P-64

pamphlet

64

..

c.

ST-.,TE OF ID.AliO

4. Bottolfsen, Governor

IDAHO B'tJU',A,U OF :tilDS AND GEOLOGY .A.•. w. Fahtenwald.. Director'

THE AERA.TtNG CAPACITY OF

~"'LOTATION

By

.. , ..

A. W. Fahrenwald

----,,--

University of Idaho Moscow. Idaho

MACHINES

THE

~~ING

CArACITY OF FLOTATION WlCHINES by .A.. W. Fah"enwald

•

Two methods of measuring the aerating capacity of self-aera.ting mechanical· . flotation machines are here presented. volume provided with three outlets.

One consists of a tank of substantial

One of these is connected by means of a

rubber tube with the air intake conduit of the flotation cell.

Another is

coupled conveniently by a piece of garden hose to a suitable source of water supply. using

The third, at the top of the tank, is fitted with a manometer tube,

wate~.

The manometer tube is provided with a valve.

The operation in determining the air intake of the cell is as follows; start with the manometer va.lve open. .'

Now run water into the tank "hy manipula-

t10n of the water valve on the garden hose line until the vQlume of water entering the tank is exactly equal to the volume of free air being taken by the balanct~

flotation cell,

This

the valve can be

complet~ly

levtlls in

th~

is hit by a test with the manometer valve.

When

closed without any change in elp.vation of the water

manometer V-tube, the volume of

wat~r

equal to -the volume of air used by the machine,

dntering the tank is just

The we.tar

hos~

is now dis-

connected from the tank and the flow in cubic feet per .inute measured.

The

method is extremely precise, I t is found thA,t a good 50(}.gram cell in propt?r operating condition make. about

1/4 cubic foot of free air per minute. If it be assumed thet all the measured energy input to the machine goes

into making new bubble (or wp..te·r) surface. knowing the volume of free air taken by the machine per minute, the size of may be calculated.

bubbl~.

The energy balance is;

1

and in turn the number of bubbles,

~otal

)1nergJ I~put in Irgtl

energy (73) of

II:

"84.

'lotal bu.bble (wa••r) aurfa.ee s: th• •

wa'er~

Total Energy Input • 50 watts

= 50 x

~O x 10 7 • 3 x 1010 ergs.

t•

Total S~face •

4l nd3 x nd2 • d42.500 aq. co . •Ob b ~herefora, d(3 x 1010) • 42,500 x 73 ~~d.. d ~j. 'xX ,10 to610 • 1 x 10-4 Ct!. or, d .001 uun~ II:

<=U6

III

In 432 cubIc inches of air, there would be (4l2 ..' 3.1416 x .0012 .) 6 ' .60r>5bl ' 1.3 x 101 , 1/1000 millimeter bubbles. Thesef1gures are slightly on the astronomical side and certainly are no' in line with the faets, althougb facta as to bubble' size in floiat1on are not known.

.-

lor purpose of ca.lculations, let us ,peculate the., the bubbles bave a

mean diameter of 2 mm. inches of air i8

The n'Q.fnber ot 2

llltll.

bubbles obtalna'Gle,from 432 cubi.

(.65~6b1 +~ ~) 1,740,000.

The tQtal

wa~ef

surtace is

(1, 740.000 + nd2 .) l30,OoO' sq. em, per m1nut~, and the total surface energy \

made by tbe machine 18 (13°,000 x

73 .) 9.490,000 ergs

per minute.

The energy input t·o tbe machine t as shown. ab?ve, 11

3 x' 1010 ercs..

Thlls.

on the assumption that t:Q.esize Qf bubble is 2 rom .• the mechanical .tf10111101' of the laboratory eell is (9.49 x l06 + 3 x 1010 x 100 .) 0.31 per oent. It is of interest to note that this efficiency figu.:re is of of magnitude as that of tbe effieiency of the ball mill t

th~

same order

The 500·gram'lab cell

"grinds" one-fourth of a cubic foot of air per minute at an eltpenditure of 50

watts.

The

flnenes~

of grind is anyone's guess -- there is no known available

method of "sizing" bubbles.

The method above described for measuring the aerat·1ng ca.paelty of a f1otat1o~

machine i8

1i~1'ed

to the study of small

experi~ental

unite of the

self~aerating type.

.

..

.

This method is hignly accurate since it measures air

intake at zero pressure and it 1s in ~bis respect that it has merit in research

The result, however._it should be pOinted

work.

measure of 'cell

efflcae,~

~t,

1s not neces8arllya

The method does not give any data as to air dis-

semination and/or bubble distribution. Another method used 1n this laboratory, .and one thet is applicable to commercial a.s wt!ll

88

small la.boratory cells, is a.s follows:

needed' is a. 1000 m.l. wide-mouth flask.

The a.ppara.tus

The bottle filled with water or pulp,

the mouth covered with the palm of the hand, is inserted, neck Q.ownward. into' the pulp,

When the hand is removed from the bottle mouth, bubbles flow into

the bottle displacing the water therein.

With a stop watch, the time required

to displace the water in the flask is a measure of the aeration at that position in the cell.

By this method the pattern of bubble distribution in the cell oan

be accurately and quickly determined~

Also, by this method'tbe aerated condi-

'tion of pulp in Bny cell, no matter what tht3 make or principle of operation, can be meesured.

In

a

number of machines in this laboratory, larg$ and small, the aerating

capacity ranges from 500 m.l. which is good, to ZOO Jr..l. per minute, which is poor.

This is the vol'Q.llle of free air escaping from th~ pulp per sq. inch of

surface per minute.

The degree of aeration in scme, cells varies as much as

100 per cen~ over the cell surface.

Cells th~t cause pulp swirling give

strong aeration at the cell core, tha.t is, around a.nd nea.r the 1mpeller shaft. •

This is due to centrifugal. action on b;,lbbles.

Needless to say. this is a. bad

condition. The accompanying da.ta. Tables I and II, were obtained from experimt3nts using the tlflask displacement" mt'thod.

Table I shows hew aeration and energy

input vary with d~pt:n of water above the impeller. data for varying pulp density.

Table II gives similar

Tne flotation cell employed in these eXp~iment8

3

was ey11ndrical in form 'and hAd a volume of exactly 1 cubic fOQt.

"

.

irapeller was 6 inches in diame\er and was feet per minute.

run

The

at eo peripheral .peed of 1600

Tk+e impeller shafi b.eu1nga were ot the antltriction type,

TABLE I.

The Effect of Pulp-Depth Upon the Aera.ting Capaci t1 and En.erQ l\eq1,l.irement Depth of PUlp

of a Flota\ion

Above 1II1peller.

C~ll

iQwer Input

Inchca (

ift

INt,

Aeration per ". in. Cell ~:r't.RerHlnut' m~l.

9·5

172

408

7·5

150

423

5·5

120

465

3·5

95

533

TABLE II.

The Effect ot Pulp Density. Upon Aerating Capaclty and Energy Input Reguireoent of a Flotation Cell in Watts

Aera.tion m.l. per sq. in. Ot Cell. Aree. per Minute

1.11

171

329

1.15

179

286

180

248

182

217

.Pulp Deusi ty

Power Input

4