JPH0747784B2 - Method for recovering zinc and lead from steelmaking dust - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering zinc and lead from steelmaking dust, and more specifically, Z contained in steelmaking dust discharged together with exhaust gas from a steelmaking furnace such as an electric furnace.
The present invention relates to a reduction roasting method using a rotary kiln for reducing and volatilizing and recovering nO and PbO.

[0002]

2. Description of the Related Art Steelmaking dust generated from a steelmaking furnace such as an electric furnace contains a relatively large amount of Zn and Pb in addition to Fe. Therefore, as a resource recycling target or an industrial waste regulation target, a process of recovering or detoxifying Zn, Pb, etc. is performed. In this case, in actual operation, the reduction roasting method using a rotary kiln is generally adopted. In the above-mentioned reduction roasting method, steelmaking dust is previously formed into suitable pellets, if necessary, and continuously charged into a rotary kiln together with an appropriate amount of a reducing agent such as coal or coke. Then, while controlling the temperature and the residence time of the reaction zone in the rotary kiln, reduction roasting is performed to reduce and volatilize Zn, P.
b is introduced into the dust collector together with the exhaust gas, and is recovered there as crude zinc oxide or the like. In such a method, Z
An effective way to maximize the reduction yield of n, Pb is to keep the reduction temperature high, thermodynamically self-evident. However, the biggest drawback of this reduction roasting method is that when the high temperature operation is maintained to obtain a high yield, the reaction product softens and melts and adheres to the inner wall of the rotary kiln. It is to grow and grow like a shape. As a result, a reaction product such as charged steel-making dust moves in the kiln, which causes an obstacle, and eventually the operation is stopped. There are a number of suggestions to improve this problem, as described below.

[0003]

The rotary roasting reduction roasting method which is generally used at present has the unavoidable drawbacks as described above. As a proposal to improve this problem, Japanese Patent Publication No. 57-1017.
No. 0, JP-A-58-141345 and Japanese Patent Publication No. 2
There is a reduction roasting method described in Japanese Patent Publication No. 47529-475. Of these, the former two aim to control the temperature distribution in the reaction zone in the kiln to increase the reduction volatilization rate of ZnO and suppress the adhesion to the inner wall by changing the mixing ratio of coke and coal and the function of the combustion burner. It was done like this. However, it cannot be said that the generation of deposits on the inner wall of the kiln is suppressed, and sufficient results have not been obtained. In the latter Japanese Patent Publication No. 2-47529, the melting point of the reaction product is raised by adjusting the CaO / SiO ₂ weight ratio of dust to 2.5 or more, and the adhesion on the inner wall is suppressed to extend the continuous operation period of the rotary kiln. I am trying to As a result, 60 hours of continuous operation, which was conventionally about 30 days,
It has been realized to extend to days. However, the melting point of the reactant in the actual reduction of dust is CaO-FeO-
The explanation using the phase diagram of the SiO ₂ system does not have sufficient persuasive power and leaves a question. According to the research conducted by the present inventor, the molten state of the reaction product also changes depending on the coke ratio of dust. In addition, it has been clarified that the addition of CaO may adversely hinder the anti-adhesion effect. Therefore, the continuous operation is limited to about 90 days at the most, and as a result, the period until the kiln repair is required is short, and the efficiency of the reduction roasting operation is not high. Is. By the way, the Zn content in the residue obtained by recovering Zn and Pb from steelmaking dust by the conventional reduction roasting method is generally 3 or less.
It is ~ 5%, and the disposal processing of the residue is subject to pollution control, and the disposal processing is restricted. Therefore, the plasma arc method has been developed as a new technique for recovering the residual Zn value to be 1.0% or less. This method has a drawback in that it is difficult to be economically viable because the power cost is high for practical use in Japan. Therefore, it is desired to employ a method in which the cost can be reduced and a high yield of Zn and Pb can be exhibited even though the reduction roasting method using a rotary kiln is adopted.

The present invention has been made in view of the above problems, and an object thereof is to suppress the generation of deposits on the inner wall of a rotary kiln and continuously operate the rotary kiln for a long period when reducing and roasting steelmaking dust in the rotary kiln. It is another object of the present invention to provide a method for recovering zinc / lead from steelmaking dust, which can achieve the above-mentioned properties and can be further recovered by increasing the reduction volatility of ZnO and PbO. By the way, the main components of the steelmaking dust discharged from the electric furnace for steelmaking are Fe, Zn, Pb, CaO, MgO,
Examples thereof include SiO ₂ , Al ₂ O ₃ and Cl. When the coke is added as a reducing agent to the steelmaking dust and charged into the rotary kiln, the redox reaction system in the kiln is F
_{e 2 O 3 -Fe 3 O 4} -FeO-Fe-PbO-Pb-
It is composed of ZnO-Zn multi-component system, and further, in the softening / melting process, CaO, MgO, SiO ₂ , A
l ₂ O ₃ acts as an important factor. Thermodynamically, the phase equilibrium of the i-element system is Gibbs-Duhm (Gibbs-Duh).
em) equation Σn _i dμ _i = 0, the degree of freedom is (i−
As is clear from what is given in 1), the reaction system in the kiln is extremely complicated. Therefore, a realistic approach is to analyze the observed phenomenon by trial and error. The present inventor conducted a laboratory test using four types of steelmaking dust based on the above-described findings. And
If 3% or more by weight of MgO is added to steelmaking dust,
The softening / melting point of the reaction product in the reduction roasting process can be increased, and the generation of deposits on the inner wall of the kiln can be significantly suppressed. In addition, ZnO can be added by adding MgO.
It has been found that the reduction volatility of O and PbO can be further increased, and the present invention has been completed by this.

[0005]

According to the present invention, a reducing agent is added to steelmaking dust, charged in a rotary kiln, and roasted by reduction to reduce and volatilize valuable metals of Zn and Pb contained in the steelmaking dust. Applies to the method of collection. The feature is that coke is used as a reducing agent, and 3% or more by weight of MgO is added to the charged steel-making dust, whereby the charge in the rotary kiln is increased. Is to raise the softening / melting point of the powder, suppress the adhesion of the charged material to the inner wall of the kiln, and recover Zn and Pb in high yield by the catalytic action of MgO. The above MgO includes S as an impurity.
When iO ₂ is contained, up to 20% of it can be mixed, and in the case of CaO, up to 30%, Al ₂
In the case of O ₃ , it may be up to 70%. further,
In order to omit the addition of coke, which is a reducing agent, to the steelmaking dust, MgO-C brick scraps in the waste refractory material of the steelmaking furnace body were added so as to be 30% or more of the charged dust weight. Good. When the steelmaking dust is charged into the rotary kiln as pellets, the pellets may be additive-containing pellets containing coke and MgO.

[0006]

[Function] When coke, which is a reducing agent, is added to the dust discharged from the electric furnace for steelmaking and charged into the rotary kiln for reduction roasting, the redox reaction system in the kiln is Fe _{2
O 3 -Fe 3 O 4 -FeO-} Fe-PbO-Pb-Zn
It is composed of a multi-element system of O-Zn. In the softening / melting process, CaO, MgO, SiO ₂ and Al ₂ O ₃ act as important factors in the reaction system. When only 20% by weight of coke is added as a reducing agent, when the heating temperature reaches 1220 ° C., all the interior parts are in a semi-molten state or a molten state. On the other hand, when 3% by weight of steelmaking dust of MgO is added, the MgO remarkably suppresses the reduction of Fe ₂ O ₃ to produce FeO. All steelmaking dust is 1260 which is the upper limit of heating temperature in the rotary kiln.
Even if the temperature is raised to ℃, it does not melt but remains in a sintered state, and its melting point rises obviously. Further, as can be seen from the generation process of steelmaking dust, its components do not change specifically, so that the phenomenon of increasing the melting point by adding MgO is universal. This is remarkable in the field of steel dust processing by rotary kilns. At the same time, it is also one of the characteristics that the inventors have found that the reduction volatility of ZnO and PbO is further increased. The porosity of the reaction interface is maintained by adding MgO, and Z
This is because it is considered that the reduction and volatilization of nO and PbO are promoted. In addition, the added MgO includes SiO ₂ , Ca
The impurities of O and Al ₂ O ₃ may be mixed individually so as to be 20% or less, 30% or less, and 70% or less, respectively. These impurities react with each other and contribute to increase the melting point of the reaction product that is reduced and roasted in the rotary kiln. If instead of MgO, MgO-C brick scraps are selected from the waste refractories of the steelmaking furnace and crushed and added so as to be 30% or more of the weight of the charged dust, the use of coke as a reducing agent becomes possible. Omitted. In addition, by incorporating coke and MgO when the steel dust is charged into the rotary kiln as pellets, it is possible to perform low temperature reduction roasting at a low temperature of 100 ° C. which was not possible with the conventional reduction roasting method. .

[0007]

The present invention will be described in detail below. According to the present invention, coke is added to steelmaking dust as a reducing agent, charged into a rotary kiln, and reduction-roasted to obtain Zn contained in the steelmaking dust.
MgO (magnesia) is added when the valuable metals of (zinc) and Pb (lead) are reduced and volatilized and recovered. Here, the use of coke as a reducing agent is as conventionally done. In actual operation, steelmaking dust formed into suitable pellets is continuously charged into a rotary kiln together with coke. And
3% or more of the weight of the steelmaking dust charged is added and MgO is reduced and roasted. The addition of MgO raises the softening / melting point of the charge in the rotary kiln, and suppresses the reaction product from adhering to the inner wall of the kiln. In addition, Zn and Pb can be recovered in high yield by the catalytic action of MgO.

Next, the details will be described. The main component of the dust discharged from the electric furnace for steelmaking is Fe
Is 25-45% by weight, Zn is 10-29% by weight, Pb is 2-5% by weight, CaO is 1-3% by weight, MgO is 0-2.
% By weight, ₂ to 5% by weight of SiO _{2 and} 1 to _{3 of} Al ₂ O ₃
%, Cl is 2 to 6% by weight. When a coke, which is a reducing agent, is added to the steelmaking dust and charged into a rotary kiln for reduction roasting, the redox reaction system in the kiln is Fe ₂ O ₃ —Fe ₃ O ₄ —FeO—F.
It is composed of a multi-element system of e-PbO-Pb-ZnO-Zn. Furthermore, during the softening / melting process, Ca is added to this reaction system.
O, MgO, SiO ₂ and Al ₂ O ₃ act as important factors. In consideration of the above, the present inventor conducted a reduction roasting test in a laboratory with four types of steelmaking dusts A to D shown in the leftmost column of Table 1 (those generated by four different steelmaking makers). .

[Table 1] In the test, MgO-C brick waste was used instead of MgO. Here, simulating the state of being charged into a rotary kiln, the steelmaking dust has a grain size of 7.93 to 5.6.
6 mm pellets, coke lumps with grain size 4.00
In the range of up to 3.36 mm, MgO is Mg
O-C (magnesia carbon) brick scraps were crushed to have a particle size of 4.00 to 3.36 mm. Then, each predetermined amount was charged into the crucible so as to form layers alternately, and heated to a predetermined temperature while aerating 6 liter / min of air.

The softening / melting state of the reaction product in the crucible is Mg
The melting point was clearly increased by the addition of O 2. That is, when only 20% by weight of coke is added to the steelmaking dust and heated to 1050 ° C. (the temperature at which Fe ₂ O ₃ in the steelmaking dust is reduced) and held for 80 minutes, the reaction product is exfoliated from the crucible. It was possible, but it became a sintered state. 20% by weight coke and 5% by weight steelmaking dust
And MgO-C brick waste granules, which was heated to 1050 ° C. and held for 80 minutes, the reaction product becomes powdery.
It was found that the melting point was clearly elevated. When only 10% by weight of coke was added to the steelmaking dust and heated to 1260 ° C. (the temperature at which ZnO in the steelmaking dust is reduced) and held for 80 minutes, the reaction product was fused to the crucible. Steelmaking dust with 10% by weight coke and 5% by weight
When MgO-C brick granules of No. 2 were added, and the mixture was heated to 1260 ° C. and held for 80 minutes, the reaction product was sintered, but could be peeled off from the crucible. When only 20% by weight of coke was added to the steelmaking dust and the mixture was heated to 1260 ° C. and held for 80 minutes, the reaction product was fused to the crucible. 20% by weight coke and 5% by weight steelmaking dust
When the MgO-C brick waste particles were added and heated to 1260 ° C. and held for 80 minutes, the reaction product was sintered, but could be separated from the crucible.

From this, it can be seen that, for example, when 5% of MgO-C brick waste is added, the melting point of the charge rises and the formation of deposits on the inner wall of the kiln can be prevented.
In other words, it can be seen from Table 2 that MgO significantly reduces Fe ₂ O ₃ to form FeO.

[Table 2] In the melting test of each of the four kinds of steelmaking dust, the following was obtained. When only coke is added (20%), the heating temperature is 1
When the temperature reaches 220 ° C., all are in a semi-molten state or a molten state. However, when 5% of MgO was added to each steelmaking dust, all the dust did not melt even at 1260 ° C. which is the upper limit of the heating temperature in the rotary kiln,
Stay in the sintered state. It is clear that the increase in the melting point of this reaction product is a result of suppressing the production of FeO. Also,
Since the components of dust do not change specifically in terms of the generation process (see Table 1), the melting point increase phenomenon due to the addition of MgO is universal. This is a remarkable effect in the field of processing steelmaking dust by a rotary kiln.

At the same time, the reduction volatility of ZnO and PbO is
As shown in FIG. 1, it was also found that the addition of MgO—C brick waste with a dust weight ratio of 5% was improved over the case where MgO—C brick waste was not added. This is due to the catalytic action of MgO, and the Zn recovery rate is at least 5% or more and the Pb recovery rate is at least 1 as compared with the conventional reduction roasting method.
It is improved by 2% or more. Although the catalytic function of MgO is not clear, it is considered that the reaction proceeds to the topochemical state, so that it can be explained by the unreacted nuclear model. That is, by suppressing the reduction of Fe ₂ O ₃ by adding MgO, the porosity of the reaction interface is maintained, and therefore ZnO,
This is because it is considered that the reduction and volatilization of PbO is promoted.

On the other hand, coke or MgO is added to steelmaking dust.
The results when the amount of -C brick waste added was changed are shown in FIG. When the addition amount of only coke is increased, a Zn recovery rate of almost 100% is obtained at a 30% weight ratio. When the addition amount of only MgO-C brick waste was increased, a considerable recovery rate was obtained at a weight ratio of 30%, but no significant improvement in recovery rate was observed even when the content was increased to 40%. . However, it can be seen that a recovery rate of 90% or more can be obtained, though it is not as high as in the case of 30% by weight of coke. For this reason, MgO-C brick waste (with a carbon content of 17% or more) among refractories that become industrial waste in the repair of steelmaking electric furnaces and other heating furnaces without using expensive coke If used, Zn and Pb can be recovered with a high reduction volatility comparable to coke. Therefore, the use of coke can be omitted. The added MgO contains S as an impurity.
When iO ₂ is included, the content is set to 20% or less, the content of CaO is set to 30% or less, and the content of Al ₂ O ₃ is set to 70% or less, the mixture is allowed and the reduction roasting reaction product in the rotary kiln is allowed. It was also confirmed that it is possible to raise the melting point of.

From the above, it was confirmed that industrial waste such as MgO-C bricks can be effectively utilized and that it can be realized even when applied to an actual rotary kiln. Further, when the steelmaking dust is charged into the rotary kiln as pellets, if the pellets are made into additive-containing pellets containing coke and MgO, it is impossible to achieve the conventional reduction roasting method at 100 ° C. It has also been found that low temperature reduction roasting is possible. It was also confirmed by this that the life of the rotary kiln can be extended and a high yield can be obtained in which the Zn content in the residue can be 1.0% or less.

[0014]

According to the present invention, since the melting point of the reaction product to be reduced and roasted can be increased, the generation of ring-shaped deposits on the inner wall of the kiln is significantly suppressed. As a result, it is expected that the rotary kiln will be continuously operated for at least 300 days or more, as compared with the conventional reduction roasting method in which continuous operation has been limited to about 90 days at the longest. Furthermore, as compared with the conventional reduction roasting method, due to the catalytic action of MgO, Z
It is possible to improve the recovery rate of n by at least 5% or more and the recovery rate of Pb by at least 12% or more. If MgO is contained, for example, alumina brick
% Mixed can be used. Therefore, it is also suitable from the viewpoint of resource recycling. Further, as MgO added to the steelmaking dust, a magnesia-based brick that becomes industrial waste can be adopted. This depends on the actual amount of recovered MgO-C brick waste, but if the used MgO-C brick waste of 30% or more of the weight of steelmaking dust charged in the rotary kiln is added, coke addition can be omitted. It also helps reduce pollution caused by industrial waste. In addition, dust is coke and MgO.
If the pellets are embedded in, the low temperature reduction roasting method is realized, the life of the rotary kiln is extended, and the Zn content in the residue is 1.0% or less, and the Zn yield is increased, and the power consumption is increased. An extremely low-priced operation is realized as compared with the costly plasma arc method.

[Brief description of drawings]

FIG. 1 shows that the reduction volatility of ZnO and PbO in dust is M
The graph showing the relation between the recovery rate of Zn and Pb and the roasting temperature which shows that it increases when gO is added.

FIG. 2 shows the case where only coke is added to the dust and M
The graph which showed the Zn recovery rate when adding only gO-C brick waste, and the relationship of each addition amount.

Claims (3)

[Claims] 1. A method for recovering valuable metals of Zn and Pb contained in the steelmaking dust by reducing and volatilizing them by adding a reducing agent to the steelmaking dust, charging the rotary kiln, and reducing and roasting it. Is a coke, and in order to raise the softening / melting point of the charge in the rotary kiln and prevent the charge from adhering to the inner wall of the kiln, 3% or more of the weight of the steelmaking dust charged is used. MgO
Is added to recover Zn and Pb in high yield by the catalytic action of MgO.
How to recover lead. 2. The impurities in the MgO are SiO ₂
20% or less in the case of CaO, 30% or less in the case of CaO, and 70% or less in the case of Al ₂ O ₃ , zinc / lead from the steelmaking dust according to claim 1 characterized. How to collect. 3. As the reducing agent, instead of the coke, MgO among refractory materials discarded when repairing various furnace bodies is used.
The zinc-lead is recovered from the steelmaking dust according to claim 1, characterized in that -C brick waste is adopted and the MgO-C brick waste is added so as to be 30% or more of the weight of the charged dust. Method.