Method for removing oxalate in sodium aluminate solution and removing vanadium in cooperation with sodium aluminate solution

Abstract

The invention relates to the field of comprehensive recycling of resources, in particular to a method for removing oxalate and removing vanadium in a sodium aluminate solution. The method comprises the following steps: evaporating, concentrating and crystallizing a high-concentration first sodium aluminate solution to obtain a seed crystal, adding the seed crystal into a low-concentration second sodium aluminate solution, inducing oxalate to separate out crystals at a relatively high temperature, filtering to remove oxalate, and further cooling and crystallizing filtrate to recover high-grade vanadium salt. According to the method, oxalate crystal seeds do not need to be additionally added, high-efficiency removal of oxalate at the high temperature is achieved under the condition of low cost, vanadium pentoxide is not prone to being separated out at the high temperature, therefore, vanadium can be further efficiently recycled, and the content of impurities in the recycled vanadium pentoxide is low.

Description

Technical Field

[0001] The invention relates to the field of comprehensive resource recycling, and in particular to a method for removing oxalate and synergistically removing vanadium from a sodium aluminate solution. Background Art

[0002] At present, gibbsite-type bauxite is an important raw material for the production of alumina, but the organic content is high. The use of high-organic bauxite causes the organic matter in the alumina production process to gradually enrich, which has a negative impact on the decomposition, sedimentation and other processes. Therefore, it is very necessary to remove organic matter in the Bayer process mother liquor. At present, the methods for removing organic matter mainly include bauxite roasting method, mother liquor roasting method, ion exchange method, crystallization method, precipitation method, wet oxidation method, etc. Among them, the crystallization method is to make the organic matter in the Bayer process mother liquor, mainly sodium oxalate, destabilize and crystallize by evaporation concentration, adding crystal seeds, etc. The method is simple to operate, has a good sodium oxalate removal effect, is easy to industrially produce, and has a wide range of industrial applications. In addition, the Bayer process mother liquor also contains a variety of trace elements, among which the trace element vanadium has a high economic value. The crystallization method can be used to extract vanadium from the sodium aluminate solution, and the vanadium can be further recycled.

[0003] Among the specific methods currently using crystallization to remove organic matter and simultaneously recover vanadium, for example, Chinese patent CN116199575A concentrates Bayer liquor by evaporation, then cools and crystallizes to precipitate vanadium salt, and then heats the filtrate to increase the concentration of caustic soda to precipitate oxalate, thereby achieving oxalate removal and vanadium recovery. However, this method is complicated to operate, and oxalate will also precipitate during the vanadium precipitation process, resulting in a low vanadium content in the precipitated vanadium crystals. Chinese patent CN1930086A concentrates sodium aluminate solution to the saturated concentration of oxalate and then uses ultrasonic treatment to induce oxalate precipitation. This method has complex equipment and operation, consumes a lot of energy, and there is still a situation where oxalate and vanadate precipitate simultaneously. Chinese patent CN115010174A performs multiple reverse washing and multiple filtration on the low-grade vanadium salt obtained by evaporation, concentration, cooling and crystallization to remove sodium oxalate impurities therein and improve the grade of the vanadium salt. This method is complicated to operate and has a lengthy process flow.

[0004] Therefore, it is currently necessary to develop a method for simply and efficiently removing oxalate from the Bayer process mother liquor while recovering high-grade vanadium salts. Summary of the invention

[0005] In order to develop a method for removing oxalate with a simple process and low cost and recovering high-grade vanadium salts, the technical solution of the present invention is proposed:

[0006] A method for removing oxalate and synergistically removing vanadium from a sodium aluminate solution comprises the following steps:

[0007] Step 1: After evaporating and concentrating the first sodium aluminate solution in the alumina production process, the temperature is controlled for crystallization, and filter to obtain filter cake A and filtrate A. After evaporating and concentrating, the oxalate content of the first sodium aluminate solution is ≥2g / L, the caustic soda Nk concentration is controlled at 270-340g / L, and the temperature during the crystallization process is ≥70°C;

[0008] Step 2: After evaporating and concentrating the second sodium aluminate solution in the alumina production process and cooling it, the filter cake A obtained in step 1 is added, the temperature is controlled for crystallization, and filter cake B and filtrate B are obtained by filtration. After evaporating and concentrating the second sodium aluminate solution, the oxalate content is ≥1.5 g / L, the caustic soda Nk concentration is controlled at 180-240 g / L, and the temperature during the crystallization process is controlled within the range of greater than 60° C. and less than 70° C.;

[0009] Step 3: Cool the filtrate B in step 2 to crystallize, and filter to obtain filter cake C and filtrate C.

[0010] Furthermore, in step 1, the temperature is controlled within the range of 70-110° C. for crystallization.

[0011] Furthermore, in step 1, after evaporation and concentration, the temperature is maintained for crystallization.

[0012] Furthermore, the crystallization process time in step 1 is ≥ 2h.

[0013] Furthermore, in the step 2, the second sodium aluminate solution has a vanadium pentoxide content of ≥0.7 g / L after evaporation and concentration.

[0014] Furthermore, in step 2, the amount of filter cake A added is 5-20 g / L, the crystallization process time is ≥8 h, the oxalate removal rate is ≥60%, and the vanadium pentoxide removal rate is ≤5%.

[0015] Furthermore, the suspended matter concentration in the filtrate B obtained in step 2 is ≤0.05 g / L.

[0016] Furthermore, the filtering equipment in the filtering process in step 2 uses filter cloth, and the air permeability of the filter cloth is ≤100L / ㎡ / s.

[0017] Furthermore, the filter cake B obtained in step 2 has an oxalate content of ≥8% and a vanadium pentoxide content of ≤0.5%, and can be used to return to the batching process of sintered alumina production as a batching raw material, and its content meets the batching content requirements.

[0018] Furthermore, the crystallization temperature in step 3 is controlled at 30-45° C., the crystallization time is 0.5-4 h, and the filter cake C has a natural vanadium pentoxide content of 5-15%. The natural filter cake refers to the filter cake that is not dried or otherwise treated after filtration, i.e., the liquid-containing filter cake.

[0019] The beneficial effects of the present invention are:

[0020] (1) The high-concentration first sodium aluminate solution is evaporated, concentrated and crystallized to obtain seed crystals, which are added to the low-concentration second sodium aluminate solution to induce the precipitation and crystallization of oxalate, so that the low-concentration sodium aluminate solution can achieve efficient oxalate removal at a higher temperature. The filter cake precipitated from the high-concentration sodium aluminate solution is used as seed crystals, which reduces the cost of purchasing other oxalate removal additives. In addition, at higher temperatures, vanadium pentoxide in the low-concentration sodium aluminate solution is almost not precipitated, thereby improving the subsequent recovery rate of vanadium salts and reducing the vanadium content in the precipitated oxalate, which can be used to return to the batching process of sintering alumina production as a batching raw material, and its content meets the batching content requirements;

[0021] (2) In addition, when the high-concentration first sodium aluminate solution is evaporated, concentrated and crystallized at a relatively high temperature, part of the sodium carbonate crystals are precipitated and removed, which also reduces the sodium carbonate content in the process liquid phase, which is helpful for the control of alumina production;

[0022] (3) By controlling the time of the vanadium precipitation stage, the content of impurities in the filter cake C vanadium slag is controlled. Since the precipitation rate of vanadium pentoxide is fast, while the precipitation rate of other impurities is slow, high-grade vanadium pentoxide can be recovered by controlling the appropriate time and temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of the method for removing oxalate and synergistically removing vanadium using sodium aluminate solution is shown. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] Embodiment 1:

[0026] After the high-concentration first sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 290 g / L and the oxalate concentration was 2.5 g / L. It was then crystallized at 95°C for 2 hours and filtered to obtain filter cake A and filtrate A. After the low-concentration second sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 210 g / L, the oxalate concentration was 2 g / L, and the vanadium pentoxide concentration was 0.8 g / L. It was cooled to 65°C and kept warm, and filter cake A was added in an amount of 5 g / L. It was left for crystallization for 8 hours and filtered to obtain filter cake B and filtrate B. Filtrate B was clear, with suspended matter ≤0.05 g / L, oxalate removal rate of 60%, and vanadium pentoxide removal rate of 0%. Filtrate B was further cooled to 35°C, left for crystallization for 1 hour, and filtered to obtain filter cake C and filtrate C: the vanadium pentoxide content in natural-based filter cake C was 7%, and the recovery rate was 80%.

[0027] Embodiment 2:

[0028] After the high-concentration first sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 300 g / L and the oxalate concentration was 2.6 g / L. It was then crystallized at 90°C for 3 hours and filtered to obtain filter cake A and filtrate A. After the low-concentration second sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 200 g / L, the oxalate concentration was 2.1 g / L, and the vanadium pentoxide concentration was 0.9 g / L. It was cooled to 62°C and kept warm, and filter cake A was added in an amount of 10 g / L. It was left for crystallization for 12 hours and filtered to obtain filter cake B and filtrate B. Filtrate B was clear, with suspended matter ≤0.05 g / L, oxalate removal rate of 70%, and vanadium pentoxide removal rate of 5%. Filtrate B was further cooled to 30°C, left for crystallization for 1 hour, and filtered to obtain filter cake C and filtrate C: the vanadium pentoxide content in natural-based filter cake C was 8%, and the recovery rate was 82%.

[0029] Embodiment 3:

[0030] After the high-concentration first sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 300 g / L and the oxalate concentration was 2.6 g / L. It was then crystallized at 100°C for 3 hours and filtered to obtain filter cake A and filtrate A. After the low-concentration second sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 200 g / L, the oxalate concentration was 2.1 g / L, and the vanadium pentoxide concentration was 0.9 g / L. It was cooled to 62°C and kept warm, and filter cake A was added in an amount of 20 g / L. It was left for crystallization for 12 hours and filtered to obtain filter cake B and filtrate B. Filtrate B was clear, with suspended matter ≤0.03 g / L, oxalate removal rate of 70%, and vanadium pentoxide removal rate of 5%. Filtrate B was further cooled to 30°C, left for crystallization for 4 hours, and filtered to obtain filter cake C and filtrate C: the natural-based filter cake C had a vanadium pentoxide content of 6% and a recovery rate of 90%.

[0031] Embodiment 4:

[0032] After the high-concentration first sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 290 g / L and the oxalate concentration was 2.5 g / L. It was then crystallized at 85°C for 2 hours and filtered to obtain filter cake A and filtrate A. After the low-concentration second sodium aluminate solution was evaporated and concentrated, the caustic Nk concentration was 210 g / L, the oxalate concentration was 2 g / L, and the vanadium pentoxide concentration was 0.8 g / L. Filter cake A was added in an amount of 20 g / L, cooled to 68°C and kept warm, and crystallized for 8 hours. Filter cake B and filtrate B were filtered. Filtrate B was clear, with suspended matter ≤0.03 g / L, oxalate removal rate of 60%, and vanadium pentoxide removal rate of 3%. Filtrate B was cooled to 30°C, crystallized for 1 hour, and filtered to obtain filter cake C and filtrate C: the natural-based filter cake C had a vanadium pentoxide content of 8% and a recovery rate of 92%.

[0033] Embodiment 5:

[0034] The high-concentration first sodium aluminate solution was concentrated by evaporation, with the caustic soda Nk concentration being 300 g / L and the oxalate concentration being 2.6 g / L. It was then crystallized at 94° C. for 3 h and filtered to obtain filter cake A and filtrate A. After the low-concentration second sodium aluminate solution is evaporated and concentrated, the caustic soda Nk concentration is 200g / L, the oxalate concentration is 2.1g / L, and the vanadium pentoxide concentration is 0.9g / L. The solution is cooled to 62°C and kept warm. Filter cake A is added in an amount of 20g / L, and the solution is allowed to crystallize for 12 hours. Filter cake B and filtrate B are obtained by filtration. Filter cloth is used as the filtering equipment in the filtration process. The air permeability of the filter cloth is ≤100L / ㎡ / s. Filtrate B is clear, and suspended matter is ≤0.03g / L. The oxalate removal rate is 70%, and the vanadium pentoxide removal rate is 5%. Filtrate B is further cooled to 30°C, allowed to crystallize for 2 hours, and filtered to obtain filter cake C and filtrate C: the vanadium pentoxide content in the natural-based filter cake C is 7.5%, and the recovery rate is 91%.

[0035] Comparative Example 1:

[0036] After the low concentration sodium aluminate solution was concentrated by evaporation, the caustic soda Nk concentration was 200 g / L, the oxalate concentration was 2.1 g / L, and the vanadium pentoxide concentration was 0.9 g / L. The solution was cooled to 65°C and kept warm, and allowed to crystallize for 12 hours. The filter cake B and filtrate B were obtained by filtration. The filtrate B was clear, with suspended matter ≤0.05 g / L, oxalate removal rate of 5%, and vanadium pentoxide removal rate of 2%. The filtrate B was further cooled to 30°C, allowed to crystallize for 4 hours, and filter cake C and filtrate C were obtained: the vanadium pentoxide content in the natural-based filter cake C was 5%, and the recovery rate was 92%.

[0037] Comparative Example 2:

[0038] After the low concentration of sodium aluminate solution was concentrated by evaporation, the caustic soda Nk concentration was 200 g / L, the oxalate concentration was 2.1 g / L, and the vanadium pentoxide concentration was 0.9 g / L. The solution was cooled to 50°C and kept warm, and allowed to crystallize for 12 hours. The filter cake B and filtrate B were obtained by filtration. The filtrate B was clear, and the suspended matter was ≤0.05 g / L. The oxalate removal rate was 38%, and the vanadium pentoxide removal rate was 44%. The filtrate B was further cooled to 30°C, allowed to crystallize for 5 hours, and filtered to obtain filter cake C and filtrate C: the vanadium pentoxide content in the natural-based filter cake C was 2%, and the recovery rate was 50%.

[0039] Some exemplary embodiments of the present invention are described above. It can be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. The features in these embodiments can be recombined in a suitable manner, and the scheme obtained thereby is still within the protection scope required by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the protection scope required by the present invention.

Claims

1. A method for removing oxalate and synergistically removing vanadium from sodium aluminate solution, characterized in that: The following steps are involved: Step 1: After evaporating and concentrating the first sodium aluminate solution in the alumina production process, the temperature is controlled for crystallization, and filter to obtain filter cake A and filtrate A. After evaporating and concentrating, the oxalate content of the first sodium aluminate solution is ≥2g / L, the caustic soda Nk concentration is controlled at 270-340g / L, and the temperature during the crystallization process is ≥70°C; Step 2: After evaporating and concentrating the second sodium aluminate solution in the alumina production process and cooling it, the filter cake A obtained in step 1 is added, the temperature is controlled for crystallization, and filter cake B and filtrate B are obtained by filtration. After evaporating and concentrating the second sodium aluminate solution, the oxalate content is ≥1.5 g / L, the caustic soda Nk concentration is controlled at 180-240 g / L, and the temperature during the crystallization process is controlled within the range of greater than 60° C. and less than 70° C.; Step 3: Cool the filtrate B in step 2 to crystallize, and filter to obtain filter cake C and filtrate C.

2. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: In the step 1, the temperature is controlled within the range of 70-110° C. for crystallization.

3. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: In the step 1, after evaporation and concentration, the temperature is maintained for crystallization.

4. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: The crystallization process time in step 1 is ≥ 2h.

5. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: In the step 2, the second sodium aluminate solution has a vanadium pentoxide content of ≥0.7 g / L after evaporation and concentration.

6. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: In the step 2, the amount of filter cake A added is 5-20 g / L, the crystallization process time is ≥8 h, the oxalate removal rate is ≥60%, and the vanadium pentoxide removal rate is ≤5%.

7. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: The suspended matter concentration in the filtrate B obtained in step 2 is ≤0.05 g / L.

8. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 7, characterized in that: The filtering equipment in the filtering process in step 2 uses filter cloth, and the air permeability of the filter cloth is ≤100L / ㎡ / s.

9. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: The filter cake B obtained in step 2 has an oxalate content of ≥8% and a vanadium pentoxide content of ≤0.5%.

10. The method for removing oxalate and synergistically removing vanadium from sodium aluminate solution according to claim 1, characterized in that: The crystallization temperature in step 3 is controlled at 30-45° C., the crystallization time is 0.5-4 hours, and the natural-based vanadium pentoxide content of the filter cake C is 5-15%.

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