypsum.

Description

technical field [0001] The invention belongs to the category of hydrochloric acid wet-process phosphoric acid and its purification technology Background technique [0002] Phosphate rock can be decomposed by nitric acid, sulfuric acid, and hydrochloric acid. The nitric acid method has not been widely used because it requires a large amount of stainless steel and platinum metal catalysts to build a plant, and the production cost is also higher. The hydrochloric acid method is rarely used by people because of its strong corrosion on equipment and low acid concentration. It was only after the 1960s that hydrochloric acid wet-process phosphoric acid technology was promoted into large-scale production at home and abroad, but the application The scope and product variety are very limited. The most abroad are hydrochloric acid decomposition of high-grade phosphate rock, and organic solvent extraction to purify phosphoric acid. In the 1970s, more than 40 hydrochloric acid feed calci...

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Problems solved by technology

Sulfuric acid wet-process phosphoric acid occupies an absolute dominant position at home and abroad. The process and equipment of this method are relatively simple. The disadvantage is that only rich ore and good ore can be used to produce phosphoric acid P 2 o 5 The concentration is lower and the impurity content is higher, so it is difficult to comprehensively extract the useful associated elements in phosphate rock. Because the iron-aluminum phosphate in it is in a metastable state, it will continue to precipitate during storage and transportation and block the pipeline valve, which is difficult Phosphoric acid as a commodity for long-distance transportation can only be produced locally and processed into fertilizer or feed phosphate. It is more difficult to purify industrial-grade, food-grade phosphoric acid, and the loss of phosphorus is greater. Phosphogypsum will take up valuable land to be stacked, and it will also cause phosphorus and fluorine pollution to the surrounding environment when it rains

But also seldom report from wet-process phosphoric acid to make polyphosphoric acid, the one is because sulfuric acid wet-process iron-aluminum phosphate impurity is too many, in the process of concentration, can constantly separate out, therefore will pass through several times of concentration filtration, concentrate again, filter again, to generate P 2 o 5 = about 50% concentrated phosphoric acid, to be concentrated again to reach P 2 o 5 =70-80%, it is very difficult, but the hydrochloric acid wet-process phosphoric acid of the 201110006702.7 patent can reach P 2 o 5 =84% polyphosphoric acid is required, but the color of the product is black, which has not yet reached the high-purity quality index

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