JP4944851B2 - Method for producing hydraulic composition - Google Patents

Description

  The present invention relates to a hydraulic composition excellent in hexavalent chromium fixing ability and a method for producing the same.

  When processing waste containing hazardous substances, it is obliged to detoxify it by some means. Cement has the ability to fix toxic substances such as heavy metals, so it is used for the solidification of hazardous waste, but more than 99.99% of general heavy metals can be fixed, while hexavalent chromium is fixed a little. The rate is said to be low.

Addition of blast furnace slag is effective for improving the fixation rate of hexavalent chromium, but the effect is low at the initial stage of cement hydration, and the hexavalent chromium fixation rate is about 99.0%. Improvement of the fixation rate was desired. In addition, there is a technology to reduce hexavalent chromium to poorly soluble trivalent chromium by adding a reducing agent such as ferrous sulfate (FeSO ₄ ) to the cement. There was a problem that the effect of ferrous iron was lowered, the effect was lowered after the cement was hardened, and when the addition amount was large, the setting of the cement was delayed, and the physical properties of the cement were also adversely affected. For this reason, it is desired to develop a technology for fixing hexavalent chromium in cement, which can be effective for a long time with the use of a smaller amount of additive and does not affect the physical properties of the cement. It was.

  Accordingly, an object of the present invention is to provide a hydraulic composition in which the fixing ability of hexavalent chromium is remarkably improved by using a very small amount of an additive which does not change the physical properties of cement.

The present inventors view of such circumstances, the result of extensive studies to develop a superior hydraulic composition to a fixed capacity of the hexavalent chromium, elemental sulfur be blended into a hydraulic material, without the drawbacks, The inventors found that a hydraulic composition excellent in hexavalent chromium fixing ability was obtained, and completed the present invention.

The present invention is formulated in the manufacturing process of the hydraulic composition, at any stage to grinding before milling hydraulic materials, elemental sulfur, 10 ppm or more with respect to the dry weight of the binding components of the hydraulic composition A method for producing a hydraulic composition for immobilizing hexavalent chromium, the method comprising producing a hydraulic composition for immobilizing hexavalent chromium, wherein the temperature of the hydraulic material during pulverization is 35 to 110 ° C. It is to provide.

The hydraulic composition produced according to the present invention has a high ability to fix hexavalent chromium even if the amount of the additive is small. In addition, this effect is exhibited before the hydraulic material is cured, and continues even after the curing.

The mechanism of fixation of hexavalent chromium in the present invention is considered to be due to reduction of hexavalent chromium by elemental sulfur and conversion to trivalent chromium. Hexavalent chromium is known to be highly water-soluble, and when it is contained in a hydraulic composition, it elutes not only before its hardening but also slightly after hardening when its structure is densified. On the other hand, trivalent chromium is hardly soluble, and precipitates easily in a high pH state such as cement, and hardly leaches out of the system even before curing.

The time when the reduction effect due to elemental sulfur is expressed depends on its fineness, and when it is necessary to reduce hexavalent chromium at an early stage, it is desirable to increase the degree of fineness of elemental sulfur . A preferable fineness is a Blaine specific surface area of 3000 to 15000 cm ² / g, particularly preferably 9000 to 15000 cm ² / g.

Cement is mentioned as a hydraulic material which is the object of blending elemental sulfur , and more specifically, Portland cement, jet cement, alumina cement, white cement, mixed cement, belite cement, eco-cement, etc. . Here, Portland cement includes normal Portland cement, early strength, moderate heat, white color, ultra-early strength, sulfate-resistant cement, etc., and jet cement contains super-fast hardening containing calcium fluoroaluminate. Cement and mixed cement include slag cement, fly ash cement, silica cement, blast furnace slag cement, cement containing fine limestone powder, and the like. Belite cement is a special cement with low heat build-up, and ecocement is a calcined product made from one or more types of waste incineration ash such as municipal waste incineration ash and sewage sludge incineration ash. A cement made of a fired product containing one or more of calcium carbonate, calcium fluoroaluminate, calcium aluminate, and calcium silicate.

The content of elemental sulfur in the hydraulic composition of the present invention, the dry weight of the binding components of the hydraulic composition to be more 10 ppm, preferably in order to effectively secure the hexavalent chromium, Further, it is preferably 100 ppm or more, particularly 1000 ppm or more. The term “binding component” as used herein refers to a component having a binding function in the presence of water such as a cement component, a blast furnace slag, and a latent hydraulic substance in the hydraulic composition.

  The hydraulic composition of the present invention may contain a non-binding component in addition to the above-described binding component. Examples of the non-binding component include sand, gravel, or coal ash used as an alternative to the sand. And various fine aggregates such as molten slag and coarse aggregates. Further, a reducing agent such as ferrous sulfate may be added as a non-binding component. In particular, ferrous sulfate has an effect of enhancing the reduction of chromium in the mixture of the hydraulic composition of the present invention and the waste that has not yet solidified.

  The hydraulic composition of the present invention further includes an AE agent, an AE water reducing agent, a water reducing agent, a high performance water reducing agent, a coagulation adjusting agent, an anti-proofing agent, which are usually used for the purpose of improving rheological properties, rust prevention and other purposes. Various admixtures such as a rusting agent may be used in combination.

Moreover, the reduction effect of hexavalent chromium by the blending of simple sulfur depends on the temperature of the hydraulic material at the time of blending or after blending, and the temperature is preferably 35 to 110 ° C. When the addition temperature is less than 35 ° C., the hexavalent chromium reducing effect is low, and when the addition temperature exceeds 110 ° C., the alkali sulfate in the hydraulic material is dehydrated and adversely affects the physical properties.

The timing of adding the elemental sulfur to the hydraulic material is not particularly limited, and may be any stage from before the hydraulic material is pulverized to kneading with water. However, when the hydraulic material is cement, the cement at the time of pulverization is used. The temperature in the mill is usually controlled at about 90 to 110 ° C., and from the viewpoint of the relationship between the reduction effect of hexavalent chromium and the temperature described above, if added before or simultaneously with the grinding of the hydraulic material, Since it heats to the said temperature at the time of subsequent grinding | pulverization, a separate heat source is not required and it is preferable.

  Hazardous waste containing hexavalent chromium to which the present invention is applicable is not particularly limited, but various dust generated from incineration ash, etc., various incineration ash generated from incineration of sludge and municipal waste, metal and plastic, waste water Examples include various sludges and various waste liquids generated during treatment and sewage treatment.

  In order to immobilize harmful substances using the hydraulic composition of the present invention, the binding component and the hazardous waste in the hydraulic composition of the present invention are mixed in advance, and kneaded water is added thereto for kneading. A typical method is to add a non-binding component as necessary. When sufficient mixing cannot be performed by the above procedure due to the properties of hazardous waste, etc., the hydraulic composition of the present invention, hazardous waste and kneaded water can be mixed simultaneously. Further, a hazardous waste and water may be mixed in advance, and the hydraulic composition of the present invention may be added thereto. That is, finally, if the binding component in the hydraulic composition of the present invention, the non-binding component added as necessary, hazardous waste and kneaded water are sufficiently mixed, the order of mixing is It doesn't matter.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated still in detail, this invention is not limited to this.

Reference example 1
Ordinary Portland cement with chemical composition shown in Table 1, sulfur pure drug 0, 10, 100, 1000 or 10000 ppm, iron sulfide (FeS) or sodium sulfite (Na ₂ SO ₃ ) 1000 ppm as sulfur, or Table 2 A hydraulic composition of the present invention was prepared by blending 2% (100 ppm as sulfur) of municipal waste molten slag having a chemical composition. This composition was mixed with sludge having the chemical composition shown in Table 3 at a weight ratio of 10:90. Further, this mixture and water were kneaded at a weight ratio of 2: 1. The kneading was performed with a Hobart mixer, and after kneading, it was sealed and cured at 20 ° C. until the age of 28 days.

  The cured body after curing was subjected to a dissolution test according to Environmental Agency Notification No. 13. That is, the particle size of the hardened cement was adjusted to 0.5 to 5.0 mm, mixed with 10 times as much water as the hardened cement, and shaken at 20 ° C. for 6 hours. The filtrate after shaking was analyzed by ICP spectroscopic analysis to determine the elution amount of hexavalent chromium. The results are shown in Table 4.

  In ordinary cement to which no sulfur substance having a sulfur atom with an oxidation number of 4 or less was added, 20.5 ppm out of 1200 ppm hexavalent chromium contained in the sludge. On the other hand, in the cement added with 10 ppm of sulfur, the elution amount of hexavalent chromium decreased to 15.0 ppm and to 1.3 ppm when added 100 ppm. Moreover, when 1000 ppm and 10000 ppm were added, they were 0.12 and 0.11 ppm, and when 1000 ppm or more was added, there was no significant difference. When 1000 ppm of iron sulfide was added as sulfur, the elution amount of hexavalent chromium was 0.14 ppm, which was almost the same as that obtained with sulfur pure drug. When 1000 ppm of sulfur was added as sodium sulfite, the elution amount of hexavalent chromium was 0.21 ppm, and the elution amount increased slightly compared with the case of sulfur pure drug. In addition, when 100 ppm of sulfur was added as municipal waste molten slag, the elution amount of hexavalent chromium was 1.5 ppm, and the elution amount increased slightly compared to the case of sulfur pure drug.

Example 1
Ordinary portland cement clinker prior to grinding of the chemical compositions shown in Table 1, the sulfur Junyaku was 1000ppm added 1000 or 10000 ppm, or sodium sulfite (Na2 SO3) as a sulfur was added further 2% by weight of gypsum as a SO ₃ The hydraulic composition of the present invention was prepared by pulverizing with an experimental mill. The temperature during this pulverization was 40 ° C. This composition was mixed with sludge having the chemical composition shown in Table 3 at a weight ratio of 10:90. Further, this mixture and water were kneaded at a weight ratio of 2: 1. The kneading was performed with a Hobart mixer, and after kneading, it was sealed and cured at 20 ° C. until the age of 28 days.

  The cured body after curing was subjected to a dissolution test according to Environmental Agency Notification No. 13. That is, the particle size of the hardened cement was adjusted to 0.5 to 5.0 mm, mixed with 10 times as much water as the hardened cement, and shaken at 20 ° C. for 6 hours. The filtrate after shaking was analyzed by ICP spectroscopic analysis to determine the elution amount of hexavalent chromium. The results are shown in Table 5.

  In the hydraulic composition to which 1000 ppm of sulfur pure drug was added, the elution amount of hexavalent chromium was 0.03 ppm, which was about a quarter of that in the case of the same sulfur addition amount in Table 4. Moreover, even when 10000 ppm of sulfur pure drug was added, the elution amount of hexavalent chromium was 0.02 ppm, and there was no significant difference. When 1000 ppm of sulfur was added as sodium sulfite, the elution amount of hexavalent chromium was 0.04 ppm, and the elution amount increased slightly compared to the case of sulfur pure drug. It could be confirmed.

Claims (1)

Hexavalent chromium containing 10 ppm or more of elemental sulfur with respect to the dry weight of the binding component in the hydraulic composition at any stage of the hydraulic composition manufacturing process, from before grinding to grinding. A method for producing a hydraulic composition for fixing hexavalent chromium, comprising a method for producing a hydraulic composition for immobilization, wherein the temperature of the hydraulic material during pulverization is set to 35 to 110 ° C.