JP2016199789A - Acid treatment method for steel slag - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel slag treatment method for efficiently separating a gypsum component from steel slag and producing calcium ferrite from the obtained gypsum component for use as a dephosphorization agent or an iron manufacturing raw material.SOLUTION: An acid treatment method for steel slag includes: a slurrying step of charging steel slag into water to prepare alkaline slurry; a pH adjustment step with sulfuric acid of adding sulfuric acid while stirring the slurry and monitoring a pH value and controlling the added amount so as to maintain a pH value between 3.0 and 3.5; a solid-liquid separation step of solid-liquid separating the obtained slurry after the pH adjustment; and a calcium ferrite production step of, after drying recovered solid, granulating the solid with dust mainly comprising iron oxide and carbon-containing powder and firing the granulated material to obtain calcium ferrite.SELECTED DRAWING: None

Description

  The present invention relates to an acid treatment method for steel slag.

Steel slag generated from refining processes such as ironworks blast furnaces, converters, hot metal pretreatment furnaces, etc. is iron oxide, Ca ₂ SiO ₄ , CaSiO ₃ , CaO, MgO, Al ₂ O ₃ , SiO ₂ , P ₂ O. _{5 and the} like, and when applied to land areas such as roadbed materials and building foundation materials without aging treatment or carbonation treatment of expandable CaO or MgO, CaO, Ca ₂ SiO ₄ , CaSiO ₃ and MgO Reacts with rainwater and the pH of the effluent rises to over 8.5 and exceeds the environmental standard, and the volume expands by about 5 to 20% along with the hydroxylation reaction. It tends to become cloudy water.

These phenomena are caused by the following reactions (1) to (3) and dissolution equilibrium.
1) pH increase and swelling:
CaO + H ₂ O → Ca (OH) ₂ (1)
Ca (OH) ₂ → Ca ²⁺ + 2OH ⁻ (equilibrium pH> 12) (2)
2) Other pH increases:
Dissolution equilibrium pH of Ca ₂ SiO ₄ = 11.5
Dissolution equilibrium of CaSiO ₃ pH = 10.4
3) Cloudiness due to carbonation:
CaO + CO ₂ → CaCO ₃ ↓ (3)
(CaCO ₃ dissolution equilibrium pH = 10.5)

That is, when rainwater or the like is applied to steel slag, CaO alone reacts with water to produce Ca (OH) ₂ . This Ca (OH) ₂ is ionized to increase the OH ⁻ ion concentration in the water, which is the main cause of the increase to pH> 12.0. In addition, carbonation proceeds by carbon dioxide dissolved in the air or acid rainwater, and insoluble CaCO ₃ is generated, which is a major cause of cloudy water.

Therefore, at present, in order to suppress the expansion phenomenon associated with the hydroxylation reaction of steel slag, the steel slag is naturally cooled and crushed, and then piled outdoors or artificially brought into contact with high-temperature steam, The hydroxylation reaction shown in Formula (1) is caused to stabilize CaO and MgO. Further, as the carbonation treatment, the carbonation shown in the above formula (3) is performed in advance to further stabilize CaO and MgO.
However, this aging treatment or carbonation treatment requires a long time and a high cost, and there is a problem that a very large space is required in the steelworks. In addition, when the steam aging process is performed efficiently, equipment costs such as piping for allowing steam to spread evenly and efficiently and a heavy machine for returning to the top and bottom are generated.

As a processing technique for steel slag that is difficult to handle in this way, modified steelmaking that forms a calcium sulfate layer on the steelmaking slag particle surface layer by holding granular steelmaking slag having an average particle size of 25 to 1 mm in a sulfuric acid solution. A method for producing slag is known (see Patent Document 1).
The modified steelmaking slag of Patent Document 1 has a calcium sulfate layer formed on the surface of steelmaking slag particles, and exhibits excellent resistance to pH rise, cloudiness, and consolidation when immersed in seawater. It is described that it can be used by immersing it in seawater as a marine environmental restoration material such as sand cover material and backfill material.

Moreover, the processing method of the steel plate which precipitates iron, silicic acid, and a calcium content by melt | dissolving a steel plate with an acid and adjusts pH, and isolate | separates it is known (refer patent document 2).
In the processing method of Patent Document 2, it is described that the recovered CaSO ₄ and SiO ₂ can be used for cement raw materials, aggregates, and the like.

In Patent Document 3, by treating steelmaking slag powder obtained by classifying steelmaking slag to a particle size of less than 500 μm with a sulfuric acid solution in a dissolution tank, Ca content is separated into insoluble CaSO ₄ , and at least Al, Cr, Mn Further, it is described that the P and Fe components can be separated and dissolved, and the reaction solution of the steelmaking slag and sulfuric acid is subjected to solid-liquid separation and drying treatment to recover CaSO ₄ and can be used as a sintering auxiliary material.
In the treatment method of Patent Document 3, it is described that gypsumization is performed by directly introducing steelmaking slag having a limited particle size into a sulfuric acid solution having a low pH (strong acidity).
As described above, as a reuse method of steel slag, particularly as a reuse method after acid treatment, conventionally, use as a cement raw material, an aggregate, etc., or a sintering auxiliary raw material has been disclosed. As a new application of steel slag, the present inventors have focused on reusing it as calcium ferrite that can be used as a dephosphorizing agent in the steel process.
Here, calcium ferrite is a general term for 2CaO · Fe ₂ O ₃ , CaO · Fe ₂ O ₃ and CaO · 2Fe ₂ O ₃ , and is used as a dephosphorizing agent for molten iron. It is disclosed.
In Patent Document 5, after waste gypsum board is crushed, an iron oxide-containing raw material, a S i O 2 -containing raw material, and an Al 2 O 3 -containing raw material are blended, mixed, desulfurized, and 1 0 0 0 to 1 There is disclosed a method for producing calcium ferrite by firing at a temperature of 300 ° C.
However, a method for producing calcium ferrite that can be effectively used as a dephosphorizing agent using steel slag as one of raw materials has not been known so far.

JP 2011-207653 A JP 52-11190 A JP 2014-169199 A JP 2000-256731 A JP 2004-315277 A

  An object of the present invention is to provide a method for treating steel slag that efficiently separates a gypsum component from steel slag, produces calcium ferrite from the obtained gypsum component, and uses it as a dephosphorizing agent or a raw material for iron making.

  The present invention has been made to solve the above-mentioned problems based on this finding, and the gist thereof is as follows.

(1) Slurry process to make alkaline slurry by adding steel slag into water, and stirring the slurry, adding sulfuric acid and adjusting the input amount while monitoring the pH value The pH adjustment step with sulfuric acid for maintaining the pH value at 3.0 to 3.5, the solid-liquid separation step for solid-liquid separation of the obtained slurry after pH adjustment, and the recovered solid after drying, And a calcium ferrite generation step of obtaining calcium ferrite by calcining with a dust mainly composed of iron oxide and carbon-containing powder to obtain calcium ferrite.
(2) The acid treatment method for steel slag according to (1), wherein the concentration of the solid content of the slurry before solid-liquid separation in the solid-liquid separation step is in the range of 10 to 50% by mass.
(3) The method for acid treatment of steel slag according to (1) or (2), wherein the solid after drying collected in the solid-liquid separation step contains 70% by mass or more of gypsum.
(4) It includes a metal hydroxide filtration step of stepwise raising the pH of the liquid separated in the solid-liquid separation step and filtering out the metal hydroxide precipitated in the pH range of each step. The method for acid treatment of steel slag according to any one of (1) to (3), wherein:
(5) In the calcium ferrite production step, the carbon-containing powder is coke powder, and the dried solid, the iron oxide-based dust, and the coke powder are 60 to 85% by mass and 30 to 10%, respectively. The acid treatment of steel slag according to any one of (1) to (4), wherein the mixture is granulated at a ratio of 20% by mass and 20 to 5% by mass, and then fired at 900 to 1250 ° C. Method.
(6) The acid treatment method for steel slag according to any one of (1) to (5), wherein the firing is performed in a rotary kiln.
(7) In the calcium ferrite generation step, the alumina-containing material is added so that the alumina content in the calcium ferrite is 3 to 15% by mass. The acid processing method of the steel slag as described in one.

  The method for treating steel slag according to the present invention can efficiently separate at least a gypsum component from steel slag and produce calcium sulfate ferrite useful as a dephosphorizing agent or a raw material for iron making used in the iron making process.

It is a figure which shows the relationship between various metal ions and pH.

Hereinafter, embodiments of the present invention will be described in detail.
In the steel slag treatment method of the present embodiment, the step of turning the steel slag into water to make an alkaline slurry having a pH value of 10 or more, stirring the slurry, and gradually monitoring the pH value, A step of adding 10% or more sulfuric acid, a step of stabilizing the pH value of 3.0 to 3.5 as a result of adding sulfuric acid, a step of solid-liquid separation of the obtained slurry, and a recovered solid After drying, the step of granulating and firing with Fe-O-based dust and C powder to obtain calcium ferrite, and filtering the metal hydroxide precipitated in each pH range while gradually raising the pH of the filtrate. And a separate step.

<Slurry process>
First, when steel slag is thrown into water, the volume ratio of water is preferably larger than the volume ratio of slag. Moreover, since it is preferable that the pH value is stabilized by stirring, it is preferable to classify the particle size to less than 10 mm, more preferably 5 mm or less, and still more preferably 2 mm or less.
At this time, when the particle size of the steel slag is 10 mm or more, even if the sulfuric acid reforming process described later is performed, only the surface layer portion of the steel slag powder is plastered, and the inside of the steel slag is not sufficiently plastered. Inefficient. More preferably the particle size is 0.125 mm or less, and more preferably 0.074 mm or less, in which not only the surface layer portion of the steel slag but also the inside can be sufficiently plastered.

The method for classifying steel slag is not particularly limited as long as it can be classified, such as sieving with a vibration type screen having a predetermined mesh.
The jumping screen is an industrial classification method. Steel slag is placed on a screen mat with a predetermined mesh size, and the screen mat is moved up and down, so that the steel slag on the screen mat is raised up, inverted, and crushed. And sieving to a predetermined particle size. As this classification method, for example, it is preferable to use a jumping screen device manufactured by Eurus Techno.

<PH adjustment process>
Next, 10% or more of sulfuric acid is gradually added while monitoring the slurry obtained by classification in a stainless steel reaction vessel so that the pH value does not fall below 3.
Steel slag powder contains complex oxides such as CaSiO ₃ , Ca ₂ SiO ₄ , Ca ₃ SiO ₅ , Ca ₂ Al ₂ O ₅ containing free CaO and Ca, MgO, etc. Only Ca in the steel slag is made into gypsum, becomes insoluble, and is recovered as CaSO ₄ by drying after solid-liquid separation. Further, by this sulfuric acid reforming treatment, at least Si, Mg, Al, Mn, P and Fe, Cr, Cd, etc. in the steel slag are dissolved and ionized and separated in the sulfuric acid solution.
In this sulfuric acid reforming treatment, it is preferable to adjust the amount of steel slag powder input so that the solid content of the slurry is 10 to 50% by mass. If the solid-liquid concentration is within the above range, the added steel slag powder is gypsumized and dissolved other than Ca smoothly, and the solid after drying containing 70% by mass or more of gypsum is recovered in the solid-liquid separation step. can do. On the other hand, when the solid-liquid concentration is less than 10% by mass, the efficiency of the gypsumization or dissolution reaction tank becomes large and the efficiency is low, and when the amount of steel slag input is larger than 50% by mass, the viscosity in the reaction tank increases and stirring or Since recovery becomes inefficient, it is not preferable.

The sulfuric acid concentration gradually added in the sulfuric acid reforming treatment is preferably 10 to 50% by mass. On the other hand, if the sulfuric acid concentration is less than 10%, there is a possibility that the steel slag thrown into water is not sufficiently plastered. On the other hand, if the sulfuric acid concentration exceeds 50%, the amount of dissolution in a sulfuric acid solution other than Ca increases rapidly, which may reduce the purity of gypsum.
The sulfuric acid used in the sulfuric acid solution may be sulfuric acid produced from the S component discharged from the coke oven, sulfuric acid recovered by a desulfurizer, waste sulfuric acid discharged by pickling treatment of steel plates, steel pipes, steel bars, etc. I do not care. Conventionally, sulfuric acid produced from the S component discharged excessively from the coke oven was produced by reacting with NH ₃ to produce ammonium sulfate or neutralizing with NaOH, and then dumped into the ocean. By increasing the opportunity to use charcoal, sulfuric acid derived from the coke oven becomes redundant, and it is possible to produce an effect of reducing the disposal cost.

The sulfuric acid reforming treatment of steel slag is preferably performed in a pH range of 3 to 3.5. In general, the large reaction tank is preferably made of metal in terms of cost and maintenance. By performing sulfuric acid reforming treatment at a pH within the above range, not only can the Ca component in the steel slag be gypsumized, but also valuable materials such as Fe and P ₂ O ₅ can be transferred into the solution, Valuables such as Fe and P ₂ O ₅ can be selectively separated.
In the sulfuric acid reforming treatment of steel slag, it is preferable to react so that solid matter having a large specific gravity does not settle in an upward flow when stirring in the reaction tank in order to cause a uniform reaction.
The time for the sulfuric acid reforming treatment of the steel slag is preferably 30 minutes or more and 3 hours or less. More preferably, it is 30 minutes or more and 90 minutes or less. If the treatment time is less than 30 minutes, the total amount of steel slag in the reaction tank may not be sufficiently plastered and dissolved other than Ca, and the treatment effect will vary greatly even if it exceeds 3 hours. Therefore, the processing cost may increase.

<Solid-liquid separation process>
Next, the treated solution is subjected to solid-liquid separation to recover CaSO ₄ .
For solid-liquid separation, there is no need to use special acid-resistant materials because the pH is 3 or more, and filtration, centrifugation, pressure dehydration (roller press, filter press, screw press), multiple disk rotation dehydration, multiple dehydration Examples include a normal specification method using a plate wave filter and the like, and a method using a flocculant utilizing a chemical action (a polymer having a hydrated functional group, a polymer having a network structure with a molecular weight of tens of millions).

The drying process after the solid-liquid separation is not particularly limited, and may be natural drying by leaving it in a room temperature environment, for example. In a room temperature environment, for example, if it is left for about 12 hours, it will be sufficiently dried. Either a half hydrate (CaSO ₄ .1 / 2H ₂ O) or a dihydrate (CaSO ₄ .2H ₂ O) may be used.

  The sulfuric acid solution from which the solid content has been removed by solid-liquid separation contains at least Al, Si, Mn, Mg, P and Fe, and a trace amount of Cr and Cd. In the case where valuables are not recovered from the sulfuric acid solution after the solid-liquid separation, after the neutralization treatment, it is confirmed that P, Cr, Cd, etc. are within the standard, and then dumped into the ocean.

<Calcium ferrite production process>
In this step, the collected solid is dried, granulated with iron oxide-based dust and carbon powder, and then fired to obtain calcium ferrite.
The gypsum dried after solid-liquid separation (hereinafter referred to as “sulfuric acid-modified slag”) does not need to be washed. In the next step, it is effective to crush to a particle size distribution that is easy to mix in order to fit within the particle size distribution of lower purity iron oxide (dust etc.) or carbon powder.
Sulfuric acid-modified slag can be produced with calcium ferrite (CF) useful as a dephosphorizing agent in the iron making process by firing with iron oxide and carbon powder.
Calcium ferrite (CF) useful as a dephosphorizing agent includes sulfuric acid-modified slag, iron oxide (such as dust) having a FeO content of 50% by mass or more, and carbon powder (for example, coke dry quench (CDQ) powder). 60 to 85% by mass, 30 to 10% by mass, and 20 to 5% by mass, respectively, and calcined (heat treated) at 900 to 1,250 ° C. after granulation. It can be recycled in steelworks where steel slag is generated. For the firing, various firing furnaces can be used, but a rotary kiln is preferable because it can be continuously processed, and an external heating rotary kiln is more preferable because contamination of impurities and the like can be suppressed. Here, when the temperature is lower than 900 ° C., the CF reaction does not proceed, and when the temperature is higher than 1,250 ° C., the reaction with the melting or the inner wall of the firing furnace occurs.
By adding coke powder, gypsum (CaSO ₄ · 1 / 2H ₂ O) reacts with C, and gypsum is decomposed into CaO + CaS + SO ₂ + CO ₂ in the temperature range of 900 to 1,050 ° C., and the S content is 14%. To fall. Furthermore, calcium ferrite is produced by the reaction represented by the following formula in the temperature range of 1,050 to 1,250 ° C .;
2CaO + Fe ₂ O ₃ → 2CaO · Fe ₂ O ₃
2CaS + O ₂ + Fe ₂ O ₃ → 2CaO · Fe ₂ O ₃ + SO ₂
At this time, the S content simultaneously decreases to 1 to 2% by mass.
On the other hand, if the sulfuric acid-modified slag is less than 60% by mass, the Ca source is insufficient, Fe and C are excessive, and if it exceeds 85% by mass, the Ca source is excessive and Fe and C are insufficient. Absent. If the Fe content in the dust is less than 50%, the reaction efficiency and purity of the calcium ferritization decrease, which is not preferable.
Further, if the dust having Fe content of 50% or more exceeds 30% by mass, the Fe content is excessive, Ca and C are insufficient, and if it is less than 10% by mass, the Fe content is insufficient, and Ca and C are excessive. Therefore, it is not preferable. Further, if the coke powder exceeds 20% by mass, the C content is excessive and Ca and Fe are insufficient, and if it is less than 5% by mass, the C content is insufficient and Ca and Fe are excessive.
In the calcium ferrite production step, by adding an alumina-containing material, the alumina content in the calcium ferrite is 3 to 15% by mass, more preferably 2 to 11% by mass, thereby improving the performance as a dephosphorizing agent. It can also be made.
Even if the above firing conditions are not met, sulfuric acid-modified slag can be mixed with iron oxide (dust etc.) and carbon powder, fired into calcium ferrite, and used for sintering raw materials and other iron making processes it can.

<Metal hydroxide filtration process>
FIG. 1 shows the relationship between various metal ions and pH. It is a figure quoted from JOGMEC publicly available material. Various metal ions can be precipitated as hydroxides by adjusting the pH.
In the present application, the filtrate obtained by solid-liquid separation after the sulfuric acid reforming reaction of steel slag is used to hydroxylate useful components and components that should be avoided in the steel manufacturing process and environmental measures in their respective pH ranges. Separated and separated as a product.

  EXAMPLES Next, although an Example demonstrates this invention in more detail, this invention is not restrict | limited at all by these examples.

<Example 1>
First, each steel slag having a particle size range of 30 to 0 mm, 10 to 0 mm, 5 to 0 mm, and 2 to 0 mm (a blast furnace slow cooling slag, a converter slag) is prepared, and further 2 to 0 mm of the steel slag is further pulverized. Classification was also performed and particle size ranges of less than 500 μm, less than 250 μm, less than 125 μm, and less than 74 μm were prepared. Table 1 below shows the composition of steelmaking slag powder.

Also, 10% by mass and 15% by mass sulfuric acid solution of pickling waste liquid, 20% by mass, 30% by mass, 40% by mass and 50% by mass of coke-forming sulfuric acid (discharged from the coke oven). Sulfuric acid produced from S component) was prepared.
Purified water (used for filtration, descaling, etc.) in the steelworks yard 4 to 8 kg in a reaction tank (stainless steel (SUS316L), φ300 x h300 mm, internal volume = approx. 30 liters) and blast furnaces of each particle size shown in Table 2 1 to 4 kg of water granulated and converter slag were added and stirred, and after confirming that each slurry had become an alkaline slurry having a pH of 10 or more, each sulfuric acid was added dropwise.
When using a reaction tank made of SUS316L, each sulfuric acid was dropped and added so as not to fall below the depassivation pH of SUS316L. After the start of sulfuric acid dropping, the time until the pH value was stabilized at 3 to 3.5, The slurry concentration at that time is also shown in Table 2. Table 2 also shows the weight of sulfuric acid-modified slag dried after solid-liquid separation using a combination of centrifugal separation and suction filtration, and the proportion of gypsum components obtained by analyzing the solids by fluorescent X-rays.

  Table 3 shows the amount of metal hydroxide recovered in each pH range by adjusting the pH of the filtrate side in Table 2.

  Dust (FeO ratio, 50 to 65% by mass) and carbon powder (purity 80 to 95% by mass) are added to the solid-liquid separation and the dried product in Table 2 at the weight ratios shown in Table 4, respectively, and briquette molding and bread mold Table 4 shows the ratio of formation of calcium ferrite (CF), which is the target product after firing (heat treatment) at the heat treatment temperature and time shown in Table 4 using an external heating rotary kiln after rolling granulation with a pelletizer. Show.

According to Example 1 of the present invention, the pH is less than 3 during the sulfuric acid reforming reaction without greatly depending on each slag type of blast furnace granulation or converter and particle size of 30 to 0.074 mm. Therefore, the reaction tank (for example, made of SUS316L and without rubber lining) was not corroded, and a sulfuric acid-modified slag having a high degree of gypsum was stably obtained.
Appropriate amounts of dust and carbon (coke powder) generated in the steelworks are added to the modified slag, granulated, and heat-treated with a rotary kiln to obtain high-purity calcium ferrite of 75 mass% or more in the solid after heat treatment. It was. And as described in Table 4, it was confirmed that the dephosphorization performance in the hot metal was improved by 5 to 20% by mixing ₃ to 15% by mass and an appropriate amount of Al ₂ O ₃ . On the other hand, it is possible to separate useful (Fe) and repellent (Al to Cd) metal components such as Fe, Al, Cr, Pb, Cd, Mn, etc. in steel slag from the filtrate produced when sulfuric acid is reformed. (Table 3).

<Example 2>
Tables 5 to 7 show Example 2 of the present invention.

In Example 2, the requirement of claim 1 of the present invention was satisfied, but the solid content of the slurry before solid-liquid separation in the solid-liquid separation step was slightly high, and the gypsum ratio after drying was low. Since the calcium ferrite ratio after firing was low and the amount of Al ₂ O ₃ mixed was small, the function as a dephosphorizing agent could not be expressed. Further, from the filtrate produced when the sulfuric acid is reformed, the recovered amounts of useful (Fe) and repellent (Al to Cd) metal components such as Fe, Al, Cr, Pb, Cd, and Mn in steel slag are also shown in the examples. The result was reduced to about 1/2 to 1/10 of.
However, even the calcium ferrite prepared in this manner can effectively recycle the Fe and Ca components contained in the steel slag by using it as a sintering raw material for the iron making process.

  The gypsum component is separated from the steel slag, calcium ferrite is produced from the obtained gypsum component, and can be used for the treatment of steel slag used as a dephosphorizing agent or a raw material for iron making.

Claims (7)

  By adding steel slag into water, a slurrying step to make an alkaline slurry, stirring the slurry, monitoring the pH value, adding sulfuric acid, and adjusting the input amount, pH PH adjustment step with sulfuric acid maintaining the value at 3.0 to 3.5, solid-liquid separation step for solid-liquid separation of the obtained slurry after pH adjustment, and drying the recovered solid, the solid is then converted to iron oxide A method for producing an acid treatment of steel slag, comprising: a calcium ferrite production step for obtaining calcium ferrite by firing after granulation with main dust and carbon-containing powder.   The acid treatment method for steel slag according to claim 1, wherein the concentration of the solid content of the slurry before solid-liquid separation in the solid-liquid separation step is in the range of 10 to 50 mass%.   The method for acid treatment of steel slag according to claim 1 or 2, wherein the solid after drying collected in the solid-liquid separation step contains 70 mass% or more of gypsum.   The method includes a metal hydroxide filtration step of stepwise raising the pH of the liquid separated in the solid-liquid separation step and filtering out the metal hydroxide precipitated in the pH range of each step. The steel slag acid treatment method according to any one of claims 1 to 3.   In the calcium ferrite production step, the carbon-containing powder is coke powder, and the solid after drying, the dust mainly composed of iron oxide, and the coke powder are 60 to 85 mass%, 30 to 10 mass%, The acid treatment method for steel slag according to any one of claims 1 to 4, wherein the mixture is granulated at a rate of 20 to 5 mass% and granulated, and then fired at 900 to 1250 ° C.   The said baking is performed by a rotary kiln, The acid treatment method of the steel slag as described in any one of Claim 1 thru | or 5 characterized by the above-mentioned.   The steel according to any one of claims 1 to 6, wherein, in the calcium ferrite generation step, the alumina-containing material is added so that the alumina content in the calcium ferrite is 3 to 15% by mass. Acid treatment method for slag.

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