CN105779792B - A kind of method for preparing low impurity content rare earth hydrate - Google Patents

Abstract

The invention discloses a method for preparing rare earth hydroxide with low impurity content, which mainly includes two aspects. On the one hand, the precipitation reaction is carried out by adding sodium hydroxide solution to the rare earth sulfuric acid solution, and then the above solution is subjected to solid-liquid separation to obtain a precipitated product and a mother liquor, and the precipitated product is washed with water and dried to finally obtain a sulfate with a content of less than 0.5wt. % rare earth hydroxides. On the other hand, adding sulfate-containing rare earth hydroxide precipitates into sodium hydroxide solution for stirring and removing impurities; then aging, solid-liquid separation to obtain the precipitated product and mother liquor, washing the precipitated product with water, drying, and finally obtaining sulfuric acid Rare earth hydroxides with a root content of less than 0.5 wt.%. The above method adopts the method of reaction aging under strong alkaline conditions or washing under strong alkaline conditions, introducing hydroxide and sulfate radicals for competitive coordination to prevent them from entering the precipitated product, and aging under strong alkaline conditions , which is conducive to improving the surface properties of the precipitate and obtaining a product with a better crystal form of the precipitate.

Description

A method for preparing rare earth hydroxide with low impurity content

technical field

The invention relates to the field of rare earth hydrometallurgy, in particular to a method for preparing rare earth hydroxide with low impurity content.

Background technique

Rare earth (Rare Earth, referred to as RE) is the 15 lanthanide elements with atomic numbers from 57 to 71 in the third subgroup of the periodic table of chemical elements, namely lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd ), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb ), lutetium (Lu), plus scandium (Sc) and yttrium (Y), which are similar in electronic structure and chemical properties, a total of 17 elements. Due to their unique 4f sublayer electronic structure, large atomic magnetic moment, strong spin-orbit coupling, and variable coordination numbers, the compounds formed by rare earth elements have very rich magnetic, optical, electrical, and catalytic properties. Functional properties, known as "the vitamin of modern industry" and "treasure house of new materials".

Among them, rare earth hydroxides are important precursors of rare earth oxides, and hydroxides themselves have important uses, such as cerium-rich rare earth hydroxides are mainly used as glass decolorizers and clarifiers, and can also be used to smelt cerium-rich rare earth ferrosilicon alloys Raw materials; and lanthanum hydroxide can also be directly used in glass, ceramics and electronics industries. As the precursor of rare earth oxides, rare earth hydroxides have a high rare earth content of about 70%, which can greatly improve production efficiency, and the rare earth hydroxides require low temperature and low energy consumption to obtain rare earth oxides. At present, there are various methods for smelting and separating rare earth elements, involving many acidic rare earth solution systems. Among them, sulfuric acid has the characteristics of high stability, low volatility, and weak corrosion to equipment, and is widely used in smelting and separation processes, such as sulfuric acid roasting of Baotou mine method (ZL86105043), rare earth ammonium sulfate eluent of ion-adsorbed rare earth mines in South China (97114216. 5), rare earth sulfur and phosphorus mixed acid solution produced in the process of sulfuric acid treatment of phosphate rock (ZL200910078794. 2), etc. Therefore, the process of enriching and recovering rare earths in sulfuric acid rare earth solution or mixed acid solution system is more common. Precipitation method Due to the simple reaction process, low cost and easy industrial production, the precipitation method is widely used in industry to enrich and recover rare earths in rare earth sulfate solution. That is to add a precipitant to the rare earth sulfate solution to convert the rare earth into precipitates, so as to achieve the purpose of enrichment and recovery, and then separate and dry to finally prepare the rare earth hydroxide. Currently, methods commonly used for precipitation and crystallization of rare earth sulfate solutions include oxalic acid precipitation, carbonate precipitation, and hydroxide precipitation. The precipitants used in the hydroxide precipitation method include sodium hydroxide, magnesium oxide (200710102777.9), calcium oxide (200810175913.1), etc. Among them, ammonia water is seldom used due to serious ammonia nitrogen pollution and high cost of wastewater treatment. Calcium oxide and magnesium oxide are solid alkaline compounds, which have a certain solubility in water, so it is easy to introduce calcium and magnesium precipitation during the precipitation process. At present, sodium hydroxide is the main precipitating agent for preparing rare earth hydroxide by industrial precipitation method. However, the rare earth hydroxide obtained by the sodium hydroxide precipitation method has a relatively high sulfate radical impurity content, and the reasons for this problem include two points. First of all, the rare earth hydroxide obtained by the sodium hydroxide precipitation method is easy to colloid, and the filtration performance is poor, which affects the production efficiency and is easy to absorb impurity ions. Secondly, the sulfate radicals in the rare earth precipitation mother liquor may exist in rare earth hydroxide in two states: adsorption/encapsulation state and participation in coordination precipitation. The precipitated sulfate group cannot be removed by water washing, and after roasting, it still affects the purity of rare earth oxides, thereby affecting product quality. For example, the leaching solution of ion-adsorption type rare earth ore in the south is enriched by precipitation and enrichment with alkaline substances to obtain the sulfate radical contained in the rare earth concentrate, which will increase the load of the extraction and separation process and produce a calcium sulfate three-phase product. Therefore, it is necessary to add chlorine in the smelting and separation process. barium to remove it. The impurity content of rare earth hydroxide is one of the important reasons restricting the development of rare earth enrichment solution by hydroxide precipitation.

Therefore, how to use the sodium hydroxide precipitation method to prepare rare earth hydroxides with good crystal form and low impurity content is a problem that is widely concerned and needs to be solved urgently.

Contents of the invention

The invention aims at the problem that the sulfate radical in the rare earth hydroxide precipitation obtained by the sodium hydroxide precipitation method of the current rare earth solution is too high, and provides a method for preparing the rare earth hydroxide with a simple process and convenient operation.

In order to achieve the above object, a method for preparing rare earth hydroxide with low impurity content is provided, comprising the following steps:

S1. Add sodium hydroxide solution to the sulfuric acid rare earth solution to carry out precipitation reaction, control the pH of the precipitation end point to 13-14, and then age at 40-80°C for 1-6 hours;

S2, the product obtained in step S1 is subjected to solid-liquid separation to obtain a precipitated product and a mother liquor, and the precipitated product is washed with water, and the washing is stopped when the sulfate radical in the water-washed filtrate is less than 10 ppm;

S3. Drying the washed precipitated product to obtain a rare earth hydroxide with a sulfate content of less than 0.5 wt.%.

Further, the concentration of the rare earth sulfate solution in the step S1 is 0.3-20 g/L.

Further, the concentration of the sodium hydroxide solution in the step S1 is 5-80 g/L.

According to another aspect of the present invention, another method for preparing rare earth hydroxide with low impurity content is provided, comprising the following steps:

(1) Add sulfate-containing rare earth hydroxide precipitates into sodium hydroxide solution for stirring and removing impurities. The reaction temperature for stirring and removing impurities is 30-60°C, and the time for stirring and removing impurities is 0.5-2h. The concentration of sodium hydroxide solution 2-10g/L;

(2) Then age at 30-60°C for 1-2 hours, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, and stop washing when the sulfate radical in the water-washed filtrate is less than 10 ppm;

(3) Drying the washed precipitated product to obtain a rare earth hydroxide with a sulfate content of less than 0.5 wt.%.

Further, the sulfate content in the rare earth hydroxide precipitate containing sulfate in the step (1) is 1wt.%~15wt.%.

Further, in the step (1), the liquid-solid ratio of the sodium hydroxide solution to the sulfate-containing rare earth hydroxide precipitate is 1:1-3:1L/Kg.

Further, the sulfate-containing rare earth hydroxide precipitation is obtained by directly adding an alkaline precipitant to the rare earth sulfate solution for precipitation, followed by solid-liquid separation.

In one aspect of the present invention, the precipitation reaction is carried out by adding sodium hydroxide solution to the rare earth sulfate solution, controlling the pH of the precipitation end point to be 13-14, aging at 40-80°C for 1-6 hours, and then subjecting the above solution to solid-liquid After separation, the precipitated product and mother liquor are obtained, and the precipitated product is washed with water, and the washing is stopped when the sulfate radical in the water washing filtrate is less than 10 ppm; the washed precipitated product is dried, and finally a rare earth hydroxide with a sulfate radical content of less than 0.5wt.% is obtained . In another aspect of the present invention, the sulfate radical-containing rare earth hydroxide precipitate is added into the sodium hydroxide solution for stirring and removing impurities, the reaction temperature for stirring and removing impurities is 30-60°C, and the time for stirring and removing impurities is 0.5-2h; The concentration of the sodium solution is 2-10g/L; then aging at 30-60°C for 1-2 hours, the precipitated product and mother liquor are obtained after solid-liquid separation, and the precipitated product is washed with water. When the sulfate radical in the water-washed filtrate is less than 10ppm Stop washing; dry the precipitated product after washing, and finally obtain a rare earth hydroxide with a sulfate content of less than 0.5 wt.%. The above method adopts the method of reaction aging under strong alkaline conditions or washing under strong alkaline conditions, introducing hydroxide and sulfate radicals for competitive coordination to prevent them from entering the precipitated product, and aging under strong alkaline conditions , which is conducive to improving the surface properties of the precipitation and obtaining products with better precipitation crystal forms, thereby reducing its adsorption of impurities. The process is simple and easy to control, and the effect of removing impurities is obvious. At the same time, the strong alkaline mother liquor can be recycled.

detailed description

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below in conjunction with embodiments.

The application provides two schemes for preparing rare earth hydroxides with low impurity content. Scheme one includes the following steps: S1. Add sodium hydroxide solution to the rare earth sulfate solution for precipitation reaction, control the pH of the precipitation end point to be 13-14, and then set the pH at 40 Aging at -80°C for 1-6 hours; S2, separating the product obtained in step S1 into a solid-liquid separation to obtain a precipitated product and a mother liquor, washing the precipitated product, and stopping washing when the sulfate radical in the water-washed filtrate is less than 10 ppm; S3, The washed precipitated product is dried to obtain a rare earth hydroxide with a sulfate radical content of less than 0.5 wt.%.

In the above step S1, the concentration of the rare earth sulfate solution is preferably 0.3-20g/L, and the concentration of the sodium hydroxide solution is 5-80g/L; considering the solubility of the rare earth sulfate and the possibility of precipitation of the rare earth sulfate double salt, A rare earth concentration of 0.3-20 g/L was chosen. The pH of the precipitation end point is selected to be 13-14. The purpose is to control the reaction system as a strong alkaline solution to ensure the existence of a large number of hydroxide ions. The introduced hydroxide will compete with the sulfate for coordination to avoid the coordination and adsorption of the sulfate on the hydrogen rare earth oxides. In addition, under strong alkali conditions, the surface properties of the rare earth hydroxide can be changed, and precipitation with good crystallization effect can be easily obtained, thereby reducing the physical adsorption of the rare earth hydroxide to sulfate. Aging at 40-80°C is conducive to the full occurrence of coordination competition reaction and crystallization process, and the rare earth hydroxide with good filtration performance can be obtained.

Scheme 2 includes the following steps: (1) adding sulfate-containing rare earth hydroxide precipitates into sodium hydroxide solution for stirring and removing impurities, the reaction temperature for stirring and removing impurities is 30-60°C, and the time for stirring and removing impurities is 0.5-2h. The concentration of sodium hydroxide solution is 2-10g/L; (2) Then aging at 30-60°C for 1-2 hours, after solid-liquid separation, the precipitated product and mother liquor are obtained, and the precipitated product is washed with water, and when the water-washed filtrate Stop washing when the sulfate radical is less than 10ppm; (3) Dry the precipitated product after washing to obtain a rare earth hydroxide with a sulfate radical content of less than 0.5wt.%.

In the above step (1), the concentration of the sodium hydroxide solution is 2-10g/L. The purpose of controlling this range is to ensure that there is a certain amount of hydroxide ions and rare earth hydroxides in the system that are brought into the sulfuric acid during the stirring process. The competitive coordination of the radical ions allows the removal of the coordinated adsorbed sulfate ions. In addition, impurity removal and aging are carried out at 25-50°C, which is beneficial to obtain better impurity removal effect and crystallization effect.

Both of the above two schemes have obtained the rare earth hydroxide with a sulfate content less than 0.5wt.%, which greatly reduces the content of impurity sulfate in the rare earth hydroxide. Both schemes use the method of reaction aging under strong alkaline conditions or washing under strong alkaline conditions to introduce hydroxide ions and sulfate radicals for competitive coordination. The coordination ability between the root and the rare earth is strong, so the hydroxide can replace the sulfate and coordinate with the rare earth; at the same time, under the condition of strong alkali, it is beneficial to improve the surface properties of the precipitate and obtain a product with a better crystal form of the precipitate, thereby reducing its impact on impurities. The adsorption process is simple and easy to control, and the effect of removing impurities is obvious. At the same time, the strong alkaline mother liquor can be recycled.

In addition, this method can also be used in the rare earth chloride system, and the rare earth hydroxide with low chlorine content is prepared by the hydroxide precipitation method. Similar to the above principle, the coordination constant of hydroxide and rare earth is larger than that of chloride ion , the formed complex is more stable, so it can remove the chlorine radical in the rare earth hydroxide, especially the chlorine radical adsorbed by coordination.

The method for preparing rare earth hydroxide with low impurity content provided by the present invention will be further described below in conjunction with specific examples.

Comparative Example 1

Take 5L of the ion-adsorption type rare earth ore ammonium sulfate leaching solution after impurity removal treatment, the rare earth concentration is 0.3g/L (REO), and the sulfate concentration is 15g/L. Use 5g/L sodium hydroxide solution as the precipitant, control the pH of the precipitation end point to 9.5, and then age at 40°C for 6 hours to separate the solid and liquid to obtain the precipitated product and mother liquor. Stop washing when the sulfate radical is 9ppm; the precipitated product after washing is dried to obtain rare earth hydroxide with a sulfate radical content of 11.54wt.%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 80 minutes.

Comparative Example 2

Magnesium sulfate leaching the ion-adsorption type rare earth ore obtained after the leaching solution is precipitated with sodium hydroxide to obtain a rare earth hydroxide containing 13.10% sulfate, and the sulfate-containing rare earth hydroxide precipitate is added to water for stirring to remove impurities, stirring to remove The reaction temperature of impurities is 30°C, the time of stirring and removing impurities is 2 hours; the ratio of liquid to solid is 3:1. Then age at 30°C for 2 hours, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, and stop washing when the sulfate radical in the water-washed filtrate is 9 ppm; dry the washed precipitated product to obtain sulfuric acid Rare earth hydroxide with a root content of 11.34 wt.%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 67 minutes.

Example 1

Take 5L of the ion-adsorption type rare earth ore ammonium sulfate leaching solution after impurity removal treatment, the rare earth concentration is 0.3g/L (REO), and the sulfate concentration is 15g/L. Use 5g/L sodium hydroxide solution as the precipitating agent, control the pH of the precipitation end point to 13.0, then age at 40°C for 6 hours, and then perform solid-liquid separation to obtain the precipitated product and mother liquor, wash the precipitated product with water, and wash it in the filtrate Stop washing when the sulfate radical is 9ppm; dry the precipitated product after washing to obtain a rare earth hydroxide with a sulfate radical content of 0.47wt.%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 15 minutes.

Example 2

Magnesium sulfate leaching the ion-adsorption type rare earth ore obtained after the leaching solution is precipitated with sodium hydroxide to obtain a rare earth hydroxide containing 13.10% sulfate, and the sulfate-containing rare earth hydroxide is precipitated by adding 2g/L sodium hydroxide solution The reaction temperature of stirring and removing impurities is 30° C., the time of stirring and removing impurities is 2 hours; the liquid-solid ratio is 3:1. Then age at 30°C for 2 hours, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, and stop washing when the sulfate radical in the water-washed filtrate is 9 ppm; dry the washed precipitated product to obtain sulfuric acid Rare earth hydroxide with a root content of 0.46wt.%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 14 minutes.

Example 3

Take 5L of ion-adsorption type rare earth ore leach solution after impurity removal treatment, its rare earth concentration is 1.0g/L (REO calculation), sulfate concentration is 20g/L. Use 10g/L sodium hydroxide solution as the precipitant, control the pH of the precipitation end point to 13.2, and then age at 50°C for 4 hours to separate the solid and liquid to obtain the precipitated product and mother liquor, wash the precipitated product with water, and wash it in the filtrate Stop washing when the sulfate radical is 10ppm; dry the precipitated product after washing to obtain a rare earth hydroxide with a sulfate radical content of 0.39wt.%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 20 minutes.

Example 4

Take 5L of lanthanum sulfate solution, whose rare earth concentration is 5.0g/L (REO), use 30g/L sodium hydroxide solution as the precipitant, control the pH of the precipitation end point to 14.0, and then age at 60°C for 3h before solidification. Obtain precipitation product and mother liquor after liquid separation, the precipitation product is washed, stop washing when the sulfate radical in the washing filtrate is 9ppm; The precipitation product after washing is carried out drying process, obtains the lanthanum hydroxide that sulfate radical content is 0.38wt.%. . The solid-liquid separation is carried out by means of suction filtration, and the required time is 14 minutes.

Example 5

Take 5L of yttrium sulfate solution, whose rare earth concentration is 10.0g/L (REO), use 50g/L sodium hydroxide solution as the precipitant, control the pH of the precipitation end point to 13.5, and then age at 70°C for 1h before solidification Obtain precipitation product and mother liquor after liquid separation, the precipitation product is washed, stop washing when the sulfate radical in the washing filtrate is 9ppm; The precipitation product after washing is carried out dry treatment, obtains the sulfate radical content and is the yttrium hydroxide of 0.44wt.%. . The solid-liquid separation is carried out by means of suction filtration, and the required time is 12 minutes.

Example 6

Take 5L of mixed solution of praseodymium and neodymium sulfate (the molar ratio of praseodymium and neodymium is 1:1), the rare earth concentration is 15.0g/L (REO), and 65g/L sodium hydroxide solution is used as the precipitant, and the pH of the precipitation end point is controlled to be 13.8 , and then aged at 80°C for 2h, then solid-liquid separation was carried out to obtain the precipitated product and mother liquor, the precipitated product was washed with water, and the washing was stopped when the sulfate radical in the water-washed filtrate was 9 ppm; the washed precipitated product was dried to obtain Neodymium praseodymium hydroxide with a sulfate content of 0.43 wt.%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 15 minutes.

Example 7

Take 5L of yttrium sulfate solution, whose rare earth concentration is 20.0g/L (REO), use 80g/L sodium hydroxide solution as the precipitant, control the pH of the precipitation end point to 14.0, and then age at 65°C for 4h before solidification. Obtain precipitated product and mother liquor after liquid separation, the precipitated product is washed with water, stop washing when the sulfate radical in the washing filtrate is 9ppm; The precipitated product after washing is carried out drying process, obtains the sulfate radical content and is the yttrium hydroxide of 0.35wt.%. . The solid-liquid separation is carried out by means of suction filtration, and the required time is 12 minutes.

Example 8

After the lanthanum sulfate solution sodium hydroxide precipitates, the lanthanum hydroxide containing sulfate is 15.0%, and the sulfate-containing lanthanum hydroxide precipitate is added to the sodium hydroxide solution of 10g/L to stir and remove impurities, and the reaction of stirring and removing impurities The temperature is 60°C, the time for stirring and removing impurities is 0.5h; the liquid-solid ratio is 1:1. Then age at 60°C for 2 hours, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, stop washing when the sulfate radical in the water-washed filtrate is 9 ppm; dry the washed precipitated product to obtain sulfuric acid Lanthanum hydroxide with a root content of 0.49%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 12 minutes.

Example 9

After terbium sulfate solution sodium hydroxide precipitates, obtain terbium hydroxide containing sulfate radicals of 1.0%, add this sulfate radical-containing terbium hydroxide precipitate into 4g/L sodium hydroxide solution for stirring and impurity removal, the reaction of stirring and removing impurities The temperature is 35°C, the time for stirring and removing impurities is 1h; the liquid-solid ratio is 2:1. Then age at 45°C for 1 hour, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, and stop washing when the sulfate radical in the water-washed filtrate is 9 ppm; dry the washed precipitated product to obtain sulfuric acid Terbium hydroxide with a root content of 0.31%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 15 minutes.

Example 10

Praseodymium neodymium sulfate (praseodymium neodymium molar ratio is 1:1) is precipitated with ammonia water to obtain praseodymium neodymium hydroxide containing 3.0% sulfate radical, and the sulfate radical containing praseodymium neodymium hydroxide precipitate is added to 6g/L sodium hydroxide solution The reaction temperature of stirring and removing impurities is 50° C., the time of stirring and removing impurities is 0.8 h; the liquid-solid ratio is 1.5:1. Then age at 50°C for 1.3 hours, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, stop washing when the sulfate radical in the water-washed filtrate is 9 ppm; dry the washed precipitated product to obtain sulfuric acid Neodymium Praseodymium Hydroxide with root content of 0.38%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 17 minutes.

Example 11

After precipitation of calcium hydroxide in yttrium sulfate solution, yttrium hydroxide containing 8.0% sulfate is obtained, and this sulfate-containing yttrium hydroxide precipitate is added to 8g/L sodium hydroxide solution for stirring and impurity removal, and the reaction of stirring and removing impurities The temperature is 40°C, the time for stirring and removing impurities is 1.3h; the liquid-solid ratio is 2.5:1. Then age at 45°C for 1.6 hours, obtain the precipitated product and mother liquor after solid-liquid separation, wash the precipitated product with water, and stop washing when the sulfate radical in the water-washed filtrate is 9 ppm; dry the washed precipitated product to obtain sulfuric acid Yttrium hydroxide with a root content of 0.44%. The solid-liquid separation is carried out by means of suction filtration, and the required time is 14 minutes.

Claims (7)

1. A kind of 1. method for preparing low impurity content rare earth hydrate, it is characterised in that comprise the following steps：

   S1, carry out precipitation reaction toward adding sodium hydroxide solution in rare earth sulfate solution, it is 13-14 control and precipitate terminal pH, so 1-6 hours are aged at 40-80 DEG C afterwards；

   S2, precipitated product and mother liquor are obtained after the product that step S1 is obtained is carried out into separation of solid and liquid, precipitated product are washed, Stop washing when washing sulfate radical in filtrate and being less than 10ppm；

   S3, processing is dried to the precipitated product after washing, obtains the rare earth hydrate that sulfate radical content is less than 0.5wt.%.
2. 2. according to the method for claim 1, it is characterised in that the concentration of sodium hydroxide solution is 5- in the step S1 80g/L。
3. 3. according to the method for claim 1, it is characterised in that the concentration of rare earth sulfate solution is 0.3- in the step S1 20g/L。
4. A kind of 4. method for preparing low impurity content rare earth hydrate, it is characterised in that comprise the following steps：

   （1）The rare earth hydrate precipitation of containing sulfate radicals is added in sodium hydroxide solution and is stirred removal of impurities, stirs the anti-of removal of impurities It is 30-60 DEG C to answer temperature, and stirring is 0.5-2h except miscellaneous time, and the concentration of sodium hydroxide solution is 2-10g/L；

   （2）Then 1-2 hours are aged at 30-60 DEG C, precipitated product and mother liquor are obtained after separation of solid and liquid, precipitated product is carried out Washing, stop washing when washing sulfate radical in filtrate and being less than 10ppm；

   （3）Processing is dried to the precipitated product after washing, obtains the rare earth hydrate that sulfate radical content is less than 0.5wt.%.
5. 5. according to the method for claim 4, it is characterised in that the step（1）The rare earth hydrate of middle containing sulfate radicals sinks Sulfate radical content is 1wt.%-15wt.% in shallow lake.
6. 6. according to the method for claim 4, it is characterised in that the step（1）Middle sodium hydroxide solution and containing sulfate radicals Rare earth hydrate precipitation liquid-solid ratio be 1:1—3:1L/Kg.
7. 7. according to the method for claim 4, it is characterised in that the rare earth hydrate precipitation of the containing sulfate radicals is by past Alkaline precipitating agent precipitation is directly added into rare earth sulfate solution, is then obtained after separation of solid and liquid.