JPS5842133B2 - Rare earth hydroxide manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for producing rare earth hydroxides.

Specifically, the present invention relates to an industrially advantageous method for producing rare earth hydroxides from ores containing rare earth phosphates.

Ores containing rare earth phosphates, such as monazite, are treated with a concentrated aqueous solution of caustic soda to decompose the rare earth phosphates into rare earth hydroxides and sodium phosphate, and water is added to suppress the precipitation of sodium phosphate. The solid rare earth hydroxide is separated and obtained, and the residual liquid containing sodium phosphate and unreacted caustic soda after the separation is concentrated until the boiling point is 137 ° C, and 99φ of sodium phosphate is precipitated as crystals. and separate
It has been known that the resulting aqueous solution of caustic soda having a concentration of 47φ can be recycled to decompose the ore.

(September 1, 1960, published by the New Metals Association, pages 40-41 of "Rare Earths") In the alkaline decomposition method for ores containing rare earth phosphates, three times the mole of phosphorus in the ore is used. A sodium component is required, but when treating the residual liquid as described above, the sodium component combined with the phosphorus component is taken out of the system as sodium phosphate, so a large amount of expensive caustic soda is required.

Furthermore, in the treatment of the residual liquid described above, the caustic soda aqueous solution is concentrated with the precipitation of sodium phosphate crystals, so there is a risk of bumping and the like.Furthermore, the concentrate solidifies when cooled, so Separation of the crystals from the caustic aqueous solution must be carried out at a high temperature similar to the concentration temperature, and the operation is not easy.

In addition, the sodium phosphate crystals separated by the above separation have an aqueous caustic soda solution attached to them, but if you try to recover them by washing, the sodium phosphate will also dissolve, making it impossible to recover a highly pure caustic soda bath solution. I was not completely satisfied that I could not do it.

The present inventors have conducted extensive research into an industrially advantageous method for carrying out alkaline decomposition of ores containing rare earth phosphates. When a calcium or magnesium hydroxide is applied to an aqueous solution containing an alkali phosphate after separation, the alkali phosphate can be easily converted into a calcium or magnesium phosphate and a caustic alkali, and the resulting solid calcium Or, the magnesium phosphate can be separated from the aqueous caustic solution at room temperature, and the aqueous caustic solution after the separation can be adjusted in concentration by concentration, addition of caustic alkali, or a combination thereof to decompose the ore. The present invention was completed based on the knowledge that the utilization rate of caustic alkali can be dramatically improved since it can be reused.

That is, the present invention aims to increase the utilization rate of caustic alkali and produce rare earth hydroxides industrially advantageously. In the method for producing rare earth hydroxides, the rare earth phosphate is decomposed into rare earth hydroxide and alkali phosphate, and the generated solid rare earth hydroxide is separated from an aqueous solution containing alkali phosphate. A calcium or magnesium hydroxide is applied to the aqueous solution containing the alkali phosphate to convert the alkali phosphate in the aqueous solution into a calcium or magnesium phosphate and a caustic alkali, and the resulting solid calcium or magnesium hydroxide is This is achieved by separating the phosphate from the aqueous caustic alkaline solution and recycling the resulting aqueous caustic alkali solution for decomposition of the ore.

The present invention will be explained in detail below.

The rare earths in the present invention refer to elements having an atomic number of 57 to 71, and a group of elements including yttrium, thorium, and scandium, and examples of ores containing rare earth phosphates include monazite and xenotime.

The alkali decomposition of the ore is carried out using a caustic alkali aqueous solution with a concentration of 30 to 50% by weight, using a known method such as the method described in "Rare Earths" above.
Treatment is carried out at a temperature of around °C for several hours to decompose rare earth phosphates into rare earth hydroxides and alkali phosphates, then hot water is added to suppress the precipitation of alkali phosphates, and the solid rare earth hydroxides are filtered. Separate and obtain by means of.

Examples of the caustic alkali used here include caustic soda and caustic potash, but it is preferable to use caustic soda from an industrial standpoint.

The amount of caustic alkali used is 1 to 2 times the weight of the ore, usually about 1.3 to 1.7 times the weight of the ore.

The aqueous solution containing the alkali phosphate after the separation of the rare earth hydroxide is an aqueous solution containing the alkali phosphate produced by the above decomposition and the caustic alkali used in excess.

In the present invention, this aqueous solution is treated with calcium or magnesium hydroxide to convert the alkali phosphate into calcium or magnesium phosphate and caustic alkali.

To make calcium or magnesium hydroxide act, (1) Mix a powder or pellet of calcium or magnesium hydroxide, or a slurry of these in water or aqueous caustic phosphate with the aqueous alkali phosphate solution.

(2) Powder or small lumps of calcium or magnesium oxide are mixed with the aqueous alkali phosphate solution and allowed to act while being slaked.

(2) A slurry obtained by slaked an oxide of calcium or magnesium (J) with water or an aqueous caustic alkali solution is mixed with the aqueous alkali phosphate solution.

Methods such as (1) mixing calcium or magnesium oxide, or (2) mixing a slurry, particularly method (2) are preferred.

The amount of calcium or magnesium hydroxide used is
The amount is about 3 to 14 times the mole, preferably about 3 to 7 times the mole of the alkali phosphate in the aqueous solution containing the alkali phosphate.

If the amount is less than 3 times the mole, the alkali phosphate cannot be converted sufficiently.

On the other hand, if you use too much, you won't be able to expect any special effects from using too much, and unreacted calcium or magnesium hydroxide will increase, increasing the burden of the subsequent filtration, so it's not a good idea. do not have.

The temperature at which calcium or magnesium hydroxide is applied is 50 to 100°C, preferably 70 to 10°C.
It is about 0°C.

At too low a temperature, the reaction progresses slowly.

On the other hand, even if the temperature exceeds 100°C, no special effects can be expected.

In addition, in this conversion of alkali phosphate, the concentration of caustic alkali in the aqueous solution after the conversion reaction of alkali phosphate is
It is preferable to set the weight to 0 to 32 weight φ, preferably 20 to 30 weight φ, and adjust the amount of caustic alkali used during decomposition of the ore and/or the amount of hot water added after the decomposition as appropriate. Then, the alkali phosphate is dissolved in water after the conversion reaction is completed.

It is better to control the concentration of caustic alkali in the liquid.

If the caustic alkali concentration is too high, the alkali phosphate will remain, which is not preferable.

On the other hand, if the caustic alkali concentration is too low, it is disadvantageous because it increases the burden of concentration adjustment such as concentration in order to reuse the caustic aqueous solution for decomposing the ore.

When carrying out the conversion reaction of alkali phosphate in this manner, the produced calcium or magnesium phosphate precipitates as a solid and can be separated from the aqueous caustic alkali solution at room temperature.

The aqueous caustic alkali solution obtained by separating calcium or magnesium phosphates is too concentrated to be used directly for the alkaline decomposition of ores, so it is necessary to concentrate it, add fresh caustic alkali, or combine both. Depending on the method, the concentration is adjusted to about 50% by weight and recycled for alkaline decomposition of the ore.

When the method of the present invention is used, the utilization rate of caustic alkali can be significantly improved with easy operation, and therefore, the industrial value is extremely large.

EXAMPLES The present invention will be specifically explained below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

In the examples, "parts" and "a lot" refer to "parts by weight" and "parts by weight," respectively.

Example l 100 parts of crushed Malaysian monazite and a 50% caustic soda aqueous solution were placed in an autoclave and heated at 160°C.
Alkaline decomposition was carried out at a temperature of 2 hours.

234 parts of hot water was added to the reaction mixture, and the mixture was filtered at 90° C. to separate a solid containing rare earth hydroxide and washed with water.

The filtrate and wash liquor were 598 parts in total and contained 11.3% sodium phosphate and 17.1% caustic soda.

This aqueous solution containing sodium phosphate was charged into a stirring tank, and 36.395% of calcium oxide was added at a temperature of 90°C, and 36.39% of calcium oxide was added at the same temperature.
The sodium phosphate was changed into calcium phosphate and caustic soda by stirring for hours, and the solids were separated at room temperature and washed with water.

The resulting solid weighed 70.7 parts when dried and consisted of 85.2 parts of calcium phosphate and unreacted calcium hydroxide.

The total amount of solution and washing solution was 631 parts, and this solution (containing 22.6% caustic soda and 0.53% sodium phosphate, the conversion rate of the sodium phosphate to caustic soda was 94%).
．． It was 1%.

Concentrate this caustic soda aqueous solution to make a 50% caustic soda aqueous solution, add 14.8 parts of 50% caustic soda aqueous solution to this to prepare 300 parts of 50φ caustic soda aqueous solution,
Same as above using this E? A. When monazite was subjected to alkaline decomposition, the same results as above were obtained.

Example 2 Sodium phosphate-containing aqueous solution 59 obtained by performing alkaline decomposition and separating rare earth hydroxides in the same manner as in Example 1
8 parts of calcium oxide was placed in a stirring tank, and 36 parts of calcium oxide was added to this.
Add 3 parts to 723 parts of 30% caustic soda aqueous solution and heat at 80°C.
Add the calcium hydroxide slurry obtained by stirring for 1 hour to slake it, stir at a temperature of 80°C for 3 hours to change the sodium phosphate into calcium phosphate and caustic soda, bring it to room temperature, separate the solids, and wash with water. .

The resulting solid weighed 71.8 parts when dried and consisted of 80.4 pieces of calcium phosphate and unreacted calcium hydroxide.

The total amount of filtrate and washing liquid was 1446 parts, and this liquid contained 24.7% of caustic soda and 0.42% of sodium phosphate, and when calculated excluding the caustic soda used in preparing the above calcium hydroxide slurry, the above The conversion rate from sodium phosphate to caustic soda was 93.0φ.

Using a 50oIo caustic soda aqueous solution obtained by concentrating this caustic soda aqueous solution, monazite was subjected to alkaline decomposition in the same manner as described above, and the same results as above were obtained.

Further, the 30φ caustic soda aqueous solution prepared by adding the 50φ caustic soda aqueous solution to the 24.7φ caustic soda aqueous solution could be used in the preparation of the above calcium hydroxide slurry without any inconvenience.

Claims (1)

[Claims] 1 An ore containing rare earth phosphates is treated with an aqueous caustic alkali solution to decompose the rare earth phosphates into rare earth hydroxides and alkali phosphates, and the solid rare earth hydroxides produced are separated from the aqueous solution containing alkali phosphates. In the method for producing rare earth hydroxides obtained by separation, calcium or magnesium hydroxide is allowed to act on the aqueous solution containing the alkali phosphate after separation, and the alkali phosphate in the aqueous solution is converted into calcium or magnesium phosphate. Production of a rare earth hydroxide characterized by converting it into a caustic alkali, separating the generated solid calcium or magnesium phosphate from a caustic aqueous solution, and recycling the obtained caustic aqueous solution for decomposition of the ore. Law.