Method for preparing low-chromium ammonium polyvanadate

Abstract

The invention discloses a method for preparing low-chromium ammonium polyvanadate, which comprises the following steps: pretreating an impurity removal solution to ensure that the turbidity of the impurity removal solution is not more than 200UTN; adding an oxidizing agent into the pretreated impurity-removed liquid for oxidation to obtain a purified liquid; the purified liquid is subjected to acidic ammonium salt vanadium precipitation, and low-chromium ammonium polyvanadate is obtained; wherein the impurity removal liquid is obtained by selectively reducing sodium vanadium solution and removing chromium and silicon; in addition, different oxidation processes are selected based on the oxidation-reduction potential, the pH value and / or the chromium concentration of the impurity removal liquid. According to the method, different oxidation measures need to be adopted for impurity removal liquid with different properties, so that the oxidation efficiency is improved, the oxidation cost is reduced, and the quality of vanadium precipitates is improved. Different oxidation methods are designed by utilizing the reaction characteristics of chromium and different oxides and combining the pH value of a solution and the oxidation-reduction potential. The method has the characteristics of high oxidation efficiency, low oxidation cost, good vanadium product quality, high vanadium precipitation rate, easy determination of parameter boundaries and strong operability.

Description

Technical Field

[0001] The invention relates to the technical field of vanadium oxide preparation, and in particular to a method for preparing low-chromium ammonium polyvanadate. Background Art

[0002] Vanadium is a very rare metal element, mainly used in the steel industry to improve the strength, toughness and other properties of steel products. In recent years, the application of vanadium in non-steel fields has become more and more extensive, such as the hot energy storage field, vanadium-based positive electrode materials, and the research and application of all-vanadium liquid flow batteries have become more and more mature. There are also many applications in chemical catalysis, medicine, metal vanadium, vanadium alloys, titanium alloys and other fields. The application characteristics of vanadium in non-steel fields determine that the quality requirements of vanadium oxide are very high. For example, excessive concentrations of chromium and other pollutants in vanadium electrolytes will have an adverse effect on the function of the electrolyte and reduce the charge state due to electrolyte imbalance, which directly shortens the service life of vanadium batteries. The sodium roasting of vanadium slag-water leaching vanadium extraction process is still the most widely used vanadium extraction process. Due to the similar properties of vanadium and chromium, part of the chromium is leached together with vanadium in the form of chromate during leaching. During the vanadium precipitation process, chromium will enter the precipitate of amino polyvanadate or amino metavanadate. This phenomenon leads to an increase in the chromium content in vanadium pentoxide, thereby reducing the purity of the product. Therefore, it is necessary to reduce the chromium content in the vanadium liquid, and then reduce the amount of chromium entering the vanadium product, so as to improve the quality of the vanadium product and meet the diversified market demand. In the industry, chromium reduction is often used to separate vanadium and chromium, and then the impurity removal liquid is used to precipitate vanadium to prepare vanadium products. However, such methods rarely involve the operation of oxidizing the impurity removal liquid, resulting in serious excessive chromium content when the impurity removal liquid is used to produce vanadium products, large consumption of ammonium salt for vanadium precipitation, and low vanadium precipitation rate.

[0003] The prior art discloses a method for preparing low-silicon ammonium polyvanadate by reducing vanadium precipitation and desiliconization, specifically, adding acid to a vanadium-containing solution, adjusting the pH value to 5-6, adding a reducing agent for reduction reaction, and obtaining a reduced vanadium solution; adjusting the pH value of the reduced vanadium solution to 2-3, adding an ammonium salt for reaction, and after the reaction is completed, filtering to obtain a vanadium precipitation filter cake, and washing the filter cake with deionized water by pulping, and then drying. According to the method for preparing low-silicon ammonium polyvanadate by reducing vanadium precipitation and desiliconization described in the present invention, deep desiliconization of a vanadium-containing solution can be achieved, and the silicon content in the prepared APV is reduced to below 20ppm, with excellent desiliconization effect. This method does not oxidize the impurity removal liquid, and the excess reducing agent will reduce the vanadium under acidic conditions, which will affect the vanadium precipitation.

[0004] The prior art discloses a method for directly precipitating vanadium from an acidic, impure vanadium-containing solution. During oxidation treatment, an oxidant is added to the vanadium-containing solution, and oxidation is carried out at 40 to 70° C. for 0.2 to 1.0 h to obtain an oxidized vanadium solution. The amount of the oxidant added is 1.0 to 2.5 times the theoretical molar amount of the oxidant required to completely oxidize the low-valent vanadium in the vanadium-containing solution into pentavalent vanadium. The method clearly points out that the low-valent vanadium in the vanadium solution will affect the vanadium precipitation rate.

[0005] Based on this, the existing technology still needs to be improved. Summary of the invention

[0006] In order to solve the above technical problems, the embodiment of the present invention provides a method for preparing low-chromium ammonium polyvanadate to solve the technical problem in the prior art that low-valent vanadium affects the vanadium precipitation rate.

[0007] In order to solve the above technical problems, some embodiments of the present invention disclose a method for preparing low-chromium ammonium polyvanadate, comprising: Pre-treat the impurity removal liquid so that the turbidity of the impurity removal liquid is no more than 200 UTN; adding an oxidant to the pretreated impurity removal liquid for oxidation to obtain a purified liquid; The purified liquid is subjected to acidic ammonium salt precipitation of vanadium to obtain low-chromium ammonium polyvanadate; Wherein, the impurity removal liquid is the impurity removal liquid obtained by selectively reducing chromium and silicon with sodium vanadium solution; Furthermore, different oxidation processes are selected based on the redox potential, pH value and / or chromium concentration of the impurity removal solution.

[0008] In some embodiments, selecting different oxidation processes based on the redox potential, pH value and / or chromium concentration of the impurity removal solution includes: using a first oxidation process, a second oxidation process and a third oxidation process in sequence for oxidation as the pH value of the impurity removal solution increases, the redox potential decreases and the chromium concentration decreases; Among them, the first oxidation process is to use one of ammonium persulfate and sodium persulfate or a mixture of the two; the second oxidation process is to first oxidize with hydrogen peroxide and then oxidize with sodium persulfate or ammonium persulfate; the third oxidation process is to oxidize with hydrogen peroxide.

[0009] In some embodiments, selecting different oxidation processes based on the redox potential, pH value and / or chromium concentration of the impurity removal solution includes: When the pH of the impurity removal solution measured at 60° C. is ≤10.0, the redox potential is 0 mV to 180 mV, and the chromium concentration is 0.3 g / L to 0.8 g / L, oxidation is performed using one of ammonium persulfate and sodium persulfate or a mixture of the two.

[0010] In some embodiments, when oxidation is performed using one of ammonium persulfate and sodium persulfate or a mixture of the two, the amount of oxidant added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~7, oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥400mV.

[0011] In some embodiments, selecting different oxidation processes based on the redox potential, pH value and / or chromium concentration of the impurity removal solution includes: When the pH of the impurity removal liquid measured at 60°C is 10.0-10.6, the redox potential is greater than -100mV and less than or equal to 0mV, and the chromium concentration is greater than 0.03g / L and less than or equal to 0.3g / L, first oxidize with hydrogen peroxide and then oxidize with sodium persulfate or ammonium persulfate.

[0012] In some embodiments, when the oxidation is first performed with hydrogen peroxide and then with sodium persulfate or ammonium persulfate, the amount of hydrogen peroxide added is 0.05% by weight. （双氧水中的氧） / Cr （钒液中的Cr） =1~3, oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV; based on the molar ratio, the amount of ammonium persulfate or sodium persulfate added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~3, oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥300mV.

[0013] In some embodiments, selecting different oxidation processes based on the redox potential, pH value and / or chromium concentration of the impurity removal solution includes: When the pH of the impurity removal solution measured at 60°C is 10.6-11.6, the redox potential is -450mV--100mV, and the chromium concentration is <0.03g / L, hydrogen peroxide oxidation is used.

[0014] In some embodiments, when hydrogen peroxide is used for oxidation, the amount of hydrogen peroxide added is 0 （双氧水中的氧） / Cr （钒液中的Cr） =2~7, oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV.

[0015] In some embodiments, subjecting the purified liquid to acidic ammonium salt precipitation of vanadium comprises: The purified liquid is diluted to V of 25g / L-35g / L. The pH of the diluted purified liquid is adjusted to 5.0-6.0 for the first time. The pH temperature is adjusted to 20℃-70℃ for the first time. After the pH is adjusted, ammonium salt is added. The amount of ammonium salt added is TV / ammonium sulfate = 1.2-2.0 by mass ratio. Then the second acid adjustment is carried out, the pH value is adjusted to 2.0-2.3, and then the temperature is raised to 90°C-100°C and kept for 35min-90min, and ammonium polyvanadate and vanadium precipitation supernatant are obtained after solid-liquid separation.

[0016] In some embodiments, when the purified liquid is subjected to acidic ammonium salt precipitation of vanadium, the amount of ammonium salt added is TV / ammonium sulfate = 1.2 to 1.6 by mass ratio; Alternatively, the obtained ammonium polyvanadate is washed once, the washing water is prepared by clean water and sulfuric acid, the washing water pH is controlled to be 2.0-5.0, the washing water temperature is 50°C-90°C, the washing water volume is 0.05-0.1 times the mass of the vanadium precipitation purification liquid, and the washing water filtrate is returned to the diluted purification liquid.

[0017] By adopting the above technical solution, the present invention has at least the following beneficial effects: The present invention provides a method for preparing low-chromium ammonium polyvanadate. For impurity removal liquids of different properties, different oxidation measures need to be taken to improve oxidation efficiency, reduce oxidation costs, and improve the quality of vanadium precipitates. The present invention utilizes the reaction characteristics of chromium with different oxides, combines solution pH and redox potential, and designs different oxidation methods. The method has the characteristics of high oxidation efficiency, low oxidation cost, good vanadium product quality, high vanadium precipitation rate, easy determination of parameter limits, and strong operability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A flow chart of a method for preparing low-chromium ammonium polyvanadate disclosed in some embodiments of the present invention; Figure 2 This is a schematic diagram of the reaction between chromium and hydrogen peroxide in a method for preparing low-chromium ammonium polyvanadate disclosed in some embodiments of the present invention. DETAILED DESCRIPTION

[0020] The following is a further detailed description of the embodiments of the present disclosure in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present disclosure, but cannot be used to limit the scope of the present disclosure. The present disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

[0021] The present disclosure provides these embodiments to make the present disclosure thorough and complete, and to fully express the scope of the present disclosure to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of the parts and steps, the composition of the materials, the numerical expressions and the numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary, and not as limiting.

[0022] It should be noted that, in the description of the present disclosure, unless otherwise specified, the meaning of "multiple" is greater than or equal to two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating the orientation or positional relationship, are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present disclosure. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0023] In addition, the words "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different parts. "Vertical" does not mean vertical in the strict sense, but is within the tolerance range. "Parallel" does not mean parallel in the strict sense, but is within the tolerance range. "Include" or "comprising" and similar words mean that the elements before the word include the elements listed after the word, and do not exclude the possibility of including other elements.

[0024] It should also be noted that in the description of the present disclosure, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present disclosure can be understood according to the specific circumstances. When a specific device is described as being located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0025] All terms used in the present disclosure have the same meanings as those understood by those of ordinary skill in the art to which the present disclosure belongs, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries, for example, should be interpreted as having meanings consistent with their meanings in the context of the relevant technology, and should not be interpreted in an idealized or extremely formal sense, unless explicitly defined as such herein.

[0026] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0027] like Figure 1 As shown, some embodiments of the present invention disclose a method for preparing low-chromium ammonium polyvanadate, wherein the raw material used is a de-doping liquid obtained by selectively reducing chromium and silicon with sodium vanadium solution, the de-doping liquid has an oxidation-reduction potential of -450 mV to 180 mV, a chromium concentration of 0.001 g / L to 0.8 g / L, and a vanadium concentration of 30 g / L to 60 g / L. If the de-doping liquid is not oxidized for vanadium precipitation, most of the trivalent chromium in the de-doping liquid will enter the vanadium product. When the chromium content in the de-doping liquid exceeds the upper limit, the chromium content of the vanadium product will exceed the standard. At the same time, the more tetravalent vanadium in the vanadium liquid cannot be effectively precipitated, thereby reducing the vanadium precipitation rate. Therefore, the de-doping liquid obtained by selectively reducing chromium and silicon with sodium vanadium solution needs to be oxidized.

[0028] There are three situations in which sodium vanadium solution selectively reduces chromium and silicon: ① When the pH of the vanadium solution is high, the main reactions for selective reduction and chromium removal are as follows: 8CrO4 2- +6S 2- +23H2O = 8Cr(OH)3↓+3S2O3 2- +22OH - In this process, the hexavalent chromium in the solution mainly consumes the reducing agent. There are more low-valent sulfates in the impurity removal solution, some vanadates, low trivalent chromium content, and no hexavalent chromium. When the impurity removal solution does not oxidize vanadium precipitation, the low-valent sulfates and some vanadates in the impurity removal solution will cause more tetravalent vanadium in the vanadium solution to be unable to be effectively precipitated under the conditions of acidic ammonium salt vanadium precipitation, thereby reducing the vanadium precipitation rate.

[0029] ②When the pH of vanadium solution is moderate, the main reactions are as follows: 8CrO4 2- +6S 2- +23H2O = 8Cr(OH)3↓+3S2O3 2- +22OH - 4V2O7 4- +2S 2- +7H2O = S2O32- +14OH - +2V4O9 2- In this process, the reducing agent is mainly consumed by hexavalent chromium and pentavalent vanadium in the solution. Vanadium and chromium compete to consume the reducing agent, resulting in incomplete removal of chromium in the impurity removal liquid. The impurity removal liquid contains more low-valent sulfates and a certain amount of hexavalent chromium, trivalent chromium and vanadate.

[0030] ③When the pH of vanadium solution is low, the main reactions are as follows: 8CrO4 2- +6S 2- +23H2O = 8Cr(OH)3↓+3S2O3 2- +22OH - 4V2O7 4- +2S 2- +7H2O = S2O3 2- +14OH - +2V4O9 2- 2V4O9 2- +S2O3 2- +2H + = 4V2O3↓+2SO4 2- +H2O Most of the reducing agent during chromium removal is consumed by hexavalent chromium and pentavalent vanadium, the content of low-valent sulfate and trivalent chromium is low, and the chromium content in the impurity removal liquid is high, mainly hexavalent chromium.

[0031] If the impurity removal liquid is not oxidized for vanadium precipitation, most of the trivalent chromium in the impurity removal liquid will enter the vanadium product. When the chromium content in the impurity removal liquid exceeds the upper limit, the chromium content of the vanadium product will exceed the standard. At the same time, the more tetravalent vanadium in the vanadium liquid cannot be effectively precipitated, which leads to a decrease in the vanadium precipitation rate. Therefore, the impurity removal liquid after the selective reduction of chromium and silicon by sodium vanadium liquid needs to be oxidized. Different oxidation measures need to be taken for impurity removal liquids of different properties to improve oxidation efficiency, reduce oxidation costs, and improve the quality of vanadium precipitates.

[0032] When the pH value of the impurity removal liquid is high (the selective reduction chromium removal effect is better, the redox potential of the impurity removal liquid is -450mV~-100mV, and the chromium concentration is <0.03g / L), the chromium content in the impurity removal liquid is low at this time, and most of the reducing agent during chromium removal is consumed by hexavalent chromium. There are more low-valent sulfates, some vanadates, low trivalent chromium content, and no hexavalent chromium. This impurity removal liquid can be completely oxidized with hydrogen peroxide. Excessive hydrogen peroxide will not cause quality problems of vanadium precipitate APV, that is, most of the chromium enters the product and will not cause product impurities to exceed the standard.

[0033] When the pH of the impurity removal liquid is moderate (the selective reduction chromium removal effect is general, the redox potential of the impurity removal liquid is -100mV~0mV, and the chromium concentration is 0.03g / L~0.3g / L), at this time, in the impurity removal liquid (containing a certain amount of hexavalent chromium and trivalent chromium), most of the reducing agent during chromium removal is consumed by hexavalent chromium, and there are more low-valent sulfates and a lower content of trivalent chromium. If this impurity removal liquid is completely oxidized with hydrogen peroxide, it is not easy to control the amount of hydrogen peroxide added. When the amount of hydrogen peroxide added is large, it will also appear under acidic vanadium precipitation conditions. Hydrogen peroxide will reduce the hexavalent chromium in the impurity removal liquid to trivalent chromium, increasing the probability of chromium entering the vanadium precipitate APV. When the amount of hydrogen peroxide added is small, it cannot completely oxidize the low-valent sulfates, low-valent vanadium and trivalent chromium in the impurity removal liquid, and the effect on controlling the chromium content and improving the vanadium precipitation rate is limited. This impurity removal liquid can first be oxidized with part of the hydrogen peroxide, and then oxidized with sodium persulfate or ammonium persulfate. This method can not only effectively improve the oxidation efficiency, but also greatly reduce the oxidation cost.

[0034] When the pH of the impurity removal liquid is low (the selective reduction chromium removal effect is poor, the redox potential of the impurity removal liquid is greater than 0mV, and the chromium concentration is greater than 0.3g / L), the chromium content in the impurity removal liquid is relatively high (mainly hexavalent chromium), and most of the reducing agent during chromium removal is consumed by hexavalent chromium and pentavalent vanadium, and the content of low-valent sulfate and trivalent chromium is relatively low. If the impurity removal liquid is oxidized with hydrogen peroxide, hydrogen peroxide is not enough to oxidize trivalent chromium, and there is no substance in the solution that can completely consume hydrogen peroxide. Most of the added hydrogen peroxide will remain in the impurity removal liquid. When the impurity removal liquid is subjected to acidic ammonium salt vanadium precipitation, under acidic conditions, hydrogen peroxide will reduce the hexavalent chromium in the impurity removal liquid to trivalent chromium, increasing the probability of chromium entering the vanadium precipitate APV, making the chromium content in the oxidized vanadium precipitation APV higher than that in the impurity removal liquid non-oxidized vanadium precipitation APV. This impurity removal liquid can be oxidized with sodium persulfate or ammonium persulfate.

[0035] That is to say, when the pH of the impurity removal liquid is low, the redox potential of the impurity removal liquid is greater than 0mV, and the chromium concentration is greater than 0.3g / L, the impurity removal liquid can be oxidized by sodium persulfate or ammonium persulfate; when the redox potential of the impurity removal liquid is -100 to 0mV and the chromium concentration is 0.03g / L to 0.3g / L, the impurity removal liquid can first be partially oxidized by hydrogen peroxide, and then oxidized by sodium persulfate or ammonium persulfate, which can not only effectively improve the oxidation efficiency, but also greatly reduce the oxidation cost; when the redox potential of the impurity removal liquid is -450mV to -100mV and the chromium concentration is less than 0.03g / L, the impurity removal liquid can be completely oxidized by hydrogen peroxide. After the purification liquid is oxidized, the pH is adjusted, ammonium salt is added, and then the temperature is raised to precipitate ammonium polyvanadate.

[0036] The main reason is that the oxidation cost of ammonium persulfate or sodium persulfate is about ten times that of hydrogen peroxide; under low pH conditions, hydrogen peroxide is not enough to oxidize trivalent chromium to hexavalent chromium. At this time, if hydrogen peroxide is used as an oxidant, under the subsequent acidic ammonium salt vanadium precipitation conditions, hydrogen peroxide can reduce hexavalent chromium to trivalent chromium, and most of the trivalent chromium will enter the vanadium precipitate APV, resulting in serious excess of chromium. Figure 2 The reaction shown.

[0037] Cr 3+ +3OH - = Cr(OH)3↓(Ⅰ) Cr(OH)3+OH - =CrO 2- +2H2O(Ⅱ) 2CrO 2- +3H2O2+2OH - =2CrO4 2- +4H2O(Ⅲ) 2CrO4 2- +7H2O2+2OH - = 2CrO8 3- +8H2O(Ⅳ) 4CrO8 3- +2H2O = 4CrO4 2- +4OH - +7O 2 ↑(Ⅴ) 2CrO4 2- +2H + ⇌Cr2O7 2- +H2O(VI) 8H++Cr2O7 2- +3H2O2=2Cr 3+ +7H2O+3O 2 ↑ (VII) After the sodium vanadium solution selectively reduces the chromium and silicon co-removal, the impurity removal liquid is oxidized through the above oxidation measures, which can improve the quality of the purified liquid after oxidation of the impurity removal liquid, improve the vanadium precipitation rate of the purified liquid, reduce the trivalent chromium in the purified liquid, and then reduce the Cr content in the vanadium precipitate APV, thereby improving the quality of vanadium products.

[0038] A method for preparing low-chromium ammonium polyvanadate disclosed in some embodiments of the present invention, wherein the composition of the vanadium liquid is shown in Table 1, and the composition of the impurity removal liquid is shown in Table 2, comprises: a. Pretreatment of the impurity removal liquid; which includes: filtering the impurity removal liquid after selective reduction of chromium and silicon by sodium vanadium solution to control its turbidity to ≤200 UTN (scattering turbidity unit).

[0039] Table 1

[0040] Table 2

[0041] b. Adding an oxidant to the impurity removal liquid for oxidation to obtain a purified liquid; If the pH of the impurity removal solution is ≤10.0 (measured at 60℃), the redox potential is 0mV~180mV, and the chromium concentration is 0.3g / L~0.8g / L, then ammonium persulfate or sodium persulfate, or a mixture of the two, should be used for oxidation. The amount of oxidant added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~7 (substance ratio), oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥400mV; If the pH of the impurity removal solution is 10.0-10.6 (measured at 60°C), the redox potential is -100mV-0mV, and the chromium concentration is 0.03g / L-0.3g / L, the impurity removal solution can be partially oxidized with hydrogen peroxide and then oxidized with sodium persulfate or ammonium persulfate. The amount of hydrogen peroxide added is 0 （双氧水中的氧） / Cr （钒液中的Cr） =1~3 (amount ratio of substances), oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV; the amount of ammonium persulfate or sodium persulfate added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~3 (substance ratio), oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥300mV; If the pH of the impurity removal solution is 10.6-11.6 (measured at 60℃), the redox potential is -450mV--100mV, and the chromium concentration is <0.03g / L, the impurity removal solution can be oxidized by hydrogen peroxide. The amount of hydrogen peroxide added is O （双氧水中的氧） / Cr （钒液中的Cr） =2~7 (molar ratio), oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV.

[0042] If one or more of the measured pH value, redox potential and chromium concentration is in an intermediate state or a critical value, an oxidation treatment method close to the value can be selected.

[0043] c. Use the purified liquid to precipitate vanadium with acidic ammonium salt. To precipitate APV, the vanadium precipitation solution, i.e., the purified liquid, needs to be diluted to a V of 25 g / L to 35 g / L. The diluent can be clean water or a vanadium precipitation supernatant (the main components of the vanadium precipitation supernatant are sodium sulfate and ammonium sulfate solution, see Table 3). The diluted vanadium precipitation solution is first adjusted to pH = 5.0 to 6.0, and the first pH adjustment temperature is 20°C to 70°C. After the pH is adjusted, ammonium salt is added, and the amount of ammonium salt added is TV / ammonium sulfate = 1.2 to 2.0 (mass ratio), and the preferred amount of ammonium salt added is TV / ammonium sulfate = 1.2 to 2.0 (mass ratio). Ammonium sulfate = 1.2 ~ 1.6 (mass ratio), and then the second acid adjustment is carried out, the second pH is adjusted to 2.0 ~ 2.3, and then the temperature is raised to 90 ℃ ~ 100 ℃ and kept for 35min ~ 90min, and high-quality APV and vanadium precipitation supernatant are obtained after solid-liquid separation; the obtained APV is washed once, and the washing water is prepared by clean water + sulfuric acid, and the washing water pH is controlled to be 2.0 ~ 5.0, the washing water temperature is 50 ℃ ~ 90 ℃, and the washing water volume is 0.05 ~ 0.1 times the volume of vanadium precipitation purification liquid. The washing water filtrate is returned to the diluted purification liquid.

[0044] Table 3

[0045] When the present invention is implemented, 200 mL of impurity-removing vanadium liquid is measured with a measuring cylinder, and its turbidity is controlled to be ≤200 UTN (scattering turbidity unit); the pH and redox potential of the impurity-removing liquid are measured. If the pH of the impurity-removing liquid is ≤10.0 (measured at 60° C.), the redox potential is 0 mV to 180 mV, and the chromium concentration is 0.3 g / L to 0.8 g / L, ammonium persulfate or sodium persulfate, or a mixture of the two, is used for oxidation, and the amount of the oxidant added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~7 (molar ratio), oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥400mV; if the pH of the impurity removal liquid is 10.0~10.6 (measured at 60℃), the redox potential is -100mV~0mV, and the chromium concentration is 0.03g / L~0.3g / L, this impurity removal liquid can be partially oxidized by hydrogen peroxide first, and then oxidized by sodium persulfate or ammonium persulfate. The amount of hydrogen peroxide added is O （双氧水中的氧） / Cr (Cr in vanadium liquid) = 1 to 3 (substance ratio), oxidation temperature is 50℃ to 90℃, oxidation time is 10min to 60min, and the ORP value after oxidation is controlled to be ≥ 100mV; the amount of ammonium persulfate or sodium persulfate added is S （氧化剂中的硫） / Cr （钒液中的Cr）=2~3 (amount ratio of substances), oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥300mV; if the pH of the impurity removal liquid is 10.6~11.6 (measured at 60℃), the redox potential is -450mV~-100mV, and the chromium concentration is <0.03g / L, this impurity removal liquid can be oxidized with hydrogen peroxide, and the amount of hydrogen peroxide added is O （双氧水中的氧） / Cr （钒液中的Cr） =2~7 (molar ratio), oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV; to precipitate APV, the purified liquid needs to be diluted to V of 25g / L~35g / L. The diluent can be clean water or vanadium precipitation supernatant. The diluted vanadium precipitation liquid is first adjusted to pH=5.0~6.0. The first pH adjustment temperature is 20℃~70℃. After adjusting the pH, add ammonium salt. The amount of ammonium salt added is TV / ammonium sulfate=1.2~2.0 (mass ratio) The preferred amount of ammonium salt added is TV / ammonium sulfate = 1.2-1.6 (mass ratio), and then the second acid adjustment is performed, the second pH is adjusted to 2.0-2.3, and then the temperature is raised to 90°C-100°C and kept for 35min-90min. After solid-liquid separation, high-quality APV and vanadium precipitation supernatant are obtained; the obtained APV is washed once, and the washing water is prepared by clear water + sulfuric acid, the washing water pH is controlled to 2.0-5.0, the washing water temperature is 50°C-90°C, the washing water volume is 0.05-0.1 times the volume of the vanadium precipitation purification liquid, and the washing water filtrate is returned to the diluted purification liquid.

[0046] Example 1 The Cr concentration in the original vanadium solution is 2.7 g / L, and the composition of the impurity-removing solution is shown in Table 4.

[0047] Table 4

[0048] Use a measuring cylinder to measure 200mL of the impurity-removing vanadium solution, whose turbidity is 200 UTN (scattering turbidity unit); measure the pH and redox potential of the impurity-removing solution. The pH of the impurity-removing solution is 10.8 (measured at 60℃), the redox potential is -350mV, and the chromium concentration is 0.002g / L. This impurity-removing solution can be oxidized with hydrogen peroxide. The amount of hydrogen peroxide added is O (oxygen in hydrogen peroxide) / Cr (Cr in vanadium solution) = 2 (molar ratio), about 1.176mL of 30% hydrogen peroxide, the oxidation temperature is 50℃, the oxidation time is 10min, and the ORP value after oxidation is controlled to be 120mV; to precipitate APV, the purified solution needs to be diluted to V of 35g / L, and the diluent is clean water 85.7mL, the diluted vanadium precipitation solution was adjusted to pH=5.0 for the first time, and the pH temperature was 50℃ for the first time. After adjusting the pH, ammonium salt was added, and the amount of ammonium salt added was TV / ammonium sulfate=1.2 (mass ratio) 12g ammonium sulfate, and then the second acid adjustment was performed, and the pH was adjusted to 2.0 for the second time, and then the temperature was raised to 90℃ for 35min. After solid-liquid separation, high-quality APV and vanadium precipitation supernatant were obtained. The obtained APV was washed once, and the washing water was adjusted with clean water + sulfuric acid, and the washing water pH was controlled to 2.0, the washing water temperature was 90℃, and the washing water volume was 0.1 times the amount of vanadium precipitation purification liquid 20mL, and the washing water filtrate was returned to the diluted purification liquid. The composition of high-quality APV is shown in Table 5.

[0049] Table 5

[0050] Example 2 The Cr concentration in the original vanadium solution is 2.7 g / L, and the composition of the impurity-removing solution is shown in Table 6.

[0051] Table 6

[0052] Use a measuring cylinder to measure 200mL of the impurity-removing vanadium solution, whose turbidity is 20 UTN (scattering turbidity unit); measure the pH and redox potential of the impurity-removing solution. The pH of the impurity-removing solution is 10.4 (measured at 60℃), the redox potential is -80mV, and when the chromium concentration is 0.2g / L, the impurity-removing solution can be oxidized by hydrogen peroxide. The amount of hydrogen peroxide added is O (oxygen in hydrogen peroxide) / Cr (Cr in vanadium solution) = 1 (molar ratio), about 0.588mL of 30% hydrogen peroxide, the oxidation temperature is 50℃, the oxidation time is 10min, and the ORP value after oxidation is controlled to be 110mV; the amount of sodium persulfate added is S (sulfur in the oxidant) / Cr (Cr in the vanadium solution) = 2 (molar ratio) 2.47g, the oxidation temperature is 30℃, the oxidation time is 10min, and the ORP value after oxidation is 350mV. To precipitate APV, the purified liquid needs to be diluted to V=35g / L, and the diluent is 79mL of the supernatant of vanadium precipitation. The diluted vanadium precipitation liquid is adjusted to pH=6.0 for the first time, and the temperature of the first pH adjustment is 30℃. After adjusting the pH, add ammonium salt, and the amount of ammonium salt added is TV / ammonium sulfate=1.6 (mass ratio) 15.71g ammonium sulfate, and then adjust the acid for the second time, and adjust the pH to 2.3 for the second time, then heat to 90℃ and keep warm for 60min, and obtain high-quality APV and vanadium precipitation supernatant after solid-liquid separation. The obtained APV is washed once, and the washing water is adjusted by clean water + sulfuric acid, and the washing water pH is controlled to 5, the washing water temperature is 50℃, and the washing water volume is 0.1 times the amount of vanadium precipitation purification liquid 20mL, and the washing water filtrate is returned to the diluted purification liquid. The composition of high-quality APV is shown in Table 7.

[0053] Table 7

[0054] Example 3 The Cr concentration in the original vanadium solution is 2.7 g / L, and the composition of the impurity-removing solution is shown in Table 8.

[0055] Table 8

[0056] Use a measuring cylinder to measure 200mL of the impurity-removing vanadium solution, whose turbidity is 1.9UTN (scattering turbidity unit); measure the pH and redox potential of the impurity-removing solution. When the pH of the impurity-removing solution is 9.8 (measured at 60℃), the redox potential is 140mV, and the chromium concentration is 0.8g / L, the impurity-removing solution can be oxidized by ammonium persulfate. The amount of ammonium persulfate added is S (sulfur in the oxidant) / Cr (Cr in the vanadium solution) = 5 (molar ratio) 5.92g, the oxidation temperature is 30℃, the oxidation time is 60min, and the ORP value after oxidation is 450mV. To precipitate APV, the purified liquid needs to be diluted to V=35g / L, and the diluent is 74mL of the supernatant of vanadium precipitation. The diluted vanadium precipitation liquid is adjusted to pH=5.5 for the first time, and the temperature of the first pH adjustment is 30℃. After adjusting the pH, add ammonium salt, and the amount of ammonium salt added is TV / ammonium sulfate=1.3 (mass ratio) 12.50g ammonium sulfate, and then adjust the acid for the second time, and adjust the pH to 2.1 for the second time, then heat to 95℃ and keep warm for 90min, and obtain high-quality APV and vanadium precipitation supernatant after solid-liquid separation. The obtained APV is washed once, and the washing water is adjusted by clean water + sulfuric acid, and the washing water pH=3 is controlled, the washing water temperature is 90℃, and the washing water volume is 0.1 times the amount of vanadium precipitation purification liquid 20mL, and the washing water filtrate is returned to the diluted purification liquid. The composition of high-quality APV is shown in Table 9.

[0057] Table 9

[0058] So far, various embodiments of the present disclosure have been described in detail. In order to avoid obscuring the concept of the present disclosure, some details known in the art are not described. Based on the above description, those skilled in the art can fully understand how to implement the technical solution disclosed here.

[0059] Although some specific embodiments of the present disclosure have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. It should be understood by those skilled in the art that the above embodiments may be modified or some technical features may be replaced by equivalents without departing from the scope and spirit of the present disclosure. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there is no structural conflict.

Claims

1. A method for preparing low-chromium ammonium polyvanadate, characterized in that: include: Pre-treat the impurity removal liquid so that the turbidity of the impurity removal liquid is no more than 200 UTN; adding an oxidant to the pretreated impurity removal liquid for oxidation to obtain a purified liquid; The purified liquid is subjected to acidic ammonium salt precipitation of vanadium to obtain low-chromium ammonium polyvanadate; Wherein, the impurity removal liquid is the impurity removal liquid obtained by selectively reducing chromium and silicon with sodium vanadium solution; Furthermore, different oxidation processes are selected based on the redox potential, pH value and / or chromium concentration of the impurity removal solution.

2. The method for preparing low-chromium ammonium polyvanadate according to claim 1, characterized in that: Selecting different oxidation processes based on the redox potential, pH value and / or chromium concentration of the impurity removal solution includes: using the first oxidation process, the second oxidation process and the third oxidation process in sequence for oxidation as the pH value of the impurity removal solution increases, the redox potential decreases and the chromium concentration decreases; Among them, the first oxidation process is to use one of ammonium persulfate and sodium persulfate or a mixture of the two; the second oxidation process is to first oxidize with hydrogen peroxide and then oxidize with sodium persulfate or ammonium persulfate; the third oxidation process is to oxidize with hydrogen peroxide.

3. The method for preparing low-chromium ammonium polyvanadate according to claim 1, characterized in that: Different oxidation processes are selected based on the redox potential, pH and / or chromium concentration of the impurity removal solution, including: When the pH of the impurity removal solution measured at 60° C. is ≤10.0, the redox potential is 0 mV to 180 mV, and the chromium concentration is 0.3 g / L to 0.8 g / L, oxidation is performed using one of ammonium persulfate and sodium persulfate or a mixture of the two.

4. The method for preparing low-chromium ammonium polyvanadate according to claim 3, characterized in that: When using one of ammonium persulfate and sodium persulfate or a mixture of the two for oxidation, the amount of oxidant added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~7, oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥400mV.

5. The method for preparing low-chromium ammonium polyvanadate according to claim 1, characterized in that: Different oxidation processes are selected based on the redox potential, pH and / or chromium concentration of the impurity removal solution, including: When the pH of the impurity removal liquid measured at 60°C is 10.0-10.6, the redox potential is greater than -100mV and less than or equal to 0mV, and the chromium concentration is greater than 0.03g / L and less than or equal to 0.3g / L, first oxidize with hydrogen peroxide and then oxidize with sodium persulfate or ammonium persulfate.

6. The method for preparing low-chromium ammonium polyvanadate according to claim 5, characterized in that: When the oxidation is first performed with hydrogen peroxide and then with sodium persulfate or ammonium persulfate, the amount of hydrogen peroxide added is 0 （双氧水中的氧） / Cr （钒液中的Cr） =1~3, oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV; based on the molar ratio, the amount of ammonium persulfate or sodium persulfate added is S （氧化剂中的硫） / Cr （钒液中的Cr） =2~3, oxidation temperature is 30℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥300mV.

7. The method for preparing low-chromium ammonium polyvanadate according to claim 1, characterized in that: Different oxidation processes are selected based on the redox potential, pH and / or chromium concentration of the impurity removal solution, including: When the pH of the impurity removal solution measured at 60°C is 10.6-11.6, the redox potential is -450mV--100mV, and the chromium concentration is <0.03g / L, hydrogen peroxide oxidation is used.

8. The method for preparing low-chromium ammonium polyvanadate according to claim 7, characterized in that: When hydrogen peroxide is used for oxidation, the amount of hydrogen peroxide added is 0 （双氧水中的氧） / Cr （钒液中的Cr） =2~7, oxidation temperature is 50℃~90℃, oxidation time is 10min~60min, and the ORP value after oxidation is controlled to be ≥100mV.

9. The method for preparing low-chromium ammonium polyvanadate according to claim 1, characterized in that: The purification liquid is subjected to acidic ammonium salt precipitation of vanadium, including: The purified liquid is diluted to V of 25g / L-35g / L. The pH of the diluted purified liquid is adjusted to 5.0-6.0 for the first time. The pH temperature is adjusted to 20℃-70℃ for the first time. After the pH is adjusted, ammonium salt is added. The amount of ammonium salt added is TV / ammonium sulfate = 1.2-2.0 by mass ratio. Then the second acid adjustment is carried out, and the pH value is adjusted to 2.0-2.3 for the second time. Then the temperature is raised to 90°C-100°C and kept for 35min-90min. After solid-liquid separation, ammonium polyvanadate and vanadium precipitation supernatant are obtained.

10. The method for preparing low-chromium ammonium polyvanadate according to claim 9, characterized in that: When the purified liquid is subjected to acidic ammonium salt precipitation of vanadium, the amount of ammonium salt added is TV / ammonium sulfate = 1.2 to 1.6 by mass ratio; Alternatively, the obtained ammonium polyvanadate is washed once, the washing water is prepared by clean water and sulfuric acid, the washing water pH is controlled to be 2.0-5.0, the washing water temperature is 50°C-90°C, the washing water volume is 0.05-0.1 times the mass of the vanadium precipitation purification liquid, and the washing water filtrate is returned to the diluted purification liquid.

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