Na2S (I), Na ethylphenyldithiocarbamate (II) and Na dibutyldithiocarbamate (III) were used as purifn. agents. The pptn. of impurities (Cd, F, Fe and SO4 ions) was carried out at 20 degrees C for 0.5 h. I was the most efficient purifn. agent allowing for removal of 100% and 90% of Cd and F ions, resp. II removed 100%, 35% and 20% of Cd, F and Fe ions, resp. and III removed 70% and 20% of Cd and F ions, resp.