JPH0138049B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for crystallizing basic zinc carbonate, etc.

[Conventional technology]

Zinc oxide is used as a pigment for paints and as a vulcanization accelerator for tires, and a dry method or a wet method is used to produce zinc oxide.

On the other hand, the present applicant has disclosed that
When recovering ZnO from kiln dust, etc. of reduced iron equipment at a steelworks, Zn-containing substances are
We proposed that an effective method is to bring Zn into contact with a liquid containing NH ₄ OH and (NH) ₄ CO ₃ (hereinafter referred to as a solution), dissolve Zn, and then crystallize it by heating.

On the other hand, when performing a heating crystallization operation, the crystallization tank is
Usually, one or more groups are provided.

[Problem that the invention seeks to solve]

The reaction according to the prior invention described above is as follows.

Γ dissolution process Zn+(NH ₄ ) ₂ CO ₃ +2NH ₄ OH→ [Zn(NH ₃ ) ₄ ]CO ₃ +H ₂ ↑+2H ₂ O …(1) Γ ion replacement reaction process Me ²⁺ +Zn→Me↓+Zn ²⁺ …(2) Γ crystallization process ●5 [Zn(NH ₃ ) ₄ ] CO ₃ +3H ₂ O→ 2ZnCO ₃・3Zn(OH) ₂ ↓+3CO ₂ ↑ +2ONH ₃ ↑ …(3A) ●4 [Zn(NH _{3 )} ) ₄ ]CO ₃ +4H ₂ O ZnCO ₃・3Zn(OH) ₂・H ₂ O↓ +3CO ₂ ↑+16NH ₃ ↑ …(3B) In this case, the reaction of 3A accounts for more than 90%,
3B's reaction is thought to be small.

By the way, in the crystallization process, when the conventional technology is adopted as it is and the crystallization process is carried out in a crystallization tank, it is advantageous to operate multiple crystallization tanks in a multi-effect manner. If you want to reduce the ammonia concentration to less than 1000 ppm by evaporating and distilling ammonia by guiding the generated steam one after another to the next effect tank, you will need a large number of crystallization tanks and a large amount of steam. shall be.

According to a specific example, an ammonia concentration of 1000 ppm was achieved by operating the crystallization process for 2 hours in 2 crystallization tanks using the conventional method.
If you try to reduce the amount below, the steam amount will be 300Kg/Hr.
Requires. Moreover, since the operation is similar to simple distillation, it is a batch system and cannot be operated continuously.

In contrast, the present inventors have discovered that the reaction in the crystallization step described above can be carried out in a distillation column. This is completely outside the common sense of chemical engineering technology.

However, when performing crystallization operation in a distillation column, if a solution with an initial Zn concentration of 10% by weight or more (hereinafter % is weight%) is distilled and crystallized,
The solid content concentration in the product slurry is 20% or more.
The upper several stages of the distillation column are a region where the volatility of ammonia is high and the amount of evaporation is large due to the distillation characteristics of ammonia, so a large amount of zinc carbonate is crystallized. As a result, crystals adhered heavily to the internal walls and plates of the distillation column, and the bubble cap column became clogged after just one day of operation, requiring operation to be stopped and cleaning.

However, in order to clean it, the distillation column must be dismantled, and industrial practical application based on cleaning is impractical.

Therefore, the present inventors attempted to change the material of the bubble bell tower and the tower type to a perforated tower, but the results were not much different.

The present invention provides a crystallization method and apparatus that can be operated for a long time without crystals adhering to the distillation column, and that can generate highly pure crystals when obtaining zinc carbonate. It's about doing.

[Means for solving problems]

The method of the present invention for solving the above problems uses basic ammonium zinc carbonate {[Zn(NH ₃ ) ₄ ]CO ₃ }
Basic zinc carbonate [ _2ZnCO3・3Zn(OH) ₂ or/and
When crystallizing ZnCO _3.3Zn (OH) _{2.H 2} O] (hereinafter referred to as zinc carbonate), one or more crystallization tanks and a distillation column having multiple trays are combined, and the zinc solution is After being supplied to the crystallization tank and performing a certain percentage of crystallization operation, the final distillation crystallization operation is performed in the distillation column, and the distillation vapor generated by the heat given to the bottom of the distillation column is transferred to the distillation column. The zinc solution is sent from the top to the previous crystallization tank, and the flow of the zinc solution to the final distillation column and the flow of the distillation vapor to the first crystallization tank are in a countercurrent state. .

Furthermore, the apparatus of the present invention includes one or more crystallization tanks and a distillation column having a plurality of trays and to which heat is applied at the bottom, and the ammonium zinc carbonate solution led to the crystallization tank is finally The structure is such that the distilled vapor that is supplied to the distillation column and generated in the distillation column is ultimately led to the first crystallization tank, and furthermore, at this time, the flow of the zinc solution and the distilled vapor are brought into countercurrent contact, and the product crystals are formed. It is characterized in that the slurry is extracted from the bottom of the distillation column.

[Effect]

In the present invention, a distillation column is used to perform the crystallization operation. As a result, the number of bases including this distillation column and crystallization tank is generally about 3 to 5, and the number of bases and the occupied area are significantly larger than when performing the crystallization operation using only the crystallization tank. reduction (for example, the base becomes 1/4)
do. Further, as for the amount of steam used, only the heated steam supplied to the distillation column is sufficient. That is, the solution/slurry in the distillation column is heated by this heated steam, and the solution is subjected to an ammonia stripping action from the bottom to the middle area of the distillation column, and as a result, the ammonia vapor generated reacts as it moves upward. Since the amount of produced vapor is increased and the distilled vapor is successively guided to the crystallization tank while still in a high temperature state, the amount of vapor supplied to the distillation column can be reduced, and the advantage is that continuous operation is possible. .

On the other hand, if there is only a distillation column, as mentioned above,
Since crystals will adhere to the inside of the column, a crystallization tank is installed before that, and the required amount of crystallization is performed in this crystallization tank, and the feed liquid with a low concentration of Zn is supplied to the distillation column. , crystal adhesion within the distillation column is greatly reduced. Furthermore, the agitation effect of the distillation vapor rising inside the distillation column also reduces the adhesion of crystals.

Moreover, since the zinc solution and the distilled vapor in the distillation column are brought into countercurrent contact with each other as a whole, continuous operation with high crystallization efficiency is possible.

[Specific examples of the invention]

The present invention will be explained in more detail below with reference to specific examples shown in the drawings.

Figure 2 shows an example of a flow sheet used to recover zinc carbonate from Zn-containing materials discharged from galvanizing equipment, etc. at a steelworks. First, the entire process will be explained using Figure 2. .

The target Zn-containing material 50 is dissolved in a solution containing NH ₄ OH and (NH ₄ ) ₂ CO ₃ . That is, the Zn-containing material 50 is added to the final dissolving tank of the three dissolving tanks 51, and the solution and the Zn-containing material 50 are dissolved in countercurrent contact, and the dissolving agent liquid passes through the sedimentation separation tank and undergoes ion replacement in the three groups. The solution is purified 52 by being introduced into a tank and a sedimentation tank. Metal zinc powder 53 is added to the third ion replacement tank and subjected to an ion replacement reaction.

The liquid after the ion replacement reaction step passes through a filtration step 54 and is led to a crystallization step 55 according to the present invention. The illustrated crystallizer includes four crystallizers 1A to 1D and a distillation column 2. Subsequently, the product slurry is supplied to a filter 56 and dried in a dryer 57 to form a product 58.

On the other hand, distillation vapor consisting of carbon dioxide gas, ammonia and water vapor in the distillation column 2 is transferred to the first crystallization tank 1.
From A, the solution is led to a solution preparation device 59 consisting of an absorption tower, where carbon dioxide gas and ammonia 60 are added, and the solution is returned to the dissolution tank as a solution with a predetermined concentration. Note that undissolved residues from the dissolution and ion replacement reactions are removed from the first dissolution tank and then discharged to the outside of the system via the residue dissolution tank and the filter 61.

Next, the present invention, which can be suitably used in the above process flow, will be explained with reference to FIG. It is guided to the first crystallization tank 1A through the crystallization tank 1A. Each crystallization tank 1A~1
D has the same structure and has a draft tube 4, a stirring blade 5, and a Kratzker pipe 6 inside.

From the first tank 1A to the final fourth tank 1D, the liquid that has been crystallized by the heat of the live steam 7 that is directly blown into the distillation column 2 is sequentially supplied to the previous tank through the supply liquid pipes 8B to 8D.
It is designed to be supplied as a zinc solution through the

A low zinc concentration solution with a Zn concentration of about 1 to 5% is extracted from the bottom of the final fourth crystallization tank 1D by a pump 9 and sent to the top of the distillation column 2 through a feed pipe 8B.
Supplied via.

The distillation column 2 has, for example, 20 perforated plates 2a, 2a, . . . , and live steam 7 is directly blown into the bottom of the column. 10 is a stirring blade.

In distillation column 2, the above-mentioned (3A) or (3B)
The following reaction occurs, a crystallization operation is performed, and the basic zinc carbonate slurry is extracted from the bottom of the column by a slurry pump 11, and transferred to the subsequent filtration and drying steps. The steam generated in the distillation column 2 rises inside the column and is led from the top of the column through the steam supply pipe 12A to the Kratzker pipe 6 of the fourth and final crystallization tank 1D. It is said to be the heat source for crystallization.

Distilled vapor in this example is the sum total of the upward flow of the live steam in the distillation column, the ammonia vapor produced by heating reaction in each ascending process in the column, and the CO ₂ vapor produced in the upper part of the column. In the case where the ammonia is discharged from the top of the distillation column, the vapor becomes ammonia-rich vapor as a whole and is used as a crystallization heat source for the crystallization tank group in the first stage.

Further, the distilled vapor in the fourth crystallization tank 1D is guided to the third crystallization tank 1C by the vapor supply pipe 12B. In this way, the distilled vapor is sequentially supplied to the previous crystallization tank via the steam supply pipes 12C and 12D, and finally the distilled vapor from the first crystallization tank is transferred to the solution adjustment step. .

Thus, in the present invention, the overall flow of zinc solution and distilled vapor is in countercurrent contact.

In the above example, four crystallization tanks were provided, but one or other number of crystallization tanks may be used. In any case, the Zn concentration transferred from the final crystallization tank to the distillation column 2 is preferably about 1 to 5%, especially about 2 to 3.5%, so the Zn concentration of the raw zinc solution (usually about 10%)
Therefore, it is necessary for each crystallization tank to bear the cost. In addition, the crystallization rate of each crystallization tank is 30~
100Kg/m ³ is preferred. Furthermore, in the case of four crystallization tanks, the ammonia concentration increases successively, for example, about 3%, 4%, 6%, and 8% in the order of the fourth to first crystallization tanks.

〔Example〕

By the process shown in Figures 1 and 2,
from galvanized dust etc. discharged from steelworks.
Zn-containing material was treated.

However, there are only two crystallization tanks, and the liquid capacity is 50. The distillation column was 200 mmφ x 6900 mmH, and 12 stainless steel perforated plate plates each having a large number of 8 x 100 mm elongated holes were arranged as shelves inside the column body, which was made of stainless steel and had a rubber lining on its inner surface.

[Zn(NH ₃ ) ₄ ] with a Zn concentration of 10.2% to the first crystallization tank
CO ₃ solution was supplied at a rate of 100/hr. On the other hand,
Approximately 60 kg/hr of live steam at 110°C is placed at the bottom of the distillation column.
Injected directly. As a result, the temperatures at the first crystallization tank, second crystallization tank, and distillation column top were approximately 80, 90, and 100°C.
It was warm at ℃. Ammonia concentration at the bottom of the tower is 200~
It was 500ppm.

And from the bottom of the distillation column, 100 to 120/Hr
A slurry was obtained, and when this was filtered and dried, zinc carbonate with high purity was obtained, containing less than 5 ppm of Fe and less than 1 ppm of heavy metals such as Pb.

Furthermore, it has been found that continuous operation for at least one month is possible by washing with a dissolving solution for about one hour per day. Moreover, the amount of steam used was found to be at least 1/5 or less compared to the case where only parallel crystallization tanks were used, according to a trial calculation based on comparison with the above experimental results. .

〔Effect of the invention〕

As described above, the present invention combines a crystallization tank and an improved distillation column that enables crystallization, and brings the zinc solution and distilled vapor into countercurrent contact, which makes it possible to overcome conventional methods. Compared to this, the amount of steam used is less than 1/5, and there is no crystal adhesion inside the distillation column.
It has the advantage of being able to operate continuously for long periods of time and producing highly pure products.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a specific example of the present invention, and FIG. 2 is a flow sheet of the entire process in which the present invention is preferably used. 1A to 1D...Crystallization tank, 2...Distillation column, 2a...
... Shelf, 3... Stock solution of zinc solution, 8A to 8E...
Supply liquid pipe, 11...Slurry pump, 12A~1
2E...Steam supply pipe.

Claims (1)

[Claims] 1. When crystallizing basic zinc carbonate from an ammonium zinc carbonate solution, one or more crystallization tanks;
After the zinc solution is supplied to the crystallization tank and a certain proportion of the crystallization operation is performed, the final crystallization operation is performed in the distillation tower, and the lower part of the distillation tower is The distilled vapor generated by the heat applied to the column is sent from the top of the column to the previous crystallization tank.
A crystallization method characterized in that the flow of the solution to the final distillation column and the flow of the distilled vapor to the first crystallization tank are in a countercurrent state. 2. Equipped with one or more crystallization tanks and a distillation column having a plurality of trays and to which heat is applied at the bottom, the ammonium zinc carbonate solution led to the crystallization tank is finally supplied to the distillation column, The distillation vapor generated in the distillation column is configured to be finally led to the first crystallization tank, and furthermore, at that time, the flow of the zinc solution and the distillation vapor are brought into countercurrent contact, and the product crystal slurry is transferred to the column of the distillation column. A crystallizer characterized in that it is configured to be extracted from a bottom portion.