A method for separating vanadium and chromium from high-chromium vanadium slag

Abstract

The present invention provides a method for separating vanadium and chromium from high-chromium vanadium slag, relating to the field of chemical engineering. Using high-chromium vanadium slag as the primary raw material, the method employs a combination of calcined roasting and slow cooling roasting of tailings to significantly improve both the purity of V2O5 and the recovery rate of chromium. This method achieves efficient, simple, and rapid separation of vanadium and chromium from high-chromium vanadium slag, achieving a final V2O5 purity of up to 98.3% and a chromium recovery rate of up to 95%, achieving the goal of green and clean separation of vanadium and chromium.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, in particular to a method for separating vanadium and chromium from high-chromium vanadium slag. Background Art

[0002] High-chromium vanadium slag is an important chromium-containing raw material. However, due to the similar physical and chemical properties of vanadium and chromium, efficient separation of vanadium and chromium is difficult to achieve. Currently, commonly used vanadium-chromium separation processes in the prior art include sodium roasting-simultaneous leaching of vanadium and chromium and a two-step roasting-leaching method. However, simple "roasting-leaching" vanadium-chromium slag generally suffers from problems such as high roasting temperature, poor vanadium product quality, low chromium conversion rate, significant harm from chromium-containing wastewater, and high treatment process costs. Furthermore, the process flow is complex and production costs are high. Furthermore, further separation of vanadium and chromium from the secondary roasting leachate (low-vanadium, high-chromium solution) is difficult, ultimately failing to achieve efficient separation of vanadium and chromium.

[0003] Furthermore, the extraction process described above typically produces a certain amount of hexavalent chromium, which is water-soluble and easily absorbed by the human body. It is an internationally recognized carcinogen, highly hazardous, and difficult to control. Therefore, GB31573-2015, the "Inorganic Chemical Industry Pollutant Discharge Standard," stipulates that only wastewater with a hexavalent chromium content of less than 0.1 mg / L and a total chromium content of less than 0.5 mg / L meets discharge standards.

[0004] Therefore, how to provide an efficient, simple and fast method for separating vanadium and chromium from high-chromium vanadium slag is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0005] To solve the above problems, the present invention provides a method for separating vanadium and chromium from high-chromium vanadium slag, which specifically comprises the following steps:

[0006] (1) The high-chromium vanadium slag was calcined and acid-leached at 50°C for 1 hour using 50% dilute sulfuric acid at a solid-liquid ratio of 2:1 to obtain V-rich vanadium slag. 4+ and V 5+ Vanadium-rich leaching solution and vanadium-extracting tailings;

[0007] (2) adding CaCl2 to the vanadium-rich leachate to remove impurities and then filtering to obtain a pure vanadium-rich solution, adding 50% H2SO4 dropwise to adjust the pH value to 2.0-3.0, then adding (NH4)2SO4, heating to 85-95°C, and continuing the reaction for 20 minutes after the solution begins to become turbid, filtering to obtain ammonium polyvanadate, drying the ammonium polyvanadate, and calcining to obtain high-purity V2O5;

[0008] (3) cooling the vanadium extraction tailings in step (1) to obtain coarse-grained magnetic ferrochrome spar after the temperature drops to 673K;

[0009] (4) After grinding and magnetic separation of ferrochrome spar, vanadium and chromium in high-chromium vanadium slag are efficiently separated.

[0010] Furthermore, the calcination calcination temperature is 850° C. to 1050° C., and the calcination calcination time is 4 hours.

[0011] The present invention reduces the calcification roasting temperature of the vanadium-chromium slag. At this temperature, the chromium element is difficult to be converted and most of it enters the vanadium extraction tailings.

[0012] Furthermore, the weight ratio of the vanadium-rich leaching solution, CaCl2, and (NH4)2SO4 is 1000:1:50.

[0013] Furthermore, the calcination temperature is 500° C. and the calcination time is 3 hours.

[0014] Furthermore, the purity of V2O5 in the extract after vanadium precipitation and drying is 96.67-99.34 wt%.

[0015] Furthermore, the starting temperature of the cooling treatment of the vanadium-extracting tailings is 1773K, and the cooling rate is 1-20K / min.

[0016] Furthermore, the starting temperature of the cooling treatment of the vanadium-extracting tailings is 1573K, and the cooling rate is 1-20K / min.

[0017] Furthermore, the starting temperature of the cooling treatment of the vanadium-extracting tailings is 1373K, and the cooling rate is 1-20K / min.

[0018] Furthermore, the starting temperature of the cooling treatment of the vanadium-extracting tailings is 1173K, and the cooling rate is 1-20K / min.

[0019] Furthermore, the starting temperature of the cooling treatment of the vanadium-extracting tailings is 973K, and the cooling rate is 1-20K / min.

[0020] The present invention achieves grain coarsening of ferrochrome spar by strictly controlling the processing temperature and cooling rate at different stages, thereby improving the monomer dissociation degree of ferrochrome spar in the subsequent grinding stage, and providing favorable conditions for magnetic separation.

[0021] Furthermore, the average particle size of the ferrochrome spar after the cooling treatment is 21.4 to 88.5 μm.

[0022] Preferably, the average particle size of the ferrochrome spar after the cooling treatment is 41.8 to 87.4 μm.

[0023] Preferably, the average particle size of the ferrochrome spar after the cooling treatment is 87.4 μm.

[0024] Compared with the prior art, the present invention has the following beneficial technical effects:

[0025] (1) The present invention first adopts calcination roasting-leaching liquid to extract vanadium. During this process, 98.4% of the chromium element is retained in the vanadium extraction tailings, which significantly reduces the chromium doping in the vanadium product, thereby improving the purity of V2O5. The vanadium extraction tailings are then subjected to cooling roasting-magnetic separation treatment, which greatly improves the chromium recovery rate. By cooling and slow cooling, the ferrochrome crystal grains are coarsened, and the monomer dissociation degree of the ferrochrome crystal is increased. Magnetic separation is used to achieve efficient enrichment of chromium elements, and efficient, simple and rapid separation of vanadium and chromium in high-chromium vanadium slag is achieved. The final vanadium purity can reach 98.3%, and the chromium recovery rate can reach 95%;

[0026] (2) As a base metal, chromium is more than ten times more valuable than vanadium. However, vanadium and chromium have similar properties and are difficult to separate. The recovery of chromium resources from high-chromium vanadium slag by magnetic separation of ferrochrome crystal phase reduces the impact of chromium on the purity of vanadium products.

[0027] (3) The chromium in the ferrochrome spar (FeCr2O4) obtained by cooling, roasting and magnetic separation of the vanadium extraction tailings of the present invention exists in the +3 valence state, which reduces the formation of highly toxic hexavalent chromium. The hexavalent chromium content in the treated wastewater is less than 0.1 mg / L, and the total chromium content is less than 0.5 mg / L, which meets the emission requirements specified in GB31573-2015 "Inorganic Chemical Industry Pollutant Emission Standards", thereby achieving the purpose of green and clean chromium extraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below with reference to the accompanying drawings.

[0029] Figure 1 This is a process flow chart of the method for separating vanadium and chromium from high-chromium vanadium slag according to the present invention. DETAILED DESCRIPTION

[0030] The technical solution provided by the present invention is further described below in conjunction with embodiments.

[0031] The method for measuring the average particle size of ferrochrome spar of the present invention is as follows:

[0032] The high chromium vanadium slag was calcined and acid-leached at 50°C for 1 hour with a solid-liquid ratio of 2:1 using 50% dilute sulfuric acid to obtain V-rich vanadium slag. 4+ and V 5+ vanadium-rich leachate and vanadium extraction tailings, take 200 mL of vanadium-rich leachate, add 0.18 g of CaCl2 to remove impurities, and then filter to obtain pure vanadium-rich solution, add 50% H2SO4 dropwise to adjust the pH value to 2.5, add 10.42 g of (NH4)2SO4, heat to 90°C, and continue to react for 20 minutes after the solution begins to become turbid, filter to obtain ammonium polyvanadate, and calcine the dried ammonium vanadate in a muffle furnace at 500°C for 3 hours to obtain high-purity V2O5;

[0033] The vanadium extraction tailings were placed in a crucible and suspended in the quenching chamber of a tubular furnace. The crucible was sealed and evacuated to -0.1 MPa, and then filled with argon (99.999% purity). Subsequently, the furnace was heated to the desired temperature at a heating rate of 3 K / min, and the argon flow rate was maintained at 200 mL / min during the entire heating and cooling process.

[0034] After the temperature is raised to a specific temperature, the crucible is lowered to the constant temperature zone of the tube furnace;

[0035] Subsequently, the molten slag was cooled to 673 K at different cooling rates, and finally, the crucible was quickly taken out of the furnace and quenched;

[0036] The sample was ground for SEM examination, and 12 fields of view were randomly selected and the average particle size of the ferrochrome spar was counted and calculated using image plus pro 6.0 software.

[0037] Example 1

[0038] The high-chromium vanadium slag was calcined and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 1773K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min respectively.

[0039] The chromium recovery rates at different cooling rates are as follows:

[0040] Cooling rate 20K / min 15K / min 10K / min 5K / min 1K / min Average particle size 41.8μm 55.2μm 69.6μm 87.4μm 88.5μm Chromium recovery rate 55.67％ 72.83％ 84.47％ 95.31％ 96.83％

[0041] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. Therefore, considering the average particle size of the ferrochrome spar obtained by cooling and the economic cost, when the cooling rate of the vanadium tailings is selected to be 5K / min, ferrochrome spar with an average particle size of 87.4μm can be formed, and finally the ferrochrome spar is recovered by grinding and magnetic separation.

[0042] Example 2

[0043] The high-chromium vanadium slag was calcined and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 1573K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min respectively.

[0044] The chromium recovery rates at different cooling rates are as follows:

[0045] Cooling rate 20K / min 15K / min 10K / min 5K / min 1K / min Average particle size 32.8μm 45.4μm 59.5μm 71.3μm 72.5μm Chromium recovery rate 50.72％ 64.31％ 74.83％ 83.72％ 85.67％

[0046] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. Therefore, considering the average particle size of the ferrochrome spar obtained by cooling and the economic cost, when the cooling rate of the vanadium tailings is selected to be 5K / min, ferrochrome spar with an average particle size of 71.3μm can be formed, and finally the ferrochrome spar is recovered by grinding and magnetic separation.

[0047] Example 3

[0048] The high-chromium vanadium slag was calcined and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 1373K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min, respectively.

[0049] The chromium recovery rates at different cooling rates are as follows:

[0050] Cooling rate 20K / min 15K / min 10K / min 5K / min 1K / min Average particle size 28.6μm 39.4μm 43.5μm 57.6μm 68.8μm Chromium recovery rate 47.67％ 61.72％ 68.31％ 70.83％ 71.47％

[0051] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. Therefore, considering the average particle size of the ferrochrome spar obtained by cooling and the economic cost, when the cooling rate of the vanadium tailings is selected to be 5K / min, ferrochrome spar with an average particle size of 57.6μm can be formed, and finally the ferrochrome spar is recovered by grinding and magnetic separation.

[0052] Example 4

[0053] The high-chromium vanadium slag was calcined and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 1173K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min, respectively.

[0054] The chromium recovery rates at different cooling rates are as follows:

[0055] Cooling rate 20K / min 15K / min 10K / min 5K / min 1K / min Average particle size 18.3μm 21.9μm 35.6μm 49.9μm 51.5μm Chromium recovery rate 42.47％ 57.31％ 62.83％ 65.72％ 65.47％

[0056] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. Therefore, considering the average particle size of the ferrochrome spar obtained by cooling and the economic cost, when the cooling rate of the vanadium extraction tailings is selected to be 5K / min, ferrochrome spar with an average particle size of 49.9μm can be formed, and finally the ferrochrome spar is recovered by grinding and magnetic separation.

[0057] Example 5

[0058] The high-chromium vanadium slag was calcined and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 973K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min, respectively.

[0059] The chromium recovery rates at different cooling rates are as follows:

[0060] Cooling rate 20K / min 15K / min 10K / min 5K / min 1K / min Average particle size 11.4μm 18.1μm 25.8μm 38.6μm 40.7μm Chromium recovery rate 31.67％ 42.72％ 4434％ 45.83％ 46.47％

[0061] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. Therefore, considering the average particle size of the ferrochrome spar obtained by cooling and the economic cost, when the cooling rate of the vanadium extraction tailings is selected to be 5K / min, ferrochrome spar with an average particle size of 38.6μm can be formed, and finally the ferrochrome spar is recovered by grinding and magnetic separation.

[0062] Comparative Example 1

[0063] The high-chromium vanadium slag was calcified and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 1973K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min respectively.

[0064] The chromium recovery rates at different cooling rates are as follows:

[0065]

[0066]

[0067] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. When the cooling rate is 5K / min, the average particle size of the formed ferrochrome spar is 6.4μm.

[0068] Comparative Example 2

[0069] The high-chromium vanadium slag was calcined and roasted at 850°C, and V2O5 with a purity of 98.3wt% was obtained after preliminary leaching and precipitation; the vanadium extraction tailings were cooled from 773K to 673K ​​at cooling rates of 20K / min, 15K / min, 10K / min, 5K / min and 1K / min respectively.

[0070] The chromium recovery rates at different cooling rates are as follows:

[0071] Cooling rate 20K / min 15K / min 10K / min 5K / min 1K / min Average particle size 1.3μm 1.8μm 2.3μm 2.5μm 3.3μm Chromium recovery rate 1.87％ 1.93％ 1.97％ 5.81％ 6.53％

[0072] It can be seen from the table that as the cooling rate decreases, the achievable ferrochrome spar particle size increases more slowly, and the required cooling and roasting treatment time is also longer. When the cooling rate is 5K / min, the average particle size of the formed ferrochrome spar is 2.5μm.

[0073] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A method for separating vanadium and chromium from high-chromium vanadium slag, characterized in that: The following steps are involved: (1) The high-chromium vanadium slag was calcined and acid-leached at 50°C for 1 h using 50% dilute sulfuric acid at a solid-liquid ratio of 2:1 to obtain V-rich vanadium slag. 4+ and V 5+ Vanadium-rich leaching solution and vanadium-extracting tailings; (2) CaCl2 was added to the vanadium-rich leachate to remove impurities and then filtered to obtain a pure vanadium-rich solution. 50% H2SO4 was added dropwise to adjust the pH value to 2.0-3.0, and then (NH4)2SO4 was added. The solution was heated to 85-95°C. After the solution began to become turbid, the reaction was continued for 20 minutes. Ammonium polyvanadate was filtered to obtain the ammonium polyvanadate, which was dried and calcined to obtain high-purity V2O5. (3) cooling the vanadium extraction tailings in step (1) from 1773 K to 673 K at a rate of 5 K / min or 1 K / min to obtain coarse-grained magnetic ferrochrome spar; (4) After grinding and magnetic separation of ferrochrome spar, vanadium and chromium in high-chromium vanadium slag are efficiently separated.

2. The method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that: The calcination temperature is 850° C. to 1050° C., and the calcination time is 4 h.

3. The method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that: The weight ratio of the vanadium-rich leaching solution, CaCl2, and (NH4)2SO4 is 1000:1:

50.

4. The method for separating vanadium and chromium from high-chromium vanadium slag according to claim 1, characterized in that: The average particle size of the ferrochrome spar after the cooling treatment is 21.4-88.5 μm.

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