KR100206485B1 - Thiocyanide removal form coke oven wash water - Google Patents

Abstract

A method is provided for providing a high concentration of thiocyanate compound contained in condensate wastewater of coke oven gas generated in a coke process.

First, the condensate wastewater is equalized and the pH is set to 5-8. Then, the divalent copper ions in the wastewater are reduced to monovalent copper ions, and then the monovalent copper ions are reacted with thiocyanate to convert to low solubility copper thiocyanate. Then, polymer aggregates are added and the solids are separated.

According to the above method, the high concentration thiocyanate ions contained in the waste water can be easily and stably removed.

Description

How to remove the thiocyanate compounds in the condensate of coke oven gas

1 is a schematic diagram of a thiocyanate removal process for carrying out the process according to the invention.

Figure 2 is a graph showing the effect of removing the thiocyanate according to the copper sulfate input concentration in the present invention.

3 is a graph showing the effect of removing the thiocyanate according to the sodium sulfite input amount in the present invention.

Figure 4 is a graph showing the effect of removing the thiocyanate according to the pH change in the present invention.

5 is a graph showing the thiocyanide removal effect according to the amount of sodium hypochlorite added after the injection of ferrous sulfate 800 mg / L, calcined lime 1200 mg / L in the conventional method.

* Explanation of symbols for main parts of the drawings

1: equalization tank 2: pH adjusting tank

3: chemical reaction tank 4: separation tank

The present invention relates to a method for treating thiocyanate-containing wastewater, and more particularly, to a method for removing high concentration of thiocyanate compounds contained in condensate wastewater of coke oven gas generated in a coke plant.

The condensate of the coke oven gas is generated by the temperature difference between the inside and the outside of the coke oven gas pipe when the coke oven gas generated in the coal distillation process is transferred to the pipe for use as a heat source of each plant. The condensate generated in this way contains thiocyanide at a high concentration of 3,000-6,000 mg / L, as well as a large amount of cyanide, sulfur compounds, and chlorine ions. Moreover, thiocyanide is less toxic than cyanide compounds, but since thiocyan 1mg / L detects a chemical oxygen demand (COD) of about 1mg / L, treatment with thiocyanate wastewater is necessary.

The main methods for removing the thiocyanate compounds in the conventional wastewater include biological treatment method, oxidation method with sodium hypochlorite, heating the aqueous thiocyanate solution at 200 ° C. or higher to decompose and remove with hydrogen sulfide, carbon dioxide and ammonia, There is a method of treating a high concentration of thiocyan with a chemical which generates pure oxygen and oxygen under a copper-aluminum catalyst obtained by adding an aqueous sodium hydroxide solution to an aluminum-copper alloy, and then treating the remaining thiocyanate with a microorganism.

However, the most commonly used biological treatment method can be stably treated up to 500 mg / L of thiocyanate concentration, but in order to effectively treat thiocyanide by microorganisms, nutrients such as nitrogen and phosphorus are added and activated. Sludge concentration and activity management, pH, dissolved oxygen management is required, there is a problem that the size of the reactor is too large and the operation operation is very complicated. Furthermore, wastewater containing high concentrations of thiocyanate (3,000-6,000mg / L), such as condensate from coke oven gas, and high concentrations of substances that are toxic to microorganisms such as cyanide, sulfur, and chlorine It is difficult. The method of using sodium hypochlorite has the disadvantage of not only insufficient treatment efficiency in treating wastewater containing high concentration of thiocyanate, such as condensate of coke gas, but also causing problems such as corrosion of equipment due to residual chlorine. The method of decomposing the thiocyanic acid wastewater by heating it to 200 ° C. or higher and decomposing it into hydrogen sulfide, carbon dioxide and ammonia requires a reaction under pressure, which leads to complicated reactions and high operating costs, as well as incidental gaseous contaminants. There is a need to reprocess hydrogen sulfide that causes odors. In addition, a method in which a high concentration of thiocyanate is treated by contacting a group generating pure oxygen and oxygen under a copper-aluminum catalyst obtained by adding an aqueous solution of sodium hydroxide to an aluminum-copper alloy, and then treating the remaining thiocyanate by a microorganism is a copper-aluminum alloy catalyst. There is a need for a process to prepare the secondary, and there is a hassle to secondary treatment of the untreated thiocyanate by the microbial treatment process.

It is an object of the present invention to provide a more improved thiocyanide removal method that solves the problems of the conventional method.

The thiocyan compound removing method according to the present invention comprises the steps of equalizing the condensate wastewater of the coke oven gas containing thiocyan so that the supply flow rate and concentration are constant; Adjusting the pH to 5-8 by adding sulfuric acid to the equalized wastewater; Copper sulfate was dissolved by adding 3-5 times the concentration of thiocyanate in the wastewater to the pH-adjusted wastewater, and then sodium sulfite, a strong reducing agent, was added at a concentration of 0.3-0.5 times the concentration of copper sulfate. Reducing the temporary copper ions to monovalent copper ions; Reacting the monovalent copper ions with thiocyanate in the wastewater to convert copper thiocyanate with low solubility and good precipitation; And adding a polymer flocculant to separate solids after flocculation and floc increase. It includes.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

In the method of the present invention, equalization is first performed to constantly adjust the concentration and flow rate of the contaminants contained in the condensate of the coke oven gas.

Equalization can be carried out using a mechanical stirrer or other known usable stirring means.

The equalized wastewater is subjected to a pH adjustment step.

In general, the condensate in the coke oven gas has a pH range of 8-10, and the condensate is adjusted to a pH range of 5-8 with sulfuric acid.

If the pH is lowered below 5, the amount of chemicals used is increased, and the cost of the chemicals is excessive, as well as the burden of increasing the pH again when discharging the treated water after treatment.

On the other hand, when the pH is 8 or more, copper ions are easily hydrated before the reaction with thiocyanate in the subsequent process, so that the treatment efficiency of thiocyanate in the wastewater is reduced, and the size of the floc formed during the reaction is also poor, making it difficult to separate solid-liquid.

The copper sulfate and sodium sulfite which are added and reacted afterwards are preferably 3-5 times the concentration of thiocyanate contained in the waste water in the case of copper sulfate, and 0.3-0.5 times the concentration of copper sulfate which is added to the sodium sulfite.

When the copper sulfate is added at less than three times the concentration of thiocyanate contained in the wastewater, the removal efficiency of the thiocyanate is drastically reduced, and when it is more than five times, the treatment efficiency is very small compared to the optimal concentration of the present invention, while the cost and sludge generation amount of the chemical are very small. There is an increasing problem. In addition, when sodium sulfite is added at 0.3 or less than the concentration of copper sulfate, the concentration of sodium sulfate is low, so that the concentration of divalent copper ion in water is partially reduced to copper monovalent ions. In this case, the treatment efficiency is no longer increased while the drug cost is increased.

As described above, after adjusting the condensed wastewater of the coke oven gas to pH 5-8 and reacting by adding copper sulfate and sodium sulfite, copper sulfate is reduced to monovalent copper ions by sodium sulfite as a strong reducing agent according to the following reaction formula (1). .

CuSO ₄ .nH ₂ O + Na ₂ SO ₃ + 3H ₂ O --- Cu ⁺ + 2NaOH + 2H ₂ SO ₄ ...... (1)

SCN ^{- +} Cu + --- CuSCN ......................................... ...... (2)

The monovalent copper ions formed in Formula (1) react with thiocyanate in the wastewater according to Formula (2) to form copper thiocyanate having low solubility and excellent precipitation, and solid-liquid separation thereof in coke gas condensed water. Can effectively remove the thiocyanate.

This reaction is completed within 30 minutes in a reactor using a 200-300 rpm mechanical stirrer, requiring simple operation and small equipment.

1 is a diagram showing a step of removing thiocyan in accordance with the method of the present invention, the coke oven gas condensate wastewater inflow into the wastewater equalization tank (1) to equalize with a stirrer and then adjust the pH ( The pH is adjusted to 5-8 by the addition of sulfuric acid in 2) and then introduced into the chemical reaction tank (3). In the chemical reaction tank (3), copper sulfate and sodium sulfite added are reacted to form monovalent copper ions. The copper ions react with thiocyanate in the wastewater to form copper thiocyanate with low solubility and good sedimentation. Then, a polymer flocculant is added to coagulate the thiocyanate and increase the floc size. ) Is separated into solids and discharged into the treated water.

The dosage of the polymer flocculant is preferably in the range of 2-4 mg / L.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described.

EXAMPLE

This embodiment is to determine the removal effect of the cyan compound contained in the condensate of the coke oven gas when removed according to the method of the present invention.

The condensate of coke oven gas containing thiocyanate at a concentration of 3165 mg / L was introduced into an equalizing bath as shown in FIG. 1, followed by stirring to uniformly adjust the concentration of contaminants.

The pH of the equalized wastewater was measured to be 9.0.

Copper sulfate and sodium sulfite were added to the reactor for reaction for 30 minutes to convert thiocyanate in the wastewater into copper thiocyanate, a poorly soluble substance.

Then, the wastewater was introduced into the solid-liquid separation tank and PAA was added at a rate of 3 mg / L as a polymer flocculant to increase flocculation and floc size, and the sludge-diluted poorly soluble material of the supernatant was separated and wastewater treatment was performed. Figure 2 shows the effect of reducing the thiocyanate according to the change in the amount of copper sulfate input under the condition that the pH is adjusted to 7.5 and a certain concentration of sodium nitrite is added according to the above method. As shown in FIG. 2, when the amount of copper sulfate input less than 3 times the initial concentration of thiocyanate in the raw wastewater is 8 g / L or less, the SCN concentration in the treated water is 1000 mg / L or more, but the treatment efficiency is insufficient. In this case, the thiocyan treatment efficiency rapidly increases to less than 250 mg / L of SCN concentration in the treated water, and when it is 12 g / L, it is removed to almost 95%. However, it can be seen that the SCN reduction efficiency no longer increases when the copper sulfate input is more than five times the initial SCN concentration. FIG. 3 shows the thiocyanate reduction effect according to the change of the sodium sulfite input amount under the condition in which copper sulfate of a certain concentration was added according to the above method. As can be seen in Figure 3, when the sodium sulfite is added 4g / L or less, the thiocyanate reduction efficiency is very poor, but when added more than the thiocyanate removal efficiency can be seen that more than 95%. However, it can be seen that the addition of sodium sulfite over 6mg / L no longer increases the thiocyanate removal efficiency. FIG. 4 shows the thiocyanate reduction effect according to the pH change under the condition that a certain amount of copper sulfate and sodium sulfite were added. As can be seen in FIG. 4, when pH is above 8, the thiocyanate removal efficiency in wastewater is insufficient. When pH is below 8, the thiocyanate removal efficiency is rapidly increased. It can be seen that the percentage is maintained.

[Comparative Example]

The wastewater containing cyanide compound as in Example was subjected to the cyanide compound removal experiment by sodium hypochlorite oxidation.

As shown in FIG. 5, 800 mg / L of ferrous sulfate and 1200 mg / L of calcined lime were first reacted with the COG wastewater introduced, and then a thiocyanate removal experiment was performed according to the change in the amount of sodium hypochlorite. . At this time, the pH of the reactor was adjusted to 7.5, which is considered to be the most effective. According to FIG. 5, even though the sodium hypochlorite injection amount was increased to 3000 mg / L, the thiocyanate compound in the wastewater was hardly removed.

As described above, in the method according to the present invention, in order to remove the high concentration of thiocyanate ions contained in the condensate of the coke oven gas, the wastewater is equalized to adjust the pH appropriately, and then copper sulphate and sodium sulfite are used as chemical reagents. By converting cyan into poorly soluble substances, it is possible to easily and stably remove high concentrations of thiocyan ions contained in the wastewater without being affected by other pollutants in the wastewater.

Claims (2)

Equalizing the wastewater by adjusting the flow rate and concentration of the condensate wastewater of the coke oven gas to be constantly supplied; Adjusting the equalized wastewater to pH 5-8 with sulfuric acid; Copper sulfate was added 3-5 times compared to the thiocyanate concentration contained in the wastewater adjusted to pH and dissolved therein. Then, sodium sulfite, a strong reducing agent, was added at a concentration of 0.3-0.5 relative to the concentration of copper sulfate to react with divalent copper dissolved in the wastewater. Reducing the ions to monovalent copper ions; Reacting monovalent copper ions formed in the step with thiocyanate in the wastewater to convert copper thiocyanate with low solubility; And adding a polymer flocculant to improve solidification effect and floc size to separate the solid and liquid. Thiocyanate ion removal method contained in the condensed water of the coke oven gas comprising a. The method of claim 1, wherein the dose of the polymer flocculant is 2-4 mg / L as the volume center of the entire treatment.