JPS6366786B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the effective use of waste sulfuric acid discharged from the sulfuric acid method titanium oxide production process and so-called pickling waste sulfuric acid discharged from the pickling process of steel materials. The waste sulfuric acid used as a raw material in the present invention becomes a source of pollution if discharged outside the factory as it is, so gypsum has been produced by diluting it. However, since the reaction is carried out after dilution, the equipment becomes large and treatment of iron-containing wastewater is also required, which is disadvantageous in terms of economy. Therefore, the present inventors conducted various research on methods for obtaining compounds useful as raw materials without diluting waste sulfuric acid, and as a result, we found that waste sulfuric acid containing Fe ²⁺ ions and having a free sulfuric acid concentration of 240 g/ or more was oxidized in advance. to make a sulfuric acid solution containing Fe ³⁺ ions, and add Ca agent and Al to this solution.
The present invention was completed based on the discovery that a cured composition having a strength suitable for use as a material for civil engineering and construction can be obtained by reacting an agent with a compound. The feature of the present invention is that free sulfuric acid (hereinafter referred to as F) in waste sulfuric acid is
- abbreviated as H ₂ SO ₄ ). In other words, waste sulfuric acid discharged from the sulfuric acid method titanium oxide manufacturing process and so-called pickling waste sulfuric acid discharged from the pickling process of steel materials exist in various concentrations, but as a result of various studies, F
- If the H ₂ SO ₄ concentration is not 240 g/ or more, Ca agent and Al
The objective of the present invention cannot be achieved because the reaction product with the agent contains a large amount of free water and the cured composition does not have sufficient strength. However, even if waste sulfuric acid has a F-H ₂ SO ₄ concentration of 240g/or less, it can be concentrated by an appropriate method and F-
It goes without saying that it can be used in the present invention if the H ₂ SO ₄ concentration is 240 g/or higher. The present invention will be explained in detail below. The waste sulfuric acid used as a raw material has a F-H ₂ SO ₄ concentration of 240g/
Use the above. In addition, the waste sulfuric acid discharged from the sulfuric acid method titanium oxide production process and the so-called pickling waste sulfuric acid discharged from the steel pickling process are
Oxidizing agent known because it exists in the state of Fe ²⁺ ions,
For example, oxidize with oxygen, sodium perchlorate, etc. to form Fe ³⁺
It needs to be ionized. The reason for changing Fe ²⁺ ions to Fe ³⁺ ions is
This is to ensure that it exists as stable Fe(OH) ₃ in the cured composition, which will be described later. Divalent Fe(OH) ₂ oxidizes when left in the air, lowering the PH of the cured composition and reducing its strength. It is from. When a predetermined amount of the thus obtained waste sulfuric acid containing Fe ³⁺ ions is placed in a mixer, such as a kneader, and a neutralizing equivalent or more of Ca agent and an appropriate amount of Al agent are added to all the sulfuric acid groups in this solution while stirring. The reaction proceeds exothermically, and after kneading for 10 to 30 minutes, a hard cured composition is obtained when left for several hours. The order of addition of the Ca agent and the Al agent is not particularly limited, and the Ca agent and then the Al agent may be added to the waste sulfuric acid, or vice versa, or they may be added simultaneously. The Ca agents used here are calcium carbonate (CaCO ₃ ), quicklime (CaO), and slaked lime (Ca(OH) ₂ ).
Especially in the case of quicklime, the heat of neutralization is large and the temperature of the reactants rises, the reaction rate becomes faster and water evaporates, producing a cured product with less free water. It is particularly suitable because the strength also increases. In the case of calcium carbonate and slaked lime, the heat of reaction is relatively small, but the reaction proceeds sufficiently and a product with sufficient strength is obtained. The amount of Ca agent used must be at least the neutralization equivalent of total sulfuric acid (hereinafter abbreviated as T-H ₂ SO ₄ ); if it is less than the equivalent, the cured composition will become acidic and the strength will increase due to the amount of free water. low. The preferred range is T-
It is 120 to 150% of the equivalent amount of H ₂ SO ₄ , and even if it is used in an amount of 150% or more, the increase in strength is not so large and it is not economical. The Al agent used is one or two of fly ash and alumina cement, both of which have soluble Al as a main component, and fly ash is particularly preferred from the economic point of view. Fly ash is a by-product of coal combustion in coal-fired power plants, and its chemical components include SiO ₂ and Al ₂ O ₃ as main components, including the following components: _SiO2 52-58%, _{Al2O3 25} %, _{Fe2O3 3-6} %,
MgO 1-2%, CaO3-7% Alumina cement is mainly composed of Al ₂ O ₃ and CaO, and is composed of the following components, for example. Al ₂ O ₃ 49%, CaO 40%, Fe ₂ O ₃ 4.5%, SiO ₂ 4%,
MgO0.5% These Al agents contain Al ₂ O ₃ in their components.
mainly contributes to the curing reaction, and the amount to be used is determined based on the Al ₂ O ₃ content. The amount of the Al agent used is sufficient to be less than the neutralization equivalent of T--H ₂ SO ₄ and is preferably in the range of 20 to 50% of the neutralization equivalent. If it is less than 20%, the strength of the cured composition will be low, and if it is more than 50%, the strength will not increase so much and it is not economical. The cured product obtained in the present invention is a novel dihydrate-ettringite-ferric hydroxide cured composition. The free moisture content of the cured composition obtained by the present invention is 35%
It has a uniaxial compressive strength of 3 kg/cm ² or more, and is suitable for use as landfill soil as it is, as well as for road construction. It can also be molded into building materials such as architectural wall materials and floor materials. The treatment method of the present invention does not generate any liquid or so-called waste water, and is a rational and economical method for completely treating waste sulfuric acid. In this way, the present invention aims to effectively utilize waste sulfuric acid, which is a source of pollution, as a raw material, and to efficiently obtain a useful cured composition. This will be explained in detail below using Examples. Example 1 Waste sulfuric acid (F-H ₂ SO ₄ 300g/, T-H ₂ SO ₄ 383g/,
_{NOx at} 40℃ in 1 ^m3
Convert _FeSO4 to _Fe2 by blowing _O2 gas in the presence of gas
Oxidized to (SO ₄ ) ₃ . The obtained Fe ³⁺ ion-containing waste sulfuric acid (hereinafter abbreviated as oxidized waste acid) had the following composition. (F-H ₂ SO ₄ 273g/, T-H ₂ SO ₄ 383g/,
Fe ₂ (SO ₄ ) ₃ 152g/) This oxidized waste acid 1 was separated into 3 beakers and 390g of calcium carbonate was added under stirring to form CaSO ₄ .
A brown slurry containing 2H ₂ O and Fe(OH) ₃ was obtained. Next, the entire amount of this slurry was transferred to a kneader, and 58 g of slaked lime and fly ash (25% by weight as Al ₂ O ₃ ) were added.
Add 106g of (containing) at the same time, mix well for 10 minutes, pour the kneaded mixture into a mold with a diameter of 50mm and a height of 100mm, and store it in a sealed container for one week.
Unconfined compressive strength was measured according to JISA1216. The compressive strength was 3.1Kg/cm ² . Also, the free water content of the cured composition was 35%. Examples 2 to 6, Comparative Examples 2 to 3 Using the same oxidized waste acids prepared in Example 1, experiments were conducted in the same manner as in Example 1, but under various conditions. The results are shown in Table 1.

[Table] Comparative example 1 F-H ₂ SO ₄ 203g/, T-H ₂ SO ₄ 257g/,
The so-called pickling waste sulfuric acid 1 containing 83 g/FeSO ₄ was heated to 40° C., and O ₂ gas was blown into it in the presence of NO _X gas to oxidize FeSO ₄ to Fe ₂ (SO ₄ ) ₃ . The obtained oxidized waste acid had the following composition. (F-H ₂ SO ₄ 176g/, T-H ₂ SO ₄ 257g/,
Fe ₂ (SO ₄ ) ₃ 109g/) Oxidized waste acid was charged into a kneader, and while stirring, 262g of calcium carbonate, 39g of slaked lime, and 71g of fly ash were added.
After kneading for 10 minutes, the mixture was poured into a mold in the same manner as in Example 1, and stored in an airtight container for one week.
Unconfined compressive strength was measured. The unconfined compressive strength of the cured composition is as low as 0.9Kg/ ^cm2 ;
Free moisture reached 43%. Generally, it is said that unconfined compressive strength of 3 Kg/cm ² is required for landfill soil and road subgrade soil, and the cured composition of Comparative Example 1 cannot withstand this use. Example 7 The same oxidized waste acid 1 prepared in Example 1 was placed in a kneader, and 328 g of quicklime was added uniformly over 5 minutes, followed by reaction with stirring. After 4 to 5 minutes, a rapid reaction occurred and steam was generated violently. Subsequently, 265 g of fly ash (containing 25% as Al ₂ O ₃ ) was added and kneaded for 10 minutes.
It was molded into a size of 500 mm x 400 mm (thickness x width x length), stored in an airtight container for one week, and removed from the mold to obtain a cured composition. The free moisture content of the resulting cured composition was 11%. This cured composition was heated to release free moisture in an air bath at 45°C.
Dried to 2.0%. When the obtained dried product was subjected to a bending test according to the bending test method JISA-1408 for architectural boards, the bending failure load was 55 kg.
It was hot. This value is sufficient to withstand use as a construction board, etc.

Claims (1)

[Claims] 1 Contains Fe ²⁺ ions and has a free sulfuric acid concentration of 240
1. A method for producing a curing composition, which comprises pre-oxidizing waste sulfuric acid in an amount of 1.5 g/g or more to obtain a sulfuric acid solution containing Fe ³⁺ ions, and reacting this solution with a Ca agent and an Al agent. 2. The method according to claim 1, wherein the waste sulfuric acid is waste sulfuric acid discharged from a sulfuric acid method titanium oxide manufacturing process and so-called pickling waste sulfuric acid discharged from a pickling process of steel materials. 3. The method according to claim 1, wherein the Ca agent is one or more selected from the group of calcium carbonate, quicklime, and slaked lime. 4. The method according to claim 1, wherein the Al agent is one or more selected from the group of fly ash and alumina cement. 5 Ca agent with a neutralization equivalent of 120 to 150% of the total sulfate radicals (SO ^2- ₄ ) in the waste sulfuric acid and 20% of the neutralization equivalent with respect to the total sulfate radicals (SO ^2- ₄ ) in the waste sulfuric acid The method according to claim 1, wherein ~50% of the Al agent is reacted.