Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

SEPARATION OF THE RARE EARTHS. 241

phate is thereby formed, but this is partially hydrolyzed, and an insoluble basic

salt precipitates. By neutralizing the acid set free by the hydrolysis, a com-

plete precipitation is made possible, but on the other hand, it is necessary to

keep the liquid slightly acid to prevent the other rare earths from precipi-

tating with the cerium. All of the cerium is thrown down in this way, but

it is contaminated with some lanthanum and didymium.

Lanthanum and didymium are thrown out of the nitrate as potassium

double sulphates; the yttrium earths remain in solution and can be precipi-

tated as oxalates by adding ammonium oxalate.

The products of this separation are then each further separated and

purified.

Dissolve 100 g. of the raw material by warming it on the water

bath in 200 g. of concentrated nitric acid. The crude carbonate

dissolves very quickly, but, if cerium oxalate is used, the addi-

tion of fuming nitric acid is necessary to effect solution. Evapo-

rate the solution on the water bath until it is of sirupy consis-

tency, and then take it up in 1500 c.c. of water. Add 35 g. of

ammonium persulphate to this solution and heat it to boiling in

a large evaporating dish. Stir the liquid by means of a mechan-

ical stirrer, and add powdered magnesium carbonate in small por-

tions to the boiling mixture until finally Congo paper is no longer

turned blue, although litmus is still reddened by the solution, —

toward the last the magnesium carbonate should be added very

cautiously. The reaction is complete when, even after boiling

for five minutes, the liquid does not become acid to Congo paper,

although it must still turn litmus red. About 40 g. of the mag-

nesium carbonate are required. Allow the dull-yellow precipi-

tate to settle, drain it on the suction filter while it is still warm,

and wash it with hot water.

Test the filtrate for cerium as follows: To 2 c.c. of the solution

add ammonium chloride and then ammonia; filter off and wash

the precipitate and then dissolve it in 5 to 10 c.c. of hot concen-

trated potassium carbonate solution. Treat the solution with

hydrogen peroxide and some ammonia, and warm it. A slimy

precipitate is produced, and if cerium is present both the solu-

tion and the supernatant liquid are of an orange-yellow color; if

cerium is absent the precipitate is white or a faint pink. The

test is less sensitive if the original solution is warmed directly with

hydrogen peroxide and sodium carbonate. If the above tests

show that cerium is present, add more ammonium persulphate to