Procedure for removal of sodium and bromine from KCl involves zone refining in dilute halogen atmosphere. Distribution of Na and Br at concentrations of parts per million is followed by neutron-activation analyses

Susman, S.

English

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August 1969
	 Brief 69-10241 
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Zone Purification of Potassium Chloride 
The problem: 
Development of a direct procedure for purifying 
untreated KCI and removing two common interfer-
ences: Na and Br. Color-center investigations in 
alkali halides frequently require a controlled composi-
tion with respect to foreign alkali-metal ions and 
foreign halogen ions. These ions, occurring in un-
known concentrations, interfere with optical, kinetic, 
and spin-resonance measurements. 
The solution: 
A simple procedure for rapid removal and quantita-
tive estimation of Na and Br in KCI. The procedure 
for purifying untreated stock-bottle KCI involves 
zone refining in a dilute halogen atmosphere. The 
distribution of Na and Br at concentrations of parts 
per million is followed by neutron-activation analyses. 
Computer-analyzed distributions in refined ingots 
yield K Na = 0.53 ± 0.03 and K Br = 0.72 ± 0.02. 
How it's done: 
- For the zone melting of KCI in a controlled atmos-
phere a boat of trapezoidal cross section with 5° taper-
ing sides was fabricated from quartz. The boat slipped 
with minimum clearance into a quartz tube, 26 mm in 
bore, that was coupled to a vacuum and gas handling 
system. 
Reagent-grade KCI served as a starting charge. The 
loaded boat was inserted into the quartz environment 
tube, and the system was evacuated to I x 10-6torr. 
Ambient temperatures were increased from 20° to 
420°C over a 24-hour period during which the system 
pressure did not exceed I x 10 - torr. Next a gaseous 
mixture of 2% HCI in 98% prepurified argon was 
passed over activated charcoal at dry-ice temperature 
and introduced into the environment tube. With the
ambient temperature maintained at 420°C, the sys-
tem was evacuated and backfilled twice. The powder 
charge was then allowed to remain in contact with 
the static halogen atmosphere for 18 hours at 420°C. 
Controlled dehydration and halide treatment are 
required to reduce hydroxide contamination in the KCI 
melt. Ingot adhesion to the quartz boat walls is pre-
vented; thus boat breakage is obviated during early 
passages of the molten zone. A 2% mixture of the 
halogen in an inert gas accomplishes this without the 
bubble formation attendant on zone melting in a pure 
halogen atmosphere. 
After a final backfill cycle, the dilute halide gas 
was permitted to flow over the boat at I cm'/min in 
the direction of slow zone travel. Two molten zones 
were simultaneously passed through the 17-inch-long 
ingot at 2.0 inch/hr with an ambient temperature 
maintained at 540°C. The ratio of ingot length to 
molten-zone length was varied from 6.8:1 to 9:1. 
Quantitative estimations of concentrations (ppm) 
of Na and Br in a KCI matrix were readily obtained 
by neutron-activation techniques. Solid chips weighing 
from 5 to 10 mg were irradiated for 72 hours at 1013 
neutrons per square centimeter per second (thermal). 
Possible surface contamination was removed by im-
mersion of the irradiated chips in methanol. Separa- 
tion of 15-hour (half life) Na 24 from 34-hour Br82, 
and removal of the 12-hour K 42 background, pro-
ceeded on a 2-mm bore, by 10-cm ling, column of 
zirconium tungstate. The KCI chip was placed atop 
the resin bed, and the column's tip was plugged 
temporarily. The sample was completely dissolved 
in a minimum amount of 0.0IM NH 4CI containing 
Na 22 tracer. Less than 5 ml of 0.0IM NH 4 CI was 
needed for complete elution of Br 82 . After change in 
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the eluant concentration to 0.IM NH 4 CI, it was 
possible to elute Na 22 ' 24 with tO ml of eluant with 
more than 95% recovery of the tracer. 
Counting was done with a 3 by 3-inch Nat detector. 
At Na and Br concentrations of 10 Mg/g, the standard 
deviation is ± 4%. The absolute error is estimated at 
no more than 10% on the basis of comparison with 
colorometric and flame-photometric analyses at Na 
and Br concentrations higher by one to two orders of 
magnitude. 
References: 
For more details see S. Susman, J. Chem. Phys. 
47(1), 83 (July 1967).
Note: 
Inquiries may be directed to: 
Office of Industrial Cooperation 
Argonne National Laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B69-10241
Source: S. Susman
Solid State Science Division 
(ARG-10377) 
Patent status: 
Inquiries concerning rights for commercial use of 
this innovation may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 69-10241	 Category 03


Zone purification of potassium chloride

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