Transformation method of sulfuric acid rare earth roasted ore

Abstract

The invention discloses a transformation method of sulfuric acid rare earth roasted ore. The transformation method comprises the following steps: (1) carrying out primary transformation reaction on the sulfuric acid rare earth roasted ore, a calcium transformation agent and primary slurry mixing to obtain a primary transformation solid product and a primary transformation liquid product; (2) carrying out (N + 1)-time transformation reaction on the N-time-transformed solid product, a calcium transformation agent and the (N + 1)-time mixed slurry to obtain an (N + 1)-time-transformed solid product and an (N + 1)-time-transformed liquid product; repeating the steps until M times of transformation solid products and M times of transformation liquid products are obtained; wherein M is an integer from 2 to 6, and N is an integer from 1 to M-1; wherein the calcium transformation agent is selected from one or more of calcium oxide, calcium chloride and calcium hydroxide. The transformation method reduces the yield of sulfate wastewater.

Description

Technical Field

[0001] This invention relates to a method for transforming rare earth sulfate roasted ore. Background Technology

[0002] High-temperature roasting with concentrated sulfuric acid is currently one of the mainstream processes for treating mixed rare earth concentrate from Bayan Obo. After roasting, the rare earth concentrate produces rare earth sulfate roasted ore (mainly containing rare earth sulfate, calcium sulfate, and thorium-containing substances). This rare earth sulfate roasted ore is then leached with water to obtain a rare earth sulfate solution. After purification and impurity removal, the solution is converted into a rare earth chloride solution. Currently, commonly used industrial conversion methods include P507 or P204 extraction or ammonium bicarbonate precipitation. However, due to the low solubility of rare earth sulfate, both conversion methods generate large amounts of low-concentration sulfate wastewater. The treatment of this sulfate wastewater places a heavy burden on enterprises; therefore, developing new rare earth sulfate conversion processes that avoid generating large amounts of wastewater is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a method for converting rare earth sulfate roasted ore into rare earth minerals, which can reduce the production of sulfate wastewater. Furthermore, this conversion method has a high rare earth conversion rate.

[0004] The present invention achieves the above objectives through the following technical solutions.

[0005] This invention provides a method for transforming rare earth sulfate roasted ore, comprising the following steps:

[0006] (1) The rare earth sulfate roasted ore, calcium conversion agent and primary slurry are subjected to a primary conversion reaction to obtain a primary conversion solid product and a primary conversion liquid product.

[0007] (2) The Nth transformation solid product, calcium transformation agent and N+1th transformation slurry are subjected to N+1 transformation reaction to obtain N+1th transformation solid product and N+1th transformation liquid product; repeat this step to obtain Mth transformation solid product and Mth transformation liquid product; where M is selected from integers from 2 to 6, and N is an integer from 1 to M-1.

[0008] The calcium conversion agent is selected from one or more of calcium oxide, calcium chloride, and calcium hydroxide.

[0009] In step (1), the ratio of the amount of rare earth elements in the rare earth sulfate roasted ore to the amount of calcium conversion agent is 1:(1.2-1.5); the rare earth elements are calculated as REO; the ratio of the total mass of the rare earth sulfate roasted ore and the calcium conversion agent to the volume of the primary slurry is 1kg:(1-5)L.

[0010] The rare earth sulfate roasted ore of the present invention can be a rare earth sulfate roasted ore formed by high-temperature roasting of Bayan Obo mixed rare earth concentrate with concentrated sulfuric acid.

[0011] In rare earth sulfate roasted ore, the REO content can be 30–40 wt%. In some embodiments, the REO content is 32–35 wt%.

[0012] The calcium conversion agent is selected from one or more of calcium oxide, calcium chloride, and calcium hydroxide. In some embodiments, the calcium conversion agent is selected from one or more of calcium oxide and calcium hydroxide. According to one embodiment of the present invention, the calcium conversion agent is calcium oxide. In other embodiments, the calcium conversion agent is calcium chloride.

[0013] According to the transformation method of the present invention, preferably, in step (1), the reaction is carried out under stirring or grinding conditions, the reaction temperature is 20-90°C, and the reaction time is 30-240 min.

[0014] In some embodiments, step (1) is performed under stirring conditions. In other embodiments, step (1) is performed under grinding conditions.

[0015] In step (1), the reaction temperature can be 20–90°C. In some embodiments, the reaction temperature is 40–60°C. This helps the reaction to proceed fully.

[0016] In step (1), the reaction time can be 30–240 min. In some embodiments, the reaction time is 30–50 min. In other embodiments, the reaction time is 220–240 min. This helps the reaction to proceed fully.

[0017] The molar ratio of rare earth elements to calcium conversion agent in rare earth sulfate roasted ore is 1:(1.2-1.5). In some embodiments, the molar ratio of rare earth elements to calcium conversion agent in rare earth sulfate roasted ore is 1:(1.3-1.4). Rare earth elements are expressed as REO. This improves conversion efficiency.

[0018] In step (1), the ratio of the total mass of rare earth sulfate roasted ore and calcium conversion agent to the volume of the primary slurry is 1 kg:(1-5) L. In some embodiments, the ratio of the total mass of rare earth sulfate roasted ore and calcium conversion agent to the volume of the primary slurry is 1 kg:(1-3) L. This reduces wastewater generation and increases the concentration of REO in the primary conversion liquid product.

[0019] According to the transformation method of the present invention, preferably, the calcium transformation agent is selected from one or more of calcium oxide and calcium hydroxide;

[0020] The primary slurry preparation solution is selected from one or more of water, primary transformation liquid products, and N+1 primary transformation liquid products.

[0021] The transformation method according to the present invention preferably further includes the following steps:

[0022] The solid product from the M-transformation was dissolved in hydrochloric acid to obtain a rare earth chloride solution and a solid slag.

[0023] According to the transformation method of the present invention, preferably, the solid product of the Mth transformation is dissolved in hydrochloric acid with a concentration of 6-12 mol / L at 20-80°C for 30-120 min.

[0024] The concentration of hydrochloric acid can be 6–12 mol / L; preferably 8–10 mol / L.

[0025] The ratio of the amount of rare earth element in the solid product of the M-transformation to the amount of HCl in hydrochloric acid can be 1:(2.5-4); preferably 1:(3-3.5).

[0026] The solid product of the M-transformation is dissolved in hydrochloric acid at 20–80°C; preferably 20–50°C for 30–120 min; preferably 60–90 min.

[0027] According to the transformation method of the present invention, preferably, in step (2), in each transformation reaction, the ratio of the amount of untransformed rare earth elements to the amount of calcium transforming agent in the Nth transformation solid product is 1:(1.2~1.9); wherein the rare earth elements are calculated as REO.

[0028] Preferably, in step (2), in each transformation reaction, the ratio of the amount of untransformed rare earth elements to the amount of calcium transforming agent in the Nth transformation solid product is 1:(1.5~1.8); wherein, the rare earth elements are calculated as REO.

[0029] Untransformed rare earth elements refer to rare earth elements that exist in the Nth transformation solid product in the form of rare earth sulfate.

[0030] When the calcium conversion agent is selected from calcium oxide or calcium hydroxide, the primary conversion solid product mainly consists of rare earth hydroxide and calcium sulfate. Step (2) further converts the incompletely converted rare earth sulfate from the primary conversion solid product. After the rare earth sulfate is completely converted, it is dissolved in hydrochloric acid to obtain a rare earth chloride solution. The 1-M conversion liquid products obtained by this method can be used as 1-M slurry preparation solutions.

[0031] According to the transformation method of the present invention, preferably, the calcium transformation agent is calcium chloride;

[0032] The primary slurry is selected from the secondary transformation liquid product obtained by the secondary transformation reaction of water or other batches of rare earth sulfate roasted ore.

[0033] The Nth slurry is selected from the N+1th transformation liquid product obtained by the N+1th transformation reaction of water or other batches of rare earth sulfate roasted ore.

[0034] The transformation liquid product obtained by this method can be used as a slurry for the next-stage transformation reaction of other batches of rare earth sulfate roasted ore.

[0035] According to the transformation method of the present invention, preferably, the concentration of REO in the primary transformation liquid product is ≥70 g / L;

[0036] In step (2), in each transformation reaction, the ratio of the amount of rare earth elements to the amount of calcium transforming agent in the Nth transformation solid product is 1:(1.2~1.9); wherein, the rare earth elements are calculated as REO.

[0037] More preferably, the concentration of REO in the primary transformation liquid product is ≥100 g / L.

[0038] More preferably, in step (2), in each transformation reaction, the ratio of the amount of rare earth element to the amount of calcium transforming agent in the Nth transformation solid product is 1:(1.5~1.7); wherein the rare earth element is calculated as REO.

[0039] When the calcium conversion agent is calcium chloride, the primary conversion liquid product is a rare earth chloride solution. In step (2), the unconverted rare earth sulfate in the primary conversion solid product is further converted, and the resulting N+1 primary conversion liquid product can be used as the Nth slurry for the Nth conversion of other batches of rare earth sulfate roasted ore, thereby further increasing the concentration of REO in the primary conversion liquid product.

[0040] According to the transformation method of the present invention, preferably, in step (2), the reaction is carried out under stirring or grinding conditions, the reaction temperature is 20-90°C, and the reaction time for each transformation is 30-240 min.

[0041] In some embodiments, step (2) is performed under stirred conditions. In other embodiments, step (2) is performed under milled conditions.

[0042] In step (2), the reaction temperature can be 20–90°C. In some embodiments, the reaction temperature is 40–60°C. This helps the reaction to proceed fully.

[0043] In step (2), the reaction time for each transformation can be 30–100 min. In some embodiments, the reaction time is 30–40 min. In other embodiments, the reaction time is 60–80 min. This helps the reaction to proceed fully.

[0044] According to the transformation method of the present invention, preferably, in step (2), the ratio of the total mass of the Nth transformation solid product and the calcium transformation agent to the volume of the N+1th slurry is 1 kg: (1-5) L.

[0045] More preferably, in step (2), the total mass of the Nth transformation solid product and the calcium transformation agent and the volume ratio of the N+1th slurry are 1 kg: (2-3) L.

[0046] In some implementations, M = 2, then N is 1. This includes the following steps:

[0047] (1) The rare earth sulfate roasted ore, calcium conversion agent and primary slurry are subjected to a primary conversion reaction to obtain a primary conversion solid product and a primary conversion liquid product.

[0048] (2) The primary transformation solid product, calcium transformation agent and secondary slurry are subjected to a secondary transformation reaction to obtain a secondary transformation solid product and a secondary transformation liquid product.

[0049] In some implementations, M = 5, and N is an integer from 1 to 4. That is, it includes the following steps:

[0050] (1) The rare earth sulfate roasted ore, calcium conversion agent and primary slurry are subjected to a primary conversion reaction to obtain a primary conversion solid product and a primary conversion liquid product.

[0051] (2) The primary transformation solid product, calcium transformation agent and secondary slurry are subjected to a secondary transformation reaction to obtain a secondary transformation solid product and a secondary transformation liquid product.

[0052] The reaction temperature can be 20–90℃; preferably 20–40℃. The reaction time can be 30–100 min; preferably 40–70 min.

[0053] In the secondary transformation reaction, the molar ratio of rare earth elements in the primary transformation solid product to the molar ratio of calcium transforming agent can be 1:(1.5-1.7); preferably 1:(1.5-1.6); wherein the rare earth elements are calculated as REO. When the calcium transforming agent is selected from one or more of calcium oxide and calcium hydroxide, the molar ratio of rare earth elements in the primary transformation solid product is calculated as the molar ratio of untransformed rare earth elements in the primary transformation solid product.

[0054] In the secondary transformation reaction, the ratio of the total mass of the primary transformation solid product and the calcium transformation agent to the volume of the secondary slurry can be 1 kg: (2-3) L.

[0055] Optionally, the secondary transformation liquid product may be used as a primary slurry in the primary transformation reaction of other batches of rare earth sulfate roasted ore.

[0056] The secondary transformation solid product, calcium transformation agent, and tertiary slurry were subjected to a tertiary transformation reaction to obtain a tertiary transformation solid product and a tertiary transformation liquid product.

[0057] The reaction temperature can be 20–90℃; preferably 20–40℃. The reaction time can be 30–100 min; preferably 40–70 min.

[0058] In the tertiary transformation reaction, the molar ratio of rare earth elements in the secondary transformation solid product to the molar ratio of calcium transforming agent can be 1:(1.5-1.7); preferably 1:(1.5-1.6); wherein the rare earth elements are calculated as REO. When the calcium transforming agent is selected from one or more of calcium oxide and calcium hydroxide, the molar ratio of rare earth elements in the secondary transformation solid product is calculated as the molar ratio of untransformed rare earth elements in the secondary transformation solid product.

[0059] In the tertiary transformation reaction, the ratio of the total mass of the secondary transformation solid product and the calcium transformation agent to the volume of the tertiary slurry can be 1 kg: (2-3) L.

[0060] Optionally, the tertiary transformation liquid product may be used as a secondary slurry in the secondary transformation reaction of other batches of rare earth sulfate roasted ore.

[0061] The tertiary solid product, calcium transforming agent, and tertiary slurry were subjected to a tertiary transformation reaction to obtain a tertiary solid product and a tertiary liquid product.

[0062] The reaction temperature can be 20–90℃; preferably 20–40℃. The reaction time can be 30–100 min; preferably 40–70 min.

[0063] In the four-stage transformation reaction, the molar ratio of rare earth elements in the solid product of the third stage transformation to the molar ratio of calcium transforming agent can be 1:(1.5-1.7); preferably 1:(1.5-1.6); wherein the rare earth elements are calculated as REO. When the calcium transforming agent is selected from one or more of calcium oxide and calcium hydroxide, the molar ratio of rare earth elements in the solid product of the third stage transformation is calculated as the molar ratio of untransformed rare earth elements in the solid product of the third stage transformation.

[0064] In the four transformation reactions, the ratio of the total mass of the solid products of the third transformation and the calcium transformation agent to the volume of the slurry of the fourth transformation can be 1 kg:(2-3) L.

[0065] Optionally, the quaternary transformation liquid product is used as the tertiary slurry in the tertiary transformation reaction of other batches of rare earth sulfate roasted ore.

[0066] The four-stage transformation solid product, the calcium transformation agent, and the five-stage slurry were subjected to a five-stage transformation reaction to obtain a five-stage transformation solid product and a five-stage transformation liquid product.

[0067] The reaction temperature can be 20–90℃; preferably 20–40℃. The reaction time can be 30–100 min; preferably 40–70 min.

[0068] In the five-stage transformation reaction, the ratio of the amount of rare earth elements in the solid product of the fourth stage transformation to the amount of calcium transforming agent can be 1:(1.5-1.7); preferably 1:(1.5-1.6); wherein the rare earth elements are calculated as REO. When the calcium transforming agent is selected from one or more of calcium oxide and calcium hydroxide, the amount of rare earth elements in the solid product of the fourth stage transformation is calculated as the amount of untransformed rare earth elements in the solid product of the fourth stage transformation.

[0069] In the five transformation reactions, the ratio of the total mass of the solid products of the fourth transformation and the calcium transformation agent to the volume of the slurry of the fifth transformation can be 1 kg:(2-3) L.

[0070] Optionally, the quintuple transformation liquid product can be used as the quintuple slurry in the quintuple transformation reaction of other batches of rare earth sulfate roasted ore.

[0071] The conversion method of this invention can separate sulfate ions from rare earth chloride solution in the form of solid calcium sulfate from roasted rare earth sulfate ore, reducing the production of sulfate wastewater and essentially eliminating the generation of industrial wastewater. The liquid product produced by this invention can be reused as a slurry preparation, reducing wastewater treatment costs and improving the conversion efficiency of rare earth elements. The conversion method of this invention has a high rare earth conversion rate and a low sulfate content in the converted solid. Detailed Implementation

[0072] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0073] The raw materials are described below:

[0074] The rare earth sulfate roasted ore is a rare earth sulfate roasted ore formed by roasting the Bayan Obo mixed rare earth concentrate at high temperature with concentrated sulfuric acid.

[0075] Example 1

[0076] (1) Rare earth sulfate roasted ore (REO content 33.58 wt%), calcium oxide, and water (first-stage slurry) were subjected to a one-stage transformation reaction at 90℃ and under grinding conditions for 30 min to obtain a one-stage transformation solid product and a one-stage transformation liquid product. The molar ratio of rare earth elements in the rare earth sulfate roasted ore to the molar ratio of calcium oxide was 1:1.3; wherein, the rare earth elements were calculated as REO. The total mass ratio of rare earth sulfate roasted ore and calcium oxide to the volume ratio of water was 1 kg:1 L.

[0077] (2) The primary transformation solid product, calcium oxide, and water (secondary slurry) were subjected to a secondary transformation reaction at 60°C and under grinding conditions for 30 min to obtain a secondary transformation solid product and a secondary transformation liquid product. The molar ratio of untransformed rare earth elements to calcium oxide in the primary transformation solid product was 1:1.5; wherein, the rare earth elements were calculated as REO. The total mass ratio of the primary transformation solid product and calcium oxide to the volume ratio of water was 1 kg:1 L.

[0078] (3) The secondary transformation solid product was dissolved in 8 mol / L hydrochloric acid at 20 °C for 90 min to obtain rare earth chloride solution and solid residue (containing calcium sulfate). The ratio of the amount of rare earth element in the secondary transformation solid product to the amount of HCl contained in the hydrochloric acid was 1:3; wherein, the rare earth element was calculated as REO.

[0079] The primary transformation liquid product obtained in step (1) and the secondary transformation liquid product obtained in step (2) can be used as a slurry in step (1) and / or step (2).

[0080] The conversion rate of rare earth elements is 96%.

[0081] The conversion rate of rare earth elements is calculated using the following formula:

[0082] The conversion rate of rare earth elements = (amount of rare earth elements in the rare earth chloride solution / amount of rare earth elements in the rare earth sulfate roasted ore) × 100%

[0083] Example 2

[0084] (1) Rare earth sulfate roasted ore (REO content 33.58 wt%), calcium chloride, and water (first-stage slurry) were subjected to a one-stage transformation reaction at 20℃ with stirring for 240 min to obtain a one-stage transformation solid product and a one-stage transformation liquid product (REO concentration 80 g / L). The molar ratio of rare earth elements in the rare earth sulfate roasted ore to the molar ratio of calcium chloride was 1:1.5; wherein, the rare earth elements were calculated as REO. The total mass ratio of rare earth sulfate roasted ore and calcium chloride to the volume ratio of water was 1 kg:3 L.

[0085] (2) The primary transformation solid product, calcium chloride, and water (secondary slurry) were subjected to a secondary transformation reaction at 20°C with stirring for 60 min to obtain a secondary transformation solid product and a secondary transformation liquid product. The molar ratio of rare earth elements in the primary transformation solid product to that in calcium chloride was 1:1.6; wherein, the rare earth elements were calculated as REO. The total mass ratio of the primary transformation solid product and calcium chloride to the volume of water was 1 kg:3 L.

[0086] The secondary transformation liquid product is used as a slurry for the primary transformation reaction of other batches of rare earth sulfate roasted ore.

[0087] The secondary transformation solid product, calcium chloride, and water (tertiary conditioning solution) were subjected to a tertiary transformation reaction at 20°C with stirring for 60 min to obtain a tertiary transformation solid product and a tertiary transformation liquid product. The molar ratio of rare earth elements in the secondary transformation solid product to that in calcium chloride was 1:1.6; the rare earth elements were represented as REO. The total mass ratio of the secondary transformation solid product and calcium chloride to the volume ratio of water was 1 kg:3 L.

[0088] The tertiary transformation liquid product is used as a slurry for the secondary transformation reaction of other batches of rare earth sulfate roasted ore.

[0089] The tertiary transformation solid product, calcium chloride, and water (quaternary slurry) were reacted in a quaternary transformation reaction at 20°C with stirring for 60 min to obtain a quaternary transformation solid product and a quaternary transformation liquid product. The molar ratio of rare earth elements in the tertiary transformation solid product to the molar ratio of calcium chloride was 1:1.6; the rare earth elements were represented as REO. The total mass ratio of the tertiary transformation solid product and calcium chloride to the volume ratio of water was 1 kg:3 L.

[0090] The liquid product from the fourth transformation was used as a slurry for the third transformation reaction of other batches of rare earth sulfate roasted ore.

[0091] The quaternary solid product, calcium chloride, and water (fifth-stage slurry) were reacted in a five-stage reaction at 20°C with stirring for 60 min to obtain a five-stage solid product and a five-stage liquid product. The molar ratio of rare earth elements to calcium chloride in the quaternary solid product was 1:1.6; the rare earth elements were represented as REO. The total mass ratio of the quaternary solid product and calcium chloride to the volume ratio of water was 1 kg:3 L.

[0092] The liquid product from the fifth transformation was used as a slurry for the fourth transformation reaction of other batches of rare earth sulfate roasted ore.

[0093] The conversion rate of rare earth elements is 97%.

[0094] The conversion rate of rare earth elements is calculated using the following formula:

[0095] The conversion rate of rare earth elements = 1 - (the amount of rare earth elements contained in the solid products of the fifth conversion / the amount of rare earth elements contained in the rare earth sulfate roasted ore) × 100%

[0096] Example 3

[0097] (1) Rare earth sulfate roasted ore (REO content 33.58 wt%), calcium chloride, and water (first-stage slurry) were subjected to a one-stage transformation reaction at 50℃ and under grinding conditions for 30 min to obtain a one-stage transformation solid product and a one-stage transformation liquid product (REO concentration 125 g / L). The molar ratio of rare earth elements in the rare earth sulfate roasted ore to the molar ratio of calcium chloride was 1:1.4; wherein, the rare earth elements were calculated as REO. The total mass ratio of rare earth sulfate roasted ore and calcium chloride to the volume ratio of water was 1 kg:2 L.

[0098] (2) The primary transformation solid product, calcium chloride, and water (secondary slurry) were subjected to a secondary transformation reaction at 50°C and under grinding conditions for 30 min to obtain a secondary transformation solid product and a secondary transformation liquid product. The molar ratio of rare earth elements in the primary transformation solid product to that in calcium chloride was 1:1.6; wherein, the rare earth elements were calculated as REO. The total mass ratio of the primary transformation solid product and calcium chloride to the volume ratio of water was 1 kg:2 L.

[0099] The secondary transformation liquid product is used as a slurry for the primary transformation reaction of other batches of rare earth sulfate roasted ore.

[0100] The conversion rate of rare earth elements is 96.5%.

[0101] The conversion rate of rare earth elements is calculated using the following formula:

[0102] The conversion rate of rare earth elements = 1 - (the amount of rare earth elements contained in the solid product of secondary conversion / the amount of rare earth elements contained in the rare earth sulfate roasted ore) × 100%

[0103] This invention is not limited to the above-described embodiments. Any modifications, improvements, or substitutions that can be conceived by those skilled in the art without departing from the essential content of this invention fall within the scope of this invention.

Claims

1. A method for transforming rare earth sulfate roasted ore, characterized in that, Includes the following steps: (1) The rare earth sulfate roasted ore, calcium conversion agent and primary slurry are subjected to a primary conversion reaction to obtain a primary conversion solid product and a primary conversion liquid product. (2) The Nth transformation solid product, calcium transformation agent and N+1th transformation slurry are subjected to N+1 transformation reaction to obtain N+1th transformation solid product and N+1th transformation liquid product; repeat this step to obtain Mth transformation solid product and Mth transformation liquid product; where M is selected from integers from 2 to 6, and N is an integer from 1 to M-1. The calcium conversion agent is selected from one or more of calcium oxide, calcium chloride, and calcium hydroxide. In step (1), the ratio of the amount of rare earth elements in the rare earth sulfate roasted ore to the amount of calcium conversion agent is 1:(1.2-1.5); the rare earth elements are calculated as REO; the ratio of the total mass of the rare earth sulfate roasted ore and the calcium conversion agent to the volume of the primary slurry is 1kg:(1-5)L.

2. The transformation method according to claim 1, characterized in that, In step (1), the reaction is carried out under stirring or grinding conditions, the reaction temperature is 20-90℃, and the reaction time is 30-240min.

3. The transformation method according to claim 1, characterized in that, The calcium conversion agent is selected from one or more of calcium oxide and calcium hydroxide; The primary slurry preparation solution is selected from one or more of water, primary transformation liquid products, and N+1 primary transformation liquid products.

4. The transformation method according to claim 3, characterized in that, It also includes the following steps: The solid product from the M-transformation was dissolved in hydrochloric acid to obtain a rare earth chloride solution and a solid slag.

5. The transformation method according to claim 4, characterized in that, The solid product of the M-transformation was dissolved in hydrochloric acid with a concentration of 6–12 mol / L at 20–80 °C for 30–120 min.

6. The transformation method according to claim 3, characterized in that, In step (2), in each transformation reaction, the ratio of the amount of untransformed rare earth element to the amount of calcium transforming agent in the Nth transformation solid product is 1:(1.2~1.9). Rare earth elements are expressed as REO.

7. The transformation method according to claim 1, characterized in that, The calcium conversion agent is calcium chloride; The primary slurry is selected from the secondary transformation liquid product obtained by the secondary transformation reaction of water or other batches of rare earth sulfate roasted ore. The Nth slurry is selected from the N+1th transformation liquid product obtained by the N+1th transformation reaction of water or other batches of rare earth sulfate roasted ore.

8. The transformation method according to claim 7, characterized in that, In the primary transformation liquid product, the concentration of REO is ≥70 g / L; In step (2), in each transformation reaction, the ratio of the amount of rare earth elements to the amount of calcium transforming agent in the Nth transformation solid product is 1:(1.2~1.9); wherein, the rare earth elements are calculated as REO.

9. The transformation method according to claim 1, characterized in that, In step (2), the reaction is carried out under stirring or grinding conditions, the reaction temperature is 20-90℃, and the reaction time for each transformation is 30-240 min.

10. The transformation method according to any one of claims 1 to 9, characterized in that, In step (2), the ratio of the total mass of the Nth transformation solid product and the calcium transformation agent to the volume of the N+1th slurry in each transformation reaction is 1 kg: (1-5) L.