JPS6154094B2 - - Google Patents

Description

[Detailed description of the invention]

This invention is a method for efficiently recovering valuable metals such as zinc, lead, and cadmium from dust discharged from metal smelting furnaces, undissolved residues generated from chemical treatment processes, and other industrial waste. It is related to. Dust discharged from metal smelting furnaces, undissolved residues generated from chemical processing processes, and other industrial wastes often contain valuable metals such as zinc, lead, and cadmium. The generated dust contains approximately 20% Zn, approximately 4% Pb, and approximately 4% Cd.
0.1%, and the zinc dissolution residue contains about 0.1% Zn.
28%, Pb content is approximately 6%. Disposing of such dust, residue, industrial waste, etc. as is is extremely uneconomical in terms of effective use of resources, and since these valuable metals are also harmful substances, it has been considered a major problem from a pollution standpoint. . Therefore, various methods for recovering the above-mentioned valuable metals have been studied, and the reduction and volatilization recovery method has been put into practical use as a relatively easy method. In this method, the materials to be treated such as dust, residue, industrial waste, etc. are charged into a rotary kiln or other reduction furnace, and the valuable metals contained are reduced and volatilized at high temperatures using a solid carbonaceous reducing agent. This is then cooled and the reduced valuable metals are recovered in a metal state or in a reoxidized state by the atmosphere inside the furnace. However, the conventional methods described above have low processing efficiency, so in order to increase the recovery efficiency of valuable metals,
A large amount of reducing agent is required, which is not economical. Therefore, the inventors of the present invention have conducted intensive research on a method for efficiently and economically recovering the valuable metals, and as a result, they have first reoxidized the semi-reduced iron-based metal near the outlet of the rotary kiln. We developed a method for efficiently recovering valuable metals by effectively utilizing the reaction heat generated by oxidation to promote the reduction reaction of valuable metals (hereinafter referred to as the basic invention method), and filed a patent application (Japanese Patent Application No. 110348-1982). (Special Publication No. 57-44737)). According to this method, as a result of the activation of the reduction reaction of valuable metals, valuable metals can be efficiently recovered using a smaller amount of solid carbonaceous reducing agent than in the past.
This invention relates to an improvement of the basic invention method described above, and it is possible to further increase the recovery efficiency of valuable metals, further reduce the amount of solid carbonaceous reducing agent and fuel used, and improve the operating rate of the rotary kiln. This method provides a method for recovering valuable metals, in which a workpiece containing valuable metals and iron-based metals is charged into a rotary kiln together with a solid carbonaceous reducing agent consisting of coke and coal, and the solid carbonaceous reducing agent In the method for recovering valuable metals by reducing and recovering the valuable metals contained in the object to be treated, FeO
The amount of fuel is the sum of the amount required to reduce the oxidation level to the desired degree of oxidation and the amount equal to or less than the sum of the above two amounts. 100~300Kg
While maintaining the internal pressure of the rotary kiln at a positive pressure, the primary air of the burner is enriched with oxygen depending on the operating conditions, creating an oxidizing atmosphere inside the rotary kiln near its discharge side. The other part is in a reducing atmosphere zone, and the iron-based metal that has been reduced to an oxidation degree of about FeO in the reducing atmosphere zone is reoxidized in the oxidizing atmosphere zone to generate high-temperature reaction heat. The present invention is characterized in that the temperature of the reducing atmosphere zone adjacent to the oxidizing atmosphere zone is rapidly increased, thus promoting the reduction reaction of valuable metals in the object to be treated in this zone, and recovering valuable metals with high efficiency. It has the following. Next, this invention will be explained with reference to the drawings. 1st
In the figure, an example of equipment used in the method of the present invention is shown in a schematic explanatory diagram. In the drawing,
1 is a rotary kiln, 2 is a furnace bottom lid provided on the inlet 1a side that serves as a charging port for processing agents in the rotary kiln 1, 3 is a furnace front lid provided on the outlet 1b side that serves as a clinker discharge port, and 4 is a A charging chute 5 provided in the furnace bottom hood 2 is a high-pressure spray burner provided in the furnace front hood 3, and the tip of the burner 5 faces into the rotary kiln 1. 6 is a duct connected to the furnace bottom hood 2, 7 is a chamber,
8 is a cyclone, 9 is a bag filter type dust collector,
10 is a fan, 11 is a chimney, 12 is a conveyance mechanism for collected dust, 13 is a chute provided in the front hood 3, and 14 is a rotary cooler. The atmosphere inside the rotary kiln 1 is maintained at an oxidizing atmosphere near the outlet 1b and at a reducing atmosphere elsewhere.
The solid carbonaceous reducing agent is charged into the rotary kiln together with the materials to be treated such as dust, residue, and industrial waste.
Coke and highly reactive coal with high volatile content are used together. The amount of this solid carbonaceous reducing agent charged is the amount required to reduce the valuable metals in the object to be treated, and the amount required to reduce the iron-based metals in the object to be oxidized to approximately FeO level. The total amount is equal to or less than the sum of the above two required amounts, and as a result, the iron-based metal in the processed material is not reduced to metallic iron, and the inside of the rotary kiln will be described later. An effective temperature profile can be created. A workpiece containing valuable metals and a reducing agent consisting of coal and coke are charged into the rotary kiln 1 through a chute 4 provided in the bottom lid 2, and are moved in the direction of the arrow by the rotation of the rotary kiln 1. As shown in 15, it sequentially moves to the exit 1b. A high pressure spray burner 5 is provided on the outlet 1b side,
100~300KgG/ with primary air from the burner 5
By burning a fuel such as kerosene that is sprayed at a high pressure of ^cm2 , the iron content in the material to be treated, which has been reduced to almost FeO level, is reoxidized, resulting in heat generation and surplus in the solid carbonaceous reducing agent. This amount of combustion heat causes the temperature inside the rotary kiln near the outlet 1b to rise rapidly. As a result, the valuable metals contained in the material to be treated are actively reduced and volatilized, oxidized by oxygen in the atmosphere, turned into fine powder, and flow from the front hood 3 toward the bottom hood 2 in the direction of arrow 16. It is carried by the exhaust gas and discharged from the furnace bottom hood 2. and,
The dust passes through a duct 6 and a chamber 7 and is collected by a cyclone 8 and a bag filter type dust collector 9, and then transported and collected by a dust transport mechanism 12. On the other hand, the reoxidized iron becomes iron oxide clinker and is carried out from the rotary kiln 1 through the chute 13 of the furnace front hood 3, cooled to a predetermined temperature by the rotary cooler 14, and then carried out. In this invention, a high-pressure spray burner 5 is provided in the front hood 3 toward the inside of the rotary kiln 1, and while maintaining the pressure inside the rotary kiln 1 at a positive pressure, the primary It operates by enriching the air with oxygen. That is, the high pressure spray burner 5 is 100 to 300KgG/cm ²
Since the fuel is atomized at a high pressure of 6 to 7 KgG/cm ² like a normal burner, the oil droplets become extremely fine particles, so the contact area with oxygen is reduced per unit weight. As a result, complete combustion occurs with an air amount close to the theoretical air amount. Therefore, while the temperature of the flame is 1300-1400℃ for ordinary burners, it is 1500-1500℃ for high-pressure spray burners.
It reaches 1600℃ and can be raised to 1600-2000℃ if oxygen-enriched air is used as the primary air. As a result, the ambient temperature near the outlet 1b of the rotary kiln 1 is increased, the reduction reaction is promoted, and the formation of a wall on the inner wall of the rotary kiln 1 is prevented. This high-pressure spray burner 5 can be tilted at an angle of about 40 degrees vertically and horizontally with respect to the axis of the rotary kiln 1, and has a rotating fin on the outside and inside of the burner body. It is possible to supplementally attach outer tubes provided with this at predetermined intervals. Therefore, by preparing various outer tubes with different lengths, mounting positions, rotation angles, etc. of the swivel fins and attaching them to the outer tube according to the situation, the length of the frame can be controlled. By controlling the length and temperature of this frame and controlling the burner angle described above, the rotary kiln 1
The formation of walls on the inner walls of the pipe is accurately suppressed, and even if some walls are formed, they can be removed with almost no interruption to operation. Furthermore, by maintaining the pressure inside the rotary kiln 1 at a positive pressure, the surplus air ratio can be kept low, the amount of gas passing through the kiln can be reduced, and the inside of the kiln can be maintained at a high temperature. In this case, if the inside of the rotary kiln 1 becomes excessively positive pressure (1.5 to 2.0 mmH ₂ O), there is a risk that the flame of the high-pressure spray burner 5 will blow out, but this is because the primary air of the high-pressure spray gas burner 5 is enriched with oxygen. This can be solved by Such oxygen enrichment of the primary air is also achieved in rotary kiln 1.
This has the effect of rapid heating to prevent or remove internal walls and to raise the temperature near the outlet of the rotary kiln 1 to a high temperature. The oxygen enrichment mentioned above is suitably carried out by increasing the oxygen content in the primary air in the range of 3 to 10%. The basic idea of the method of this invention is not just a reductive volatilization method as mentioned above, but is to effectively utilize the reaction heat accompanying the reoxidation of the partially reduced residual metal oxide. Although the presence of metal to be reoxidized is required, since smelting furnace dust, undissolved metal residue, industrial waste, etc. contain a considerable amount of iron, no additional iron source is required. It's okay. Generally, it is sufficient that the material to be treated contains about 15% or more of T and Fe. FIG. 2 shows an example of the temperature profile within the rotary kiln 1 along with a comparative example. In the drawing, the horizontal axis is the length from the entrance 1a of the rotary kiln, and in this example, the total length of the rotary kiln is 24 m, and T ₁ to _{T 5} written on the horizontal axis
is the temperature measurement position inside the rotary kiln. The vertical axis is the temperature inside the rotary kiln. a indicates the reducing atmosphere zone in the rotary kiln, b indicates the oxidizing atmosphere zone, the solid line curve represents the temperature distribution according to the method of this invention, the dashed-dotted curve represents the temperature distribution according to the basic invention method described above, and , dotted line curves respectively show the temperature distribution in the conventional reduction volatilization recovery method. In the method of this invention, the temperature distribution inside the rotary kiln is set at about 600°C or less from the inlet to point A at temperature measurement position _T2 , which is about one-third of the total length of the rotary kiln. Iron is reduced from Fe ₂ O ₃ to Fe ₃ O ₄ by the coal volatiles in the solid carbonaceous reducing agent. Said A
The temperature is approximately 600 to 950°C from point B to temperature measurement position _T4 , which is approximately two-thirds of the total length of the rotary kiln, and during this time, Fe ₃ O ₄ in the dust is
is reduced to an oxidation degree of approximately FeO. Next, from point B to point C at temperature measurement position _T5 in oxidizing atmosphere zone b, the temperature inside the rotary kiln is rapidly increased from about 950°C to 1400°C or higher. Such a sudden rise in temperature is caused by the re-oxidation of the iron in the dust that has been reduced to an oxidation degree of about FeO, which occurs in the oxidizing atmosphere zone b.
This is caused by the heat generated when it becomes Fe ₃ O ₄ and the surplus combustion heat in the solid carbonaceous reducing agent. In the reducing atmosphere zone between the high-temperature zones from point B to point C, valuable metals such as zinc, lead, and cadmium contained in the dust are actively reduced and volatilized. Zinc and lead volatilized in this way,
Valuable metals such as cadmium are produced in rotary kiln 1.
The dust is re-oxidized in the furnace and becomes dust containing zinc oxide, etc., and as mentioned above, it is carried by the exhaust gas flowing from the front hood 3 toward the bottom hood 2 as shown by the arrow 17, and is discharged from the bottom hood 2. will be collected. As can be seen from FIG. 2, the temperature distribution in the method of the present invention is such that the temperature profile remains low up to about two-thirds from the inlet 1a of the rotary kiln 1, and rapidly rises to about 1400°C at the one-third close to the outlet 1b. is formed. Such a temperature distribution is a major feature of the method of the present invention, and thereby, valuable metals in the object to be treated can be reduced and recovered with extremely high efficiency at a one-third location near the outlet 1b. is possible,
Moreover, the amount of reducing agent used can be small, the length of the rotary kiln 1 can be shortened, and recovery can be performed more economically than the conventional method as well as the prior invention. Next, the method of this invention will be explained with reference to examples. Steelmaking electric furnace dust having the composition shown in Table 1 below was granulated using a granulator to form pellets with an average particle size of 12 mm.

[Table] Coke and coal having properties shown in Table 2 below were used as solid carbonaceous reducing agents.

[Table] The above-mentioned pellet-like dust and solid carbonaceous reducing agent were charged into a rotary kiln with a shell inner diameter of 3.2 m and a length of 24 m. The amount of dust charged is 6.5
T/H, and the charging amount of solid carbonaceous reducing agent is 410Kg/H (63.0Kg per dust ton) for coke and 273Kg/H (42.0Kg per dust ton) for coal. A slidable high-pressure spray burner was installed on the outlet side of the rotary kiln, and 32 kg of kerosene per tonne of dust was blown into the burner along with primary air. During blowing, we continuously perform oxygen enrichment operation that increases the oxygen content in the primary air by approximately 4%, preventing and removing walls in the rotary kiln, increasing the temperature near the rotary kiln exit side, Efforts were made to prevent burner frames from blowing out. Furnace pressure in the outlet hood was maintained at 0.5-2.0 mm _H2O throughout the entire run time. Further, the fuel injection pressure of the high-pressure spray burner was 100 to 300 KgG/cm ² . The temperature inside the rotary kiln was detected by a thermometer at temperature measuring positions T ₁ to _{T 5} and controlled to have the temperature profile shown in FIG. 2 above. As a result, the iron oxide in the dust is reduced to a degree of oxidation of approximately FeO up to the temperature measuring position _T4 , which is approximately two-thirds of the rotary kiln, and then the iron oxide in the dust is reduced to a degree of oxidation of about FeO, and then the atmospheric temperature in the kiln rapidly increases. Valuable metals such as zinc, lead, and cadmium were reduced and recovered as dust containing zinc oxide.
In addition, in the oxidizing atmosphere zone, the iron oxide that has been reduced to an oxidation degree of about FeO is reoxidized and the excess reducing agent is burned, and the high temperature heat makes the reduction reaction of the valuable metals efficient. It was held in Table 3 shows the composition of the dust containing oxides of valuable metals recovered, and Table 4 shows the composition of the clinker.

【table】

[Table] As can be seen from Tables 3 and 4 above, valuable metals such as zinc, lead, and cadmium could be recovered from the dust with high efficiency. Table 5 shows the amount of solid carbonaceous reducing agent and kerosene used per tonne of dust and the amount of dust treated for the method of this invention and the conventional method.

[Table] In Table 5 above, the amount of dust processed is the amount of dust processed per day per 1 m ³ of internal volume of the rotary kiln. As is clear from Table 5 above, according to the method of this invention, the amount of solid carbonaceous reducing agent and kerosene used is small compared to the conventional method as well as compared to the basic method of the invention, and in particular, the amount of dust treated is It has improved significantly. The above-mentioned example is an example in which valuable metals were recovered from steelmaking electric furnace dust as the object to be treated.
Not limited to this, for example, undissolved residues from zinc dissolution having a composition as shown in Table 6 below may be treated by the method of the present invention alone or in combination with steelmaking electric furnace dust, and the valuables in the residue may be treated. Of course, the metal can be recovered.

[Table] As detailed above, according to the method of this invention,
When compared with the conventional method, and even when compared with the basic invention method by the present inventors, it is possible to remove valuable metals such as zinc, lead, and cadmium from the processed material using a small amount of solid carbonaceous reducing agent and fuel. It is industrially superior, as it can be collected efficiently and there is no wall formation or growth inside the rotary kiln, which greatly improves the operating rate of the rotary kiln and the processing efficiency of the processed materials. This will bring about a positive effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of equipment used in the method of this invention, and FIG. 2 is a diagram showing an example of a temperature profile in a rotary kiln according to the method of this invention, together with a comparative example. In the drawings: 1... Rotary kiln, 1a... Inlet, 1b
...Exit, 2...Furnace butt hood, 3...Furnace front hood, 4...Dust charging chute, 5...Burner, 6...Duct, 7...Chamber, 8...Cyclone, 9...Bug Filter type dust collector, 10...
...Fan, 11...Chimney, 12...Dust conveyance path, 13...Chute, 14...Rotary cooler, 15, 16...Arrow.

Claims (1)

[Scope of Claims] 1. A workpiece containing valuable metals and iron-based metals is charged into a rotary kiln together with a solid carbonaceous reducing agent consisting of coke and coal, and the solid carbonaceous reducing agent In the method for recovering valuable metals by reducing and recovering the valuable metals contained in the material to be treated, the charging amount of the solid carbonaceous reducing agent is adjusted to the amount necessary for reducing the valuable metals contained in the material to be treated. FeO
The amount of fuel is the sum of the amount required to reduce the oxidation level to the desired degree of oxidation and the amount equal to or less than the sum of the above two amounts. 100~300Kg
While spraying at a high pressure of G/cm ² and maintaining the internal pressure of the rotary kiln at a positive pressure, the primary air of the high-pressure spray burner is enriched with oxygen according to the operating conditions, and the inside of the rotary kiln is heated near its discharge side. are in an oxidizing atmosphere zone, and the others are in a reducing atmosphere zone, and the iron-based metal that has been reduced to an oxidation level of about FeO in the reducing atmosphere zone is reoxidized in the oxidizing atmosphere zone to perform a high-temperature reaction. By generating heat, the temperature of the reducing atmosphere zone adjacent to the oxidizing atmosphere zone is rapidly increased, thus promoting the reduction reaction of valuable metals in the object to be treated in this zone, and efficiently removing valuable metals. A method for recovering valuable metals.