Method for producing rare earth transition metal alloy powder

Abstract

A method for producing rare earth transition metal alloy powder is provided that allows for efficient acid cleaning while minimizing the environmental impact problems that arise in industrial production. [Solution] A method for producing rare earth transition metal alloy powder, comprising the following steps: a reduction-diffusion step of heating a raw material mixture containing at least a rare earth metal, a transition metal, and oxygen, and a reducing agent, in a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and by-products derived from the reducing agent; and a wet treatment step of washing the reaction product to obtain rare earth transition metal alloy powder, wherein the wet treatment step comprises a sub-step of adding and disintegrating the reaction product in water to produce an alloy powder slurry; a sub-step of washing the alloy powder slurry with water; and a sub-step of adding a buffer and hydrochloric acid to the alloy powder slurry that has undergone the water washing treatment to acid wash the alloy powder slurry, wherein the buffer is a carboxylic acid, and the buffer ratio [N1 / (N1+N2)], which is the ratio of the amount of carboxyl groups contained in the carboxylic acid to the sum of the amount of carboxyl groups contained in the carboxylic acid (N1) and the amount of hydrochloric acid (N2), is 5 mol% or more and 90 mol% or less.

Claims

1. A method for producing rare earth transition metal alloy powder, comprising the following steps: A reduction-diffusion step involves heating a mixture of alloying raw materials containing rare earth metals, transition metals, and oxygen, as well as a reducing agent, under a non-oxidizing atmosphere to obtain a reaction product containing a rare earth transition metal alloy and by-products derived from the reducing agent. The process includes a wet treatment step of washing the reaction product to obtain rare earth transition metal alloy powder, The wet processing step includes a sub-step of preparing an alloy powder slurry by adding and disintegrating the reaction product in water, a sub-step of subjecting the alloy powder slurry to a water washing treatment, and a sub-step of subjecting the alloy powder slurry to an acid washing treatment by adding a buffer and hydrochloric acid to the water-washed alloy powder slurry. The buffer solution is a carboxylic acid, The buffer solution ratio [N1 / (N1+N2)], which is the ratio of the amount of carboxyl groups contained in the carboxylic acid (N1) to the sum of the amount of carboxyl groups contained in the carboxylic acid (N1) and the amount of hydrochloric acid (N2), is 5 mol% or more and 90 mol% or less. A method of acid washing in which a buffer solution is first added to the alloy powder slurry, and then hydrochloric acid is added.

2. The method according to claim 1, wherein the buffer solution ratio [N1 / (N1+N2)] is 5 mol% or more and 50 mol% or less.

3. The method according to claim 1 or 2, wherein the carboxylic acid is at least one selected from the group consisting of formic acid, acetic acid, citric acid, gluconic acid, oxalic acid, and glycolic acid.

4. The reduction-diffusion step, the nitriding step, and the wet treatment step are included in this order. In the nitriding step, while heating the reaction product obtained in the reduction-diffusion step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare earth transition metal alloy component in the reaction product. The method according to claim 1 or 2, wherein the wet treatment step involves washing the reaction product nitrided in the nitriding step.

5. The reduction-diffusion step, the hydrogen treatment step, the nitriding step, and the wet treatment step are included in this order. In the hydrogen treatment step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it. In the nitriding step, while heating the reaction product that was crushed in the hydrogen treatment step, a stream of nitrogen-containing gas is passed through the reaction product, thereby nitriding the rare earth transition metal alloy component in the reaction product. The method according to claim 1 or 2, wherein the wet treatment step involves washing the reaction product nitrided in the nitriding step.

6. The reduction-diffusion step, the hydrogen treatment step, the wet treatment step, and the nitriding step are included in this order. In the hydrogen treatment step, the reaction product obtained in the reduction-diffusion step is exposed to a hydrogen atmosphere, thereby absorbing hydrogen and disintegrating it. In the wet treatment step, the reaction product crushed in the hydrogen treatment step is subjected to a washing treatment to obtain a rare earth transition metal alloy powder. The method according to claim 1 or 2, wherein in the nitriding step, a stream of nitrogen-containing air is passed over the rare earth transition metal alloy powder obtained by the cleaning step in the wet treatment step while heating the powder, thereby obtaining nitrided rare earth transition metal alloy powder.

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