Method for Recycling Rare Earth and Fluorine from Waste Residue Produced by Vacuum Calcium Thermal Reduction Method for Producing Terbium

Abstract

The present invention relates to a method for recycling rare earths and fluorine from terbium-containing waste residues produced by vacuum calcium thermal reduction, belonging to the field of industrial waste residue treatment. The raw material is the calcium-terbium waste residue produced by calcium thermal reduction to produce metallic terbium. The calcium-terbium waste residue is fully dried and exposed in the air to convert the massive calcium-terbium waste residue into powder form. Then, magnetic separation is carried out to obtain terbium rare earth enriched powder and calcium fluoride powder respectively. The terbium rare earth enriched powder is leached with sulfuric acid to be converted into a rare earth sulfate system feed liquid. An excessive amount of oxalic acid is added to the supernatant, and terbium oxalate precipitate is separated by solid-liquid separation. The supernatant is cooled to precipitate oxalic acid crystals. Finally, terbium oxalate is calcined to obtain terbium oxide. By adding a simple pretreatment step of drying in the air, the massive calcium-terbium waste residue is converted into powder form, enabling the subsequent creative use of magnetic separation to separate calcium fluoride and terbium elements, greatly reducing the usage amount of acid-base chemical reagents and energy consumption, and having extremely strong operability.

Description

Technical Field

[0001] The present invention relates to the technical field of industrial waste residue treatment, and particularly relates to a method for recycling rare earth and fluorine in the waste residue produced by the production of terbium by vacuum calcium thermal reduction method. Background Art

[0002] As an essential additive for high-end neodymium-iron-boron permanent magnet materials, metallic terbium can greatly improve its intrinsic coercivity performance. In industrial production, vacuum calcium thermal reduction method is usually adopted to produce metals such as dysprosium, terbium, gadolinium, and yttrium. Rare earth fluoride and calcium are subjected to vacuum calcium thermal reduction and secondary refining to obtain rare earth metals with a purity of more than 99.5%. The by-product is calcium fluoride slag. According to theoretical calculation, for every ton of rare earth metal terbium produced, 736 kg of calcium fluoride slag will be generated. Along with the generation of calcium fluoride slag, some rare earth scraps and incompletely converted materials enter the calcium fluoride slag. Therefore, the recovery of rare earth resources in the by-product calcium fluoride produced by the vacuum calcium thermal reduction method for producing metallic terbium is particularly important.

[0003] According to production experience and the inspection of rare earth in calcium fluoride slag, its rare earth (calculated as REO) content is usually 2 - 5%. The main components of the rare earth are rare earth metals, rare earth oxides, rare earth fluorides, and fluorine oxides. These calcium fluoride slags are usually treated as industrial waste, seriously wasting precious rare earth and fluorine resources. Therefore, it is particularly important to study a method for recovering terbium and fluorine elements from calcium fluoride slag.

[0004] In the prior art, Chen Dongying et al. (Chen Dongying, Ouyang Hong, Lu Nengdi. Comprehensive utilization research of calcium thermal reduction rare earth slag containing 5 - 7% rare earth [J]. Jiangxi Nonferrous Metals, 2004, 03: 27 - 30.) used mixed acid leaching to treat calcium thermal reduction rare earth slag containing 5 - 7% rare earth, and its rare earth recovery rate was 65.41%, with a relatively low yield. In Chinese invention patent CN201510680718.4, sodium silicate was used for mixed roasting, water leaching and then hydrochloric acid extraction to obtain rare earth filtrate; in Chinese invention patent CN201610521415.2, the smelting slag was mixed with sodium carbonate and then roasted, followed by water leaching and hydrochloric acid leaching to obtain rare earth liquor; however, this method is relatively complicated. At the same time, the above methods all use chemical methods to extract rare earth. Since calcium fluoride accounts for more than 95% of it, a large amount of chemicals such as hydrochloric acid are required, and high-temperature roasting is required, which is neither environmentally friendly nor energy-saving. Summary of the Invention

[0005] The present invention provides a more efficient, energy-saving and environmentally friendly method for recycling rare earth and fluorine in the waste residue produced by the production of terbium by vacuum calcium thermal reduction method in view of the above problems existing in the prior art.

[0006] The technical solution for the present invention to solve the above technical problems is as follows:

[0007] Method for recycling rare earth and fluorine from waste residue in production of terbium metal by vacuum calcium thermal reduction method, characterized in that the calcium-terbium waste residue material produced by calcium thermal reduction method in industrial production is used as raw material, and the method comprises the following steps:

[0008] Step 1: The calcium-terbium waste residue material is fully exposed and dried in the air to convert the massive calcium-terbium waste residue material into powdery form; the natural aging time of the exposure and drying is generally more than 3 days, preferably 7 - 30 days;

[0009] In this process, the calcium-terbium waste residue material is fully exposed in the air. The excessive calcium added in production therein reacts with oxygen in the air and absorbs carbon dioxide and water in the air, so that the calcium-terbium waste residue is completely turned into powder, and at the same time, the terbium metal therein will not be oxidized; meanwhile, it also lays a foundation for the next magnetic separation operation, making it possible to separate the massive calcium-terbium waste residue material that could not be separated by magnetic separation before;

[0010] The chemical reaction equations involved in this process are:

[0011] 2Ca + O2 → 2CaO

[0012] Step 2: The powder obtained in Step 1 is separated by a magnetic separator to obtain terbium rare earth enriched powder and calcium fluoride powder respectively;

[0013] Step 3: The terbium rare earth enriched powder obtained in Step 2 is leached under heating conditions in a sulfuric acid system and completely converted into a rare earth sulfate system liquid material. After standing, the supernatant is collected, and rare earth ions exist in the supernatant;

[0014] The chemical reaction equations involved in this process are:

[0015] 2Tb + 3H2SO4 → Tb2(SO4)3 + 3H2(g)

[0016] 2TbF3 + 3H2SO4 → Tb2(SO4)3 + 6HF(g)

[0017] Tb4O7 + 3H2SO4 → 2Tb2(SO4)3 + 2O2(g) + 3H2O

[0018] 2TbOF + 3H2SO4 → Tb2(SO4)3 + 2HF(g) + 2H2O

[0019] Step 4: Excessive oxalic acid is added to the supernatant to adjust the pH value, and after standing, terbium oxalate precipitate is obtained through solid-liquid separation. The supernatant of the solid-liquid separation is cooled to precipitate oxalic acid crystals; the remaining filtrate after filtration can be recycled, and there is no waste liquid discharge. The precipitated oxalic acid crystals can also be reused after filtration;

[0020] The chemical reaction equations involved in this process are:

[0021] Tb2(SO4)3 + H2C2O4 → Tb2(C2O4)3(s) + H2SO4

[0022] Step 5: Calcinate the terbium oxalate obtained in Step 4 to dehydrate and decarburize it, obtaining terbium oxide; the calcination temperature is preferably about 1000 °C.

[0023] Furthermore, the magnetic separator in Step 2 uses a dry or wet magnetic separator. According to its property of small particle size, wet magnetic separation is preferably used.

[0024] Furthermore, the calcium fluoride powder collected in Step 2 is used as a raw material for industrial production of hydrogen fluoride.

[0025] Furthermore, in Step 3, the leaching in the sulfuric acid system uses a multi-stage sulfuric acid precipitation tank. A plurality of partition plates are sequentially arranged in the multi-stage sulfuric acid precipitation tank, and the heights of the partition plates along the feeding direction decrease in sequence.

[0026] Furthermore, the sulfuric acid system is a mixture of concentrated sulfuric acid and water with a volume ratio of 1:2 - 3.

[0027] Furthermore, in Step 3, the temperature of the heating leaching is 40 - 360 °C, preferably 120 °C; the leaching time increases with the increase of the input amount of the terbium rare earth enriched powder and is not less than 1 h, preferably 6 h.

[0028] Furthermore, in Step 3, the heating leaching process is accompanied by stirring, and the stirring speed is 10 r / min - 40 r / min.

[0029] Furthermore, in Step 3, the waste gas generated during the reaction process is exhausted by suction and led to a condenser. The hydrogen fluoride gas therein is condensed, collected, and formed into a hydrogen fluoride solution, which can be filled into barrels for sale.

[0030] Furthermore, in Step 4, the pH value is adjusted to 1.5 - 3.

[0031] Furthermore, the concentration of the added oxalic acid in Step 4 is preferably 20%.

[0032] Furthermore, in Step 4, the temperature is reduced to below 30 °C, preferably below 15 °C.

[0033] The beneficial effects of the present invention are:

[0034] 1. By adding a simple pre-treatment step of air drying, the present invention converts massive calcium-terbium waste residue into powder form, enabling the subsequent creative use of magnetic separation to separate calcium fluoride and terbium elements. After the separation by this process sequence, the proportion of the terbium rare earth enriched powder to be processed is greatly reduced (below 5%) in the original waste residue. That is, through the above simple and feasible steps, the amount of terbium rare earth enriched powder that needs chemical treatment can be greatly reduced, the usage of acid-base chemical reagents can be minimized, and energy consumption can be reduced. The operability is extremely strong, and it is applicable to the resource recycling of rare earths and fluorine in calcium-terbium waste residue generated in the preparation of metallic terbium.

[0035] 2. The present invention successively undergoes the technological steps of air drying, magnetic separation, acid leaching, and calcination. During this process, water, acid solution, and oxalic acid can all be reused, avoiding waste discharge. Moreover, the rare earth recovery rate using the process method of the present invention is greater than 99%, and the purity reaches 4N. The rare earths that have not been recovered temporarily also circulate in the acid solution. After the dynamic reaction reaches equilibrium, it will reach a saturated state without causing resource waste. The terbium oxide prepared by this method has high purity and can be used to produce metallic terbium, magneto-optical glass, fluorescent powder, magneto-optical storage, chemical additives, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the process flow block diagram of the present invention;

[0037] Figure 2 is the structural schematic diagram of the multi-stage sulfuric acid precipitation tank of the present invention;

[0038] In the figure, 1. First-stage precipitation tank, 2. Second-stage precipitation tank, 3. Third-stage precipitation tank, 11. First baffle, 12. Second baffle. DETAILED DESCRIPTION OF THE INVENTION

[0039] The principle and characteristics of the present invention will be described below. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0040] Example 1

[0041] As Figure 1 shown, the method for recycling rare earths and fluorine from the waste residue in the production of metallic terbium by vacuum calcium thermal reduction method in this example includes the following steps:

[0042] Step 1: Take the calcium-terbium waste residue generated during the production of metallic terbium by calcium thermal reduction method. After collection and full exposure to air for 12 days, the massive calcium-terbium waste residue is converted into powder form. Weigh 100 kg of the calcium-terbium waste residue for standby. Through laboratory tests, it is known that the total rare earth content (calculated as REO) is 3.6%.

[0043] Step 2: After separation by a wet magnetic separator, rare earth terbium enriched powder and calcium fluoride powder are obtained.

[0044] Step 3: Add the rare earth terbium enriched powder obtained in Step 2 into a sulfuric acid system for leaching. The sulfuric acid system uses a mixture of concentrated sulfuric acid and water with a volume ratio of 1:2.5. Set the leaching temperature at 120°C. Under the action of stirring, after 10 hours, let it stand, and collect the supernatant;

[0045] Step 4: Add an excessive amount of oxalic acid solution to the supernatant, adjust the pH value to 2, let it stand, and obtain terbium oxalate precipitate through solid-liquid separation; after solid-liquid separation, cool the liquid to below 25°C and filter to collect oxalic acid crystals. The reaction waste gas is condensed and recovered as liquid hydrogen fluoride through a PVC pipe and a condenser.

[0046] Step 5: Burn the terbium oxalate in a temperature-controlled rotary kiln to dehydrate and decarbonize it, obtaining brownish-black terbium oxide. After weighing, it shows 3.57 kg, and the recovery rate is 99.17%.

[0047] Example 2

[0048] The method for recycling rare earth and fluorine from the waste residue in the production of terbium metal by vacuum calcium thermal reduction method in this example includes the following steps:

[0049] Step 1: Take the calcium-terbium waste residue produced during the production of terbium metal by calcium thermal reduction method. After collection and full exposure to air for 12 days, the massive calcium-terbium waste residue is converted into a powdery form. Weigh 100 kg of the calcium-terbium waste residue for standby. Through laboratory tests, it is known that the total rare earth content (calculated as REO) is 2.5%;

[0050] Step 2: After separation by a wet magnetic separator, obtain rare earth terbium enriched powder and calcium fluoride powder;

[0051] Step 3: Add the rare earth terbium enriched powder obtained in Step 2 into a sulfuric acid system for leaching. The sulfuric acid system uses a mixture of concentrated sulfuric acid and water with a volume ratio of 1:2. Set the leaching temperature at 40°C. Under the action of stirring, after 10 hours, let it stand, and collect the supernatant;

[0052] Step 4: Add an excessive amount of oxalic acid solution to the supernatant, adjust the pH value to 3, let it stand, and obtain terbium oxalate precipitate through solid-liquid separation; after solid-liquid separation, cool the liquid to below 30°C and filter to collect oxalic acid crystals. The reaction waste gas is condensed and recovered as liquid hydrogen fluoride through a PVC pipe and a condenser.

[0053] Step 5: Burn the terbium oxalate in a temperature-controlled rotary kiln to dehydrate and decarbonize it, obtaining brownish-black terbium oxide. After weighing, it shows 2.48 kg, and the recovery rate is 99.20%.

[0054] Example 3

[0055] The method for recycling rare earth and fluorine from the waste residue in the production of terbium metal by vacuum calcium thermal reduction method in this example includes the following steps:

[0056] Step 1: Take the calcium-terbium waste residue produced during the production of metallic terbium by the calcium thermal reduction method. After collection and full exposure to the air for 12 days, the massive calcium-terbium waste residue is transformed into a powdery form. Weigh 100 kg of the calcium-terbium waste residue for standby. As known from laboratory tests, the total rare earth content (calculated as REO) is 4.0%.

[0057] Step 2: Obtain rare earth terbium enriched powder and calcium fluoride powder after separation by a wet magnetic separator.

[0058] Step 3: Add the rare earth terbium enriched powder obtained in Step 2 to a sulfuric acid system for leaching. The sulfuric acid system uses a mixture of concentrated sulfuric acid and water with a volume ratio of 1:3. Set the leaching temperature at 250 °C. Under the action of stirring, after 10 hours, let it stand and collect the supernatant.

[0059] Step 4: Add an excessive amount of oxalic acid solution to the supernatant, adjust the pH value to 1.5, let it stand, and obtain terbium oxalate precipitate through solid-liquid separation; after solid-liquid separation, cool the liquid to 15 °C and filter to collect oxalic acid crystals. The reaction waste gas is condensed and recovered as liquid hydrogen fluoride through a PVC pipe and a condenser.

[0060] Step 5: Burn the terbium oxalate in a temperature-controlled rotary kiln for dehydration and decarburization to obtain brownish-black terbium oxide, which weighs 3.97 kg after weighing, and the recovery rate is 99.25%.

[0061] Example 4

[0062] The method for recycling rare earth and fluorine from the waste residue in the production of metallic terbium by the vacuum calcium thermal reduction method in this example includes the following steps:

[0063] Step 1: Take the calcium-terbium waste residue produced during the production of metallic terbium by the calcium thermal reduction method. After collection and full exposure to the air for 12 days, the massive calcium-terbium waste residue is transformed into a powdery form. Weigh 100 kg of the calcium-terbium waste residue for standby. As known from laboratory tests, the total rare earth content (calculated as REO) is 4.4%.

[0064] Step 2: Obtain rare earth terbium enriched powder and calcium fluoride powder after separation by a wet magnetic separator.

[0065] Step 3: Add the rare earth terbium enriched powder obtained in Step 2 to a sulfuric acid system for leaching. The sulfuric acid system uses a mixture of concentrated sulfuric acid and water with a volume ratio of 1:3. Set the leaching temperature at 360 °C. Under the action of stirring, after 10 hours, let it stand and collect the supernatant.

[0066] Step 4: Add an excessive amount of oxalic acid solution to the supernatant, adjust the pH value to 1.5, let it stand, and obtain terbium oxalate precipitate through solid-liquid separation; after solid-liquid separation, the liquid is cooled to 15 °C and filtered to collect oxalic acid crystals, and the reaction exhaust gas is condensed and recovered as liquid hydrogen fluoride through a PVC pipe and a condenser.

[0067] Step 5: Burn the terbium oxalate in a temperature-controlled rotary kiln to dehydrate and decarbonize it, obtaining brownish-black terbium oxide, which weighs 4.36 kg after weighing, and the yield is 99.09%.

[0068] In the above-mentioned embodiment, in Step 3, a multi-stage sulfuric acid precipitation tank is used for leaching in a sulfuric acid system, as Figure 2 shown. A plurality of partition plates are successively arranged therein, and the heights of the partition plates along the feeding direction decrease successively. The sulfuric acid precipitation tank in the above-mentioned embodiment is specifically divided into three levels. Between the first-stage precipitation tank 1 and the second-stage precipitation tank 2, and between the second-stage precipitation tank 2 and the third-stage precipitation tank 3, a first partition plate 11 and a second partition plate 12 are successively provided. The first partition plate 11 is higher than the second partition plate 12. The main dissolution reaction occurs in the first-stage precipitation tank 1. After the reaction, the supernatant rich in rare earth flows through the first partition plate 11 into the second-stage precipitation tank 2. In the second-stage precipitation tank 2, a primary precipitation occurs in the supernatant. The supernatant in the second-stage precipitation tank 2 continues to flow through the second partition plate 12 to the third-stage precipitation tank 3 to form a secondary precipitation, and finally the reaction supernatant in the last-stage precipitation tank, that is, the third-stage precipitation tank 3, is collected.

[0069] Further analysis and testing of the terbium oxide obtained in the above-mentioned embodiment show that the purity of the terbium oxide reaches 4N. Its composition is shown in Table 1 below:

[0070] Table 1 Composition analysis of terbium oxide obtained in Examples 1-4

[0071]

Claims

1. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal, characterized in that, Using the calcium-terbium waste residue produced in the industrial production of terbium metal by calcium thermal reduction method as raw material, it includes the following steps: Step 1: The calcium-terbium waste residue is fully exposed and dried in the air to convert the massive calcium-terbium waste residue into powder form; Step 2: The powder obtained in Step 1 is separated by a magnetic separator to obtain terbium rare earth enriched powder and calcium fluoride powder respectively; Step 3: The terbium rare earth enriched powder obtained in Step 2 is leached under heating conditions in a sulfuric acid system and completely converted into a rare earth sulfate system liquid. After standing, the supernatant is collected; Step 4: Excessive oxalic acid is added to the supernatant, the pH value is adjusted, and after standing, terbium oxalate precipitate is obtained through solid-liquid separation. The supernatant of the solid-liquid separation precipitates oxalic acid crystals after cooling; Step 5: The terbium oxalate obtained in Step 4 is calcined to dehydrate and decarbonize to obtain terbium oxide.

2. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1, characterized in that, The magnetic separator in Step 2 uses a dry or wet magnetic separator.

3. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1, characterized in that, The calcium fluoride powder collected in Step 2 is used as a raw material for the industrial manufacture of hydrogen fluoride.

4. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1, characterized in that, In Step 3, the leaching in the sulfuric acid system uses a multi-stage sulfuric acid precipitation tank. A plurality of partition plates are sequentially arranged in the multi-stage sulfuric acid precipitation tank, and the heights of the partition plates along the feed direction decrease in sequence.

5. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1 or 4, characterized in that, The sulfuric acid system is a mixture of concentrated sulfuric acid and water with a volume ratio of 1:2 - 3.

6. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1 or 4, characterized in that, The temperature of the heating leaching in Step 3 is 40 - 360 °C.

7. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1 or 4, characterized in that, Stirring is carried out during the heating leaching process in Step 3.

8. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1, characterized in that, The waste gas generated during the reaction process in Step 4 is exhausted by suction and led to a condenser, and the condenser condenses and recovers liquid hydrogen fluoride.

9. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1, characterized in that, In Step 4, the pH value is adjusted to 1.5 - 3.

10. Method for recycling rare earths and fluorine from waste residues produced by vacuum calcium thermal reduction method for producing terbium metal according to claim 1, characterized in that, In Step 4, the temperature is reduced to below 30 °C.

Images