JPS6149243B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is an improvement of the invention described in the previously filed Japanese Patent Application Laid-open No. 52-134893. In the said application, the applicant has described a method for suppressing post-precipitation in phosphoric acid "wet process"("post-precipitation"), which refers to the precipitation of sludge from solids suspended or dissolved in freshly prepared phosphoric acid. ). The process of the application starts from a "wet process" phosphoric acid with a P ₂ O ₅ content of 22 to 35% by weight and includes the following steps: (1) At least one of the suspended solids present in the starting acid is (2) add to the resulting acid 0.05 to 2.0 weight percent of particles of aluminum silicate based on the P ₂ O ₅ in the acid; (3) heat the resulting mixture to remove the silicic acid. dissolving the aluminum and concentrating the acid; (4) crystallizing the concentrated solution to precipitate a solid; and (5) separating a supernatant phosphoric acid substantially free of the solid from the precipitated solid. do. The inventor has determined that the acid to which aluminum silicate is added is more than 35% by weight P ₂ O ₅ , i.e. 46% by weight.
We have now discovered that the above method can be carried out even when concentrated to P ₂ O ₅ . Thus, the method of the invention includes preconcentrating the acid to a P ₂ O ₅ content in the above range prior to step (2). This method uses the same weight of the more concentrated acid above.
Having a lower volume for P ₂ O ₅ has advantages in terms of storage capacity required on site.
In view of the disclosure of said application, it is surprising that the improvements of the present invention can be implemented satisfactorily. In the case of the earlier application, the acid is usually added in a process such that the P ₂ O ₅ content is 42-52% by weight after adding pearlite.
It is concentrated in (3). It would have been inferred from this that concentrating above 35% by weight before adding perlite would not give good results. The process of the present invention involves first clarifying the starting wet phosphoric acid to remove at least 85% of the suspended solids [step (1)], carrying out the preconcentration step described above, and then adding perlite [step (2)]. ]And then the above (3)
The most convenient operation is to perform steps (5) in succession. Alternatively, preconcentration can be performed before clarification, ie before step (1). Next, pearlite is added after clarification and steps (3) to (5) are performed in the same manner. In step (3), perlite is dissolved by heating acid containing 36-46% by weight _P2O5 , which has a higher concentration than normal wet _process phosphoric acid. This process results in the loss of water and _{the P2O5} content is preferably 42-52% by weight.
Since the concentration is increased to P ₂ O ₅ , it can also be considered as further enrichment. Thus 46% _P2O5 acid _is 47-52
concentrated _to % _P2O5 , and 36% _{P2O5 is} 42-52%
It is concentrated to P ₂ O ₅ . Apart from the preconcentration step, the preferred features of all other aspects of the method are as described in the applicant's aforementioned patent application. The applicant summarizes the following features of particular importance. For further details and details of devices that can be used, reference is made to the above-mentioned application. The clarification step is preferably substantially free of suspended solids (usually no more than 3% by volume of acid,
(preferably not more than 2% by volume of acid). The proportion of pearlite is usually from 0.05 to _2.0 % by weight, preferably from 0.2 to 1.0% by weight, based on the _P2O5 content of the acid. A more preferable percentage of pearlite is 0.25.
~0.75% by weight, most preferably 0.3-0.4% by weight. The correct concentration step, i.e. step (3), is 42-52% by weight.
It is preferred to provide _{a P2O5} concentration. In this step it is necessary to heat the acid to dissolve the pearlite. Crystallization step (4) is preferably carried out on a continuous flow basis, with the product from step (3) being fed as a stream to the crystallization zone, supernatant acid being removed from said zone by overflow and precipitated. The solids are allowed to settle under gravity and are removed from the zone as underflow. Following step (5), the acid can be further concentrated, for example to up to 63% by weight P ₂ O ₅ . The invention is illustrated by the following examples. All percentages are by weight. Example: The wet method phosphoric acid obtained as the “first liquid” was
Solids were removed by clarification using polyacrylamide flocculant alone (no other additives).
The clarified acid _was then preconcentrated to 43-45% _P2O5 and divided into two portions. 0.5% perlite based _{on P2O5} in acid was added in one portion (according to the invention). Add nothing to the other part (for comparison). Both portions were then concentrated to 50-51% _P2O5 and allowed to settle _overnight to precipitate a solid. The supernatant phosphoric acid was then separated from the solids by decantation.
The supernatant phosphoric acid was then further concentrated to _60-61 % _P2O5 . This operation was performed on a laboratory scale. All concentration operations were performed by boiling the acid under reduced pressure. Detailed results are shown in the table below. They exhibit the advantageous effects of the present invention in reducing the solids concentration and post-precipitation of the product acid to very low levels (virtually zero).

【table】

[Table] Additional relationships The original patent (Patent No. 993243, Japanese Patent Publication No. 54-28392) states that the P ₂ O ₅ content is 22 to 35% by weight, and at least 85% by volume of the suspended solids are removed. Adding 0.05-2.0% by weight _of aluminum silicate particles based on the weight of _P2O5 to wet method phosphoric acid, concentrating the resulting mixture to dissolve the aluminum silicate,
The resulting concentrate is crystallized to precipitate a solid;
This is a method for separating and taking out the upper layer of liquid phosphoric acid that does not substantially contain solids, and the purpose is to produce wet-method phosphoric acid that does not cause post-precipitation. The main part of the invention is to perform concentration, dissolution, and crystallization. In contrast, the present invention uses the method of the original invention, except that pearlite particles are used as aluminum silicate particles and that the P ₂ O ₅ content is preconcentrated to 35-46% by weight before adding them. The invention is the same as that of the original invention, and includes the main parts of the essential matters for the structure of the original invention as the main parts of the essential matters for the structure thereof, and achieves the same purpose.

Claims (1)

[Scope of Claims] 1. A method for producing wet phosphoric acid with substantially no post-precipitation starting from wet phosphoric acid having a P ₂ O ₅ content of 22 to 35% by weight, comprising (1) starting removing at least 85% by volume of the suspended solids present in the acid; (2) adding to the resulting acid 0.05 to _2.0 % by weight of particles of perlite, based on the _P2O5 in the acid; (3) heating the resulting mixture to dissolve the perlite and concentrate the acid; (4) crystallize the concentrated solution to precipitate a solid; and (5) render the precipitated solid substantially free of the solid. A method comprising separating supernatant phosphoric acid, characterized in that prior to step (2), the acid is preconcentrated to a P ₂ O ₅ content of 35 to 46% by weight. 2. The method according to claim 1, wherein the acid is preconcentrated after step (1) and before step (2). 3. The method according to claim 1, wherein the acid is preconcentrated before step (1). 4. The proportion of added pearlite is 0.25 to _0.75 % by weight, preferably 0.3% by weight based on the _P2O5 content of the acid.
2. The method of claim 1, wherein the amount is 0.4% by weight. 5. The crystallization is carried out on a continuous flow basis, with the product from step (3) being fed as a stream into the crystallization zone, from which the supernatant acid is removed by overflow, and the precipitated solids are allowed to settle under gravity. The method according to any one of claims 1 to 4, wherein the underflow is removed from the band. 6 Claim 1 further concentrating the acid obtained from step (5) to a P ₂ O ₅ content of 63% by weight
The method according to any one of items 5 to 5. 7 In step (3), the acid is converted into 42 to 52% by weight of P ₂ O ₅
Claim 1 of concentrating so that the content is
6. The method according to any one of items 6 to 6.