JPH0696149B2 - Method for treating suspension containing metal hydroxide - Google Patents

Description

The present invention relates to a suspension containing a metal hydroxide, for example, waste water discharged from a metal surface treatment factory such as a plating factory, an electrolytic polishing factory, and an alumite factory. In order to remove heavy metal ions such as zinc, nickel, aluminum, tin, etc. contained in the liquid, a liquid from a suspension of metal hydroxide produced by reacting with a neutralizing agent such as caustic soda, sodium carbonate, slaked lime, limestone, etc. The present invention relates to a solid-liquid separation process for removing metal hydroxide contained therein.

[Prior Art] Conventionally, a precipitation separation method, a floatation separation method, a filtration separation method, an adsorption separation method, and the like are known as methods for separating a suspended solid substance from a suspension containing a suspended substance.

In particular, when the specific gravity is relatively heavy like metal hydroxides and the amount of discharged water is large, the precipitation method (for example, P.95- "of" solid-liquid separation technology "issued by Gihodo Publishing Co., Ltd. on November 10, 1979) Since 98) is expected to be the cheapest and stable treatment, it is commonly used.

However, metal hydroxide flocs produced by the reaction of metal ions such as zinc, aluminum, tin, and iron with caustic soda and slaked lime have poor sedimentation property and solid-liquid separation is difficult as it is. A method is employed in which the flocs are added to increase the size of the flocs to accelerate the sedimentation rate.

However, although the flock generated by such a method has a large apparent particle size, the particles are loosely bound to each other and a large amount of water is contained inside, so the density is small and the apparent particle size increases the sedimentation rate. Can't expect. Also, the concentration and dehydration are not good.

[Problems to be Solved by the Invention] The present invention provides a dense floc having a property fundamentally different from that of a conventional flocculation-precipitation floc, a strong binding force, and a high-density floc to form. In addition to increasing the sedimentation speed several times faster than the sedimentation speed, the efficiency and stability of the coagulation separation treatment can be increased and the concentration can be increased so that the filtration step used as a finishing process after the coagulation sedimentation that is conventionally required can be omitted. It is an object of the present invention to provide a solid-liquid separation method for simultaneously producing sludge having good properties and dehydration properties.

[Means and Actions for Solving Problems] In general, metal hydroxides are positively charged. Therefore, the addition of an anionic polymer flocculant causes the action of charge neutralization and adsorption crosslinking to form flocs. To do.

The inventors of the present invention, the conventional floc flocs as shown above,
Before forming coarse floc, add ionic fine-particle flocculant and blast furnace granulated slag fine powder at the same time as the addition of anionic polymer flocculant in order to create dense, strong and high-density floc with different properties. A cationic polymer flocculant was added to.

Granulated blast furnace granulated slag is incorporated into the flocs that are being formed by the action of the anionic polymer flocculant and forms a large number of nuclei.

Further, by the action of the cationic polymer flocculant, the cationic polymer flocculant and the metal hydroxide / blast furnace granulated slag fine powder are adsorbed and crosslinked, and at the same time, a complex network structure is formed with the anionic polymer flocculant.

The cationic polymer flocculant has a large number of adsorption active sites in the molecular chain, and thus can form a floc having a strong binding force.

At this time, both the metal hydroxide and the cationic polymer flocculant may be positively charged, so that a dispersion phenomenon occurs in part and the floc becomes small.

However, this floc is a floc having a very strong binding force, and the molecular chains are entangled by a gentle disturbance to form a dense, high-density floc having a strong binding force.

The liquid composed of such floc groups is further made to flow into the solid-liquid separation tank in an upward flow.

In the solid-liquid separation tank, the stirring blade slowly rotates, where the stirring blade and the flocs collide with each other, and the water in the flocs is discharged. In addition, the rolling motion forms a round and tight flock.

The flock made in this way is a very well-tightened flock with a diameter of 1 mm to 3 mm, and although it has a small particle size, it is a dense flock with granulated blast furnace granulated slag as its core, so it has a high density, It is possible to increase the sedimentation speed 10 times or more compared to the flocculation method of Flocc.

Further, the floc group formed in the solid-liquid separation tank is intermittently or continuously withdrawn as a slurry, and the concentration and dewatering property of this slurry are considerably better than those of the conventional method.

Explaining in detail the substance that becomes the core of the above-mentioned floc, for example, a substance having high colloidal properties, high swelling property and water supply property such as bentonite will absorb water several times its dry volume or more. , The diameter of the flock becomes large.

Although this floc contains water inside, the floc diameter is considerably large, so that the sedimentation velocity is considerably high. However, the dewatering property is not so good, and even if a compaction filtration tank as will be described later is formed, a large gap causes the unformed flocs to flow out, which causes unstable treated water quality. Further, those which are not easily compatible with hydroxide such as magnetite are not suitable as an additive because they hardly form nuclei of flocs.

Therefore, the inventors repeatedly carried out various tests on a substance serving as a nucleus for adsorbing and cross-linking with metal hydroxide to form flocs, and as a result, crushed and classified the granulated slag generated as a by-product from the blast furnace of the steel industry. It was found that granulated fine powder having an average particle size of about 50μ is the most effective.

Using this granulated blast furnace fine powder with an average particle size of about 50μ,
Water granules are easily incorporated into the metal hydroxide and become the nuclei of flocs. This water granulation has a high specific gravity of 2-3, is effective in increasing the sedimentation rate of the formed flocs, and has a high concentration property.
The dehydration property is also good.

As a method of stirring and flowing in the slurry zone, the stirring blade is slowly rotated, the blade and the floc and the floc are collided to expel the water in the floc, and a rolling motion is caused to form a round floc, and dehydration is performed. Basically, you can use any method that encourages you.

However, it is difficult for a propeller-type stirrer, such as a propeller-type stirrer, which causes a convection motion in the vertical direction to form a fine floc by the dehydration action.

The inventors have made stirring blades of various shapes and repeated experiments, and as a result, reached the following stirring blades.

First, the function was divided into the part that causes turbulent motion and the part that causes rolling motion.

In other words, the part where the blades and the flocs collide with each other and the dehydration occurs is the part that causes the turbulent motion, and the part that makes the flocs round by regular rotation is the part that causes the rolling motion. .

Into the sludge blanket zone, grid-like blades were installed to cause raw water to flow from the lower part in an upward flow and to cause turbulent motion in the lower part. The lattice-shaped blade is a combination of flat plates and has a lattice-shaped cross section.

Moreover, a cross blade, which is a combination of two flat plates in a cross shape, is installed on the upper portion thereof.

If the depth of the tank becomes deep, these two types of blades are divided into the upper part and the lower part, and multiple blades can be stacked together. Further, the two types of blades are fixed to the same shaft and are rotated at the same rotation speed. Also, the length of the blade does not reach the outer circumference of the tank,
It is better to have a certain length.

The present treatment system can have a great effect by providing a compaction filtration portion in the sludge blanket zone, above the stirring flow portion, that is, the portion that causes turbulent flow and rolling motion.

In other words, in the agitation flow section, the flocs collide with each other, the flocs collide with the blades repeatedly, and the dense and strong binding pellets with a diameter of 1 to 3 mm formed by rolling motion are pushed upward by upward flow. However, if this floc group is further fixed to a portion where there is no stirring motion, solid-liquid separation occurs and an interface is formed. Above the interface, clear water is discharged as treated water.

Further, a portion below the interface becomes a sludge blanket zone, but here, a consolidation phenomenon occurs in a place where there is no stirring motion. This consolidated layer is a dense floc group having a diameter of 1 to 3 mm and has a kind of filtration function. That is, unformed flocs, molten heavy metals, SS, etc. are trapped in the gaps of these flocs.

Alternatively, it is adsorbed and taken into the floc.

Therefore, the treatment is very stable, and the process such as sand filtration, which is usually used as the secondary treatment after coagulation and sedimentation, becomes unnecessary.

Further, the slurry drawn out from this consolidated zone has a high slurry concentration and a good concentration property.

In some cases, concentration is also unnecessary.

It also has good dehydration properties. Usually, flocs formed by coagulating sedimentation of waste liquids such as plating solutions are difficult to dehydrate, and the water content does not fall below 80% unless dehydrated by a filter press or the like.

However, the flocs produced by this process are easy to dehydrate, and can be easily dehydrated with a simple belt press.
It is possible to keep the water content below 80%.

Therefore, according to the present invention, a suspension containing a metal hydroxide can be treated stably and efficiently.

[Example] As shown in Fig. 1, zinc ion 110 mg /, chromium ion 67 mg /, iron ion 17 m generated from the electrogalvanizing plant.
The pH of the waste liquid containing g / was raised to 11 with slaked lime, and 4 mg / of polyacrylamide type anionic polymer flocculant 2 was added to the suspension 1 containing the metal hydroxide obtained by neutralization, and the average particle size was 50μ. 1000 mg / g of granulated blast furnace slag 3 was added and rapidly stirred for 30 seconds, and then 2 mg / g of a polyacrylamide-based cationic polymer flocculant 4 was added and allowed to flow into the solid-liquid separation tank 5 in an upward flow.

The solid-liquid separation tank has a stirring blade 6 having several lattice-shaped blades stacked on the lower part and several cross-shaped blades stacked on the upper part at 40 rpm.
Is spinning at.

A PVC column having a column diameter of 100 mm and a height of 400 mm was used as the solid-liquid separation tank.

The flocs 7 that have flowed into the solid-liquid separation tank undergo a dehydration phenomenon and rolling motion in the column, and become pellet-like dense flocs of 1 to 3 mm. Further, a compaction phenomenon also occurs at the upper part of the stirring blade to form a sludge blanket zone.

In this blanket zone, it is possible to obtain an OFR of 10 m / Hr.

The clear water that was solid-liquid separated by this column was discharged from the top, and SS3mg /, iron ion 0.1mg /, zinc ion 0.2mg /
, Which is a very good treated water of chromium ion 0.1 mg /.

Further, since the consolidated portion has a filtering function, the treatment is stable and the unformed flocs do not float.

Further, the slurry 9 pulled out from the compaction zone is easily subjected to the leaf test, and the cake water content is 80%, so that the water can be dehydrated quite efficiently.

[Conventional Example] For comparison with the present invention, the case where bentonite used as a precipitation accelerator is added as a conventional example is shown below.

As in the example, zinc ions 110 mg /, chromium ions 67 mg /, iron ions 17 mg / generated from the electrogalvanizing plant.
The pH of the waste liquid containing slag is raised to 11 with slaked lime, 4 mg of polyacrylamide-based anionic polymer flocculant 2 and 1000 of bentonite are added to the suspension 1 containing metal hydroxide formed by neutralization.
mg / addition, followed by rapid stirring for 30 seconds, and then 2 mg / addition of polyacrylamide-based cationic polymer flocculant 4 was made to flow into the solid-liquid separation tank 5 in an upward flow.

The solid-liquid separation tank has a stirring blade 6 having several lattice-shaped blades stacked on the lower part and several cross-shaped blades stacked on the upper part at 40 rpm.
Is spinning at.

As the solid-liquid separation tank, a PVC column having a column diameter of 100 mm and a height of 400 mm was used.

The flocs that flowed into this solid-liquid separation tank did not form dense and high-density flocs in the column as when adding blast furnace slag. This is also because bentonite did not function as a nucleus and could not promote the entanglement phenomenon of polymer coagulant molecular chains.

As a result, the OFR could be as low as 5 m / Hr in this column. Also, if the OFR is raised to 10 m / Hr as when adding granulated blast furnace slag, the treated water becomes turbid and SS is 20 m.
It deteriorated to g / and SS leaked.

Further, when the extracted slurry was subjected to a leaf test, the water content of the cake was considerably deteriorated to 85%.

Similarly, when magnetite was added, the same effect as when adding granulated blast furnace slag was not obtained.

Next, in the above-mentioned conventional example, magnetite was used instead of bentonite, and the same treatment was performed.

The flocs flowing into this solid-liquid separation tank could not form dense and high-density flocs, and the OFR could only be increased to about 5 m / Hr in the column.

Also, when OFR was raised to 10m / Hr as in the case of adding granulated blast furnace slag, SS leaked and treated water SS deteriorated to 25mg /.

[Effect of the Invention] According to the present invention, the metal hydroxide in the liquid can be efficiently removed from the suspension containing the metal hydroxide. That is,
The solid-liquid separation tank becomes compact because the sedimentation speed can be very high.

Further, a filter which is usually installed as a secondary treatment for coagulating sedimentation is unnecessary.

The drawn-out slurry has excellent concentrating and dehydrating properties, and a concentrating tank is not necessary, and a dehydrator may be a simple bell press or a vacuum filter.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an outline of an embodiment example of the present invention. 1 ... Neutralizing plating solution, 2 ... Anionic polymer flocculant, 3 ... Granulated blast furnace slag, 4 ... Cationic polymer flocculant, 5 ... Solid-liquid separation tank, 6 ... Stirring blade, 7 ... Flock, 8 ... Treated water, 9 ... Slurry (sludge).

Claims (3)

[Claims] 1. A suspension containing a metal hydroxide, an anionic polymer flocculant and blast-furnace granulated slag fine powder are added at the same time and rapidly stirred, and then a cationic polymer flocculant is added. After adsorbing and cross-linking the system polymer flocculant, the metal hydroxide and the granulated blast furnace slag fine powder, the suspension is allowed to flow upward into the sludge blanket zone which is agitated and rotated by the rotating flow to separate the flocculation and separation. A method for treating a suspension containing a metal hydroxide, which is characterized by carrying out. 2. As a method of stirring and flowing in a sludge blanket zone, a lattice-shaped rotary blade that causes turbulent motion is provided at the bottom of a solid-liquid separation tank, and a cross-shaped rotary blade that causes rolling motion is provided at the upper part. The method for treating a suspension containing a metal hydroxide according to claim 1, further comprising: 3. A sludge blanket zone is provided with a rotary blade-free zone above the sludge blanket zone, and the flocs formed in this zone are consolidated to provide the same function as sand filtration. A method for treating a suspension containing a metal hydroxide as described above.