JPH0616805B2 - Method for producing liquid coagulating sedimentation agent using coal ash as a main raw material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is a chemical treatment of coal ash produced as a by-product at the time of combustion from a coal-fired power plant to modify a coal ash-containing component, to adsorb, A method for producing a coagulation-sedimentation agent for wastewater treatment, which enables the removal of pollutants contained in flue gas desulfurization wastewater from thermal power plants, factory wastewater and general wastewater at a low cost by having a coagulation-sedimentation effect Is.

(Prior Art) In recent years, in Japan, a number of alternative oil energies have been developed under national policies in order to reduce dependence on oil, and coal energy is considered to be promising among them.
Due to the expansion of coal-fired power in the future, 62
The generation of coal ash of about 0,000 tons is expected, and its effective use and disposal problems are major issues.

Combustion of pulverized coal usually produces 10 to 25% by weight of coal ash, which is the amount of coal thrown. Currently, the effective use of coal ash in Japan is partially cement admixture (1710,000 tons / 3,390,000). Tons), cement raw materials, fertilizers, etc., but the effective utilization rate is about 50%, and most of the rest is disposed of in landfills as waste ash. Land reclamation area There is a need for early development of effective utilization technology for coal ash in view of the difficult situation. Therefore, the effective component in coal ash was utilized to develop a water treatment agent different from the conventional one. .

(Problems to be Solved by the Invention) In view of the above-mentioned problems, the present invention has been subjected to various tests in order to effectively utilize coal ash, and is effective in alumina, silica, iron, etc. contained in coal ash. Due to the alteration of the components, we have found the characteristics of adsorbing and coagulating sediment components contained in flue gas desulfurization wastewater of coal-fired power plants, factory wastewater and wastewater, and using it as a coagulating sedimentation agent for wastewater treatment, coal It was carried out for the purpose of producing a coagulating sedimentation agent for wastewater treatment using ash as a raw material.

In general wastewater treatment, various wastewater treatments have been performed using an inorganic coagulant or an organic coagulant. As an example, the inorganic coagulant includes aluminum sulfate, polyaluminum chloride, sodium aluminate, iron sulfate, iron chloride, coppar chloride, and the like, and as the organic coagulant,
Many polymer flocculants such as anion type, cation type and nonion type are used. However, wastewater treatment agents such as inorganic coagulants and organic coagulants have effective characteristics, but due to floc floating problems, problems with various treatment chemicals, and problems associated with complication of treatment equipment process, etc. There are problems such as high cost per water.

Therefore, the present invention is intended to provide a method for producing a coagulating sedimentation agent for wastewater treatment, which can solve or avoid the above-mentioned problems by modifying and utilizing the active ingredient of coal ash.

(Means for Solving Problems) The present invention relates to useful components contained in coal ash (see Table-1).
It is made into a liquid coal ash having an adsorption, aggregation, and sedimentation effect by chemically treating and degrading.

That is, coal ash was added to a sodium hydroxide aqueous solution having a concentration of 5 to 50% by weight, and heat treatment was performed until the glassy phase in the coal ash became dissolved or swollen (80 ° C. at room temperature).
~ 95 ° C), silicic acid compounds, aluminum compounds,
By producing the hydroxylated compounds, it is possible to obtain a substance having an adsorption, aggregation and sedimentation effect. Further, by injecting and stirring sulfuric acid compounds having a concentration of 10 to 98% by weight into the hydroxylated compounds until an acidic range (PH = 1 to 2), silicic acid compounds, aluminum compounds, and sulfuric acid compounds are obtained. By generating it, a substance having an adsorption / aggregation sedimentation effect can be obtained.

This means that coal ash can be effectively used in unused fields, and compared to conventional inorganic or organic flocculants,
Wastewater can be treated in a short time and at low cost.

General wastewater has a coagulation-sedimentation effect different from the conventional activated sludge treatment method, and is expected to be used in new fields.

(Operation) That is, when the coal ash is heat-treated with an aqueous sodium hydroxide solution, the aluminosilicate forming the glassy phase of the coal ash is dissolved or swelled and decomposes.

As a result, silica, which has been confined in the glassy phase of coal ash, reacts with sodium hydroxide to produce sodium silicate. Furthermore, by reaction with alumina, which is another substance with a high content, aluminum silicate is produced, and a hydroxide compound of other substances is simultaneously produced, adsorbed,
It transforms into a substance with the effect of aggregation and sedimentation.

In addition, by adding sulfuric acid to this, gelation of sodium silicate produces silica and sodium sulfate,
In addition to the generation of aluminum sulfate from aluminum hydroxide and sodium aluminate, the generation of iron sulfate from iron hydroxide, etc., other substances contained also become sulfuric acid compounds, which are transformed into substances with adsorption, condensation and sedimentation effects.

The operation will be briefly described below.

1. Alkali treatment of coal ash When coal ash is added to an aqueous sodium hydroxide solution and subjected to heat treatment, it partially dissolves and a gel-like substance precipitates. This is a chemical composition of coal ash that reacts with sodium hydroxide and has the ability to adsorb, agglomerate, and settle into a composition containing the following chemicals:

2. Acid treatment of coal ash Acidic (PH = 1 to 2) to the alkali-treated solution of the above 1
When sulfuric acid is added to the composition, the composition is changed to a composition mainly having the following chemical substances, which has adsorption, aggregation and sedimentation ability.

(Example 1) Using actual wastewater, coal ash was treated with an aqueous sodium hydroxide solution 12
A flocculation-sedimentation test of a flocculation-sedimentation agent produced by subjecting the mixture to a concentration of wt% by immersion, stirring, and heat treatment (alkali treatment) was performed. For the sample water, the flue gas desulfurization equipment gypsum separation clear water was used. The results are shown in (Table-2).

By adding an appropriate amount of alkali-treated coagulating sedimentation agent to the wastewater to be treated, dissolving it well in the treated water and adjusting it to an arbitrary pH value, aluminum hydroxide, sodium aluminate polymer removal of contaminants, aluminum silicate Adsorption of heavy metals and the like to the polymer is simultaneously taken up by these polymers, the self-weight is increased, the sediment is rapidly separated, and the sludge is concentrated.

(Example 2) Using actual wastewater, coal ash is treated with an aqueous sodium hydroxide solution 12
A liquid hydroxide compound produced by dipping, stirring and heat-treating in a solution having a concentration of 25% by weight contains 25% by weight of sulfuric acid with a pH of 1 to 1.
A coagulation-sedimentation test was conducted on the coagulation-sedimentation agent produced (sulfuric acid treatment) by pouring and stirring until it reached 2. The sample water was subjected to a flue gas desulfurization apparatus cooling dust removal tower liquid, and the pH of the treated water was adjusted using a 5 wt% calcium hydroxide aqueous solution. The results are shown in (Table 3).

A suitable amount of a sulfuric acid-treated coagulating sedimentation agent is added to the wastewater to be treated, and it is dissolved in the treated water well and adjusted to an arbitrary pH value. By gelation of sodium silicate, silica,
In addition to the formation of sodium sulfate, aluminum hydroxide, sodium aluminate sulfate, iron hydroxide and iron sulfate, other substances also become sulfuric acid compounds, which have adsorption, aggregation and sedimentation effects.

(Example 3) Using actual wastewater, coal ash is treated with an aqueous sodium hydroxide solution 12
A liquid hydroxide compound produced by dipping, stirring and heat-treating in a solution having a concentration of 25% by weight contains 25% by weight of sulfuric acid with a pH of 1 to 1.
After adding the aggregating-precipitating agent produced by pouring and stirring until 2 (sulfuric acid treatment), an adsorption aggregating-sedimentation test was carried out when the pH was adjusted with an aqueous calcium hydroxide solution. The sample water was prepared by using a flue gas desulfurizer cooling dust removal tower liquid, and the pH of the treatment water was adjusted by using a 5 wt% calcium hydroxide aqueous solution. The results are shown in (Table 4).

By adding an aqueous solution of calcium hydroxide to the pH adjusting treatment, the negatively charged pollutant components are aggregated by charge neutralization and removed by sedimentation, and aluminum sulfate, iron sulfate, etc., which are the substances containing a flocculating precipitant treated with sulfuric acid, etc. Adsorption of pollutant components to the aluminum hydroxide, iron hydroxide, and other polymers, and adsorption of heavy metals and the like to aluminum silicate, resulting in the inclusion of aluminum hydroxide flocs, resulting in large growth of the flocs. The sediment is removed. Further, the addition of calcium hydroxide causes a neutralization reaction to generate gypsum. At that time, when gypsum is produced by neutralization, the adsorption or coagulation sedimentation effect is promoted by the solid phase adsorption and coprecipitation phenomenon. In addition, since gypsum has a low solubility in water, it is also taken into flocs, and further contributes to the sedimentation separation rate and the concentration of separated sludge.

(Example 4) In order to compare the aggregation time with the existing inorganic aggregating agent, an experiment was conducted using aluminum sulfate and an anionic polymer. For the sample water, the flue gas desulfurization device gypsum separation supernatant water was used, and the criterion was determined by the time when it was recognized that the flocs were approximately settled. The results are shown in (Table-5).

(Effects of the Invention) The present invention has a feature of adsorbing, aggregating, and settling pollutant components contained in factory wastewater and general wastewater by subjecting the coal ash to the above-described chemical treatment. It can be manufactured at low cost because it is used as the main raw material. In addition, when compared with other inorganic coagulants, the floc sedimentation effect is excellent, there is no problem of adsorption of treated wastewater, and efficient drainage of harmful heavy metals such as adsorption of aluminum silicate. Processing becomes possible.

In addition, since it is composed of an inorganic substance, the concern about secondary pollution is avoided, which greatly contributes to the expansion of the effective use range of coal ash, the omission of treatment equipment, and the reduction of treatment costs. Water can be discharged as fresh water that conforms to the water quality standards, and it is very effective in terms of reusing useful water sources.

Claims (2)

[Claims] 1. An alumina component containing coal ash, which is obtained by immersing and stirring pulverized coal combustion ash (coal ash) generated from a coal-fired power plant in a sodium hydroxide aqueous solution having a concentration of 5 to 50% by weight.
A method for producing an aggregating and precipitating agent, which comprises subjecting a liquid hydroxide compound to heat treatment until a chemical substance such as a silica component is dissolved or swelled to produce a liquid hydroxide compound, which has adsorption and aggregating and sedimenting effects. 2. A liquid sulfuric acid obtained by the method according to claim 1, in which sulfuric acid having a concentration of 10 to 98% by weight is poured into the liquid hydroxide compound until pH becomes 1 to 2, and the mixture is stirred. A method for producing an aggregating and precipitating agent, which comprises producing a compound and having an adsorption and an aggregating and sedimenting effect.