JPH01219049A - Additive for cement and its production - Google Patents

Abstract

PURPOSE:To obtain an additive to cement which is not impaired in its effect even when it is used together with another cement additive such as water reducing agent, etc., by using waste liquid produced by the decyanation and/or desulfurization of coke oven gas, wherein said cement additive consists primarily of alkali thiocyanate and contains substantially no carbonate ion. CONSTITUTION:Waste liquid contg. ammonium thiocyanate or alkali thiocyanate discharged from a decyanation stage and/or desulfurization stage of coke oven gas is heated under normal pressure. Thus, water is distilled and CO3<2-> ions are removed substantially. Then, an alkali hydroxide such as NaOH, etc., or carbonate, etc., is added to said waste liquid freed of CO3<2-> ions, and NH4 salt is transformed to alkali metal salt by double decomposition. By this method, an inexpensive cement additive consisting primarily of alkali thiocyanate as primary component and contg. substantially no CO3<2-> ion, is obtd.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a cement additive obtained from a waste liquid discharged from a process in which coke oven gas is decyanized and/or desulfurized with an aqueous absorption liquid containing alkali ions; and its manufacturing method.

(Prior art and problems to be solved by the invention) In the past, calcium chloride, which is inexpensive and highly effective, has been used as a cement additive to promote the strength development of cement compositions or to prevent freezing at low temperatures. has been commonly used. However, since it has been found that chloride ions have the disadvantage of causing rust in the reinforcing bars in concrete, the use of calcium chloride in cement compositions is now strictly regulated.

The use of thiocyanates as chloride-free cement additives has been known for a long time [German Patent No. 578,716 (1933)]; The drawback is that it is difficult to use as an additive.

As a countermeasure, alkali metal-based or alkaline earth metal-based treatment obtained by processing coke oven gas by the Fumax-Rodax method? A cement composition characterized by containing 0.02 to 2.0% by weight of fi, (from which suspended matter such as free sulfur has been removed) in terms of solid content (Japanese Unexamined Patent Publication No. 61-286253 Alternatively, an amount of calcium hydroxide sufficient to convert the entire amount of ammonium salts in the waste liquid into calcium salts is added to a coke oven gas wet desulfurization liquid containing ammonium thiocyanate and ammonium thiosulfate to form a reaction mixture. A method characterized in that the ammonia produced in the reaction mixture is removed from the reaction mixture at a temperature at which the thiosulfate in the reaction mixture does not thermally decompose (JP-A-62-2
The use of inexpensive thiocyanates has been proposed, such as in Japanese Patent Publication No. 46811).

If the coke oven gas wet desulfurization waste liquid is an ammonia-based waste liquid, it can be subjected to a double decomposition reaction with an alkali metal hydroxide or carbonate to convert it into an alkali metal thiocyanate. When other cement additives coexist, precipitation occurs, which reduces the intended effect of the additives and significantly impairs commercial value.

The inventors of the present invention have made the following findings as a result of extensive testing and research in order to eliminate the above-mentioned drawbacks of the aqueous solution of alkali metal thiocyanate obtained from the wet desulfurization waste liquid of coke oven gas. In other words, carbon dioxide contained in the gas is dissolved in the wet desulfurization waste liquid of coke oven gas, and when ammonia-based desulfurization waste liquid is metathesized to alkali metal salts, alkali metal carbonates or carbonic acid When a hydrogen salt is used, carbonate ions will be present in the liquid.

On the other hand, other additives such as water-reducing agents such as lignin sulfonates, oxycarboxylate salts, and phosphorus sulfonates are often used in cement, but recently it has become difficult to add these as calcium salts. many. Therefore, we have discovered that carbonate ions contained in an aqueous solution of alkali metal thiocyanate react with these calcium ions, producing calcium carbonate precipitates, resulting in the above-mentioned disadvantages, and have completed the present invention. be.

(Means for Solving the Problems) Here, in its ILi aspect, the present invention provides thiocyanide produced from ammonium thiocyanate or alkali metal salt-containing waste liquid discharged from a coke oven gas decyanization and/or desulfurization process. It is a cement additive whose main component is an acid alkali metal salt and does not substantially contain carbonate ions.

According to another aspect, the present invention decarboxylates an ammonium thiocyanate or alkali metal salt-containing waste liquid discharged from a coke oven gas decyanization and/or desulfurization process, and when the liquid contains an ammonium thiocyanate salt. The method includes converting the ammonium salt into an alkali metal salt by double decomposition with at least one compound selected from alkali metal hydroxides, carbonates, and hydrogen carbonates before or at the same time as the decarboxylation. The present invention is characterized by a method for producing a cement additive containing an alkali metal thiocyanate as a main component and containing substantially no carbonate ions.

(Function) Examples of decyanization and/or desulfurization treatments for coke oven gas that produce waste liquid containing thiocyanate include the following.

(1) Cyanide treatment in which coke oven gas is washed with a sulfur suspension and/or a polysulfide-containing solution.

When a sulfur suspension is used, polysulfides are first formed by reaction with hydrogen sulfide in the coke oven gas. Cyanide removal occurs when cyanide reacts with polysulfides and is absorbed into the liquid as thiocyanate. When an absorption liquid containing alkali metal ions is used, such as when sodium is used as an alkali source, an alkali metal thiocyanate salt is produced. When alkali metal ions are not present in the absorption liquid, ammonium thiocyanate salt is produced by absorbing ammonia in the coke oven gas into water. This decyanation treatment yields a solution containing less sulfur-containing compounds (eg, thiosulfate ions, etc.) other than thiocyanate.

(2) Desulfurization treatment in which coke oven gas is washed with an alkaline aqueous solution (wet desulfurization of coke oven gas), #1 reduction catalyst (
When using an alkaline absorption liquid containing sodium naphthoquinone sulfonate, picric acid, sodium anthraquinone sulfonate, etc., hydrogen sulfide is removed as colloidal sulfur and the catalyst is regenerated by oxidation. At this time, other acidic gases (HCN, Gol, etc.) are also absorbed at the same time, so that desulfurization and decyanization are achieved simultaneously. The absorption liquid is recycled and used, but since thiocyanate and thiosulfate produced by side reactions accumulate in the liquid, a portion of the absorption liquid is extracted and used as waste liquid. Therefore, in addition to thiocyanate ions, thiosulfate ions and sulfate ions are present in this waste liquid as alkali metal salts or ammonium salts depending on the type of alkali ions present.

The above-mentioned waste liquids are representative examples, and other appropriate coke oven gas decyanization and/or desulfurization waste liquids containing ammonium thiocyanate or alkali metal salts can be used.

As an additive for accelerating cement hardening, alkali metal salts of thiocyanate are suitable because alkali metal salts are more effective and the presence of ammonium ions makes it difficult to use in the field due to the ammonia odor. Therefore, when the thiocyanate contained in the desulfurization and/or desulfurization waste liquid to be used is an ammonium salt, metathesis with at least one compound selected from alkali metal hydroxides, carbonates, and hydrogen carbonates is required. It is converted into an alkali metal salt by reaction and used as an additive for cement. Although potassium and the like can be used as the alkali metal, it is preferable to use sodium.

The metathesis reaction between ammonium thiocyanate and an alkali metal hydroxide, carbonate, and hydrogen carbonate will be described below, taking as an example the case where the alkali metal is sodium.

? 1LSCN+NaOH-+Na5CN+Nus+Ht
O2NHJSCN + NazCO3→2NaSCN
+ (Nut)zcOsNHJCM + NaHCOs
=NaSCN + NLHCOsIf ammonium thiosulfate is present, it undergoes double decomposition in the same manner as above to produce an alkali metal thiosulfate salt.

Therefore, when carbonate or hydrogen carbonate is used as the alkali metal compound, carbonate ions will remain in the liquid.

On the other hand, since coke oven gas contains a considerable amount of carbon dioxide gas, carbon dioxide gas is dissolved in the desulfurization or decyanization waste liquid of coke oven gas. Therefore, even when hydroxide is used as the alkali metal compound in the metathesis described above, a considerable amount of carbonate ions derived from dissolved carbon dioxide still exist in the liquid. As mentioned above, this carbonate ion causes disadvantages when used as a cement additive, so in the present invention, the obtained solution is decarboxylated by an appropriate method to substantially remove carbonate ions from the liquid. do.

If this carbonate ion exists in the form of an ammonium salt, that is, ammonium carbonate or ammonium hydrogen carbonate, it easily decomposes into ammonia and carbon dioxide gas by heating and volatilizes from the liquid. Removal is easy. However, when carbonate ions are present as alkali metal carbonates or hydrogen carbonates, it is not easy to remove carbonate ions from the liquid by heating alone, and dissolved carbonate ions remain in the liquid.

Therefore, when the waste liquid contains an ammonium salt, the amount of the alkali metal compound added in the waste liquid is If the amount is equivalent to the total amount of thiocyanate and thiosulfate and other sulfur oxysates that may be present in small amounts,
Since all carbonate ions in the liquid exist as ammonium carbonate or ammonium hydrogen carbonate, this is convenient for removing ammonia and carbonate ions. However, in reality, the alkali metal compound is usually added in an excessive amount. In that case, an alkali metal carbonate and/or bicarbonate will be present. Further, even when the alkaline content in the waste liquid is not an ammonium salt but an alkali metal salt, such as a sodium salt, dissolved carbonate ions exist as an alkali metal carbonate or a hydrogen carbonate.

Under these circumstances, as a result of examining methods for removing carbonate ions existing as alkali metal carbonates or hydrogen carbonates, that is, decarboxylation, the pH decreased to 9 or less, preferably 8 or less, and more preferably 6 or less. It has been found that carbonate ions can be removed efficiently and easily by adding acid in this manner. Examples of acids that can be used include sulfuric acid, nitric acid, nitrous acid, formic acid, and acetic acid, and these can be used alone or in a mixture of two or more. Decarboxylation will be more complete if the pH is lowered and then reduced pressure, heating, rapid stirring, bubbling, etc. are performed.

The order of decarboxylation and salt conversion by the metathesis reaction described above is not particularly limited, and decarboxylation can be performed before or after salt conversion, or simultaneously. However, it will be appreciated that when alkali metal carbonates or bicarbonates are used in metathesis, it is preferable to defer decarboxylation.

If free sulfur or sulfide is present in the obtained alkali metal thiocyanate solution, it is preferable to remove these by appropriate means. For example, small amounts of dissolved sulfide can be removed by oxidative treatment (eg, air aeration or treatment with an oxidizing agent such as hydrogen peroxide) to precipitate free sulfur. Free sulfur can be removed by any suitable means such as filtration. Sulfide removal is preferably carried out after the metathesis reaction.

When wet desulfurization waste liquid from coke oven gas is used, a considerable amount of thiosulfate coexists in the solution in addition to thiocyanate as mentioned above, but the dissolved thiosulfate ion is particularly important for use as a cement additive. There is no problem. However, if you want to remove thiosulfate, add calcium hydroxide or calcium oxide in an amount equivalent to the sulfur oxylate such as thiosulfate present in the solution and heat it to about 60°C. The sulfur oxylate preferentially reacts with calcium and decomposes into free sulfur and calcium sulfite, which precipitate. Therefore, by removing these precipitates, thiosulfate can be substantially removed. This treatment is preferably carried out when the content of thiosulfate is high.

Since it is more convenient for cement additives to be in liquid form, the solution containing an alkali metal thiocyanate as a main component can be used as is by simply concentrating or diluting it as necessary. Note that when the residual ammonia content is large, it is preferable to remove ammonia by appropriate means such as heating under reduced pressure.

(Effects of the Invention) According to the present invention, a cement additive containing an alkali metal thiocyanate as a main component can be produced at low cost from desulfurization and/or desulfurization waste liquid of coke oven gas.

This cement additive is substantially free of carbonate ions, so when used in conjunction with other cement additives such as water reducers, it reacts with them and impairs the effectiveness of both cement additives. It does not have the disadvantages found in other cement additives.

Hereinafter, the present invention will be specifically illustrated with reference to Examples.

In the examples, parts and percentages are by weight unless otherwise specified.

Implementation ■ The free sulfur recovered from the wet desulfurization equipment for upper coke oven gas is suspended in water, and the undesulfurized coke oven gas is washed with this sulfur suspension to remove cyanogen.
A desyanide waste liquid having the composition shown in the table was obtained. Note that free sulfur was previously removed from this waste liquid by filtration.

Table 1 1000 parts of this decyanization waste liquid was placed in a glass distillation flask and heated to 105°C under normal pressure to distill off 200 parts of water. Due to this heating, the carbonate ions in the decyanizing waste liquid are reduced to 0.
It was reduced to less than 1%. Add to this 48% sodium hydroxide 1
23 parts (1,07 equivalents) was added, and 100 to 11 parts were added under normal pressure.
Heating to 0°C and distilling off ammonia together with water; 35.
310 parts of a 4% aqueous sodium thiocyanate solution was obtained.

This one contained 0.4% sulfide ions, so 8
Air aeration was carried out at 0° C. for 1 hour, and the generated sulfur particles were filtered off to obtain an aqueous solution useful as an additive for cement having the composition shown in Table 2. This product did not cause precipitation when mixed with a formalin condensate of calcium naphthalene sulfonate or calcium nitrite.

Table 2: After adding 123 parts of 48% sodium hydroxide to 1000 parts of the desyanation waste liquid used in Example 1,
The mixture was heated and concentrated at 10° C. to obtain 307 parts of a 35.7% aqueous sodium thiocyanate solution. This product formed a precipitate when mixed with a formalin condensate of calcium naphthalene sulfonate or calcium nitrite.

Sodium thiocyanate aqueous solution 10 obtained in Example 1
0 parts was adjusted to pH 8.1 with 10% sulfuric acid. This is 35
Stirred for 1 hour under reduced pressure of 0 mFIg. The carbonate ion concentration of the resulting aqueous solution decreased to less than 0.1%. Even when this liquid was mixed with a formalin condensate of calcium naphthalene sulfonate or calcium nitrite, no precipitation occurred.

Claims (4)

[Claims] (1) The main component is an alkali metal thiocyanate, which is produced from a waste liquid containing ammonium thiocyanate or an alkali metal salt discharged from the decyanization and/or desulfurization process of coke oven gas, and does not substantially contain carbonate ions. Cement additive. (2) The cement additive according to claim 1, which is substantially free of free sulfur and/or sulfides. (3) Decarboxylate waste liquid containing ammonium thiocyanate or alkali metal salt discharged from the coke oven gas decyanization and/or desulfurization process, and if the liquid contains ammonium thiocyanate salt, before or after decarboxylation or An alkali metal salt of thiocyanate characterized by converting an ammonium salt into an alkali metal salt by double decomposition with at least one compound selected from alkali metal hydroxides, carbonates, and hydrogen carbonates simultaneously with decarboxylation. A method for producing an additive for cement which contains substantially no carbonate ions. 4. The method according to claim 3, further comprising a step of removing free sulfur and/or removing sulfide ions by oxidation after metathesis.