molybdenum to Mo(VI).
A measured aliquot of the sample solution is added to a measured aliquot of previously analyzed ammonium molybdate solution.
After thorough
mixing, the solution is brought to pH 5 with ammonium acetate -acetic acid
buffer, and 0.1 M Pb(NO, )2 solution is added to precipitate the molybdenum
lead molybdate.
The sample is centrifuged and the supernatant is discarded.
The precipitate is dissolved in $ M HCl! and the solution is poured through a
column packed with anion exchange resin (Dow Chemical Company Resin
"Dowex A-1"'), previously treated with 9 M HCl.
When all the active solution
has passed through, the molybdenum is located in an adsorbed band at the top
of the resin column.
The following solutions are then passed in turn through
the column to remove impurities:
0.1 MHC}; 1 mi. H,0;
10 milliliters (ml.) of 9 MHC1; 10 ml. of
5 ml. of 3 M NH,OH; l ml. H,0.
The molybdenum
is then removed from the resin by passing through 15 ml. of 4 M HNO,.
A
few drops each of sodium tungstate solution and silver nitrate solution are
added to the eluate and the solutions mixed, then sufficient dilute hydrochloric
acid is added to precipitate the added silver as silver chloride,
The solution
is digested in a hot-water bath to coagulate the mixed precipitates of tungstic
acid and silver chloride and the precipitates are centrifuged off and discarded.
The tungsten and silver precipitations are repeated.
A small quantity of a so-
lution containing Fe?}, La’, Tet# and zr*4 is then added to the supernatant
and precipitated with NH,OH at pH 10 or higher for further decontamination.
The precipitate is rejected.
More Fe? and La? are added to the supernatant
(which is ammoniacal) and the resulting precipitate rejected.
The supernatant
solution is then acidified with acetic acid to pH 5 and 0.1 M Pb (NO,), solution
is added to precipitate the molybdenum as lead molybdate.
is washed with water and acetone and dried.
The precipitate
.
The dry precipitate is transferred to a weighed aluminum dish, the dish
and contents are re-weighed, and the precipitate fixed in place by a few drops
of diluted lacquer.
difference.
The weight of recovered lead molybdate is determined by
The small dish is fastened with adhesive tape to a support suitable
for insertion into the counting equipment and is counted once or twice daily
for several days. The lacquer must be thoroughly dry before the counting is
started, since the lacquer solvent exerts a pronounced effect on the counting
rate.
SUL GEE
- 54 -
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