CS256541B1 - Process for obtaining the salt of rare earth elements - Google Patents

Abstract

The raw material to be processed is treated with a decomposing mixture of hydrochloric acid and alkali metal iodide, preferably in superstoichiometric amounts. The method can be used not only for lead powders and waste after its use, but also for catalysts based on peroxynitrite.

Description

The invention relates to a process for obtaining rare earth salts.

Cerium oxide, prepared by high temperature annealing, is very difficult to decompose with common acids and alkaline melting is generally recommended for decomposition. Also, mixtures of cerium oxide with other oxides are difficult to decompose if the content of cerium oxide in the mixture is greater than about 45%. Typical representatives of such mixtures are rare earth polishing powders. The cerium oxide content ranges from 45 to 100%, the other components being mainly oxides of lanthanum, neodymium and praseodymium.

Since polishing powders are mainly used in the form of aqueous suspensions, several methods have been proposed for obtaining rare earth elements from waste sludge produced by glass polishing.

It is known to recover rare earth elements from waste sludge after glass polishing by drying and annealing the waste sludge and decomposing the annealed sludge with sulfuric acid.

Another method involves annealing the waste sludge together with ammonium carbonate (15-30%) at 400-500 ° C for 2-4 hours. The melt decomposes reducing nitric acid at a temperature of 100-120 ° C.

In the other methods proposed, the heat treatment of the raw material (annealing, melting with carbonate) is not carried out and the decomposition is carried out only by the wet method - dissolution in nitric acid in a mixture of acid and hydrogen peroxide.

Drying and annealing the waste sludge is energy intensive, similar to the decomposition with nitric acid, which must be carried out at boiling. The decomposition of nitric acid / hydrogen peroxide mixtures can be applied with sufficient efficiency only to the aqueous suspension of the polishing powder used.

In the preparation of polishing powders, a proportion which does not satisfy its physical properties (e.g. granuloipetric composition) is omitted for use as a polishing agent. In the present case, the above methods do not make it possible to use this waste as a source of rare earths.

The method of obtaining seems more advantageous and versatile. rare earth salts of waste polishing powders, glass polishing sludges and other mixtures, the main component of which is cerium dioxide according to the invention, characterized in that the treated raw material, optionally in the form of an aqueous suspension, is treated with a decomposition mixture of hydrochloric acid; an alkali metal iodide in an amount equal to or greater than the stoichiometrically required. The treatment of the decomposition mixture can be carried out with stirring.

The invention is based on the discovery that iodide ions significantly accelerate the decomposition of cerium oxide in an acidic environment.

The main advantages of the method according to the invention are low demands and simple and fast execution. It is also possible to process raw materials which cannot be processed by known methods.

The use of other mineral acids is theoretically possible, but it is less preferred either because of the oxidizing effects (nitric acid, perchloric acid) or because they form poorly soluble salts with rare earth elements (sulfuric acid, phosphoric acid). The type of iodide used is not critical.

For decomposition, the polishing powder is mixed with hydrochloric acid and iodide in at least a stoichiometric ratio, most preferably using a hydrochloric acid concentration of 15 to 35% in a 10 to 20% excess. The iodide, e.g. potassium iodide, is added in solution together with the acid, or in particular as a solid salt, preferably again in a 10-20% excess. Decomposition does not require heating of the reaction mixture. Depending on the amount to be treated, the concentration and the excess acid, the decomposition time with stirring is between 15 and 60 minutes. If the reaction mixture is left for an extended period of time, eg overnight, the decomposition proceeds without stirring. The rate of decomposition can be increased by heating to 70-120 ° C, but in the case of a mixture of potassium iodide and concentrated hydrochloric acid, the effect of heating is not very pronounced, since the mixture itself is very effective.

2565A 1

When processing waste polishing sludge, the method is similar, the sludge does not require any pretreatment, but partial dewatering is preferable, for example · sedimentation ·

After decomposition, an undecomposed portion, mostly mechanical impurities or polished glass, is removed from the reaction mixture, for example by filtration or sedimentation.

The process according to the invention makes it possible to process not only waste polishing powders, but also wastes from the production of polishing powders and catalysts, based on cerium oxide.

Example 1

The raw material was fraction polishing powder falling off 2 ^L 3 ^C during sifting. Composition: CeCl · - 20.2 Her La _of 0 → 5.4% IId ₂ O ₃ - 3.1 "1> 3 g of this polishing powder was mixed with 10 g of potassium iodide and 50 ml of hydrochloric acid 18 > 3. The mixture was left without water for 20 hours, the mixture was mixed with a stick from time to time. After 20 hours the polishing powder was completely distributed.

Example 2

Waste sludge was used and 63.9% was removed by sedimentation, the content of rare earths is mainly polished glass.

700 g of waste sludge was from polishing glass, of which t water. Ingredients: water dry matter - 68.1 Å, the rest mixed in a beaker of 135 g of potassium iodide and 430 g of 35% hydrochloric acid were added in portions. The mixture was stirred without heating for 1 hour. After standing for 4 hours, the mixture was filtered, and the filtrate was analyzed. 940 ml of filtrate was obtained, the rare earth content was 165 g / l. 90.1% of the rare earths were passed into the filtrate.

Claims (2)

SUBJECT OF THE INVENTION Process for obtaining rare-earth salts from waste polishing powders, glass polishing sludges and other mixtures, the main component of which is cerium oxide, characterized in that the treated feedstock is in the form of an aqueous suspension and treated with a decomposition mixture of hydrochloric acid and alkaline iodide. metal in an amount equal to or greater than the stechioraetriols required. Ř 2. Process according to claim 1 _, characterized in that the digestion mixture is treated with stirring by the decomposition mixture.