Method for preparing calcium thiocyanate by using desulfurization waste liquid

Abstract

The application provides a method for preparing calcium thiocyanate by using desulfurization waste liquid, calcium nitrate and ammonium thiocyanate are respectively dissolved into 30-50% solution, the calcium nitrate solution is slowly dropped into the hot ammonium thiocyanate solution under the conditions of heating and stirring, under the heating state, the double decomposition reaction occurs to generate calcium thiocyanate and ammonium nitrate, with the continuous heating and the evaporation of water, the concentration of calcium thiocyanate gradually increases, the ammonium nitrate is heated and decomposed to generate nitrogen oxide and ammonia gas, the generated process gas rich in nitrogen oxide and ammonia gas is condensed and introduced into the coking ammonia removal and denitration section for treatment, and finally the evaporation and concentration obtain about 50% calcium thiocyanate product. The method uses industrial waste to provide raw materials, and the production cost is low; the process tail gas generated in the reaction only needs to be treated by the existing ammonia removal and denitration device of the coking enterprise, without increasing additional equipment, thereby saving the expenditure; and the method has environmental protection benefit, social benefit and economic benefit.

Description

Technical Field

[0001] This invention belongs to the field of coking wastewater recycling and treatment technology, specifically relating to a method for preparing calcium thiocyanate using desulfurization wastewater. Background Technology

[0002] Hydrogen sulfide and hydrogen cyanide in coke oven gas are harmful substances that can corrode production equipment, cause catalyst poisoning, and lead to air pollution and human health problems during subsequent production processes. Since the 1980s, my country's coke oven gas desulfurization and decyanation processes have continuously improved and developed, with new technologies constantly being applied to industrial production. Wet oxidation desulfurization technology, in particular, has seen rapid development and is widely used in the coking industry. Currently, wet processes include HPF, FRC, TH, modified ADA, tannin-based (TV) process, PDS, and others. These processes offer significant desulfurization effects, but they also generate side reactions, with the main byproducts being thiocyanate, thiosulfate, and sulfate. The accumulation of these byproducts increases the viscosity of the desulfurization liquid, significantly reducing desulfurization efficiency. Therefore, coking plants regularly discharge desulfurization wastewater. Currently, the main treatment methods for this wastewater are the extraction of ammonium thiocyanate and sodium thiocyanate for resource utilization or incineration for acid production. Calcium thiocyanate is an inorganic compound with the chemical formula Ca(SCN)2, mainly used in the pesticide, pharmaceutical, electroplating, textile, construction, and chemical reagent industries. Appearance: White crystalline powder, easily soluble in water, ethanol, methanol, and acetone. Extracting calcium thiocyanate from desulfurization wastewater is a practical method for the resource-based treatment of coking desulfurization wastewater. Therefore, how to extract high-purity calcium thiocyanate from desulfurization wastewater is of great significance for transforming desulfurization wastewater into an effective secondary resource and reducing environmental pollution. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing calcium thiocyanate using desulfurization wastewater, thereby solving the above-mentioned problem.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for preparing calcium thiocyanate using desulfurization wastewater, comprising the following steps:

[0005] (1) Extract ammonium thiocyanate and calcium nitrate from desulfurization waste liquid, and dissolve the ammonium thiocyanate and calcium nitrate into ammonium thiocyanate solution and calcium nitrate solution, respectively.

[0006] (2) Under heating conditions, the calcium nitrate solution is slowly added dropwise to the ammonium thiocyanate solution while stirring, so that the two undergo a double decomposition reaction to generate calcium thiocyanate and ammonium nitrate.

[0007] (3) Continue heating to evaporate the water, and finally evaporate and concentrate to obtain calcium thiocyanate product.

[0008] As a preferred embodiment of the method for preparing calcium thiocyanate from desulfurization waste liquid according to the present invention, in step (1), the mass percentage of the ammonium thiocyanate solution is 30-50%.

[0009] As a preferred embodiment of the method for preparing calcium thiocyanate from desulfurization waste liquid according to the present invention, in step (1), the mass percentage of the calcium nitrate solution is 30-50%.

[0010] As a preferred embodiment of the method for preparing calcium thiocyanate from desulfurization waste liquid according to the present invention, in step (2), the heating temperature is 70-80℃.

[0011] As a preferred embodiment of the method for preparing calcium thiocyanate from desulfurization waste liquid according to the present invention, in step (2), the stirring speed is 60-80 r / min.

[0012] As a preferred embodiment of the method for preparing calcium thiocyanate using desulfurization waste liquid according to the present invention, in step (2), the calcium nitrate solution is slowly added dropwise to the ammonium thiocyanate solution, and the addition is completed in 2 to 3 hours.

[0013] As a preferred embodiment of the method for preparing calcium thiocyanate using desulfurization waste liquid according to the present invention, in step (2), the metathesis reaction simultaneously decomposes to produce nitrogen oxides and ammonia, and the nitrogen oxides and ammonia are condensed and then fed into the coking deammoniation and denitrification section for treatment.

[0014] As a preferred embodiment of the method for preparing calcium thiocyanate from desulfurization waste liquid according to the present invention, in step (3), the heating temperature is 100-120℃.

[0015] As a preferred embodiment of the method for preparing calcium thiocyanate from desulfurization waste liquid according to the present invention, in step (3), the mass percentage of the calcium thiocyanate product is 50-52%.

[0016] Compared with existing technologies, the present invention proposes a method for preparing calcium thiocyanate using desulfurization wastewater. Its advantages are: the raw materials are ammonium thiocyanate and calcium nitrate extracted from desulfurization and decyanation wastewater from coke oven gas in coking plants, utilizing industrial waste to provide raw materials, thus resulting in low production costs; the process tail gas generated by the reaction only needs to be treated harmlessly using the existing ammonia and nitrate removal equipment in the coking plant, without the need for additional equipment, saving equipment expenditures; and it has good environmental, social, and economic benefits. Detailed Implementation

[0017] This invention provides a method for preparing calcium thiocyanate using desulfurization wastewater. The principle is as follows: calcium nitrate and ammonium thiocyanate are dissolved into 30-50% solutions respectively. Under heating conditions of 70-80℃ and stirring at 60-80 r / min, the calcium nitrate solution is slowly added dropwise to the hot ammonium thiocyanate solution. The addition is completed in 2-3 hours. Under heating conditions of 100-120℃, a double decomposition reaction occurs to generate calcium thiocyanate and ammonium nitrate. With continuous heating and the evaporation of water, the concentration of calcium thiocyanate gradually increases. Ammonium nitrate undergoes thermal decomposition to produce nitrogen oxides and ammonia. The process gas rich in nitrogen oxides and ammonia is condensed and incorporated into the coking deammoniation and denitrification section for treatment. Finally, the product is evaporated and concentrated to obtain calcium thiocyanate product with a concentration of about 50%.

[0018] Key control factors in the process:

[0019] ① In the preparation of ammonium sulfate and calcium nitrate solutions, the content should be controlled at 30-50%;

[0020] ② While stirring, slowly add the calcium nitrate solution dropwise into the hot ammonium thiocyanate solution. The addition should be slow, and the temperature should be carefully controlled to prevent a violent reaction and boiling. Calcium thiocyanate and ammonium nitrate will be generated.

[0021] ③ With continued heating and evaporation of moisture, the concentration of calcium thiocyanate gradually increases. Ammonium nitrate decomposes upon heating to produce nitrogen oxides and ammonia.

[0022] ④ The process gases rich in nitrogen oxides and ammonia generated are condensed and then incorporated into the coking deammoniation and denitrification sections for further treatment;

[0023] ⑤ Finally, the product is evaporated and concentrated to obtain calcium thiocyanate with a purity of about 50%.

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to specific embodiments.

[0025] First, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] For specific implementation details, please refer to Examples 1-2 below: Example 1

[0027] 1000g of ammonium sulfate solid, white crystalline, extracted from desulfurization wastewater of a coking plant, was dissolved in 2000g of water. 2158g of calcium nitrate solid, white in appearance, was dissolved in 3000g of water. While heating the ammonium thiocyanate solution, calcium nitrate solution was slowly added dropwise to the hot ammonium thiocyanate solution with stirring. Under heating, a double decomposition reaction occurred, producing calcium thiocyanate and ammonium nitrate. With continued heating and the evaporation of water, the concentration of calcium thiocyanate gradually increased. Ammonium nitrate underwent thermal decomposition to produce nitrogen oxides and ammonia. The resulting process gas, rich in nitrogen oxides and ammonia, was subjected to acid washing followed by alkali washing for harmless treatment (simulating ammonia and nitrate removal). Finally, evaporation and concentration yielded 4105g of 51.1% calcium thiocyanate product. Example 2

[0028] 500g of ammonium sulfate solid, white crystalline, extracted from desulfurization wastewater of a coking plant, was dissolved in 1000g of water. 1079g of calcium nitrate solid, white in appearance, was dissolved in 2000g of water. While heating the ammonium thiocyanate solution, calcium nitrate solution was slowly added dropwise to the hot ammonium thiocyanate solution with stirring. Under heating, a double decomposition reaction occurred, producing calcium thiocyanate and ammonium nitrate. With continued heating and evaporation of water, the concentration of calcium thiocyanate gradually increased. Ammonium nitrate underwent thermal decomposition to produce nitrogen oxides and ammonia. The resulting process gas, rich in nitrogen oxides and ammonia, was subjected to acid washing followed by alkali washing for harmless treatment (simulating ammonia and nitrate removal). Finally, evaporation and concentration yielded 2052g of 50.6% calcium thiocyanate product.

[0029] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing calcium thiocyanate from desulfurization wastewater, characterized in that, Includes the following steps: (1) Extract ammonium thiocyanate and calcium nitrate from desulfurization wastewater, and dissolve the ammonium thiocyanate and calcium nitrate into ammonium thiocyanate solution and calcium nitrate solution respectively, wherein the mass percentage of the ammonium thiocyanate solution is 30-50% and the mass percentage of the calcium nitrate solution is 30-50%; (2) Under heating conditions, the calcium nitrate solution is slowly added dropwise to the ammonium thiocyanate solution while stirring, so that the two undergo a metathesis reaction to generate calcium thiocyanate and ammonium nitrate. The heating temperature is 70-80℃, the stirring speed is 60-80r / min, and the calcium nitrate solution is slowly added dropwise to the ammonium thiocyanate solution over 2-3 hours. The metathesis reaction simultaneously decomposes to produce nitrogen oxides and ammonia. The nitrogen oxides and ammonia are condensed and then fed into the coking deammoniation and denitrification section for treatment. (3) Continue heating to evaporate the water, and finally evaporate and concentrate to obtain calcium thiocyanate product, wherein the heating temperature is 100-120℃, and the mass percentage of the calcium thiocyanate product is 50-52%.