JPH03161099A - Treatment process for waste sludge containing bentonite - Google Patents

Abstract

PURPOSE:To manufacture a granular material to be dehydrated by a simple operation by adding specified acrylic water-soluble polymer in the specified wt.% per suspended solid matter to sludge and mixing therein, and then adding water-soluble polyvalent metal salt in the specified wt.% per suspended solid and mixing therein. CONSTITUTION:Bentonite waste sludge is fed into a polymer mixing tank 1 and 0.2-5wt.% per suspended solid in the sludge of anionic acryl water-soluble polymer containing 15mol% or more of acrylic acid monomer unit and of 2-million or more molecular weight is added and mixed therein. After being mixed uniformly, said mixture is mixed with polyvalent metal salt water solution slowly by a multi-stage agitating element 4 of a granulating tank 3 and turned into granular slurry. The same is dehydrated by a belt press 5 and turned into a cake and discharged. The cake can be fed out easily and used for landfilling. Also, a solidifying agent such as cement can be blended in.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for dewatering bentonite-containing waste mud generated from civil engineering works such as mud water shield construction method and underground continuous wall construction method.

[Prior Art] Bentonite-containing waste mud generated from civil engineering works has high fluidity, and is transported by vacuum truck and treated as industrial waste. Various coagulation methods have been proposed in order to dewater the waste mud so that it can be transported by dump trucks and disposed of in landfills. For example, JP-A-50-81963 discloses a method of adding an organic polymer flocculant after adding cement or calcium hydroxide;
No. 548 discloses a method in which calcium hydroxide is added, left to stand, and then dehydrated.

Also, JP-A-54-155186, JP-A-55-
44301 and JP-A-56-56289 disclose a method of adding a mixed aqueous solution of an organic polymer flocculant and a water-soluble calcium salt. Also, JP-A-55-5
Japanese Patent No. 1485 discloses a method in which an iron salt or an aluminum salt is added to waste mud water, an alkali is added thereto, the pH is adjusted to 6.5 or higher, and an organic polymer flocculant is added.

All of these conventional techniques involve coagulation by the crosslinking adsorption effect of an organic polymer flocculant, and do not utilize the phenomenon of dispersion destruction of a suspension after addition of a water-soluble polymer.

[Problems with the conventional technology] Because bentonite-containing mud water has a high concentration and bentonite is hydrophilic, it does not flocculate with the addition of an anionic organic polymer flocculant, and many minerals such as calcium, iron, and aluminum cannot be flocculated. When valence metal ions are added, bentonite becomes hydrophobic and loses fluidity, making it difficult to mix with organic polymer flocculants, and unless diluted, flocs will be destroyed due to strong shearing force.

Furthermore, when a large amount of organic polymer IMk agent is added, the liquid becomes viscous, which impairs filterability and causes redispersion of particles, making it difficult to coagulate and dehydrate bentonite-containing waste mud.

[Problem of the Invention] An object of the present invention is to enable dewatering of waste mud containing highly concentrated bentonite by filtration or centrifugation without diluting it. In other words, the aim is to develop an appropriate method for using organic polymer flocculants for bentonite-containing waste mud, and to obtain granular material that can be easily dehydrated in narrow spaces such as civil engineering construction sites in cities. shall be. .

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention is configured as follows.

In the present invention, an acrylic water-soluble polymer having a molecular weight of 2 million or more and containing 15 mol% or more of acrylic acid monomer units is added to muddy water in an amount of 0.2 to 5% by weight based on suspended solids, and then water-soluble It is characterized in that the granules obtained by adding and mixing a polyvalent metal salt in an amount of 1% by weight or more based on the suspended solids are dehydrated.

Further, the present invention provides that the polyvalent metal salt is selected from calcium salts, magnesium salts, aluminum salts, and iron salts.

[Function] As described above, the present invention consists of a first step of adding and mixing an acrylic water-soluble polymer to muddy water containing bentonite, and a second step of adding and mixing the water-soluble polymer.

In the first step, the dispersion state of the muddy water remains unchanged and the fluidity is good, so it is easy to mix the acrylic water-soluble polymer. Next, when a polyvalent metal salt is added, the waste mud is separated into granular solids that are easily dehydrated and clear water.

In normal flocculation treatment, flocs are generated when water-soluble polymers are mixed together. In this case, the water-soluble polymers are mixed non-uniformly and dehydration is poor.

On the other hand, in the present invention, when a water-soluble polymer is added, bentonite is hydrophilic and no aggregation occurs.

At this point, it is assumed that the water-soluble polymer is adsorbed on the surface of the suspended solids. Next, when a polyvalent metal salt is added, the hydrophobicity of bentonite and the insolubilization and precipitation of water-soluble polymers occur, resulting in granulation. This phenomenon occurs due to the bond between the carboxyl group in the acrylic water-soluble polymer and the polyvalent metal ion, and other hydrophilic functional groups such as sulfone group, hydroxyl group, ado group, and quaternary In the case of ammonium base, etc., precipitation phenomenon due to polyvalent metal ions does not occur and granulation does not occur. Therefore, it is essential for the present invention to use an acrylic water-soluble polymer containing a large amount of carboxyl groups. Additionally, low molecular weight sodium polyacrylate or cellulose derivatives are generally added to bentonite mud as dispersants. However, granulation does not occur even when polyvalent metal salts are added to waste mud containing a dispersant. This is due to the fact that the dispersant has a low molecular weight and therefore has little effect in adhering suspended solids. In the present invention, since a polymer having a molecular weight of 2 million or more is used, the effect of coating and adhering suspended solids is strong, and granulation occurs as bentonite becomes hydrophobic. Such a phenomenon cannot be explained by the crosslinking adsorption effect in the usual aggregation theory, and is a phenomenon unique to the present invention.

(Example) An example of a device used in the present invention will be described with reference to the drawings. The bentonite waste sludge is introduced into the polymer mixing tank 1, and the agitator 2
After being uniformly mixed with acrylic water-soluble polymer,
It is led to a granulation tank 3 and is gently mixed with a polyvalent metal salt aqueous solution by a multistage stirring blade 4 to form a granule slurry. The granular slurry is dehydrated by a belt press 5 and discharged as a cake. A particularly important step in the series of operations is mixing with the polyvalent metal salt aqueous solution in the granulation tank. Gentle mixing is performed at all locations in the tank, and the suspended solids are reduced to a particle size of 1 mm.
Granulate the above amount. If stirring is too strong, fine particles will be generated, making dehydration difficult. The purpose of mixing the acrylic water-soluble polymer and waste mud can be achieved as long as they are mixed uniformly, and it is also possible to mix them with chemicals in the waste mud pipe.

The acrylic water-soluble polymer used in the present invention has at least 20
It has a molecular weight of 0,000 or more, preferably 3,000,000 or more, and contains at least 15 mol% or more, preferably 25,000,000 or more in the polymer structure.
Those having acrylic acid monomer units of mol % or more are preferred.

Polymers with such a molecular structure include polyacrylamide hydrolyzate, polyacrylate, and acrylamide.
Examples include acrylate copolymers. It is also permissible to contain other monomer units as long as they do not prevent the precipitation effect due to carboxyl groups. It is preferable to add the acrylic water-soluble polymer in a liquid form such as a water solution or water-in-oil emulsion with a viscosity of 10, ooocp or less. This has the disadvantage that the required amount of addition is large because it creates insufficient dissolution.

When water-in-oil emulsion is added directly, it is necessary to perform strong stirring immediately after contact with the waste mud to promote dispersion, but there is an advantage that no dissolution operation is required.

These acrylic water-soluble polymers! ! 0 for cloudy solids
．． 5 to 5% by weight is added and mixed.

If the amount is less than 0.5% by weight, waste mud containing a large amount of bentonite cannot be granulated, and adding too much is economically disadvantageous.

Calcium salts, magnesium salts, aluminum salts, and iron salts are used as water-soluble polyvalent metal salts used to granulate waste mud mixed with polymers. Zinc salts, copper salts, etc. are toxic and unsuitable. Organic polycations such as polyamines also have a granulation effect, but are too expensive compared to metal salts.

The most preferred water-soluble polyvalent metal salt used in the present invention is chloride, followed by sulfate. Specifically, calcium chloride, magnesium chloride, (poly)aluminum chloride, ferrous chloride, and ferric chloride are most preferred, and magnesium sulfate, aluminum sulfate, ferrous sulfate, (poly)ferric sulfate, etc. Next. These water-soluble polyvalent metal salts are added in a water-soluble form in an amount of 1% by weight or more based on the suspended solids in the mud. The water used for dissolving the polyvalent metal salt does not require any special water quality, and if a dehydrating solution obtained by dehydrating the granular material slurry is used, the amount of discharged water will not increase. Furthermore, since unused polyvalent metal ions are present in this desorbed liquid, some of them can be injected into the granulation tank to increase utilization efficiency. The granular slurry that has been removed from the granulation tank can be naturally dehydrated by piling it up in the open or gravity filtered using a nylon screen or wire mesh, but in order to lower the moisture content, dewatering using a belt press, filter press, decanter, etc. It is preferable to use a machine. In particular, belt presses are compact and are the most desirable dewatering machines for use at construction sites.

The cake discharged from the dehydrator can be easily transported by dump truck and used for landfill. It is also possible to simply dehydrate by gravity filtration and then add a solidifying agent such as cement. This will be explained in more detail below using specific examples.

Example 1 A partially hydrolyzed polyacrylamide commercially available as an organic polymer flocculant and a powder of sodium polyacrylate were subjected to a test.

Table 1 shows the physical properties of each polymer.

Table-1 ・AAM-AMPS copolymer is acrylamide and 2-
This shows a copolymer of sodium acrylamide methylpropanesulfonate.

A dewatering test was conducted on waste mud generated from a certain mud water shield construction site. The physical properties of the waste mud were as follows: suspended solids concentration: 13.8%, funnel viscosity: 44 seconds, and pH: 11.1.

The polymer powders listed in Table 1 were made into a 1% aqueous solution and added to the polymer mixing tank 1, and the polyvalent metal salt was made into a 10% aqueous solution and added to the granulation tank.

Table 2 shows the test results of dewatering the granular material slurry using a belt press.

The dosing amount of the polymer sample and polyvalent metal salt is the pure amount added per suspended solid. In addition, when adding a solution in which a polyvalent metal salt and a polymer sample were mixed in advance at the same dosage amount as shown in Table 2 to the polymer mixing tank, and when adding it to the granulation tank,
Dehydration was impossible in all cases when the polyvalent metal salt was added to the granulation tank, and when the polymer sample was added to the granulation tank after the polyvalent metal salt was added to the polymer mixing tank.

Table 2 Example 2 A dewatering test of waste mud generated from a certain underground continuous wall construction site was conducted using the sample and device of Example 1.

The physical properties of the waste mud were as follows: suspended solids concentration: 12.5%, funnel viscosity: 36.8 seconds, and pH: 11.9.

Table-3 Tama sweets 4 People coming out Co., Ltd. Kyoritsu Kogyo llI Research Institute Figure-1 hand Continued Supplementary Positive book <direction formula> peace precepts 2 years March 3rd

Claims (3)

[Claims] (1) Anionic acrylic water-soluble polymer having a molecular weight of 2 million or more and containing 15 mol% or more of acrylic acid monomer units is added and mixed in an amount of 0.2 to 5% by weight based on the suspended solids in the mud, and then dissolved in water. A method for treating waste sludge containing bentonite, which comprises dehydrating granules obtained by adding and mixing polyvalent metal salts. (2) The method for treating bentonite-containing waste mud according to claim 1, wherein the water-soluble polyvalent metal salt is selected from calcium salts, magnesium salts, aluminum salts, iron salts, and mixtures thereof. (3) The method for treating bentonite-containing waste mud according to claim 1, wherein the amount of the water-soluble polyvalent metal salt added is 1% by weight or more based on the suspended solids in the mud.