SU671716A3 - Method of purifying phosphoric acid - Google Patents

Description

keep at .20-70 ° C until conversion

Calcium sulfate hemihydrate to dihydrate.

The expediency of the selected parameters

process is due to the fact that the precipitation

Calcium sulfate hemihydrate is carried out at 70-100 ° C, since it is in this temperature range that calcium sulfate hemihydrate is formed, which is illustrated in the table.

The rate of conversion of the hemihydrate to dihydrate decreases with increasing concentration of phosphorus pentoxide in the suspension.

Turnaround time

CaS04-l / 2 HjO in CaS04-2H2O, min

Taking these data into account, the conversion is carried out in a recycled "dilute filtrate that contains from O to 30% phosphorus pentoxide.

The conversion of the hemihydrate to dihydrate is carried out at 20-70 ° C, since the conversion rate is low below 20 ° C, and it does not occur above 70 ° C.

The proposed method allows to reduce the loss of PaOs to 0.7%.

Example 1. In the reactor, 156.29 kg / h are mixed, containing 51.26% PgOs preheated to 80 ° C and treated with hydrogen sulfide crude phosphoric acid containing 3.32% H2SO4; 0.51% F; 0.16% C, as well as traces of copper and arsenic, with 0.56 kg / h of activated carbon, 1.52 kg / h of silicic acid, 0.8 kg / h of 50% sodium hydroxide solution and recycled pulp flow. At the same time, a dose of 2.97 kg / h of quicklime is added at 95 ° C. The pulp is continuously pumped from the reactor to the receiving tank and kept there for 2 hours at a temperature of 85 ° C. Then the pulp is filtered in a pressure filter with a slowly increasing pressure from 0 to 6 atm.

138.65 kg / h of filtrate containing 52.0% PrOe is removed from the filter; 0.30% SO4;

0.13% Ca and 0.17% F, and through the pipeline serves in the reserve tank. The separated sludge (23.0 kg / h), consisting of calcium sulfate hemihydrate, sodium silicofluoride, activated carbon, as well as arsenic sulfide and copper, is pumped to the second reactor and mixed with 65 kg / h of accumulated filtrates from the second filtration. The recycled solution contains 21.9% PjOs; 0.66% 504; 0.27% Ca and 0.56% F.

After treatment at 50 ° C, filter for 45 minutes. On a continuous filter, the separated dihydrate sludge is washed with 20.85 kg / h of fresh water. The filtrate and the washings are mixed and a 29.25 kg / h solution is obtained, which is combined with the main filtrate from the first filtration. The result is 167.90 kg / h of purified final solution containing 46.75% PaOs; 0.37% SO4, 0.15% Ca and 0.24% P. The loss of PgOs is 0.7%.

Example 2. In the reactor, 100 l / h of phosphoric acid treated with hydrogen sulfide, preliminarily heated to 80 ° С, containing 51% P2O5; 2.5% H2SO4; 0.51% F; 0.2% carbon and traces of copper and arsenic, from 1.91 kg / h of sodium sulfate. A stream of phosphoric acid with precipitated calcium sulfate hemihydrate, sodium silicofluoride, heavy metal sulphides and activated carbon and with absorbed organic components is simultaneously circulated from the receiving tank. To the mixture from the bunker in the reactor, Ca 6 3 was added in doses through a belt balance with doses of 5.46 kg / h. 0.71 kg / h of diatomite and 0.5 kg / h of activated carbon are added simultaneously. The pulp is pumped into the tank and then filtered on a pressure filter. The filtered calcium sulfate hemihydrate is recrystallized in the dihydrate as in Example 1, filtered from the mother liquor and washed with water. The mother liquor and wash water are mixed in the collection. Two thirds of the solution is recycled to the reactor and one part is combined with the filtrate from the first filtration in the storage tank. The solution contains 47.5% PsOj; 0.31% 804; 0.19% F. The loss of PjOs is 0.7%.

Claims (2)

1. A method of purifying phosphoric acid by treating it with calcium compounds and crystalline calcium sulfate in the presence of alkali metal compounds and silicic acid, sulfides and adsorbents, followed by separation of the acid from the precipitate, characterized in that, in order to reduce losses phosphoric acid, calcium sulfate hemihydrate is used as calcium sulfate, the process is carried out at 70-100 ° C, the resulting pulp is divided into three parts, two of which are returned to the processing stage after 45-60 minutes, and the third part filter, the precipitate thus obtained is suspended until it is suspended in O-30 weight. % of thioxy. phosphorus, and at 20-70 ° C, is maintained until the calcium sulfate hemihydrate is converted to calcium sulfate dihydrate. Information sources, taken into account in the examination 1. Japanese Patent No. 22403, Cl. 15 In 53, op flare. 1969. 2. The patent of Germany No. 1265725, cl. 12 25/22, publ. 1970.