JPS592727B2 - How to recover zinc from zinc dross - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering zinc from zinc dross for the purpose of improving quality, purity variation, thermal efficiency, working efficiency, working environment, safety, etc.

Dross generated during the conventional hot-dip galvanizing process
To recover zinc by redissolving the flux (
A method of separating a metal and a metal oxide using a flux (fluxing agent),
■ A method in which impurity metals such as iron and aluminum are made into an alloy and separated from highly pure zinc, ■ A method in which impurities are separated by the difference in specific gravity of the melt produced based on the temperature difference, or ■
A widely used method is to oxidize and separate impurities by blowing air into the melt (usually called drossing).

However, in method (■), the flux used generates a large amount of harmful smoke and gas, and at the same time the surrounding temperature rises rapidly, resulting in an extremely poor working environment. When using a furnace),
When the water adhering to the tojisu lump melts, it causes a steam explosion,
It is not easy to mix the raw materials, and the quality of the recovered metal is unstable, resulting in a high incidence of defective products. It takes a considerable amount of time to remove the top layer (the impurity layer) separated by the difference in specific gravity, and a considerable amount of the next layer (the high-purity non-defective layer) must also be pumped out. However, the yield of good products is poor.
In addition, there is a large variation in quality within a lot, and method (2) requires pressurized air equipment, and the blown air also induces oxidation of the zinc, causing the bubbles to burst on the surface of the melt. Each of the conventional methods has a number of drawbacks, such as the fact that hot substances scatter violently, which is unfavorable from a safety standpoint.

This invention was made in order to solve all the drawbacks of the conventional method, and it is possible to remove the dross generated during the hot-dip galvanizing process by sealing the chi of an open-well reverberatory furnace that has a chi-sealing part and a furnace opening. At the furnace opening, which is lower temperature than the closed part, the melt is divided into a layer containing many impurities such as iron and aluminum and a layer containing high-purity zinc, based on the difference in specific gravity of each component contained in the melt. After separating into layers, this high-purity zinc melt is transferred into a holding furnace, and a portion of the melt taken out from the holding furnace is dropped from a reflux gutter onto the melt surface in the holding furnace to perform drossing. The present invention provides a method for recovering zinc from zinc dross, which is characterized by refluxing the zinc into a holding furnace, sending the lower melt to a continuous casting machine, and continuously injecting it into a mold. The details will be described below.

The dross generated during the hot-dip galvanizing process is usually zinc 9
4-98%, aluminum 0.5-2.0%, iron 0.5
~3.0% lead, 0.1~1.0% lead, and minute amounts thereof, and is often supplied in brick-shaped, bell-shaped, etc. blocks.

To explain using FIG. 1, such a dross mass 2 is
While opening and closing the charging port door 3 of the open-well type reverberatory furnace A, the charging device 1 feeds the material into the furnace as appropriate.

The open-well type reverberatory furnace A is partitioned by a partition wall having an outlet gate 6, and has a sealed part I and a furnace opening 8,
A suitable number of burners 4 and a dregs outlet door 5 are provided.

In order to feed the dross lump 2 into such a reverberatory furnace A and melt it, the dross lump 2 is melted by the burner 4, and then the dross outlet door 5 is opened and an appropriate amount of flux (fluxing agent) is poured in and stirred. The ambient temperature in the sealed part 7 is about 900 to 1000°C when scraping and removing the oxides floating on the surface of the metal melt, and the melt temperature is about 60°C at the highest point.
The temperature reaches 0 to 700℃, and the furnace opening 8Φ melt temperature is about 450℃.
~500°C.

The melt at the furnace opening 8 is divided into three layers depending on the specific gravity difference of the constituent components.The uppermost layer a is rich in iron and aluminum, and the middle layer is a relatively high-grade zinc layer. , those containing relatively large amounts of iron, lead, etc. are separated into the lowest layer C.

Therefore, the melt in the intermediate layer is transferred to the holding furnace B using the metal pump 9.

Note that instead of using the metal pump 9, a melt extraction port (not shown in the drawing) may be provided in the furnace wall at the furnace opening, and the melt may be transferred to the holding furnace using the head.

The transferred melt is maintained at approximately 430 to 470°C in the holding furnace B, and is further transferred to the continuous casting machine C by the metal pump 10.
A pourer 11 having a reflux gutter 12 is provided in order to reflux a portion of the melt transferred during that time.

In this way, while the melt is being transferred from the reverberatory furnace A to the holding furnace B by the metal pump 9, bubbles generated when the melt comes into contact with the air, and bubbles generated when the melt is transferred from the pourer 11 to the reflux gutter 12 and held. Bubbles generated during the return to furnace B float to the surface of the melt in holding furnace B, forming an upper layer d. If this is removed, an oxidation process, ie drossing, is performed, which is exactly the same as the conventional air blowing method. can be done.

Further, the melt in the lower layer e transferred from the pourer 11 to the continuous casting machine C is poured into the mold 14 via the distributor 13.

An example of this is shown in FIG. 2, in which a plurality of molds 14 mounted on an endless traveling body 16 are successively arranged directly below a rotatable distributor 13 in which a plurality of nozzles 15 are arranged radially. , and if the tip of one nozzle is caught on the edge of the corresponding mold, by continuously driving the endless running body 16, the distributor 13 will also rotate in synchrony with this, and each This is preferable because the melt can be smoothly poured into the mold.

It goes without saying that insulating materials are used in the necessary parts of the equipment described above to prevent heat dissipation, and in addition, although not shown in the drawings, both reverberatory furnace A and holding furnace B are equipped with liquid level gauges and temperature gauges. If a meter is installed and drive devices such as the charging device 1, metal pump 9, metal pump 10, and continuous casting machine C are operated in accordance with these instructions, automatic control becomes possible.

According to the method of this invention, even if there is considerable variation in the quality of the raw material dross, only the amounts of the layers a, b, and d mentioned above will change, and the quality of the recovered product will be extremely stable. It is of high quality, has low heat loss during the recovery process, and can significantly improve work efficiency, work environment, and safety.

Examples and comparative examples are shown below.

[Example 1] A reverberatory furnace A with a capacity of 15 tons in the closed part and 5 tons in the furnace opening, a holding furnace B with a capacity of 1.5 tons, and one
A continuous casting machine C having a mold with a capacity of 5 kg is connected as shown in Fig. 1, and Zn is 94 to 98% and AI is 0.5 to 2.
0%, Fe 0.5-3.0%, Pb 0.1-1.0
The dross mass 2 containing a small amount of Cd, Cd, etc. was placed in a reverberatory furnace A, and the ambient temperature in the sealed part 7 of the reverberatory furnace A was set to 970°C to obtain a melt at about 650°C.

At the furnace opening 8, this melt was separated into three layers: the top layer a, the middle layer and the bottom layer C, and the temperature of the middle layer was about 470°C.

The molten liquid of the intermediate layer is transferred to the holding furnace B by the metal pump 9, and continuous operation is performed while sequentially replenishing the reverberatory furnace with an amount of dross mass 2 commensurate with the transferred amount.
Then, the melt in the lower layer e was poured into the mold 14 of the continuous casting machine C and cast into a 25 kg lump.

When all operations have become steady, open the furnace opening 8 of reverberatory furnace A.
Analysis of the uppermost layer a, the middle layer S and the lowermost layer C1, and the upper layer d and the lower layer e in the holding furnace B was conducted, and the values shown in Table 1 were obtained.

[Example 2] In Example 1, one piece of 25 kg obtained from continuous casting machine C
24 cast products (products) were successively sampled, and each component was analyzed.

The results are summarized in Table 2, and it was clear that the variations in the ingredients were extremely small and the quality of zinc was constant and high quality.

[Comparative Example 1] One ton of dross lump similar to that used in Example 1 was placed in a pot (crucible) furnace with a capacity of 1 ton, and after completely melting, the melt was cooled to about 470 ° C. After removing the bubbles that floated on top of the melt, the melt was poured into a mold to make ingots weighing 25 kg each, and 24 ingots were randomly selected from the obtained ingot group and a component analysis was performed on each ingot. Ta.

The results are also listed in Table 2, and compared to the results of Example 2,
The quality was low and the variation was large, which was not a desirable result.

[Example 3] In Comparative Example 1 (using a pot furnace), the recovery rate of high-grade zinc (usually referred to as upper and lower) relative to the raw material dross in Example 2 and Comparative Example 1 was determined. %）・・・・・・・・・
...15% defective dross (called Naka-shita, Zn
88-96%, AI 0.9-4.0%, Fe1-4%
)・・・・・・・・・13% Top and bottom (Zn97.7-99.1%)・・・・・・
While it was 72%, in Example 2 (method of the present invention), oxide (equivalent to the above)...
・15% defective dross (Zn 89.8-90.5%, A
14~5%, Fe4~5%)...
・・・・・・・・・4% Ucho (Zn99.4%)
......81%, Example 2
It was clear that when using the method of the present invention shown in Figure 1, the quality of the upper and lower parts was high, and the recovery rate was approximately 10% higher.

Additionally, the total oxide and waste dross was about 9% lower than when using a pot furnace.

[Example 4] Two workers were engaged in the operation of processing raw material dross at a rate of about 1.5 tons per hour using the same equipment as in Example 1, and one of them was engaged in an operation in which raw material dross was processed at a rate of approximately 1.5 tons per hour. One person was in charge of loading the furnace, drawing out the scraps, and pumping up defective dross, while another person was responsible for sorting out the castings (products) that came out of the continuous caster, managing the molten metal in the holding furnace, and I was in charge of the foam removal work.

As a result, the cooling time, quality adjustment work, casting work, etc. during the process of the conventional method are completely unnecessary, the work of pumping up defective dross is reduced to about 1/3, and the production volume of -shift is 8 to 9 It was possible to produce 4 to 4.5 tons per worker.

It was clear that such production volume could be further increased by increasing the skill level of the workers or by automating the equipment.

[Comparative Example 2] Five pot furnaces with a capacity of 1 ton, the same as in Comparative Example 1, were installed, and two workers were in charge of operating the furnaces for melting and scraping work. ...Approximately 4 hours of cooling and pumping up defective dross... Approximately 1.5 hours of quality adjustment and casting work...... Approximately 1.5 hours of sorting of cast items...・・・・・・・・・・・・・・・
・・・・・・・・・It took about 1 hour.

Here, quality adjustment work means that after melting the dross in a pot furnace and cooling it, removing the defective dross that floats to the top layer,
Since the aluminum content in the melt does not fall below the standard value,
This is a process to adjust the quality of the melt and the amount of 10 tons to 1 ton by adding raw material that does not contain aluminum to compensate for the amount of defective dross that was removed.

Therefore, according to this method, the production amount for the -shift is 5 tons, that is, 2.5 tons per worker,
There were few measures to increase production through improvements in equipment or skill level, and it was clear that the method was considerably inferior to the method according to the present invention.

[Example 5] Under the operating conditions shown in Example 4 and Comparative Example 2, continuous operation was carried out in three shifts, and the vertical production and gas usage at that time were measured.

When the respective gas usage amounts were converted into per ton of upper and lower gases, it was 27.9 kg/ton under the conditions of Example 4, whereas it was 31.4 kg under the conditions of Comparative Example 2.
/ton.

Therefore, according to the method of the present invention, it was possible to save at least about 11% compared to the conventional method using a pot furnace.

[Brief explanation of the drawing]

FIG. 1 is a simplified apparatus diagram showing an example of the method of the present invention, and FIG. 2 is an enlarged sectional view of the main parts of the continuous casting machine in FIG. 1. A...Reverberatory furnace, B...Holding furnace, C...
... Continuous casting machine, 1 ... Charging device, 2 ...
...Dross mass, 3...Charging port, 4...
・Burner, 5...Drag removal exit door, 6...
・Outlet gate, 7... Ch sealing section, 8...
・Furnace opening, 9...Metal pump, 10...
...Metal pump, 11...Water pourer, 12.
...reflux gutter, 13...distributor, 14.
...Mold, 15...Nozzle, 16...
...Endless running body, a...Top layer, b...
... middle layer, C ... bottom layer, d ... upper layer, e ... bottom layer.

Claims (1)

[Claims] 1 The dross generated in the hot-dip galvanizing process is melted in the sealed part of an open-well reverberatory furnace, which has a sealed part and a furnace opening, and the dross contained in the melt is melted in the furnace opening, which is lower in temperature than the sealed part. Based on the difference in specific gravity of each component, this high-purity zinc melt is separated into a layer containing many impurities such as iron and aluminum and a layer containing high-purity zinc.Then, this high-purity zinc melt is transferred to a holding furnace and held. A part of the melt taken out from the furnace is dropped from the reflux gutter onto the melt surface in the holding furnace and refluxed into the holding furnace while drossing, and the lower melt is further sent to the continuous casting machine to continuously cast the mold. A method for recovering zinc from zinc dross, characterized by injecting it into a zinc dross.