CN212712757U - Recycling system of fluosilicic acid in phosphoric acid extraction process - Google Patents
Recycling system of fluosilicic acid in phosphoric acid extraction process Download PDFInfo
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Abstract
The invention belongs to the field of phosphoric acid preparation, and particularly relates to a recycling system of fluosilicic acid in a phosphoric acid extraction system, which comprises an extraction tank, a filter and a washing tower, wherein the upper end of the extraction tank is provided with a phosphorite slurry inlet, a sulfuric acid inlet and a tail gas outlet, the tail gas outlet is connected with the lower end of the washing tower, the upper end of the washing tower is provided with a spraying device, tail gas enters the washing tower and is sprayed and washed with water to form a fluosilicic acid solution, the fluosilicic acid solution returns to the extraction tank through a lift pump for extraction, and the washing tail gas is emptied; the slurry outlet of the extraction tank is connected with the filter, and the slurry enters the filter to form phosphoric acid and phosphogypsum. The invention provides a recycling process of fluosilicic acid in the phosphoric acid extraction process, which can effectively collect fluorine-containing tail gas, avoid directly discharging polluted air and realize the utilization of hazardous waste; and fluosilicic acid formed by fluorine-containing tail gas and water is added into the extraction tank, so that the extraction rate can be effectively improved.
Description
Technical Field
The invention belongs to the field of phosphoric acid preparation, and particularly relates to a recycling system of fluosilicic acid in a phosphoric acid extraction process.
Background
The wet-process phosphoric acid production process comprises a semi-water method, a dihydrate method and a semi-water dihydrate method, wherein the dihydrate method is the most mature process. No matter which wet-process phosphoric acid production process is adopted, the extraction process of decomposing phosphorite by sulfuric acid is inevitable. The quality of the phosphorite is different, and the fluorine content is also different. In the phosphoric acid extraction process, sulfuric acid reacts with phosphate ore, and fluorine escapes in the form of hydrogen fluoride; since the phosphate ore also contains a large amount of silicon dioxide, hydrogen fluoride reacts with the silicon dioxide to produce fluosilicic acid, and the fluosilicic acid reacts with the silicon dioxide to produce silicon tetrafluoride and water, fluorine finally escapes substantially in the form of silicon tetrafluoride gas. Therefore, how to better realize fluorine removal and how to treat the fluorine-removed fluosilicic acid is an important problem.
Disclosure of Invention
In order to solve the problems, the invention provides a recycling system of fluosilicic acid in the phosphoric acid extraction process, which can realize recycling of the fluosilicic acid.
The specific technical scheme is as follows: a cyclic utilization system of fluosilicic acid in a phosphoric acid extraction process is characterized by comprising an extraction tank, a filter and a washing tower, wherein a phosphorite slurry inlet, a sulfuric acid inlet and a tail gas outlet are formed in the upper end of the extraction tank, the tail gas outlet is connected with the lower end of the washing tower, a spraying device is arranged at the upper end of the washing tower, tail gas enters the washing tower and is sprayed and washed with water to form a fluosilicic acid solution, the fluosilicic acid solution returns to the extraction tank through a lift pump for extraction, and the washing tail gas is emptied;
the slurry outlet of the extraction tank is connected with the filter, and the slurry enters the filter to form phosphoric acid and phosphogypsum.
A process for recycling fluosilicic acid in the extraction process of phosphoric acid comprises the following steps: phosphorus ore pulp and sulfuric acid are added into the extraction tank for full reaction, and the fluosilicic acid solution formed after tail gas generated in the extraction tank is washed by a washing tower is returned to the extraction tank.
Has the advantages that: (1) the system provided by the invention can effectively collect the fluorine-containing tail gas, avoid directly discharging polluted air and realize the utilization of hazardous waste;
(2) the fluorine-containing tail gas and water form fluosilicic acid which is added into the extraction tank, so that the extraction rate can be effectively improved, the reason is that the fluosilicic acid is a strong acid (the pH is 1.6 (the pH is close to nitric acid without considering decomposition) under the condition of strong acidity of 0.03 mol/L), and the comprehensive action of the fluosilicic acid can effectively promote the dissolution and reaction of phosphate ore.
Drawings
FIG. 1 is a schematic diagram of the system connection of the present invention.
Detailed Description
A cyclic utilization system of fluosilicic acid in a phosphoric acid extraction process is characterized by comprising an extraction tank, a filter and a washing tower, wherein a phosphorite slurry inlet, a sulfuric acid inlet and a tail gas outlet are formed in the upper end of the extraction tank, the tail gas outlet is connected with the lower end of the washing tower, a spraying device is arranged at the upper end of the washing tower, tail gas enters the washing tower and is sprayed and washed with water to form a fluosilicic acid solution, the fluosilicic acid solution returns to the extraction tank through a lift pump for extraction, and the washing tail gas is emptied; the slurry outlet of the extraction tank is connected with the filter, and the slurry enters the filter to form phosphoric acid and phosphogypsum.
A process for recycling fluosilicic acid in the extraction process of phosphoric acid comprises the following steps: and (3) returning the fluosilicic acid solution formed after tail gas generated in the extraction tank is washed by the washing tower into the extraction tank. After the fluosilicic acid returns to the extraction system, mixed acid is formed with sulfuric acid and phosphoric acid, participates in the decomposition of phosphorite together, and is combined with ferrous ions, sodium ions and the like to form solution which exists in the extracted phosphoric acid, and a small part of the solution is taken away with the phosphogypsum by fluoride and fluosilicate precipitate. The fluorine-containing tail gas and water form fluosilicic acid which is added into the extraction tank, so that the extraction rate can be effectively improved, the reason is that the fluosilicic acid is a strong acid (the pH is 1.6 (the pH is close to nitric acid without considering decomposition) under the condition of strong acidity of 0.03 mol/L), and the comprehensive action of the fluosilicic acid can effectively promote the dissolution and reaction of phosphate ore.
5H2SiF6+ Ca5F(PO4)3=CaSiF6+ 3H3PO4+HF
Examples
Phosphate rock slurry containing 30-35 wt% of water is added into an extraction tank from a phosphate rock slurry inlet of the extraction tank, fluosilicic acid solution returned by a tail gas washing system is added into the extraction tank, the extraction tank is composed of 16 chambers, and each chamber is internally provided with two layers of blade stirrers.
The flow rate of 98 wt% concentrated sulfuric acid and phosphorite slurry is set according to a certain proportion, the sulfuric acid is premixed with the cleaning solution from the filtering procedure in the mixing tee after being metered, and then the mixture is added into the reaction tank, and the flow rate and concentration of the returned cleaning solution depend on the solid content and liquid phase P in the reaction tank2O5The concentration is controlled to ensure that the solid content of the reaction slurry is controlled to be 28-30 wt%, and the concentration of the product acid is controlled to be about 12-15% P2O5。
The main reaction with sulfuric acid after the extraction tank: ca5F(PO4)3+5H2SO4+mH2O==3H3PO4+5CaSO4.m/5H2O+HF、
5H2SiF6+ Ca5F(PO4)3=CaSiF6+ 3H3PO4+HF
Because the phosphorite contains a certain amount of silicon dioxide, side reactions occur simultaneously: 6HF + SiO2+==H2SiF6+2H2O，H2SiF6And (3) thermal decomposition: h2SiF6==SiF4+2HF,SiF4The gas phase product and other gas phase products generated by the reaction enter a tail gas absorption system; the slurry outlet of the extraction tank is connected with the filter, and the slurry enters the filter to form phosphoric acid and phosphogypsum, and the extraction rate is shown in table 1.
The tail gas absorption system comprises a Venturi scrubbing tower, a first vertical re-spraying scrubbing tower, a second vertical re-spraying scrubbing tower demister and a matched scrubbing solution circulating pool;
the tail gas from the extraction tank and the filter firstly enters a Venturi washing tower under the action of an induced draft fan, then enters a first vertical re-spraying washing tower after being washed, is circularly eluted in the washing tower and then enters a second vertical re-spraying washing tower, is washed by a circulating washing liquid for defluorination and then enters a demister after being washed by a process water, the demister recovers liquid and returns to a second washing circulation tank (the tail gas absorption system adopts the existing general washing technology), the tail gas is pumped away by the induced draft fan, the fluorine content of the tail gas meets the environmental protection standard (the index is shown as an accessory 1), and the tail gas is discharged into the atmosphere through a tail gas chimney.
The upper layer of the second vertical type re-spraying washing tower is washed by process water, the washed washing liquid enters a second washing circulation tank, the washing liquid in the second circulation tank is conveyed to the lower layer of the second vertical type re-spraying washing tower through a pump for circulation washing, and meanwhile, part of the washing liquid is supplemented to the first circulation tank to be used as the washing liquid of the first vertical type re-spraying washing tower;
the washing liquid in the first circulating tank is conveyed to a first vertical re-spraying washing tower through a pump to be subjected to two-stage defluorination circulating washing, and meanwhile, part of the washing liquid is supplemented to a Venturi washing circulating tank to be used as the washing liquid of the Venturi washing tower;
washing liquor in the circulating tank of the Venturi washing tower is conveyed to the first Venturi washing tower through the pump to be subjected to defluorination circulating washing, meanwhile, part of the washing liquor is supplemented into the extraction tank, washing circulating liquor contains a certain amount of fluosilicic acid, and the comprehensive effect of the washing circulating liquor can effectively promote the dissolution and reaction of phosphate ores. The reason is that the fluosilicic acid itself is a strong acid (the pH is 1.6 at a concentration of 0.03mol/L, which is strong in acidity (the acidity is close to that of nitric acid regardless of decomposition)), and the extraction rate can be effectively increased (the influence on the extraction rate is shown in tables 1 and 2).
The tail gas index can reach the standard by controlling the washing amount of the process water, and the liquid level of each washing tank is controlled to be stable by adjusting the supplement amount of the washing water.
Monitoring result of extraction tail gas of calcium hydrogen by Yunnan Haochen environmental protection technology limited company
TABLE 1 rate of extraction of fluorosilicic acid after return to extraction tank under normal operating conditions
TABLE 2 percent extraction under normal operating conditions after fluosilicic acid is not returned to the extraction tank
Claims (1)
1. A cyclic utilization system of fluosilicic acid in a phosphoric acid extraction process is characterized by comprising an extraction tank, a filter and a washing tower, wherein a phosphorite slurry inlet, a sulfuric acid inlet and a tail gas outlet are formed in the upper end of the extraction tank, the tail gas outlet is connected with the lower end of the washing tower, a spraying device is arranged at the upper end of the washing tower, tail gas enters the washing tower and is sprayed and washed with water to form a fluosilicic acid solution, the fluosilicic acid solution returns to the extraction tank through a lift pump for extraction, and the washing tail gas is emptied;
the slurry outlet of the extraction tank is connected with the filter, and the slurry enters the filter to form phosphoric acid and phosphogypsum.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116281904A (en) * | 2023-01-17 | 2023-06-23 | 昆明川金诺化工股份有限公司 | Method for reducing content of byproduct phosphorus fluosilicate in semi-water wet method phosphoric acid production |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116281904A (en) * | 2023-01-17 | 2023-06-23 | 昆明川金诺化工股份有限公司 | Method for reducing content of byproduct phosphorus fluosilicate in semi-water wet method phosphoric acid production |
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