Method and device for stepwise recovery of vanadium and chromium from vanadium tailing wastewater of vanadium-titanium ore

Abstract

The application discloses a method and device for step-by-step recovery of vanadium and chromium in vanadium extraction terminal wastewater of vanadium-titanium ore, and the method comprises the following steps: pH adjustment filtering, biological aerobic selective reduction, alkaline elution, precipitation roasting, reduction vanadium precipitation and filtering roasting. In the biological aerobic selective reduction step of the method, the hexavalent chromium in the wastewater is reduced by the reduction microorganism under the aerobic condition, and the chromium is separated from the liquid phase. Compared with the traditional chemical reduction treatment method, the method can realize efficient recovery of vanadium in the vanadium extraction terminal wastewater, obtain vanadium sheet and high-purity chromium green products, and realize product added value upgrading.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of vanadium-titanium ore smelting, and particularly relates to a method for stepwise recovery of vanadium and chromium in vanadium-titanium ore vanadium extraction terminal wastewater. BACKGROUND

[0002] Vanadium is a rare and precious metal widely used in materials, chemical industry, aerospace and other fields, and is mainly extracted from vanadium-titanium ore through smelting. This process often produces vanadium-titanium ore vanadium extraction terminal wastewater with high chromium and vanadium abundance. Removing vanadium and chromium heavy metals from vanadium-titanium ore vanadium extraction terminal wastewater while recycling and recycling vanadium and chromium rare metals not only meets the treatment needs of vanadium-titanium ore vanadium extraction terminal wastewater, but also uses wastewater as a resource for extracting vanadium and chromium, which can improve the economic benefits of the process and the utilization efficiency of resources. The main technology for recycling vanadium-titanium ore vanadium extraction wastewater is a chemical method based on reduction precipitation. First, a reducing agent is used to reduce vanadium and chromium to Cr 3+ and V 3+ , and then sodium hydroxide solution is added to adjust the pH to generate chromium / vanadium hydroxide precipitate. Then, through processes such as acid dissolution, impurity removal, filtration and spray drying, basic chromium sulfate is produced. In the reduction process, due to the similar potential range of V(IV) / V(III) and Cr(III), it is difficult to selectively reduce Cr(VI) and V(V) with a chemical reducing agent, resulting in vanadium entering the precipitate together and being unable to be independently separated to form a product. Therefore, this process cannot effectively extract vanadium. In addition, the chromium product has low purity and low added value. SUMMARY

[0003] Based on the technical problems presented in the background, the purpose of the present application is to provide a method and device for stepwise recovery of vanadium and chromium in vanadium-titanium ore vanadium extraction terminal wastewater, in order to improve the vanadium and chromium recycling degree of vanadium-titanium ore vanadium extraction terminal wastewater, realize stepwise extraction of vanadium and chromium rare metals, and improve the added value of recycled products and resource utilization.

[0004] The method for stepwise recovery of vanadium and chromium in vanadium-titanium ore vanadium extraction terminal wastewater proposed by the present application comprises the following steps:

[0005] (1) Adjust the pH of vanadium-titanium ore vanadium extraction terminal wastewater to 6-9 by adding liquid alkali, so that iron and silicon substances are precipitated and coagulated, and iron and silicon precipitates are removed by solid-liquid separation to obtain iron and silicon removal wastewater;

[0006] (2) Pass the iron and silicon removal wastewater obtained in step (1) into a reaction tank I containing chromium-reducing bacterial microbial suspended filler and carbon source, control the dissolved oxygen concentration to 0.5-4 mg / L by aeration, and the hydraulic retention time is 5-10 hours, and then solid-liquid separation is performed to obtain chromium sludge and chromium removal wastewater I;

[0007] (3) passing the chromium removal wastewater I obtained in step (2) into a reaction tank II containing chromium-reducing microbial suspended filler and a carbon source, controlling the dissolved oxygen concentration to be 0.5-4 mg / L by aeration, and performing solid-liquid separation to obtain chromium sludge and chromium removal wastewater II after a hydraulic retention time of 5-10 hours;

[0008] (4) adding a reducing agent to the chromium removal wastewater II obtained in step (3) and performing solid-liquid separation to obtain vanadium slag;

[0009] (5) washing and drying the vanadium slag obtained in step (4) in water, and calcining the vanadium slag at a temperature of 300-600°C to obtain high-purity vanadium pentoxide product;

[0010] (6) calcining, alkali washing and drying the chromium sludge obtained in steps (2) and (3) to obtain chromium green product.

[0011] Further, the community composition of the chromium-reducing bacteria in steps (2) and (3) mainly comprises at least one of Serratia, Bacillus, Xenorhabdus, Pantoea or Achromobacter.

[0012] Further, the carbon source in steps (2) and (3) is at least one of sodium lactate, sodium acetate, sodium citrate or glucose.

[0013] Further, the stoichiometric ratio of the carbon source to chromium in steps (2) and (3) is 0.8-2.2:1.

[0014] Further, the chromium-reducing microbial suspended filler in steps (2) and (3) is a polyurethane-ether sulfone high-molecular porous material on which chromium-reducing microorganisms are loaded to form a film, the porosity of the material is 10000-17000 m 2 / m 3 , and the thickness of the biofilm is 1.5-1.8 mm.

[0015] Further, the reducing agent added in step (4) is at least one of sodium pyrosulfite, ascorbic acid or sodium bisulfite.

[0016] Further, the amount-of-substance ratio of the reducing agent to vanadium in step (4) is 1.1-1.5:1.

[0017] Further, the calcination temperature of the vanadium slag in step (5) is 500-800°C, and the calcination time is 30-60 min.

[0018] Further, the calcination temperature of the chromium sludge in step (6) is 400-700°C, and the calcination time is 30-60 min; and the washing conditions of the calcined chromium sludge in step (6) are as follows: liquid-solid ratio of 5-20 mL / g, concentration of sodium hydroxide solution of 0.2-2 mol / L, washing temperature of 10-30°C, and washing times of 1-5.

[0019] The device for the method for recovering vanadium and chromium from the end-of-line wastewater of a vanadium-titanium ore vanadium recovery process comprises a pH adjusting device, a reaction tank I, a reaction tank II, a chromium removal wastewater reducing device, a reduced-state chromium removal wastewater solid-liquid separation device, a vanadium residue elution and drying integrated device, a chromium mud roasting device, and a chromium mud elution and drying integrated device.

[0020] In the present application, first, pH adjustment is performed to cause iron to form a hydroxide precipitate and generate a coagulation effect, thereby promoting the settlement of silica gel suspended in the liquid phase, and helping to avoid filter membrane blockage. The removal of iron and silicon can avoid the precipitation of iron and silicon along with chromium when the pH rises during the biochemical process, and help to improve the purity of the chromium product.

[0021] The iron and silicon removal wastewater is treated in two-step aerobic biochemical reaction tanks (steps (2) and (3)), in which chromium is selectively reduced to Cr(III) by microbial enzymatic reaction and forms Cr(OH)3 precipitate, while vanadium still exists in the form of VO2 + The selective step-by-step reduction of chromium and vanadium is achieved by forming VO2

[0022] The microbial reduction of chromium and the separation process from vanadium can be enhanced by adjusting the dissolved oxygen concentration in the aerobic biochemical process. Since Cr2O3*3H2O exists in the corresponding Eh-pH range, VO2 and V2O3 forms also exist, i.e. both chromium and vanadium are in low-valence state precipitates. In the narrow Eh-ph range, it is difficult to select a suitable reducing agent to selectively reduce chromium and vanadium for separation. Some microorganisms can selectively reduce chromium under aerobic conditions through enzymatic reaction, and since Eh Cr(VI) >Eh O2 >Ehv(v), which has no reducing effect on pentavalent vanadium under aerobic conditions. Therefore, maintaining a certain dissolved oxygen concentration not only promotes the metabolism and enzyme production of microorganisms, but also maintains the stability of pentavalent vanadium.

[0023] The chromium mud obtained after solid-liquid separation is roasted to decompose the main phase Cr(OH)3 in it into chromium sesquioxide (chrome green). The small amount of organic matter contained in the chromium mud is decomposed into gas by combustion.

[0024] The chromium removal wastewater is reduced by a reducing agent, and VO2 + V(OH)3 and V2O5 are produced by reduction. x H2O precipitate, and the vanadium form is converted to V2O5 by roasting to obtain vanadium pentoxide product.

[0025] When treated by aerobic biochemical reaction tank, the carbon source and chromium molecular ratio needs to be controlled, and the carbon source / chromium stoichiometric ratio is required to be 0.8-2.2:3, so as to ensure that the microorganism has sufficient electron donor and substrate, maintain high enzyme activity, and fully reduce chromium. When the carbon source / chromium stoichiometric ratio is less than 0.8:1, the insufficient electron donor leads to insufficient reduction of chromium, thereby reducing the extraction rate of chromium and the purity of subsequent vanadium products.

[0026] When roasting chromium slag, the roasting time and temperature need to be controlled. The roasting time and temperature are controlled to improve the decomposition conversion rate of Cr(OH)3 and the decomposition rate of organic matter, and to avoid the presence of chromium hydroxide impurities and organic matter residues in chromium green products.

[0027] When vanadium in chromium removal wastewater is reduced by adding a reducing agent, the reducing agent and vanadium molecular ratio needs to be controlled, and the reducing agent / vanadium molecular ratio is required to be 1.1-1.5:1, so as to ensure that the reducing agent reacts with vanadium and fully reduces vanadium. When the reducing agent / vanadium molecular ratio is 1.1-1.5:1, the insufficient reducing agent leads to insufficient reduction of vanadium, thereby reducing the extraction rate of vanadium.

[0028] When roasting vanadium slag, the roasting time and temperature need to be controlled. The roasting time and temperature are controlled to improve the decomposition conversion rate of V(OH)3 and V2O5· x H2O, and to avoid the presence of vanadium hydroxide impurities in vanadium pentoxide products.

[0029] The beneficial effects of the method are as follows:

[0030] Controlling the appropriate ratio of carbon source and reducing agent, roasting temperature and time, the chromium in vanadium-titanium ore vanadium extraction terminal wastewater is selectively reduced to chromium hydroxide by biological aerobic reduction, so that chromium and vanadium are separated; it is beneficial to step-by-step extraction of vanadium and chromium to form high-value-added high-purity products.

[0031] After the vanadium in the chromium removal wastewater is reduced by the reducing agent, it is converted into V(OH)3 and V2O5· x H2O precipitate, vanadium is extracted alone, which is beneficial to the subsequent production of high-value-added vanadium pentoxide products. The present application can significantly improve the resource utilization degree and product added value of vanadium-titanium ore vanadium extraction terminal wastewater, and efficiently extract chromium and vanadium in steps to form two high-value-added products.

[0032] In summary, the present application can improve the resource degree and product added value of vanadium extraction terminal wastewater of vanadium-titanium ore, and efficiently convert vanadium and chromium in the wastewater to form two high added value products. The step-by-step selective reduction process of chromium and vanadium involved in the present application has the advantages of simple process, low cost, green and efficient, etc., and avoids the defects of low product purity and low added value of traditional methods. Considering the huge amount of vanadium extraction terminal wastewater of vanadium-titanium ore produced every year, the present application has broad market application prospect, can produce huge economic benefits, and is beneficial to the green and efficient recycling treatment of smelting wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0033] The present application will be further described below in combination with the drawings and examples.

[0034] Figure 1 The process flow chart of the method for step-by-step recovery of vanadium and chromium in vanadium extraction terminal wastewater of vanadium-titanium ore.

[0035] Figure 2 The K-edge XANES spectrum and analysis results of chromium in chromium-vanadium products.

[0036] Figure 3 The K-edge XANES spectrum and analysis results of vanadium in chromium-vanadium products.

[0037] Figure 4 The device for step-by-step recovery of vanadium and chromium in vanadium extraction terminal wastewater of vanadium-titanium ore. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of description and simplification of the description of the present application, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0040] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more unless otherwise explicitly specified.

[0041] This embodiment provides a method for the stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore, referring to... Figure 1 This includes the following steps:

[0042] (1) The pH of the vanadium-titanium ore extraction end wastewater is adjusted to 6-9 by adding liquid alkali, so that the iron and silicon substances precipitate and coagulate. The iron and silicon precipitate is removed by solid-liquid separation to obtain iron and silicon removed wastewater.

[0043] (2) The iron and silicon removal wastewater obtained in step (1) is fed into reaction tank I containing chromium-reducing bacteria microbial suspension packing and carbon source. The dissolved oxygen concentration is controlled by aeration at 0.5~4 mg / L, the hydraulic retention is 5~10 hours, and solid-liquid separation is performed to obtain chromium mud and chromium removal wastewater I.

[0044] (3) The chromium removal wastewater I obtained in step (2) is introduced into the reaction tank II containing chromium-reducing bacteria microbial suspension packing and carbon source. The dissolved oxygen concentration is controlled by aeration at 0.5~4 mg / L, the hydraulic retention is 5~10 hours, and solid-liquid separation is performed to obtain chromium mud and chromium removal wastewater II.

[0045] (4) Add a reducing agent to the chromium removal wastewater II obtained in step (3) and separate the solid and liquid to obtain vanadium slag;

[0046] (5) The vanadium slag obtained in step (4) is washed and dried in water, and then roasted at 300~600°C to obtain a high-purity vanadium pentoxide product;

[0047] (6) The chromium mud obtained in steps (2) and (3) is roasted, alkaline washed and dried to obtain chromium green product.

[0048] The community composition of the chromium-reducing bacteria described in steps (2) and (3) mainly includes at least one of the genera *Serratia*, *Bacillus*, *Leucobacterium*, *Alternaria*, or *Achromobacterium*.

[0049] The carbon source mentioned in steps (2) and (3) is at least one of sodium lactate, sodium acetate, sodium citrate or glucose.

[0050] The stoichiometric ratio of carbon source to chromium in steps (2) and (3) is 0.8 to 2.2:1.

[0051] The chromium-reducing microbial suspension filler described in steps (2) and (3) is a chromium-reducing microbial-loaded polyurethane-ether sulfone porous material, and the porosity is 10000-17000 m 2 / m 3 , and the biofilm thickness is 1.5-1.8 mm.

[0052] The reducing agent added in step (4) is at least one of sodium pyrosulfite, ascorbic acid or sodium bisulfite.

[0053] The molar ratio of the reducing agent to vanadium substance in step (4) is 1.1-1.5:1.

[0054] The roasting temperature of the vanadium slag in step (5) is 500-800°C, and the roasting time is 30-60 min.

[0055] The roasting temperature of the chromium mud in step (6) is 400-700°C, and the roasting time is 30-60 min; the elution conditions of the chromium mud after roasting in step (6) are as follows: the liquid-solid ratio is 5-20 mL / g, the concentration of the sodium hydroxide solution is 0.2-2 mol / L, the elution temperature is 10-30°C, and the elution times are 1-5.

[0056] Figure 2 and Figure 3 The K-edge XANES spectrum of chromium / vanadium of the chromium vanadium product and the analysis results are shown. The carbon source is sodium lactate, the carbon source / chromium molecular ratio is 4:3, the reducing agent is sodium pyrosulfite, the reducing agent / vanadium molecular ratio is 1.3:1, the chromium slag roasting temperature is 700°C, and the roasting time is 40 min. The alkaline elution conditions of the chromium slag roasting product are as follows: the sodium hydroxide concentration is 0.5 mol / L, the liquid-solid ratio is 10 mL / g, the elution temperature is 20°C, and the elution times are 3. The vanadium slag roasting temperature is 500°C, and the roasting time is 50 min.

[0057] As Figure 4 shown, another aspect of the embodiment provides a device for the method of step-by-step recovery of vanadium from vanadium-containing tailing wastewater of a vanadium titanate, including a pH adjusting device 100, a reaction tank I 200, a reaction tank II 300, a chromium removal wastewater reducing device 400, a reduced-state chromium removal wastewater solid-liquid separation device 500, a vanadium slag elution and drying integrated device 600, a chromium mud roasting device 700, and a chromium mud elution and drying integrated device 800. The pH adjusting device is used for pH adjustment in step (1), the reaction tank I and the reaction tank II are used for reduction in steps (2) and (3), the chromium removal wastewater reducing device and the reduced-state chromium removal wastewater solid-liquid separation device are used for step (4), the vanadium slag elution and drying integrated device is used for step (5), and the chromium mud roasting device and the chromium mud elution and drying integrated device are used for step (6).

[0058] To highlight the technical problems, technical solutions and advantages to be solved by the present application, the specific embodiments are described in detail below.

[0059] The vanadium-titanium magnetite smelting plant end-of-line wastewater selected in the embodiments and comparative examples of the present application mainly contains the chemical components shown in Table 1.

[0060] Table 1 Main chemical components of vanadium-titanium ore end-of-line wastewater for vanadium extraction

[0061]

[0062] Comparative Example 1

[0063] By adding 12 g / L of sodium pyrosulfite to the vanadium-titanium ore end-of-line wastewater for vanadium extraction, the chromium and vanadium in the liquid phase were reduced, and chromium-vanadium precipitate was obtained by solid-liquid separation. The obtained chromium-vanadium precipitate was calcined at 900 °C for 90 min to obtain a crude chrome green product. Under this condition, the chromium recovery rate was 87.7%, the vanadium recovery rate was 76.4%, the Cr2O3 content in the crude chrome green product was 81.6%, and the V2O5 content was 3.97%. At this time, the purity of the chrome green product was low, and most of the vanadium entered the crude chrome green. It can be seen that direct chemical reduction precipitation cannot extract chromium and vanadium step by step.

[0064] Comparative Example 2

[0065] By adding 8 g / L of sodium pyrosulfite to the vanadium-titanium ore end-of-line wastewater for vanadium extraction, the chromium and vanadium in the liquid phase were reduced, and chromium-vanadium precipitate was obtained by solid-liquid separation. The obtained chromium-vanadium precipitate was calcined at 900 °C for 90 min to obtain a crude chrome green product. Under this condition, the chromium recovery rate was 78.5%, the vanadium recovery rate was 49.8%, the Cr2O3 content in the crude chrome green product was 86.5%, and the V2O5 content was 5.37%. At this time, the purity of the chrome green product was low, and most of the vanadium entered the crude chrome green. It can be seen that reducing the amount of reducing agent will reduce the chromium and vanadium recovery rate, and cannot extract chromium and vanadium step by step.

[0066] Comparative Example 3

[0067] By adding 10 g / L of ascorbic acid to the vanadium-titanium ore end-of-line wastewater for vanadium extraction, the chromium and vanadium in the liquid phase were reduced, and chromium-vanadium precipitate was obtained by solid-liquid separation. The obtained chromium-vanadium precipitate was calcined at 900 °C for 90 min to obtain a crude chrome green product. Under this condition, the chromium recovery rate was 92.5%, the vanadium recovery rate was 62.4%, the Cr2O3 content in the crude chrome green product was 85.1%, and the V2O5 content was 2.15%. At this time, the purity of the chrome green product was low, and most of the vanadium entered the crude chrome green. It can be seen that adjusting the type of reducing agent cannot extract chromium and vanadium step by step. Embodiment

[0068] The pH of the vanadium-titanium ore vanadium extraction end wastewater is adjusted to 8.5 by adding liquid alkali, so that iron-silicon substances are precipitated and coagulated, iron-silicon precipitates are removed by solid-liquid separation, and iron-silicon-removed wastewater is obtained; the iron-silicon-removed wastewater in step (1) is passed into two-stage reaction tanks containing chromium-reducing bacteria biological suspended fillers and a carbon source, the hydraulic retention time is 8 hours, the carbon source is selected to be sodium lactate, the carbon source / chromium molecule ratio is 2.2:1, and chromium mud and chromium-removed wastewater are obtained by solid-liquid separation; the chromium mud is calcined at 700 °C for 50 min, and the chromium residue calcination product is eluted 3 times at 20 °C with 1.0 mol / L sodium hydroxide concentration at a liquid-solid ratio of 10 mL / g. In the chromium-removed wastewater, a reducing agent sodium pyrosulfite is added, the reducing agent / vanadium molecule ratio is 1.5:1, after solid-liquid separation, the vanadium residue is calcined at 500 °C for 40 min. Under the above conditions, the chromium recovery rate is 99.3%, the Cr2O3 content in chromium green is 99.7%, the vanadium recovery rate is 96.2%, and the V2O5 content in the vanadium pentoxide product is 94.5%. Example

[0069] The pH of the vanadium-titanium ore vanadium extraction end wastewater is adjusted to 8.5 by adding liquid alkali, so that iron-silicon substances are precipitated and coagulated, iron-silicon precipitates are removed by solid-liquid separation, and iron-silicon-removed wastewater is obtained; the iron-silicon-removed wastewater in step (1) is passed into two-stage reaction tanks containing chromium-reducing bacteria biological suspended fillers and a carbon source, the hydraulic retention time is 8 hours, the carbon source is selected to be sodium lactate, the carbon source / chromium molecule ratio is 1.7:1, and chromium mud and chromium-removed wastewater are obtained by solid-liquid separation; the chromium mud is calcined at 700 °C for 40 min, and the chromium residue calcination product is eluted 4 times at 20 °C with 1.5 mol / L sodium hydroxide concentration at a liquid-solid ratio of 20 mL / g. In the chromium-removed wastewater, a reducing agent ascorbic acid is added, the reducing agent / vanadium molecule ratio is 1.3:1, after solid-liquid separation, the vanadium residue is calcined at 500 °C for 40 min. Under the above conditions, the chromium recovery rate is 98.4%, the Cr2O3 content in chromium green is 98.2%, the vanadium recovery rate is 89.2%, and the V2O5 content in the vanadium pentoxide product is 90.1%. Example

[0070] The pH of the vanadium-titanium ore end vanadium extraction wastewater is adjusted to 8.5 by adding liquid alkali, so that iron and silicon substances are precipitated and coagulated, iron and silicon precipitates are removed by solid-liquid separation to obtain iron and silicon removal wastewater; the iron and silicon removal wastewater in step (1) is introduced into two-stage reaction tanks containing chromium-reducing bacteria biological suspended fillers and carbon sources, the hydraulic retention time is 8 hours, the carbon source is selected as sodium citrate, the carbon source / chromium molecule ratio is 1.5:1, and chromium mud and chromium removal wastewater are obtained by solid-liquid separation; the chromium mud is calcined at 600 °C for 40 min, and the chromium residue calcination product is eluted 4 times at 20 °C with 0.5 mol / L sodium hydroxide concentration at a liquid-solid ratio of 10 mL / g. Add reducing agent ascorbic acid to the chromium removal wastewater, the reducing agent / vanadium molecule ratio is 1.2:1, after solid-liquid separation, the vanadium residue is calcined at 500 °C for 40 min. Under the above conditions, the chromium recovery rate is 95.9%, the Cr2O3 content in chromium green is 88.2%, the vanadium recovery rate is 83.5%, and the V2O5 content in the vanadium pentoxide product is 90.8%.

[0071] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the purpose and scope of the present application, and they should be covered in the scope of the claims of the present application.

Claims

1. A method for the stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore, characterized in that, Includes the following steps: (1) The pH of the vanadium-titanium ore extraction end wastewater is adjusted to 6-9 by adding liquid alkali, so that the iron and silicon substances precipitate and coagulate. The iron and silicon precipitate is removed by solid-liquid separation to obtain iron and silicon removed wastewater. (2) The iron and silicon removal wastewater obtained in step (1) is fed into reaction tank I containing chromium-reducing bacteria microbial suspension packing and carbon source. The dissolved oxygen concentration is controlled by aeration at 0.5~4 mg / L, the hydraulic retention is 5~10 hours, and solid-liquid separation is performed to obtain chromium mud and chromium removal wastewater I. (3) The chromium removal wastewater I obtained in step (2) is introduced into the reaction tank II containing chromium-reducing bacteria microbial suspension packing and carbon source. The dissolved oxygen concentration is controlled by aeration at 0.5~4 mg / L, the hydraulic retention is 5~10 hours, and solid-liquid separation is performed to obtain chromium mud and chromium removal wastewater II. (4) Add a reducing agent to the chromium removal wastewater II obtained in step (3) and separate the solid and liquid to obtain vanadium slag; (5) The vanadium slag obtained in step (4) is washed and dried in water, and then roasted at 300~600°C to obtain a high-purity vanadium pentoxide product; (6) The chromium mud obtained in steps (2) and (3) is roasted, alkaline washed and dried to obtain chromium green product; The community composition of the chromium-reducing bacteria described in steps (2) and (3) mainly includes Serratia spp. , Bacillus, Leucobacterium , At least one of the genera *Alternaria* or *Achromobacter*.

2. The method for stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore as described in claim 1, characterized in that, The carbon source mentioned in steps (2) and (3) is at least one of sodium lactate, sodium acetate, sodium citrate or glucose.

3. A method for the stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore, as described in claim 1 or 2, characterized in that... The stoichiometric ratio of carbon source to chromium in steps (2) and (3) is 0.8 to 2.2:

1.

4. The method for stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore as described in claim 1, characterized in that, The chromium-reducing microbial suspension packing material mentioned in steps (2) and (3) is a polyurethane-ether sulfone polymer porous material with a porosity of 10,000~17,000 μm supported by chromium-reducing microorganisms. 2 / m 3 The biofilm thickness is 1.5~1.8 mm.

5. The method for stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore as described in claim 1, characterized in that, In step (4), the reducing agent added is at least one of sodium metabisulfite, ascorbic acid, or sodium bisulfite.

6. A method for stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore, as described in claim 1 or 5, characterized in that... In step (4), the molar ratio of reducing agent to vanadium is 1.1 to 1.5:

1.

7. The method for stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore as described in claim 1, characterized in that, In step (5), the vanadium slag is roasted at a temperature of 500~800 °C for 30~60 min.

8. The method for stepwise recovery of vanadium and chromium from wastewater at the end of vanadium extraction from vanadium-titanium ore as described in claim 1, characterized in that, In step (6), the calcination temperature of the chromium mud is 400~700 °C and the calcination time is 30~60 min; the elution conditions of the chromium mud after calcination in step (6) are: liquid-solid ratio of 5~20 mL / g, sodium hydroxide solution concentration of 0.2~2 mol / L, elution temperature of 10~30 °C, and elution times of 1~5.

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