Chemical Properties
amorphous, radioactive powder(s); pure material is white, but impurities impart yellow, orange, or pink color [HAW93]
Description
Radium carbonate has the molecular formula of
RaCO3 and the molecular weight of grams per mole.
Most of the compounds of radium are more insoluble
than the corresponding barium compounds and concentrate
in the precipitate upon fractional precipitation of
barium-radium mixtures. One notable exception is
radium carbonate, which is more soluble than barium
carbonate and, hence, concentrates in the soluble fraction
(filtrate) when barium–radium carbonate mixtures
are fractionally separated.
Radium carbonate is soluble in dilute acids, and more
soluble in concentrated ammonium carbonate solution
than BaCO3.
Physical properties
Its
volubility is 2.1×10-4 g/100 ml of water at 18°C. For
this reason, precipitation as the sulfate is a common practice
for the recovery of radium, particularly with the
addition of bariumcarrier. Radium Carbonate is soluble in concentrated sulfuric
acid, but precipitates upon dilution of the acid. It is converted
to radium carbonate by fusion with sodium
carbonate (a technique frequently used for the dissolution
of radiferous barium sulfate because the resulting
barium-radium carbonates are soluble in any dilute
mineral acid).
Uses
The principal use of radium carbonate has been in
medicine and to prepare other radium compounds.
Preparation
In general, RaCO3 is prepared in conjunction
with BaCO3 and then separated. Radium sulfate is
the most insoluble of the alkaline earth sulfates and probably
the most insoluble radium compound known.
Radium carbonate may also be prepared by precipitation
from neutral or weakly alkaline solutions of radium
salts with a solution of ammonium carbonate. Gram
quantities of radiumhave been recovered from a concentrated
solution of radium nitrate by precipitation as the
carbonate. The radium nitrate solution was adjusted to
pH 9.2-9.5 with concentrated ammonium hydroxide.
Carbon dioxide gas was bubbled into the solution until
the pH was just slightly above 7.0. To insure complete
precipitation of radium carbonate, ethyl alcohol
and some additional ammonium hydroxide solution
were added. The radium carbonate was filtered and
washed with 90% ethyl alcohol. It was first dried at
110°C to remove the alcohol and weighed as RaCO3.
