Method for producing iron-containing clinker

Abstract

To improve productivity of iron-containing clinker by inhibiting formation of deposits onto an inner wall of a reduction roasting rotary kiln derived from "iron-containing dehydration cake", when producing "iron-containing clinker" from steel dust and "iron-containing dehydration cake that contains an iron hydroxide" by reduction roasting treatment.SOLUTION: A method for producing iron-containing clinker includes: a pre-mixing step S10 of granulating steel dust to obtain pellets for reduction roasting; and a reduction roasting step S20 of roasting pellets for reduction roasting, obtained in the pre-mixing step S10, and an iron-containing dehydrated cake that contains iron hydroxide, in a reducing atmosphere, wherein the iron-containing dehydrated cake is directly charged into the reduction roasting step S20 without being fed into the pre-mixing step S10.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing iron-containing clinker. More specifically, the present invention relates to a method for producing "iron-containing clinker" that contains a large amount of reduced iron and can be used as an iron source from "iron-containing dehydrated cake," which is an intermediate product of smelting, e.g., iron and steel dust generated from blast furnaces, electric furnaces, etc. in the steel industry and which contains iron in the form of hydroxide, and is discharged, for example, from non-ferrous metal smelting. [Background technology]

[0002] Steel dust generated from blast furnaces, electric furnaces, etc. in the steel industry is widely used as a raw material for manufacturing zinc oxide ore, which is used as a raw material for zinc ingots in zinc smelters. Zinc oxide ore can be obtained by subjecting zinc-containing raw materials such as steel dust to a reduction roasting treatment by the Weltz process. This reduction roasting treatment of steel dust, etc. is generally performed by a reduction roasting treatment using a rotary kiln. The reduction roasting residue that remains in the kiln without volatilization due to the reduction roasting treatment is recovered as an iron source containing a large amount of reduced iron (see Patent Document 1). The iron source thus recovered is effectively used as an iron raw material for steel manufacturers as a product called "iron-containing clinker".

[0003] On the other hand, in many non-ferrous metal smelting processes, dehydrated cake containing iron in the form of hydroxide (referred to as "iron-containing dehydrated cake" in this specification) is discharged as a smelting intermediate. There are efforts being made to use this "iron-containing dehydrated cake" as a raw material for producing "iron-containing clinker" that can be used as an iron source by subjecting it to reduction roasting treatment by the Weltz process, just like steel dust.

[0004] In the reduction roasting treatment by the Weltz process, the raw material steel dust is charged into a rotary kiln where the reduction roasting treatment is performed together with a reducing agent such as carbon. In this case, in order to further improve the zinc recovery rate, it is widely practiced to mix and granulate the steel dust to be charged into the rotary kiln with the reducing agent in advance and form it into pellets with a size of about 5 to 10 mm (see Patent Document 2). In addition, when the above-mentioned "iron-containing dehydrated cake" is charged as an iron source in the reduction roasting treatment by the Weltz process, conventionally, the "iron-containing dehydrated cake" is also mixed and granulated with the steel dust as another iron source, and then charged into the rotary kiln where the reduction roasting treatment is performed in a pelletized state.

[0005] However, as described above, when the mixed raw material obtained by mixing and granulating the "iron-containing dehydrated cake containing iron hydroxide" with steel dust and pelletizing it was charged into a rotary kiln for reduction roasting, a particularly large amount of deposits were often formed on the inner sidewall of the lorry kiln, compared with the case where only steel dust was charged. In order to remove such deposits, the operation of the reduction roasting rotary kiln had to be stopped to perform the work of removing the deposits, which resulted in a problem of a decrease in the operating rate of the reduction roasting rotary kiln.

[0006] For example, Patent Document 1 discloses a technique for suppressing the formation of deposits on the inner wall of a rotary kiln in which a reduction roasting process is performed when reducing iron is produced from a raw material containing zinc, by charging a CaO source into the rotary kiln and optimizing the particle size of the CaO source to be added and the CaO / SiO2 ratio in the raw material. However, there is no mention of any technical means for avoiding the formation of a large amount of deposits, which becomes a problem when using a dehydrated cake containing iron in the form of hydroxide. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2013-159797 A [Patent Document 2] JP 2015-120948 A Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to improve the productivity of iron-containing clinker by suppressing the formation of deposits derived from the "iron-containing dehydrated cake" on the inner wall of a reduction-roasting rotary kiln when producing "iron-containing clinker" from steel dust and "iron-containing dehydrated cake containing iron hydroxide" by a reduction-roasting treatment. [Means for solving the problem]

[0009] The inventors of the present invention found that the above-mentioned problems can be solved by a process in which the "iron-containing dehydrated cake" is directly charged into a reducing roasting process, without being fed into a pre-mixing process in which raw materials such as steel dust are pelletized, and thus completed the present invention. More specifically, the present invention provides the following.

[0010] (1) A method for producing iron-containing clinker using iron and steel dust containing iron oxides and zinc oxides, and iron-containing dehydrated cake containing iron hydroxide as raw materials, the method comprising: a pre-mixing step of granulating the iron and steel dust to obtain pellets for reduction roasting; and a reducing roasting step of roasting the pellets for reduction roasting obtained in the pre-mixing step and the iron-containing dehydrated cake in a reducing atmosphere, wherein the iron-containing dehydrated cake is directly charged into the reducing roasting step without being fed into the pre-mixing step.

[0011] According to the method for producing ferrous clinker in (1), when producing "ferrous clinker" from steel dust and "ferrous dehydrated cake containing iron hydroxide" by reduction roasting treatment, the formation of deposits originating from the "ferrous dehydrated cake" on the inner wall of the reduction roasting rotary kiln can be suppressed, thereby improving the productivity of the ferrous clinker.

[0012] (2) The method for producing iron-containing clinker according to (1), wherein the iron hydroxide is obtained by precipitating iron dissolved in the liquid.

[0013] According to the method for producing iron-containing clinker of (2), the above-mentioned effects achieved by the method for producing iron-containing clinker of (1) can be exhibited at a better level. Effect of the Invention

[0014] According to the present invention, when "iron-containing clinker" is produced from steel dust and "iron-containing dehydrated cake containing iron hydroxide" by reduction roasting treatment, the formation of deposits originating from the "iron-containing dehydrated cake" on the inner wall of a reduction roasting rotary kiln can be suppressed, thereby improving the productivity of the iron-containing clinker. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow chart showing an example of an embodiment of the "method for producing iron-containing clinker" of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] <Overall composition> As shown in Fig. 1, the "manufacturing method for iron-containing clinker" of the present invention is a process in which the iron and steel dust is granulated to obtain "pellets for reduction roasting" in a pre-mixing step S10, and the "iron-containing dehydrated cake containing iron hydroxide" is charged into the reducing roasting step S20 together with the "pellets for reduction roasting" obtained in the pre-mixing step S10, and "iron-containing clinker" containing a large amount of reduced iron is recovered. Note that in the "manufacturing method for iron-containing clinker" of the present invention, it is not necessary that all of the iron and steel dust charged into the reducing roasting step S20 is pellets granulated in the pre-mixing step S10, and it is sufficient that at least a part of the iron and steel dust is pellets granulated in the pre-mixing step S10.

[0017] The "method for producing iron-containing clinker" can be implemented in an existing crude zinc oxide production facility that performs a process for recovering zinc oxide from steel dust by further performing a wet process S30, a dry heating process S40, etc. in addition to the above-mentioned preliminary mixing process S10 and reducing roasting process S20, as shown in FIG. 1.

[0018] <Pre-mixing process> The pre-mixing step S10 is a step prior to the reduction roasting step S20 in which steel dust and, if necessary, a reducing agent such as coke powder are mixed and granulated to obtain "pellets for reduction roasting."

[0019] In the preliminary mixing step S10, the mixing and granulation process for obtaining the "pellets for reduction roasting" can be carried out using a known pelletizing device. This process, so-called pelletizing, can be carried out, for example, by continuously supplying steel dust and coke powder to a predetermined pellet composition using a rotary pan pelletizer or a two-shaft variable speed pin granulator, and mixing and granulating the mixture while adding mist-like moisture. The size of the "pellets for reduction roasting" is preferably in the range of about 1 mm to 20 mm in order to improve the zinc recovery rate in addition to ease of handling. The moisture content of the "pellets for reduction roasting" is preferably in the range of about 10% by mass to 15% by mass in order to control the particle size in addition to the conditions for granulation.

[0020] <Reduction roasting process> The reduction roasting step S20 is a step of recovering "iron-containing clinker" containing a large amount of reduced iron by roasting "iron-containing dehydrated cake containing iron hydroxide" together with "pellets for reduction roasting" obtained in the preliminary mixing step S10 in a reducing atmosphere. In addition to the above-mentioned raw materials ("iron-containing dehydrated cake containing iron hydroxide" and "pellets for reduction roasting"), in this reduction roasting step S20, a reducing agent such as coke powder and a composition adjuster such as limestone are also added as necessary. In this specification, "iron-containing dehydrated cake" generally means "dehydrated cake containing iron hydroxide", but is mainly intended to be used as a smelting intermediate in a non-ferrous metal smelting process.

[0021] The reduction roasting step S20 can be performed using a rotary kiln that performs the reduction roasting step of the Welz process described above. In this rotary kiln, zinc oxide (ZnO) contained in the steel dust is reduced and roasted, and the volatilized metallic zinc is reoxidized in the exhaust gas to become powdered zinc oxide (ZnO). Meanwhile, the reduction roasting residue that remains in the kiln without volatilizing due to the reduction roasting process contains a large amount of reduced iron, so this reduction roasting residue is recovered from the kiln discharge end as "iron-containing clinker" that is useful as an iron source.

[0022] The "method for producing iron-containing clinker" of the present invention is characterized in that the above-mentioned pre-mixing step S10, in which steel dust containing iron mainly in the form of oxide is mixed with a reducing agent and granulated, is an essential step, while the above-mentioned "iron-containing dehydrated cake" is not charged into the pre-mixing step S10 but is directly charged into a rotary kiln in which the reduction roasting step S20 is carried out.

[0023] Here, the "iron-containing dehydrated cake containing iron hydroxide" is usually dehydrated by a dehydrator such as a filter press, and is a highly viscous solid containing about 35% moisture. In the conventional production of iron-containing clinker, in which the "iron-containing dehydrated cake" was mixed and granulated with steel dust and the like to form pellets, which were then charged into a rotary kiln, which is a reduction roasting furnace for performing reduction roasting, a large amount of deposits were generated on the inner sidewall of the reduction roasting rotary kiln. This is thought to be due to the fact that the highly viscous "iron-containing dehydrated cake" was not sufficiently uniformly dispersed in the pellets when mixed and granulated with the steel dust, and the iron hydroxide derived from the "iron-containing dehydrated cake" was unevenly distributed in the pellets. When pellets in which iron hydroxide is unevenly distributed are loaded into a rotary kiln that performs the reduction roasting step S20, the degree of reduction of the charged material in the furnace varies, and low-melting-point substances mainly composed of iron oxide (FeO) are formed locally. After melting in the reduction roasting rotary kiln, these low-melting-point substances adhere to the inner side walls of the rotary kiln, forming the above-mentioned deposits.

[0024] In contrast, in the "method for producing iron-containing clinker" of the present invention, the "iron-containing dehydrated cake" is directly charged into the rotary kiln for reduction roasting without going through the preliminary mixing step S10. More specifically, the "iron-containing dehydrated cake" is charged into the rotary kiln for performing the reduction roasting step S20 by a feeder different from the above feeder for the "pellets for reduction roasting" using a quantitative feeder similar to the quantitative feeder for cutting out the "pellets for reduction roasting" containing the steel dust obtained in the preliminary mixing step S10.

[0025] In the "method of producing iron-containing clinker" of the present invention, the "iron-containing dehydrated cake" is directly charged into the rotary kiln for carrying out the reduction roasting step S20 without going through the preliminary mixing step S10, and is pulverized while moving through the rotary kiln while being heated and dried. The powder (iron hydroxide) derived from the pulverized "iron-containing dehydrated cake" is uniformly dispersed and penetrated into the above-mentioned "pellets for reduction roasting" containing steel dust while moving through the furnace due to stirring caused by the rotation of the rotary kiln. The granulated material thus formed in the furnace becomes reduction roasting residue containing most of the iron contained therein in a sufficiently reduced form, and this reduction roasting residue is recovered as "iron-containing clinker" from the discharge end of the rotary kiln for carrying out the reduction roasting step S20.

[0026] Here, the "iron-containing dehydrated cake" used as a raw material in the "method for producing iron-containing clinker" of the present invention is preferably a cake mainly composed of iron hydroxide obtained by precipitating iron dissolved in a liquid, such as a precipitate obtained by precipitating iron contained in a liquid in the form of hydroxide in a hydrometallurgical process or the like. Since such hydroxide is obtained in the form of extremely fine particles, the "iron-containing dehydrated cake" made of such iron hydroxide becomes in the form of extremely fine particles with a very small particle size by stirring in a rotary kiln performing the reduction roasting process S20. By becoming in the form of extremely fine particles with a very small particle size, the iron hydroxide derived from the "iron-containing dehydrated cake" can be more easily and more uniformly dispersed and penetrated into the "pellets for reduction roasting", which are granulated products containing steel dust.

[0027] The "iron-containing clinker" obtainable by the "production method for iron-containing clinker" of the present invention, which comprises the steps described above, has a sufficiently high iron content and can be preferably used as an iron source by cement manufacturers and steel manufacturers.

[0028] <Wet process> The wet process S30 is a process in the overall process of producing zinc oxide ore, in which the zinc-containing crude zinc oxide (crude zinc oxide dust) recovered in the reduction roasting process S20 is subjected to wet processing to separate water-soluble impurities such as halogen components into a liquid phase, thereby obtaining high-purity crude zinc oxide as a crude zinc oxide cake.

[0029] <Dry heating process> The drying and heating step S40 is a step in which the crude zinc oxide cake recovered in the wet step S30 is charged into a drying and heating apparatus and calcined to obtain zinc oxide ore (calcined ore) which is a raw material for zinc smelting. EXAMPLES

[0030] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0031] <Example> As an example, a test run was carried out under the following conditions to obtain "iron-containing clinker" using steel dust and "iron-containing dehydrated cake containing iron hydroxide" as raw materials by the "iron-containing clinker manufacturing method" of the present invention. In addition, the preliminary mixing step and the reduction roasting step were carried out in the above-mentioned manner in this test run.

[0032] As the "iron-containing dehydrated cake containing iron hydroxide", a dehydrated cake containing 50 mass% of iron in the form of hydroxide was used. This "iron-containing dehydrated cake" was charged into the reduction roasting rotary kiln using separate fixed quantity feeders at a ratio of 20 mass% to 180 t / day of "pellets for reduction roasting" containing steel dust obtained by the preliminary mixing process, that is, 36 t / day, and the reduction roasting process was carried out. The coke powder was supplied in an amount of 25 mass% of the total of the steel dust and iron hydroxide, and the limestone powder was supplied in an amount of 14 mass% of the total of the steel dust and iron hydroxide.

[0033] The reduction roasting rotary kiln, which performs the reduction roasting process, was heated to a furnace temperature of 1400°C. Impurities such as chlorine and sulfur contained in the "iron-containing dehydrated cake" and "pellets for reduction roasting" were volatilized and removed in the form of lead chloride, cadmium chloride, etc., and "iron-containing clinker" was collected from the discharge end of the reduction roasting rotary kiln.

[0034] After continuing the above test operation for one month, the temperature of the reduction roasting rotary kiln was lowered and the inside of the furnace was inspected. It was found that almost no deposits had formed on the inner wall of the furnace.

[0035] <Comparative Example> The "iron-containing dehydrated cake containing iron hydroxide" used in the examples was fed into a premixing step together with steel dust and the like, and all the iron source materials were mixed and granulated in advance to obtain pellets, which were then charged into a rotary kiln using a quantitative feeder to carry out the reduction roasting step. A comparative example test operation was carried out in a manner in which the reduction roasting step was carried out under the same conditions as in the above examples, except that the "iron-containing dehydrated cake containing iron hydroxide" was mixed and granulated in advance together with steel dust to form pellets. In this operation, immediately after the start of operation, a part of the charge began to adhere to the inner wall of the furnace in the reduction roasting rotary kiln, and after two weeks of operation, the inside of the reduction roasting rotary kiln was completely clogged with the adhered matter. In order to remove the adhered matter, it was necessary to stop operation for a total of five days to perform the temperature lowering, adhered matter removal, and temperature raising operations.

[0036] From the results of the above test operations, it was confirmed that, according to the "method for producing iron-containing clinker" of the present invention, when producing "iron-containing clinker" from steel dust and "iron-containing dehydrated cake containing iron hydroxide" by reduction roasting treatment, the formation of deposits originating from the "iron-containing dehydrated cake" on the inner wall of the reduction roasting rotary kiln can be suppressed, thereby improving the productivity of iron-containing clinker. [Explanation of symbols]

[0037] S10 Pre-mixing process S20 Reduction roasting process S30 Wet Engineering S40 Drying and Heating Engineering

Claims

1. iron and steel dust containing iron oxides and zinc oxides; a ferrous dehydrated cake containing iron hydroxide; A method for producing iron-containing clinker using the following as a raw material: A pre-mixing step of granulating the steel dust to obtain pellets for reduction roasting; a reduction roasting step of roasting the pellets for reduction roasting obtained in the pre-mixing step and the iron-containing dehydrated cake in a reducing atmosphere; Equipped with The iron-containing dehydrated cake is not fed into the pre-mixing step, but is directly fed into the reduction roasting step. Method for producing iron-containing clinker.

2. 2. The method for producing iron-containing clinker according to claim 1, wherein the iron hydroxide is obtained by precipitating iron dissolved in the liquid.

Images