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Патент USA US3044857

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United States Patent 0
1
‘
3,044,849
3,044,849
1
‘Patented July 17, 1962
2
ing progresses. It has thus become common practice to
add more glue during the leaching process so as to bring
the total amount between 1.0 and 2.0 lbs./ ton ore, which
adds appreciably to the cost of uranium processing in
view of the small amount of uranium in each. ton, of. Ore
It is the primary object of this invention to overcome
‘
PREVENTION OF SETTLING 0F URANIUM PULP
BY POLYVINYL ALCOHOL
Frederick W. Matthews and‘ Max Mort, St. Hilaire, Que
bec, Canada, assignors' to Canadian Industries Lim
ited, Montreal, Quebec, Canada, a, corporation of
Canada
No Drawing- Filed Sept. 14, 1959, Ser. No. 839,562
Claims priority, application Canada Oct. 11, 1958,
2. Claims. (Cl. 23—14.5)
the foregoing disadvantages by providing a new suspend
ing agent for the uranium pulp, which agent is more e?ec
tive than the animal glue and is also more stable under
10 the leaching conditions. Other objects of the invention
This invention relates to the extraction of uranium
will appear hereinafter.
from its ores and, more particularly, to the prevention of
Broadly speaking, these subjects are accomplished by
settling of the pulped o're during the leaching thereof.
incorporating polyvinyl alcohol with the pulp in. a con
Many uranium ores contain the uranium in such forms
centration of at least 0.01 pound per ton of uranium ore
as uranium titanite, uraninite and pitchblende dispersed 15 contained in the pulp.
‘
'
as ?ne particles through an essentially quartzite matrix.
The effectiveness of the polyvinyl alcohol as suspend
The amount of U308 mayrange, for example, from 2.0
ing agent does not appear to be dependent to a great ex
to 20.0 pounds per ton of ore. To extract the uranium,
the ore is ?rst crushed, and then ground under water until
about 55% of the ore passes a 200 mesh screen.
a tent on its molecular weight or hydroxyl content, having
regard to the fact that polyvinyl alcohol is produced by
This 20 hydrolysis of polyvinyl acetate. Thus, the following com
?nely divided ore, when slurried in water, is normally
mercial grades of polyvinyl alcohol were tested and all
found to be effective forthe purpose of the invention.
known as uranium pulp, and in the next stage of the proc
ess, the pulp is brought to 60%-70% solids and leached
with sulphuric acid under oxidizing conditions. It is with
25
this leaching step that this invention is concerned.
The leaching is normally done in a wooden stave or rub
Viscosity in centipoises of 4% aqueous solution at 20° C.
ber lined tank or series of tanks measuring roughly 30 ft.
deep by 32 ft. in diameter. The pulp is brought into con
tact with sulphuric acid of about 5% strength containing
55-65
a small amount, viz. 2-3 pounds per ton of ore, of so 30
dium chlorate at a temperature of about 45 ° C. The
leaching is continued for about 48 hours and the ura
nium becomes oxidized to the uranyl state and remains in
Degree of
Hydrolysis,’
percent
99-100
0
.___
97'. 9-98. 7
solution, probably as uranyl sulphate. It is vital to the
success of the leaching process that the pulp, containing 35
for example 65-68% solids, be kept in motion by con
The solid ponyvinyl alcohols of 99-100% degree of
hydrolysis and medium or high viscosity ‘dissolve slowly
through the pulp. Very large and powerful stirrers are
in the leaching solution and it is preferable that they be
used, and there has been in the past considerable loss and
incorporated with the pulp in the form of aqueous solu
40
damage caused by the tendency of the pulp to settle from
tions of any convenient strength, rather than in solid
the liquor as a semi-solid mass. Such settling may over
form.
load the motor or bend the stirrers, and is particularly
The invention will be more fully illustrated by the fol
likely to occur at any interruption of the electrical power
lowing example which, however, its not intended to limit
or compressed air supply. Once the pulp has settled and
the invention.
the damage is done, the tank must be emptied by removal 45
EXAMPLE
of all pulp and lengthy and costly mechanical repairs may
A
simple
test
was
devised
for comparing the e?ective
follow. Moreover, this tendency to settle increases the
ness of various suspending agents. This test consists in
power requirements of the stirrer by a large factor.
pouring a sample of the pulp containing the leaching
In order to decrease the danger of such settling, it has
become common practice to incorporate a suspending 50 chemicals and particular suspending agent into a wide
bore powder funnel of speci?ed dimensions. The bore
agent in the pulp during the leaching procedure, the pre
of the funnel is plugged at the bottom with a rubber stop~
ferred agent having heretofore been animal glue. The
per and the pulp allowed to settle for 15 minutes. The
glue is usually added with the sodium chlorate, since on
stopper is then removed and the time for the contents of
the initial addition of sulphuric acid to some uranium
stant stirring and in some cases by compressed air blown
ores there is emission of hydrogen sulphide, i.e. the con 55 the funnel to ?ow out is noted. This time is an excellent
measure of the tendency of the pulp to settle, and the
ditions are reducing. The pulp is air blown until the
size of the funnel and its bore may be varied to measure
hydrogen sulphide is drawn off and the sodium chlorate
this tendency over several ranges. Thus a pulp which is
and glue are then added. Initially about 0.3 lb‘. glue are
added per ton of ore.
-
e?ectively suspended by either glue or polyvinyl alcohol
By the term “suspending agen ” as used herein is meant 60 may ?ow out of a given funnel in 5-7 seconds but a pulp
an agent which not only slows down the settling of the
pulp from the leaching‘liquor but also changes the na
ture of the semi-solid‘ mass it it should be allowed to set
tle.
In the absence of a suspending agent the settled
mass is hard like wet sand 'but in the presence of an
e?ective agent the mass is much less dense and is capable
with no agent or in which the agent has become ineffec
tive will not ?ow out of the same funnel at all.
Various suspending agents were incorporated with sep
arate samples of a uranium pulp containing 68% solids.
65 to which were added 4 cc. of sulphuric acid and 0.5 g.
of sodium chlorate per 200 g. of ore. Each sample was
stirred and brought to 45° C. and tested by the above
of being stirred into suspension again with little elfort.
method using a funnel with a 1.3 cm. diameter bore.
However, experience has shown that glue is not stable
Since high molecular weight glues are more effective
under the acid oxidizing conditions prevailing during the 70 than those of low molecular weight, a glue of the former
leaching process. Moreover, even in the presence of glue,
type was compared with three samples of polyvinyl al
the tendency of the pulp to settle increases as the leach
cohol with the results shown in Table I.
3,044,849
4
It is permissible to add the polyvinyl alcohol at the be
Table l
ginning of the leach, and no deleterious effect is occa
sioned thereby.
Flow-Out Test Time (seconds)
Leaching Time (Hours)
‘
‘
~
_
5 alcohol than those above in Table II can be used for
Polyvinyl Alcohols
particularly difficult ores. It is economically desirable
to use the minimum e?ective amount of suspending agent,
‘but the process of this invention is not to be limited to
small amounts shown in the example, but only by the
Glue
1
7
28
g
'
2
3
between 5 an d 10
’
'
10
31
following claims.
What we claim is:
m
m
~
It should be noted that a greater quantity of polyvinyl
15
9
V.
1. In a process wherein ?nely ground uranium ore is
15. 5
slurried with dilute sulphuric acid and leached under oxi
dizing conditions, the improvement which comprises in
The concentration of glue was 0.3 lb./ton which corre
sponds to the ?rst addition in a leaching proceess, while 15 corporating with the slurry at least 0.01 lb. of polyvinyl
that of polyvinyl alcohol was only 0.05 pound per ton of
alcohol per ton of ore.
ore. ‘It can thus be seen that the e?ectiveness of the glue
was lost in 6 hours, and therefore more glue must be
2. The improvement claimed in claim 1 wherein a
polyvinyl alcohol having a viscosity of at least 25 centi
poises in 4% aqueous solution and a degree of hydrolysis
of at least 99% is incorporated with the slurry in the
added in practice, whereas the polyvinyl alcohol was still
e?ective after 48 hours, the usual total leaching time.
A similar experiment was conducted to establish the
effect of decreasing amounts of polyvinyl alcohol.
form of an aqueous solution.
In
this‘ case the polyvinyl alcohol had a viscosity of 19-25
and a dagree of hydrolysis of 86-89%. The results of
the experiment are given in Table II.
25
Table II
Concentration of Polyvinyl Alcohol
Test Time of Two
(lbs/ton of ore)
Samples (seconds)
30
10
15
8
16
16
18
55
18
20
63
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,738,253
2,868,618
Thunaes et a1. ________ __ Mar. 13, 1956
Oberg et a1. __________ __ Jan. 13, 1959
OTHER REFERENCES
Rosenbaum et al.: “Int. Conf. on Peaceful Uses of
Atomic Energy," vol. 8, pages 38-44, August 8-20, 1955.
Kirk and Othmer: “Encyclopedia of Chemical Tech
' nology,” vol. 14, pages 713, 715.
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