JPS5940783B2 - Manufacturing method of hardened gypsum body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel method for producing a hardened gypsum body, and particularly to a method in which iron hydroxide is present when gypsum is kneaded with cement and solidified.

Recently, many factories have adopted a flue gas deflow process to prevent air pollution caused by sulfur oxides, and the amount of gypsum produced, including that produced from this process, has become staggering.

For this reason, research and development of new and more effective uses for gypsum are actively being conducted.

One of the effective uses of gypsum is as a building material.

For example, gypsum is mixed with cement, lime, etc., and the mixture is solidified into an oxidized product5.

In order to use it as a building material, it must be particularly strong (compressive strength,
However, a hardened material made by simply mixing and solidifying gypsum with cement, lime, etc. does not have sufficient strength.

The present inventors added various compounds when gypsum was kneaded with cement and solidified, and investigated the improvement of strength by adding various compounds.

As a result, it was found that the presence of iron compounds, especially hydroxides, significantly increases the strength of the resulting cured product.

The present invention is a method in which hydraulic cement is blended with gypsum, and if necessary, an early strengthening agent, a dispersant, and a set retardant are blended, water is added, mixed, molded, and hardened. A gypsum characterized in that ~80% by weight is replaced with iron hydroxide, and the cement is blended in an amount of 30 to 100 parts by weight per 100 parts by weight of the total solid content of gypsum and iron hydroxide;
This is a method for producing a cured product.

The hydraulic cement used in the present invention may be any ordinary cement such as Portland cement, blast furnace cement, or silica cement, and does not particularly need to be a quick-setting cement such as jet cement.

Examples of gypsum include gypsum recovered from other flue gas desulfurization processes for natural gypsum, and gypsum byproducts from wet phosphoric acid production and titanium dioxide pigment production; these include dihydrate gypsum,
It can be used in a wide variety of ways, not limited to hemihydrate gypsum.

One advantage of the present invention is that the gypsum does not need to be of high purity or high quality.

For example, waste sulfuric acid containing a large amount of iron discharged from the titanium dioxide pigment manufacturing process is simply neutralized with an alkaline substance such as lime without controlling the pH. Although various metal compounds derived from the above are contained as impurities, such gypsum compositions can also be used as they are.

In particular, if the iron content in this gypsum composition is hydroxide and the amount is within the range specified in the present application, there is no need to separately add iron hydroxide from outside the thread, and the present invention It is highly desirable as a raw material for gypsum.

In addition, if the content of iron hydroxide is insufficient than the specified amount in this application, just add the insufficient amount of iron hydroxide, and if it is too much, add gypsum and/or Cement can be added and used.

The iron hydroxide used in the present invention may be ferrous hydroxide, ferric hydroxide, or a mixture thereof.

In the method of the present invention, the above-mentioned gypsum and hydraulic cement are kneaded and solidified by adding water in the presence of iron hydroxide.

The amount of hydraulic cement is 30 to 100 parts by weight, preferably 4 parts by weight, per 100 parts by weight of the total solid content of gypsum and iron hydroxide.
It is 0 to 80 parts by weight.

Even if the amount of cement exceeds this range, no significant improvement in strength can be expected and it is not economical.

If it decreases, the strength will decrease, which is not preferable.

The amount of iron hydroxide is such that it can replace 10-80% by weight of the gypsum solids, preferably 20-60% by weight.

If the amount of iron hydroxide exceeds the above range, the fluidity of the kneaded product will deteriorate, making kneading difficult, and the resulting cured product will shrink undesirably.

Although it is possible to use a dispersant to improve the fluidity of the kneaded product, sufficient fluidity cannot be obtained with the usual amount used, and kneading is difficult unless the amount of water is increased.

On the other hand, if the amount of water is too large, the strength will decrease.

Furthermore, even if a large amount of dispersant is added, the strength of the cured product will decrease.

If the amount of iron hydroxide decreases, the effects of the present invention cannot be obtained.

Water is added so as to obtain a kneaded material with appropriate fluidity.

Mixing ratio of cement, type of gypsum, amount of iron hydroxide,
The amount of water required varies depending on the type and amount of aluminized substances, so it cannot be generalized, but for example, iron hydroxide is 10 to 10% of the solid content of gypsum and iron hydroxide.
When the solid content is 80% by weight and the cement content is 30 to 100% by weight, the amount of water added is about 0.3 to 1.2 times, preferably about 0.4 to 0.9 times, the solid content.

A hardened gypsum body is obtained by placing the kneaded product obtained in the manner described above in an arbitrary mold, curing in humid air for a predetermined period of time, and drying according to a conventional method.

The hardened gypsum body obtained by the method of the present invention has a strength suitable for use as a construction and civil engineering material.

Building materials and civil engineering materials are required to have excellent water resistance as well as strength, but in order to improve water resistance, aluminum compounds such as activated alumina and aluminum hydroxide are added at 0.0% per mole of plaster. The ettringite structure (3cao-A1203/3
It is also possible to produce a cured product of caso4.31-32H2o).

Example 1 100 parts by weight of dihydrate gypsum and a predetermined amount of Portland cement, manufactured by neutralizing waste sulfuric acid discharged in the sulfuric acid titanium dioxide pigment manufacturing process with calcium carbonate while controlling the pH to 4 or less, and having the composition shown in Table 1. A predetermined amount of iron hydroxide (ferric hydroxide) was placed in a universal mixer, water was added so that the amount was 1.2 times the amount of cement (based on weight), and the mixture was kneaded for 3 to 5 minutes.

After that, it was placed in a mortar form (vertical 4 crIL x horizontal 4 (m
%, temperature 25°C).

The compressive strength of the cured product obtained at this time was measured after a compression/tensile universal test.

In addition, the compressive strength of the cured product obtained by further drying the 7-day moist air-cured organisms for 28 days and the cured product dried at room temperature for 17 days was measured.

The results are shown in Table 2. As a comparative example, (5) the results of the cured product in the absence of iron hydroxide (in the presence of 0 iron hydroxide and in the case of mixing 0 titanium hydroxide and oxide) The compressive strength is also shown in Table 2.

Example 2 As raw gypsum, a gypsum composition obtained by neutralizing waste sulfuric acid from a sulfuric acid titanium dioxide pigment manufacturing factory with slaked lime without pH control is used, and iron hydroxide is not added from outside the threads. Except for the above, the mixture was kneaded with Portland cement and solidified in the same manner as in Example 1 to obtain a hardened gypsum body.

This product was cured in a humid air for 28 days in the same manner as in Example 1, and then dried at room temperature for 17 days, after which the compressive strength was measured and the results shown in Table 4 were obtained.

For comparison, the strength of a hardened body obtained by solidifying and molding the gypsum of Cloth 1 only with cement without adding iron hydroxide is also shown in Clothing 4.

Moreover, the composition of the above-mentioned gypsum composition used here is as shown in Table 3.

In the table, the iron content is listed as Fe2O3, but judging from the manufacturing process of the gypsum composition, it is clear that the iron content is in the form of hydroxide, and in fact, analysis by X-ray diffraction shows that the iron content is in the form of hydroxide. No peak appeared, indicating hydroxide.

In Table 4, the amount of hydroxide was 25.94 parts by weight. In Example 8 and Comparative Example, the strength of the Comparative Example was greater, but in the case of Comparative Example, the hardened product The strength is greater because the amount of cement in the sample is greater than that in Example 8.

Therefore, it is necessary to compare Example 6 and Comparative Example, both of which have the same proportion of cement, and it can be seen that the strength of the cured product of the present invention is significantly improved.

Example 3 * In order to improve the water resistance of the cured product of the present invention, a predetermined amount of activated alumina was added to the cured product obtained at the same blending ratio as in Example 7 of Example 2. The results shown in Table 5 were obtained.

In addition, the cured product used here (4cIIlX4CTL×4
crIL) has a surface area of 96 ffl, and this
The sample was left standing in 00ml of water, and the amount of gypsum elution was measured every week and the water draining was updated.

In the above table, the elution rate is the ratio of the amount of gypsum eluted to the amount of gypsum in the hardened body (expressed as a percentage).

Claims (1)

[Claims] 1. Mix hydraulic cement with plaster, add early strengthening agent, dispersant, and setting retardant as necessary, add water to mix wires,
In the molding and curing method, the gypsum solids content is 10 to 8.
0% by weight is replaced with iron hydroxide, and cement contains 30 to 1 part by weight per 100 parts by weight of the total solid content of gypsum and iron hydroxide.
A method for producing a hardened gypsum body, characterized in that 00 parts by weight are blended.