Note: Descriptions are shown in the official language in which they were submitted.
3'~
The primary source of retrieval of coal presently in this country
is so-called deep mined coal. This coal is coal that is mined Erom a
substantial distance Erom the surEace of the earth or at a depth of l00
feet or more. The coal is taken directly to a preparation plant to
exclude weathering or oxidation from the atmosphere. Deep mined coal may
be also defined as a coal whose oxygen content doe~ not increase 1% Erom
the source to its preparation. It is realized that all types of coal have
innate oxygen content in the natural state and oxygen content of all coals
including deep mined coal varies as is apparent from the following citation,
A.A. Agroskin, Chemistry and Technology of Coal, 1961, page 33, trans-
lated by the Israel Program for Scientific Translations 1966:
Carbon 77.9 - 88.3%
Hydrogen ~.2 - 5.7%
Nitrogen 1.0 - 1.7%
Oxygen 5.2 - 16.2%
However, it is found that deep mined coal which is transported without ~ ;
delay to the point of coal preparation and processing avoids the deleteri-
ous effect on flotation caused by weathering or oxidation~ Further it
has been found that where the weathering or oxidizing is kept below 1% the
flotation characteristics of the coal are more favoura~le than coal which
by some means has
'~ .
.
. , . :
: ' , ' . . . ' .: .: :
-
~ea..il,-red l;i or greater.
Th;s cl,-~leterious effc?ct o:E an increas~ o~ o.^ygen i~
,
coal has ~een n~r~ted by SZ~Ve~a1 autnors, e.~J., S. C. Sun,
"Pa,r-t 3~ Proth Flo-tz,-tion," in Coal. Preparation, eds. Joseph IJ
_ ____
" L~_onard and David R~ Mitchell, 3d Edition, The ~.erican Institute
of Minin~, ~letallurgicalr and Petroleum Engineers, Inc~, New t
York, 1968, page 1~-67r "~The unfloatability of oxyge~ and
mineral matter is indica-ted by the nonfloata~le li~nite and
animal charcoal~ The deleterious ef~ect of oxygen on the
floatabili~y of coals and coke has been descrihed . . , .~l
. Also, the problem of oxidation a~d.time is approach~d
' ~., by-D. ~. Brown, Chap-ter ~O.~ "Coa~ F.~otation," pages 5.18-~37...~ l.
At paye 526 in the section entitled "The Effecl o~ Weatheri~g
, and Oxidation on Coal Floatability,"' the author states that
15 ~ Freshly mined coal generally ~loats better t-han t~at which ~-
has been exposed to the atmosphere for a few hours or days.
The effect is at-,'ri~utea to surface oxidation which takes place
readily at normal atmospheric temperatures, ls characterised
. by the formation of acidic groups at the coal surfacer and resul,s
' in ~ reduction of the hydrophobicity and floata~ility o~ -the
coal.l' Where coal is artificially o~îdized using potassiwn
.' permanganate solution~ the author si_ates tha~ there is also a '
loss of 10a-'_ability and the water-receding contact ang]e is
,' reduced to ~ero, although the water advancing angle remains hig~
25 1I Brown ~lso restates the ~act that reactivlt~ towards oxygen
va~ies ~ith the ran~ of co~ ow ra~k. coa.ls are re~dily
oxicli.zed ~nd lZrlse ll~uch o~ thei~ ~lo~tab1lit~f but there is a
! ~eneral decre~se o.~ re~ct~v-~.ty ~s the c~rbon content increases.
l, So-called stxîp m~ned co~l, whie~ is outs;de the
li g2~.bit o this irvention~ is de~ined as coal which has beer,
~I removed, rom near the surface of the-~ earth or less than 100 feet
,., ....... .. ,
(~
deep an~ which has ~eat~lered or increased its nakive oxygen
COIltellt: by 1% or more~ Into this categor~ of ~leathered or strip
mined coal would also be included dee~ mined coal ~7hich h~s been
brought to the surface and allowed to weather or o~idize :Eor '
a subst~ntial pexiod of ti~e to increase the oxygen content 1%
~1 or more and unavorably in1uence -the floatability of the coal.
'`I As is kno~.~n, flotation is a process for separatiny
! finely ground minerals such as coal particles frolQ t~eir
associate waste or gangue by means of the af~inity o surfaces
: . 10 ,, ,of these part.icles for air bubbles, which is a method or con- i-
.. .. , 'l,.. centratin~ ,coal particles. In the flotation process a hydro-
Il phobic coating is placed on the particles ~Jhich acts as a bridge~
., . ,l. so that ~he particles may attach to the air bubble and be '
. ~' floated, since the"air bu~ble will not normall~ adhere to a
j , , . , . ... . .. . . ~ .
15 ~,~, clean mineral surface such as coal. ~.
In fxoth ~lotation o~ coal a froth is ormea as
: . aforesaid by introduciny air into a so-called pulp which con-
~, tains the impure finely d-vided coal particles and water con- .
ininy a.'~rothing agent. The flotation separation o coal fxo~.
20 ¦~ the residue or gangu depends upon the relative wetta~il.ity of
~, surfaces and the contact angle, which i.s ~he angle created h~
" the solid air bubble in-terface.
In -the development of flota-tion to date, three gener~
classes of reagents have been u-tilized: ~1) collectors or
: 2s ~¦¦ promoters, (3? modiiers~ and (3~ rothers. ~ .
The promoters consist almost exclusively in this .¦
~ ar~ o keroserle and uel oil.
:~
~: : -3- .
-
~ lodiE.icrs are such re~ a~irlrJ acJ~.lts ~s yH recJulators,
activators, depressantst dis~crsants, and flocculants.
~ frot~incJ a~ent i5 uti~iz~ to provide a stable
flotation froth persistent enou~h to facilitate the coal
separa-tion but not so persi.stent that it cannot be broken to
allow subsequent handliny. Examples of co~only used frothing
agents are pine oil, creosote, cres~lic acid, and alcohols such
' as 4-methyl-2-pentanol~ Alcohol frothexs are preferred in
the present invention and additional alcohols are illustrated
by amyl and butyl alcohols, terpeneol and cresols~ An addi- ,~
tional preferred alco~ol is methyl isobutylcarbinol (MIBC),
.
~' whi'ch is an aliphatic alc'ohol'in'common'use as'~ froth'er.
he present tr,eating agents ~'Jhich are wate~solu~le, ..'
polyacrylates are useful as promoters and frot~ing aids, ' ' 'i
. . .
.. . . .
P~IOR ART
. , U,S~ 2,740/522 Aimone et al - The patentee utilizes
:, ~ water-soluble pol.ymers in amounts .0nl l~s~-ton to 1.0 lbs/ton
with a pre.ferred amount of.O.01 l~s/ton to ~2 lbs~ton. ', .
i, Example 16 (column 7~ shows the flotation of Penns~lvania
! ant~racite coal fines conditioned with 0~2 lbs~ton o~ the sodi~ !
j .
: :. sa~t of hydrolyzed polyacrylonitrile ~o produce ~ ~ous~er con- ~.
centrate~ A second portion of the example utilizes 0.5 lbs/ton
ji of polymer This p~tent appears equivalent to British Patent
,'~749,213. ' . , I :
25 ! :: : uqs~ 3,6~6~923 Miller - Concentr~ion o~ coal by .¦
1~ ,
t~tion,
U.S, 3,4Q8~2g3 D~ani - ConceDtration o~ coal fines
:and cla,y by mean~ o~ a se~llen~ial addition of an anionic polymer ,
; ¦ ~ollowed by a cationic pol~mer to ~OL~ a floc,
., :
,, , ~
The above prior art did not deal with the problems envisagecl with
the attempts to use flotation concentration of an invertible water-in-oil
emulsion on deep mined coal.
In a first aspect this invention provides a method of increasing
the yield of deep mined coal undergoing a concentration treatment of froth
flotation by using as a flotation promoter an invertible water-in-oil emul-
sion of sodium polyacrylate in a dosage calculated as 0.017 - 0.5 lb of
dry sodium polyacrylate per ton of dry coal.
In a second aspect this invention provides a treating agent for
deep mined coal undergoing froth flotation which comprises an invertible
water-in-oil emulsion of sodium polyacrylate in a dosage calculated as
0.017 - 0.5 lb of dry sodium polyacrylate per ton of dry coal and conform-
ing to the following formula:
a) from 5-50% by weight of the emulsion of an aliphatic hydro-
carbon li~uid;
b) from 70-95% by weight of the emulsion of an aqueous phase
consisting of water and from between 10-50% by weight of the
emulsion finely divided particles of wa-ter-soluble sodium
polyacrylate;
c) from about 0.25 - 10.0% by weight of hydrophobic surfactants
capable of stabilizing the emulsion.
The treating agent for the present invention may be defined as
a promoter or frothing agent which is a latex or water-in-oil emulsion
of a water-soluble anionic linear addition polymer of a polymerizable
monoethylenically unsaturated compound having an average molecular weight
of about 100,000 to 1,000,000 and more, with a preferred molecular weight
of about 1,000,000 or more.
A specially preferred promoter or frothing aid is sodium poly-
acrylate. The dosage of this latter treating agent is in the range of 0.05
- 1.5 lbs of sodium polyacrylate latex per ton of dry coal (0.017 - 0.5 lb
of dry sodium polyacryla-te per ton of dry coal) and i-t is utilized con-
ventlonally as a 0.5-2% solution. Utiliza-tion has resulted in a 6~.6% coal
.,7 -5-
,',t J
31 ~ ~
recovery as opposed to 16.4% recovery when usirlg the dry polymer precipi-
tate of sodium polyacrylate.
Also operable in the present invention, together with the anionic
sodium polyacrylate, are minor percentages of the non-anionic sodium poly-
acrylamide in the form of a mixture or copolymer wherein the percentile
of polyacrylamide is up to 25% of the total. Such addition of polyacryl-
amide does not modify the basic anionic character of the polymer, which is
a necessary criteria.
Table 1
Coal Flotation Using Latex Polymers
Dosage (lbs/ton)
Equivalent % Coal
Promoter Effective to Latex _covery
1) Sodium polyacrylate
latex emulsion 0.3 0.3 64.6
2) Sodium polyacrylate
dry 0.1 0.3 16.4
2a) Sodium polyacrylate
dry 1.0 3.0 36.6
3) Azo-bis-isobutyro-
nitrile 0.006 0.3 37.3
3a) Azo-bis~isobutyro- ~ ``
nitrile 0.06 3.0 34.5
4) Sorbi~an monooleate
(SPAN 80*, ICI) 0.0066 0.3 20.1
4a) S~rbitan monooleate
(SPAN 80*, ICI 0.066 3.0 32.2
The results above for parallel studies in oxidized coal indicated
the superiority of the latex form. For example, in Table 1 above? Promoter
No. 1 showed 64.6% coal recovery and included the reaction to the latex
emulsion containing sodlum polyacrylate and ingredients 3 and 4. The in-
divldual effect of the dry precipitate 2 at 16.4 and 36.6, depending on
concentratlon, are also given. The individual effect of the azo initiator
and the emulsifier (SPAN 80*) are set out.
: ` :
* Trademarks
l; ( (
3'~
.i T~\_I.E 2
Comparati~e ~tiVitY of the PrrJ~oter
wi-th L~tex Polyme.rs
.,
Run Dosage Dosage
No. Frother ~ on) Promoter (l~/ion) -O Recovery*
1MIBC** 0.2I,OPS*** O O
" 0.2 " 0.112.6
'. 3 " ~.2 " 0.273,0
! 4 0.2 0 ~86.3
Il 5 " 0.2 .l 0.7t~10.~ !
il 0.2~2 Fuel ~il 0.8044~9
. 7 " ` 002 . " 0~501~.7
,i ~ . 0.2 '~ 0,307,0
il 9 ~ 0.2 La-tex 0,2010~7
. ,.. . - .. Pol.y~er A2
" . ~.2 " . ~.30.. .15.~ .
. : . ..
1 11 - " 0.~ " ' 0~4~18.0
. . . 12 " ` 0.2 Latex
Polymer 2 ~0.30 40~9
& PueI Oil tO.50 .
li - : - - -
j, * ~ Recovery is on total solids, not ac~ual coal in float -
l' .
** Methyl isobutylcarbinol
li *** Low odor paraffin solvent
20 ,l Cc,al: An analogous study usiny oxidiY.ed coal
..I . Polymer A2 is derived from monomer star~ing mate~ial ~ a-~
. ¦ page 8 post. .
: , ,' . I
: I It is noted that, with reEerence to Runs 2 tutilizi~g I -
¦ LOPS) and 11 (utilizing the latex`emuls.ion pol~mer) ~nd con~ . ¦
¦ sidering that the amount of I,OPS in the starting material is
: ¦ in the~range 20-30%, the activity indicated ln the percen~ i
:;~ : 1, recovery of coal-sho~.~7s a dis-tinct increase o~ from 2.6 to 18~: 1 ,
: _7_ I
.
:: : ' : ' '
T~IE L~TEX
The preparation of the water-in-oil latex from monomers, its
polymerization to a water-in-oil emulsion, and its subsequent inversion
to an oil-in-water emulsion in use are described in one or mo~e of the
following patents:
United States 3,997,429 Kane et al
United States 3,624,019 Anderson et al
United States 3,734,873 Anderson et al ~: -
United States 3,826,771 Anderson et al .
A monomer starting material (A) useful for frothing oxidized
coal has a composition as follows:
Water 27.0
Caustic soda (50%) 23.0
Acid acrylic glacial 20.9
Low odor paraffin solvent
(LOPS~ 19.3 ::
Sorbitan monooleate ~:.
(SPAN 80*, ICI) 1.0
Azo-bis-isobutyronitrile
(catalyst) 0.03
Espesol 3-E* (a liquid aromatic
hydrocarbon blend, Charter
International) 8.5
Polyiso~utylene (stabilizer3 0.27
Aluminum tristearate :
(stabilizer) 0.0002
.,
.: . .
* Trademarks
:
~ 8-
The po:Lymerized sodium polyacrylate may be produced by poly-
merization of, for example, the above recipe according to the teachings
of United States 3,284,393 VanderhoEf et al using a free radical type
catalyst.
A typical water-in-oil polymeric emulsion contains
1) Erom between 10-50% by weight of sodium polyacrylate
~ ) from 5-50% by weight of the emulsion of an aliphatic
hydrocarbon liquid
3) from 70-95% by weight of the emulsion of an aqueous phase
consisting of water and polyacrylate (s-tep 1)
4) from about 0.25 - 10.0% by weight of hydrophobic surfactants
capable of forming a stable emulsion oE the monomers (e.g., alkylated
hydrocarbons such as toluene and xylene).
The above-noted composition i6 not self inverting but a varlety
of inverting techniques are set out in United States 3,624,019 (supra)
at column 3, lines 49-57. The presence of any of a group of activators
will cause the polymer emulsion to self invert. Such activators may be
selected from:
1) Surfonic N-95* (Jefferson Chemical Co.), a nonyl-phenol with
10 moles ethylene oxide
2) Triton N-101* (Rohm & Haas), nonylphenoxy polyethoxyethanol
3) Makon 10* (Stepan Chemical Co.), alkyl phenoxy polyoxyethylene
ethanol
4) Lgepal C0* 630 (GAF), nonylphenoxy poly(ethyleneoxy)-ethanol.
* Trademarks
. 9_
3 ~
,
In -the present case -the activai-.or may be placed in
separate vehicle with ~J~ter ~lternativel~, an activa-tor ma~
be adcled later -to -the ~olymerized composi-tion or a self in-~ert
; mode~ ~n e~pl.anation o~ the action of the inversion technique
; is that a normal la-tex will generally be added to water con~
tainin~ a hydrophilic surfac~ant~ as, for exampler Surfonic N95,
j thereby causing the emulsion to invert and allowing the polymer
', previously in the discon-tinuous phase to wind up in ~he con~
i. tinuous phase of the water-in-oîl emulsion . This ~ of course,
~ allows the polymer to solubi-lize. For self-inYert:ing emulsions, .
the same originàl emuIs~on~is careully ~alanced so t~at, wh~n. - i
! added to water, the emulsion inverts, thereby allowing the
Il, polymer to solu~ilize,
. . .. ... ..... . ... . ... ., ,,
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Results: This preliminary study shows increased
recovery rate in at least one run. Separate studies in th-ree
different widely distributed coal mines have confirmed the
preliminary results shown above for increased recovery utilizing
a polyacrylate emulsion type treating agent such as Treating
Agent A. These latter studies showed the use of the water-in-
oil emulsion of sodium polyacrylate composition significantly
increased the recovery o-f deep mined coal in three divergent
coal mines, one from 78.7% to 90.8%, another from 85.3% to 97.4%,
and another from 91.3% to 93.6%.
: .
" .
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u~ ~ ~) ~ N
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3~
Referring to Table 4, the coal was uniformly treated with 3.5
gallons per hour of promoter feed which was achieved by feeding 270 gallons
of 1.3% solulion on an hourly basis. This treating agent was prepared from
~lonomer A described on page 8, ante, which is polymerized according to Van-
derhoff 3,284,393 and the proportion is used as set out a-t page 9~ an-te, and
is Polymer A.
The evaluation above is to determine tons of solids in the froth
cell tailings before and after the addition of the promoter. This was done
by multiplying the flow rate leaving the float cells by the percent solids
and specific gravity of the tailings. To convert to tons per hour, multiply
appropriate factors of 8.34 pounds per ton and 60 minutes per hour and di- -
vide by 2,000 pounds per ton as given by the formula:
TP~I Flow Rate GPM x 8.34#Gal. x 60 min./hr. x Specific Gravity x % Solids
_ Slurry
2,000#/Ton
Results of the calculations were:
Solids in Tailings
Coal BeforeWi~h Polymer ADifference
#1 59 TPH17 TPH 42 TPH
#4 53 TPH24 TPH 29 TPH
#2 ~ 90 TPH~3 IPH 47 TPH
~t5
Also calculations showed the fo:Llowing filter cake yield:
Filter Cake Yield
CoalBe~ore With Polymer A Difference
#l 42 TPH77 TPH 35 TPH
#4 34 TPH53 TPH l9 TPH
#2 ~ 13 TPH58 TPH 45 TPH
~: ' ,
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- 1~ - ' ~
