JP4818092B2 - Method for suppressing elution of fluorine in steelmaking slag - Google Patents

Description

  The present invention relates to a technique for producing low-elution steelmaking slag in accordance with soil environmental standards by suppressing fluorine elution from steel-making slag containing fluorine into water.

  Steelmaking slag generated from steelmaking converters, steelmaking electric furnaces, etc. contains silicon oxide, calcium oxide, iron oxide, magnesium oxide, etc., and in the furnace, it is in a molten state or a state where the melt and solid are mixed. Yes. This steelmaking slag becomes a mixture of powder and lump after cooling. Due to its physical and chemical properties, it is used as a fertilizer, ground improvement material, cement material, civil engineering material, etc.

  Steelmaking slag is discharged from the steelmaking converter (converter slag), discharged from the steelmaking electric furnace (electric furnace slag), existing on the molten steel in the molten steel pan (no refining reaction is performed in the molten steel pan) In some cases, there are cases in which refining is performed in a molten steel smelting furnace (ladle furnace, powder injection, vacuum degassing furnace, etc .: molten steel slag), and what remains in the tundish of a continuous casting machine (tundish Slag) and those generated during hot metal refining (hot metal slag).

  Each has a different chemical component range, but generally contains silicon oxide, aluminum oxide, calcium oxide, magnesium oxide, phosphorus oxide, iron oxide, manganese oxide, and as trace elements, titanium oxide, chromium oxide, Contains nickel oxide, sulfur, etc.

  In steelmaking processes that perform special treatment when producing high-purity steels and special alloy steels, additives that promote dephosphorization and desulfurization reactions, dissolution accelerators that lower the slag melting point, and oxides that are difficult to dissolve Fluorite (calcium fluoride) may be added as a solvent for dissolving slag in slag.

  In particular, fluorite is added when manufacturing a steel having a low content of sulfur or phosphorus, or when refining in a molten steel pan. At this time, fluorine is substituted into anions such as oxygen and incorporated into the mineral composition constituting the steelmaking slag. Thus, depending on the manufacturing method in the steelmaking process, the steelmaking slag is in a state containing fluorine.

  Thus, when fluorite is used in the steelmaking process, fluorine is contained in the steelmaking slag, and this fluorine may be easily eluted from the steelmaking slag. Incidentally, in normal steelmaking slag, the elution of fluorine is 0.8 mg / liter or less, but the concentration of eluted fluorine from fluorine-containing steelmaking slag may be about 1 to 6 mg / liter.

  In 2001, the regulation of fluorine elution amount was added to the soil environmental standards, so when using steelmaking slag in the soil environment, the amount of fluorine elution from steelmaking slag must be 0.8 mg / liter or less. There is. Therefore, for this purpose, techniques for suppressing the elution of fluorine from steelmaking slag have been proposed.

For example, Patent Document 1 proposes a fluorine elution suppression method in which water-soluble calcium compounds (CaO, Ca (OH) ₂ , CaSO ₄ ) are mixed with steel slag. This method is a method for suppressing the dissolution of CaF as much as possible by increasing the calcium ion concentration in water.

  Patent Document 2 discloses a method for suppressing fluorine elution as a form of fluorapatite by adding a phosphorus compound to steelmaking slag when producing stainless steel or high nickel steel, and performing hot water treatment after the addition. Has been proposed.

  On the other hand, although it is not a method for suppressing elution of fluorine in steelmaking slag, Patent Document 3 describes a method in which a phosphoric acid compound and a calcium compound are added to a fluorine-containing solid waste and kneaded.

JP-A-2005-239509 JP 2003-226906 A JP 2002-331272 A

  As described above, even in the prior art, it has been possible to suppress the elution of fluorine from the steelmaking slag. However, these conventional techniques have technical and economic problems as described below.

  First, the method described in Patent Document 1 is a method for suppressing the elution of fluorine by adding a calcium compound. In this method, when the calcium ion concentration in water is increased, after treatment, And fluorine combine to form calcium fluoride and immobilize fluorine.

  However, in this method, since calcium fluoride is formed, the fluorine concentration in the water decreases for a short time after the treatment, but when the eluted fluorine concentration of the original steelmaking slag is high, 1 to 3 mg over time. There was a problem of returning to 1 / liter. Therefore, with this method, it is difficult to suppress the elution of fluorine stably for a long period of time.

  Moreover, although the method described in Patent Document 2 is to fix fluorine with fluoroapatite, heat treatment is required to ensure the reaction. Therefore, the energy efficiency is low and the processing cost is high. Moreover, the said method is a method of suppressing a fluorine elution from the production | generation slag at the time of manufacturing stainless steel, Fe-Ni alloy steel, and Ni base alloy with an electric furnace.

The specific technical contents quantitatively show the relationship between the chemical composition of slag and the amount of phosphoric acid added. As described in Table 1 of paragraphs [0028] and [0029] of Patent Document 2, this type of slag has a basicity ((CaO mass%) / (SiO ₂ mass%)) of mainly 2 to 2. 3. A slag with a relatively low basicity of 3.5 at maximum. It also contains chromium oxide and nickel oxide attributed to special steel components to some extent.

  The steelmaking slag of stainless steel contains, for example, iron oxide, as described in FIGS. 13 and 79 of p696 and FIGS. 13 and 85 of p699 of the Iron and Steel Handbook 3rd edition II made by Japan Iron and Steel Association. The rate is 3% by mass or less, and the chromium oxide content is 3.5% by mass or more. Compared with ordinary steelmaking slag, the iron oxide ratio is significantly lower and the chromium oxide ratio is higher.

  Iron oxide and chromium oxide interact with phosphate ions. In particular, chromium oxide forms chromate ions that compete with the reaction of phosphate ions, and therefore the apatite compound production conditions differ when the concentration in the steelmaking slag is different. As for iron oxide, the reaction between iron ions and phosphate ions in water affects the production of apatite compounds.

  As described above, the processing technique of Patent Document 2 has a different chemical composition from that of general steelmaking slag, and also has different conditions for suppressing fluorine elution, so that general steelmaking that occurs when producing ordinary steel is performed. The technology was not applicable to slag.

  Moreover, the method described in Patent Document 3 reacts phosphoric acid and calcium ions with waste containing fluorine to form an apatite-based inorganic substance, and incorporates fluorine into this to suppress fluorine elution. This is a common waste disposal technique. The addition amount of phosphoric acid was also regulated only under the condition of 0.5 to 20% by mass (vs. waste), and a technique for economical addition amount was not established.

  Furthermore, it is not considered to apply this technique to highly basic substances such as steelmaking slag, and a method for appropriately and economically suppressing elution of fluorine in steelmaking slag has not been established. That is, steelmaking slag contains calcium oxide, magnesium oxide, aluminum oxide, silicon oxide, and the like, and is a substance that elutes calcium ions, magnesium ions, aluminate ions, and the like into water, and has an elution pH of 10 or more. As a result, there is a difference in aqueous chemical reactivity from the fluorine elution of general substances.

  Therefore, in order to suppress the fluorine elution of steelmaking slag, different processing conditions from the fluorine elution suppression method of ordinary substances are necessary, but a method considering this has not been established. As a result, there are problems such as incomplete processing and inability to effectively suppress elution of fluorine, and a large amount of processing agent, which increases processing costs.

  As described above, in any of the conventional techniques, there has been no method for effectively and economically suppressing fluorine elution of steel-making slag containing fluorine. Accordingly, there is a need for a new technique for overcoming the drawbacks of these conventional techniques and reliably suppressing fluorine elution with an inexpensive process.

  The present invention has been made to solve the problems of these conventional techniques, and the gist thereof is as shown in the following (1) to (12).

(1) After cooling and solidifying the steelmaking slag containing fluorine to room temperature, phosphoric acid or phosphate is added to the steelmaking slag. In this case, as the steelmaking slag, one having an elution pH of 11 or more when immersed in water is used. For this treatment, an aqueous solution containing phosphate ions is used, and water-soluble calcium ions eluted from the steelmaking slag are also present in the aqueous solution. In addition, water-soluble calcium sources other than steelmaking slag are not added to this aqueous solution. In this aqueous solution, from the reaction of phosphate ions, calcium ions and fluorine, to form apatitic compound containing fluorine, eluting suppress this by fixing the fluorine.

( 2 ) In the method (1 ), the amount of water-soluble calcium ions present in water is 0.95 times or more in terms of (calcium oxide equivalent mass / phosphoric acid mass).

(3) In the method of (1) or (2), the mass ratio of free Ca 2 O contained in the steelmaking slag to the amount of steelmaking slag is 2% by mass (CaO conversion) or more, and the steelmaking slag contains phosphoric acid or phosphate. aqueous solution was added to the eluted suppress fluorine.

(4) In the method of (1) or (2), an aqueous solution of phosphoric acid or phosphate is added to the steelmaking slag having a mass ratio of 2% by mass or more (CaO equivalent) to the amount of free CaO contained in the steelmaking slag. It was added to elute suppressed fluorine.

( 5 ) In the method of (1) or (2), steelmaking slag having high basicity is used. Among steelmaking slags, when using converter slag or electric furnace slag, [(CaO mass%) + (MgO mass%)] / (SiO ₂ mass%) is used as a basic index, and this value is 3 .7 above steelmaking slag, with addition of an aqueous solution of phosphoric acid or phosphate to elute suppressed fluorine.

( 6 ) In the method of (1) or (2), steelmaking slag having high basicity is used. When using the steelmaking slag discharged from the molten steel pan or the steelmaking slag discharged from the tundish of the continuous casting apparatus, [(CaO mass%) + (Al ₂ O ₃ mass%)] / the (SiO ₂ mass%) as an indicator of the basic, this value using the steel slag is 4 or more, the formulation steel slag, by adding an aqueous solution of phosphoric acid or phosphate to elute suppressed fluorine.

( 7 ) In any one of the methods (1) to ( 6 ), the fluorine concentration eluted in the water in which the steelmaking slag is immersed is measured in advance. A phosphorous oxide-containing compound containing phosphoric acid more than 20 times the amount of phosphoric acid required to make the total fluorine amount calculated from the fluorine concentration and the water amount into fluoroapatite is added, and the fluorine concentration of water is adjusted to 0.8 mg / liter. Below.

( 8 ) In any one of the methods ( 1) to (6) , first, the equilibrium concentration value and pH of the fluorine that is eluted from the steelmaking slag are measured. When the measured pH is 11 or more, the following formula (1) is used as the relationship between the equilibrium concentration value of fluorine and the minimum amount of phosphoric acid to be added to the steelmaking slag.
(Addition ratio of steel slag phosphoric acid (mass%)) = 0.037 (fluorine equilibrium concentration value (mg / l)) ² +0.079 (fluorine equilibrium concentration value (mg / l)) − 0.0866 (1 )
By substituting the equilibrium concentration value into the equation (1), the minimum amount of phosphoric acid to be added is determined. An aqueous solution containing a phosphoric acid amount of 1 or more times the minimum phosphoric acid amount is sprayed on the steelmaking slag, and phosphoric acid, calcium ions and fluorine are reacted in the aqueous solution and on the steelmaking slag surface to suppress fluorine elution, and the ultimate fluorine concentration is 0 Less than 8 mg / liter.

( 9 ) In the method of ( 8 ), after adding an aqueous solution containing phosphoric acid or phosphate, the adhesion moisture of the steelmaking slag is maintained at 3% by mass or more for 2 days or more.

  According to the present invention, fluorine elution of steelmaking slag having a fluorine elution concentration of 0.8 mg / liter or more can be suppressed. As a result, this type of steelmaking slag, which has been limited to be used for applications embedded in the soil, is used in civil engineering applications such as soil improvement materials for ground improvement, sand pile materials, roadbed materials, and embankment of heavy equipment intrusion paths. Can be used in general. Moreover, since it can process with few chemical | medical agents by implementing this invention, the elution of fluorine of steelmaking slag can be suppressed cheaply and stably.

  Steelmaking slag used in the present invention is generated when producing ordinary steel. Steelmaking slag includes converter slag, electric furnace slag, molten steel pan slag, tundish slag, hot metal slag, and the like. In general, these slags contain silicon oxide, aluminum oxide, calcium oxide, magnesium oxide, phosphorus oxide, iron oxide, manganese oxide, and as trace elements, titanium oxide, chromium oxide, niobium oxide, sulfur, etc. Including.

  The converter slag is composed of 10 to 25% by mass of silicon oxide, 35 to 50% by mass of calcium oxide, 2 to 8% by mass of magnesium oxide, T.O. It contains about 10 to 25% by mass in terms of Fe. The electric furnace slag is composed of 10 to 25% by mass of silicon oxide, 25 to 40% by mass of calcium oxide, 1 to 8% by mass of magnesium oxide, T.I. It contains about 5 to 15% by mass in terms of Fe.

  Molten steel ladle slag and tundish slag are chemically similar, 8 to 25% by mass of silicon oxide, 30 to 45% by mass of calcium oxide, 1 to 4% by mass of magnesium oxide, and 10 to 10% of aluminum oxide. Contains about 45% by mass. The molten iron slag is composed of 10 to 25% by mass of silicon oxide, 25 to 40% by mass of calcium oxide, iron oxide, T.I. It contains about 2 to 5% by mass in terms of Fe.

  Here, ordinary steel is a total of 5 metals (nickel, chrome) having properties close to iron, such as stainless steel (containing a lot of nickel and chromium) and tool steel (containing a lot of molybdenum, chromium, etc.). Excluding steel containing more than 1%. The steelmaking slag components are also different. For example, the steelmaking slag of stainless steel has an iron oxide content of T.I. Fe conversion is 3% by mass or less, and the chromium oxide content is 3.5% by mass or more. Compared with steelmaking slag of ordinary steel, the iron oxide ratio is significantly lower and the chromium oxide ratio is higher.

  In the present invention, since chromium oxide forms chromate ions competing with the reaction of phosphate ions, it has been found that the conditions for producing apatite compounds differ greatly when the concentration in the steelmaking slag is different. As for iron oxide, it has been found that the reaction between iron ions and phosphate ions in water affects the formation of apatite compounds. Therefore, particularly when the chromium oxide concentration is high, the processing conditions of the present invention may not always match.

  In the steelmaking process, fluorite (calcium fluoride) is used as an additive for promoting dephosphorization and desulfurization reactions, a dissolution accelerator for lowering the melting point of slag, and a solvent for dissolving difficult-to-dissolve oxides in slag. May be. In particular, it is added when producing steel with a low content of sulfur or phosphorus or when refining in a molten steel pan. This fluorine is substituted into anions such as oxygen and incorporated into the mineral composition constituting the steelmaking slag. In some cases, it may elute to a concentration of 0.8 mg / liter or more of fluorine in the immersion water contained in the steelmaking slag.

  In the present invention, such a steelmaking slag having a fluorine elution of 0.8 mg / liter or more is used. In addition, the steelmaking slag component after a molten state or solidifying is chemically analyzed. First, steelmaking slag is made into normal temperature (about 80 degrees C or less), and this is crushed and classified to the size of 30 mm or less. By this operation, 50% or more of the steelmaking slag is 5 mm or less.

  A part of this steelmaking slag is sampled and immersed in water by a method based on JIS standard K0058, and the fluorine elution concentration is measured. However, if quick analysis is required, pulverized steelmaking slag is immersed in 5 to 10 times the mass of water, and the fluorine concentration of this water is measured using an ion meter, simple colorimetric analysis kit, colorimeter, etc. Use to measure.

  Also, the pH of this water may be measured. There are several methods for measuring the elution pH in water. For convenience, there is a method in which steelmaking slag is immersed in water having a mass of about 2 to 10 times as it is, and after a sufficient time has passed, it is measured with a pH meter or the like. However, for accuracy, it is better to measure the pH value of the test solution prepared by the method described in the attached table of Ministry of the Environment Notification No. 46 in 1991.

  In addition, when wanting to improve processing efficiency further, the free CaO ratio of this steelmaking slag is measured. The free CaO ratio is the ratio (calculated in terms of CaO) of calcium oxide or calcium hydroxide present in the form of calcium oxide that is not included in other mineral compositions among the calcium oxide contained in the steelmaking slag at room temperature.

  In order to suppress the elution of fluorine from the steelmaking slag, the steelmaking slag is treated with water containing phosphate ions and calcium ions. Here, the form of the phosphate ion to be added is preferably phosphoric acid or phosphate. Here, the phosphate is a compound of phosphoric acid and positive ions such as sodium phosphate, sodium hydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, and ammonium phosphate, and includes a polymer containing phosphoric acid.

In principle, the amount of phosphoric acid required to suppress the elution of fluorine from the steelmaking slag is an amount corresponding to the amount of fluorine contained in the steelmaking slag. The amount in this case is an amount determined according to the reaction formula (1) for forming fluoroapatite from calcium ions, phosphate ions and fluorine ions.
5Ca ²⁺ +3 PO ₄ ³⁻ + F ⁻ = Ca ₅ (PO ₄ ) ₃ F (1)

However, in the present invention, the condition for the stable presence of fluorine ions in the fluoroapatite produced by the reaction formula (1) is to coexist with a molecule having a hydroxyl group: Ca ₅ (PO ₄ ) ₃ OH.

  In general, a molecule having a fluorine group and a molecule having a hydroxyl group may be up to about 1: 1. The phosphoric acid addition ratio that satisfies this condition is about 30 times the fluorine content (mass%) of the steelmaking slag. This has the disadvantage that when the fluorine content is 0.5% by mass, the phosphoric acid addition rate is 15% by mass or more and the slaked lime addition rate is 15% by mass or more.

Therefore, the present inventors investigated the relationship between the amount of fluorine eluted from steelmaking slag and the amount of phosphoric acid to be added (the amount necessary for a reduction to fluorine 0.8 mg / lit or less). As a result, it was first found that the amount of fluorine eluted was about several to 30% of the amount of fluorine containing steelmaking slag. Moreover, when the ratio of Ca ₅ (PO ₄ ) ₃ F and Ca ₅ (PO ₄ ) ₃ OH in the precipitated crystals was investigated, it was found that this ratio was influenced by the pH of water.

Furthermore, it was found that Ca ₅ (PO ₄ ) ₃ F is more easily stabilized at high pH. As a result, the addition amount of phosphoric acid and a calcium ion source can be suppressed under high pH conditions. Furthermore, under high pH conditions, there is an effect of increasing the concentration of calcium ions in water.

  If the pH is 11 or more, and more desirably 12 or more, water-soluble calcium ions that can stably suppress fluorine elution are stably present. Therefore, a better treatment condition in the present invention is that the pH of the aqueous phosphoric acid solution during treatment is 11 or more, preferably 12 or more. The detailed reason will be described later.

  Under this condition, the mass of phosphoric acid to be added is 20 times the ratio of the stoichiometric amount (necessary phosphoric acid amount) for making the amount of the measured fluorine concentration eluted into water into fluorapatite. The above proved to be good. That is, in a state where the steelmaking slag is immersed in water, it is sufficient to add phosphoric acid 18 times the amount of phosphoric acid necessary for the eluted fluorine.

  On the other hand, under the condition of pH lower than this, the mass of phosphoric acid to be added needs to be 20 times or more with respect to the measured value of the fluorine concentration which is eluted and reached in water. Therefore, phosphoric acid corresponding to 20 times the necessary amount of phosphoric acid may be added to make the fluorine concentration in water under 0.8 mg / liter under all conditions.

  In addition, the amount of calcium ions that should be present in water should be excessive in the formation of fluoroapatite, and there should be more calcium ions than the chemical equivalent of the mass balance in reaction formula (1). It is necessary to do. That is, 5/3 times or more of the number of moles of phosphoric acid is necessary, and this is a mass of 0.95 times (calculated as calcium oxide) or more of phosphoric acid when calculated by molecular weight.

  Under such high pH conditions, a high calcium ion concentration in water is a favorable condition for the production of fluoroapatite. As shown in FIG. 2, when the pH is less than 11, the calcium ion concentration in water is low, whereas when the pH is 11 or more, the calcium ion concentration increases. In water with such a high calcium ion concentration, the reaction between phosphoric acid and calcium ions is rapid, and precipitation of the apatite compound is completed in a relatively short time (several hours to 2 days).

  Therefore, if pH is 11 or more, fluorine elution suppression is completed in a short time. When the pH is 12 or more, the calcium ion concentration is 150 mg / liter or more, and the reaction rate is further improved. From the relationship between this pH and calcium ions, if the pH is 11 or more, an additional calcium ion source is not necessarily required.

  On the other hand, if the pH is less than 11, additional calcium ions need to be added to the water. In this case, by adding a water-soluble calcium compound such as calcium oxide, calcium hydroxide or calcium acetate, the same reaction conditions as in the case of pH 11 or higher can be created.

  Next, the inventors conducted an experiment in which an aqueous solution containing phosphoric acid and calcium ions was sprayed on steelmaking slag to suppress fluorine elution, and the amount of phosphoric acid added necessary for suppressing fluorine elution was determined. In this experiment, the fluorine elution concentration before addition of phosphoric acid and calcium ions and the phosphoric acid addition ratio (mass ratio with respect to steelmaking slag) when the fluorine elution value becomes 0.8 mg / liter after addition of phosphoric acid and calcium ions were investigated.

The experimental conditions were such that the pH of the elution water was 11-13. This result has a relationship as shown in FIG. When this relationship is subjected to multiple regression and summarized by mathematical formulas,
(Steel slag phosphate addition ratio (mass%))
= 0.037 (F elution (mg / l)) ² +0.079 (F elution (mg / l))
−0.0866 Equation (1). Therefore, fluorine addition can be suppressed up to 0.8 mg / liter by adding phosphoric acid in an amount greater than the amount calculated by equation (1).

  Further, if the amount of phosphoric acid added is increased up to 4 times the amount obtained by the formula (1), the fluorine elution becomes 0.3 to 0.5 mg / liter. Further, if the amount of phosphoric acid added is 10 times that of the formula (1), the elution of fluorine can be reduced to 0.3 mg / liter or less. Therefore, it is preferable that the addition amount of phosphoric acid is at least one times the amount obtained by the equation (1).

  However, even if phosphoric acid and calcium ions are added in a large amount in excess of this range, the decrease in fluorine elution concentration is small, so that it is not desirable to add a large amount except in special cases.

  Next, a method for adding calcium ions will be described. In this aqueous solution, calcium ions are present. As described above, the amount of calcium ions dissolved in water is preferably 0.95 times the phosphoric acid mass (CaO equivalent) or more. Although there is no restriction | limiting in the upper limit of the quantity of calcium ion, Generally it is good within 2 times the amount of phosphoric acid. As the calcium ions, water-soluble calcium compounds such as calcium hydroxide, calcium oxide, and calcium acetate are used.

  In order to carry out the treatment at a high pH, which is a better condition of the present invention, it is preferable to use calcium hydroxide or calcium oxide. Furthermore, it is preferable to use these from the viewpoint of cost.

The present inventors have clarified that when calcium ions are dissolved using calcium hydroxide or calcium oxide, there is a relationship between pH and calcium ion elution concentration as shown in FIG. On the other hand, the elution fluorine concentration of the high alkali steelmaking slag targeted by the present invention is about 0.8 to 8 mg / liter. This is because 8 mg / liter is the (Ca ²⁺ + 2F ⁻ → CaF) equilibrium value of calcium fluoride, and this value is the upper limit of fluorine elution of highly alkaline steel slag containing free CaO.

If these two relationships are combined, for example, when the fluorine elution concentration is 1 mg / liter, the calcium ion requirement (minimum amount for forming Ca ₅ (PO ₄ ) ₃ F) is 10 mg / liter (calcium ion). In the case of a fluorine concentration of 8 mg / liter, the calcium ion requirement is about 100 mg / liter.

  Considering the formation ratio of molecules having a hydroxyl group, the calcium ion concentration needs to be higher. Therefore, as a result of experiments, when phosphoric acid was added and calcium ions were abundant, it was found that the added phosphate ions and calcium ions react quickly and immobilize fluorine quickly. .

  When phosphoric acid is added to water when calcium ions of about 100 mg / liter or more are present and undissolved calcium hydroxide is present in water, phosphoric acid reacts rapidly with calcium ions and reaction In order to compensate for the reduced calcium ions in water that are fixed in the solid, calcium hydroxide and the like are dissolved, and the production of apatite continues sequentially.

  As a result, the reaction rate is fast if the calcium ion in water before the reaction is about 100 mg / liter or more and calcium hydroxide or the like is present in the water. What is necessary is just above, and if it is 11.5 or more, a more reliable reaction can be expected.

  When the basicity of the steelmaking slag increases, the pH of the immersion water increases and the amount of calcium ion elution from the steelmaking slag increases. Therefore, the effect of stabilizing the fluorine elution suppression reaction and the effect of reducing the amount of added calcium oxide or calcium hydroxide can be obtained at the same time. Therefore, the fluorine elution suppression treatment conditions for highly basic steelmaking slag are different from those for other substances, and there are conditions for efficient implementation.

  Here, when the ratio of the basic substance and the acidic substance is adopted as an index indicating the alkalinity of the steelmaking slag, it is good for estimating the calcium ion addition amount. As a result of various experiments, the present inventors have found that the basic value as a factor for determining the elution pH from steelmaking slag is preferably the following value.

For converter slag and electric furnace slag, where the ratio of calcium oxide and magnesium oxide is relatively high and the ratio of aluminum oxide is low,
[(CaO mass%) + (MgO mass%)] / (SiO ₂ mass%) (basicity 1)
Also, in the ladle slag and tundish slag, which have a relatively high ratio of aluminum oxide,
[(CaO mass%) + (Al ₂ O ₃ mass%)] / (SiO ₂ mass%) (basicity 2)
Should be used.

  In the case of converter slag / electric furnace slag, if basicity 1 is 3.7 or more, the elution pH is surely 11 or more, and if basicity 1 is 3.9 or more, the elution pH is It will definitely be 12 or more. On the other hand, in molten steel pan slag and tundish slag, if the basicity 2 is 4 or more, the elution pH is surely 11 or more, and if the basicity 1 is 4.5 or more, the elution pH is sure. 12 or more.

  Therefore, stable high pH conditions can be achieved by setting the basicity 1 or basicity 2 of these steelmaking slags to a value higher than the above.

  Free CaO contained in steelmaking slag is in the form of calcium oxide or calcium hydroxide, and when it comes into contact with water, it becomes water-soluble calcium ions. Therefore, when using steelmaking slag with a lot of flow CaO, calcium oxide, calcium hydroxide, etc. There is an effect that the amount of addition of can be reduced. In our experiment, if there is a 2 mass% calcium ion source in terms of calcium oxide, the total amount of calcium ions required to suppress elution of fluorine can be supplied. Therefore, in this case, it is not necessary to add an additional calcium ion source.

  The addition amount of calcium oxide, calcium hydroxide, and the like is calculated so that the total amount with free CaO is 2% by mass (CaO conversion) or more, and the ratio is added. In addition, when free CaO is 2 mass% or more, it is not necessary to add an additional calcium ion source. If the basicity condition of steelmaking slag is converter slag / electric furnace slag, basicity 1 is 3.7 or more, and molten steel pan slag / tundish slag and basicity 2 is 4 or more, free Since CaO is 2% by mass or more, such a high basicity condition is desirable also in this respect.

  The phosphoric acid concentration of the aqueous solution is preferably 0.3 to 8% by mass. This is because the reaction rate on the steelmaking slag surface decreases when the content is 0.3% by mass or less. Further, when the content is 8% by mass or more, since the phosphoric acid concentration is high (accordingly, calcium ion calcium is high), the ratio of apatite formation unrelated to the reaction of incorporating fluorine increases.

  The amount of the aqueous solution containing phosphoric acid is 5 to 40% of the mass of the steelmaking slag. The steelmaking slag is brought into contact with the aqueous solution. Specifically, in a state where the steelmaking slag is in contact with the aqueous solution, the state in which the moisture content of the steelmaking slag is 3% by mass or more is maintained for 2 days or more, preferably 4 days or more, and is cured. That is, excessive drying of the steelmaking slag is suppressed. The curing temperature at this time may be room temperature.

  In addition, holding at 80 ° C. or higher by a method such as steam heating produces a better result, but it is not always necessary. This is a feature of the present invention, and the treatment described in Patent Document 2 and Patent Document 3 often requires heat treatment because the production rate of fluoroapatite is slow, but in the present invention, There is an advantage that it is not necessary, and there is an effect of improving heat utilization efficiency.

  The steelmaking slag with suppressed elution of contained fluorine is shipped as a product by the above procedure. At the time of shipment, there are two types of sale: treated steelmaking slag alone and mixed blast furnace slag and crushed concrete. These applications are general civil engineering applications such as earth and sand substitutes for ground improvement, materials for sand piles (sand compaction, etc.), roadbed materials, and embankments for heavy equipment intrusion paths.

Tables 1 and 2 show the results of fluorine elution suppression treatment in which various steelmaking slags were sprayed with water containing phosphoric acid and calcium ions. Steelmaking slag used was converter slag, electric furnace slag, hot metal slag, molten steel pan slag, and tundish slag. Of the basicities listed in Table 1, the calculation of the basicity to be adopted differs depending on the brand of the steelmaking slag, but the basicity surrounded by the thick frame represents the basicity of the steelmaking slag. Degree. In addition, the chromium oxide density | concentration of the steelmaking slag used for the present Example was all 3 mass% or less.

  As a method for suppressing fluorine elution in Example 1, an aqueous solution containing phosphoric acid was sprayed on steelmaking slag to suppress fluorine elution of the steelmaking slag. Table 1 shows data on chemical composition, basicity, and elution pH of steelmaking slag. Table 2 shows the results of fluorine elution suppression treatment using phosphoric acid and calcium ions.

  In the phosphoric acid addition treatment of slag 1 to slag 10, both are reduced to an elution concentration of 0.8 mg / liter or less. However, since slag 5 and slag 7 were not conditions with high basicity 1 or basicity 2, the elution pH was somewhat low and the amount of phosphoric acid added was large. On the other hand, in other slag processing, 0.8 mg / liter can be achieved at a phosphoric acid addition ratio of about 1 to 4 times the ratio obtained by the equation (1).

  Moreover, when free CaO was 2 mass% or more, the CaO conversion ratio of calcium ion was the same as that of free CaO, and it was possible to suppress fluorine elution without adding an additional calcium ion source. Therefore, in the fluorine elution suppression treatment under conditions of high basicity, fluorine elution could be suppressed even under conditions where the amount of phosphoric acid added was small and calcium ions were hardly added.

  Tables 3 and 4 show the results of the fluorine concentration reduction treatment of water in which various steelmaking slags are immersed. As shown in Table 3, the steelmaking slag used was converter slag, electric furnace slag, molten steel pan slag, and tundish slag. Table 3 shows data on chemical composition, basicity, and elution pH of steelmaking slag. In addition, Table 4 shows the treatment results of fluorine elution suppression using phosphoric acid and calcium ions. The amount of phosphoric acid added was 45 to 66 times the amount of phosphoric acid required by the amount of dissolved fluorine in water.

Since the elution pH of the steelmaking slag used in this treatment was 11.6 to 12.5, and there was sufficient or excess calcium ions relative to the amount of phosphoric acid, additional calcium ions were added. There wasn't. Therefore, the amount of phosphoric acid added was small, and no calcium ion was added, so that economical treatment could be performed.

  As described above, according to the present invention, fluorine elution of steelmaking slag having a fluorine elution concentration of 0.8 mg / liter or more can be suppressed. As a result, this type of steelmaking slag, which has been limited to be used for applications embedded in the soil, is used in civil engineering applications such as soil improvement materials for ground improvement, sand pile materials, roadbed materials, and embankment of heavy equipment intrusion paths. Can be used in general. Moreover, since it can process with few chemical | medical agents by implementing this invention, the elution of fluorine of steelmaking slag can be suppressed cheaply and stably. Therefore, the present invention has high applicability in the slag processing industry and the slag utilization industry.

The relationship between the concentration of fluorine eluting from steelmaking slag and the amount of phosphoric acid added to suppress the concentration of eluted fluorine to 0.8 mg / liter (vs. steelmaking slag mass%) under conditions where the pH of water is 11 or more FIG. It is a figure which shows the relationship between the pH of the water in which the steelmaking slag is immersed, and calcium ion concentration.

Claims (9)

By adding phosphoric acid or phosphate to steelmaking slag having an reached pH value of 11 or more in the immersed water, and without adding a calcium ion source other than steelmaking slag, by reaction of phosphoric acid, water-soluble calcium ions and fluorine , suppressing the elution method of steelmaking slag fluorine, characterized by suppressing the elution of fluorine. Phosphoric acid or phosphate is added to suppress elution of fluorine so that the amount of water-soluble calcium ions present in water is 0.95 times or more in terms of (calcium oxide equivalent mass / phosphoric acid mass). The method for suppressing fluorine elution in steelmaking slag according to claim 1. The mass ratio of the free CaO contained in the steelmaking slag with respect to the amount of steelmaking slag is 2% by mass (calculated as CaO) or more, and an aqueous solution of phosphoric acid or phosphate is added to the steelmaking slag to suppress elution of fluorine. The method for suppressing elution of fluorine in steelmaking slag according to claim 1 or 2. An aqueous solution of phosphoric acid or phosphate is added to a steelmaking slag having a mass ratio of 2% by mass (calculated as CaO) to the amount of free CaO contained in the steelmaking slag to suppress elution of fluorine. The method for suppressing elution of fluorine in a steelmaking slag according to claim 1 or 2. As the steelmaking slag, [(CaO mass%) + (MgO mass%)] / (SiO ₂ mass%) is 3.7 or more converter slag or electric furnace slag, and the steelmaking slag is phosphoric acid or phosphate. The method for suppressing elution of fluorine in steelmaking slag according to claim 1, wherein elution of fluorine is suppressed by adding an aqueous solution. As the steel slag, [(CaO mass%) + _(Al 2 _{O 3} wt%)] / (SiO ₂ mass%) is 4 or more, steel slag discharged from the ladle or the continuous casting device 3. The fluorine in steelmaking slag according to claim 1, wherein the steelmaking slag discharged from the tundish is used to add an aqueous solution of phosphoric acid or phosphate to the steelmaking slag to suppress elution of fluorine. Elution suppression method. In advance, the concentration of fluorine eluted in the water in contact with the steelmaking slag is measured, and the total amount of fluorine calculated from the fluorine concentration contains phosphoric acid that is 20 times or more the amount of phosphoric acid required to make fluoroapatite. with the addition of phosphorus pentoxide containing compounds, suppressing the elution method of steelmaking slag fluorine according to any one of claims 1 to 6, wherein the eluting suppress fluorine. In the method for suppressing elution of fluorine contained in the steelmaking slag having an reached pH value of 11 or more, the equilibrium concentration value of fluorine that is eluted from the steelmaking slag is measured in advance, and (addition of steelmaking slag phosphate is added) Ratio (mass%)) = 0.037 (fluorine equilibrium concentration value (mg / l)) ² +0.079 (fluorine equilibrium concentration value (mg / l))-0.0866
Substituting the equilibrium concentration value into the formula, the minimum amount of phosphoric acid to be added is determined, and an aqueous solution containing phosphoric acid at least one time of the minimum amount of phosphoric acid is sprinkled on the steelmaking slag so The method for suppressing elution of fluorine in steelmaking slag according to any one of claims 1 to 6 , wherein phosphoric acid, calcium ions and fluorine are reacted. The method for suppressing elution of fluorine in steelmaking slag according to claim 8, wherein the adhesion water of steelmaking slag is maintained at 3% by mass or more for 2 days or more after adding the aqueous solution containing phosphoric acid or phosphate.

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