JP2001081520A - Method of treating waste solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To execute the treatment without greatly costing for chemicals, fuel, equipment or the like, by using the one in which the whole or a part is substituted by a waste solution contg. an Na compound and/or pulp fiber when producing a fired pellet, as blending water. SOLUTION: A prescribed amount of the bleached waste solution of pulp (containing about 0.5 to 1.5 mass % Na and about 2 to 13 mass % pulp fiber) is added to pellet raw material powder composed of iron ore powder, limestone or the like, which is granulated by a pan type pelletizer to form into a raw pellet. The raw pellelt is charged to a traveling grade so as to form into a layer of a prescribed thickness. In the grade, at a drying zone, the moisture contained in the raw pellelt is removed, at a water removing zone, the water of crystallization is removed, and, at a preheating zone, an acmite compound having the low m.p. is formed, and moreover, the pulp fiber is burnt to form into a preheated pellet having high strength so as to withstand rolling by a rotary kiln in the following stage. The pellet is charged to the kiln and is fired, and the pulp fiber left in the burning is perfectly burnt away.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating waste liquid generated in the bleaching step of pulp, which is a raw material for papermaking, and more particularly to a method for treating waste liquid containing a sodium compound and / or pulp fiber. is there.

[0002]

2. Description of the Related Art Papermaking pulp is manufactured by a method in which wood chips are digested with chemicals to dissolve non-fibers such as lignin to extract only the fiber content. Mechanical pulp, and deinked pulp that is regenerated by deinking waste paper using chemicals and the like. The fiber extracted by these methods is referred to as unbleached pulp, and the unbleached pulp is bleached with a chemical to increase the whiteness, thereby obtaining a raw material for papermaking (bleached pulp).

[0003] Bleaching of mechanical pulp and deinked pulp is performed using a high-concentration bleaching tower, for example, with an aqueous solution of 1% by mass of hydrogen peroxide and 5% by mass of sodium silicate at 60 to 70 ° C for 2 to 4 hours. On the other hand, the bleaching of chemical pulp is usually performed in four to six stages by combining four kinds of processes of chlorination, alkali treatment, hypochlorous acid treatment, and chlorine dioxide treatment.
In the alkaline treatment step, sodium hydroxide is usually used as a chemical.

[0004] Therefore, regardless of the type of pulp, a waste liquid containing an alkali compound (particularly a sodium compound) is generated from the bleaching step. Furthermore, a large amount of fine pulp fibers are mixed in these waste liquids. In the present circumstances,
These waste liquids are neutralized with an alkali neutralizing agent (sulfuric acid, hydrochloric acid, etc.), and then guided to a sedimentation facility, where fine pulp fibers are precipitated and removed, and then discharged. Further, the sediment (sludge) is discarded as waste or incinerated.

[0005]

As described above, at present, a large amount of an alkali neutralizing agent and a sedimentation facility are required in order to treat an effluent containing an alkali compound from a bleaching step. Furthermore, dumping sludge as waste is becoming more difficult due to the recent tightening of environmental regulations.
On the other hand, separate equipment is required for incineration,
Fuel for incineration is also needed. Therefore, the cost of treating the wastewater containing an alkali compound from the bleaching step is very large, and the development of an inexpensive treatment method is desired.

[0006] In order to reduce the sludge treatment cost, research and development for reducing the amount of sludge and recovering methane as a fuel by purifying pulp fibers in the sludge by methane fermentation at 50 to 60 ° C to digest the methane as a fuel have been advanced. ,
There is a problem that the equipment cost for methane fermentation increases.

Therefore, the present invention provides a method for granulating iron ore pellets, which is a raw material of a blast furnace (blast furnace) for producing pig iron, without using any waste liquid containing an alkali compound and pulp fibers generated in the bleaching step. An inexpensive waste liquid treatment method that eliminates the need for alkali neutralizers, sedimentation equipment, sludge incineration equipment, incineration fuel, etc., or can reduce or reduce it by directly using it in the process or in the pseudo-granulation process of sintered ore It is intended to provide. Further, the present invention is not limited to the treatment of pulp bleaching waste liquid, but also provides a low-priced treatment method for waste liquid containing alkali compounds generated in other industries (for example, degreasing waste liquid of rolled steel sheet) by the same method. It is also intended to do so.

[Means for Solving the Problems]

[0008] In order to achieve the above-mentioned object, among the present invention, the invention according to claim 1 is characterized in that granulated water is added to fine iron ore and granulated, followed by drying, water separation and preheating. After that, when firing is further performed to produce fired pellets, the blending water is used by replacing all or part of the water with a waste liquid containing a sodium compound and / or pulp fiber. . In addition, two types of granulation of pellets are used: a wet granulation method using iron ore (wet powder) having attached moisture as it is, and a dry granulation method using iron ore (dry powder) from which attached moisture is removed. . The sum of the attached moisture and the blending water is referred to as granulated moisture. Therefore, in the case of the dry granulation method, the granulation moisture is the same as the blended water.

The pellets (raw pellets) granulated with the compounding water in which all or a part thereof is replaced with a waste liquid containing a sodium compound and / or pulp fiber are subjected to a drying process at a gas temperature of 180 to 250 ° C. and only water. Is removed, and sodium compounds (such as sodium hydroxide and sodium silicate) and / or pulp fibers remain in the pellets. In the next water separation treatment step, 1 to 3% by mass of crystal water in the fine iron ore is removed at 250 to 400 ° C., but at such a low temperature, the remaining sodium compound and pulp fiber hardly change.

[0010] In the next pre-heat treatment step, the pellets are heated to about 1000 ° C, so that the sodium compound remaining in the pellets reacts with Fe ₂ O _{3 as} a main component of iron ore and SiO _{2 as} a gangue component in the iron ore. Acumite compound (Na ₂ O.
Fe ₂ O ₃ .4SiO ₂ ) and other low melting point compounds,
The low-melting compound forms a liquid phase at the contact point between the iron ore powders and causes liquid phase sintering to bond the iron ore powders together. further,
With the progress of the liquid phase sintering, the reaction due to the mutual diffusion between the low melting point compound in the liquid phase and Fe ₂ O ₃ of the iron ore progresses,
The liquid phase becomes a high melting point compound, the liquid phase disappears, and the liquid phase sintering is completed. In addition, the akumite compound is 1000 ° C.
It is known that a composition range having the following melting points is wide and a low melting point composition of 760 ° C. can be obtained (Koichi Morioka et al .:
CAMP-ISIJ, Vol. 11 (1998) p. 9
14). Further, the heating gas used in the preheating process pulp fibers remaining in the pellets because it contains O ₂ 15 to 18 volume% is lost by combustion.

[0011] Even if the pulp fibers remain unburned in the pre-heat treatment step, the pellets (pre-heated pellets) pre-heat treated in the subsequent sintering treatment step have higher temperatures of 1250 to 13
At 50 ° C., preheating almost the same O ₂ 15-18% by volume
The pulp fiber is completely burned out and disappears because it is calcined with a gas containing.

[0012] It should be noted that even if voids are generated due to the burning of the pulp fibers and the porosity increases, there is no danger that the strength of the preheated pellets or the fired pellets will decrease. This is because the strength of the preheated pellets is significantly improved by the liquid phase sintering in the above preheat treatment step as compared with the ordinary preheated pellets formed only by solid phase sintering (the aforementioned Koichi Morioka et al .: CAMP).
-ISIJ, Vol. 11 (1998) p. 914). Therefore, the yield can be improved by increasing the strength of the preheated pellets or product pellets, or the production amount of the product pellets can be increased by maintaining the strength of the preheated pellets or product pellets at the same level as usual.

As described above, the waste liquid containing the sodium compound and / or pulp fiber substituted for all or a part of the compounding water used in the granulation treatment step is treated with water in the treatment step from drying to baking. evaporated to become vapor, the pulp fibers become harmless water vapor and CO ₂ by combustion, can be discharged into the atmosphere together with the exhaust gas of the fired pellets manufacturing process. Since the heat of combustion of the pulp fiber is effectively used in the preheating or firing process of the pellets, it also contributes to a reduction in fuel consumption for manufacturing fired pellets.

On the other hand, the sodium compound is charged into the blast furnace while remaining in the fired pellets as a high melting point compound produced by reacting with Fe ₂ O ₃ . In the blast furnace, Fe ₂
The O ₃ component is reduced to metallic iron, melts and separates into metallic iron and a sodium compound. The separated molten sodium compound is diluted into a large amount of slag generated from gangue components of iron ore and ash of coke, so there is almost no difference in composition from ordinary blast furnace slag, and this slag is cooled after discharging from the blast furnace. It solidifies and is effectively used for roadbed materials.

Therefore, the waste liquid containing the sodium compound and / or pulp fiber can be inexpensively processed without requiring expensive pretreatment such as neutralization and sludge treatment. Further, although not a direct problem to be solved by the present invention, it also contributes to an improvement in the yield of the product fired pellets, an increase in the production amount, and a reduction in the unit fuel consumption for manufacturing the fired pellets.

According to a second aspect of the present invention, a compounding water is added to iron ore powder, auxiliary raw materials (limestone, quicklime, quartzite, serpentine, etc.) and solid fuel such as coke powder, coal powder and the like, and the mixture is kneaded. In producing a sintered ore by sintering the granulated mixed raw material, all or a part of the blended water is replaced with a waste liquid containing a sodium compound and / or pulp fiber. Things. The iron ore powder is usually used while having an attached moisture of 4 to 6% by mass (external number), and the total of the attached moisture and the mixed water is referred to as mixed raw material moisture.

[0017] By adding and kneading the compounding water in which the waste liquid is completely or partially substituted, the viscosity of the compounding water is reduced due to the effect of the sodium compound contained in the waste liquid. As a result, the mixing of the iron ore powder and the auxiliary material can be made more uniform, and the compounding water containing the sodium compound can also be substantially uniformly infiltrated on the surfaces of the iron ore powder and the auxiliary material. Further, the infiltrated compounding water also diffuses into the attached moisture of the iron ore powder, so that the concentration of the sodium compound on the surface of the iron ore powder can be increased. After the kneading, the quasi-granulated mixed raw material is filled on a pallet of a sintering machine (for example, a Dwyroid type sintering machine), and the solid fuel in the mixed raw material on the surface layer is ignited. After ignition, in the process of burning the solid fuel while sucking air downward and sintering the mixed raw material filled with the combustion heat to form a sintered cake, the mixed raw material is dried and then heated to 1150 to 1200 ° C. By heating, a melt is generated by a slag reaction between the iron ore in the mixed raw material and the auxiliary raw material. The liquid ore sintering of the iron ore powder is performed by the melt, and after cooling, the required strength of the sintered ore is obtained by bonding of the iron ore powder with the melt. At this time, as described above, the iron ore powder and the auxiliary material are more uniformly mixed in the kneading stage than usual, and after the moisture is removed by drying the mixed material, the sodium compound also remains on the surface of the iron ore and the auxiliary material. Since it is substantially uniformly dispersed, the formation of a melt is promoted by forming a low-melting compound such as the above-described alumite compound, and the generation of the melt is uniform over the entire sintered cake, and the amount of the melt is reduced. Can increase. That is, since the akumite compound has a wide composition range having a melting point of 900 ° C. or less, the above-mentioned (Morioka Koichi et al .: CAMP-ISIJ, Vo)
l. 11 (1998) p. 914), and a melt can be generated from a temperature lower than the normal sintering temperature (1150 to 1200 ° C.) of the ore. The generated melt promotes the generation of the melt by the slag reaction between the iron ore powder and the auxiliary material, thereby generating a sufficient amount of the melt for sintering the iron ore powder and improving the strength of the sintered ore. Can be. Therefore, the yield of the product sinter can be improved, or the production amount can be increased if the strength of the sinter is maintained at the same level as usual.

On the other hand, the pulp fibers contained in the waste liquid are:
In the heating stage after the mixed raw material is dried, O ₂ passing through the packed bed of the mixed raw material is contained at a high concentration (14 to 18% by volume).
Burned with hot gas and disappears. There is a concern that the strength of the sintered ore may be reduced due to the formation of voids due to the disappearance of the pulp fibers. .

As described above, of the waste liquid containing the sodium compound and / or pulp fiber substituted for all or a part of the compounding water used in the kneading and pseudo-granulating steps, the water is used in the sintering step. Evaporates to water vapor,
The pulp fibers burn to harmless water vapor and CO ₂ and can be released to the atmosphere along with the exhaust gases of the sinter production process. In addition, since the combustion heat of the pulp fiber is effectively used, it also contributes to a reduction in the unit consumption of solid fuel.

On the other hand, the sodium compound is charged into the blast furnace while remaining in the sintered ore as a slag reaction product, and is diluted in the slag through the same reaction as described in the first aspect of the present invention. Is effectively used for roadbed materials.

Therefore, the waste liquid containing the sodium compound and / or the pulp fiber can be treated at a low cost without requiring expensive pretreatment such as neutralization treatment and sludge treatment. Further, it is not a direct solution problem of the present invention, but also contributes to improvement of the yield of the product sintered ore, increase of the production amount, and reduction of the basic unit of solid fuel.

According to a third aspect of the present invention, the waste liquid containing the sodium compound and / or pulp fiber is a waste liquid generated from a pulp bleaching step. Since the waste liquid generated from the pulp bleaching process contains sodium compounds such as sodium silicate and sodium hydroxide and pulp fibers, it has the same effect as the first or second aspect of the present invention.

The invention according to claim 4 is characterized in that the sodium concentration of the granulated water or mixed raw material water after replacing all or a part of the mixed water with the waste liquid is 0.05 to 2% by mass. Having. The replacement amount of the waste liquid containing the sodium compound with respect to the compounding water should be controlled by the amount of sodium remaining in the granulated pellets after drying or the mixed raw material for sintering. 0.005% by mass of residual sodium in dried granules or mixed raw material
With the above, liquid phase sintering of iron ore powder can be caused. Since both the granulated water content of the pellets and the raw material water content for sintering are about 6 to 9% by mass, the sodium concentration of the granulated water content or the mixed raw material water content may be 0.05 to 0.08% by mass or more. By increasing the amount of residual sodium, the amount of waste liquid to be treated can be increased, and the strength of fired pellets and sintered ore can be improved, which is preferable.

On the other hand, if the amount of residual sodium in the dried granulated material or the mixed raw material increases, the reduced powderability of the fired pellets and sintered ore deteriorates, and the refractory material in the blast furnace during blast furnace operation increases. Since an adverse effect such as alkali adhesion and alkali circulation is caused, the upper limit of the amount of residual sodium is 0.1%.
12% by mass, which is 1.3 to 2.0% by mass in terms of sodium concentration of granulated water or mixed raw material water.
Therefore, it is preferable to use the waste liquid as it is or to appropriately dilute the waste liquid with water and use it at a predetermined sodium concentration so as to fall within the above upper and lower limits, depending on the content of the sodium compound.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.
This will be described with an example. (1) How to treat waste liquid in the fired pellet manufacturing process
Regarding the method, the preferred practice of the invention as claimed in claims 1 and 3
One embodiment of the application is shown below. Iron ore powder (T.Fe: 57 ~
(69% by mass) 94 to 96 parts and limestone or
Average particle size 40 obtained by mixing and pulverizing 4 to 6 parts of dolomite
Pulp bleaching waste liquid (N
a: 0.5 to 1.5% by mass, Si: 2 to 6% by mass, pal
Fiber: 2 to 13% by mass)
Raw pellets granulated to a diameter of 9.5 to 11 mm with a retirer
Around 30cm in pellet layer thickness for traveling great
Insert so that it becomes. Great for drying, syneresis and preheating
Consists of a zone, and at drying, the gas temperature is 180-250 ° C.
The moisture content of the raw pellets is removed, and 250-40
At 0 ° C., 1 to 3% by mass of crystal water is removed.
Sodium silicate in waste pulp by heating at ~ 1100 ° C
And Fe in iron ore powder_TwoO _ThreeTo react with a low melting point
And pulp fibers are burned.
The residence time of the pellets in the great is 15-25 minutes
Crush strength to withstand rolling in a rotary kiln
Preheat pellets of higher strength (eg 10 kg / P)
The preheated pellets are loaded into a rotary kiln
And firing at 1250-1350 ° C for 10-15 minutes.
Completely burns out the unburned pulp fibers in the Great
To lose. As described above, sodium compound and pulp
Pretreatment of bleaching waste liquor of fiber-containing pulp
It can be processed in the fired pellet manufacturing process
You.

(2) Regarding a method for treating a waste liquid in the sinter production process, a preferred embodiment of the invention according to claims 2 and 3 will be described below. Iron ore powder of 10 mm or less (T. Fe: 57 to 68% by mass, attached moisture: about 3 to 5
86 to 90 parts by mass (external number) 10 to 14 parts of limestone or quicklime, coke powder or anthracite powder 3 as an auxiliary material
~ 5 parts, and the same pulp bleaching waste liquid (Na:
0.5 to 1.5% by mass, Si: 2 to 6% by mass, pulp fiber: 2 to 13% by mass), and kneading with a drum mixer to obtain a total water content of 6 to 8 parts by adding 1 to 5 parts. Pseudo-granulated mixed raw material. The mixed raw material is filled on a pallet of a Dwyroid type sintering machine, and ignites coke powder or anthracite powder in the mixed raw material on the surface layer. After ignition 15-25
By sucking air downward for a minute, the coke powder or anthracite powder is burned, and the mixed material is sintered by the combustion heat to form a sintered cake. After evaporating the water in the process from the ignition to the production of the sintered cake, a high temperature state of 900 ° C. or more (up to 1250 to 1300 ° C.) is changed to 2 to 4 ° C.
As described above, sodium silicate in the waste pulp and Fe ₂ O ₃ in the iron ore powder are reacted with each other to produce a low-melting-point alumite compound and burn and extinguish the pulp fiber. As described above, the pulp bleaching waste liquid containing the sodium compound and the pulp fiber can be treated in the sinter ore production process without prior treatment.

[0027]

EXAMPLES Based on the reaction mechanism described above, the present invention provides
It is expected that not only the bleaching waste liquor of pulp but also the treatment of waste liquor (containing no pulp fiber) containing sodium compounds generated from other industries will have the same effect. As an example to confirm the effect of the present invention, and waste liquid generated from the degreasing process of rolled steel sheet in steel production,
The following experiment was performed using an aqueous solution of a sodium silicate reagent as a simulated waste liquid.

(Example 1) Experiment on wastewater treatment method in fired pellet manufacturing process As wastewater containing a sodium compound, it is generated in a treatment step of removing oils and fats used in a rolling step for plating steel sheets after rolling. An experiment was performed using the two kinds of waste liquids. One is a steel plate degreasing waste liquid containing 0.6% by mass of sodium orthosilicate, and the other is a caustic soda waste liquid containing 0.5% by mass of sodium hydroxide. Also,
A 1.0% by mass aqueous solution of sodium metasilicate reagent (JIS No. 3) was also used as the pseudo waste liquid. For comparison,
Tap water was used. Further, in order to investigate the effect of mixing a plurality of types of waste liquid, a sodium metasilicate reagent equivalent to 0.5% by mass (JIS) was added to the caustic soda waste liquid.
No. 3 product) was used. (See Table 1)

To a dry powder of Hamasley ore (analyzed values are shown in Table 2) crushed to a Blaine index of 2000 cm ² / g, about 8% by mass (external number) of each of the test liquids was added as blending water to obtain a granule. Raw pellets having a diameter of 9.5 to 11 mm were granulated. After performing a drying treatment of holding the raw pellets at 110 ° C. for 180 minutes to remove moisture, the dried pellets are heated in the air at 1000 ° C. for 10 minutes by an electric furnace to form preheated pellets, and after cooling, The crush strength was measured. Table 3 shows the experimental results.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

Experiment No. 3 in Table 3 As shown in 1-3,
When granulated with tap water, the crush strength of the preheated pellet is 10
On the other hand, the strength of the preheated pellet was increased to 23 kg / P when granulated with the steel plate degreasing waste liquid, while the strength was 23 kg / P. Also,
1.0 mass% sodium metasilicate reagent (JIS No. 3 product)
The crush strength of the preheated pellet is 2 even when granulated with an aqueous solution.
It increased to 0 kg / P. From these experimental results, it was confirmed that the strength of the preheated pellets can be increased by drying the raw pellets granulated with the aqueous solutions containing various sodium silicates and heating them at 1000 ° C. for a certain period of time.
This is considered to be an effect of increasing the strength of the preheated pellet by progressing the liquid phase sintering due to the formation of the low-melting-point alumite compound described above.

Even if a waste liquid containing sodium silicate is used, the strength of the preheated pellets can be increased with almost the same effect without using a chemical such as an expensive sodium silicate reagent. It is possible to simultaneously improve the yield or productivity of fired product pellets based on the improvement in the strength of the pellets.

Next, in Experiment No. 1 of Table 1, From 1, 4, 5
When granulated with tap water, the crush strength of the preheated pellet is 10
The strength of the preheated pellet increases to 15 kg / P when granulated with sodium hydroxide waste liquid, whereas the sodium metasilicate reagent (JIS No. 3 product) is dissolved in the sodium hydroxide waste liquid by 0.5 mass% corresponding to 0.5 mass%. When the granulation was carried out at, the crushing strength of the preheated pellet was further increased to obtain 23 kg / P. From these experimental results, it was confirmed that the crushing strength of the preheated pellet also increased when granulation was performed with an aqueous solution containing only sodium hydroxide as a sodium compound. However, the degree of the increase in the crushing strength is smaller than in the case where an aqueous solution of sodium silicate having a similar concentration is used. Although the detailed reaction mechanism is unknown, when sodium silicate is used, an akumite compound can be easily generated by reaction with Fe ₂ O ₃ , but when only sodium hydroxide is used, an akumite compound is formed. Fe ₂ O ₃
Must also react with the gangue component SiO ₂ ,
The slower reaction than the reaction between sodium silicate and Fe ₂ O ₃ is considered to be the reason for the small increase in the crushing strength.

However, when sodium silicate is added to an aqueous solution of sodium hydroxide, the reaction mechanism is unknown, but the preheating is more than a value obtained by adding the degree of increase in the crushing strength of the preheated pellets when each aqueous solution is used alone. It was found that the crushing strength of the pellet increased.

Therefore, when treating a waste liquid containing sodium hydroxide, the waste liquid may be used alone, but two or more kinds of waste liquids may be mixed and used, for example, mixed with a waste liquid containing sodium silicate. It is also effective to use it.

(Example 2) Experiment on waste liquid treatment method in sinter ore production process After mixing -10 mm iron ore powder, auxiliary raw material, and coke powder at the mixing ratio shown in Table 4, the mixed raw material water content was reduced to 7%.
Tap water or an aqueous solution of sodium metasilicate was added so as to have a mass% (external number) and the sodium metasilicate concentration shown in Table 5, and the mixture was pseudo-granulated with a drum mixer.
Kinds of mixed raw materials (Sample A: Comparative Example, Sample B: Inventive Example)
Was manufactured. Table 6 shows the components of the blended iron ore powder used in this example.

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

[Table 6]

A sintering experiment using a sintering pot was performed on the two kinds of mixed raw materials. In this sintering experiment, the diameter was 100 m
m, filling the mixed raw material in a sintering pot having a height of 300 mm,
Subsequently, the top surface of the layer was ignited, and sintering was performed while suctioning air at a suction pressure of 3500 Pa. After sintering, the drop strength of the product sinter was measured. In addition, the drop strength, after repeating the operation of dropping the product sintered ore at a time from a height of 2 m onto an iron table four times, sieving the entire amount with a 5 mm and 10 mm sieve, and 5 to 10 mm and 10 mm or more Is calculated. Table 7 shows the experimental results.

[0043]

[Table 7]

From Table 7, it can be seen that the composition ratio of 10 mm or more after the drop strength test was increased.
It was confirmed that Sample No. was superior in drop strength of the product sintered ore to Sample A of Comparative Example. This is considered to be the effect of increasing the strength of the product sintered ore by accelerating the liquid phase sintering by the low melting point alumite compound formed by the presence of sodium metasilicate.

In the above examples (Examples 1 and 2), the waste liquid containing a sodium compound was a steel plate degreasing waste liquid or an aqueous solution of a sodium silicate reagent.
Of course, the present invention is not limited to these, and waste liquid generated in the bleaching step of mechanical pulp or deinked pulp is considered to have the same effect. That is, although pulp fibers are mixed in the bleaching waste liquid of these pulp, it is confirmed from the above examples that the sodium compound significantly increases the preheated pellet crushing strength, so that the strength decrease due to the burning and disappearance of the pulp fibers is not at all. It is determined that this is not a problem.

[0046]

As described above, according to the first and third aspects of the present invention, in the granulation step of the iron ore pellet production process, all or a part of the compounding water is converted to a sodium compound and / or Alternatively, by replacing effluent containing pulp fiber and using it, the waste liquor can be inexpensively processed between the drying process and the baking process without the need for pretreatment such as neutralization, sedimentation, and sludge incineration. It is possible to do. Furthermore, it is possible to increase the yield of product fired pellets, increase the production amount of the fired pellet manufacturing process, and reduce the fuel consumption rate of the fired pellet manufacturing process.

According to the second and third aspects of the present invention, in the iron ore sinter production process, the whole or a part of the compounding water is replaced with a waste liquid containing a sodium compound and / or pulp fiber, and is used. In the sintering process, this waste liquid can be processed at low cost without requiring any pre-treatment such as neutralization treatment, precipitation treatment and sludge incineration treatment. Further, it is possible to increase the yield of the product sinter, increase the production amount of the sinter production process, and reduce the fuel consumption rate of the sinter production process.

According to a fourth aspect of the present invention, the sodium concentration of the granulated water or mixed raw material water after replacing all or a part of the mixed water with the waste liquid is 0.05 to 2% by mass. In addition to the effects of the invention of claims 1 to 3,
This makes it possible to prevent the reduction pulverizability of the product fired pellets and the product sintered ore from deteriorating, and to avoid problems due to alkali circulation and the like in the blast furnace.

Claims (4)

[Claims] Claims 1. A fine iron ore is granulated by adding a compounding water thereto.
Subsequently, after performing each treatment of drying, water separation, and preheating, when further sintering to produce sintered pellets, all or a part of the blended water is replaced with a waste liquid containing a sodium compound and / or pulp fiber. A method for treating waste liquid, characterized in that it is used as a waste liquid. 2. Mixing water is added to iron ore powder, auxiliary raw material, and solid fuel powder and kneaded, and then the mixed raw material subjected to pseudo-granulation is sintered to produce a sintered ore. A waste liquid containing a sodium compound and / or a pulp fiber, wherein the waste liquid contains a sodium compound and / or a pulp fiber. 3. The method for treating waste liquid according to claim 1, wherein the waste liquid is waste liquid generated in a pulp bleaching step. 4. The method according to claim 1, wherein the sodium concentration of the granulated water or mixed raw material water after replacing all or a part of the mixed water with the waste liquid is 0.05 to 2% by mass. The wastewater treatment method described in the above.