Method for preparing copper smelting raw materials

Abstract

To provide a preparation method of a copper refining raw material, capable of suppressing instability of the operation of a copper refining furnace caused by drying failure of a miscellaneous raw material in a wet state.SOLUTION: A preparation method of a copper refining raw material comprising a copper concentrate and a miscellaneous raw material in a wet state includes steps of: expanding the miscellaneous raw material in a wet state in a layering state on a surface, and scattering so as to cover from above the miscellaneous raw material in a wet state, a moisture absorbent which preferably contains copper represented by flue cinder recovered from exhaust gas of a copper refining furnace, and has a particle size smaller than that of the miscellaneous raw material in a wet state; keeping for a predetermined time a state that the miscellaneous raw material and the moisture absorbent are brought into contact with each other; and mixing the moisture absorbent with the copper concentrate while disintegrating the miscellaneous raw material whose moisture percentage is lowered due to being kept.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for preparing a copper smelting raw material composed of copper concentrate and wet miscellaneous raw materials.

Background Art

[0002] In pyrometallurgical copper smelting, copper concentrate mainly composed of chalcopyrite with a copper grade increased to about 30% by pretreatment such as flotation is charged into a smelting furnace such as an autogenous furnace as a raw material, and high-grade crude copper with a copper grade of about 98% is produced by performing processes such as combustion here. The anode produced by casting this crude copper is electrolytically refined to produce electrolytic copper. In the above smelting furnace, high-temperature exhaust gas containing a large amount of sulfur dioxide is generated. Therefore, this exhaust gas is sent to a sulfuric acid plant as a raw material for sulfuric acid after heat recovery in a waste heat boiler. In this sulfuric acid plant, in the process of removing dust contained in the exhaust gas discharged from the above smelting furnace and in the process of treating waste acid by-produced in the purification system process, a muddy precipitate in which impurities are concentrated is generated. Also, in the purification process of the electrolytic solution used in the above electrolytic refining, a muddy precipitate in which impurities are concentrated is generated.

[0003] Since the muddy precipitates generated in the above sulfuric acid plant and electrolytic refining contain copper, usually these precipitates are recovered and mixed with the above copper concentrate as miscellaneous raw materials and charged into the smelting furnace. At that time, since the properties such as the composition and particle size of the above miscellaneous raw materials are different from those of the copper concentrate, simply mixing and charging into the smelting furnace may cause the operation of the smelting furnace to become unstable. Therefore, it is desirable to mix these miscellaneous raw materials and copper concentrate while adjusting so that the properties of the mixed raw materials after mixing become substantially uniform.

[0004] For example, Patent Document 1 proposes a technique of quantitatively cutting out and adding miscellaneous raw materials onto copper concentrate being conveyed by a belt conveyor as a method of mixing copper concentrate and miscellaneous raw materials so that the properties of the raw materials become substantially uniform. Further, Patent Document 2 proposes a technique, although not directed to muddy sediments, of spreading different types of solid particles on the conveyor surfaces of a plurality of belt conveyors and dropping these solid particles from the downstream ends of each of these belt conveyors toward the same position.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In the case of wet raw materials such as the above-mentioned muddy sediments, as time passes, the adhering water evaporates and hardens on the surface portion, and evaporation is hindered by this hardened surface portion inside, so that a high moisture content is maintained. For this reason, even if the above-mentioned wet raw materials are preheated in a drying facility, the internal moisture cannot be sufficiently evaporated, and they are discharged from the drying facility in a state of poor drying containing residual moisture. As a result, when this preheated wet raw material is charged into a smelting furnace, the residual moisture evaporates in the smelting furnace, inhibiting the reaction of the copper concentrate, or the amount of moisture to be evaporated varies with time, making the operation of the smelting furnace unstable. Further, since the above-mentioned wet raw materials generally have a large mass in the form of lumps, there is a risk of conveyance failure in an air conveyance facility using a gas flow flowing through a pipe for conveying copper concentrate in the form of powder or granules.

[0007] As a countermeasure against the above problems, the hardened shell-like part is broken by pressing the bucket of a shovel loader against the wet raw material to apply a load, or by scooping up the wet raw material with the bucket and dropping it onto the floor from a height of about 4 to 5 m. By taking these countermeasures, the inside of the wet raw material with a high moisture content can be dispersed when mixing with copper concentrate, so that it can be charged into a smelting furnace using a pneumatic conveying facility. However, the above operations require a great deal of labor, and it took about two to three days to prepare a mixture of copper concentrate and wet raw material. In addition, there were sometimes significant variations in the properties of the mixture after mixing due to individual differences in the work. The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for preparing a copper smelting raw material capable of suppressing instability in the operation of a smelting furnace caused by poor drying of wet miscellaneous raw materials.

Means for Solving the Problems

[0008] The inventors of the present invention considered that the shell-like part on the surface formed by the drying of the lump of wet miscellaneous raw materials does not cover the entire surface of the lump, and there are places where the wet part is exposed due to variations in the components of the miscellaneous raw materials and conditions of the storage location such as sunlight and temperature. Therefore, the miscellaneous raw materials inside the mountain-shaped part were extracted from the wet miscellaneous raw materials stored in a mountain-shaped stack, mixed with a moisture absorbent and held for a while, and then mixed with copper concentrate and charged into a drying facility or a smelting facility. As a result, it was found that the operation of these facilities could be stabilized, and the present invention was completed.

[0009] That is, the method for preparing a copper smelting raw material according to the present invention is a method for preparing a copper smelting raw material comprising copper concentrate and wet miscellaneous raw materials, wherein the wet miscellaneous raw materials are with a thickness of 2 to 10 cm spread in a layer on the surface and covered from above with having a finer particle size than the miscellaneous raw materials a step of spraying a moisture absorbent, and a step of holding these miscellaneous raw materials and the moisture absorbent in contact with each other for a predetermined time to reduce the moisture content of the miscellaneous raw materials step, the water characterized by comprising a step of mixing the miscellaneous raw materials with a reduced fraction while crushing them with the moisture absorbent and copper concentrate.

Effects of the Invention

[0010] According to the present invention, it is possible to suppress the operation of the smelting furnace from becoming unstable due to poor drying of the wet miscellaneous raw materials.

Brief Description of the Drawings

[0011]

Figure 1

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Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of a method for preparing a copper smelting raw material according to the present invention will be described in detail. The method for preparing a copper smelting raw material according to this embodiment of the present invention targets two types of granular raw materials processed in dry copper smelting. One of them is a miscellaneous raw material containing moisture and in a wet state, which can be exemplified by precipitates generated by adding a sulfurizing agent to waste acid discharged from a sulfuric acid plant. The other of the two types of granular raw materials is copper concentrate, which is usually the main raw material in a dry state. Note that the wet miscellaneous raw material is not limited to the precipitates generated in a sulfuric acid plant, and may contain copper-containing substances generated from other processes in a copper smelting plant, such as copper slime and copper slag generated in an electrolytic refining process, an electrolytic extraction process, a purification process of an electrolytic solution, etc.

[0013] As shown in FIG. 1, the method for preparing a copper smelting raw material according to an embodiment of the present invention includes a dispersion step S1 of spreading the above-mentioned wet miscellaneous raw material in a layer on a surface such as a floor surface, and a contact step S2 of spraying a moisture absorbent so as to cover the layer-spread wet miscellaneous raw material from above (it is not necessary to completely cover it, and it is sufficient if the miscellaneous raw material can be seen through the gaps), a holding step S3 of holding the wet miscellaneous raw material and the moisture absorbent in contact with each other for a predetermined time, a mixing step S4 of mixing the miscellaneous raw material with a reduced moisture content obtained by the holding while crushing it with the above-mentioned moisture absorbent and separately prepared copper concentrate, and a conveying step S5 of conveying the mixed raw material. Hereinafter, each of these steps will be described in detail.

[0014] 1. Dispersion step The dispersion step S1 is a step of spreading and dispersing the wet miscellaneous raw materials that are generally piled up in a mountain shape in the raw material storage area onto a flat place such as the floor using a shovel loader or the like, preferably in a layer with a thickness of about 2 to 10 cm. Thereby, the exposed area can be increased compared to the case of piling up in the above-mentioned mountain shape, so that the decrease in the moisture content of the wet miscellaneous raw materials can be promoted, and in the subsequent contact step S2, the desiccant can be brought into contact with the wet miscellaneous raw materials more uniformly. In consideration of drainage and the convenience of shovel loader operation, it is preferable to spread and disperse the wet miscellaneous raw materials on a somewhat inclined floor. Also, it may be spread and dispersed in a place with some undulations, such as on top of other raw materials or on top of dry raw materials.

[0015] 2. Contact step The contact step S2 is a step of bringing the wet miscellaneous raw materials spread on a flat place in the above-mentioned dispersion step S1 into contact by spraying a desiccant from above using a shovel loader or the like. At that time, the wet miscellaneous raw materials spread in layers may be turned upside down using a shovel loader or the like, whereby the desiccant can be brought into contact with the wet miscellaneous raw materials more uniformly.

[0016] The desiccant used in this contact step S2 is not particularly limited as long as it has a finer particle size than the above-mentioned miscellaneous raw materials and has a moisture absorption property with a lower moisture content than the wet miscellaneous raw materials. However, if it contains copper, it is particularly useful because it can also be used as a copper raw material in a smelting furnace. In addition, it is preferable to use the cumulative 50% particle diameter (D50) based on volume measured by the laser diffraction scattering method as an index for the above-mentioned particle size. Examples of the above-mentioned desiccant include copper powder such as copper slag powder, and soot collected by a waste heat boiler or an electrostatic precipitator into which exhaust gas discharged from a blast furnace or a converter is introduced.

[0017] The spraying amount of the above moisture absorbent is preferably about 30 to 300 parts by mass on a dry basis with respect to 100 parts by mass of the above-mentioned raw material mixture in a wet state on a dry basis. If the spraying amount is less than 30 parts by mass, it is difficult to obtain the moisture absorption effect. On the contrary, even if an amount exceeding 300 parts by mass is sprayed, no further moisture absorption effect can be obtained, which is disadvantageous in terms of cost.

[0018] 3. Holding step The holding step S3 is a step of reducing the moisture content of the raw material mixture in a wet state by holding the above moisture absorbent and the raw material mixture in a wet state in contact with each other for a predetermined time. In this holding step S3, if necessary, air may be blown toward the raw material mixture in a wet state, or the raw material mixture in a wet state may be stirred using a shovel loader or the like.

[0019] The holding time of this holding step S3 is not particularly limited. However, for the raw material mixture in a wet state targeted by the preparation method of the embodiment of the present invention, the longer the holding time of the holding step S3, the more the moisture content tends to decrease. Even after about 8 hours from the start, the moisture content decreases significantly. However, when the elapsed time from the start exceeds about 24 hours, the rate of decrease in the moisture content becomes extremely slow. Therefore, about 8 to 24 hours is appropriate as the above-mentioned predetermined holding time.

[0020] It is considered that the decrease in the moisture content of the raw material mixture in a wet state by the moisture absorbent mainly occurs due to the movement of moisture by capillary action occurring at the contact portion between the raw material mixture in a wet state and the moisture absorbent. In addition, the soot generated in the copper smelting furnace usually contains copper sulfide scattered from the copper smelting furnace and copper sulfate obtained by burning it. Since this is dried by heating, it has the form of anhydrous copper sulfate. The anhydrous copper sulfate in this soot undergoes a hydration reaction with the adsorbed water contained in the raw material mixture in a wet state and generates heat, so it is expected to promote the evaporation of the adsorbed water. Furthermore, since anhydrous copper sulfate takes in the above-mentioned adsorbed water as crystal water and becomes copper sulfate pentahydrate, it is also expected that the moisture content of the raw material mixture in a wet state will decrease thereby.

[0021] 4. Mixing step The mixing step S4 is a step of mixing the miscellaneous raw materials with a reduced moisture content in the above-mentioned holding step S3 while crushing them with a moisture absorbent and separately prepared copper concentrate. At the time of this mixing, the mixing ratio of the miscellaneous raw materials containing the moisture absorbent and the copper concentrate is preferably 1 to 15 parts by mass on a dry basis with respect to 100 parts by mass of the copper concentrate on a dry basis. There is no particular limitation on the mixing method in this mixing step S4. For example, it may be mixed by stirring using a shovel loader or the like, or it may be mixed using a general powder and granule mixer.

[0022] Alternatively, as shown in FIG. 2, copper concentrate is cut out in a fixed amount from a copper concentrate hopper 2 provided above the upstream end of one or more belt conveyors 1 through a first fixed-quantity cutting device 3 such as a rotary feeder and spread on the conveyor surface of the belt conveyor 1. At the same time, miscellaneous raw materials are cut out in a fixed amount from a miscellaneous raw material hopper 4 provided downstream of the copper concentrate hopper 2 in the conveying direction of the conveyor 1 through a second fixed-quantity cutting device 5 such as a rotary feeder and spread on the copper concentrate on the conveyor surface for mixing. In the case of FIG. 2, a mixed raw material with an adjusted mixing ratio of copper concentrate and miscellaneous raw materials can be received in a mixing hopper 6 by controlling the cutting amounts from both hoppers 2 and 4. Also, since the degree of mixing increases as the number of belt conveyors 1 provided in series increases, it is preferably about 2 to 4 units.

[0023] Also, as shown in Fig. 3, copper concentrate is cut out in a fixed amount from a copper concentrate hopper 12 provided above the upstream end of the first belt conveyor 11A through a first fixed-amount cutting device 13 such as a rotary feeder and spread on the conveyor surface of the first belt conveyor 11A. At the same time, miscellaneous raw materials are cut out in a fixed amount from a miscellaneous raw material hopper 14 provided above the upstream end of the second belt conveyor 11B through a second fixed-amount cutting device 15 such as a rotary feeder and spread on the conveyor surface of the second belt conveyor 11B. The copper concentrate and the miscellaneous raw materials may be mixed by dropping them from the downstream ends of both the first and second belt conveyors 11A and 11B into the same mixing hopper 16. At that time, at least one of the first fixed-amount cutting device 13 and the second fixed-amount cutting device 15 may be operated intermittently or they may be operated alternately. In the case of Fig. 3, a mixed raw material with an adjusted mixing ratio of copper concentrate and miscellaneous raw materials can be received in the mixing hopper 16 by controlling the cutting amount from both hoppers 12 and 14 or by controlling the running speeds of both belt conveyors 11A and 11B.

[0024] In any of the cases of Figs. 2 and 3 described above, it is preferable to ensure a drop height of 50 cm or more when dropping the miscellaneous raw materials onto the conveyor surface of the belt conveyor and when dropping the mixed raw material from the downstream end of the belt conveyor. This makes it possible to charge the miscellaneous raw materials into the drying equipment or smelting furnace in a loosened state of the lumps. Since the cohesive force between the particles of the miscellaneous raw materials that have undergone the dehydration step S3 has decreased, the lumpy miscellaneous raw materials can be easily crushed in any of the above mixing methods. In addition, since the moisture content of the miscellaneous raw materials has decreased and they are less sticky, they can be easily mixed with the copper concentrate.

[0025] 5. Conveying Process The conveying step S5 is a step of conveying the mixed raw material obtained in the above mixing step S4 to a smelting furnace or drying equipment in the previous stage thereof. This drying equipment dries the mixed raw material by preheating and then charges it into the smelting furnace. For example, a rotary steam dryer composed of a cylindrical body installed rotatably with its central axis slightly inclined from the horizontal direction can be mentioned. This dryer dries the object to be dried charged from one end thereof by a steam pipe while stirring it by the rotation of the cylindrical body and moving it in the direction of the central axis.

[0026] There is no particular limitation on the method for conveying the above mixed raw material, and it may be by a general mechanical conveying method such as a belt conveyor or a bucket conveyor, but an air conveying method that conveys using the air flow of air flowing in a pipe is preferred. The air conveying method can be roughly classified into low-concentration conveying in which powder particles are conveyed in a dispersed state by high-speed air and high-concentration conveying in which powder particles are conveyed in a plug shape by a low-speed air flow. Among these, in the case of copper smelting raw materials, high-concentration conveying is preferred because it can suppress the wear of the transport pipe and can convey with a relatively small air consumption without separating the mixed raw material.

[0027] A general configuration diagram of the above high-concentration conveying is shown in FIG. 4. The air conveying equipment shown in this FIG. 4 is mainly composed of a supply source tank 20 provided at the bottom of the above mixing hoppers 6 and 16, a transport pipe 21 having one end connected to the bottom of the supply source tank 20, and a supply destination tank 22 connected to the other end of the transport pipe 21, and compressed air for air conveying is introduced into the supply source tank 20.

[0028] As described above, by adopting the method for preparing copper smelting raw materials according to the embodiment of the present invention, it is possible to reduce the moisture content inside the wet miscellaneous raw materials, thereby preventing the operation of the smelting furnace from becoming unstable due to poor drying. Further, as the moisture content of the wet miscellaneous raw materials decreases, the cohesive force between particles decreases, making it possible to easily break them into a state where they can be crushed. Therefore, when physical forces such as the impact during falling from the belt conveyor and the friction with the transport pipe during pneumatic transport are applied, the materials become moderately loosened, and thus the drying efficiency in the drying equipment can be increased. Furthermore, after the moisture content decreases, the crushed miscellaneous raw materials contain almost no lumps formed by the aggregation of particles, so it is less likely to cause poor transportation even when pneumatic transport is adopted.

Example

[0029] (Example) Precipitates generated by adding a sulfiding agent to waste acid by-produced in the purification process of a sulfuric acid manufacturing plant were prepared as wet miscellaneous raw materials, mixed with copper concentrate, and charged into drying equipment. Before mixing with the copper concentrate, the wet miscellaneous raw materials were spread in a layer about 2 cm thick on the floor surface, and copper-containing powder (copper slag powder) having the same mass as the miscellaneous raw materials on a dry basis was uniformly sprayed thereon using a shovel loader as a moisture absorbent. After spraying the moisture absorbent, the moisture content of the wet miscellaneous raw materials was reduced by holding them in that state for 24 hours.

[0030] The moisture content of the wet miscellaneous raw materials before spreading on the floor surface and the moisture content of the miscellaneous raw materials after 24 hours had passed since spreading on the floor surface were determined from the mass change when drying was carried out at an ambient temperature of 105°C for 30 minutes. As shown in FIG. 5, by holding for 24 hours in contact with the copper-containing powder, the moisture content decreased from 23.8% by mass to 8.6% by mass. On the other hand, the copper-containing powder increased from 3.5% by mass to 5.2% by mass. It is considered that the portion of the decreased moisture content that was not taken up by the copper-containing powder evaporated or dripped off.

[0031] After the above-mentioned 24-hour holding was completed, the miscellaneous raw materials were scooped up with the bucket of a shovel loader together with the copper-containing powder and dropped onto the floor from a height of about 50 cm. At that time, when comparing the size of the lump of miscellaneous raw materials before dropping and the size of the lump of miscellaneous raw materials after dropping, the lump after dropping was on average crushed into pieces about one-fourth to one-eighth as fine as the lump before dropping.

[0032] The miscellaneous raw materials and copper-containing powder dropped in this way were scooped up and put into a powder mixer, and further copper concentrate was put in and mixed. At that time, the mixing ratio was set so that there were 5 parts by mass (dry basis) of miscellaneous raw materials with respect to 100 parts by mass (dry basis) of the copper concentrate. A part of the obtained mixed raw material was charged into a drying furnace via a belt conveyor, and was charged into a smelting furnace from the drying furnace via a chain conveyor and an air conveyor. As a result, these drying furnace and smelting furnace could be stably operated without any particular problems.

[0033] (Comparative Example 1) The same amount of wet miscellaneous raw materials and copper-containing powder as in the example were prepared, but these were not spread on the floor or held for 24 hours, and were simply dropped onto the floor from a height of about 50 cm with the bucket of a shovel loader. As a result, the size of the lump of miscellaneous raw materials before dropping and the size of the lump after dropping were almost the same. Thereafter, when attempting to mix with copper concentrate and charge into a smelting furnace via a drying furnace in the same manner as in the example, an equipment protection stop due to an increase in the current value occurred in the chain conveyor, and a blockage due to small pieces occurred in the air conveyor.

[0034] (Comparative Example 2) Copper smelting raw materials were prepared in the same manner as in Comparative Example 1 above, except that the wet miscellaneous raw materials and copper-containing powder were dropped from a height of 4 to 5 m instead of from a height of 50 cm. As a result, although the size of the lump of miscellaneous raw materials became on average about one-half as fine after dropping as before dropping, many lumps were still included that were about the same size as those before dropping.

[0035] (Comparative Example 3) In the examples, the wet miscellaneous raw materials and the copper-containing powder were repeatedly dropped under the same conditions as in Comparative Example 2 until they reached a size approximately the same as that of the miscellaneous raw materials obtained when dropped from a height of about 50 cm. Thereafter, they were mixed with copper concentrate in the same manner as in the examples and charged into a smelting furnace via a drying furnace. Then, the slag produced from the smelting furnace was sampled three times at the start of the treatment in the smelting furnace, 8 hours after the start of the treatment, and 16 hours after the start of the treatment, and the magnetite (Fe3O4) grade thereof was analyzed. The reason for analyzing the Fe3O4 grade in this way is that when the operation of the smelting furnace becomes unstable, variations occur in the progress of the reaction and the Fe3O4 grade of the slag increases. Therefore, the stability of the operation can be evaluated by using the Fe3O4 grade as an index.

[0036] The analysis results are shown in FIG. 6 together with the results analyzed in the same manner as in the above examples. In FIG. 6, the Fe3O4 grade before the start of the treatment was set to 1.0. As can be seen from the results of FIG. 6, in Comparative Example 3, the Fe3O4 grade in the slag withdrawn from the smelting furnace increased to about 1.04 times the reference value 8 hours and 16 hours after the start of the treatment, while in the example, it decreased to about 0.95 times 16 hours after the start of the treatment. Therefore, it can be seen that the operation of the smelting furnace is more stable in the example than in Comparative Example 3. Here, the reference value is the value obtained by analyzing the slag sampled when the operation is in a steady state when only dry copper concentrate without wet miscellaneous raw materials is charged into the smelting furnace as a raw material.

Explanation of Signs

[0037] 1 Belt conveyor 2, 12 Copper concentrate hopper 3, 13 First metering cutter 4, 14 Miscellaneous raw material hopper 5, 15 Second metering cutter 6, 16 Mixing hopper 11A First belt conveyor 11B Second belt conveyor 20 Supply source tank 21 Transport pipe 22 Supply destination tank

Claims

1. A method for preparing a copper smelting raw material composed of copper concentrate and wet miscellaneous raw materials, comprising the steps of spreading the wet miscellaneous raw materials in a layer with a thickness of 2 to 10 cm on a surface and spraying a moisture absorbent having a finer particle size than the miscellaneous raw materials so as to cover the same from above; reducing the moisture content of the miscellaneous raw materials by holding the miscellaneous raw materials and the moisture absorbent in contact with each other for a predetermined time; and mixing the moisture absorbent and the copper concentrate while crushing the miscellaneous raw materials with a reduced moisture content. A method for preparing a copper smelting raw material, characterized in that it consists of these steps.

2. The method for preparing a copper smelting raw material according to claim 1, characterized in that the moisture absorbent contains copper.

3. The method for preparing a copper smelting raw material according to claim 1 or 2, characterized in that the moisture absorbent is soot recovered from the exhaust gas of a copper smelting furnace.

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