JP2913189B2 - Silica-based flocculant and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novel method used for extracting, aggregating, and removing water inclusions contained in water, ie, various dissolved substances, fine particles, suspended substances, and the like. The present invention relates to a novel silica-based flocculant and a novel method for producing the flocculant having excellent stability, particularly the polymerization and gelation of monomeric silica dissolved in water and the promotion of the phenomenon by Al ³⁺ and Ca ²⁺ etc. The present invention relates to a silica-based flocculant which exhibits excellent extraction and flocculation effects by synergistic action with a chemical reaction and an adsorption phenomenon by Al ³⁺ and Ca ²⁺ and a method for producing the same.

[Prior art] Conventionally, extraction, coagulation, and removal of dissolved substances (ions), organic and inorganic fine particles, suspended solids, and the like in sewage and various wastewaters are mainly performed using an Al coagulant, an Fe coagulant, and a polymer coagulant. Agents have been used.

Of these, the Al coagulant (Pak, Bando) uses only the coagulation effect related to the formation of hydroxides of Al.
It is effective only when the pH is near neutrality, and cannot exert its effect on acidic water or strong alkaline water. Therefore, pH regulators before and after addition ^- to (including OH feed) operation is required, also it is necessary to promote agglomeration with an organic polymer flocculant added.

In addition, the obtained sludge has poor dewatering properties, and its treatment is also difficult. Furthermore, because it is based on the ion adsorption, PO ₄ ^3- in water, SO ₄ ^2-, HCO ₃ ^- or anions such as, surfactants, emulsion, lime waste, suspended solids, such as cement waste water Not suitable for extraction, aggregation, or removal.

On the other hand, the Fe-based coagulant only exerts the coagulation effect accompanying the hydroxide generation like the Al coagulant, and even worse, the disadvantage of leaving Fe ²⁺ and Fe ³⁺ in the water after the treatment. Have. The residual ions after flocculant addition OH ^- can not be removed sufficiently even if the alkaline solution was added.

Moreover, in both cases, the use of a polymer flocculant is indispensable. However, since the polymer flocculant has particularly high hydrophilicity, there is a fear that a part of the polymer flocculant is discharged to the natural world together with the treated water.

Al coagulants, Fe coagulants, and polymer coagulants have inconveniences as described above, and are effective only for specific extraction and coagulation targets. Therefore, processing cost (including sludge processing)
It requires a delicate control, and the effect of the polymer flocculant on the environment cannot be ignored.

Accordingly, the present inventor has found that in a process in which dissolved monomer silica is polymerized by an ionic reaction in an aqueous solution and then gelled, dissolved ions and suspended solids are combined with silica or mixed with water using a phenomenon of adsorbing these. (Japanese Patent Application No. 1-136898). Then, a method using a high-concentration acid-dissolved silica-alumina solution as a kind of dissolved silica used in this method was developed.

[Problems to be Solved by the Invention] This high-concentration acid-dissolved silica-alumina solution satisfactorily extracts and coagulates contaminants in a small amount (ratio) in sewage, especially in a slightly acidic region. There was a problem that stability was lacking.

That is, this acid-dissolved silica-alumina solution is a supernatant obtained by dissolving slag powder with dilute sulfuric acid, and a substantially large excess of Al
And contains ³⁺ and Ca ²⁺ and the like, of the fused silica H ^+, OH ^- short polymerization → gelation also maintained at pH2.0 seen parallel point of polymerization signal by donating silica to promote At the time of solidification.

[Means for Solving the Problems] The present inventor has further continued research on an acid-dissolved silica-alumina solution and succeeded in developing a stabilizing technique.

That is, the silica-based flocculant of the present invention mainly comprises a silica-alumina-calcium solution obtained by dissolving a material containing acid-soluble silica, acid-soluble alumina, and acid-soluble calcium oxide such as slag with dilute sulfuric acid or dilute hydrochloric acid. Ingredients. Also, in order to ensure its long-term storage, the pH of the solution is adjusted to 2.
It adjusts to about 5 to 3.5 or decreases the amount of dissolved calcium (the amount of calcium ions) in the solution.

Silica (SiO _2), when dissolved in water OH ^- and bound (SiO
H) is considered to be normal, and it is said that the production of Si (OH) ₄ (monomer silica, monosilicic acid, silicic acid monomer) is promoted especially when the dissolved silica exceeds 100 ppm. (The Chemistry of Silicon: Ralpf K. Iler). It is known that this monomeric silica exists in water in the form of a hydrosol and has a special behavior and ionic reaction different from other ions.

That is, monomeric silica undergoes silanolization and polymerization → gelation in acidic water, and particularly has a double charge (bipolar), so that it can adsorb substances having positive and negative charges. Is known. However, it is said that the reaction rate is proportional to the OH ^- ion concentration in the pH range of 2 to 7, and that the dehydration proceeds in proportion to the hydrogen ion concentration at pH 2 or lower. Further, in a slightly acidic region around pH 4 to 6, particles grow, and particle aggregation and gelation rapidly progress in a simultaneous manner.

It is also said that depolymerization of polymer silica occurs in alkaline water at pH 9 or higher, but it is said that in weak alkaline water, polymerization → gelation proceeds due to the presence of salts. This is because monomer silica is extremely unstable and easily condensed (ion-reacted). Depending on the concentration, temperature and pH, it is polymerized (condensed) sequentially to form a dimer or trimer. And polymer silica (polysilica) is formed by the siloxane bond. H ⁺ is released in response to a signal of the condensation reaction, and the pH is moved in a direction (around pH 4 to 6) to rapidly promote the polymerization → gelation of the dissolved silica, so that the gelation of the dissolved silica is further promoted.

In this gelation, Zn, Pb, As contained in water
Metal cations such as Ca, alkaline earth metal ions such as Ca, P
Some dissolved substances such as anions and cationic surfactants such as ^3- combine with silica and polymerize integrally → gelation (extraction)
In addition, fine particles such as proteins and fats, suspended solids, suspended solids, etc. are adsorbed on silica and polymerized integrally → gelation (aggregation)
As a result, these water inclusions are separated from the water.
The present invention utilizes this phenomenon for sewage purification and the like.
In addition, the gelled silica has high stability, and has the property that back extraction does not occur in a natural state.

Further, Al ³⁺ , Ca ²⁺ , Mg ²⁺
It has been clarified by the above-mentioned application of the present inventor that the polymerization → gelation reaction proceeds rapidly in the presence of such cations. However, although Al ³⁺ alone promotes polymerization → gelation,
Ca ²⁺ and Mg ²⁺ exhibit a significant effect only when they coexist with Al ³⁺ . This is due to the alumina modification that occurs as a result of the so-called interaction in which Al ^{3+ replaces} silica at the molecular level in the silica polymer, and combines with silica to form a complex precipitate, and at the same time, generates a large amount of H ⁺ It seems to be derived from the phenomenon of

^{_{(-SiOH) m + Al 3+ =}} (-SiOH) mn · (-SiO) n Al 3+ + nH + Moreover, Al ³⁺ is pH> in water at 4 OH ^- aluminum hydroxide formed by combining with, At that time, it precipitates by adsorbing suspended substances in water and phosphate ions and other cations.

On the other hand, Ca ²⁺ and Mg ²⁺ is HCO ₃ ^- and SO ₄ ^2-and chemically bonded to enhance the product to coagulate sedimentation effect low solubility precipitate is removed by extracting them. Along with, in alkaline water,
In the presence of these salts, especially salts of 0.2N or more, the monomer silica takes a single grain growth, and the charge disappears due to neutralization.
It has the property of gelling rapidly.

The amount of monomer silica dissolved is inversely proportional to the amount of H ⁺ , and OH
^- proportional to the amount, but to obtain a practically monomer silica,
In particular, it was usually difficult to obtain a high concentration. That is, silica (SiO ₂ ) does not dissolve in a strong acid, but partially dissolves in a strong alkali, but quickly gels when the pH decreases.

Accordingly, the present inventors have conducted various studies, focused on a slag containing a large amount of silica, and dissolved it with dilute sulfuric acid and dilute hydrochloric acid. As a result, a highly concentrated acid-dissolved silica-alumina-calcium solution was easily obtained. Was done. Of course, the material containing acid-soluble silica, acid-soluble alumina and acid-soluble calcium oxide is not limited to slag, and various materials such as cement and bentonite (mixed with other materials because they do not contain calcium) are used, but they are inexpensive. And slag is most preferred in that it can be obtained in large quantities.

Slag (blast furnace slag, converter slag, electric furnace slag) is made of SiO ₂ ,
Al ₂ O ₃ , CaO, MgO, etc. constitute the main and sub components. Then, they are for example _{CaO-SiO 2, 2CaO-SiO} 2 such as calcium silicate, to form a composite crystal such as calcium silicate aluminate such as _{2CaO-SiO 2 -Al 2 O 3} .

These are easily dissolved in acids because Si, Al and Ca are bonded via O, and easily dissolved because SiO ₂ itself is mainly an α-cristobalite type called metastable silicic acid.
Slag is easily dissolved by dilute acid.

In addition, as the acid, a reducing acid such as hydrochloric acid (CH1) or an organic acid, or a neutral acid such as sulfuric acid (H ₂ SO ₄ ) (having properties of a reducing acid when diluted) is used. These are used diluted to 2N or less. If the concentration is higher than about 2N, colloidal precipitation occurs during or shortly after dissolution,
If it becomes higher, it will not dissolve. Conversely, if the concentration is too low, the amount of dissolution will decrease. More preferably, it is about 0.5 to 1.5 normal, especially about 1 normal.

Although this slag is partially used industrially,
At present, most of the waste is landfilled as industrial waste, which is preferable from the viewpoint of obtaining it at low cost and effective use of resources. Moreover, it is rich in silica as the first component, alumina as the second component, and calcium and magnesium as the third component, and is ideal as a material for the silica-based flocculant of the present invention.

However, since this solution contains a large excess of acid-soluble alumina as the second component and acid-soluble calcium oxide and magnesium oxide as the third component, depending on the pH, gelation occurs within a few minutes after dissolution. Extremely unstable. Therefore, the following experiments were performed for the pH, the concentration of each component, the stability (the time until the start of gelation), and the like by changing the pH and the type of acid. In addition, each experiment was performed at normal temperature.

[Experiment] Experiment 1 Preparation of silica-based flocculant (Part 1) Dissolve an appropriate amount of slag powder (150 mesh or less) in 1N diluted hydrochloric acid and sulfuric acid, and measure acid-dissolved silica (Si
Converted to SiO ₂ ), acid-dissolved alumina, acid-dissolved calcium (Ca
O) and the concentration of acid-soluble magnesium (MgO) were measured (Samples 1 to 8). Since the pH rises as the amount of dissolution of the slag powder increases, the dissolution was stopped by filtering the liquid at a certain pH stage. Table 1 shows the results.

In Table 1, x in Note 1 indicates that the device cannot be used, Δ indicates that the device can be used within a short time, and ○ indicates that the device can be used. Note 2 seems to be the result of alumina modification.

Experiment 2 Preparation of silica-based flocculant (No. 2) Then, slag was dissolved at the level of sample 7 in Experiment 1 (1N / HCl dissolved), and when the pH of the lysate rose above 3.2, 1N / H ₂
The dissolution is continued while SO ₄ is added in small portions to form a precipitate of calcium sulfate. In this case, it is already dissolved
CaO forms CaSO ₄ and precipitates. When the pH reached 3.1 to 3.2 again, the dissolution was stopped and the solution was extracted together with the precipitate, and the precipitate (CaSO ₄ ) was separated by filtration to obtain an aggregated solution. This process is referred to as Experiment 9, and the results are shown in Table 1.

From the above results, it can be seen that the solutions having a pH of about 3.1 (Samples 3 and 7) have excellent stability. Sample 9
Was very stable. In Experiment 1,
The amount of dissolved calcium and dissolved magnesium was smaller in the sulfuric acid solution. This may be due to precipitation associated with SO ₄ ^2- .

Experiment 3 Gelation rate of dissolved silica Next, to measure the gelation rate of dissolved silica, 1N
To a certain amount (100 ml) of / H ₂ SO ₄ and 1N / HCl, a fixed amount (6 g)
Of slag was added and dissolved by stirring.

In this case, the dissolution was stopped at every arbitrary pH, and the solution (containing precipitate) excluding the undissolved residue was drawn out to another beaker, and its coagulation behavior (gelation of silica) was examined. Table 2 shows the results.

As is clear from Table 2, both sulfuric acid and hydrochloric acid have a pH of 3.1.
The stability in the vicinity was extremely good. However, in the case where it is manufactured and consumed immediately at the site, it is almost usable if the pH is about 2.5 to 3.5.

Note that the stability of the CHl lysate, the inferior compared to H ₂ SO ₄ solution is probably because dissolution Ca salts often.

[Action] The silica-based flocculant of the present invention comprises a silica-alumina-calcium solution obtained by dissolving a material containing acid-soluble silica, acid-soluble alumina and acid-soluble calcium with a reducing acid or a neutral acid as a main component. Is what you do. Then, the polymerization-gelation phenomenon of monomers silica dissolved in water and the extraction and aggregation phenomena accompanying the promotion of the phenomenon by Al ³⁺ or Ca ²⁺ or the like, and a chemical reaction or adsorption with Al ³⁺ and Ca ²⁺ Due to the phenomenon, and furthermore, the synergistic effect with the adsorption phenomenon accompanying precipitation of other cations and anions contained in water, an excellent extraction / aggregation effect is exhibited.

Thus, the silica-based flocculant of the present invention is a mixture of water contained in water, that is, dissolved substances such as cations and anions,
Highly efficient extraction, aggregation, and removal of suspended substances and suspended substances such as proteins, fats, surfactants, and algae, and suspended substances contained in various emulsions, lime wastewater, cement wastewater, and the like.

This silica-based flocculant, by maintaining the pH at 2.5-3.5, especially around 3.1, or by lowering the CaO concentration in the liquid,
Enables long-term storage.

[Example of use] Next, an example of use of the sample 3 and the sample 7 using the silica-based aggregation liquid will be described.

Usage Example 1 Agglomeration test of algae-containing water using silica-based flocculant A 1-liter sample (pH = 6.6) was taken in a beaker, and PAC and the silica-based flocculant were added while stirring with a stirrer, and the mixture was stirred for 10 minutes and then allowed to stand. The sedimentation speed was measured by placing a part of the sample in a 500 ml measuring cylinder. The transparency of the supernatant water after standing for 30 minutes was measured. Table 3 shows the results.

In Use Example 1, the degree of visibility was good in all cases, but the sedimentation rate of the silica-based flocculant was faster than that of PAC, and the compressibility of the precipitate was also good. The concentration (ppm) of each component of the silica-based flocculant was 34.6 ppm for dissolved silica, 17.0 ppm for dissolved alumina, 11.0 ppm for dissolved calcium, 3.6 ppm for dissolved magnesium, and 7% for sample 3 (Note 1). In Note 2), 36.0 ppm of dissolved silica and 17.6 pp of dissolved alumina
m, dissolved calcium 34.0ppm, dissolved magnesium 4.6p
pm, a fraction of the PAC.

Use Example 2 Concrete drainage treatment with silica-based flocculant (Part 1: No pH adjustment) Concrete drainage (pH = 12.
3: Raw water) PAC and silica-based flocculant were added to 1 liter, and after stirring for 10 minutes, the sedimentation velocity and the visibility were measured. Table 4 shows the results.

In this example, in the case of the PAC addition, Al was dissolved and turned into a colloid, the sedimentation was 0 even after 30 minutes, the transparency was almost unchanged from the raw water, the calcium concentration was high, and the coagulation effect was almost exhibited. Absent.

On the other hand, the samples to which Samples 3 and 7 were added both formed silica-calcium-alumina-based precipitates and settled out, showing an extremely good coagulation effect. However, in this example, the concentration (ppm) of each component of the silica-based flocculant was 86.5 ppm for dissolved silica, 42.5 ppm for dissolved alumina, 27.5 ppm for dissolved calcium, 9.0 ppm for dissolved magnesium in Sample 3 (Note 1).
In Sample 7 (Note 2), the dissolved silica was 90.0 ppm, the dissolved alumina was 44.0 ppm, the dissolved calcium was 85.0 ppm, and the dissolved magnesium was 11.5 ppm. Hereinafter, use examples 3 and 4 have the same concentration.

Usage Example 3 Concrete drainage treatment with silica-based flocculant (Part 2: pH adjustment) Concrete drainage (ppm 12.1) was previously adjusted to pH = 7.0 to 7.2 with 2N / H ₂ SO ₄ to prevent PAC colloidation. Adjust,
The same treatment as in Use Example 2 was performed. The results are shown in Table-5. In the case of this example, the PAC treatment also showed a considerable aggregation effect. However, after the PAC treatment, a large amount of alkali was added to adjust the pH to sufficiently precipitate Al.

At present, pH of concrete wastewater treatment is
Adjustment is an incidental factor, and is a factor that increases costs. Nevertheless, it is extremely difficult, for example, the precipitate is not tight and poor dehydration occurs.

On the other hand, in the case of the present invention, the sedimentation rate is slightly higher than that in the use example 2 (without pH adjustment). In other words, it can be said that the silica-based flocculant of the present invention exhibits a sufficient flocculant effect without having to bother the cost and adjust the pH.

Use Example 4 Coagulation treatment of milk fat / protein in water The same treatment as in Use Example 1 was performed using an aqueous solution of 10% milk as raw water. The results are shown in Table-6.

In this example, the PAC-added one was not satisfied with the aggregation effect on the emulsion. However, although the degree of transparency is considerably better than that of raw water, cloudiness remains and the coagulation effect is not so good.

Conventionally, wastewater of this kind of food industry is generally diluted and biologically treated except for PAC treatment, or combined with biological treatment and coagulant. However, the biological treatment is bulky and difficult to manage, and has little effect on this kind of wastewater, and in any case, lacks a definitive treatment method.

On the other hand, the silica-based flocculant of the present invention has a flocculant effect, particularly effective for particles below the colloid, and has a high sedimentation speed as compared with PAC, and a silica-calcium-alumina-based precipitate is formed to precipitate. Exhibited a very good aggregation effect. The use of this silica-based flocculant eliminates the need for biological treatment.

[Effects of the Invention] As described above in detail, the coagulation liquid of the present invention is obtained by reducing a material containing acid-soluble silica, acid-soluble alumina and acid-soluble calcium oxide with a reducing acid or a neutral acid (dilute sulfuric acid or dilute hydrochloric acid).
Is a silica-based flocculant containing a silica-alumina-calcium solution as a main component obtained by dissolving the same.

Polymerization of the monomer silica → gelation proceeds remarkably by removing the stable pH (about 3.1) of the monomer silica to make it weakly acidic or by utilizing the interaction with dissolved salts (calcium ions, aluminum ions, etc.). Effective in extracting, coagulating, and removing contaminants in water.

On the other hand, this flocculant shares a large excess of Ca ²⁺ , Al ³⁺ , and Mg ²⁺ , and exhibits an effect when the pH of the target water is near neutral or more alkaline. In addition, it exhibits an interaction between the ions in the sewage and the ions in the sewage to increase the extraction / aggregation effect. For example,
In the case of high-concentration water, the dissolved silica is gelled, and at the same time, the inclusions in the water are extracted, agglomerated, and removed during the polymerization and gelation.

As described above, the present coagulant retains multifunctionality and exhibits effects not seen in conventional coagulants, such as being less susceptible to pH, having excellent coagulation effects, and easily dewatering coagulations. Can be.

In addition, when storing the aggregated solution for a long time, or when using the aggregated solution for a long period of time, adjust the pH of the aggregated solution to about 3.1 or control the Ca salt or Mg salt concentration to about 2.0 N or less. , The purpose is achieved.

In addition, the silica-based flocculant of the present invention can be obtained at low cost, and the method of use is only required to be mixed with the wastewater in the order of several to several tens of ppm and stirring, so that the processing cost is extremely low.
Therefore, it can be used not only for industrial wastewater but also for agricultural wastewater and enormous amount of quasi-natural water (lake, pond, etc.). Therefore, it greatly contributes to prevention of environmental water pollution.

Claims (3)

(57) [Claims] 1. A solution obtained by dissolving a material containing acid-soluble silica, acid-soluble alumina, and acid-soluble calcium oxide such as slag with dilute sulfuric acid or dilute sulfuric acid and dilute hydrochloric acid, and filtering off the residue. A silica-based flocculant comprising aluminum ion and calcium ion as components and having a pH of 2.5 to 3.5. 2. The silica-based flocculant according to claim 1, wherein the pH is 2.9 to 3.2. 3. When dissolving a material containing acid-soluble silica, acid-soluble alumina, and acid-soluble calcium oxide such as slag with dilute sulfuric acid and dilute hydrochloric acid, first dissolve the material with dilute hydrochloric acid, and then add an appropriate amount of dilute sulfuric acid to the solution. A method for producing a silica-based flocculant, which comprises adding calcium to form a calcium sulfate precipitate to reduce the amount of dissolved calcium in the solution and to prevent polymerization and gelation of monomeric silica.