JP2016190208A - Method for recovering gypsum from waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering gypsum from waste water, in which gypsum can be prepared/recovered efficiently by effectively utilizing inorganic ions contained in various kinds of waste water, particularly by utilizing sulfate ion-containing waste water and calcium ion-containing waste water.SOLUTION: The method for recovering gypsum from waste water comprises the steps of: mixing the calcium ion-containing waste water A with the sulfate ion-containing waste water B to produce gypsum; and recovering the produced gypsum. It is desirable that a mixing ratio x is decided, when the waste water A is mixed with the waste water B, so that a difference (Ccx-Crx) between the calculated electrical conductivity Ccx of a liquid mixture of the waste water A with the waste water B and the measured electrical conductivity Crx thereof becomes maximum. The recovered gypsum is used when cement is produced.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for collecting gypsum from wastewater, and in particular, is a method for collecting gypsum from wastewater to obtain gypsum from wastewater by effectively using sulfate ions and calcium ions contained in various types of wastewater.

  In general, gypsum used for cement setting adjustment includes exhausted dihydric gypsum obtained by treating exhaust gas from coal-fired power plants, chemical gypsum prepared by mixing and reacting sulfuric acid and lime, and a process of refining titanium. There are titanium gypsum to discharge.

  As a method for recovering gypsum, Japanese Patent Application Laid-Open No. 11-207146 (Patent Document 1) discloses a flue gas desulfurization drainage obtained by treating flue gas discharged from a coal-fired power plant with a soot mixed flue gas desulfurization device. A method is described in which solid-liquid separation is performed after evaporation and concentration, and the gypsum is recovered on the solid side.

  Japanese Patent Laid-Open No. 2001-145818 (Patent Document 2) describes exhaust gas generated when burned in a high-sulfur-containing fuel boiler, after removing nitrogen oxides with a denitration device, and then collecting dust in the exhaust gas with an electric dust collector. In which a sulfur compound in exhaust gas is neutralized with a slurry-like alkali neutralizing agent in a desulfurization apparatus, and further separated and recovered as gypsum in a gypsum recovery apparatus.

  On the other hand, various types of wastewater are actually discharged after being subjected to wastewater treatment, for example, water treatment so as to meet environmental standards, but the concentration of inorganic salts contained in wastewater is restricted by strict wastewater treatment. There is not, and it is discharged with high salt concentration.

  For example, waste sulfuric acid is treated by an industrial waste disposal contractor when it is neutralized by alkali treatment (sodium hydroxide, potassium hydroxide, waste alkali, etc.), and there are suspended substances. Solid-liquid separation is performed with a filter press or the like, and when an organic substance is present, biological treatment or the like is performed, and the wastewater is drained in a form containing inorganic ions.

  Cement companies accept and use incinerated ash and fly ash as raw materials for cement production, but the chlorine contained in the incinerated ash and fly ash is a problem in the cement production process and in cement specifications. Therefore, the received incineration ash and fly ash are washed with water. The waste water after the fly ash is washed with water contains a large amount of inorganic ions, and is discharged in a state containing these inorganic ions.

None of the conventional methods for collecting gypsum so far is a method for preparing gypsum from wastewater to be disposed of.
Moreover, in view of the situation where wastewater containing a large amount of inorganic ions is discarded without being effectively recycled, it is expected that these wastewater will be used effectively.

Japanese Patent Laid-Open No. 11-207146 JP 2001-145818 A

  Accordingly, the object of the present invention is to solve the above problems, effectively use inorganic ions contained in various wastewaters, and in particular, use wastewater containing sulfate ions and wastewater containing calcium ions to efficiently use gypsum. It is to provide a method for recovering gypsum from waste water that can be prepared and recovered.

  In order to solve the above problems, the method for recovering gypsum from wastewater of the present invention has the following technical features.

That is, the method for recovering gypsum from waste water according to claim 1 is characterized in that gypsum is produced by mixing waste water A containing calcium ions and waste water B containing sulfate ions, and the produced gypsum is recovered. This is a method for collecting gypsum from wastewater.
The gypsum recovery method from waste water according to claim 2 is the gypsum recovery method from waste water according to claim 1, wherein the waste water A containing calcium ions has a calcium ion concentration of 5000 ppm or more and the waste water B contains sulfate ions. Is a method for recovering gypsum from waste water, characterized in that the sulfate ion concentration is 5000 ppm or more.

The method for recovering gypsum from waste water according to claim 3 is the method for recovering gypsum from waste water according to claim 1 or 2, wherein the mixing ratio of waste water A and waste water B is waste water having electrical conductivity C1 (μS / cm). The calculated electrical conductivity Ccx of a mixed solution obtained by mixing A and the drainage B having an electric conductivity C2 (μS / cm) at a mixing ratio x is obtained from the following formula 1.
Ccx (μS / cm) = C1 × (1−x) + C2 × x (Expression 1)
(However, in Formula 1, the mixing ratio (mixing rate) x is x = volume of drainage B (cm ³ ) / (volume of drainage A (cm ³ ) + volume of drainage B (cm ³ ))), Ccx (μS / cm) indicates the calculated electrical conductivity when the mixing ratio is x),
The measured electrical conductivity Crx (μS / cm) of the mixed solution at the mixing ratio x is measured, and the difference (Ccx−Crx) between the calculated electrical conductivity Ccx and the measured electrical conductivity is maximized. A method for recovering gypsum from wastewater, characterized in that wastewater A and wastewater B are mixed at a mixing ratio.

  The method for recovering gypsum from waste water according to claim 4 is the method for recovering gypsum from waste water according to any one of claims 1 to 3, wherein the waste water has a calcium ion concentration and / or a sulfate ion concentration by evaporative concentration or membrane concentration. This is a method for recovering gypsum from waste water, characterized in that the gypsum that is mixed after being raised and recovered is used for cement production.

The method for recovering gypsum from wastewater of the present invention can effectively use wastewater that has been discharged and discarded, and can efficiently prepare and recover gypsum from the wastewater.
In particular, by effectively using the collected gypsum as a gypsum for cement production, it is possible to expand the effective utilization as a supply resource for gypsum having a high usage fee in the cement production process.

The relationship between the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and the amount of dihydrate gypsum produced, and the mixing rate and electrical conductivity of wastewater containing calcium ions and wastewater containing sulfate ions, It is a figure which shows the relationship with the difference (The difference (Ccx-Crx) of calculated electrical conductivity Ccx and measured electrical conductivity Crx). Other examples of the present invention, the relationship between the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and the amount of dihydrate gypsum produced, and the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and electricity It is a figure which shows the relationship with the difference of conductivity (The difference (Ccx-Crx) of calculated electrical conductivity Ccx and measured electrical conductivity Crx). Other examples of the present invention, the relationship between the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and the amount of dihydrate gypsum produced, and the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and electricity It is a figure which shows the relationship with the difference of conductivity (The difference (Ccx-Crx) of calculated electrical conductivity Ccx and measured electrical conductivity Crx). Other examples of the present invention, the relationship between the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and the amount of dihydrate gypsum produced, and the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and electricity It is a figure which shows the relationship with the difference of conductivity (The difference (Ccx-Crx) of calculated electrical conductivity Ccx and measured electrical conductivity Crx). Other examples of the present invention, the relationship between the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and the amount of dihydrate gypsum produced, and the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and electricity It is a figure which shows the relationship with the difference of conductivity (The difference (Ccx-Crx) of calculated electrical conductivity Ccx and measured electrical conductivity Crx). Other examples of the present invention, the relationship between the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and the amount of dihydrate gypsum produced, and the mixing rate of wastewater containing calcium ions and wastewater containing sulfate ions and electricity It is a figure which shows the relationship with the difference of conductivity (The difference (Ccx-Crx) of calculated electrical conductivity Ccx and measured electrical conductivity Crx). It is a powder X-ray diffraction chart which identified the deposit collect | recovered from the waste_water | drain.

The present invention will be described by the following embodiments.
The method for recovering gypsum from wastewater of the present invention is a method for recovering gypsum from wastewater, which generates gypsum by mixing wastewater A containing calcium ions and wastewater B containing sulfate ions, and recovers the generated gypsum. is there.

The wastewater of the present invention is not particularly limited as long as it is a wastewater containing inorganic ions, specifically sulfate ions and calcium ions, and wastewater discharged from various factories and various processes can be used.
For example, industrial waste collectors neutralize waste with alkali as described above. As a result, wastewater containing sodium sulfate or potassium sulfate, that is, wastewater containing sulfate ions is generated. Further, wastewater containing calcium chloride, that is, wastewater containing calcium ions, is generated from incineration ash and fly ash cleaning contractors.
In the present invention, wastewater containing these calcium ions and wastewater containing sulfate ions can be suitably used, thereby enabling effective use of wastewater that has been disposed of so far.

When regulated substances are contained in the wastewater containing inorganic ions, the wastewater after treatment to remove regulated substances such as water treatment can be used in the wastewater, but after collecting gypsum from the drainage You may perform the process which removes controlled substances, such as water treatment.
In particular, when the regulated substances are heavy metals, etc., in order to affect the quality of the cement produced using the gypsum recovered by the method of the present invention, a treatment to remove the regulated substances such as heavy metals from the waste water is performed as much as possible. It is desirable to use the drainage after

Next, gypsum is generated by mixing waste water A containing calcium ions and waste water B containing sulfate ions.
In order to improve the production efficiency of gypsum produced by the mixing, the waste water A containing calcium ions has a calcium ion concentration of 5000 ppm or more, and the waste water B containing sulfate ions has a sulfate ion concentration of 5000 ppm or more. It is desirable from the viewpoint that gypsum from can be efficiently recovered.

  In order to set the calcium ion concentration of the waste water A containing calcium ions to 5000 ppm or more and the sulfate ion concentration of the waste water B containing sulfate ions to 5000 ppm or more, the waste water A and the waste water B are calcium in the waste water by evaporation concentration or membrane concentration. It is desirable to increase the ion concentration or sulfate ion concentration.

  The mixing ratio of waste water A and waste water B for preparing gypsum varies depending on the calcium ion concentration and sulfate ion concentration contained in the waste water. It is preferable to mix the waste water A and the waste water B at a mixing ratio at which a certain gypsum can be most efficiently performed.

As a method for controlling such optimum mixing, electric conductivity can be used.
The calcium concentration and sulfate ion concentration contained in each drainage of the drainage A and drainage B are not constant but change. Therefore, it is desirable to measure the electrical conductivity and determine the mixing ratio at which gypsum precipitation is most efficient.

Specifically, the electrical conductivities C1 and C2 of the drainage A and the drainage B are measured. From these two measured values, the electrical conductivity at the mixing ratio x of the waste water A and the waste water B is obtained by the following formula 1.
Ccx = C1 × (1-x) + C2 × x Equation 1
However, in the above formula,
Mixing ratio x = volume of waste water B / (volume of waste water A + volume of waste water B)
Calculated electrical conductivity at mixing ratio x: Ccx
Measured electrical conductivity at mixing ratio x: Crx
Indicates.
Next, the actual electrical conductivity of the mixed liquid after mixing the drainage A and the drainage B is measured as Crx. From the calculated electrical conductivity Ccx and the measured electrical conductivity Crx of the mixed liquid (Ccx−Crx ), And by controlling the mixing ratio of the drainage A and the drainage B so that the calculated value is maximized, it is possible to control the amount of the gypsum precipitate generated to be maximized. Become.

  The reaction time after mixing for mixing the waste water A and the waste water B to produce gypsum is not particularly limited, and the above-described electrical conductivity is continuously measured, and the electrical conductivity is stable at a certain value. The time when the reaction has ended can be used as a measure of the end of the reaction. This is because the electric conductivity of the mixed solution decreases with the gypsum precipitation produced, but the electric conductivity stabilizes at a certain value when the gypsum crystal growth to be produced is completed. It becomes possible.

Moreover, about reaction time, after mixing two liquids, the waste_water | drain A and the waste_water | drain B, the time required for the precipitation of gypsum to be completed is several minutes to several hours, for example. When the amount of gypsum deposited is small, a longer time tends to be required. A shorter reaction time is advantageous in terms of throughput, and a method for shortening the reaction time includes a method of putting seed crystals in a wastewater mixture.
The mixing method may be either batch processing or continuous processing.

  There are no particular restrictions on the pH, temperature, and pH at the time of the seed crystal reaction when the waste water A and the waste water B are mixed to produce gypsum, but both the waste water A and the waste water B are discharged. Therefore, it is within the drainage standard, and it is desirable to set the pH to 5.0 to 9.0.

The reaction temperature is not particularly limited, but when the reaction temperature is 56 ° C. or higher, the recovered gypsum form changes from dihydrate gypsum to anhydrous gypsum.
Regardless of whether the recovered gypsum is dihydrate gypsum or anhydrous gypsum, it can be used without any problem as cement gypsum, but it is preferable to react at room temperature in terms of equipment and thermal energy.

In this way, a solid-liquid separation operation is performed to recover the gypsum generated as a precipitate in the wastewater mixture.
At that time, the larger the gypsum particle size, the higher the filtration performance and the higher the productivity. Therefore, the gypsum particle size is preferably 30 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more.

Any known method can be applied to the solid-liquid separation operation.
For example, solid-liquid separation can be performed using means such as a centrifugal separator, a filter press, and a belt press, and a centrifugal separator that can easily adjust the moisture content can be suitably applied.

Moreover, what dehydrated the obtained gypsum deposit is preferably washed with water in order to eliminate the filtrate contained in the cake.
It does not specifically limit regarding the moisture content of the gypsum to collect | recover. For example, when a centrifugal separator is applied, the moisture content can be adjusted by centrifugal force and time. However, if it is less than 5% by mass, there is a risk of dust flying due to wind etc. when stocked outdoors. Preferably, it is desirable to recover those having 5% by mass or more, more preferably 8% by mass or more. On the other hand, if it exceeds 20% by mass, the collected gypsum becomes sticky and handling may be deteriorated. Therefore, it is preferably 20% by mass or less, and preferably 15% by mass or less.

  The gypsum collected in this way can be used effectively for cement production. The cement mortar and concrete manufactured using the gypsum recovered according to the present invention causes a deterioration in setting property and a decrease in strength as compared with cement mortar and concrete manufactured using conventional gypsum. It can be used favorably as a gypsum for cement production.

Hereinafter, the present invention will be described with reference to examples.
Neutralized wastewater obtained by treating fly ash washing water as wastewater A (Solutions 1 to 3) and neutralizing industrial waste with alkali treatment. Was the waste water B (solutions 4 to 5), and the amount of inorganic ions contained in each of the solutions 1 to 5 was measured.
The results are shown in Table 1 and Table 2, respectively.

Each of the waste water A (each solution 1 to 3) and the waste water B (solution 4) were mixed at various mixing ratios, the generated precipitates were collected, and the amount produced was measured.
In addition, the mixing of the waste water A solution 1 and the waste water B solution 4 was performed in Experiment 1, the mixing of the waste water A solution 2 and the waste water B solution 4 in Experiment 2, the waste water A solution 3 and the waste water B solution 4 Was mixed as Experiment 3.
The results are shown in FIGS.
Moreover, each waste_water | drain A (each solution 1-3) and waste_water | drain B (solution 5) were mixed with various mixing rates, the produced | generated deposits were collect | recovered, and the production amount was measured.
In addition, the mixing of the waste water A solution 1 and the waste water B solution 5 was performed in Experiment 4, the mixing of the waste water A solution 2 and the waste water B solution 5 in Experiment 5, the waste water A solution 3 and the waste water B solution 5 This was designated as Experiment 6.
The results are shown in FIGS.

In addition, after drying the produced | generated deposit obtained by mixing the solution 1 of the waste_water | drain A shown in Table 1 and the solution 4 of the waste_water | drain B at 40 degreeC, powder X-ray diffraction (The Bruker company make, D8 ADVANCE) The dry precipitate was identified by analysis.
The result is shown in FIG.
From the chart of FIG. 7, it was revealed that the obtained precipitate was dihydrate gypsum.
Similarly, each precipitate obtained from the mixing of the solution 2 or 3 of the waste water A and the solution 4 of the waste water B, and also obtained from the mixing of the solutions 1 to 3 of the waste water A and the solution 5 of the waste water B. Each precipitate was also analyzed by powder X-ray diffraction (D8 ADVANCE, manufactured by Bruker) in the same manner as described above, and the dry precipitate was identified.
Therefore, it turned out that dihydrate gypsum is obtained by mixing each waste_water | drain A and each waste_water | drain B, respectively.

In addition, since the mixing ratio of each drainage varies depending on the calcium concentration and sulfate ion concentration contained in each wastewater, various ion concentrations contained in the wastewater are analyzed and measured, and the generated gypsum is generated most efficiently. It is desirable to mix at a mixing ratio, and electric conductivity was used as a method for controlling the optimum mixing.
The case where the solution 1 of the waste water A and the solution 4 of the waste water B are mixed will be specifically described below as a representative example.
The electric conductivity of the solution 1 of the waste water A is measured using a portable electric conductivity meter (CM-31P) manufactured by TOADKK, and the value is C1. The electrical conductivity of the solution 4 of one waste water B is measured in the same manner, and the value is defined as C2. In addition, C1 of the solution 1 was 76100 μS / cm, and C2 of the solution 4 was 105300 μS / cm.

From the two measured values of the electric conductivity C1 (μS / cm) of the solution 1 of the waste water A and the electric conductivity C2 (μS / cm) of the solution 4 of the waste water B, the solution 1 and the solution 4 are obtained. The electric conductivity Ccx of the mixed liquid mixed at the mixing ratio x was obtained from the following formula 1.
Ccx (μS / cm) = C1 × (1−x) + C2 × x (Expression 1)
However, in Formula 1,
Mixing ratio (mixing rate) x = volume of wastewater B solution 4 (cm ³ ) / (volume of wastewater A solution 1 (cm ³ ) + volume of wastewater B solution 4 (cm ³ ))
Ccx (μS / cm): Shows the calculated electrical conductivity when the mixing ratio is x.

Next, the measured electrical conductivity Crx (μS / cm) of the mixed solution at various mixing ratios x was measured, and then the difference in electrical conductivity (Ccx−Crx) was obtained.
The result is shown in FIG.

Similarly, the difference in electrical conductivity when the solutions 2 to 3 of the waste water A and the solution 4 of the waste water B are mixed: (Ccx−Crx) is shown in FIGS. 4 and 6 show the difference in electric conductivity (Ccx-Crx) when 3 and the solution 5 of the waste water B are mixed.
C1 of Solution 2 was 77700 μS / cm, C1 of Solution 3 was 61500 μS / cm, and C2 of Solution 5 was 70100 μS / cm.

  1 to 6, it can be seen that there is a correlation between the difference in electrical conductivity: (Ccx−Crx) and the amount of gypsum produced. Therefore, in order to efficiently recover gypsum from waste water A and waste water B, if the mixture ratio is such that the difference in electrical conductivity (Ccx-Crx) is maximized, the gypsum is recovered from the waste liquid. Can be implemented very effectively.

  Further, the wastewater A solution 2 and the wastewater B solution 4 (experimental example 2), the wastewater A solution 3 and the wastewater B solution 4 (experimental example 3), respectively, have a volume mixing ratio of 6: 4 (x = 0.0). Batch mixing was performed in 4), and the gypsum formed and precipitated was recovered by solid-liquid separation.

A trial cement (Example 1 and Example 2) was produced using the recovered gypsum.
Specifically, first, using ordinary Portland cement clinker manufactured by Sumitomo Osaka Cement Co., Ltd. as the cement clinker, the recovered gypsum was added so that the amount of SO ₃ in the resulting cement was 2% by mass, and then Trial cements (Example 1 and Example 2) were produced by adjusting the Blaine specific surface area to 3400 cm ² / g with a ball mill.

In addition, as a comparative example, a cement (Comparative Example 1) was prepared in the same manner as described above using the drained anhydrous gypsum of a coal-fired power plant.
Each obtained cement was subjected to a compressive strength test and a setting test according to JIS R 5205 at each material age of 3, 7, and 28 days.
The results are shown in Table 3.

  From the results in Table 3 above, the cement mortar produced using the gypsum recovered according to the present invention has a compressive strength and setting time equivalent to those of the comparative example, and the strength and setting time of the resulting mortar are particularly It was confirmed that it can be used effectively in the production of cement, which has an effect.

  The method for recovering gypsum from wastewater according to the present invention can be applied to effectively use wastewater containing calcium ions and wastewater containing sulfate ions, and the obtained gypsum can be used effectively for cement production. .

Claims (4)

  A method for recovering gypsum from waste water, wherein gypsum is generated by mixing waste water A containing calcium ions and waste water B containing sulfate ions, and the generated gypsum is recovered.   The method for recovering gypsum from waste water according to claim 1, wherein the waste water A containing calcium ions has a calcium ion concentration of 5000 ppm or more, and the waste water B containing sulfate ions has a sulfate ion concentration of 5000 ppm or more. Gypsum recovery method from wastewater. 3. The method for recovering gypsum from wastewater according to claim 1 or 2, wherein the mixing ratio of wastewater A and wastewater B is wastewater A having electrical conductivity C1 (μS / cm) and wastewater having electrical conductivity C2 (μS / cm). The calculated electrical conductivity Ccx of the mixed liquid in which B is mixed at the mixing ratio x is obtained from the following formula 1,
Ccx (μS / cm) = C1 × (1−x) + C2 × x (Expression 1)
(However, in Formula 1, the mixing ratio (mixing ratio) x is x = volume of drainage B (cm ³ ) / (volume of drainage A (cm ³ ) + volume of drainage B (cm ³ ))), Ccx (μS / cm) indicates the calculated electrical conductivity when the mixing ratio is x),
The measured electrical conductivity Crx (μS / cm) of the mixed liquid at the mixing ratio x is measured, and the difference (Ccx−Crx) between the calculated electrical conductivity Ccx and the measured electrical conductivity Crx is the maximum. A method for recovering gypsum from waste water, characterized in that waste water A and waste water B are mixed at a mixing ratio.   The method for recovering gypsum from wastewater according to any one of claims 1 to 3, wherein the wastewater is mixed after increasing the calcium ion concentration and / or sulfate ion concentration by evaporative concentration or membrane concentration, and the recovered gypsum is produced by cement. A method for recovering gypsum from waste water, characterized in that it is used in a waste water.

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