JP2020099897A - Sludge solidifying agent and method of sludge solidification using the same - Google Patents

Abstract

To provide a new sludge solidifying agent and a method of solidification using this agent which is capable of easily and efficiently dumping bentonite sludge and waste gypsum expected to be generated in a large amount in the future and also capable of being reused as an industrial and social resources at low cost by solving the problem of conventional lime mixing treatment, and to provide a solidification treatment method using the same.SOLUTION: A sludge solidifying agent for adding and solidifying sludge is characterized by containing gypsum powder or PS ashes, an aqueous sodium silicate solution and dilute sulfuric acid.SELECTED DRAWING: Figure 1

Description

The present invention includes a large amount of water as a shield method sludge, etc., and solidifies sludge treated as industrial waste using waste gypsum, and enables disposal disposal to the natural world, and further construction materials and civil engineering materials. The present invention relates to a sludge solidifying agent and a sludge solidifying treatment method using the same, which can be used as industrial and social resources as such.

Conventionally, in pile driving and excavation for building construction, excavation of underground tunnels by shield construction method, etc., to prevent collapse of excavation wall and excavation hole wall, stop water, and further improve efficiency of excavation work etc. A large amount of hydrous bentonite is used. After using this hydrous bentonite, sludge containing a large amount of water is generated. Such bentonite sludge is designated as industrial waste, and its disposal is a major problem.

Therefore, conventionally, bentonite sludge is carried to an intermediate treatment plant for industrial waste, and Portland cement containing lime or the like or a mixed cement mainly containing this Portland cement, or a solidifying agent having an effect equivalent to these is mixed. , It absorbs water and is converted from industrial waste into ordinary earth and sand, that is, construction soil and dumped into the natural world.

This treatment method is to mix bentonite sludge with a lime component such as Portland cement and react with water to generate high heat of about 95° C. to evaporate the water, resulting in removal of the water and solidification. It is based on the idea that the soil will become normal soil as construction soil.

However, there are cases where hexavalent chromium is contained in the soil after the treatment in which bentonite sludge is mixed with a lime component such as Portland cement to evaporate water and solidify. This is because the trivalent chromium contained in Portland cement or the like changes into hexavalent chromium when the material is treated at a high temperature in the treatment process and is mixed with the solidified substance after the treatment. In addition, hexavalent chromium is usually solidified when the cement undergoes a hydration reaction and does not elute, but when humus soil or volcanic cohesive soil that inhibits the hydration reaction is mixed during the solidification treatment, , Hexavalent chromium may elute without being sufficiently solidified. In addition, since soil treated with lime components such as Portland cement and solidified is highly alkaline, it may contaminate fields and rivers along with elution of heavy metals.

Regarding the treatment of bentonite sludge, some improvement proposals have been made so far. For example, adding a foaming agent after mixing with lime and firing it to use it as a porous lightweight aggregate (Patent Document 1), an acidic mixture mainly composed of iron oxide, sulfuric acid and calcium sulfate, and further an iron group metal It has been proposed to add a catalyst and use it as a construction/civil engineering material (Patent Document 2).

However, these proposals are not practical for treating a large amount of bentonite sludge, and problems such as complicated steps and cost increase have not been solved.

On the other hand, in recent years, the treatment of gypsum board scraps generated at construction sites and dismantling sites and aged gypsum board has also become a problem. Currently, for the treatment of waste gypsum board, a waste gypsum intermediate treatment company separates the waste gypsum board into paper powder and waste gypsum powder, and then reuses the paper powder as a papermaking raw material for the paper manufacturing company. 5-10% is reused as a gypsum board raw material, and 5-10% is reused as an ecocement raw material. However, a part of the remaining 80% is currently brought to the disposal site at a high cost or left unprocessed at the temporary storage site.

Further, since a paper manufacturing company manufactures a large amount of paper, PS ash (paper sludge) from which water has been removed by high heat treatment of the paper manufacturing residue generated in the paper manufacturing process is generated. Similar to the waste gypsum powder, a part of this PS ash is reused for recycling, but most of it is left untreated.

Therefore, it is required to develop a treating agent and a treating method that can eliminate the above-mentioned adverse effects and can be disposed of at a low cost.

JP-A-6-32676 JP, 2003-10891, A

The present invention has been made in view of the above circumstances, solves the problems of conventional lime mixing treatment, bentonite sludge, waste gypsum or PS ash expected to be generated in large quantities in the future, It is an object of the present invention to provide a new sludge solidifying agent that can be simply and efficiently dumped in nature and can be reused as an industrial/social resource at low cost, and a solidification treatment method using the same.

The present invention provides the following as a means for solving the above problems.

<1> A sludge solidifying agent for adding to and solidifying sludge, which comprises at least gypsum powder or PS ash, an aqueous sodium silicate solution, and dilute sulfuric acid.
<2> The gypsum powder or PS ash is mixed in an amount of 10 to 30 parts by mass, and the total amount of the aqueous sodium silicate solution and dilute sulfuric acid is mixed in the range of 20 to 30 parts by mass with respect to 100 parts by mass of the sludge. The sludge solidifying agent according to <1>.
<3> The sludge solidifying agent according to <1> or <2>, wherein calcium phosphate and/or calcium chloride is mixed in the range of 0.1 to 0.3 parts by mass.
<4> The sludge solidifying agent according to any one of <1> to <3>, wherein the gypsum powder is waste gypsum powder obtained from waste gypsum board.
<5> The sludge solidifying agent according to any one of <1> to <4>, which contains at least one of phosphoric acid, potassium, and ammonium sulfate.
<6> At least (a) a sludge water content adjusting step of adjusting the water content of the sludge,
(B) a water glass adding step of adding the aqueous sodium silicate solution to the sludge after the water content adjustment,
(C) a dilute sulfuric acid addition step of adding the dilute sulfuric acid,
(D) a gypsum powder PS ash addition step of adding the gypsum powder or PS ash, and a sludge solidification treatment method comprising a sludge solidification treatment method.
<7> The method for solidifying sludge according to <6>, further comprising a step of adding a hemihydrate gypsum neutral solidifying agent for promoting solidification.
<8> The method for solidifying sludge according to <6> or <7>, further including a step of adding a fluorine inhibitor to add the calcium phosphate and/or calcium chloride.
<9> The sludge solidification treatment method according to any one of <6> to <8>, wherein the sludge is bentonite sludge.
<10> A method for solidifying sludge, comprising making the sludge solidifying agent according to any one of <1> to <5> available as an industrial/social resource.

According to the present invention, the problems of the conventional lime mixing process are solved, and bentonite sludge and waste gypsum, which are expected to be generated in large quantities in the future, can be simply and efficiently naturally dumped, and further low It is possible to provide a new sludge solidifying agent which can be reused as an industrial/social resource at a cost and a solidification treatment method using the same.

It is a schematic diagram showing one embodiment of an apparatus which performs each process in the sludge solidification processing method of the present invention. It is a schematic diagram showing an embodiment of a sludge storage hopper and a vibration hopper. It is a schematic diagram showing an embodiment of a vibrating hopper. It is a schematic diagram showing a screw conveyor, (A) is a longitudinal direction perpendicular sectional view, and (B) is a side sectional view. It is a schematic diagram showing a screw conveyor and a conveyor group. It is the schematic which shows the dimension of the truck which accommodates a set of apparatuses. It is a schematic diagram showing the size of the container which stores a set of devices.

The sludge solidifying agent of the present invention is a sludge solidifying agent for solidifying by adding to sludge, and in its constitution, it is essential that gypsum powder or PS ash, an aqueous sodium silicate solution and dilute sulfuric acid are mixed and contained. There is.

The gypsum powder used for the sludge solidifying agent of the present embodiment is gypsum powder containing calcium sulfate as a main component as a sludge solidifying auxiliary agent. As the gypsum powder, generally available calcium sulfate powder can be used, but in the present invention, it is preferable to use gypsum powder obtained from waste gypsum board. Waste gypsum board is gypsum board scraps generated at construction sites and dismantling sites and gypsum boards that have deteriorated over time.Usually, they are brought to the disposal site for disposal or left unprocessed at the temporary storage site. It will be provisionally disposed of.

By using the gypsum powder obtained from the waste gypsum board as the gypsum powder as the sludge solidifying auxiliary agent, it becomes possible to efficiently reuse the waste gypsum, which has required a great deal of expense and labor for disposal up to now. The size of the gypsum powder is not particularly limited, but an average particle size of about 2 mm or less is usually considered from the viewpoint of dispersibility and reactivity. Here, the average particle diameter is obtained as a median diameter (d50, volume basis) by cumulative distribution from the measured value of the particle size distribution by the laser diffraction/scattering method using a commercially available laser diffraction/scattering type particle size distribution measuring device. be able to. The average specific gravity of gypsum powder having an average particle size of 2 mm or less is preferably about 0.35 to 0.40.

The aqueous sodium silicate solution used for the sludge solidifying agent of the present embodiment is usually called water glass, and is a substance having a starch syrup-like viscosity obtained by dissolving sodium silicate specified in JIS K1408 in water and heating it. It has a function of solidifying sludge and insolubilizing heavy metals contained in sludge. Colloid particles are stably dispersed in the sludge under normal conditions, but the dispersion cannot be maintained due to artificial fluctuation of pH due to the addition of an aqueous sodium silicate solution (alkali), and the sludge is solidified by aggregation and sedimentation. Specifically, for example, when an aqueous solution of sodium silicate is mixed in sludge having a water content of 70 to 50%, it rapidly solidifies in about 15 to 30 minutes.

Further, sodium silicate is a sodium salt of metasilicic acid (Na ₂ SiO ₃ ) composed of SiO ₂ +Na ₂ O, and this SiO ₂ is porous and multi-layered and carries nanopores of 10 to 100 nm. Heavy metals are adsorbed and insolubilized by ionic bonds in and around these porous porous layers. The principle of insolubilization is that it has a porous shape bond, but is mostly due to an ionic bond between an acidic anion and an alkaline cation.

Further, dilute sulfuric acid is added to the sludge solidifying agent of the present embodiment. Dilute sulfuric acid is a low-concentration sulfuric acid having a mass% concentration of less than about 90%, and acts on a silicate of an aqueous sodium silicate solution to produce a silica sol (colloidal silica) in which silica particles are stably dispersed. Silica sol is a general term for injection materials based on a non-alkaline water glass solution obtained by neutralizing the alkali of water glass with an acid.

In the liquid phase containing water in water glass, the OH groups (cations) on the surface of silica sol are covered with hydroxyl groups. When an acid dissolves in water, it becomes hydrogen + anion, which easily causes an ionic bond, and the specific surface area of the silica surface is very large. It has a role of promoting and assisting the ionic bond, and fine particles such as heavy metals are ionic bond near the porous state. The heavy metal becomes insoluble.

In the binding of ions and the like, in the acidic substance and the alkaline substance, the acid is ionized to become a hydrogen ion + anion, and the alkali is ionized to become a cation + hydroxide ion. In addition, the porous pores of the silica particles are ultrafine particles of 10 to 100 nm and are easy to form bonds.

Moreover, by adding dilute sulfuric acid, it becomes easy to adjust the alkaline sludge to a neutral range. Sludge (especially bentonite sludge and shield method sludge) is usually highly alkaline having a pH of 12 or more, and if the sludge is directly buried in nature, it may cause environmental pollution. It is desirable that the pH of the sludge is finally adjusted to a neutral range of about 9 which is slightly alkaline by blending dilute sulfuric acid. This is an adjustment assuming that the pH will naturally change to about pH 8 after several years due to a long-term effect such as weak acid rain. Further, by this adjustment, it becomes possible to dispose of the solidified sludge in the natural world, and to make it a reused product in the civil engineering work and agricultural fields.

In addition, in the present invention, PS ash can be added separately from the gypsum powder. PS ash is a waste material that is produced by high heat treatment of the papermaking residue generated in the papermaking process to remove water. Like the waste gypsum powder, a part of it is treated as recycled and a large amount of PS ash is left untreated. Has been done.

In the sludge solidifying agent of the present invention, with respect to the mixing ratio of each of the above-mentioned essential components, gypsum powder or PS ash, an aqueous solution of sodium silicate, and dilute sulfuric acid, the water content and properties of the sludge to be treated are appropriately considered. Although it can be adjusted and determined, usually, gypsum powder or PS ash is 10 to 30 parts by mass, preferably 15 to 25 parts by mass, and the total amount of sodium silicate aqueous solution and dilute sulfuric acid is based on 100 parts by mass of sludge. Is in the range of 20 to 30 parts by mass, preferably 23 to 28 parts by mass. By setting the mixing ratio of each component within the above range, the waste gypsum or PS ash can be efficiently disposed, and the sludge can be adjusted to an appropriate pH and reliably solidified.

The sludge solidifying agent of the present embodiment preferably contains at least one of calcium phosphate and calcium chloride in addition to the above essential components. The waste gypsum powder usually contains 3 to 7% fluorine. This variation in the fluorine content is caused by the aged deterioration of the waste material of the gypsum board at the construction site or the waste gypsum that has been used for several years to 10 years or more.

Fluorine is generated when the gypsum powder undergoes a hydration reaction with water, but by adding calcium phosphate or calcium chloride, the fluorine is combined with these to form calcium fluoride, and the generation of fluorine can be suppressed. The generated calcium fluoride is an inorganic compound composed of fluorine and calcium, which is a raw material of the fluorine compound. This calcium fluoride, which is called fluorite in nature, exists and its safety is confirmed.

Further, in the present invention, when the ordinary soil obtained by treating the bentonite sludge with the sludge solidifying agent is used as the recycled soil, phosphoric acid, potassium, and ammonium sulfate (ammonium sulfate) are used for the purpose of producing recycled soil suitable for growing plants. At least one of the above) can be blended. Phosphoric acid, potassium, and runasu each are nutrients necessary for plants, and by mixing any of these, when the recycled soil after treatment is naturally dumped as ordinary soil, it inhibits plant growth. Without using it, it can be used as a social resource useful for ecology.

The above-mentioned phosphoric acid, potassium, and flow rate can be appropriately mixed depending on the desired soil reforming suitability, and are not particularly limited, but usually, relative to 100% by mass of the sludge solidifying agent. , Phosphoric acid 0.2 to 0.7% by mass, potassium 0.1 to 0.7% by mass, and flow rate 0.2 to 0.9% by mass are considered.

The sludge to which the sludge solidifying agent of the present invention is applied is mainly bentonite sludge. Bentonite is a kind of clay, has a strong affinity with water, its suspension is used as a mud material in continuous underground wall construction method, shield construction method of tunnel excavation, etc., but in the present invention, construction using bentonite Various items that are later collected are also included. The bentonite sludge may include, for example, recovered bentonite, cement milk, excavated ground, and earth and sand.

As a method for solidifying bentonite sludge, after throwing the sludge solidifying agent of the present invention into bentonite sludge, stirring the mixture, and leaving it for about 20 hours and then for 60 to 180 minutes depending on the conditions, it can be naturally discarded as soft soil. It can be left over soil.

In the sludge solidification treatment method of the present invention, solidification treatment is performed by a method including at least the following steps (a) to (d).
(A) Sludge water content adjusting step of adjusting the water content of sludge.
(B) A water glass addition step of adding an aqueous sodium silicate solution to the sludge after the water content adjustment.
(C) A dilute sulfuric acid addition step of adding dilute sulfuric acid.
(D) Gypsum powder PS ash addition step of adding gypsum powder or PS ash.
FIG. 1 shows an embodiment of an apparatus for carrying out each step in the sludge solidification treatment method of the present invention.

In the (a) sludge water content adjusting step, first, the water content of the sludge is adjusted before adding each component in the steps after (b). Specifically, sludge is introduced into the sludge storage hopper A shown in FIGS. 1 and 2, and stored for a predetermined time, and only the upper water of the supernatant is transferred to an adjacent water tank C by a pump, a capillary drainage device, or the like. As the sludge storage hopper A, for example, a sludge storage hopper A having a size of 2 to 5 tons (cube of about 2 m) made of steel and having an opening at the top can be exemplified.

Next, the remaining sludge is transferred from the discharge port provided in the lower part of the sludge storage hopper A to the vibration hopper B to further separate water. As the vibration hopper B, for example, a vibrating device B1 which has a water discharge port at the upper part, is made of steel with a sludge capacity of 2 to 3 tons (a cube of about 1.5 m), and is electrically driven to vibrate left and right or up and down, and a high frequency wave. An example is a mounting vibration hopper B provided with a generator B2. As the vibrating device B1, for example, an electrically driven vibrator that vibrates the container body can be used, and as the high frequency generating device B2, for example, a high frequency vibrator or an ultrasonic vibrator that vibrates only sludge can be used. it can. Thereby, the water in the sludge can be efficiently separated. Further, the vibrating hopper B may have a sifter installed therein. By passing through a sieving machine, the sludge can be dispersed and sent to the next step as sludge having a large contact area with air.

The water separated by the sludge storage hopper A and the vibration hopper B is transferred to the water tank C by a pump or the like, and it is preferable to provide a filter at the water discharge port of the sludge storage hopper A and the vibration hopper B. The water discharged through the filter can be neutralized by adding a pH adjusting agent and the like, and can be appropriately discarded or returned to the site after having a water quality that meets predetermined criteria.

Further, in the present embodiment, a capillary drainage device may be provided in the sludge storage hopper A or the vibration hopper B. The capillary drainage device is a device that uses a capillary phenomenon installed at a position on the side surface of the upper part of the hopper 0.5 to 1.0 m. Specifically, a bundle of about 100 fibers with a diameter of 0.1 to 0.5 mm and a length of about 1 m is bundled with about 10 to 20 fibers to form a set, which is the upper part of the sludge storage hopper A or the vibration hopper B. This device is installed in the hole provided in the upper part and discharges only the water content of the sludge in the hopper to the water tank C by the capillary phenomenon.

(A) The adjustment of the water content of sludge in the sludge water content adjustment step can be appropriately set according to the type and water content of the sludge at the time of introduction, but the sludge after the water content adjustment is the sludge at the time of introduction. However, it is preferable to dehydrate as much as possible, and it is preferable to dehydrate at least 10 to 30%, preferably 10 to 50% of the volume of sludge at the time of introduction. By reducing the sludge volume in this step (a), the subsequent treatment time can be shortened and the treatment cost can be significantly reduced.

In the solidification treatment method of this embodiment, (a) sludge that has been dehydrated in the sludge water content adjusting step is introduced into the screw conveyor D, and the subsequent treatment steps are performed. The screw conveyor D for introducing sludge is not particularly limited as long as it can add various solidified components during the transfer, and a commonly known screw conveyor can be used, but it is more agitated with air. From the viewpoint of efficiently performing the above, it is preferable to use a trough type screw conveyor having an upper opening type external leakage prevention plate K as shown in FIG. Specifically, inside the outer cover L of a steel tube having a diameter of 20 to 50 cm, a spiral screw blade M made of steel is attached to the screw rotation center axis J, and the screw rotation center axis J is electrically rotated. As a result, a screw conveyor D for transferring and stirring sludge and a sludge solidifying agent can be exemplified.

Next, with respect to the sludge introduced into the screw conveyor D, (b) a water glass addition step of adding an aqueous sodium silicate solution to the sludge after water content adjustment, (c) a dilute sulfuric acid addition step of adding dilute sulfuric acid, (D) The gypsum powder PS ash addition step of adding gypsum powder or PS ash is sequentially performed.

(B) In the water glass addition step, the aqueous solution of sodium silicate is stored in the water glass tank E installed above the screw conveyor D, and when the sludge is conveyed by the screw conveyor D, the water glass tank E A predetermined amount of sodium silicate aqueous solution is added.

Further, in the step (c) dilute sulfuric acid addition step, dilute sulfuric acid is stored in a dilute sulfuric acid tank F installed at a position adjacent to the water glass tank E above the screw conveyor D, and sludge is removed by the screw conveyor D. A predetermined amount of dilute sulfuric acid is added from the dilute sulfuric acid tank F when being conveyed. By the (b) water glass addition step and (c) dilute sulfuric acid addition step, water glass and dilute sulfuric acid are added to the sludge, and solidification is started by stirring while contacting with air.

In the next (d) gypsum powder PS ash addition step, the gypsum powder or PS ash in the gypsum powder PS ash hopper G provided adjacent to the dilute sulfuric acid tank F above the screw conveyor D is fed to the screw conveyor D. Add to sludge transported in. As a result, the residual water in the sludge and the gypsum powder or PS ash react with each other to generate heat, and the residual water evaporates, so that the solidification reaction proceeds more rapidly.

On the other hand, it is considered that when gypsum powder or PS ash is added to the sludge, the gypsum powder or PS ash causes a hydration reaction with the residual water of the sludge to generate fluorine. Therefore, in the solidification treatment method of the present embodiment, it is preferable to provide a fluorine inhibitor addition step of adding at least either calcium phosphate or calcium chloride after the step (d) gypsum powder PS ash addition step.

Also in the fluorine inhibitor addition step, the fluorine inhibitor composed of calcium phosphate or calcium chloride can be added from the fluorine inhibitor tank H provided on the downstream side of the gypsum powder PS ash hopper G above the screw conveyor D. As a result, the generated fluorine is combined with the above-mentioned fluorine inhibitor to form calcium fluoride, and the remaining fluorine can be suppressed.

Further, in the present embodiment, a hemihydrate gypsum neutral solidifying agent can be added for the purpose of further rapid solidification. The hemihydrate gypsum neutral solidifying agent in the present invention means a solidifying agent composed of hemihydrate gypsum and/or silica fine powder polymer, and is generally available as Ecohard (registered trademark) (manufactured by Chiyoda Ute Co., Ltd.). The hemihydrate gypsum neutral solidifying agent is added to the sludge conveyed by the screw conveyor D from the hemihydrate gypsum neutral solidifying agent tank I provided adjacent to the gypsum powder PS ash hopper G above the screw conveyor D. can do. The addition amount of the hemihydrate gypsum neutral solidifying agent is considered to be in the range of 5 to 20 parts by mass with respect to 100 parts by mass of sludge. By adding a hemihydrate gypsum neutral solidifying agent, even if highly alkaline gypsum powder or PS ash is added, it can be adjusted to a neutral range and rapidly solidified.

In addition, in each of the above steps of the sludge solidification treatment method of the present embodiment, the addition amount of each component is automatically calculated and added to the sludge volume whose water content is adjusted by the (a) sludge water content adjusting step. can do. Specifically, an automatic discharge control device that controls the discharge amount is installed at the discharge port of each component tank and hopper, and the addition amount of each component automatically calculated by the computer according to the automatically measured amount of introduced sludge. Can be realized by loading the above into the screw conveyor D. In addition, by controlling the timing of addition so that a predetermined amount is gradually added, it becomes possible to disperse and add uniformly to the introduced sludge.

Furthermore, it is preferable that the set of apparatuses used in the sludge solidification treatment method of the present invention can be mounted on a movable large truck, trailer, container, or the like. In the present embodiment, the sludge storage hopper A, the vibration hopper B, the water tank C, the water glass tank E, the dilute sulfuric acid tank F, the gypsum powder PS ash hopper G, the fluorine inhibitor tank H, so as to fit within a predetermined volume. Hemihydrate gypsum neutral solidifying agent tank I tank group, a screw conveyor D provided below them, and a conveyor group for carrying sludge to which each component is added and carrying it out to the outside. Is provided.

Note that, as shown in FIG. 5, the conveyor group for carrying and carrying out sludge carries the sludge carried by the screw conveyor D downward, and then carries it in a zigzag form and carries it out to the outside. Here, by adjusting the transportation time with the conveyor group, the solidification reaction of the sludge can be further advanced by the time of unloading. The sludge carried out may be loaded on a dump truck or the like as it is for transportation, or may be temporarily placed on the site once to completely complete the solidification reaction and then loaded on a dump truck or the like for transportation.

In a conventional sludge intermediate treatment facility, sludge is dropped onto a concrete semi-underground pitch with a cube of 5 m in size and the upper part is open, stirred from the upper part with a backhoe, etc., and several pits are formed depending on the solidified state of the sludge. Although the sludge is replaced and accumulated with a considerable amount of water, the sludge is treated, but in the present invention, the sludge treatment plant in the urban area operates even when the sludge treatment plant is small, because the sludge is agitated by the vibration type sieving machine and the screw conveyor without using the pit. It can be treated and the land can be used effectively. Further, since the screw conveyor substitutes sludge agitation of the backhoe, it can contribute to a low-carbon society that does not emit noise or carbon dioxide.

Further, it is preferable that the above-mentioned set of devices is designed to be as compact as possible so that it can be transported. When it is loaded on a large-sized vehicle as shown in FIG. 6, the bed length is about 9 m and the height is 3. It is considered to fit within a size of 8 m and a width of 2.5 m. Further, in the case of being installed in a 40-foot container as shown in FIG. 7, it is considered to fit within the dimensions of height 2.5 m, length 12 m and width 2.4 m.

The present invention has been described above based on the embodiment, but the present invention is not limited to the above embodiment, and various modifications and changes can be made without departing from the scope of the invention. For example, in the embodiment of the sludge solidification treatment method, the water content of the sludge is adjusted by using the sludge storage hopper A and the vibration hopper B in the (a) sludge water content adjustment step. When the water content is relatively low, it may be directly introduced into the vibration hopper B to adjust the water content of the sludge.

In addition, (b) water glass addition step, (c) dilute sulfuric acid addition step, (d) gypsum powder PS ash addition step, fluorine inhibitor addition step, hemihydrate gypsum neutral solidifying agent addition step should be carried out in this order. However, depending on the situation, for example, water glass and dilute sulfuric acid may be mixed in advance, and (b) water glass addition step and (c) dilute sulfuric acid addition step may be performed simultaneously.

Hereinafter, practical embodiments of the sludge solidifying agent and the sludge solidification treatment method of the present invention will be exemplified. First, the sludge treatment agent was adjusted so that the following components were mixed in the following proportions with respect to 100 parts by mass of sludge.
Gypsum powder (gypsum powder crushed from waste gypsum board and passed through a 2 mm mesh): 20 parts by mass sodium silicate aqueous solution (water glass) and dilute sulfuric acid: 25 parts by mass Calcium phosphate: 0.2 parts by mass

Next, a bentonite sludge having a water content of 50% was prepared, and each component adjusted to be 15% by mass of the sludge treating agent was added to 85% by mass of the bentonite sludge and stirred, and the solidification time thereof was measured. The pH and fluorine content were measured. As a result, the solidification time was about 25 minutes, the pH was 9.3, and the fluorine content was 0.5 mg/l. The fluorine content of the waste gypsum alone was 5.9 mg/l.

From the above results, the sludge solidifying agent of the present invention can easily and quickly solidify the sludge, the pH of the solidified sludge is adjusted to an appropriate value, and the content of fluorine is low. It was confirmed that it was in the form of possible soil. No heavy metals were detected in the treated soil.

According to the sludge solidifying agent of the present invention, the treated soil can be dumped into the natural world as ordinary construction residual soil, and there is no problem of heavy metal elution as in the case of conventional lime mixing. That is, the soil after treatment is cheap and safe in a wide area as a civil engineering work aggregate such as river levee ground material, road subgrade ground material, building foundation ground material, hollow landfill material, and agricultural ground improvement material. It can be used as an industrial/social resource for various purposes.

A Sludge storage hopper B Vibration hopper B1 Vibration type device B2 High frequency vibrator C Water tank D Screw conveyor E Water glass tank F Dilute sulfuric acid tank G Gypsum powder PS ash hopper H Fluorine suppressor tank I Hemihydrate gypsum neutralizing agent tank J Screw rotation center axis K External leak prevention plate L External cover M Screw blade

Claims (10)

A sludge solidifying agent for adding to and solidifying sludge, which comprises at least gypsum powder or PS ash, an aqueous sodium silicate solution, and dilute sulfuric acid. 10 to 30 parts by mass of the gypsum powder or PS ash is added to 100 parts by mass of the sludge, and the total amount of the aqueous sodium silicate solution and dilute sulfuric acid is mixed in the range of 20 to 30 parts by mass. The sludge solidifying agent according to claim 1. The sludge solidifying agent according to claim 1 or 2, wherein calcium phosphate and/or calcium chloride is mixed in a range of 0.1 to 0.3 parts by mass. The sludge solidifying agent according to any one of claims 1 to 3, wherein the gypsum powder is waste gypsum powder obtained from waste gypsum board. At least 1 type selected from phosphoric acid, potassium, and ammonium sulfate is mix|blended, The sludge solidification agent as described in any one of Claim 1 to 4 characterized by the above-mentioned. At least (a) a sludge water content adjusting step of adjusting the water content of the sludge,
(B) a water glass adding step of adding the aqueous sodium silicate solution to the sludge after the water content adjustment,
(C) a dilute sulfuric acid addition step of adding the dilute sulfuric acid,
(D) A step of adding gypsum powder or PS ash to the step of adding gypsum powder or PS ash to a method for solidifying sludge. The method of solidifying sludge according to claim 6, further comprising a step of adding a hemihydrate gypsum neutral solidifying agent for promoting solidification. The sludge solidification treatment method according to claim 6 or 7, comprising a step of adding a fluorine inhibitor to which the calcium phosphate and/or calcium chloride is added. The sludge solidification method according to any one of claims 6 to 8, wherein the sludge is bentonite sludge. A method for solidifying sludge, comprising making the sludge solidifying agent according to any one of claims 1 to 5 usable as an industrial/social resource.