thorium thread, page-5

This following article appears to have been written in 1967
http://www.springerlink.com/content/w3ww37257ml81q6p/
Received: 13 April 1967

Summary The extraction of thorium and trivalent cerium chlorides by tri-n-butyl phosphate and di-isoamylmethyl phosphonate has been investigated as a function of hydrochloric acid molarity in the aqueous phase and solvent concentration in the organic phase. The comparative stability of the extractable metal complexes with the two solvents has been also estimated. The second solvent has been recommended, instead of the first, for the separation of thorium and the rare earth elements from hydrochloric acid media.


Article
Separation of thorium from uranium and rare-earth elements by solvent extraction with tri - n - butyl phosphate - xylene
I. A. Menzies, F. Rigby
U.K. Atomic Energy Authority (D. & E. Group), Research & Development Branch, Springfields Works, Preston, Lancs

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And this one sometime in 2007
http://www3.interscience.wiley.com/journal/114238863/abstract?CRETRY=1&SRETRY=0

Abstract
A study is made of three processes for the separation of thorium from uranium and rare-earth elements in crude thorium nitrate solutions prepared by breakdown of monazite sand. Uranium may be separated from thorium and rare-earth elements in a preliminary extraction with 5% or 40% v/v tri-n-butyl phosphate (TBP) in xylene and the thorium separated from the rare-earth elements in a subsequent extraction with 40% v/v TBP in xylene. Alternatively thorium and uranium may be extracted simultaneously from the solutions with 40% TBP in xylene and the thorium preferentially backwashed from the loaded solvent with dilute HNO3. The present work indicates that processes in which uranium only is extracted in the first operation will be the most flexible and the simplest to operate. The partition coefficients for zirconium, which occurs as an additional contaminant in solutions prepared from thorite ores, have also been determined by batch extraction with 5% and 40% TBP in xylene and the data confirmed in a continuous countercurrent system.