Treatment method of selenium-containing tail gas absorption liquid

Abstract

The invention belongs to the technical field of tail gas recovery treatment, and discloses a selenium-containing tail gas absorption liquid treatment method, which comprises: 1, adding sodium dithionite to a selenium-containing tail gas absorption liquid, and completely reacting to obtain a solution A; and 2, adding sulfuric acid or hydrochloric acid into the solution A, maintaining the pH value of the solution to be 0.1-1, carrying out a stirring reaction for 1-2 h, and carrying out solid-liquid separation to obtain solid crude selenium. According to the treatment method of the selenium-containing tail gas absorption liquid, nitrite of the selenium-containing tail gas absorption liquid is reduced through sodium dithionite, nitrous acid is prevented from being decomposed to generate nitric oxide, meanwhile, selenium can be reduced into elemental selenium through residual liquid in a specific pH environment, pollution is reduced, meanwhile, selenium in the tail gas absorption liquid is efficiently recycled, and the selenium-containing tail gas absorption liquid is obtained. The method has the advantages of short process and low cost.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas recovery and treatment, and in particular to a method for treating selenium-containing tail gas absorption liquid. Background Art

[0002] In the production process of coal burning, metallurgy, chemical industry and other fields, there are acidic gases such as nitrogen oxides (NOx) and sulfur dioxide (SO2) in the flue gas. Due to the relatively low flue gas temperature, this type of flue gas is not suitable for SCR denitrification. At present, this type of flue gas is mainly converted into nitrous acid, nitric acid and sulfite solution through spray tower absorption to form tail gas absorption liquid.

[0003] In the absorption process of the spray tower of the selenium chemical plant, in addition to nitrogen oxides, some selenium will be absorbed. The current method for recovering selenium in selenium-containing wastewater is mainly to add a reducing agent under acidic conditions to reduce it to elemental selenium. For example, prior art 1: Chinese patent application 201310472031.2 discloses a method for recovering selenium in acid sludge waste from copper smelting flue gas. Its specification states: "A method for recovering selenium in acid sludge waste from copper smelting flue gas, adding the acid sludge to a solution containing sodium hypochlorite and sodium hydroxide, performing a selenium leaching reaction, filtering to obtain deselenized slag and a sodium selenate solution, recovering lead and precious metals from the deselenized slag, and acidifying and reducing the sodium selenate solution to obtain coarse selenium powder."

[0004] However, if the existing technology is used to directly add acid to the tail gas absorption liquid to recover selenium, the nitrous acid in the spray tower solution is easily decomposed during the acid addition process to produce nitrogen oxides again, causing secondary pollution.

[0005] Therefore, the general tail gas absorption liquid needs to remove nitrite before recovering selenium. Reference can be made to prior art 2: Chinese patent application 201710480765.3 discloses a method for recovering sulfur and nitrogen resources from flue gas and producing hydroxylamine sulfate, comprising: (1) spraying and cooling the boiler flue gas for dust removal after pre-dust removal, mixing the flue gas after spraying and cooling with an oxidant for oxidation, and the oxidized flue gas enters an absorption tower for circulation spraying for simultaneous desulfurization and denitrification, thereby purifying the flue gas and obtaining SO4 2- and NO 2- (2) discharging the obtained absorption liquid for the above-mentioned spray cooling and dust removal of flue gas, wherein NO2- in the absorption liquid reacts with SO2 in the flue gas to form sulfur-nitrogen compound absorption waste liquid; (3) the sulfur-nitrogen compound absorption waste liquid is purified by decontamination to obtain hydroxylamine disulfonic acid solution, and the obtained hydroxylamine disulfonic acid solution is hydrolyzed at 95-110°C to obtain hydroxylamine sulfate solution, which is then separated and purified to obtain hydroxylamine sulfate solid.

[0006] This technology can simultaneously remove sulfur and nitrogen, and effectively handles the problem of nitrite in the tail gas absorption liquid. However, the process conditions are relatively harsh, and after removing the nitrite, selenium needs to be recovered separately. The process flow is cumbersome and the recovery cost is high. Summary of the invention

[0007] One of the purposes of the present invention is to provide a method for treating selenium-containing tail gas absorption liquid, wherein nitrite is removed by adding sodium dithionite for reaction, and selenium is reduced to selenium element in the residual reaction liquid under a specific pH environment, thereby fully recovering selenium.

[0008] To achieve the above object, the present invention provides a method for treating selenium-containing tail gas absorption liquid, comprising the following steps:

[0009] Step 1: adding sodium dithionite to the selenium-containing tail gas absorption liquid to react, and obtaining solution A after the reaction is complete;

[0010] Step 2: Add sulfuric acid or hydrochloric acid to solution A and maintain the pH of the solution at 0.1-1. After stirring for 1-2 hours, separate the solid and liquid to obtain solid crude selenium.

[0011] The reaction formula of the technical solution of the present invention is as follows:

[0012]

[0013] Preferably, the step 1 requires detecting the molar amount of nitrite in the selenium-containing tail gas absorption liquid, so that the added molar amount of sodium dithionite is 4-5 times the molar amount of nitrite.

[0014] Preferably, stirring needs to be maintained during the reaction process of step 1, the stirring speed is 300-400 r / min, and the reaction time is 1-2 h.

[0015] Furthermore, in step 2, sulfuric acid or hydrochloric acid is added and the pH value of the solution is maintained at 0.5-1.

[0016] Preferably, the concentration of the sulfuric acid is 98 wt %.

[0017] Preferably, the concentration of the hydrochloric acid is 30-35wt%.

[0018] Beneficial Effects

[0019] Compared with the prior art, the present invention provides a method for treating selenium-containing tail gas absorption liquid, in which nitrite in the selenium-containing tail gas absorption liquid is reduced by sodium dithionite to avoid the decomposition of nitrous acid to generate nitrogen oxides. Meanwhile, the residual liquid can also reduce selenium into elemental selenium under a specific pH environment, thereby reducing pollution and efficiently recovering selenium in the tail gas absorption liquid, and has the advantages of short process and low cost. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited number of modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0021] In order to explain the technical content of the present invention in detail, further description is given below in conjunction with the implementation modes.

[0022] In the following examples and comparative examples, NO2 - The content is detected by anion-IC (ion chromatography); the Se content is detected by ICP-OES (inductively coupled plasma emission spectrometer); and the molar amount of nitrite = nitrite content (g / L) / nitrite molar mass (46 g / mol).

[0023] Example 1

[0024] A method for treating selenium-containing tail gas absorption liquid comprises the following steps:

[0025] Step 1: Take 200ml of selenium-containing tail gas absorption liquid (NO2 - 4 g / L, Se 10 g / L), 10 g of sodium dithionite was added at a stirring speed of 400 r / min and reacted for 1 h to obtain solution A;

[0026] Step 2: adding 98 wt % sulfuric acid to solution A to adjust the pH value to 0.7±0.1, reacting for 1 hour, performing solid-liquid separation by filter pressing to obtain crude selenium and filtrate;

[0027] The filtrate was sampled and tested, and the NO2 - The content is 100ppm and the Se content is 301ppm.

[0028] Example 2

[0029] A method for treating selenium-containing tail gas absorption liquid comprises the following steps:

[0030] Step 1: Take 200ml of selenium-containing tail gas absorption liquid (NO2 - 4 g / L, Se 10 g / L), 10 g of sodium dithionite was added at a stirring speed of 400 r / min and reacted for 1 h to obtain solution A;

[0031] Step 2: Add 31 wt% hydrochloric acid to solution A to adjust the pH value to 0.7±0.1, react for 1 hour, perform solid-liquid separation by filter pressing, and obtain crude selenium and filtrate;

[0032] The filtrate was sampled and tested, and the NO2 -The content is 56ppm and the Se content is 210ppm.

[0033] Example 3

[0034] A method for treating selenium-containing tail gas absorption liquid comprises the following steps:

[0035] Step 1: Take 200ml of selenium-containing tail gas absorption liquid (NO2 - 4 g / L, Se 10 g / L), 10 g of sodium dithionite was added at a stirring speed of 400 r / min and reacted for 1 h to obtain solution A;

[0036] Step 2: adding 98 wt % sulfuric acid to solution A to adjust the pH value to 0.3±0.1, reacting for 1 hour, performing solid-liquid separation by filter pressing to obtain crude selenium and filtrate;

[0037] The filtrate was sampled and tested, and the NO2 - The content is 56ppm and the Se content is 210ppm.

[0038] Comparative Example 1

[0039] A method for treating selenium-containing tail gas absorption liquid comprises the following steps:

[0040] Step 1: Take 200ml of selenium-containing tail gas absorption liquid (NO2 - 4 g / L, Se 10 g / L), 3 g of sodium dithionite was added at a stirring speed of 400 r / min and reacted for 1 h to obtain solution A;

[0041] Step 2: adding 98 wt % sulfuric acid to solution A to adjust the pH value to 0.7±0.1, reacting for 1 hour, performing solid-liquid separation by filter pressing to obtain crude selenium and filtrate;

[0042] The filtrate was sampled and tested, and the NO2 - The content is 522ppm and the Se content is 3901ppm.

[0043] Comparative Example 2

[0044] A method for treating selenium-containing tail gas absorption liquid comprises the following steps:

[0045] Step 1: Take 200ml of selenium-containing tail gas absorption liquid (NO2 - 4 g / L, Se 10 g / L), 5 g of sodium dithionite was added at a stirring speed of 400 r / min and reacted for 1 h to obtain solution A;

[0046] Step 2: adding 98 wt % sulfuric acid to solution A to adjust the pH value to 0.7±0.1, reacting for 1 hour, performing solid-liquid separation by filter pressing to obtain crude selenium and filtrate;

[0047] The filtrate was sampled and tested, and the NO2 - The content is 98ppm and the Se content is 5913ppm.

[0048] According to the data of Examples 1-3, the technical solution of the present invention can effectively remove nitrite and has no nitrogen oxides. After the sodium dithionite reacts with nitrite, selenium can be further reduced by controlling the pH, thereby efficiently recovering the selenium element.

[0049] According to the data comparison between Example 1 and Comparative Example 1, adding too little sodium dithionite in step 1 will make it difficult to completely remove nitrite, thereby causing nitrogen oxides to easily appear in the subsequent selenium reduction process, polluting the environment.

[0050] According to the data comparison between Example 1 and Comparative Example 2, if the amount of sodium dithionite added in step 1 is less than the technical solution of the present invention, although nitrite can be effectively removed, selenium cannot be further reduced, resulting in a decrease in selenium recovery efficiency.

[0051] The reaction formula of the technical solution of the present invention is as follows:

[0052]

[0053] The embodiments presented herein are only embodiments selected according to the combination of all possible embodiments. The appended claims should not be limited by the embodiments describing the present invention. Some numerical ranges used in the claims include sub-ranges therein, and the changes in these ranges should also be covered by the appended claims.

Claims

1. A method for treating a selenium-containing tail gas absorption liquid, characterized in that: The steps include: Step 1: adding sodium dithionite to the selenium-containing tail gas absorption liquid to react, and obtaining solution A after the reaction is complete; Step 2: Add sulfuric acid or hydrochloric acid to solution A and maintain the pH of the solution at 0.1-1. After stirring for 1-2 hours, separate the solid and liquid to obtain solid crude selenium.

2. The method for treating selenium-containing tail gas absorption liquid according to claim 1, characterized in that: The step 1 needs to detect the molar amount of nitrite in the selenium-containing tail gas absorption liquid, so that the added molar amount of sodium dithionite is 4-5 times the molar amount of nitrite.

3. The method for treating the selenium-containing tail gas absorption liquid according to claim 1 or 2, characterized in that: During the reaction of step 1, stirring needs to be maintained at a speed of 300-400 r / min and a reaction time of 1-2 h.

4. The method for treating selenium-containing tail gas absorption liquid according to claim 1, characterized in that: In step 2, sulfuric acid or hydrochloric acid is added and the pH value of the solution is maintained at 0.5-1.

5. The method for treating the selenium-containing tail gas absorption liquid according to any one of claims 1 to 4, characterized in that: The concentration of the sulfuric acid is 98 wt %.

6. The method for treating the selenium-containing tail gas absorption liquid according to any one of claims 1 to 4, characterized in that: The concentration of the hydrochloric acid is 30-35wt%.

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