TITRATION OF THORIUM AND RARE-EARTHS WITH ETHYLENEDIAMINETETRAACETIC ACID USING SEMIMETHYLTHYMOL-BLUE BY VISUAL END-POINT INDICATION

The precision and accuracy attainable in direct complexometric titrati ons of Th4+ consecutively with either lighter (La3+, Nd3+, Sm3+, Eu3or Gd3+) or heavier lanthanides (Dy3+) in different proportions using Semimethylthymol Blue (SMTB) as a metallochromic indicator and disodiu m dihydrogen ethylenediaminetetraacetate were studied. Thorium(IV) was titrated at pH 2, the pH was adjusted to 5.5-6.0 by adding hexamethyl enetetramine (hexamine) buffer and acetylacetone-acetone solution and La3+ (or Nd3+, Sm3+, Eu3+, Gd3+ of Dy3+) was then titrated. A comparis on of the indicators SMTB and Methylthymol Blue (MTB) for successive t itrations of Th4+ and any of the rare earth ions was carried out. The proposed titration method was applied successfully to some naturally o ccurring ores and minerals containing thorium and some lanthanides and the results were satisfactory.