CA1112378A

CA1112378A - Flotation of deep mined coal with water-in-oil emulsions of sodium polyacrylate

Info

Publication number: CA1112378A
Application number: CA313,069A
Authority: CA
Inventors: Robert E. Finch
Original assignee: Nalco Chemical Co
Current assignee: ChampionX LLC
Priority date: 1978-01-19
Filing date: 1978-10-11
Publication date: 1981-11-10
Also published as: FR2414958A2; MX154137A; GB2012621A; AU507430B2; DE2850988A1; AU4177178A; FR2414958B2; GR70023B; ZA786278B; GB2012621B; ES475446A2

Abstract

ABSTRACT OF THE DISCLOSURE

A method and treating agent for increasing the yield of deep mined coal mined from a site 100 feet or more below the surface where the particles in the coal are concentrated by froth flotation. This method consists of utilizing as a promoter or frothing aid about 0.05 - 1.5 lbs of sodium polyacrylate latex per ton of dry coal (0.017 - 0.5 lb of dry sodium polyacrylate per ton of dry coal), having an average molecular weight of about 100,000 to 1,000,000 and more, with a preferred range of 1,000,000 or more. The preferred promoter or frothing aid for deep mined coal is a water-in-oil latex of sodium polyacrylate preferably used with an alcohol-type frother. The latex may be utilized neat and self inverts with the assistance of an oil-in-water surfactant (or activator) and the water in the system upon application to form an oil-in water emulsion, or it may be used as a two-part system with an activator (aqueous) to promote in-version. The latex emulsion has demonstrated superiority as a flotation promoter for deep mined coal over the dry polymer and exhibits synergism over the dry polymer and over the components of the latex emulsion includ-ing a paraffin solvent, a hydrophobic emulsifier such as sorbitan mono-oleate, a solvent such as Espesol 3-E (Charter; an aromatic blend) and stabllizers such as polyisobutylene and aluminum tristearate.

Description

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 '~ .

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-~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.

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-~ 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.

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* 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. .
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: 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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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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 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 emulsion of sodium polyacrylate in a dosage cal-culated as 0.017 - 0.5 lb. of dry sodium polyacrylate per ton of dry coal.

2. The method of Claim 1 wherein the water-in-oil emulsion contains sodium polyacrylate, a paraffinic solvent, a water-in-oil emulsifier, an oil-in-water activator, and a minor amount of stabilizers.

3. The method of Claim 1 wherein the water-in-oil sodium polyacryl-ate emulsion inverts on usage and contact with water to an oil-in-water emulsion.

4. The method of Claim 2 wherein the oil-in-water activator is add-ed separately.

5. 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 conforming to the following formula:
a) from 5-50% by weight of the emulsion of an aliphatic hydro-carbon liquid;
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 water-soluble sodium polyacrylate, c) from about 0.25 - 10.0% by weight of hydrophobic surfactants capable of stabilizing the emulsion.