Method for preparing industrial grade and food grade phosphoric acid by decomposing low grade phosphate rocks with hydrochloric acid

Abstract

The invention relates to a method for preparing industrial grade and food grade phosphoric acid by decomposing low grade phosphate rocks with hydrochloric acid. The method comprises the following processing steps: (1) decomposing phosphate rock powder with hydrochloric acid; (2) extracting to remove iron; (3) preparing dilute phosphoric acid; (4) preparing industrial grade phosphoric acid; and (5) preparing food grade phosphoric acid. Food grade phosphoric acid can be prepared only by adding deep defluorination process on the basis of the preparation steps of industrial grade phosphoric acid. The deep defluorination process adopts vacuum steam stripping process and the processing conditions are as follows: the vacuum degree is 0.075-0.090MPa, and the temperature is 95-110 DEG C. Industrial grade phosphoric acid prepared by the method of the invention meets the super grade or first-class product standards of GB / T 2091-2008; and food grade phosphoric acid meets the standards of GB 3149-2004.

Description

technical field [0001] The invention belongs to the field of preparation of industrial-grade phosphoric acid and food-grade phosphoric acid, in particular to a method for preparing industrial-grade phosphoric acid and food-grade phosphoric acid by decomposing medium and low-grade phosphate rock with hydrochloric acid. Background technique [0002] The preparation of industrial-grade phosphoric acid and food-grade phosphoric acid can use hot-process phosphoric acid or wet-process phosphoric acid as raw material. Since the production of thermal phosphoric acid has high requirements on the grade of phosphate rock and high energy consumption, the production of industrial grade phosphoric acid and food grade phosphoric acid by wet process phosphoric acid has attracted more and more attention. The research on the purification of wet-process phosphoric acid by solvent extraction has never stopped at home and abroad, and great progress has been made, but most of the research in this...

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Problems solved by technology

The problem of preparing industrial-grade phosphoric acid and food-grade phosphoric acid from sulfuric acid wet-process phosphoric acid is that a large amount of phosphogypsum is accumulated and it is difficult to recycle.

But this method has the following disadvantages: 1. to prepare calcium chlorophosphate crystals to complete the first step of purification, because calcium chlorophosphate crystallization speed is very slow, for example at 20~22 ℃, when the HCl content in the solution is about 12%, containing 9.4% P 2 o 5 P in the decomposition solution 2 o 5 The time required to drop to about 4% is 210 minutes (seeing "the research of hydrochloric acid decomposing phosphate rock circulation process ", author Wang Changhui, Yao Dingwen, chemical fertilizer industry, 1988, the 5th phase, 14~17 pages), this just needs a lot of time. Large crystallizers increase equipment investment; calcium chlorophosphate is powdery and fine-grained, which easily leads to low impurity removal efficiency, difficult filtration, and increased equipment requirements; Ca in calcium chlorophosphate slurry 2+ The content is much lower than that of Ca in the acid hydrolysis solution 2+ content, affecting the extraction efficiency of phosphoric acid in the next step, resulting in a decrease in the extraction rate

②Extract phosphoric acid with tributyl phosphate, separate impurity ions such as calcium and iron, wash and back extract to complete the second step of purification, but in the phosphoric acid solution in the presence of hydrochloric acid, Fe 3+ with Cl - The formed complex is easy to be preferentially extracted by tributyl phosphate, and it is difficult to achieve complete separation even after washing; and this method uses the second washing water and the raffinate water phase as washing liquid to wash the organic phase, and the concentration of phosphoric acid in the washing liquid is relatively high. High, high viscosity, will lead to poor washing effect, and eventually lead to Fe in the finished phosphoric acid 3+ Higher content will affect the chroma and quality of the product

As far as the industrial-grade phosphoric acid produced in this patent embodiment is concerned, the iron content can only reach the qualified product index of GB / T 2091-2003

③ The flash point and boiling point of isopropyl ether in the extraction agent used in the second extraction are very low, so it needs to be extracted at low temperature, and it is highly volatile and extremely flammable. It can form an explosive mixture with air. Heat energy can cause combustion and explosion, which is more dangerous

④Two solvent extractions and two concentrations are required, and since the temperature of the second extraction is between 0°C and 10°C, the phosphoric acid after the first concentration needs to be cooled before extraction, which increases energy consumption

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