A method for preparing ferrosilicon alloy and leaching rare earth by using neodymium iron boron waste iron tailings and silicon cutting waste

Abstract

The application provides a method for preparing ferrosilicon alloy and leaching rare earth by using neodymium iron boron waste iron tailings and silicon cutting waste, and the method comprises the following steps: (1) mixing neodymium iron boron waste iron tailings, silicon cutting waste and flux, and then performing a thermal reduction reaction to obtain ferrosilicon alloy and reduction tailings; (2) performing acid leaching treatment on the reduction tailings in step (1) to obtain a rare earth leaching solution and leaching residue. The method is short in process and is used for preparing ferrosilicon alloy by adopting a silicon thermal reduction-slag gold melting separation method, and is used for extracting rare earth elements from the reduction tailings by means of solution leaching; the method is simple in operation, short in reaction time, high in purity of the regenerated alloy, high in leaching rate of the rare earth elements, and realizes the collaborative high-value utilization of the two kinds of waste.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste recycling technology, and relates to a recycled alloy, particularly a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste tailings and silicon cutting waste. Background Technology

[0002] Neodymium iron boron (NdFeB), as the permanent magnet material with the highest magnetic energy product at room temperature, is widely used in various fields such as the electronics industry, new energy vehicles, and wind power generation. During NdFeB production, 30-40% waste is generated, and the amount of waste is increasing with the widespread application of NdFeB magnets; retired NdFeB permanent magnets also urgently need to be processed. Currently, NdFeB waste is recycled using an "oxidative roasting-hydrochloric acid preferential dissolution" process, where rare earth oxides preferentially dissolve in hydrochloric acid solution, and iron oxide is enriched in the slag to form NdFeB hydrochloric acid preferentially soluble iron slag, with an iron oxide content exceeding 80% and a rare earth content ranging from 0.3% to 0.5%. Due to the lack of a deep extraction process for NdFeB waste iron tailings, companies simply sell it at low prices as raw material for iron smelting or stockpile it, resulting in the waste of rare earth resources and environmental pollution.

[0003] CN113293307A discloses a method for extracting iron and cobalt from NdFeB waste using the hydrochloric acid-soluble method for iron tailings. The method includes the following steps: mixing the iron tailings with water to obtain a dispersed slurry; adding a concentrated acid solution to the dispersed slurry to react and obtain a reaction slurry; and adding a reducing agent to the reaction slurry at least twice to conduct a reduction reaction, obtaining leaching residue and a leachate containing iron and cobalt. However, it does not disclose an effective method for extracting rare earth elements from the iron tailings.

[0004] With the introduction of the "dual carbon" target, the adjustment of the energy structure has become more urgent. Crystalline silicon solar photovoltaic power generation has the advantages of being clean and economical, and has enormous development potential. However, in the production process of crystalline silicon solar cells, the use of wire cutting technology results in more than 30% of the crystalline silicon entering the cutting waste. This waste mainly consists of high-purity silicon, silicon oxide, and a small amount of metal impurities introduced during the cutting process, with the high-purity silicon content exceeding 80%. Current technologies, such as wet acid leaching, slag refining, and vacuum melting, are insufficient to purify the cutting waste to 6N solar grade. In recent years, the utilization of silicon cutting waste has received increasing attention.

[0005] CN112267035A discloses a method for preparing manganese silicon alloy using crystalline silicon diamond wire cutting waste, comprising the following steps: (1) separating the solid and liquid of crystalline silicon diamond wire cutting waste slurry and drying the solid material to obtain crystalline silicon diamond wire cutting waste; (2) feeding manganese-containing material powder, crystalline silicon diamond wire cutting waste powder, additives, and binders into a mixer for mixing, pressing into briquettes or pelletizing to obtain furnace charge; (3) placing the furnace charge into a melting furnace and melting to obtain manganese silicon alloy melt; (4) pouring the alloy melt out of the furnace into a steel ingot mold or sand mold to obtain manganese silicon alloy ingot.

[0006] In summary, while acid leaching reduction can recover rare earth elements from NdFeB waste tailings, it suffers from high energy consumption and poor economic efficiency. Given the strong reducing properties of silicon in silicon cutting waste, this study aims to develop a novel method for recovering rare earth elements from both silicon cutting waste and NdFeB waste tailings and co-producing ferrosilicon alloys. This method shortens the process flow, reduces energy consumption, and improves alloy purification and rare earth element leaching rates, achieving synergistic high-value utilization of both waste materials. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste. The method employs a short-process silothermic reduction-slag-metal fusion separation method to prepare ferrosilicon alloy, and extracts rare earth elements from the reduction tailings through solution leaching. The method is simple to operate, has a short reaction time, produces high purity recycled alloy, and has a high rare earth element leaching rate, achieving synergistic high-value utilization of the two types of waste.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste, the method comprising the following steps:

[0010] (1) Mix neodymium iron boron waste iron tailings, silicon cutting waste and flux, and then carry out a thermal reduction reaction to obtain ferrosilicon alloy and reduced tailings;

[0011] (2) The reduction tailings described in step (1) are subjected to acid leaching to obtain rare earth leachate and leaching residue.

[0012] This invention employs a short-process method of silicothermic reduction-slag-metal fusion to prepare ferrosilicon alloys, and extracts rare earth elements from the reduction tailings through solution leaching, achieving synergistic high-value utilization of two industrial wastes. Furthermore, the rare earth elements in the reduction tailings are further enriched, and due to the absence of coating by sparingly soluble iron oxides, the leaching properties are improved, allowing for leaching by conventional acid leaching methods, thereby achieving the extraction and recovery of rare earth elements.

[0013] It is worth noting that the addition of flux can effectively lower the melting point of NdFeB waste iron tailings, accelerate the melting of the oxide layer on the surface of silicon cutting waste, expose the high-purity silicon inside to participate in the reduction reaction, and significantly reduce the viscosity of the slag phase, promoting the polymerization of the alloy. The reaction products are ferrosilicon alloy and slag phase. There is a clear slag-metal interface between the slag phase and the ferrosilicon alloy, which is easy to separate.

[0014] As a preferred technical solution of the present invention, the mass ratio of NdFeB waste iron tailings, silicon cutting waste and flux in step (1) is 10:(3~10):(2~4), for example, it can be 10:3:2, 10:5:3, 10:7:4 or 10:10:4, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] It is worth noting that controlling the mass ratio of the three materials within a specific range has a certain influence on the polymerization of alloy particles, which is beneficial to improving the purity of ferrosilicon alloy.

[0016] Preferably, the flux in step (2) includes any one or a combination of at least two of anhydrous calcium oxide, anhydrous sodium oxide, anhydrous aluminum oxide, or anhydrous magnesium oxide, wherein typical but non-limiting combinations include a combination of anhydrous calcium oxide and anhydrous aluminum oxide, a combination of anhydrous aluminum oxide and anhydrous magnesium oxide, a combination of anhydrous calcium oxide and anhydrous aluminum oxide, or a combination of anhydrous calcium oxide, anhydrous aluminum oxide, and anhydrous magnesium oxide, etc., preferably anhydrous calcium oxide.

[0017] As a preferred technical solution of the present invention, the neodymium iron boron waste tailings in step (1) are the tailings after rare earths are extracted from neodymium iron boron waste by hydrochloric acid preferential dissolution method.

[0018] In this invention, the NdFeB waste iron tailings in step (1) are NdFeB hydrochloric acid soluble iron tailings.

[0019] Preferably, the Fe2O3 content in the NdFeB waste tailings in step (1) is 70-90 wt.%, for example, it can be 72 wt.%, 75 wt.%, 78 wt.%, 80 wt.%, 82 wt.%, 85 wt.%, 86 wt.%, or 88 wt.%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, before mixing, the NdFeB waste iron tailings in step (1) further include grinding, cleaning and drying the NdFeB waste iron tailings in sequence.

[0021] Preferably, the components in the dried NdFeB waste tailings include, by weight percentage: Fe2O3 ≥ 80 wt.%, ReO ≤ 1 wt.%, 5 wt.% ≤ Al2O3 + SiO2 ≤ 10 wt.%, and other components ≤ 5 wt.%.

[0022] As a preferred technical solution of the present invention, the silicon cutting waste in step (1) is silicon mud generated after the solar-grade crystalline silicon ingot is wire-cut.

[0023] In this invention, the silicon cutting waste in step (1) is crystalline silicon cutting waste.

[0024] Preferably, the silicon cutting waste in step (1) has a Si content of 80-98 wt.% and a SiO2 content of 2-20 wt.%.

[0025] In this invention, the Si content in the silicon cutting waste is 80-98 wt.%, for example, it can be 82 wt.%, 85 wt.%, 88 wt.%, 90 wt.%, 92 wt.%, 94 wt.%, 95 wt.%, or 97 wt.%, etc., and the SiO2 content in the silicon cutting waste is 2-20 wt.%, for example, it can be 5 wt.%, 7 wt.%, 10 wt.%, 12 wt.%, 14 wt.%, 15 wt.%, 17 wt.%, or 19 wt.%, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0026] Preferably, before mixing, the silicon cutting waste in step (1) further includes grinding, cleaning and drying the silicon cutting waste in sequence.

[0027] Preferably, the components of the dried silicon cutting waste include, by weight percentage: Si 80-90 wt.%, SiO2 content 8-10 wt.%, and other components ≤1 wt.%.

[0028] As a preferred technical solution of the present invention, the thermal reduction reaction in step (1) is carried out under a protective atmosphere.

[0029] Preferably, the protective atmosphere includes any one or a combination of at least two of air, nitrogen, or argon, wherein typical but non-limiting combinations include a combination of air and nitrogen, a combination of nitrogen and argon, or a combination of air, nitrogen, and argon, preferably argon.

[0030] In this invention, the thermal reduction reaction in step (1) is carried out in a high-temperature tubular furnace.

[0031] As a preferred technical solution of the present invention, the temperature of the thermal reduction reaction in step (1) is 1200 to 1600°C, for example, it can be 1250°C, 1300°C, 1350°C, 1400°C, 1450°C, 1500°C or 1550°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] Preferably, the holding time for the thermal reduction reaction in step (1) is 15 to 120 min, for example, it can be 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min or 110 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the thermal reduction reaction in step (1) is followed by sequential furnace cooling, mechanical crushing and separation.

[0034] As a preferred technical solution of the present invention, the silicon content in the ferrosilicon alloy in step (1) is 5-15 wt.% and the iron content is 85-95 wt.%.

[0035] In this invention, the silicon content in the ferrosilicon alloy is 5-15 wt.%, for example, it can be 7 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, or 14 wt.%, etc., and the iron content in the ferrosilicon alloy is 85-95 wt.%, for example, it can be 87 wt.%, 89 wt.%, 90 wt.%, 91 wt.%, 92 wt.%, 93 wt.%, or 94 wt.%, etc., but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] The silicon-iron alloy produced by this invention has high purity and can be applied in the fields of metallurgy, mineral processing, hydrogen production, welding rod materials, and lithium battery electrode materials.

[0037] Preferably, the rare earth element enrichment content in the reduction tailings in step (1) is 50-100%, for example, it can be 60%, 70%, 80% or 90%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] As a preferred technical solution of the present invention, before the acid leaching treatment of the reduction tailings in step (2), the reduction tailings are further subjected to mechanical crushing and grinding in sequence.

[0039] In this invention, the grinding instrument is any one of a planetary ball mill, a drum ball mill, a vibrating ball mill, or a Raymond mill, and those skilled in the art can choose according to actual needs.

[0040] Preferably, the acid leaching treatment in step (2) is carried out in an acid solution.

[0041] Preferably, the acid solution includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or nitric acid, wherein typical but non-limiting combinations include a combination of hydrochloric acid and sulfuric acid, a combination of sulfuric acid and nitric acid, or a combination of hydrochloric acid, sulfuric acid, and nitric acid, preferably hydrochloric acid.

[0042] Preferably, the concentration of the acid solution is 0.1 to 2 mol / L, for example, it can be 0.2 mol / L, 0.4 mol / L, 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.7 mol / L or 1.9 mol / L, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0043] Preferably, the solid-liquid ratio of the reduction tailings and acid solution is (20-30):1g / L, for example, it can be 22:1g / L, 24:1g / L, 25:1g / L, 26:1g / L, 28:1g / L or 29:1g / L, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0044] As a preferred technical solution of the present invention, the temperature of the acid leaching treatment in step (2) is 25 to 180°C, for example, it can be 30°C, 40°C, 50°C, 70°C, 90°C, 100°C, 120°C, 140°C or 160°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 80 to 100°C.

[0045] Preferably, the acid leaching time in step (2) is 15 to 300 min, for example, it can be 20 min, 30 min, 50 min, 60 min, 100 min, 120 min, 150 min, 180 min, 200 min, 240 min, 250 min or 270 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] In this invention, the product after acid leaching in step (2) is subjected to solid-liquid separation to obtain rare earth leachate and leachate residue.

[0047] It is worth noting that, compared with the direct leaching method for neodymium iron boron waste iron tailings, the leaching rates of rare earth elements Ce, Pr, and Nd are increased by 500-700%, 200-300%, and 50-200%, respectively, using the rare earth leaching method provided by this invention.

[0048] As a preferred technical solution of the present invention, the method includes the following steps:

[0049] (1) NdFeB waste iron tailings, silicon cutting waste and flux are mixed in a mass ratio of 10:(3~10):(2~4). Then, a thermal reduction reaction is carried out in a protective atmosphere at a temperature of 1200~1600℃ and held for 15~120min. After that, the furnace is cooled, mechanically crushed and separated in sequence to obtain ferrosilicon alloy and reduced tailings.

[0050] Wherein, the NdFeB waste tailings are the tailings after rare earth extraction from NdFeB waste using the hydrochloric acid superior dissolution method; the silicon cutting waste is the silicon sludge produced after wire cutting of solar-grade crystalline silicon ingots; the flux includes any one or a combination of at least two of anhydrous calcium oxide, anhydrous sodium oxide, anhydrous aluminum oxide, or anhydrous magnesium oxide.

[0051] The silicon-iron alloy contains 5-15 wt.% silicon and 85-95 wt.% iron; the rare earth element enrichment content in the reduction tailings is 50-100%.

[0052] (2) The reduction tailings described in step (1) are mechanically crushed and ground in sequence, and then acid leaching is performed in acid solution at a temperature of 25-180℃ for 15-300 minutes to obtain rare earth leachate and leaching residue.

[0053] The acid solution includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or nitric acid, preferably hydrochloric acid; the concentration of the acid solution is 0.1–2 mol / L; and the solid-liquid ratio of the reduction tailings to the acid solution is (20–30):1 g / L.

[0054] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] (1) This invention provides a new method for preparing ferrosilicon alloys while enriching and extracting rare earth elements. The method uses a short process of silicothermic reduction-slag-gold fusion separation to prepare ferrosilicon alloys and extracts rare earth elements from the reduction tailings by solution leaching. This achieves the synergistic high-value utilization of two typical solid wastes: neodymium iron boron waste tailings and silicon cutting waste. At the same time, the method has high applicability, low cost, and low environmental pollution.

[0057] (2) The method provided by the present invention ensures deep deoxidation of waste by adding flux and the strong reducing ability of silicon, and the high reaction temperature ensures rapid deoxidation of waste. The resulting ferrosilicon alloy has high purity. At the same time, the removal of iron element ensures the subsequent leaching of rare earth elements. The silicon content in the obtained ferrosilicon alloy is 5-15 wt.% and the iron content is 85-95 wt.%. The rare earth element enrichment content in the obtained reduction tailings is 50-100%. Attached Figure Description

[0058] Figure 1 This is a schematic flowchart of the method for preparing ferrosilicon alloy and leaching rare earths using neodymium iron boron waste iron tailings and silicon cutting waste provided in Embodiment 1 of the present invention.

[0059] Figure 2 The above are the SEM surface scan results of the ferrosilicon alloy obtained in Example 1 of this invention;

[0060] Figure 3 The image shows the XRD pattern of the reduced tailings obtained in Example 1 of this invention. Detailed Implementation

[0061] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0062] In the following embodiments and comparative examples of this invention, the NdFeB waste tailings are all tailings from NdFeB waste after rare earth extraction using the hydrochloric acid preferential solubility method; the silicon cutting waste is all silicon sludge produced after wire cutting of solar-grade crystalline silicon ingots; and the NdFeB waste tailings and silicon cutting waste were independently ground, cleaned, and dried before mixing; the components in the dried NdFeB waste tailings, by weight percentage, include: Fe2O3 ≥ 80 wt.%, ReO ≤ 1 wt.%, 5 wt.% ≤ Al2O3 + SiO2 ≤ 10 wt.%, and other components ≤ 5 wt.%; the components in the dried silicon cutting waste, by weight percentage, include: Si 80–90 wt.%, SiO2 content 8–10 wt.%, and other components ≤ 1 wt.%.

[0063] Example 1

[0064] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste. The process flow diagram is shown below. Figure 1 As shown, the method includes the following steps:

[0065] (1) Mix 10g of neodymium iron boron waste iron tailings, 5g of silicon cutting waste and 3.85g of anhydrous calcium oxide in a corundum crucible, cover it with a graphite crucible for protection, place it in a high-temperature tube furnace, and then carry out a thermal reduction reaction at 1500℃ under an argon protective atmosphere and hold for 60min. After that, carry out furnace cooling, mechanical crushing and separation in sequence to obtain ferrosilicon alloy and reduction tailings.

[0066] (2) The reduction tailings described in step (1) are mechanically crushed and ground in sequence. Then, 0.5g of reduction tailings powder is placed in a test tube, 20mL of 0.3mol / L hydrochloric acid solution is added, and then the tube is placed in a water bath at 90℃ for 240min and 500rpm. After solid-liquid separation, rare earth leachate and leachate residue are obtained.

[0067] The SEM surface scan results and EDS elemental content at each point of the silicon-iron alloy obtained in this embodiment are as follows: Figure 2 As shown in Table 1, by Figure 2 As shown in Table 1, the obtained ferrosilicon alloy contains three phases: FeSi phase, Fe5Si3 phase, and a small amount of Fe-Si solid solution phase, while cobalt is uniformly dispersed in the alloy. The XRD pattern of the reduction tailings obtained in this embodiment is shown below. Figure 3 As shown, by Figure 3 As can be seen, after reduction smelting, the iron oxide phase in the NdFeB waste iron tailings disappears, and the main phase is CaSiO3, which can be used as cement raw material. Therefore, this invention realizes the resource utilization and "zero emission" treatment of two typical industrial solid wastes.

[0068] Table 1

[0069]

[0070] Example 2

[0071] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste. The method includes the following steps:

[0072] (1) Mix 10g of neodymium iron boron waste iron tailings, 5g of silicon cutting waste and 3.85g of anhydrous calcium oxide in a corundum crucible, cover it with a graphite crucible for protection, place it in a high-temperature tube furnace, and then carry out a thermal reduction reaction at 1600℃ under an argon protective atmosphere and hold for 30min. After that, carry out furnace cooling, mechanical crushing and separation in sequence to obtain ferrosilicon alloy and reduction tailings.

[0073] (2) After mechanically crushing and grinding the reduction tailings described in step (1), 0.5g of reduction tailings powder is placed in a test tube, 20mL of 0.2mol / L hydrochloric acid solution is added, and then the tube is placed in a water bath at 90℃ for 240min and 500rpm. After solid-liquid separation, rare earth leachate and leachate residue are obtained.

[0074] XRF analysis was performed on the NdFeB waste iron tailings before and after the thermal reduction reaction in step (1) of this embodiment. The analysis results are shown in Table 2.

[0075] Table 2

[0076]

[0077] As shown in Table 2, after thermal reduction, the contents of iron oxide and cobalt oxide in NdFeB waste tailings decreased significantly, while the contents of rare earth oxides increased markedly. Due to the introduction of flux, the contents of calcium oxide and silicon oxide also increased significantly. This is because silicon has a stronger affinity for oxygen than iron and cobalt. Iron oxide and cobalt oxide are reduced into the alloy phase, and the reduction product, silicon dioxide, enters the slag phase. Rare earth elements have a stronger affinity for oxygen than silicon and are therefore not reduced. Furthermore, the mass of the reduced tailings is less than that of the unreduced NdFeB waste tailings, resulting in the enrichment of rare earth oxides.

[0078] Example 3

[0079] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste. The method includes the following steps:

[0080] (1) Mix 10g of NdFeB waste iron tailings, 5g of silicon cutting waste and 3.85g of anhydrous calcium oxide in a corundum crucible, cover it with a graphite crucible for protection, place it in a high-temperature tube furnace, and then carry out a thermal reduction reaction at 1600℃ under a nitrogen protective atmosphere and hold for 120min. After that, the furnace is cooled, mechanically crushed and separated in sequence to obtain ferrosilicon alloy and reduction tailings.

[0081] (2) After mechanically crushing and grinding the reduction tailings described in step (1), 0.5g of reduction tailings powder is placed in a test tube, 20mL of 0.4mol / L hydrochloric acid solution is added, and then the tube is placed in a water bath at 90℃ for 240min and 500rpm. After solid-liquid separation, rare earth leachate and leachate residue are obtained.

[0082] Example 4

[0083] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth using neodymium iron boron waste iron tailings and silicon cutting waste. Except for the amount of silicon cutting waste added in step (1) being 2g, all other conditions are the same as in embodiment 2.

[0084] Example 5

[0085] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth using neodymium iron boron waste iron tailings and silicon cutting waste. Except for the amount of silicon cutting waste added in step (1) being 12g, all other conditions are the same as in embodiment 2.

[0086] Example 6

[0087] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste. Except for the leaching temperature of 50°C in step (2), all other conditions are the same as in embodiment 2.

[0088] Example 7

[0089] This embodiment provides a method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste. Except for the leaching temperature of 200°C in step (2), all other conditions are the same as in embodiment 2.

[0090] Comparative Example 1

[0091] This comparative example provides a method for leaching rare earth elements from neodymium iron boron waste iron tailings. The reduction tailings are replaced with neodymium iron boron waste iron tailings, and then leaching is performed directly. All other conditions are the same as in Example 2.

[0092] The Si and Fe contents in the silicon-iron alloys obtained in the above examples and comparative examples were tested, as were the leaching rates of rare earth elements Ce, Pr, and Nd in the rare earth leachate. The results are shown in Table 3.

[0093] Table 3

[0094]

[0095]

[0096] As shown in Table 3:

[0097] (1) Using the method provided in Examples 1-3 of this invention, the silicon content in the obtained ferrosilicon alloy is 5-15 wt.% and the iron content is 85-95 wt.%, the alloy has high purity and high yield; and the leaching rate of rare earth elements Ce, Pr and Nd is high, realizing the synergistic high-value utilization of the two wastes;

[0098] (2) As can be seen from the comparison between Example 2 and Example 4-5, when the amount of silicon cutting waste added is too small, there is not enough elemental silicon to participate in the alloying process, and the silicon content in the alloy is greatly reduced. However, the amount of SiO2 introduced is also small, the slag-metal separation effect is better, and the amount of slag in the reduction tailings is small. When the amount of silicon cutting waste added is too large, there is a large amount of elemental silicon in the melt, and the silicon content in the alloy is increased. However, the introduction of a large amount of SiO2 reduces the slag-metal separation effect. Some metallic iron in the slag still participates in the subsequent leaching, which reduces the leaching rate of rare earth elements Ce, Pr, and Nd.

[0099] (3) As can be seen from the comparison between Example 2 and Example 6-7, when the leaching temperature is further reduced, the leaching rate of rare earth elements Ce, Pr and Nd also decreases; when the leaching temperature is further increased, the leaching rate of rare earth elements Ce, Pr and Nd also decreases due to the large amount of volatilization of hydrochloric acid solution.

[0100] (4) As can be seen from the comparison between Example 2 and Comparative Example 1, Comparative Example 1 uses NdFeB waste iron tailings for direct leaching without reduction smelting. Under the coating effect of the iron oxide layer, the leaching rates of rare earth elements Ce, Pr and Nd are 10.89%, 19.97% and 20.56% respectively, which are significantly lower than those of Example 2. This shows that reduction smelting to remove the iron oxide layer plays an important role in the leaching of rare earth elements.

[0101] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0102] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0103] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing ferrosilicon alloy and leaching rare earth elements using neodymium iron boron waste iron tailings and silicon cutting waste, characterized in that, The method includes the following steps: (1) Mix NdFeB waste iron tailings, silicon cutting waste and flux, and then carry out a thermal reduction reaction to obtain ferrosilicon alloy and reduced tailings; the mass ratio of NdFeB waste iron tailings, silicon cutting waste and flux is 10:5~10:3~4; (2) The reduction tailings from step (1) are subjected to acid leaching to obtain rare earth leachate and leaching residue; the acid leaching temperature is 80~100℃. The NdFeB waste tailings mentioned in step (1) are the tailings after rare earths are extracted from NdFeB waste using the hydrochloric acid superior solubility method; The Fe2O3 content in the NdFeB waste tailings in step (1) is 70~90 wt.%; Before mixing, the neodymium iron boron waste iron tailings in step (1) further include grinding, cleaning and drying the neodymium iron boron waste iron tailings in sequence; The components in the dried NdFeB waste tailings, by weight percentage, are as follows: Fe2O3 ≥ 80 wt.%, REO ≤ 1 wt.%, 5 wt.% ≤ Al2O3 + SiO2 ≤ 10 wt.%, other components ≤ 5 wt.%; The silicon cutting waste mentioned in step (1) is silicon sludge produced after wire cutting of solar-grade crystalline silicon ingots; The silicon cutting waste in step (1) contains 80-98 wt.% Si and 2-20 wt.% SiO2. Before mixing, the silicon cutting waste in step (1) further includes grinding, cleaning and drying the silicon cutting waste in sequence; The dried silicon cutting waste comprises the following components by weight percentage: Si 80~90 wt.%, SiO2 content 8~10 wt.%, and other components ≤1 wt.%; The temperature of the thermal reduction reaction in step (1) is 1200~1600℃; The acid leaching treatment in step (2) is carried out in an acid solution; The concentration of the acid solution is 0.1~2 mol / L; The solid-liquid ratio of the reduction tailings and acid solution is 20~30:1 g / L.

2. The method according to claim 1, characterized in that, The flux in step (1) includes any one or a combination of at least two of anhydrous calcium oxide, anhydrous sodium oxide, anhydrous aluminum oxide, or anhydrous magnesium oxide.

3. The method according to claim 2, characterized in that, The flux in step (1) is anhydrous calcium oxide.

4. The method according to claim 1, characterized in that, The thermal reduction reaction in step (1) is carried out under a protective atmosphere.

5. The method according to claim 4, characterized in that, The protective atmosphere includes any one or a combination of two of nitrogen or argon.

6. The method according to claim 5, characterized in that, The protective atmosphere is argon.

7. The method according to claim 1, characterized in that, The holding time for the thermal reduction reaction in step (1) is 15~120 min.

8. The method according to claim 1, characterized in that, Step (1) includes sequential furnace cooling, mechanical crushing and separation following the thermal reduction reaction.

9. The method according to claim 1, characterized in that, In step (1), the silicon content in the ferrosilicon alloy is 5-15 wt.% and the iron content is 85-95 wt.%.

10. The method according to claim 1, characterized in that, The rare earth element enrichment content in the reduction tailings in step (1) is 50-100%.

11. The method according to claim 1, characterized in that, Before acid leaching the reduction tailings in step (2), the process also includes mechanically crushing and grinding the reduction tailings in sequence.

12. The method according to claim 11, characterized in that, The acid solution includes any one or a combination of at least two of hydrochloric acid, sulfuric acid, or nitric acid.

13. The method according to claim 12, characterized in that, The acid solution is hydrochloric acid.

14. The method according to claim 1, characterized in that, The acid leaching time in step (2) is 15~300 min.

15. The method according to claim 1, characterized in that, The method includes the following steps: (1) NdFeB waste iron tailings, silicon cutting waste and flux are mixed in a mass ratio of 10:5~10:3~4. Then, a thermal reduction reaction is carried out in a protective atmosphere at a temperature of 1200~1600℃ and held for 15~120 min. After that, the furnace is cooled, mechanically crushed and separated in sequence to obtain ferrosilicon alloy and reduced tailings. Wherein, the NdFeB waste tailings are the tailings after rare earth extraction from NdFeB waste using the hydrochloric acid superior dissolution method; the silicon cutting waste is the silicon sludge produced after wire cutting of solar-grade crystalline silicon ingots; the flux includes any one or a combination of at least two of anhydrous calcium oxide, anhydrous sodium oxide, anhydrous aluminum oxide, or anhydrous magnesium oxide. The silicon-iron alloy contains 5-15 wt.% silicon and 85-95 wt.% iron; the rare earth element enrichment content in the reduction tailings is 50-100%. (2) The reduction tailings described in step (1) are mechanically crushed and ground in sequence, and then acid leaching is performed in acid solution at a temperature of 80~100℃ for 15~300 min to obtain rare earth leachate and leaching residue. The acid solution is hydrochloric acid; the concentration of the acid solution is 0.1~2 mol / L; and the solid-liquid ratio of the reduction tailings and the acid solution is 20~30:1 g / L.

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