JPH05345658A - Pollution-free sintered ceramic of soluble chromic acid salt and its production - Google Patents

Abstract

PURPOSE:To obtain a pollution-free sintered ceramic of a soluble chromic acid salt by compounding a substance containing a soluble chromic acid salt with a slag, a hydraulic cement, a silicate and a carbonaceous material at specific ratios and sintering the mixture. CONSTITUTION:A raw material mixture is produced by compounding 30-70wt.% of a substance containing a soluble chromic acid salt (e.g. waste of chromium refractory and smelting residue of chromium ore) with 4-20wt.% of slag, 5-15wt.% of a hydraulic cement, 13-37wt.% of a silicate (e.g. fly ash) and 0-6wt.% of a carbonaceous material (e.g. coal). The weight ratio of the carbonaceous material to the soluble chromic acid salt is 5-10 or above. The mixture is incorporated with 0.01-0.03 pts.wt. (based on the carbonaceous material) of Al and/or Si carbides. The obtained mixture is hydrated, kneaded, optionally cured in wet atmosphere, press-formed, dried and burnt in a strongly reducing flame atmosphere for >=1hr up to 1000 deg.C in the temperature-increasing stage and, thereafter, in a normal reducing flame atmosphere at 1000-1300 deg.C for 1-2hr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of environmental protection in which harmful waste containing a harmful soluble chromium compound that causes pollution is rendered insoluble and non-polluting to be a useful material. Specifically, used waste bricks used in cement kiln glass kiln as magnesia chrome refractory, extractable residue of chrome chemical factory, etc., and toxic substances containing soluble chromic acid as well as chromates are pollution-free materials. The present invention relates to the stabilized sintered ceramics and the manufacturing method thereof.

[0002]

[Prior Art]

(1) Among chromium compounds, in particular, tetravalent, pentavalent, and hexavalent chromates are harmful, so various attempts have been made to make safe trivalent chromium oxides. There were difficulties. (2) For the treatment of soluble chromic acid and its salts, insolubilization, adsorption method, fusion method and the like have been devised and implemented. i) First Prior Art As insolubilization, reduction roasting is performed to reduce insoluble chromium oxide (Cr ₂ O ₃ ). ii) Second conventional technique Soluble chromic acid in waste and its salts are adsorbed mainly on an inorganic adsorbent and / or waste mag bricks are crushed and then Portland cement is added to the cement hydrate. Cr ions are adsorbed on and cured. These cured products are used as a cement block. iii) Third Prior Art A waste material containing soluble chromates is mixed with glass scraps and melted to obtain a glass material.

[0003]

Object of the present invention: Problems to be solved In the reduction roasting method which is the first conventional technique, it is true that stable Cr ₂ O
It is possible to set it to ₃ . However, waste materials such as chromium-based refractory materials contain a wide variety of soluble salts of tetravalent, pentavalent, hexavalent, etc. In particular, the refractory used as the lining of the cement kiln contains K ₂ SO ₄ , KCl, N
Since it has various chemical bonds with alkalis such as a ₂ SO ₄ and these are formed as chromium salts on the surface and voids of the chromium spinel, they can be completely insolubilized even if they are directly reduced and roasted. Has the drawback of being difficult. The second prior art is a method that has been widely adopted in the past, but by mixing with hydraulic cements such as Portland cement,
It is a method of ion exchange with aluminum ions generated by the hydration reaction of cement, fixing it as a hydrate, hardening and insolubilizing it and using it for concrete blocks etc.Cement biohardening material is used for carbonation and alkali aggregate reaction etc. There is a great risk that it will deteriorate over the medium to long term and elute harmful chromium ions again.
There is a problem. The third prior art is a method of fixing chromium ions in the glass by dissolving it together with a waste glass containing soluble chromate, but it is a method of dissolving it with water for a long period of time, particularly acid rain. Under such conditions, there is a drawback that chromium ions are eluted.

The present invention eliminates all the above-mentioned drawbacks of the prior art, and after several steps, the soluble chromate is a neutral oxide which is chemically stable and can be treated by acid rain. It is an object of the present invention to make insoluble and pollution-free by converting it into a chromium spinel solid solution which does not decompose, and further to establish and provide a material that can be used for secondary use and a manufacturing method thereof.

[0005]

Constitution of the present invention: Means for solving the problems In order to achieve the above object, the composition of the sintered product according to the present invention is characterized in that the content of the soluble chromate is 30% by weight or more and 70% by weight or less. , Slag 4% by weight or more and 20% by weight or less, hydraulic cement component that adsorbs chromium ions 5% by weight or more and 15% by weight or less, silicate material 13% by weight or more and 37% by weight ], And a carbonaceous substance that performs a reducing action in an amount of 0% by weight or more and 6% by weight or less, the chromium is stabilized, insolubilized, and made pollution-free.
In addition, the soluble chromate-containing material uses, for example, waste of a chromium-based refractory and / or a chrome ore refining residue as a source of its components. Similarly, the characteristic feature of the method for producing a chromium-free pollution-free sintered ceramics of the present invention is that the raw material mixture obtained on an anhydrous basis has a weight of 5 to 10 times the soluble chromate salt of the raw material mixture. 1 to 100 parts by weight or more and 3/100 parts by weight or less of Al and Si metal of 1 to 100 parts by weight of the carbonaceous material
After adding and blending at least one species, hydro-kneading, if necessary, curing in humid air, pressure molding, and drying, in the temperature rising process, a strong reducing flame atmosphere is maintained for at least 1 hour or more, up to 1000 [° C]. Next, when the temperature exceeds 1000 [° C.] and 1300 [° C.] or less, the firing is performed in a normal reducing flame atmosphere for 1 hour or more and 2 hours or less. Furthermore, the characteristic of the manufacturing method for using the pollution-free sintered ceramics in a better, more beautiful state and at a lower price is that after each step of the manufacturing method described above, the sintered product is further heated to 600 [° C. ] Over 900
Sintering is performed in a temperature range of [° C.] or less and in a reducing atmosphere containing carbon fine particles. The structure of the present invention will be described theoretically. First, the first element uses a part of the theory of the prior art in which soluble chromate and hydraulic cement are hydrolyzed, and soluble chromium ions are ion-exchanged with Al ions by a hydration reaction to temporarily fix them. The present invention uses slag and gypsum to once produce a large amount of senyi-like ettringite (3CaO · CaSO ₄ · A).
(1 ₂ O ₃ .nH ₂ O) is generated to completely carry out the above-mentioned ion exchange so that the reduction reaction during firing is likely to occur quickly. The second factor is that, in the firing process, the reducing agent was selected so as to most efficiently reduce the Cr ⁺⁶ ion, which was generated by the dehydration reaction of the hydrate, in the state of the generator. Furthermore, a detailed description of the configuration principle will be added.

1. In the material composition of claim 1, the range of 30 [%] to 70 [%] is selected as the inorganic raw material containing soluble chromate, and it is because CrO ₃ in general symmetrical waste is selected. That is,
The content of Cr ⁺⁶ is in the range of 0.1 [%] to 2.0 [%], and when the composition is less than 30 [%], it is out of the standard range of hazardous waste for waste treatment. In some cases, the upper limit is set to 70 [%] when the total amount of the binder and the reducing agent for making a sintered body is 30 [%] or less, which is industrially used when manufacturing a sintered body product. Does not meet molding and firing conditions. Slag is used in combination with hydraulic cements to form ettringite upon hydration, or Na. K. Etlingite is produced by reacting with an aqueous solution of an alkaline salt such as. Further, in the firing process, the exothermic reaction due to crystallization at 800 to 1000 [° C.] shortens the firing time to improve the productivity, and also has the effect of reacting with the chrome refractory to lower the sintering temperature. And 0.2 to 1.0 [%] in the slag
It is a component that can also effectively utilize the reducing action of the contained carbon and sulfur (S) in the high temperature range. As the current component, the composition is adjusted in inverse proportion to the cement content, but the slag is If it exceeds 20%, the sintering temperature becomes high, which is economically unfavorable, and the range of 10 to 15% is a preferable range. Hydraulic cements include gypsum, such as Portland cement, blast furnace cement, and alumina cement, and if it is contained in an amount of 15% or more, the strength characteristics of the sintered body deteriorate. If it is 4% or less, the production of ettringite from the water residue is delayed and the productivity is lowered even if a large amount of slag is used together. As the carbonaceous material, organic materials such as wood, paper, and starch can be used, but these materials have a narrow temperature range for maintaining the reduced state in the tissue during the firing process and Cr ^{+6 in the nascent} stage and the reducing action. However, as a result of various experiments, carbonaceous substances such as coal, coke and graphite are effective in the present invention. In particular,
The carbonaceous material that partially reacts with silicate glass such as coal ash (fly ash), and the carbonaceous material enclosed in the glassy structure such as slag is effective with Cr ⁺⁶ of the generator on the high temperature side. Invented to carry out a reduction action. Grace
The content of the carbon in the carbonaceous material is adjusted depending on the content of soluble chromates such as CrO _3, At a sintering process, 5 of CrO ₃ content in anticipation of loss in the loss oxidized in the baking surface portion You need 10 times. An excessive content of 10% or more is not preferable in terms of physical properties of the sintered body.
It is also within the technical scope of the present invention to add metal Al, Mg, or ions (S) as a reducing agent.

3. The soluble chromate present in the waste, which exists in a passive form, may be completely stabilized in the reduction temperature range of 600 [° C.] or lower, In this case, it is effective to add a small amount of metal such as Al to expand the reduction region to the high temperature side. 1,000 [℃] to stabilize the reducing action
Until it is baked in a strong reducing atmosphere.

4. A smoldering treatment using a raw fuel gas, which is generally known as a technique of smoldering roof tiles, is carried out to make a more complete insolubilized product in a state in which the whole sintered body is wrapped with a carbonaceous film, and It is beautiful, and cooling in the firing process is 600-9.
It is manufactured by performing a smoke treatment in a temperature range of 00 [° C.].

[0006]

[Operation] The features of the action of the present invention are: (1) Soluble chromate is present in a complicated state such as waste brick, and is in an inactive state, an aqueous solution of an alkali salt such as CaO. The first characteristic is that it is activated as a hydrate and temporarily fixed as a hydrate, and is effectively reduced and stabilized by capturing the Cr ⁺⁶ ion of the generator at the dehydration time of the bound water in the firing process. (2) The second characteristic is that the Cr ⁺⁶ ions of the generator are kept in a reduced state over a wide temperature range during the firing temperature ^raising process, and therefore, the compounding and molding are performed in the same manner as in the usual manufacturing process of a ceramic sinter. , Complete stabilization is performed in a consistent process of firing.

1. Considering the action of the composition in the production process, the content of soluble chromate is confirmed in advance to calculate the increasing amount of the reducing agent such as carbonaceous material, and the total amount is 100 weight [in total]. %]. The chromium-containing raw material needs to be crushed to have a particle size of 1 [mm] or less, and the slag is more effective if it is a fine powder and has a large surface area. The blending amount of hydraulic cement and slag is 35% or less with respect to these blends, and after mixing and kneading by adding fresh water so as to have proper molding water in the molding process, a small amount is obtained. Is also cured for 5 hours or more, and temporarily converted into hydrate containing ettringite as a main component.
A molded clay composition for adsorbing r ⁺⁶ ions by ion exchange is prepared, pressurized and molded using a mold having a predetermined shape, and dried. Firing up to 1000 [° C], at least CO gas 20
By firing in a firing atmosphere of [%] or more, a stable reducing action was achieved, and finally chromium could be bound in the spinel and stabilized. The reaction in the firing process was carried out by dehydrating the hydrate containing Cr ⁺⁶ ions to 250
It starts from around [° C] and continues to about 500 ° C. On the other hand, the carbon component serving as a reducing agent is 350 [° C]
Combustion heat generation starts in the vicinity, and about 50 in a reducing atmosphere.
Combustion occurs continuously up to 0 [° C], but especially those that adhere to silicate glass such as lime charcoal and are partly in the form of carbide even at 600 [° C] It was confirmed by a thermal analysis experiment that an exothermic reaction due to combustion remained, and it was possible to carry out the reducing action in the state where Cr ⁺⁶ in the ^nascent stage from the hydrate had the highest reaction activity. In this way, it can be confirmed by X-ray analysis and dissolution test that the soluble chromate becomes completely insoluble CrO ₃ at a temperature up to about 1000 [° C.]. After all, according to the method of the present invention, hexavalent chromium causes a sintering reaction with CaO, FeO and other silicates in the slag of the blast furnace at a high temperature of 1000 [° C.] to form chromium Cr ⁺³ and Fe. It is possible to obtain a stabilized sintered body as the contained composite solid solution.

[0007]

Example 1 The formulation was as follows. (A) A cement rotary kiln waste brick containing 0.3 [%] of CrO ₃ was crushed to 1 [mm] or less, and a weight ratio of 50 [%] was used. (B) Slag is 15% of finely pulverized powder to 44 [μ] or less (C) Fly ash is 20 [%] of powder of 20 [μm] or less including carbon content of 8.5 [%] (D) Portland cement 15 [%] The composition clay mixed by mixing at a mixing ratio of 15% or more, and mixed and kneaded with water 15%, was aged for 12 hours, and the aggregated agglomerated earth was 2 times. After crushing to less than [mm], 10 [c
200 [k] for a cube of m] x 20 [cm] x 1 [cm]
pressure molding at a pressure of g / cm ² ] and a temperature range up to 1000 [° C.] in a reducing atmosphere of CO gas 30 [%] of 10 [° C./min]
Firing at a heating rate of 1000 to 1200 [° C]
The sintered body was fired in an atmosphere of CO gas of 5% to obtain a sintered body. Bulk specific gravity 2.3 [g / cc] Bending strength 180 [kg
/ Cm ² ]. Further, regarding the above-mentioned waste, the processed product according to the first conventional technique and the processed product according to the present invention are Cr ^{+6 according to} JISKO102-65-2-1.
The dissolution comparison test was conducted. Based on the test method, 1 [kg] of waste brick was put into 5 [l] of clear water based on the above test method, boiled for 1 hour and left to stand for 5 days to elute, and the content in the eluate was measured. As a result, the Cr ^{+ 6} of the eluate of the first conventional technology treated product was 2.5 [ppm] with respect to the national elution acceptance standard of 0.5 [ppm] of the Prime Minister's Office. Cr ^{+6 in the} eluate was very different from that obtained by the conventional method, and almost no trace was observed.

[0008]

Example 2 The formulation was as follows. Waste brick 1 [%] or less Powder 35 [%] Slag powder 20 [%] Fly ash (containing 8.5 [%] carbon) 20 [%] Kibushi clay (containing 6.2 [%] coal) 15 [ %] Portland cement 10 [%] Physical properties of the bulk specific gravity of 2.1 [g / cc] bending strength of 220 [kg / cm] are the same as in Example 1 and fired under the same conditions.
² ]. Further, regarding the above-mentioned waste, the second conventional technique and the present invention are treated as JI.
A dissolution comparison test of Cr ⁺⁶ was performed by SKO102-65-2-1. The specific method was the same as in Example 1. As a result, the elution acceptance standard of 0.5 [p
pm], Cr of the eluate of the second prior art treated product
⁺⁶ was 1.9 [ppm], but almost no trace of Cr ^{+6 in} the eluate of the treated product of the present invention was observed.

[0009]

[Effect of the present invention]

(1) Promotion of environmental protection is an important theme worldwide today. As part of this, the present invention will utilize materials both from the viewpoint of safety treatment of waste that is harmful to living organisms and the utilization of unused resources. In other words, by converting soluble chromate into a long-term stable pollution-free substance by an extremely economical treatment method, it becomes a product with a high added value as ceramics for construction materials (brick pavement boards, tiles, etc.). To provide a completely new technology to do. It has the effect of two birds with one stone. (2) It is needless to say that none of the conventional techniques can meet the local elution regulation standard of 0.1 [ppm] in the amount of Cr ⁺⁶ elution, and the national permissible standard of the Prime Minister's Order is 0.5. When it does not pass [ppm], the treated product of the present invention has almost no trace of elution of Cr ⁺⁶ , so that it is said that an epoch-making remarkable effect is obtained as compared with the conventional one. You can This is an internationally important effect, especially in the present. (3) Currently, as a lining brick for cement kiln, while it has excellent characteristics that alternative materials other than chrome magnesia refractory are not found, as a measure against pollution of abandoned bricks, production and use of chrome mag refractory is decreasing. Among them, by completing these treatment technologies, it is possible to expect excellent economic effects for the entire high heat industry.

Claims (4)

[Claims] 1. Soluble chromate-containing material 30% by weight or more and 70% by weight or less, slag 4% by weight or more and 20% by weight or less, hydraulic cement 5% by weight or more and 15% by weight %] Or less, a silicate substance 13 wt% or more and 37 wt% or less, and a carbonaceous substance 0 wt% or more and 6 wt% or less, as components, and sinter-free.
Pollution-free sintered ceramics of soluble chromate characterized by: 2. The soluble chromate-containing pollution-free sintered ceramics according to claim 1, wherein the soluble chromate-containing material is a waste material of a chromium-based refractory and / or a smelting residue of a chromium ore. .. 3. A carbonaceous material in which the composition according to claim 1 is contained in a raw material mixture obtained on an anhydrous basis in an amount of 5 times or more and 10 times or less the weight of the soluble chromate in the raw material mixture. And one or more kinds of carbides selected from Al, Ng, and Si in an amount of 1/100 parts by weight or more and 3/10 or more by weight of the carbonaceous material.
0 parts by weight or less is added and blended, hydro-kneaded, and if necessary, cured under humid air, pressure-molded and dried, and then strongly reduced for at least 1 hour or more, up to 1000 [° C] in the temperature rising process. The flame atmosphere then exceeds 1000 [° C] and exceeds 1300
A method for producing a pollution-free sintered ceramics of soluble chromate, which comprises firing in an ordinary reducing flame atmosphere for 1 hour or more and 2 hours or less at [° C.] or less. 4. After each step of the manufacturing method according to claim 3, the sintered product is further heated to 600 [° C.] or more and 900 or more.
A method for producing pollution-free sintered ceramics of soluble chromate, which comprises performing smoldering firing in a temperature range of [° C.] or less and in a reducing atmosphere containing carbon fine particles.