The present invention relates to a selective extraction of yttrium ions.
Yttrium (Y; atomic number 39) compounds have been widely used as the raw material of red fluorescent substance of a Color TV. The yttrium compounds have been also widely used in the other electronics fields such as additive for optical lens, and the yttrium compounds become important substance as industrial sources.
As a selective extraction of yttrium ions from an aqueous solution containing yttrium ions and other rare earth ions, it has been known to separate the yttrium ions by selectively extracting with an extracting reagent of a phosphoric ester. According to the conventional method, the yttrium ions could be separated from the light rare earth ions such as La, Ce, Pr, Nd, Pm, Sm, Eu components etc. However, a satisfactory result could not be attained for the separation of yttrium ions from the heavy rare earth (atomic number of 64 to 71) ions.
The ion-exchange method for selectively extracting yttrium ions by passing an aqueous solution containing yttrium ions and the heavy rare earth ions through a column packed with an ion-exchange resin has been usually used for the separation of yttrium ions from the heavy rare earth ions.
However, in the ion-exchange method, a diluted aqueous solution having low concentration should be used, whereby the concentration of the purified aqueous solution containing yttrium ions is quite low and a large apparatus and a large heat source are required for the concentration of the aqueous solution, and moreover, a flow rate of an eluent passed through the column of the ion-exchange resin is slow. Accordingly, the productivity is low.
It has been also known to separate yttrium ions from the heavy rare earth ions by the method of selectively extracting the yttrium ions by using a cation exchange liquid and an anion exchange liquid in the presence of a nitrate (U.S. Pat. No. 3,575,687) or the method of selectively extracting yttrium ions with an extracting reagent of a quaternary ammonium compound in the presence of thiocyanate ions (Japanese Patent Publication No. 4328/1970 and Japanese Unexamined Patent Publication No. 103815/1974).
However, these methods have not been satisfactory.
In the former method, the separation factor of yttrium ions from the heavy rate earth ions has been low such as about 2 to 3, and in order to obtain an yttrium compound having high purity, several tens extraction stages have been required.
In the latter method, thiocyanate ions are easily decomposed and the decomposed material may be precipitated or HCN may be produced in the extracting operation. Accordingly, the operation control has not been easy and in order to obtain an yttrium compound having high purity, several tens extraction stages have been also required.