DE721410C - Production of technically pure alkali phosphates - Google Patents

Description

Production of technically pure alkali metal phosphates generally takes place the production of commercial grade alkali phosphates from phosphoric acid in such a way that the phosphoric acid. neutralized with alkali carbonate to diphosphate will; the diphosphate obtained can then, for. B. still by further treatment with Alkali can be converted into the triphosphate. Can of pure phosphoric acid be assumed as they are z. B. is obtained thermally, so achieved In contrast to the above products, neutralization naturally leads to direct alkali metal phosphates of commercial purity.

Crude phosphoric acid, as it is e.g. B. by digestion of rock phosphates is produced by sulfuric acid, usually contains larger amounts of impurities, especially calcium, aluminum and iron. To make such phosphoric acid alkali phosphates to produce commercial purity, this must either be cleaned beforehand or the desired end products can be purified by crystallization. Usually it is crystallized twice; the products obtained then correspond. in their purity the usual trading conditions. It is known to alkali phosphates Manufacture from dilute, unpurified raw phosphoric acid by adding the raw phosphoric acid is neutralized with alkali carbonates to mono- and diphosphate and the precipitated Impurities can be removed by filtration. From the diluted Solution is only through crystallization, if necessary after previous evaporation to get a commercial product.

It has also been suggested from concentrated phosphoric acid To win alkali phosphates in such a way that the impurities after Neutralization and heating are filtered off, but it is assumed that that only relatively small amounts of impurities are present, lvie she z. B. contained in phosphoric acids are obtained by thermal reduction of Accumulate phosphates. However, this process does not work with concentrated phosphoric acids, which are produced from rock phosphates by digestion with sulfuric acid. Such Phosphoric acids contain so many impurities that only a few high concentration the diphosphate z. B. represents a pulpy mass that is without previous dilution - do not filter.

Attempts have also been made to use the Alkalipho, sphat in commercially available To obtain purity from such crude phosphoric acid with 28 to 60% P205 in such a way that the raw phosphoric acid initially with alkali metal carbonates in the monophosphate without Water addition was transferred. Most of the impurities fall in the process and is removed by filtration, as the mass is used as a monophosphate for filtration is still thin enough. Now becomes the concentrated monophosphate obtained alkali carbonate was added again, but only so much that a little less than that Half of the monophosphate is converted into the diphosphate, another falls Part of the impurities from, so that no technich complete purification is achieved.

It has been found that although the solution is not yet alkaline is, by hydrogen sulfide or sulfides, z. B. sodium sulfide, in this neutralization stage the remains of the impurities, of which mainly iron is troublesome, as Let sulphides precipitate and remove. The sulphide precipitate is highly colloidal and easily passes through the filter. The sulphides are easy to filter off, when the precipitates from the impurities that result in the neutralization of the Monophosphate to almost half the diphosphate are still present. That concentrated After further neutralization, the filtrate provides the alkali metal salts in a commercially available form Purity.

The advantage of the new method is mainly that In this way, it is possible to turn raw, highly concentrated phosphoric acid into pure water that is low in water To produce alkali phosphates, which saves considerable time and money.

The method will be explained in more detail using two exemplary embodiments: Example 1 Tookg of a commercially available raw phosphoric acid with 45.5% P205, which is contaminated with 1.5% Fee 03, 1.2% A12 03 and 0.2% CaO brought to reaction with 45 kg H20 and 35 kg ammonia soda at about 90 °. After the carbon dioxide has escaped, it is filtered and the precipitate is washed twice with 10 kg of water each time. The resulting dry filter residue is ii kg, while the monophosphate is contained in i3okg of filtrate. The filtrate is then treated with 11 kg of ammonia soda at 90 ° and, after the carbonic acid has escaped and cooling has taken place, with 0.7 kg of sodium sulfide. The impurities are filtered off and washed once with 10 g of water. The dry filter residue is i kg. The filtrate contains 109 kg of sodium phosphate, namely as Na H2 PO4, 36.5% and as Na. HP0, 29.54%, so a total of 36.36% P2055. The impurities are only 0.167.0'0, with iron only accounting for 0.0070.0. By further adding 18 kg of ammonia soda to the filtrate, all of the monophosphate is converted into diphosphate and a pure white product is obtained. EXAMPLE 2 172 kg of cura (7aophosphate with 35,350,10 P20 ;; «earth with 228 kg of sulfuric acid of 60 ° Be and 130 g of water in the heat are reacted with 35 kg of soda ash without water and proceed in the manner indicated in example i using the same amount of soda and sulfide.

Claims (1)

PATENT CLAIM: Process for the production of technically pure alkali phosphates from raw, obtained by digestion of mineral phosphates with sulfuric acid, stronger Phosphoric acid, with a P.05 content of about 28 to 600; 'o through multi-stage neutralization with alkali carbonates, characterized in that the precipitation of the impurities, mainly of iron, through hydrogen sulphide or alkali sulphides in the second Neutralization stage takes place at a little less than half that in the first Stage formed monophosphate is converted into diphosphate, and that the Abfiitrieren the sulfide happens in the presence of the precipitation constituents caused by the last Partial neutralization of monophosphate has arisen up to the stage mentioned.