Method for absorbing and extracting phosphor and fluorin from phosphoric acid produced in kiln method

Abstract

This invention discloses a method for separating phosphorus and fluorine of kiln process phosphoric acid by absorption. The method comprises: sending relatively high temperature phosphoric acid after hydration in primary and secondary hydration columns to a circulation tank for cooling, pumping into the hydration columns for circulation, sending gases after primary and secondary absorption to a Venturi absorber for re-absorption, collecting the residual acid mist by a collector, sending the absorbed gas and tail gas after fluorine absorption together to a chemical absorption column, and exhausting the tail gas. Besides, qualified fluosilicic acid can be obtained from the fluorine-containing diluted H3PO4 in the collector. The method utilizes the air with residual heat in the kiln, and has such advantages as no extra energy consumption, high phosphorus and fluorine separation efficiency, high concentration and low fluorine content in obtained H3PO4, and low P2O5 content in obtained fluosilicic acid. The obtained fluosilicic acid has a wide concentration range and a high purity, and is easy to utilize.

Description

technical field [0001] The invention relates to a method for absorption and separation of tail gas, in particular to a method for absorption and separation of phosphorous and fluorine in kiln process phosphoric acid. Background technique [0002] Phosphate rock inevitably contains fluorine element, and the fluorine-containing gas produced during the reduction process of producing yellow phosphorus and phosphoric acid from phosphorous rock is highly toxic and corrosive, and has great harm to the human body and the environment. During the production process of thermal phosphoric acid and kiln phosphoric acid, the fluorine element will escape together with the reduced phosphorus in the phosphate rock, and during the hydration process of phosphorus pentoxide, the fluorine-containing gas will be dissolved in the water at the same time and hydrolyzed to form Fluorosilicate (H 2 SiF 6 ) and other fluorine-containing solutions coexist in phosphoric acid, seriously affecting the pr...

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Problems solved by technology

During the production process of thermal phosphoric acid and kiln phosphoric acid, the fluorine element will escape together with the reduced phosphorus in the phosphate rock, and during the hydration process of phosphorus pentoxide, the fluorine-containing gas will be dissolved in the water at the same time and hydrolyzed to form Fluorosilicate (H 2 SiF 6 ) and other fluorine-containing solutions coexist in phosphoric acid, seriously affecting the product quality of phosphoric acid; 2 SiF 6 ) and other fluorine-containing solutions coexist in phosphoric acid. Due to the low concentration, the fluorine content in it is much higher than that of thermal phosphoric acid, but because it is mainly used for fertilizer production, it has little effect on the quality of phosphoric acid products; Silicic acid decomposes into hydrogen fluoride and silicon tetrafluoride escapes from phosphoric acid in a gaseous state. The higher the concentration and temperature of phosphoric acid, the lower the fluorine content remaining in phosphoric acid; but directly heating the mixed acid not only consumes high energy, but also As a result, the amount of absorbed gas increases, the separation rate of phosphorus and fluorine is not high, and high-concentration and low-fluorine phosphoric acid cannot be obtained, and P in fluorosilicic acid 2 o 5 The content of the fluorine absorption system is relatively high, and the workload of the fluorine absorption system is relatively large

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