JPH0676213B2 - Method for dissolving zinc powder in zinc carbonate recovery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to the dissolution of zinc powder in a dissolution step when recovering Zn in the form of zinc carbonate from Zn powder discharged from equipment such as an iron mill. Regarding the method.

[Conventional technology]

Zinc-containing substances containing a large amount of zinc are discharged from steel mill facilities, such as kiln dust in reduced iron facilities and Zn plating facilities. Therefore, it is desirable to recover this Zn, preferably in the form of zinc carbonate, and utilize this zinc carbonate as a raw material for zinc oxide used as a pigment or a vulcanization accelerator for tires.

Therefore, the present applicant has made many proposals as a method for producing such zinc carbonate, and confirmed its usefulness at the stage of practical application.

The outline of this production method is as described in JP-A-59-88319, in which zinc powder containing at least Fe and Pb (N
H ₄ ) ₂ CO ₃ and NH ₄ OH is contacted with an aqueous solution to dissolve the zinc powder, and metal zinc is added in this dissolution step to remove undissolved residue generated by dissolution of zinc,
Then, metallic zinc is added to the solution after the dissolution treatment, an ion substitution reaction is carried out between metallic zinc and impurities to remove a residue, and then zinc carbonate is crystallized to recover zinc carbonate.

Furthermore, as for the zinc powder dissolution step in this production method, as disclosed in, for example, Japanese Patent Publication No. 1-38050, a plurality of stirring dissolution tanks are provided in series, and the clear solution in the previous dissolution tank is dissolved next. By introducing the undissolved residue in the later dissolution tank into the previous dissolution tank, the effect of removing impurities by the countercurrent contact dissolution is enhanced.

[Problems to be Solved by the Invention]

However, the present inventor encountered the following problem in the process of making improvements thereafter.

That is, in order to convert the zinc-containing material discharged from the galvanizing plant into powder for recovering zinc carbonate, the plating dross is dried and collected by a cyclone, and the uncollected portion is further filtered by a bag filter or wet dust. ing.

However, since the bag filter and the wet dust collection originally have a small particle size and are inferior in quality, only those collected by the cyclone have been conventionally dedicated to the recovery of zinc carbonate.

However, even if the quality is inferior and the cost of external sales is low, if the quality of the finally obtained zinc carbonate is not a problem, if bag filters and wet dust can be used, it will contribute greatly to the reduction of the cost of the whole process. To do. In addition, the wet dust collection has a high zinc powder recovery efficiency and is easy to recover.

However, for the bag filter and the one collected by the wet method,
As shown in FIG. 2, the particle size is smaller than that collected by the cyclone, and a large amount of fine zinc powder having a particle size of 10 μm or less is contained.

By the way, since a fine powder having a particle size of 10 μm or less has a large specific surface area, it takes a relatively long time to wet the entire area with the solution. Therefore, when using zinc powder collected by a tap filter or wet method as a raw material for recovering zinc carbonate,
If the degree of agitation in the dissolution tank is too strong, the fine zinc powder is forced to the upper part of the dissolution tank as the liquid flows due to the stirring force before the powder gets wet with the dissolution liquid and the dissolution is performed. The product is floated and mixed in the overflow, the dissolution efficiency of zinc is reduced, and the dissolution is not sufficient, resulting in insufficient removal of impurities and moving to the next tank or the next process. The present inventors have found that the purity is lowered.

On the other hand, if the stirring force is too weak, the stirring force cannot overcome gravity, and the fine powder precipitates on the bottom of the tank while it remains undissolved, increasing the amount of slurry formed, and in order to bring the solution into countercurrent contact, the slurry is mixed. This causes an increase in the load on the pump for returning to the previous tank, and in some cases causes cavitation, causing a situation in which the return cannot be performed.

Therefore, the main object of the present invention is to enable the addition of fine metal Zn powder, and at the same time, to reduce the manufacturing cost, and further to carry out countercurrent contact without support. To provide a method.

[Means for Solving the Problems]

The above problem is to solve zinc powder containing at least Fe and Pb (N
H ₄ ) ₂ CO ₃ and NH ₄ OH is contacted with an aqueous solution to dissolve the zinc powder, and metal zinc is added in this dissolution step to remove undissolved residue generated by dissolution of zinc,
Next, in the method of adding zinc metal to the solution after the dissolution treatment, performing an ion substitution reaction between zinc metal and impurities to remove a residue, and crystallizing zinc carbonate to recover zinc carbonate, In the dissolving step, a plurality of stirring and dissolving tanks are provided in series,
The clear solution in the previous dissolution tank is introduced to the next dissolution tank, the undissolved residue in the latter dissolution tank is introduced to the previous dissolution tank, and the zinc powder having a large particle size is added to the latter dissolution tank, Zinc powder with a small particle size is put into the previous dissolution tank to perform each dissolution, and the rotation speed of the stirring blade in the previous dissolution tank is changed from the previous dissolution tank to the subsequent dissolution tank. This can be solved by controlling according to the amount of undissolved components.

[Action]

According to the present invention, the zinc powder having a large particle size is charged into the subsequent melting tank, and the zinc powder having a small particle diameter is charged into the previous melting tank to perform respective melting, Since the number of rotations of the stirring blade is controlled according to the amount of undissolved content in the clarified liquid that is transferred from the previous dissolution tank to the subsequent dissolution tank, It is possible to dissolve while preventing an increase in the amount of dissolution and an excessive amount of slurry settling at the bottom of the previous dissolution tank.

As a result, it is possible to prevent deterioration of product purity.

[Specific configuration of the invention]

 The present invention will be described in more detail below.

FIG. 1 shows a flow sheet of the basic constitution of the catalytic dissolution method according to the present invention, in which 1 to 3 are respectively first to third dissolution tanks, and the stirring tanks 4A and 4B are provided in the respective dissolution tanks 1 to 3. 4C is provided, and the central portion and the peripheral portion are partitioned by the baffle plate 5. Furthermore, on the downstream side of the third dissolution tank 3,
A settling separation tank 6 and a temporary storage tank 7 are provided, and each tank and tank 7 are connected by an overflow pipe 8 for transferring the clarified liquid to the downstream side, while the settling separation tank 6, the third dissolution tank 3, Between the second dissolution tank 3 and the first dissolution tank 1, return passages 9 to 11 having return pumps 9A to 11A in the middle for transferring the settled slurry at the bottom of each tank to the previous tank.
In addition, the settling slurry is transferred from the bottom of the first settling / separating tank 1 to the previous step or outside the system by the returning pump 12A via the returning path 12.

In the zinc dissolution equipment configured in this way, the first solution is a solution (aqueous solution) containing at least (NH ₄ ) ₂ CO ₃ and NH ₄ OH.
While being supplied to the melting tank 1, zinc powders 20 and 21 containing at least Fe and Pb are charged into the second melting tank 2 and the third melting tank 3, respectively.

The added zinc powder comes into contact with the solution and is dissolved by the stirring force of each stirrer. By this dissolution, (1)
A complex salt is formed according to the formula.

Zn + (NH ₄ ) ₂ CO ₃ + NH ₄ OH → [Zn (NH ₃ ) ₄ ] CO ₃ + 2H ₂ O + H ₂ (1) Also, metallic zinc 30 is added in this melting step. The metallic zinc 30 may be added at any appropriate position, and in the embodiment, it is added to the third melting tank 3. By this addition, ion substitution of zinc with Fe and Pb is performed. For example, if Pb is taken as an example, the ion substitution reaction of formula (2) occurs.

[Pb (NH _{3) 4]} CO ₃ + Zn → [Zn (NH _{3) 4]} CO ₃ + Pb ... (2) undissolved residues and impurities content of each tank 1-3 caused by the dissolution of such zinc powder It is extracted from the bottom and returned to the previous tank. On the other hand, the clarified liquid accompanying the dissolution is supplied from the upper part to the next tank through the overflow pipe 8.

Further, if necessary, also in an ion substitution reaction facility (not shown) provided on the downstream side of the dissolution facility shown in the figure, metallic zinc is added to the solution after the dissolution treatment, and an ion substitution reaction is carried out between metallic zinc and impurities to remove residue components. After removing, the zinc carbonate is crystallized to recover the zinc carbonate.

In the present invention, the zinc powder having a small particle diameter is charged into the preceding melting tank, that is, the second melting tank 2, and the zinc powder having a large particle diameter is charged into the following melting tank, that is, the third melting tank 3. Dissolve each.

In this case, as the zinc powder to be charged into the second melting tank 2, as shown in FIG. 2, for example, wet zinc powder having a large particle size of 10 μm or less is used as the zinc powder to be charged into the third melting tank 3. ,
Zinc powder with a large particle size collected by a cyclone is introduced.

In addition, in the present invention, among the stirrers 4A to 4C of the respective tanks 1 to 3, at least the second melting tank as the preceding melting tank is provided with the inverter 40 of the stirring motor, and the rotation speed of the stirring blades is changed. , And is controlled according to the amount of undissolved component in the clear solution that moves from the second dissolution tank 2 to the third dissolution tank.

Here, as the amount of the undissolved component in the clear solution transferred from the second dissolution tank 2 to the third dissolution tank, the transferred clear solution is sampled, and the concentration of the undissolved content and the impurity concentration are used as indicators. I can judge. The purity of the final product can also be used as an index. If necessary, the rotation speed of the stirring blade can be automatically controlled based on the signal from the detector for obtaining such an index, without depending on the operator's judgment.

〔Example〕

 Next, the effects of the present invention will be clarified by examples.

In order to investigate the behavior of the Zn dust collected by the wet dust collection or bag filter whose particle size distribution is shown in FIG. 2 at the time of stirring, a stirring experiment was conducted with the apparatus shown in FIG.

In FIG. 3, a stirring blade 51 was installed in the dissolution tank 50, and this was driven to rotate by a motor 52, and at that time, the number of rotations could be controlled by an inverter. Fine zinc powder was supplied from the storage tank 53 to the dissolution tank 50 and circulated. In addition, a sampling beaker 54
Can be freely moved in and out through the sampling hole 55.

In such a test apparatus, while changing the test time and the rotation speed of the stirring blade, a liquid near the liquid surface of the dissolution tank 50 was sampled as a sample, and the amount of undissolved Zn in this sample (undissolved per liquid amount) The quantity was measured as g / l).

The results are shown in Table 1 and FIG. The figure revealed the following. First, as the number of revolutions of the stirrer increases, the fine Zn powder floats and is mixed in the overflow, which is undissolved.
Zn content increases. On the contrary, when the number of rotations becomes low, the mixture in the overflow becomes small. Furthermore, the undissolved slurry is much accumulated in the lower part of the dissolution tank, the load of the circulation pump is increased, and cavitation is caused again.
It was confirmed that there was a possibility that it could not be sent.

On the other hand, in order to compare the conventional method (constant rotation speed) with the method of the present invention (rotation speed control), dissolution was carried out in the dissolution tank, and then zinc carbonate was obtained by crystallization to examine its quality. The results are also shown in Table 1. The quality ranks in the table are
It is ranked in the meaning of Table 2.

From Tables 1 and 2 above, according to the method of the present invention,
It can be seen that high quality zinc carbonate can be obtained even when Zn powder is used together.

〔The invention's effect〕

As described above, according to the method of the present invention, it is possible to introduce the fine metal zinc powder, and it is possible to reduce the manufacturing cost, and further, it is possible to perform countercurrent contact without any support. is there.

[Brief description of drawings]

FIG. 1 is a flow sheet of an example of a melting step according to the method of the present invention,
FIG. 2 is a diagram showing the particle size distribution of fine Zn powder and cyclone-collecting powder, FIG. 3 is a test apparatus diagram for confirming the effect of the present invention, and FIG. 4 is a graph showing the effect of stirring. 1 ... First melting tank, 2 ... Second melting tank, 3 ... Third melting tank, 4A, 4B, 4C ... Stirrer, 5 ... Baffle plate,
6 ... Sedimentation / separation tank, 7 ... Storage tank, 8 ... Overflow pipe, 9A-11A ... Return pump, 20, 21 ... Zinc powder.

Claims (1)

[Claims] 1. A zinc powder containing at least Fe and Pb (N
H ₄ ) ₂ CO ₃ and NH ₄ OH is contacted with an aqueous solution to dissolve the zinc powder, and metal zinc is added in this dissolution step to remove undissolved residue generated by dissolution of zinc,
Next, in the method of adding zinc metal to the solution after the dissolution treatment, performing an ion substitution reaction between the zinc metal and impurities to remove a residue, and crystallizing zinc carbonate to recover zinc carbonate, In the dissolving step, a plurality of stirring and dissolving tanks are provided in series,
The clear solution in the previous dissolution tank is introduced to the next dissolution tank, the undissolved residue in the latter dissolution tank is introduced to the previous dissolution tank, and the zinc powder having a large particle size is added to the latter dissolution tank, Zinc powder with a small particle size is put into the previous dissolution tank to perform each dissolution, and the rotation speed of the stirring blade in the previous dissolution tank is changed from the previous dissolution tank to the subsequent dissolution tank. A method for dissolving zinc powder in the recovery of zinc carbonate, characterized by controlling according to the amount of undissolved components.