A method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater

Abstract

The invention discloses a method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater, and belongs to the technical field of metal refining. The acidified liquid of high-concentration cyanide-containing wastewater is separated into solid and liquid, and an excess of iron powder is added to the filtrate. The overflowing mixed gas is first passed into a low-temperature soluble zinc salt weak acid solution to fully absorb the H2S and HCN gases therein to produce a ZnS and Zn(CN)2 suspension, and then a sodium hydroxide strong alkaline solution is passed into the suspension for further absorption to ensure that the H2S and HCN gases that are not completely absorbed do not overflow. Concentrated sulfuric acid is added to the ZnS and Zn(CN)2 suspension, the reaction is stirred, and the overflowing HCN gas is absorbed with an alkaline solution. The suspension after the reaction is filtered to obtain a ZnS filter residue and a Zn 2+ Filtrate. The acidified liquid after sufficient reaction with the iron powder is filtered, the residual iron powder is recycled, the pH of the filtrate is adjusted to above 11, the precipitation of iron hydroxide is filtered out and then returned to the cyanide production water system. The present invention realizes SCN ‑ CN ‑ The system can recover and absorb and separate H2S and HCN gases.

Description

Technical Field

[0001] The present invention relates to a method for treating thiocyanate in acidified liquid of cyanide-containing wastewater, and in particular to a method for removing and comprehensively recovering thiocyanate in acidified liquid of high-concentration cyanide-containing wastewater, belonging to the technical field of metal refining. Background Art

[0002] Total cyanide refers to cyanide that can form HCN under specific conditions, including a small amount of simple cyanide (CN - ) and most of the complex cyanide (Fe(CN)6 4- 、Cu(CN)3 2- 、Zn(CN)4 2- etc.). CN in high concentration cyanide wastewater - and Fe(CN)6 4- 、Cu(CN)3 2- 、Zn(CN)4 2- The content of complex cyanide is high. In addition, due to the high content of pyrite and pyrrhotite in gold concentrate, the SCN in high-concentration cyanide wastewater - The content is also relatively high. According to the mass concentration of total cyanide in cyanidation gold extraction wastewater, the wastewater can generally be divided into three types: high concentration (total cyanide greater than 800 mg / L), medium concentration (total cyanide greater than 200 mg / L~800 mg / L) and low concentration (total cyanide less than 200 mg / L). Generally, the total cyanide mass concentration of gold concentrate cyanidation wastewater is greater than 800 mg / L, which is a high-concentration cyanide-containing wastewater.

[0003] During the cyanide leaching process, the sulfur element in the sulfide ore of the gold ore and the CN in the leaching solution - , O2, chemical reaction to generate SCN - Under alkaline conditions, SCN - It has no gold leaching effect and will react with O2, consuming dissolved oxygen and affecting the leaching index of gold and silver. - CN - It is a resource with recycling value. Its enrichment and accumulation in the cyanide leaching water system is a waste of resources, and measures should be taken to recycle it.

[0004] SCN - ) is composed of a sulfur atom and a cyano group. It is an ion that is widely present in the field of chemistry and has many important applications. SCN - It can form complexes with some metal ions, and these complexes are often used as colorimetric agents or indicators for metal ions in analytical chemistry. Thiocyanate ions also have reducing properties and can react with oxidants to generate N2, CO2, and NH4. + 、SO4 2-etc., can be reduced by zinc to H2S and HCN (Zn+SCN - +3H + →Zn 2+ +H2S↑+HCN↑).

[0005] Add sulfuric acid to the high-concentration cyanide wastewater to make the wastewater acidic (pH 2-3), and the Cu(CN)3 2- 、Zn(CN)4 2- The complex cyanide in the cyanide complex ion is converted into HCN, CuCN precipitation and Zn 2+ , taking advantage of the low boiling point (26°C) and volatile characteristics of HCN, the HCN is blown off from the liquid phase with the help of air, and then the volatile HCN is absorbed by NaOH and recycled. 4- With SCN - Cannot be decomposed, although Fe(CN)6 4- Will be with Zn 2+ The reaction generates Zn2Fe(CN)6 precipitate, SCN - It will react with CuCN to form CuSCN precipitate, but due to Zn 2+ , Cu + The content is relatively low and is not enough to convert Fe(CN)6 4- and SCN - Therefore, Fe(CN)6 4- and SCN - The content is still high.

[0006] Hydrogen sulfide (H2S) is a colorless, highly toxic acidic gas that is slightly soluble in water and forms a weak acid called "hydrogensulfuric acid". Its aqueous solution contains hydrosulfate HS - and sulfide ion S 2- , S 2- Can be used with Pb 2+ 、Zn 2+ , Cu 2+ 、Ag + The sulfide precipitates are generated.

[0007] Hydrogen cyanide (HCN) is a colorless, highly toxic gas with the smell of bitter almonds. It is highly soluble in water, has a low boiling point (26°C), is volatile, and is a gas under standard conditions. - It is easy to form complex ions with various metal ions such as Cu, Fe, Zn, etc. 2- , S, etc. to generate SCN - .

[0008] At present, the SCN in wastewater or waste residue -, mainly using oxidation method to "destroy" decomposition, such as aeration, electrocatalytic oxidation, adding potassium permanganate and other oxidants. The Chinese invention patent application with publication number CN113683246A discloses "a method for purifying and treating wastewater containing thiocyanate". Its main technical measures are: wet catalytic oxidation treatment of wastewater containing thiocyanate, reaction temperature of 150℃~300℃, reaction pressure of 2~4MPa, reaction time of 2~5h; stripping of wet catalytic oxidation effluent to recover ammonia nitrogen; mixing the stripping effluent with sodium formate wastewater containing copper ions for complex precipitation to remove residual thiocyanate ions; electrocatalytic oxidation treatment of complex precipitation effluent; adsorption treatment of electrocatalytic oxidation effluent by adsorbent; distillation treatment of adsorbed effluent, and reflux of distillation residue to wet catalytic oxidation treatment.

[0009] The Chinese invention patent application with publication number CN116251325A discloses a "method for degrading thiocyanate in cyanide tailings". The main technical measures are: (1) slurrying the cyanide tailings with water and adjusting the pH value to 2-4; (2) adding a thiocyanate stripping agent to the slurry obtained in step (1) and aerating for 1-3 hours; the thiocyanate stripping agent is one or more of potassium permanganate, manganese ore powder, and 2-ethylhexanoic acid manganese; (3) adding a thiocyanate degradation agent to the slurry obtained in step (2) to remove the thiocyanate; (4) separating the slurry obtained in step (3) into solid-liquid separation.

[0010] There are few reports on the removal of thiocyanate from the acidified liquid of cyanide-containing wastewater. The Chinese invention patent application with publication number CN110980916A discloses "a method for degrading thiocyanate in cyanide-containing lean liquid under acidic conditions". Its main technical measures are: (1) controlling the pH value of the cyanide-containing lean liquid to <2, adding manganese oxide, or manganese oxide and hydrogen peroxide to oxidize and decompose the thiocyanate in the cyanide-containing lean liquid; (2) filtering the cyanide-containing lean liquid after oxidation and decomposition to obtain precipitate and filtrate, adjusting the pH value of the obtained filtrate to 6-12, and then adding oxidizing substances to remove manganese in the filtrate; (3) filtering the liquid after manganese removal in step (2) to obtain purified lean liquid and precipitate containing manganese oxide, and the precipitate containing manganese oxide is directly dried or dried by blast drying and then returned to step (1) for oxidation and decomposition of thiocyanate in the cyanide-containing lean liquid, so as to realize the recycling of manganese oxide; the purified lean liquid is returned to cyanide leaching or deep oxidation to meet the standards and then discharged.

[0011] The Chinese invention patent application with publication number CN109502811A discloses a "flocculation and precipitation purification method for thiocyanate ions in cyanide wastewater". Its main technical measures are: 1) adding concentrated sulfuric acid to the cyanide wastewater to adjust the pH value to 2-3; 2) after the acidified liquid is filtered, adding excess soluble iron salt to the filtrate to deeply remove free cyanide, stirring thoroughly and filtering; 3) adding lime milk to the filtrate to adjust the pH value to 5-9, stirring, adding polyferric sulfate or polyferric chloride to adsorb thiocyanate ions; 4) adding waste ore powder and stirring for further flocculation and sedimentation; 5) filtering after sedimentation.

[0012] The "method for purifying and treating wastewater containing thiocyanate" (CN113683246A), "method for degrading thiocyanate in cyanide tailings" (CN116251325A), "method for degrading thiocyanate in cyanide-poor liquid under acidic conditions" (CN110980916A) and "method for flocculation and precipitation purification of thiocyanate ions in cyanide-containing wastewater" (CN109502811A) all belong to the method of "destruction" decomposition by oxidation. They degrade SCN - Oxidative decomposition to generate NH4 + 、SO4 2- etc. products that are not worth recycling, or adding soluble iron salts and SCN - The reaction produces ferric thiocyanate (a red complex, not a precipitate), which is a waste of resources. Summary of the invention

[0013] The technical problem to be solved by the present invention is to provide a method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater. First, without destroying CN in SCN, - SCN is implemented under the premise - CN - recovery; second, to achieve the absorption and separation of H2S and HCN gas; third, to find a method to determine whether the solution contains S 2- or CN - method.

[0014] The technical solution of the present invention is as follows:

[0015] A method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater is carried out according to the following steps:

[0016] Step (1): acidify and filter the high-concentration cyanide-containing wastewater to achieve solid-liquid separation to obtain a filtrate and a filter residue; and detect the SCN in the filtrate. - and CN - content;

[0017] Step (2): the filtrate obtained in step (1) is placed in a reaction container, iron powder exceeding the theoretical amount of iron powder is added, and concentrated sulfuric acid is added to maintain the pH at 2-3, and the mixture is stirred for reaction; the mixed gas overflowing from the stirring reaction is passed into a No. 1 gas absorption container filled with a low-temperature soluble zinc salt weak acid solution with a temperature of 0-10° C. and a pH of 6.0-6.5 for absorption under stirring conditions, and the gas overflowing from the No. 1 gas absorption container is passed into a No. 2 gas absorption container filled with a sodium hydroxide solution with a pH>11 for absorption under stirring conditions;

[0018] Wherein, the low-temperature soluble zinc salt weak acid solution is prepared by water and a soluble zinc salt exceeding the theoretical amount of zinc added;

[0019] Step (3): after the reaction in step (2) is completed, the product in the reaction container is filtered to obtain residual iron powder and an iron ion solution as a filtrate, the pH of the iron ion solution is adjusted to above 11, filtered to obtain a filtrate and an iron hydroxide residue; and concentrated sulfuric acid is added to the suspension in the first gas absorption container to adjust the pH to below 4, the reaction is stirred, and the overflowed HCN gas is absorbed by alkaline solution to achieve HCN recovery;

[0020] Step (4) filtering the suspension after the HCN gas overflows from the 1# gas absorption container to obtain ZnS filter residue and Zn 2+ filtrate, realize H2S and HCN mixed gas absorption and separation, and realize S 2- and CN - of recycling.

[0021] Preferably, the theoretical amount of iron powder added is calculated according to the following formula:

[0022] m Fe =M Fe m SCN / M SCN ; In the formula, m Fe Indicates the theoretical amount of iron powder added, in g / L; M Fe Indicates the relative atomic mass of Fe, in g / moL; m SCN SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL.

[0023] Preferably, the theoretical amount of zinc added is calculated according to the following formula:

[0024] m Zn =M Zn m SCN / M SCN +0.5 M Zn (m SCN / M SCN +m CN / M CN );

[0025] In the formula, m Zn It indicates the theoretical amount of soluble zinc salt corresponding to the absorption of H2S and HCN gas, in g / L;

[0026] M Zn Indicates the relative molecular mass of soluble zinc salt, unit: g / moL; m SCN Indicates SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL; m CN Indicates CN in the acidified liquid of high-concentration cyanide wastewater - Content, unit: g / L; M CN Indicates CN - Relative atomic mass, unit: g / moL.

[0027] Preferably, during the reaction of step (2), it is detected whether there is S in the sodium hydroxide solution in the 2# gas absorption container. 2- or CN - ; If there is S 2- or CN - , then adjust the pH of the reaction system to 3-4.

[0028] Further preferably, whether the sodium hydroxide solution in the 2# gas absorption container contains S 2- or CN - Determine by the following method: Take a sample of sodium hydroxide solution, add soluble ferrous salt or ferric salt, and a black precipitate will form, indicating the presence of S 2- No black precipitate was generated, indicating that there was no S 2- ; After fully stirring, filter, adjust the filtrate to acidic, continue to add soluble ferrous salt or ferric salt, stir fully, and a blue precipitate is generated, indicating the presence of CN - No blue precipitate was generated, indicating the absence of CN - .

[0029] Preferably, the residual iron powder obtained in step (3) is recycled in step (2); in step (3), the pH of the iron ion solution is adjusted to above 11 and the filtrate obtained by filtration is returned to the cyanide production water system.

[0030] Preferably, the volume of the low-temperature soluble zinc salt weakly acidic solution and the volume of the sodium hydroxide solution with a pH value greater than 11 are respectively 2-3 times the volume of the filtrate obtained in step (1).

[0031] Preferably, the total cyanide mass concentration in the acidified liquid of high-concentration cyanide-containing wastewater is greater than 800 mg / L.

[0032] The positive effects of the present invention are:

[0033] First, according to the existing oxidation treatment technology, SCN - Will be destroyed and generate N2, CO2, NH4 + 、SO4 2- or reacts with soluble iron salts to form ferric thiocyanate complex ions ([Fe(SCN)6] 3- ). The present invention targets the acidified liquid of high-concentration cyanide-containing wastewater and uses relatively low-priced iron powder to convert SCN - Reduction generates H2S and HCN which has recycling value.

[0034] Second, the present invention uses a soluble zinc salt solution to absorb H2S and HCN gases simultaneously, generating ZnS and Zn(CN)2 precipitates respectively, and then adjusting the pH of the suspension of the two precipitates to below 4, so that the Zn(CN)2 precipitate dissolves and releases HCN, completing the separation and recovery of HCN. The undissolved ZnS is filtered and separated to achieve the separation and recovery of H2S. The absorption and separation problem of H2S and HCN mixed gas is solved.

[0035] Third, the present invention proposes a method for determining whether a solution contains S 2- or CN - The method is simple to operate, overcomes the problem of mutual interference between the two ions, and realizes the existence of S in the solution. 2- or CN - effective judgment. DETAILED DESCRIPTION

[0036] The present invention is further described below with reference to the embodiments.

[0037] Example 1. Implementation example of thiocyanate removal and comprehensive recovery method (I).

[0038] This example is used to specifically illustrate the use of the method of the present invention to remove SCN from the acidified liquid of a high-concentration cyanide-containing wastewater. - , and realize S 2- , CN - , Fe, and Zn recycling and utilization specific technical measures and technical effects. The specific steps are as follows:

[0039] (1) Acidify and filter the high-concentration cyanide-containing wastewater to achieve solid-liquid separation, and obtain filtrate and filter residue. Since some valuable metals in the filter residue obtained in this step have a high grade, it can be sold as a product; the filtrate is tested for SCN - and CN - The test results are shown in Table 1.

[0040] Table 1 Detection results of acidified liquid of a high concentration cyanide wastewater

[0041]

[0042] The test results are used as the basis for calculation in step (2).

[0043] (2) Take 100 ml of the filtrate obtained in step (1) and place it in a reaction container. Add 10 g (excess) iron powder and concentrated sulfuric acid to maintain the pH of the reaction system at 2-3. Stir the reaction until the mixed gas overflows and observe the consumption of the iron powder.

[0044] The mixed gas overflowing from the stirring reaction is first passed into the 1# gas absorption bottle under stirring conditions, where the H2S and HCN gases are fully absorbed by the low-temperature soluble zinc salt weak acid solution to produce ZnS and Zn(CN)2 suspensions, and then passed into the 2# gas absorption bottle under stirring conditions to be further absorbed by the sodium hydroxide strong alkaline solution to ensure that the H2S and HCN gases that are not completely absorbed do not overflow.

[0045] The 1# gas absorption bottle contains 250 ml of low-temperature soluble zinc salt weak acid solution with a temperature of 0-10°C and a pH of 6.0-6.5; the 2# gas absorption bottle contains 250 ml of sodium hydroxide solution with a pH>11.

[0046] After stirring the reaction for 8 hours, no bubbles emerged from the gas absorption bottle, and the reaction was completed.

[0047] The theoretical amount of iron powder added is based on the following reaction equation and combined with SCN in Table 1 - The content is calculated and the result is about 47.74g / L:

[0048] Fe+SCN - +3H + →Fe 2+ +H2S↑+HCN↑.

[0049] The specific calculation process is as follows:

[0050] m Fe =M Fe m SCN / M SCN =56g / moL×49.44g / L÷58g / moL=47.74g / L.

[0051] In the formula, m Fe Indicates the theoretical amount of iron powder added, in g / L; M Fe Indicates the relative atomic mass of Fe, in g / moL; m SCN SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL.

[0052] When preparing the low temperature soluble zinc salt weak acid solution, according to the following reaction equation, combined with SCN in Table 1 - Content and CN - The theoretical amount of ZnSO4·7H2O corresponding to the absorption of H2S and HCN gas overflowed from the acidified liquid filtration of a certain high-concentration cyanide-containing wastewater is calculated:

[0053] Fe+SCN - +3H + →Fe 2+ +H2S↑+HCN↑;

[0054] Zn 2+ +S 2- →ZnS↓;

[0055] Zn 2+ +2CN - →Zn(CN)2↓.

[0056] In this example, the amount of H2S and HCN gas overflowed from the acidified liquid filtration of 100 ml of the high-concentration cyanide-containing wastewater is 28.98 g / L and 23.02 g / L respectively; the theoretical amount of ZnSO4·7H2O corresponding to absorbing these H2S and HCN gases is about 36.8 g. The specific calculation process is as follows:

[0057] m H2S =M H2S m SCN / M SCN =34g / moL×49.44g / L÷58g / moL=28.98g / L.

[0058] In the formula, m H2S Indicates the amount of H2S gas overflowed from the acidification filtration of a high-concentration cyanide wastewater, in g / L; M H2S Indicates the relative molecular mass of H2S, unit: g / moL; m SCN Indicates SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN- Relative atomic mass unit is g / moL.

[0059] m HCN =M HCN m SCN / M SCN =27g / moL×49.44g / L÷58g / moL=23.02g / L.

[0060] In the formula, m HCN Indicates the amount of HCN gas overflowed from the acidification filtration of a high-concentration cyanide wastewater, in g / L; M HCN Indicates the relative molecular mass of HCN, unit: g / moL; m SCN Indicates SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL.

[0061] m Zn =M Zn m SCN / M SCN +0.5 M Zn (m SCN / M SCN +m CN / M CN )=287g / moL×49.44g / L÷58g / moL+0.5×287g / moL×(49.44g / L÷58g / moL+0.25205g / L÷26g / moL)=368.35g / L.

[0062] In the formula, m Zn Indicates the theoretical amount of soluble zinc salt corresponding to the absorption of H2S and HCN gas, unit: g / L; M Zn Indicates the relative molecular mass of ZnSO4·7H2O, unit: g / moL; m SCN Indicates SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL; m CN Indicates CN in the acidified liquid of high-concentration cyanide wastewater - Content, unit: g / L; M CN Indicates CN - Relative atomic mass, unit: g / moL.

[0063] Specifically, 250 ml of solution was prepared with clean water and 50 g (excess) ZnSO4·7H2O, and loaded into the 1# gas absorption bottle. The pH was stabilized at about 6.3 by adding concentrated sulfuric acid, and the solution temperature was measured to be 8°C. 250 ml of solution with a mass concentration of 30% was prepared with clean water and NaOH, and loaded into the 2# gas absorption bottle.

[0064] The reaction in the 1# gas absorption bottle yields a suspension of ZnS and Zn(CN)2.

[0065] (3) After the reaction is completed, the product in the reaction container is filtered to obtain residual iron powder and an iron ion solution as a filtrate, and the Fe concentration in the iron ion solution is measured to be 68.24 g / L. The residual iron powder is recycled in step (2); the pH of the iron ion solution is adjusted to above 11, filtered, and a filtrate and iron hydroxide residue are obtained; the filtrate is returned to the cyanide production system of the gold smelter to continue to be recycled as smelting water. The residue can be stored or sold for disposal.

[0066] Add concentrated sulfuric acid to the ZnS and Zn(CN)2 suspension in the 1# gas absorption bottle to adjust the pH to below 4, stir and react [Zn(CN)2 dissociates to form Zn 2+ and HCN gas] and use sodium hydroxide solution to absorb the overflowed HCN gas to achieve HCN recovery.

[0067] (4) Filter the suspension after the HCN gas overflows from step (3) to obtain ZnS filter residue and Zn as filtrate. 2+ Solution. Complete the absorption and separation of H2S and HCN mixed gas to achieve SCN - Decomposed S 2- and CN - of recycling.

[0068] Example 2. Example 2 of thiocyanate removal and comprehensive recovery method (II).

[0069] The only difference between this embodiment and embodiment (I) is that ZnCl2·4H2O is used instead of ZnSO4·7H2O.

[0070] The theoretical amount of soluble zinc salt corresponding to the absorption of H2S and HCN gas is calculated as follows:

[0071] m Zn =M Zn m SCN / M SCN +0.5 M Zn (m SCN / M SCN +m CN / MCN )=208g / moL×49.44g / L÷58g / moL+0.5×208g / moL×(49.44g / L÷58g / moL+0.25205g / L÷26g / moL)=266.96g / L.

[0072] The actual amount of ZnCl2·4H2O used is 40 g / L (excess). After the reaction in step (3) is completed, the product in the reaction container is filtered to obtain residual iron powder and an iron ion solution as a filtrate. The Fe concentration in the iron ion solution is measured to be 68.72 g / L.

[0073] Example 3: Is there S in the sodium hydroxide solution? 2- or CN - Detection example.

[0074] Purpose of detection: To determine whether the absorption is incomplete. If sulfide ions or cyanide ions are absorbed in bottle 2#, new sodium hydroxide solution should be replaced to determine whether the subsequent reaction absorption is complete.

[0075] During the reaction of step (2), detect whether there is S in the sodium hydroxide solution in the 2# gas absorption bottle. 2- or CN - , if there is S 2- or CN - , then the pH of the iron powder reduction reaction process can be appropriately increased to moderately reduce the reaction intensity, or the primary low-temperature soluble zinc salt weak acid solution absorption can be increased to enhance gas absorption. If there is no S 2- or CN - , then proceed to the next step.

[0076] The specific detection method is: take a sample of sodium hydroxide solution, add soluble ferrous salt or ferric salt, and a black precipitate is generated, indicating the presence of S 2- No black precipitate was generated, indicating that there was no S 2- ; After fully stirring, filter, adjust the filtrate to acidic, continue to add soluble ferrous salt or ferric salt, stir fully, and a blue precipitate is generated, indicating the presence of CN - No blue precipitate was generated, indicating the absence of CN - .

[0077] In the detection example of Example (I), 20 ml of sodium hydroxide solution in the 2# gas absorption bottle was taken, and a 10% FeSO4·7H2O solution was added dropwise. After sufficient stirring, it was filtered and a black FeS precipitate was generated, indicating that there was S in the solution. 2-, there is a problem that the H2S absorption in the 1# gas absorption bottle is not complete; after sufficient stirring, filter, adjust the filtrate to acidity, drop 10% FeSO4·7H2O solution, stir thoroughly, and a blue precipitate of ferric ferrocyanide or ferrous ferrocyanide is generated, indicating that there is CN in the solution - , there is a problem that the HCN absorption in the 1# gas absorption bottle is not complete. In this case, the pH of the iron powder reduction reaction process was raised to 3-4, and no S was found in the test again. 2- With CN - , indicating that H2S and HCN gases have been completely absorbed in the 1# gas absorption bottle.

[0078] Example 4. Example 1 for verifying the experimental effect of the present invention.

[0079] This verification example is for the experimental effect of Example (I) (using the solution of ZnSO4·7H2O).

[0080] The pH of the filtrate returned to the cyanide production system of the gold smelter in step (3) and continued to be used as smelting water was adjusted to about 11.5, filtered, and iron hydroxide residue was obtained. The filtrate was tested for SCN - The concentration is 4.37 g / l, calculate SCN - The removal rate was 91.16%. Detection of CN in the sodium hydroxide solution (500 mL) that absorbed the overflowed HCN gas - The content is 3840.4 mg / L, calculate CN - The recovery rate was 86.64%. In addition, no S was detected in the sodium hydroxide solution (500 mL) that absorbed the overflowed HCN gas. 2- , indicating that the separation effect of H2S and HCN is good, and there is no S 2- Mixing causes the recovered cyanide to be contaminated.

[0081] Example 5. Example 2 for verifying the experimental effect of the present invention.

[0082] This verification example is for the experimental effect of Example (II) (using the solution of ZnCl2·4H2O).

[0083] The pH of the filtrate returned to the cyanide production system of the gold smelter in step (3) and continued to be used as smelting water was adjusted to about 11.5, filtered, and iron hydroxide residue was obtained. The filtrate was tested for SCN - The concentration is 4.42 g / l, calculate SCN - The removal rate was 91.01%. Detection of CN in the sodium hydroxide solution (500 mL) that absorbed the overflowed HCN gas - The content is 3752.0 mg / L, calculate CN -The recovery rate was 84.66%. In addition, no S was detected in the sodium hydroxide solution (500 mL) that absorbed the overflowed HCN gas. 2- , indicating that the separation effect of H2S and HCN is good, and there is no S 2- Mixing causes the recovered cyanide to be contaminated.

Claims

1. A method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater, characterized in that Follow these steps: Step (1): acidify and filter the high-concentration cyanide-containing wastewater to achieve solid-liquid separation to obtain a filtrate and a filter residue; and detect the SCN in the filtrate. - and CN - content; Step (2): the filtrate obtained in step (1) is placed in a reaction container, iron powder exceeding the theoretical amount of iron powder is added, and concentrated sulfuric acid is added to maintain the pH at 2-3, and the mixture is stirred for reaction; the mixed gas overflowing from the stirring reaction is passed into a No. 1 gas absorption container filled with a low-temperature soluble zinc salt weak acid solution with a temperature of 0-10° C. and a pH of 6.0-6.5 for absorption under stirring conditions, and the gas overflowing from the No. 1 gas absorption container is passed into a No. 2 gas absorption container filled with a sodium hydroxide solution with a pH>11 for absorption under stirring conditions; Wherein, the low-temperature soluble zinc salt weak acid solution is prepared by water and a soluble zinc salt exceeding the theoretical amount of zinc added; Step (3): after the reaction in step (2) is completed, the product in the reaction container is filtered to obtain residual iron powder and an iron ion solution as a filtrate, the pH of the iron ion solution is adjusted to above 11, filtered to obtain a filtrate and an iron hydroxide residue; and concentrated sulfuric acid is added to the suspension in the first gas absorption container to adjust the pH to below 4, the reaction is stirred, and the overflowed HCN gas is absorbed by alkaline solution to achieve HCN recovery; Step (4) filtering the suspension after the HCN gas overflows from the 1# gas absorption container to obtain ZnS filter residue and Zn 2+ filtrate, realize H2S and HCN mixed gas absorption and separation, and realize S 2- and CN - of recycling.

2. The method for removing and comprehensively recovering thiocyanate from the acidified liquid of high-concentration cyanide-containing wastewater according to claim 1, characterized in that The theoretical addition amount of iron powder is calculated according to the following formula: m Fe =M Fe m SCN / M SCN ; In the formula, m Fe Indicates the theoretical amount of iron powder added, unit: g / L; M Fe Indicates the relative atomic mass of Fe, in g / moL; m SCN SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL.

3. The method for removing and comprehensively recovering thiocyanate from the acidified liquid of high-concentration cyanide-containing wastewater according to claim 1, characterized in that The theoretical amount of zinc added is calculated according to the following formula: m Zn =M Zn m SCN / M SCN +0.5 M Zn (m SCN / M SCN +m CN / M CN ); In the formula, m Zn It indicates the theoretical amount of soluble zinc salt corresponding to the absorption of H2S and HCN gas, in g / L; M Zn Indicates the relative molecular mass of soluble zinc salt, unit: g / moL; m SCN Indicates SCN in acidified liquid of high concentration cyanide wastewater - Content, unit: g / L; M SCN SCN - Relative atomic mass, unit: g / moL; m CN Indicates CN in the acidified liquid of high-concentration cyanide wastewater - Content, unit: g / L; M CN Indicates CN - Relative atomic mass, unit: g / moL.

4. The method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater according to claim 1, characterized in that: During the reaction of step (2), detect whether there is S in the sodium hydroxide solution in the 2# gas absorption container. 2- or CN - ; If there is S 2- or CN - , then adjust the pH of the reaction system to 3-4.

5. The method for removing and comprehensively recovering thiocyanate from the acidified liquid of high-concentration cyanide-containing wastewater as claimed in claim 4, characterized in that Does the sodium hydroxide solution in the 2# gas absorption container contain S? 2- or CN - Determine by the following method: Take a sample of sodium hydroxide solution, add soluble ferrous salt or ferric salt, and a black precipitate will form, indicating the presence of S 2- No black precipitate was generated, indicating that there was no S 2- ; After fully stirring, filter, adjust the filtrate to acidic, continue to add soluble ferrous salt or ferric salt, stir fully, and a blue precipitate is generated, indicating the presence of CN - No blue precipitate was generated, indicating the absence of CN - .

6. The method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater according to claim 1, characterized in that: The residual iron powder obtained in step (3) is recycled in step (2); in step (3), the pH of the iron ion solution is adjusted to above 11, and the filtrate obtained by filtration is returned to the cyanide production water system.

7. The method for removing and comprehensively recovering thiocyanate from acidified liquid of high-concentration cyanide-containing wastewater according to claim 1, characterized in that: The volume of the low-temperature soluble zinc salt weak acid solution and the volume of the sodium hydroxide solution with a pH value greater than 11 are respectively 2-3 times that of the filtrate obtained in step (1).

8. The method for removing and comprehensively recovering thiocyanate from the acidified liquid of high-concentration cyanide-containing wastewater according to any one of claims 1 to 7, characterized in that: The total cyanide mass concentration in the acidified liquid of the high-concentration cyanide-containing wastewater is greater than 800 mg / L.

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