JP2001029998A - Phosphorus immobilization method - Google Patents

Abstract

(57) [Problem] To provide a method for immobilizing phosphorus which can be immobilized in slag without volatilizing phosphorus during melting in a strong reducing atmosphere. SOLUTION: Phosphorus immobilization in which a pretreated melting object is melted in a melting furnace in a strong reducing atmosphere to fix phosphorus contained in the melting object in the slag or in a metal that is reduced and generated during melting. In the pretreatment, the ratio between the concentration of the metal element for immobilizing phosphorus volatilized at the melting treatment temperature as a phosphide and the concentration of the acidic oxide forming element for producing an acidic oxide is adjusted by the adjustment index ratio R The component adjustment of the object to be melted is performed so that the adjustment index ratio R is equal to or greater than a predetermined lower limit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for immobilizing phosphorus contained in an object to be melted, such as sewage sludge or industrial waste, in slag or in a metal that is reduced and generated during melting.

[0002]

2. Description of the Related Art Conventionally, phosphorus is volatilized when sewage sludge or the like is melted in a melting furnace. Therefore, there is a method of adjusting the components of a melting target in order to fix phosphorus in slag.
This component adjusting method uses the ratio of the concentration of P and Si, which are the acidic oxide-forming elements contained in the object to be melted, and the concentration of Ca, Fe, and Al, which are the basic oxide-forming elements, as an acid-base ratio. The lower limit of the minimum necessary limit of the acid-base ratio is determined in advance as an empirical rule, and the components of the object to be melted are adjusted so that the acid-base ratio is equal to or more than the lower limit.

[0003]

However, in the above-mentioned method, when the melting furnace is in a melting atmosphere having a relatively high degree of reduction, Ca and Al may not exhibit the phosphorus immobilizing action in some cases. Depending on the component adjustment based on the ratio, a sufficient effect of immobilizing phosphorus may not be obtained. This is because phosphorus is more likely to volatilize when melting in a reducing atmosphere having a high degree of reduction than when melting in an oxidizing atmosphere.

For example, sewage sludge contains 2 to 3% of solids per solid and sewage sludge incineration ash contains 5 to 10% by weight. Part of the gas is volatilized as gas, and the phosphorus that has migrated into the exhaust gas is condensed and deposited in the heat exchanger and flue gas treatment equipment provided at the later stage of the melting furnace, causing corrosion of the equipment and enlargement and solidification of dust,
As a result, there is a possibility that troubles such as breakage of the equipment may occur and hinder the operation of the melting facility. In addition, there is a concern about the adverse effect when the exhaust gas containing phosphorus is wet-washed and the washing wastewater is returned to the water treatment system as return water.

An object of the present invention is to provide a method for immobilizing phosphorus which can be immobilized in slag or in a metal which is reduced and generated during melting without evaporating phosphorus during melting in a strong reducing atmosphere.

[0006]

According to the present invention, there is provided a method for immobilizing phosphorus, comprising: converting a pretreated molten object into a molten slag in a strong reducing atmosphere in a melting furnace; A method for immobilizing phosphorus in slag or in a metal that is reduced and generated during melting, wherein the concentration of a metal element for immobilizing phosphorus that volatilizes at a melting treatment temperature as a phosphide in a pretreatment, The ratio of the concentration of the acidic oxide-forming element that forms the acidic oxide to the concentration is referred to as an adjustment index ratio R, and the components of the object to be melted are adjusted such that the adjustment index ratio R is equal to or greater than a predetermined lower limit.

In the above configuration, an acid-base reaction and an oxidation-reduction reaction occur in the melting furnace, and in the acid-base reaction, acidic oxides (SiO ₂ , P ₂ O _5, etc.) in the object to be melted are converted into basic oxides (CaO ₂ ). ) To form a salt, and as the content ratio of the acidic oxide increases, the ratio at which a salt cannot be formed with the basic oxide increases. This increase in acidic oxide encourage free _{P 2 O 5, P 2 O} 5 is volatilized as a single phosphorus in a redox reaction. In particular, in a strong reducing atmosphere, the oxidation-reduction reaction proceeds rapidly.

[0008] In the melting furnace, the carbon component in the object to be melted and carbon monoxide in the main combustion chamber act as a reducing agent, causing phosphorus volatilization. The carbon acting as a reducing agent reduces a metal component (eg, an iron compound) in the object to be melted to a metal (iron), and converts the reduced metal (iron) released as a simple substance to a phosphorus compound (phosphorization). Fix it in metal as iron). In other words, in melting in a strong reducing atmosphere, P or S
An acidic oxide such as i acts on phosphorus volatilization, and a metal such as Fe acts on phosphorus immobilization.

The ratio between the concentration of the metal element and the concentration of the acidic oxide-forming element has a correlation with the phosphorus immobilization ratio. Phosphorus volatilization at the time can be suppressed. Further, in the method of immobilizing phosphorus of the present invention, the metal element for immobilizing phosphorus is Fe, the element for forming an acidic oxide that forms an acidic oxide is P and Si, and the adjustment index ratio R1 = Fe / (P + Si)
[Mol / mol] is derived, and the lower limit value of the adjustment index ratio R1 necessary for immobilizing phosphorus contained in the object to be melted is determined in advance as an empirical rule, and the adjustment index ratio R1 is equal to or more than the lower limit value. As described above, the components of the object to be melted are adjusted using an iron compound as a component adjusting agent.

[0010] More preferably, the lower limit value of the adjustment index ratio 1 is set to 0.2. Further, in the method for immobilizing phosphorus of the present invention, an adjustment index ratio R2 = Fe / Si [mol / mol], where Fe is a metal element for immobilizing phosphorus and Si is an element for forming an acidic oxide that generates an acidic oxide. Is derived, and the lower limit value of the adjustment index ratio R2 necessary for immobilizing phosphorus contained in the melting target is determined in advance as an empirical rule, and the iron compound is adjusted so that the adjustment index ratio R2 is equal to or more than the lower limit value. Is used as a component adjuster to adjust the components of the object to be melted.

[0011] More preferably, the lower limit of the adjustment index ratio R2 is set to 0.3. In the method of immobilizing phosphorus according to the present invention, at least a part of the component adjusting agent is added as a chemical agent that performs a function necessary for the processing in a processing step in which an object to be melted is generated. With the above-described configuration, the iron compound or the like added as a chemical in a treatment step in which a melting target is generated, such as a sludge dewatering step, a sludge digestion step, a concentration step, a sludge feeding step, or a water treatment step in which sludge is generated, is melted. Since these remain in the object, by using them as part of the component adjuster,
It is possible to reduce the amount of the compound to be added as the component adjuster in the introduction part of the melting step.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described using a sewage sludge melting process as an example. The sewage sludge melting process reduces the inorganic content of the sludge to be melted to about 1300-
It is common to the dry phosphorus production method in that it is heated and melted at 1400 ° C., and it is considered that phosphorus is volatilized as a result of the following reaction similar to that in the dry phosphorus production.

[0013]

Embedded image The reaction of the formula (1) can be interpreted as a continuous reaction of the acid-base reaction of the following formula (2) and the oxidation-reduction reaction of the formula (3). The result of this reaction, phosphorus volatilized as gas in the form of P _4,
It is cooled in a later step of the melting process and precipitates as elementary phosphorus.

[0014]

Embedded image

[0015]

Embedded image (2) in an acid base reaction formula, acidic oxide of SiO ₂ and P ₂ O ₅ acts as an acid for receiving the O ^2-, make basic oxides and salts of donating O ^2- such as CaO . If the content of the acidic oxide increases, P ₂ O ₅ is increased proportion of not form a basic oxide and salts, such as CaO, P ₂ O ₅ is as free. Since the released P ₂ O ₅ is volatilized as P ₄ by the subsequent oxidation-reduction reaction of the formula (3), the increase in the amount of acidic oxides affects the volatilization of phosphorus. In particular, under conditions where the oxidation-reduction reaction of equation (3) proceeds rapidly, such as in a strong reducing atmosphere, the equilibrium of equation (2) is mainly a rightward reaction.

In the reaction of the formula (3), carbon acts as a reducing agent. However, in a sludge melting furnace, carbon components in the sludge and carbon monoxide in the main combustion chamber act as a reducing agent, and the phosphorus volatilizes. cause. The carbon acting as this reducing agent is
The iron in the sludge is reduced to metallic iron by the reaction of the following formula (4), and the reduced metallic iron is fixed in the metal as iron phosphide by liberating the phosphorus released as a simple phosphorus by the reaction of the formula (5). .

[0017]

Embedded image

[0018]

Embedded image That is, in melting in a strong reducing atmosphere, acidic oxides of P and Si act on phosphorus volatilization, and Fe mainly acts on phosphorus immobilization. For this reason, P and Si are taken up as acid oxide forming elements acting on phosphorus volatilization at a predetermined melting temperature, and Fe is taken up as a metal element for immobilizing the volatilized phosphorus, and the respective concentrations are taken as a denominator and a molecule, and Fe / An adjustment index ratio R1 expressed by (P + Si) and an adjustment index ratio R2 expressed by Fe / Si were derived.

By applying these adjustment index ratios R1 and R2 to sewage sludge and examining the relationship between the adjustment index ratios R1 and R2 and the phosphorus immobilization rate, the phosphorus immobilization rate has a positive correlation with both indices. Accordingly, by adjusting the components of the object to be melted using the adjustment index ratios R1 and R2 as an index, phosphorus volatilization during melting can be suppressed. At this time, it is appropriate to set the adjustment index ratio R1 to 0.2 and the adjustment index ratio R2 to 0.3 as the lower limit. The phosphorus immobilization rate was calculated as {(phosphorus concentration in slag × slag weight) + (phosphorus concentration in metal × metal weight)}.

The above results are shown in the following test examples: 1) As the reducing atmosphere becomes stronger, the amount of metal generated in the slag increases, and at the same time, the phosphorus immobilization rate decreases; The rate does not depend on the form of phosphorus in the material to be melted. 3) Ca, Fe and Al are used for immobilizing phosphorus in a weak reducing atmosphere.
The increase in the content of each element is effective, but it was also supported by the fact that only the increase in the Fe content was effective in immobilizing phosphorus in a strong reducing atmosphere.

Example A slag was produced as follows by imitating the melting treatment of sewage sludge, and the phosphorus immobilization rate on the slag was examined.

[0022]

[Table 1] Raw polymer ash (sewage sludge incineration ash) having the composition shown in Table 1 was added with 20% by weight of carbon powder assuming organic components in the sludge to obtain raw ash. Samples 1, 2, and 3 were prepared by adding equimolar amounts of metal reagents Fe ₂ O ₃ , Ca (OH) ₂ , and Al ₂ O ₃ to the raw ash.

An alumina crucible A having an opening diameter of 52 mm, a height of 67 mm, and a capacity of 90 mL, an opening diameter of 88 mm,
Alumina crucible B with height of 72 mm and capacity of 280 mL
After weighing the raw ash and each sample, the mixture was filled to capacity and melted at 1400 ° C. for 4 hours in a small electric furnace. The two crucibles A and B have substantially the same height, but the crucible A has a smaller opening diameter and the crucible A has a vertically long shape.

The weight of each of the obtained slags is measured, and the phosphorus concentration of the raw ash before and after melting and of each sample is measured by a molybdenum (ascorbic acid) absorption spectrophotometric method for the finely pulverized and acid-decomposed materials. did. For the raw ash and each sample, the phosphorus immobilization rate, that is, {(phosphorus concentration in slag × slag weight) + (phosphorus concentration in metal × metal weight)} was calculated. When melting, each crucible A,
As the degree of reduction of the melting atmosphere in B increases, the metal separates at the bottom of each of the crucibles A and B, so the weight ratio of the separated metal [metal weight / (metal weight + slag weight)] is also calculated. It was used as a measure of the oxidation-reduction strength inside each of the crucibles A and B.

For the raw ash and each sample, the adjustment index ratio R
1: Fe / (P + Si), adjustment index ratio R2: Fe / Si
Ratio, (3Ca + 2Fe + Al) / (3P + 2Si) [m
Table 2 shows the acid-base ratio, the phosphorus immobilization ratio in the crucible A and the crucible B, and the metal weight ratio defined by [mol / mol].

[0026]

[Table 2] As is clear from Table 2, the melting in the crucible A was higher in the same sample than in the crucible B, indicating that a stronger reducing atmosphere could be reproduced in the crucible A than in the crucible B. ing. In each of the crucibles, except for the sample 1, the phosphorus immobilization ratios of A and B were much lower in the crucible A.

The effect of the addition of the metal reagent is as follows. In a melting experiment using a crucible B in which the melting atmosphere has a weak reduction degree, Ca, Fe, A
l The addition of any metal reagent increased the phosphorus immobilization rate compared to the raw ash, and it was confirmed that the phosphorus immobilization rate increased with an increase in the acid-base ratio. On the other hand, a crucible B in which the melting atmosphere has a strong reduction degree
In the melting experiment at, only Fe showed the phosphorus fixing effect.
That is, the addition of Fe ₂ O ₃ reduces the adjustment index ratio R1 to 0.1.
From 17 to 0.49, the adjustment index ratio R2 is 0.25
From 0.71 to 0.71 and became a property in which phosphorus hardly volatilized in a strong reducing atmosphere.

With respect to the results of melting various samples using crucible A, adjustment index ratio R1 and adjustment index ratio R
1 and 2 show the relationship between No. 2 and the phosphorus immobilization ratio. FIG.
2 and each curve C in FIG. 2, there is a positive correlation between the adjustment index ratio R1 and the adjustment index ratio R2 and the phosphorus immobilization rate, and the adjustment index ratio R1: 0.2 or more and the adjustment index ratio R
When the ratio was 2: 0.3 or more, the phosphorus immobilization ratio was significantly increased.

From these results, when melting in a strong reducing atmosphere, the adjustment index ratio R1 or the adjustment index ratio R
It can be seen that by adjusting 2, phosphorus behavior during melting can be controlled. That is, it is effective to add the iron compound so that the adjustment index ratio R1 or the adjustment index ratio R2 has an appropriate value in order to suppress the phosphorus volatilization during melting.

As a result of suppressing phosphorus volatilization in this way, transfer of phosphorus to exhaust gas can be suppressed, problems in a heat exchanger and a flue gas treatment facility caused by phosphorus can be solved, and stable operation of the entire melting facility can be achieved. be able to. In order to perform the component adjustment in the actual melting treatment of sewage sludge, it is necessary to add an iron-based dehydration aid in a treatment process in which a melting target is generated, for example, in a sludge dewatering process, or in a coagulant in a water treatment process in which sludge is generated. By selecting an iron compound as a necessary chemical in the treatment process, such as adding an iron salt, these can be used as a part of a component adjuster and added as a component adjuster in the introduction part of the melting process The amount of the compound to be used can be reduced.

The method for immobilizing phosphorus of the present invention can be carried out on other sewage sludge incineration ash and sewage sludge as described above, as well as on other molten objects containing phosphorus, such as industrial waste.

[0032]

As described above, according to the present invention, the adjustment index ratio R between the concentration of the metal element for immobilizing phosphorus as a phosphide and the concentration of the acidic oxide-forming element for forming an acidic oxide.
However, by adjusting the components of the object to be melted so as to be equal to or more than a predetermined value, phosphorus can be fixed in the slag or in the metal that is reduced and generated at the time of melting without volatilizing the phosphorus. Failures in the smoke treatment equipment can be prevented, and stable operation of the entire melting facility can be achieved.

[Brief description of the drawings]

FIG. 1 shows an adjusted index ratio R1: Fe / (P) for sewage sludge samples having various compositions in the phosphorus immobilization method of the present invention.
+ Si) is a graph showing the relationship between slag and the immobilization rate of phosphorus in the metal.

FIG. 2 shows a method for immobilizing phosphorus according to the present invention, in which sewage sludge samples having various compositions have adjustment index ratios R1: Fe / Si
4 is a graph showing the relationship between slag and the immobilization rate of phosphorus in metal.

[Explanation of symbols]

 C Curve showing correlation

Continued on the front page (72) Inventor Takashi Tamura 2-47 Shishitsu Higashi, Namiwa-ku, Osaka-shi, Osaka Kubota Co., Ltd. (72) Inventor Tateishi Politics 56-1 Oitai, Ogori-shi, Fukuoka F-term 4D004 AA02 AA46 AB05 AC04 CA29 CA45 CB02 CC11 DA03 DA10 4D059 AA19 BB04 BK30 DA05 DA19 DA22 DA64 EB11

Claims (6)

[Claims] 1. A phosphorus fixing method in which a pretreated molten object is melted into a slag in a strong reducing atmosphere in a melting furnace, and phosphorus contained in the molten object is fixed in the slag or in a metal which is reduced and generated during melting. In the pretreatment, the ratio of the concentration of the metal element for immobilizing phosphorus volatilized at the melting treatment temperature as a phosphide to the concentration of the element for forming an acidic oxide that forms an acidic oxide is an adjustment index ratio. R
And adjusting the components of the object to be melted such that the adjustment index ratio R is equal to or greater than a predetermined lower limit. 2. The metal element for immobilizing phosphorus is Fe,
P and S are the acid oxide forming elements that form the acid oxide.
As i, the adjustment index ratio R1 = Fe / (P + Si) [mo
1 / mol], and the lower limit value of the adjustment index ratio R1 necessary for immobilizing phosphorus contained in the melting target is determined in advance as an empirical rule, so that the adjustment index ratio R1 is equal to or more than the lower limit value. 2. The method for immobilizing phosphorus according to claim 1, wherein the component of the object to be melted is adjusted using an iron compound as a component adjusting agent. 3. The method for immobilizing phosphorus according to claim 2, wherein the lower limit of the adjustment index ratio R1 is set to 0.2. 4. A metal element for immobilizing phosphorus is Fe,
The adjustment index ratio R2 = Fe / Si [mol / mol] is derived by setting the acid oxide forming element that generates the acid oxide as Si, and the adjustment index necessary for immobilizing phosphorus contained in the object to be melted. The lower limit of the ratio R2 is determined in advance as an empirical rule,
2. The method for immobilizing phosphorus according to claim 1, wherein the component adjustment of the object to be melted is performed using an iron compound as a component adjuster such that the adjustment index ratio R2 is equal to or more than the lower limit. 5. The method for immobilizing phosphorus according to claim 4, wherein the lower limit value of the adjustment index ratio R2 is set to 0.3. 6. The method according to claim 2, wherein at least a part of the component adjusting agent is added as an agent which performs a function necessary for the processing in a processing step in which the object to be melted is generated. Phosphorus immobilization method.