Process and apparatus for extracting ammonium thiocyanate

Abstract

The present application relates to the technical field of chemical wastewater recycling treatment, and discloses a method and device for extracting ammonium thiocyanate. The method comprises the following steps: performing primary solid-liquid separation on a mixed solution of pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt to precipitate anhydrous sodium sulfate; performing secondary solid-liquid separation on the solution after the primary solid-liquid separation to precipitate a mixed salt of sodium sulfate and ammonium sulfate; and performing tertiary solid-liquid separation on the solution after the secondary solid-liquid separation to obtain ammonium thiocyanate. The method can solve the problems of efficient treatment of high-purity vanadium wastewater and difficulty in treatment or resource utilization of coke oven gas desulfurization waste residue, so as to achieve waste treatment with waste and resource recycling, and greatly reduce the treatment investment cost and operation cost of the two pollutants.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical wastewater recovery and treatment, in particular to a method and device for extracting ammonium thiocyanate. BACKGROUND

[0002] High-purity vanadium production uses vanadium pentoxide or metavanadic acid as raw material, and produces an alkaline inorganic wastewater with high ammonia nitrogen and high sodium during the production process, and also has high concentration of sulfate and low amount of vanadium-containing substances (dissolved and suspended). This wastewater has been one of the difficult problems in the field of high-salinity wastewater treatment, which is difficult to treat and has poor economic adaptability. At present, the process of reducing vanadium and chromium, stripping ammonia, and multi-effect evaporation crystallization to produce sodium sulfate is adopted, which has high investment, high treatment cost, low resource utilization rate, and the effluent does not meet the standard. The desulfurization waste salt of coke oven gas is a complex salt formed by the chemical reaction of a weak alkaline solution used as an absorbent with H2S, HCN and other substances in the gas during the gas desulfurization process. The clean H2S is released for acid production, and the salt produced in the circulation process must be separated out regularly and quantitatively, which is mainly sodium thiocyanate and sodium thiosulfate. The amount of the stored salt is large, and the treatment is difficult, which seriously limits the normal production of the coking process. Therefore, a kind of efficient and economic, short process, cyclic removal and resource recycling and low investment process and method are needed to solve the problem of the two pollutants.

[0003] Therefore, there is an urgent need for a technical solution for extracting ammonium thiocyanate to solve the above problems. SUMMARY

[0004] The following presents a simplified summary of some aspects of the disclosed embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of the embodiments described in detail in the following detailed description, and is intended neither to identify key or critical elements nor to delineate the scope of such embodiments. Rather, the primary purpose of this summary is to present some concepts of the embodiments in a simplified form as a prelude to the more detailed description below.

[0005] In view of the deficiencies of the prior art, the present disclosure provides a method and device for extracting ammonium thiocyanate to solve the efficient treatment of high-purity vanadium wastewater and the difficulty in treating or resource utilization of coke oven gas desulfurization waste salt, so as to achieve waste treatment and resource recycling, and greatly reduce the treatment investment cost and operating cost of the two pollutants.

[0006] In a first aspect, the present disclosure provides a method for extracting ammonium thiocyanate, which is applied to a mixed solution of high-purity vanadium wastewater and coke oven gas desulfurization waste salt, and the method comprises the following steps: performing primary solid-liquid separation on the pretreated mixed solution of high-purity vanadium wastewater and coke oven gas desulfurization waste salt to precipitate anhydrous sodium sulfate; performing secondary solid-liquid separation on the solution after the primary solid-liquid separation to precipitate a mixed salt of sodium sulfate and ammonium sulfate; and performing tertiary solid-liquid separation on the solution after the secondary solid-liquid separation to obtain ammonium thiocyanate.

[0007] In the preferred technical scheme of the method for extracting ammonium thiocyanate, the first solid-liquid separation of the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt is performed to precipitate anhydrous sodium sulfate, which comprises stirring the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt, evaporating and concentrating the mixed solution to saturation of sodium sulfate at a temperature of 95-105 DEG C, and cooling to 85 DEG C to precipitate anhydrous sodium sulfate.

[0008] In the preferred technical scheme of the method for extracting ammonium thiocyanate, the first solid-liquid separation of the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt is performed to precipitate anhydrous sodium sulfate, which comprises stirring the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt, evaporating and concentrating the mixed solution to saturation of sodium sulfate at a temperature of 95-105 DEG C, and cooling to 85 DEG C to precipitate anhydrous sodium sulfate. + 2- -

[0009] In the preferred technical scheme of the method for extracting ammonium thiocyanate, the first solid-liquid separation of the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt is performed to precipitate anhydrous sodium sulfate, which comprises stirring the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt, evaporating and concentrating the mixed solution to saturation of sodium sulfate at a temperature of 95-105 DEG C, and cooling to 85 DEG C to precipitate anhydrous sodium sulfate.

[0010] In the preferred technical scheme of the method for extracting ammonium thiocyanate, the first solid-liquid separation of the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt is performed to precipitate anhydrous sodium sulfate, which comprises stirring the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt, evaporating and concentrating the mixed solution to saturation of sodium sulfate at a temperature of 95-105 DEG C, and cooling to 85 DEG C to precipitate anhydrous sodium sulfate. + + 2- 2- - -

[0011] In the preferred technical scheme of the method for extracting ammonium thiocyanate, the first solid-liquid separation of the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt is performed to precipitate anhydrous sodium sulfate, which comprises stirring the mixed solution of the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt, evaporating and concentrating the mixed solution to saturation of sodium sulfate at a temperature of 95-105 DEG C, and cooling to 85 DEG C to precipitate anhydrous sodium sulfate. - ​​​​​​​​​The concentration reaches 420 g / L, and the temperature is naturally cooled down. When the temperature is reduced to 55 DEG C, secondary solid-liquid separation is performed to precipitate the mixed salt of sodium sulfate and ammonium sulfate. After the mixed salt of sodium sulfate and ammonium sulfate is precipitated, it is returned to the dissolution process of the coal gas desulfurization waste salt for recycling.

[0012] In the preferred technical solution of the method for extracting ammonium thiocyanate, the "performing tertiary solid-liquid separation on the solution after the secondary solid-liquid separation to obtain ammonium thiocyanate" comprises: continuing to cool the solution after the secondary solid-liquid separation to 20 DEG C and then performing tertiary solid-liquid separation to obtain ammonium thiocyanate with a purity greater than 99%. The mother liquor after the tertiary solid-liquid separation is used instead of pure water in the dissolution process of the coal gas desulfurization waste salt.

[0013] In the second aspect, the embodiments of the present disclosure provide a device for extracting ammonium thiocyanate, which is configured to perform the method for extracting ammonium thiocyanate as described above.

[0014] The method and device for extracting ammonium thiocyanate provided by the embodiments of the present disclosure can achieve the following technical effects:

[0015] The coal gas desulfurization waste salt is treated in cooperation with the high-purity vanadium wastewater, the reductant for reducing vanadium in the treatment of the high-purity vanadium wastewater is reduced, the deamination system is saved, the treatment cost of the desulfurization waste salt is reduced, V, anhydrous sodium sulfate and ammonium thiocyanate are efficiently recovered, the environmental protection risk of substandard disposal of wastewater and waste residue is avoided, and the economic benefit is obvious.

[0016] The foregoing general description and the following description are only exemplary and explanatory, and are not used to limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0017] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitation on the embodiments, elements with the same reference numerals in the drawings are shown as similar elements, the drawings do not constitute proportional limitation, and wherein:

[0018] Figure 1 A flowchart of a method for extracting ammonium thiocyanate provided by the present application is shown;

[0019] Figure 2 A flowchart of another method for extracting ammonium thiocyanate provided by the present application is shown. DETAILED DESCRIPTION

[0020] In order to enable a more detailed understanding of the features and technical content of the embodiments of the present disclosure, the implementation of the embodiments of the present disclosure is described in detail below with reference to the accompanying drawings, which are only used for reference and do not limit the embodiments of the present disclosure. In the following technical description, in order to facilitate explanation, a plurality of details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be simplified to facilitate the drawings.

[0021] The terms "first", "second", and the like in the description and claims of the embodiments of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily have to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged as appropriate in order to implement the embodiments of the present disclosure described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0022] In the embodiments of the present disclosure, the terms "upper", "lower", "inner", "middle", "outer", "front", "back", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present disclosure and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation. In addition, in addition to indicating the orientation or positional relationship, the above-mentioned terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain attachment relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0023] In addition, the terms "set", "connected", "fixed" should be broadly understood. For example, "connected" can be fixedly connected, detachably connected, or integrally configured; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present disclosure can be understood according to the specific circumstances.

[0024] Unless otherwise specified, the term "a plurality of" means two or more.

[0025] It should be noted that the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other without conflict.

[0026] As Figure 1 As shown in the drawings, the embodiments of the present disclosure provide a method for extracting ammonium thiocyanate, comprising:

[0027] Step S1: Perform a primary solid-liquid separation on the pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt mixed solution to precipitate anhydrous sodium sulfate;

[0028] Step S2: Perform secondary solid-liquid separation on the solution after primary solid-liquid separation to precipitate a mixed salt of sodium sulfate and ammonium sulfate;

[0029] Step S3: Perform tertiary solid-liquid separation on the solution after secondary solid-liquid separation to obtain ammonium thiocyanate.

[0030] Specifically, the high-purity vanadium wastewater and coal gas desulfurization waste salt undergo a pretreatment process, primarily involving filtration to form a mixed solution. This mixed solution then undergoes primary solid-liquid separation, such as evaporation, concentration, and cooling at a specific stirring speed to precipitate anhydrous sodium sulfate. After separation, the solution is further heated and concentrated, then naturally cooled for secondary solid-liquid separation to obtain a mixed salt of sodium sulfate and ammonium sulfate. This mixed salt is returned to the coal gas desulfurization waste salt treatment process for dissolution and recycling. Further cooling is then performed for tertiary solid-liquid separation to obtain ammonium thiocyanate with a purity greater than 99%. The crystallization mother liquor is returned to dissolve the desulfurization waste salt, ensuring recycling without external discharge. The primary solid-liquid separation is also called primary crystallization, the secondary solid-liquid separation is called secondary crystallization, and the tertiary solid-liquid separation is called tertiary crystallization.

[0031] In the preferred embodiment of this application, "the mixed solution of pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt is subjected to primary solid-liquid separation to precipitate anhydrous sodium sulfate" includes: stirring the mixed solution of pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt, evaporating and concentrating it at a temperature of 95-105°C until sodium sulfate is saturated, and cooling it to 85°C to crystallize and precipitate anhydrous sodium sulfate.

[0032] Specifically, the pretreated high-purity vanadium wastewater and the coal gas desulfurization waste salt mixed solution are sent to a high-temperature reactor, stirred at a speed of 160-200 rpm and evaporated at a temperature of 95-105°C, concentrated until sodium sulfate is saturated, cooled to 85°C to crystallize and precipitate anhydrous sodium sulfate, and then subjected to primary solid-liquid separation to obtain anhydrous sodium sulfate with a purity greater than 98.5%.

[0033] like Figure 2 As shown, in the preferred embodiment of this application, "pre-treating high-purity vanadium wastewater and coal gas desulfurization waste salt to form a mixed solution" includes:

[0034] Step S11: Filter the high-purity vanadium wastewater through a flat-panel membrane filter to recover suspended vanadium compounds and obtain the first filtrate;

[0035] Step S12: Add the waste salt from coal gas desulfurization to pure water at a sodium thiosulfate concentration of 60-75 g / L and stir to dissolve. Filter the solution through an activated carbon filter to remove suspended and solid impurities to obtain the second filtrate.

[0036] Step S13: adjust the pH value of the first filtrate to 3.0-4.0, mix the second filtrate with the first filtrate at a volume ratio of 0.2-0.25:1, and react for 25-30 min, and then adjust the pH value of the reacted solution to 8.0-8.5, and filter through a flat membrane filter to obtain a mixed solution.

[0037] Specifically, the high-purity vanadium wastewater is filtered through a flat membrane filter, and a suspended vanadium compound is recovered, i.e., returned to the vanadium precipitation process, to obtain a first filtrate. The coal gas desulfurization waste salt is added to pure water at a concentration of 60-75 g / L of sodium thiosulfate (the subsequent crystallization mother liquor is used), and after being fully stirred and dissolved, suspended and solid impurities are removed through an activated carbon filter to obtain a second filtrate. The first filtrate is adjusted to a pH of 3.0-4.0 using ~30% H2SO4, and under the action of stirring at 250-300 rpm, the second filtrate is added at a volume ratio of 0.2-0.25:1 (the ratio of the concentration of sodium thiosulfate to the total amount of V is about 6-7.5:1), and fully mixed and reacted for 20-25 min, which reduces high-valence V to low-valence V on the one hand, and introduces SCN - and increases the concentration of sodium ions on the other hand. After the reaction, 20% ammonia water is added to adjust the pH to 8.0-8.5, and the mixture is filtered through a flat membrane filter to separate the precipitate and obtain a mixed filtrate.

[0038] In the preferred technical solution of the present application, a flat membrane filter is compressed by a silicon carbide ceramic membrane sheet, wherein the filtration pore size is 0.05-0.1 um, and the filtration pressure is 0.05-0.1 Mpa; the components of the first filtrate include Na+: 20-25 g / L, NH4 + : 25-35 g / L, SO4 2- : 90-120 g / L, Cl - : ≦0.02 g / L, total V: 2.0-2.5 g / L, Ca: <0.01 g / L, and the pH value is 9.0-10.0.

[0039] Specifically, the flat membrane filter is compressed by a silicon carbide ceramic membrane sheet, the filtration pore size of the flat membrane is 0.05-0.1 um, and the filtration pressure of the flat membrane filter is set to 0.05-0.1 Mpa. The flat membrane filter has a small footprint and high filtration precision.

[0040] In the preferred technical solution of the present application, the precision of the activated carbon filter is 1.0 mm, the filtration pressure is 0.04-0.6 Mpa, and the filtration speed is 5-12 m / h. In terms of mass percentage, the components of the coal gas desulfurization waste salt include 80% NaSCN, 15% Na2S2O3, and 5% Na2SO4.

[0041] Specifically, the filter material activated carbon is coconut shell columnar, and the particle size is 0.5-1.2 mm. After running for a certain period (depending on the cleanliness of the filtrate), it is sent to sintering as fuel. In addition to the main components described above, the coal gas desulfurization waste salt also includes a small amount of impurity components.

[0042] In the preferred technical scheme of the present application, the silicon carbide ceramic membrane membrane sheet is pressed into a flat membrane filter, the filter pore size is 0.05-0.1 um, and the filter pressure is 0.05-0.1 Mpa. The mixed solution components include Na + : 20-25 g / L, NH4 + : 20-30 g / L, SO4 2- : 95-130 g / L, S2O3 2- : 0.5-2.0 g / L, SCN - : 50-65 g / L, Cl - : <0.05 g / L, total V <0.01 g / L, Ca: ~0.05 g / L, and the pH value of the mixed solution is 8.2-8.7.

[0043] Specifically, the flat membrane filter is pressed by a silicon carbide ceramic membrane membrane sheet, and the filter pore size of the flat membrane is 0.05-0.1 um. The flat membrane filter is provided with a filter pressure of 0.05-0.1 Mpa. The sludge obtained by filtration is washed and dried by plate and frame filter pressing to be used as V2O5 raw material.

[0044] In the preferred technical scheme of the present application, the solution after the first solid-liquid separation is subjected to the second solid-liquid separation to precipitate sodium sulfate and ammonium sulfate mixed salt, which includes: continuing to heat and concentrate the solution after the first solid-liquid separation to SCN - concentration reaches 420 g / L, and the temperature is naturally cooled to 55℃. The second solid-liquid separation is performed to precipitate sodium sulfate and ammonium sulfate mixed salt. After the sodium sulfate and ammonium sulfate mixed salt is precipitated, it is returned to the dissolution process of the coal gas desulfurization waste salt for recycling.

[0045] Specifically, the solution after the first solid-liquid separation has precipitated anhydrous sodium sulfate with a purity of more than 98.5%. The remaining solution is continuously heated, and the crystallization time is 2.5 hours. The sodium sulfate and ammonium sulfate mixed salt needs a certain concentration, so it can continue to be dissolved in the dissolution step of the gas desulfurization waste salt for recycling.

[0046] In the preferred technical scheme of the present application, the solution after the second solid-liquid separation is subjected to the third solid-liquid separation to obtain ammonium thiocyanate, which includes: continuing to cool the solution after the second solid-liquid separation to 20℃ and then performing the third solid-liquid separation to obtain ammonium thiocyanate with a purity of more than 99%. The mother liquor after the third solid-liquid separation is used instead of pure water in the dissolution process of the coal gas desulfurization waste salt.

[0047] Specifically, the solution after secondary solid-liquid separation continues to cool down for crystallization for 1 hour. The remaining solution after that is called crystallization mother liquor, which is returned to the dissolving process of the coal gas desulfurization waste salt to replace the pure water used in the first time, and is recycled without being discharged.

[0048] In the present application, the high-purity vanadium wastewater and desulfurization waste salt are pretreated, the pH of the high-purity vanadium wastewater is adjusted to 3.0-4.0 under the stirring action of 250-300 rpm, the prepared desulfurization waste salt solution is added at a volume ratio of 0.2-0.25:1, after sufficient reaction for 25-30 min, 20% ammonia water is added to adjust the pH to 8.0-8.5, and then it is filtered into a flat plate membrane filter, and the filtrate after filtration is fed into an evaporation reactor, after evaporation and concentration, anhydrous sodium sulfate and ammonium thiocyanate are recovered by stepwise separation, and the crystallization mother liquor is returned to the desulfurization waste salt dissolving tank for recycling.

[0049] The coal gas desulfurization waste salt cooperates with the treatment of high-purity vanadium wastewater, reduces the reductant for reducing vanadium in the treatment of high-purity vanadium wastewater, saves the deamination system, reduces the treatment cost of the desulfurization waste salt, efficiently recovers V, anhydrous sodium sulfate and ammonium thiocyanate, avoids the environmental protection risk of substandard disposal of wastewater and waste residue, and has obvious economic benefits.

[0050] The present disclosure will be further described below in combination with specific embodiments.

[0051] Embodiment 1

[0052] The high-purity vanadium wastewater is filtered through a flat plate membrane filter to recover the suspended vanadium compounds, to obtain a first filtrate, 30% sulfuric acid is added to adjust the pH to 3.2, and the solution composition is Na + : 22.6 g / L, NH4 + : 34.1 g / L, SO4 2- : 118 g / L, Cl - : 0.01 g / L, total V: 2.2 g / L, Ca: <0.01 g / L.

[0053] 70 g of desulfurization waste salt is dissolved in 40°C 100 ml water under the stirring speed of 300 rpm, after being filtered through an activated carbon filter, the suspended matter SS is less than 1 mg / L, and the organic matter content is lower than 0.1 mg / L. The second filtrate composition is Na+: 15.4 g / L, S2O32-: 72.8 g / L, SO42-: 2.3 g / L, SCN-: 402 g / L, Ca <1 mg / L.

[0054] The second filtrate: first filtrate is mixed at a volume ratio (desulfurization waste salt filtrate: high-purity vanadium wastewater) of 0.25:1 under a stirring speed of 300 rpm, fully reacted for 25 min, 20% ammonia water is added to adjust the pH to 8.5, filtered through a flat membrane filter to obtain a mixed solution, and the filtrate components are: temperature 40°C, pH 8.26, Na + : ~21.7 g / L, NH4 + : 27.2 g / L, SO4 2- : 126 g / L, Cl - <0.01 g / L, total V: 1.89 g / L, SCN - : 81 g / L, S2O3 2- : 1.4 g / L, Ca <0.01 g / L.

[0055] The mixed solution is poured into an evaporation reactor, the evaporation temperature is controlled at 100°C, and concentrated to a slurry that appears crystallization, discharged and cooled to 85°C to obtain anhydrous sodium sulfate solid, and the supernatant is continuously poured into the reactor for evaporation and concentration until the SCN - concentration reaches more than 425 g / L, and naturally cooled to reduce the temperature, when the temperature reaches 55°C, the solid is separated, and the clear liquid is continuously cooled to 20°C to obtain ammonium thiocyanate solid. The anhydrous sodium sulfate is dried and analyzed, the purity reaches 99.5%, ammonium sulfate 0.4%, and moisture 0.1%, and the first recovery rate is 92.2%; the ammonium thiocyanate is dried and analyzed, the purity reaches 99.2%, ammonium sulfate 0.3%, and moisture 0.5%, and the first recovery rate is 60.6%; and the mixed salt of sodium sulfate and ammonium sulfate is returned to the dissolution process of coal gas desulfurization waste salt for redissolution and circulation.

[0056] Example 2

[0057] The high-purity vanadium wastewater is filtered through a flat membrane filter to recover the suspended vanadium compounds to obtain a first filtrate, and 30% sulfuric acid is added to adjust the pH to 3.5, and the solution components are: Na+: 24 g / L, NH4+: 30.9 g / L, SO42-: 108 g / L, Cl-: 0.01 g / L, total V: 2.4 g / L, and Ca: <0.01 g / L.

[0058] 65 g of desulfurization waste salt is dissolved in 40°C 100 ml water under a stirring speed of 300 rpm, filtered through an activated carbon filter, and the suspended matter SS is less than 1 mg / L, and the organic matter content is lower than 0.1 mg / L. The second filtrate components are: Na + : 16.8 g / L, S2O3 2- : 66.2 g / L, SO4 2- : 2.0 g / L, SCN-: 376 g / L, Ca <1 mg / L.

[0059] The second filtrate: first filtrate was mixed at a volume ratio (desulfurization waste salt filtrate: high-purity vanadium wastewater) of 0.2:1 under a stirring speed of 250 rpm, reacted fully for 20 min, 20% ammonia water was added to adjust the pH to 8.3, and filtered through a flat membrane filter to obtain a mixed solution, and the filtrate components of the mixed solution were: temperature 38°C, pH 8.15, Na + : ~ 24.8 g / L, NH4 + : 28.1 g / L, SO4 2- : 122.6 g / L, Cl - <0.01 g / L, total V: 2.2 g / L, SCN - : 68 g / L, S2O3 2- : 0.8 g / L, Ca <0.01 g / L.

[0060] The mixed solution was poured into an evaporation reactor, the evaporation temperature was controlled at 105°C, and concentrated to a slurry with crystals, and the slurry was discharged and cooled to 85°C to obtain anhydrous sodium sulfate solid, and the supernatant was continuously poured into the reactor for evaporation and concentration until the SCN - concentration reached more than 425 g / L, and the temperature was naturally cooled to 55°C, the solid was separated, and the clear liquid was continuously cooled to 20°C to obtain ammonium thiocyanate solid. The anhydrous sodium sulfate was dried and analyzed, the purity reached 99.2%, ammonium sulfate was 0.7%, and the moisture content was 0.1%, and the first recovery rate was 91.0%; the ammonium thiocyanate was dried and analyzed, the purity reached 99.4%, ammonium sulfate was 0.4%, and the moisture content was 0.2%, and the first recovery rate was 62.5%; the mixed salt of sodium sulfate and ammonium sulfate was returned to the dissolution process of the coal gas desulfurization waste salt for redissolution and circulation.

[0061] Example 3

[0062] The high-purity vanadium wastewater was filtered through a flat membrane filter to recover the suspended vanadium compounds to obtain a first filtrate, and 30% sulfuric acid was added to adjust the pH to 4.0, and the solution components were: Na + : 21.1 g / L, NH4 + : 28.2 g / L, SO4 2- : 96 g / L, Cl - : 0.01 g / L, total V: 2.06 g / L, Ca: 12 mg / L.

[0063] 68 g of desulfurization waste salt was dissolved in 100 ml of water at 40°C under a stirring speed of 300 rpm, and filtered through an activated carbon filter, and the suspended solids SS were less than 1 mg / L, and the organic matter content was less than 0.1 mg / L. A second filtrate was obtained, and the components were: Na + : 18.6 g / L, S2O3 2- : 71.4 g / L, SO4 2- : 2.3 g / L, SCN -: 390 g / L, Ca: 1 mg / L.

[0064] The second filtrate: first filtrate was mixed at a volume ratio (desulfurization waste salt filtrate: high-purity vanadium waste water) of 0.2:1 under a stirring speed of 250 rpm, reacted for 20 min, 20% ammonia water was added to adjust the pH to 8.0, and filtered through a flat membrane filter. The filtrate composition was: temperature 40°C, pH 7.98, Na + : ~22.6 g / L, NH4 + : 25.5 g / L, SO4 2- : 113.8 g / L, Cl - <0.01 g / L, total V: 1.84 g / L, SCN - : 70.9 g / L, S2O3 2- : 0.5 g / L, Ca: 10 mg / L.

[0065] The filtrate obtained from the mixed solution was poured into an evaporation reactor, the evaporation temperature was controlled at 95°C, and concentrated until crystals appeared in the slurry. The slurry was cooled to 85°C, and anhydrous sodium sulfate solid was obtained. The supernatant was continuously poured into the reactor for evaporation and concentration until the SCN - concentration reached 420 g / L or above. The temperature was naturally cooled to 55°C, the solid was separated, the supernatant was continuously cooled to 20°C, and ammonium thiocyanate solid was obtained. The anhydrous sodium sulfate was dried and analyzed, the purity reached 98.6%, ammonium sulfate was 1.2%, and the moisture content was 0.2%. The first recovery rate was 88.9%. The ammonium thiocyanate was dried and analyzed, the purity reached 99.3%, ammonium sulfate was 0.5%, and the moisture content was 0.2%. The first recovery rate was 60.8%. The mixed salt of sodium sulfate and ammonium sulfate was returned to the dissolution process of the coal gas desulfurization waste salt for re-dissolution and circulation.

[0066] Embodiments of the present disclosure provide an apparatus configured to perform the method for extracting ammonium thiocyanate as described above.

[0067] The above merely provides the preferred embodiments of the present application, but is not intended to limit the scope of the present application; any modification or equivalent replacement within the spirit and scope of the present application shall be encompassed in the protection scope of the claims of the present application.

[0068] Those skilled in the art should understand that the above discussion of any embodiment is only exemplary, and is not intended to mean that the scope of the embodiments disclosed by the present application (including claims) is limited to these examples; under the idea of the embodiments of the present application, the above embodiments or technical features among different embodiments can also be combined, and there are many other changes of different aspects of the embodiments of the present application as described above, which are not provided in details for the sake of brevity. Therefore, any omission, modification, equivalent replacement, improvement, etc. made within the spirit and principle of the embodiments of the present application shall be included in the protection scope of the embodiments of the present application.

Claims

1. A method for extracting ammonium thiocyanate, characterized in that, The method is applied to a mixed solution of high-purity vanadium wastewater and coal gas desulfurization waste salt, wherein the pretreatment of the high-purity vanadium wastewater and coal gas desulfurization waste salt to form the mixed solution includes: The high-purity vanadium wastewater is filtered through a flat-panel membrane filter to recover suspended vanadium compounds and obtain the first filtrate. The waste salt from coal gas desulfurization was added to pure water at a sodium thiosulfate concentration of 60-75 g / L and stirred to dissolve. The solution was then filtered through an activated carbon filter to remove suspended and solid impurities, thus obtaining the second filtrate. Adjust the pH of the first filtrate to 3.0-4.0, mix the second filtrate and the first filtrate at a volume ratio of 0.2-0.25:1, and react for 25-30 minutes. Adjust the pH of the reacted solution to 8.0-8.5 and filter it through a flat sheet membrane filter to obtain a mixed solution. The method includes the following steps: The pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt mixed solution were subjected to primary solid-liquid separation to precipitate anhydrous sodium sulfate. The solution after primary solid-liquid separation is subjected to secondary solid-liquid separation to precipitate a mixed salt of sodium sulfate and ammonium sulfate. The solution after secondary solid-liquid separation is subjected to tertiary solid-liquid separation to obtain ammonium thiocyanate.

2. The method according to claim 1, characterized in that, The step of performing a primary solid-liquid separation on the pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt mixture to precipitate anhydrous sodium sulfate includes: The pretreated high-purity vanadium wastewater and coal gas desulfurization waste salt mixed solution were stirred, evaporated and concentrated at 95~105℃ until sodium sulfate was saturated, and then cooled to 85℃ to crystallize and precipitate anhydrous sodium sulfate.

3. The method according to claim 1, characterized in that, A flat-panel membrane filter using silicon carbide ceramic membrane sheets is employed, with a pore size of 0.05~0.1µm and a filtration pressure of 0.05~0.1MPa. The first filtrate contains Na... + 20~25g / L, NH4 + 25~35g / L, SO4 2- 90~120g / L, Cl - : ≤0.02g / L, Total V: 2.0~2.5g / L, Ca: <0.01g / L, pH value 9.0~10.

0.

4. The method according to claim 1, characterized in that, The activated carbon filter has a precision of 1.0 mm, a filtration pressure of 0.04~0.6 MPa, and a filtration speed of 5~12 m / h. By mass percentage, the waste salt composition of coal gas desulfurization includes 80% NaSCN, 15% Na2S2O3, and 5% Na2SO4.

5. The method according to claim 1, characterized in that, A flat-panel membrane filter using silicon carbide ceramic membrane sheets is employed, with a pore size of 0.05~0.1µm and a filtration pressure of 0.05~0.1MPa. The mixed solution components include Na. + 20~25g / L, NH4 + 20~30g / L, SO4 2- 95~130g / L, S2O3 2- 0.5~2.0g / L, SCN - 50~65g / L, Cl - : <0.05g / L, total V <0.01g / L, Ca: ~0.05g / L, pH of mixed solution 8.2~8.

7.

6. The method according to claim 1, characterized in that, The step of performing a secondary solid-liquid separation on the solution after the primary solid-liquid separation to precipitate a mixed salt of sodium sulfate and ammonium sulfate includes: The solution after primary solid-liquid separation is further concentrated by heating to SCN. - When the concentration reaches 420 g / L, it is allowed to cool naturally until the temperature drops to 55°C. Then, a two-stage solid-liquid separation is performed to precipitate a mixed salt of sodium sulfate and ammonium sulfate. The precipitated sodium sulfate and ammonium sulfate mixed salt is recycled back into the dissolution process of waste salt from coal gas desulfurization.

7. The method according to claim 1, characterized in that, The step of performing tertiary solid-liquid separation on the solution after secondary solid-liquid separation to obtain ammonium thiocyanate includes: The solution after the secondary solid-liquid separation is further cooled to 20°C and then subjected to tertiary solid-liquid separation to obtain ammonium thiocyanate with a purity greater than 99%.

8. The method according to claim 7, characterized in that, The step of performing tertiary solid-liquid separation on the solution after secondary solid-liquid separation to obtain ammonium thiocyanate includes: The mother liquor after the three-stage solid-liquid separation is used to replace the pure water in the dissolution process of waste salt from coal gas desulfurization.

9. An apparatus for extracting ammonium thiocyanate, characterized in that, The apparatus is configured to perform the method for extracting ammonium thiocyanate as described in any one of claims 1 to 8.

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