JP6459860B2 - Method for producing zinc oxide ore - Google Patents

Description

  The present invention relates to a method for producing zinc oxide ore. More specifically, the zinc-containing steel dust and zinc-containing steel dust pellets generated in the steel manufacturing process are reduced, volatilized, or the rough zinc oxide dust obtained by wet purification of the crude zinc oxide dust. The present invention relates to a method for producing zinc oxide ore from zinc dust.

  Conventionally, zinc oxide ore obtained by separating and removing impurities from a zinc-containing ore such as crude zinc oxide has been widely used as a raw material for zinc bullion in a zinc smelter.

  Crude zinc oxide is a by-product generated from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry, for example, and reduced roasting into steel dust and steel dust pellets that contain a relatively large amount of zinc in addition to iron components. It can be obtained by processing. This reduction roasting treatment of steel dust is generally performed by reduction roasting (so-called Welts method) using a rotary kiln. Zinc contained in steel dust reduced and roasted by this method is reduced and volatilized in a rotary kiln for reduction roasting and recovered as crude zinc oxide dust.

  Naturally, the halogen concentration in the final product zinc is required to be extremely low. Further, in order to use zinc oxide ore as a raw material for zinc smelting by the ISP smelting method or the like, it is necessary to reduce the halogen concentration of zinc oxide ore to a value allowed in each smelting process. In order to reduce the halogen concentration of zinc oxide ore, as a method of separating and removing halogen from the reduced zinc oxide after reduction roasting, the halogen is volatilized and separated by baking in a rotary kiln for drying and heating (patent) Reference 1).

More specifically, in Patent Document 1, in order to remove lead chloride or a chloride component from crude zinc oxide, a gas having a water vapor concentration of 10 to 20% is added to the crude zinc oxide for 1.5 to 5%. A method for producing high-purity zinc oxide ore is disclosed, which is roasted in a continuous rotary furnace so that the maximum temperature reaches 1000 to 1250 ° C. while being supplied at a gas amount ratio of 0.5 Nm ³ / kg.

  In general, a rotary kiln for drying and heating is based on a system in which a material ore is fired by heating the inside of a furnace by jetting a flame from an oil burner. However, in such a heating method using a burner, as disclosed in Patent Document 1, in order to make the firing temperature as high as 1250 ° C., the amount of fuel and air to be ejected is increased to increase the strength of the flame. As a result, the burner frame expands, and in other words, the cross-sectional area of the burner frame also increases. Then, the spread flame directly hits a part of the wall surface in the kiln and is in an excessively heated state locally. In this state, zinc oxide ore melts at a specific location on the discharge end side in the kiln, and deposits in the furnace called coaching, ring, beco, etc. (hereinafter collectively referred to as “coaching”) are generated, Will grow. If the growth of the coaching proceeds beyond an allowable range, the raw material becomes an obstacle when moving in the rotary kiln, and there is a problem that the operation is finally stopped for maintenance work.

  In order to solve this problem, as a zinc oxide ore production method, a lifter is installed on the inner wall of the rotary kiln to lift up the material ore moving through the kiln, so that the air contact in the ore kiln A method for producing zinc oxide ore that promotes the volatilization of halogen by substantially improving the rate is disclosed (see Patent Document 2). However, this manufacturing method has a problem that there is concern about wear of the lifter part, and there is a problem that installation, maintenance, and repair of the lifter part take time and cost, and there are other means that can increase productivity. It was sought after.

JP-A-9-125169 JP 2014-162960 A

  In the production of zinc oxide ore, the present invention suppresses the generation of coating in a rotary kiln for drying and heating, while maintaining a high halogen removal rate in the furnace, and producing high-grade zinc oxide ore with high productivity. It aims at providing the manufacturing method which can be manufactured below.

  In the rotary kiln used in the drying and heating step, the inventors have introduced a predetermined amount of air from the discharge end side that discharges zinc oxide ore to increase the chance of contact between oxygen in the air and zinc oxide ore. The present inventors have found that the above problems can be solved and have completed the present invention. Specifically, the present invention provides the following.

(1) A method for producing zinc oxide ore comprising a drying and heating step of making zinc oxide ore by firing a raw material containing zinc and fluorine using a rotary kiln, wherein the rotary kiln is provided with a discharge end side. From the above, a method for producing zinc oxide ore in which air having a space velocity of 49 or more and 60 or less is introduced as defined in the following definition.
Space velocity = inflow air flow rate (Nm ³ / h) / rotary kiln furnace volume (m ³ )

  (2) The method for producing zinc oxide ore according to (1), wherein air of 49 to 60 is introduced as the space velocity by blowing additional air from the discharge end side.

(3) The internal diameter of the rotary kiln is 2 m or more and 4 m or less, the length is 20 m or more and 50 m or less, and additional air of 16 or more and 27 or less is blown from the discharge end side as an N value according to the following definition. A method for producing zinc oxide ore.
N value = injection air flow rate (Nm ³ / h) / rotary kiln furnace volume (m ³ )

  (4) The raw material is crude zinc oxide dust having a fluorine content of 0.2% by mass or more and 1.0% by mass or less in terms of dry matter, and the crude zinc oxide dust is fired at 900 ° C. or more and 1200 ° C. or less. The manufacturing method of the zinc oxide ore as described in (3) which manufactures the zinc oxide ore containing the fluorine whose fluorine content of dry ore conversion is 0.6 mass% or less.

  (5) The raw material is a crude zinc oxide dust having a fluorine content in a dry matter equivalent of 0.2% by mass or more and 0.5% by mass or less, and is dried while blowing additional air of 22 or more as the N value. The method for producing a zinc oxide ore according to (4), wherein a zinc oxide ore having a fluorine content in terms of ore of 0.05% by mass or less is produced.

  According to the present invention, in the production of zinc oxide ore, the production of high-quality zinc oxide ore is maintained while maintaining the high halogen removal rate in the furnace while suppressing the generation of coating in the rotary kiln for drying and heating. The manufacturing method which can be manufactured under the property can be provided.

It is sectional drawing which shows typically the structure by the side of the discharge end about the rotary kiln used for the manufacturing method of this invention. It is a figure which shows the relationship between N value which concerns on this invention, and the temperature in the fixed hood at the discharge end side of a rotary kiln. It is a figure which shows the relationship between N value which concerns on this invention, and a fluorine volatility.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<Method for producing zinc oxide ore>
The method for producing zinc oxide ore according to the present invention includes a rotary kiln used in the “dry heating step” described in detail below (hereinafter, also simply referred to as “rotary kiln” or “DRK”), and zinc oxide ore. A high-grade oxidation is maintained while maintaining a high halogen removal rate in the furnace by increasing the chance of contact between oxygen in the air and zinc oxide ore by flowing a predetermined amount of air from the discharge end side that discharges This is a production method capable of producing zinc ore.

  The method for producing zinc oxide ore according to the present invention is a method for producing the effects described above by applying this to the drying and heating step in a general overall process for producing zinc oxide ore. The general overall process of zinc oxide ore production is a reduction roasting process in which zinc containing ore such as steel dust is reduced and roasted to obtain crude zinc oxide, and the halogen components are separated and removed from the crude zinc oxide obtained in the same process. Thus, an overall process including at least a wet process for obtaining a crude zinc oxide cake and a dry heating process for obtaining a zinc oxide ore by drying and heating the crude zinc oxide cake obtained in the same process is assumed.

[Reduction roasting process]
In the reduction roasting process, the raw material etc. which pelletized steel dust with the reducing material previously are processed by the reduction roasting method by the rotary kiln (RRK) for reduction roasting. In this step, the raw material pellets are continuously charged into the RRK together with limestone and the like. The raw material derived from steel dust is reduced and roasted in the RRK furnace, and the volatilized metallic zinc is re-oxidized in the furnace to powdery zinc oxide. Powdered zinc oxide is introduced into the dust collector together with the exhaust gas from the RRK, captured, and recovered as crude zinc oxide.

[Wet process]
In the wet process following the reduction roasting process, impurities such as fluorine contained in the crude zinc oxide obtained in the reduction roasting process are separated and extracted into the treatment liquid, and further impurities from the crude zinc oxide by solid-liquid separation treatment. Is removed by a water washing method to obtain a crude zinc oxide cake. More specifically, in a state where halogen-based impurities such as fluorine are removed in the treatment liquid, the treatment liquid in which the impurities are distributed is removed from the slurry by solid-liquid separation. As a result, the crude zinc oxide slurry becomes a higher concentration crude zinc oxide cake.

[Dry heating process]
In the drying and heating process, the crude zinc oxide cake obtained in the wet process is put into a rotary kiln (DRK) for drying and heating and baked to produce high-grade zinc oxide ore while further reducing the halogen concentration. Perform dry processing.

  The moisture content of the crude zinc oxide cake to be treated in this step is generally 20% by mass or more and 30% by mass or less. Further, the general composition of the crude zinc oxide cake is as follows: zinc is 61 mass% or more and 68 mass% or less, lead is 7 mass% or more and 10 mass% or less, chlorine is 0.3 mass% or more and 0.9 mass% or less, Fluorine is 0.2% by mass or more and 1.5% by mass or less (both are based on dry amount). Such a crude zinc oxide cake is put into the DRK by a quantitative charging device such as a screw feeder in the form of a water-containing cake.

  The exhaust gas generated by the DRK is sucked from the charging end side, removed through a wet exhaust gas cleaning facility and a wet electric dust collector, and discharged from the chimney through a fan or other exhaust fan. The crude zinc oxide cake charged into the DRK is granulated into pellets at the charging end inside a rotary kiln having a length of about 30 m, then dried, heated, and baked at the discharge end.

  The temperature of the zinc oxide ore burned from the rotary kiln is continuously measured and monitored with a radiation thermometer. Here, the firing temperature is maintained at a temperature of 900 ° C. or higher and 1200 ° C. or lower, preferably 1050 ° C. or higher and 1150 ° C. or lower, at the temperature of zinc oxide ore. The DRK is provided with an oil burner on the discharge end side for discharging zinc oxide ore, and is heated by direct fire from the discharge end side. The firing temperature can be adjusted by the amount of heavy oil supplied to the oil burner. By monitoring the discharged zinc oxide ore temperature, the amount of oil, for example, heavy oil, used in the oil burner is generally adjusted in the range of 400 L / h to 700 L / h.

  In the drying and heating step, the size of the zinc oxide ore discharged from the DRK is generally 1 mm or more and 6 mm or less, and the general composition thereof is 60% by mass to 70% by mass of zinc and 3% by mass or more of lead. 5% by mass or less, chlorine is 0.5% by mass or more and 1.5% by mass or less, and fluorine is about 0.6% by mass or less (both are based on dry amount). The fluorine content may be further controlled to be 0.05% by mass or less depending on the application. In addition, the yield of zinc oxide ore in a general zinc oxide production process is about 6 t / h or more and 10 t / h or less.

(Rotary kiln (DRK) for drying and heating)
Here, the rotary kiln for dry heating according to the present invention used in the implementation of the method for producing zinc oxide ore of the present invention will be described. FIG. 1 is a cross-sectional view schematically showing a configuration on the discharge end side which is a technical feature of a rotary kiln 1 which is a typical example of a rotary kiln for drying and heating according to the present invention.

  The rotary kiln 1 rotates to a kiln body 10 that is a hollow cylindrical kiln, a fixed hood 30 that covers one end of the kiln body, an oil burner 40 that blows hot air to heat the inside of the kiln body 10, and the kiln body 10. It is a rotary heating furnace provided with a drive gear (not shown) for transmitting force.

  In the rotary kiln 1, the inside of the kiln main body 10 is heated to a high temperature by the oil burner 40, and the crude zinc oxide cake is subjected to a heat drying process while rotating the kiln main body 10 by the drive gear. The crude zinc oxide cake moves along the inside of the kiln body 10 toward the discharge end 11 while being stirred and roasted along the inclination of the kiln body 10. As discharged. The kiln main body 10 is made of steel, and a refractory layer is formed on the inner side by a regular refractory (brick) or an irregular refractory (castable) with a thickness of about 25 mm to 30 mm. In general, the outer diameter is 3.3 m, the length is 30 m, and the exterior is about 25 mm thick. In this invention, the rotary kiln provided with the kiln main body from 2 m to 4 m in inner diameter and 20 m to 50 m in length is assumed as the applicable range.

  According to the method for producing zinc oxide ore of the present invention, a predetermined amount of air, that is, air having a space velocity of 49 or more and 60 or less as defined below, is caused to flow from the discharge end side of the rotary kiln that discharges zinc oxide ore. Thereby, the contact opportunity of oxygen in the air and zinc oxide ore can be increased, and the fluorine content in zinc oxide ore can be reduced. Accordingly, there is no need to increase the flame strength to the limit where no coaching is generated as in the conventional method. Therefore, according to the method for producing zinc oxide ore of the present invention, it is possible to obtain an effect that the generation and growth of the coating due to the spread flame directly hitting the inner wall of the kiln main body can be suppressed.

In the present specification, in the implementation of the production method of the present invention, the air flow rate (Nm ³ / h) introduced from the discharge end side discharging zinc oxide sinter is defined as the furnace volume (m ³ ) of the kiln body of the rotary kiln. The value divided by is defined as “space velocity”. The space velocity mentioned here is considered to have the same meaning as SV (Space Velocity) in an absorption facility or column using packing.
(Space velocity) = (Inflow air flow rate (Nm ³ / h)) / (Internal furnace volume of kiln body (m ³ ))
Furthermore, a value obtained by dividing the flow rate of air blown into the kiln main body (Nm ³ / h) by the furnace volume (m ³ ) of the kiln main body of the rotary kiln is defined as “N value”.
(N value) = ( Blowing air flow rate (Nm ³ / h)) / (Internal furnace volume of kiln body (m ³ ))

  There is no particular limitation on the method of flowing the air in the predetermined amount range from the discharge end 11 side of the rotary kiln 1 that discharges zinc oxide ore. However, the DRK has a configuration in which seal air (2a in FIG. 1) for preventing gas leakage is blown into a ring-shaped seal portion that forms a gap between the rotating portion and the fixed portion on the discharge end side. Since there are many things, the flow rate of this seal air 2a is increased more than the minimum flow rate required for sealing, and additional air (2b in FIG. 1) for introducing this seal air 2a into the kiln main body 10 The means to do can be illustrated as an example of a preferred embodiment of the present invention. By blowing the additional air 2b by increasing the amount of the seal air, the air flow along the circumferential inner wall in the kiln main body 10 is formed simultaneously with the prevention of the gas leakage which is the original purpose. This is also preferable in that local excessive heating of the inner wall of the kiln body 10 due to floating can be prevented. The “additional air” in the present specification is, for example, an air flow that is not supposed to be actively introduced into the furnace, such as the seal air 2a, for the purpose of achieving the object of the present invention. It is a concept that indicates the air that is actively introduced into the kiln body as an additional air flow to achieve a prescribed space velocity or N value defined.

For example, assuming that the furnace volume of the kiln main body is 184 m ³ as a rotary kiln having the above-mentioned general size range within the assumed range of the present invention, the additional air 2b is injected at 3000 to 5000 Nm ³ / h. Corresponds to 16 to 27 as the N value. In this case, the total flow rate of the exhaust gas (air 2c) sucked from the charging end side of the kiln main body is 9000 Nm ³ / h or more and 11000 Nm ³ / h or less (including the flow rate of the additional air 2b). To 60). The flow rate of the seal air 2a necessary for the original sealing, which is the original purpose, is 2000 Nm ³ / h or more and 3000 Nm ³ / h or less, and this flow rate is set to 3000 Nm ³ / h or more and 5000 Nm ³ / h or less. Thus, the total flow rate of the air 2c flowing into the kiln main body can be adjusted to the above range.

The blowing amount of the additional air 2b is appropriately adjusted according to the fluorine content of zinc oxide ore, which is finally the management target. For example, when the fluorine content is required to be 0.6% by mass or less, the blowing amount of additional air 2b introduced into the kiln body is set to 3000 Nm ³ / h or more and 5000 Nm ³ / h or less (N value of 16 to 27), and when the fluorine content is required to be 0.05% by mass or less, the blowing amount of the additional air 2b is 4000 Nm ³ / h or more and 5000 Nm ³ / h or less (N value is 22 to 27). ), It is possible to maintain the desired fluorine volatilization rate while performing within a range of 1050 ° C. or higher and 1150 ° C. or lower, which is a firing temperature with a low risk of causing the rotary kiln to stop operating.

The fluorine compound remaining in the zinc oxide dust is presumed to take the form of volatile (for example, lead chlorofluoride (PbFCl)) or non-volatile (for example, calcium difluoride (CaF ₂ )). Of these, the volatile substance (PbFCl) can be volatilized and removed by maintaining the calcination temperature within the range of 1050 ° C to 1150 ° C. On the other hand, since the non-volatile substance (CaF ₂ ) is a very stable compound, it is not decomposed and volatilized in the drying / heating rotary kiln and is fixed to zinc oxide ore.

  The reason why the volatilization of fluorine in zinc oxide ore is promoted by the increase of the air blowing flow rate from the discharge end side of the drying / heating rotary kiln is considered to be as follows. That is, if the flow rate of air passing through the drying / heating rotary kiln increases, the oxygen partial pressure in the kiln increases and a large amount of oxygen necessary to promote the volatilization of lead is supplied. Is promoted. On the other hand, since the fluorine in zinc oxide ore exists in the form of PbFCl, it volatilizes with the volatilization of lead in the rotary kiln for drying and heating. Therefore, it is considered that when the volatilization of lead is promoted, the volatilization rate of fluorine increases accordingly. Further, as an effect of the air flow, it is considered that fluorine present in the gas phase portion of the solid-gas interface of zinc oxide ore is replaced with air to promote the volatilization of fluorine.

  As mentioned above, although embodiment of this invention was described, this invention is not restricted to embodiment mentioned above. The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

A test operation for verifying the effects of the present invention was performed using the rotary kiln shown below. The rotary kiln for test operation is made of steel with an outer diameter of 3.3 m, the same length of 30 m, and an outer thickness of the kiln body of 25 mm, and a standard refractory with a thickness of 25 to 30 mm on the inside ( Brick) and a refractory layer formed by an irregular refractory (castable) were used. The furnace volume of the kiln main body of this rotary kiln was 184 m ³ . As raw materials, zinc is 20% by mass to 35% by mass, lead is 1% by mass to 3% by mass, iron is 10% by mass to 35% by mass, chromium is less than 0.1% by mass, and fluorine is 1.0% by mass. Steel dust pellets having a composition of mass% and cadmium of 1.0 mass% (both based on the dry amount) were used.
The crude zinc oxide dust cake obtained by processing the raw material in the reduction roasting step and the wet refining step was put into the rotary kiln for the test operation. The fluorine content of the crude zinc oxide dust cake was 0.31% by mass or more and 0.43% by mass or less (dry basis).

The firing temperature by the rotary kiln is in the range of 1050 ° C. or more and 1150 ° C. or less, and only the flow rate of seal air blown as additional air is in the range of 2000 Nm ³ / h or more and 6000 Nm ³ / h or less (N value is equivalent to 11 to 33). The test operation was performed at various times.

  In the process of changing the flow rate of sealing air, the temperature in the hood on the discharge end side was also measured, and the relationship between the space velocity and N value obtained from the result and the temperature in the hood was shown in FIG.

  As can be seen from FIG. 2, the temperature in the hood tends to decrease if the space velocity and the N value increase, but if the N value exceeds 25, the temperature in the hood rapidly decreases. When the temperature in the hood is 700 ° C. or lower, the firing temperature cannot be maintained, and sufficient firing cannot be performed. As a result, the volatilization of fluorine is difficult to proceed, and it is understood that the N value needs to be 27 or less.

  Further, the fluorine content in the produced crude zinc oxide was analyzed, and the value was divided by the fluorine content in the charged crude zinc oxide dust to obtain the fluorine volatility. The analysis of fluorine was performed by the fluorescent X-ray method. The relationship between the space velocity and N value obtained from the result and the fluorine volatilization rate is shown in FIG.

  From FIG. 3, it can be seen that by setting the N value to 15 or more, the volatilization rate of fluorine can be set to 60% or more. If the volatilization rate of fluorine can be 60% or more, from a crude zinc oxide dust containing 0.2 to 1.5% by mass of fluorine in terms of dry matter, fluorine content of 0.6% or less Of zinc oxide ore can be produced.

  Moreover, it turns out that the volatility of fluorine can be made 90% or more by making N value 22 or more. If the volatilization rate of fluorine can be 90% or more, from a crude zinc oxide dust containing 0.2% by mass or more and 0.5% by mass or less of fluorine in terms of dry matter, fluorine content of 0.05% by mass or less Of zinc oxide ore can be produced.

  As mentioned above, according to the manufacturing method of the zinc oxide ore of this invention, operation of the rotary kiln for a drying heating process is in the range of about 1050 degreeC or more and 1150 degrees C or less which is a calcination temperature with a small risk of causing the operation stop of a rotary kiln. While performing, it is possible to stably produce high-grade zinc oxide ore with a fluorine content of 0.6% by mass or less, or extremely high-grade zinc oxide ore with the same content of 0.05% by mass or less. I understand that I can do it.

DESCRIPTION OF SYMBOLS 1 Rotary kiln 10 Kiln main body 11 Discharge end 30 Fixed hood 40 Oil burner 50 Burner frame 60 Fired product 2a Seal air 2b Additional air 2c Air

Claims (3)

A method for producing zinc oxide ore comprising a drying and heating step of making zinc oxide ore by firing a raw material containing zinc and fluorine using a rotary kiln,
The flow rate of seal air that is blown to prevent gas leakage into the ring-shaped seal part that forms a gap between the rotary part and the fixed part on the discharge end side of the rotary kiln is greater than the minimum flow rate required for sealing. by varying the total flow rate of air flowing into the kiln body through the discharge end for discharging the zinc oxide ore of the rotary kiln is a management target in a range of 49 or more and 60 or less as a space velocity due to the following definitions A method for producing zinc oxide ore , wherein the zinc oxide ore is adjusted to have a space velocity according to the fluorine content of the zinc oxide ore.
Space velocity = inflow air flow rate (Nm ³ / h) / rotary kiln furnace volume (m ³ ) The raw material is crude zinc oxide dust having a fluorine content in terms of dry matter of 0.2% by mass or more and 1.0% by mass or less,
By firing the crude zinc oxide dust at 900 ° C. or more and 1200 ° C. or less,
Method for producing a zinc oxide ore according to claim 1, the fluorine content of the dry ore converted to produce a zinc oxide ore containing the following fluorine 0.6 mass%. The raw material is crude zinc oxide dust having a fluorine content in terms of dry matter of 0.2% by mass or more and 0.5% by mass or less,
While adjusting the total flow rate of the air to be 55 or more as the space velocity,
The manufacturing method of the zinc oxide ore of Claim 2 which manufactures the zinc oxide ore whose fluorine content of dry ore conversion is 0.05 mass% or less.

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