Sat Feb 23 00:28:37 2002 Page 2 of 9

RESEARCH NEEDS IN FLOtCULAllON

~)~.",;;.

i';~,,'~;~

Brij M. Mclldg11Center for Research tn ~n1ng and Mineral Resources

Department of Materia1s Science and EngineeringUntversity of Flortda

Gainesvfl1e. Florida 32611

P. So8asundaranHenry Kru.b School of Mines

Department of Mineral EngfneeringCol'-fa ~iYers1ty

New York. New York 10027

~

~~!Aggregation of fine particles with or without added poly~e~s is

of major iruportance in mineral. chellica'l and cerl..lc industries.Although flocculation phenoMenon is ext!ftsively applied in these andother industries. the bas1c forces fnvolved in pol~r adsorption andsubsequent aggregation of pol~r-coated particles a~e not wetlestablished. Most of the successful applications are so far based anempirical test results. It is important that fundamentals of thevarious processes 1nvolved in aggregation are u~der5tood for achievingoptillUn results.

RESEARCH NE~"DS

~f:1~j ~velOD8ent in Pol.Yller AdsorDtiOll and Floccu1a~

Polyner adsorption is characterized by (i) .ostly non sel~t1veadsorption. (ii) difficulty in desorbin9 the adsorbed MOlecules(frrevers1bfi1ty of adsorption). and (1i1) preferent1a1 adsorption ofhigh molecular weight tractions. The theo~etic.1 and expe~1~ta1ISpects of po 1ymer .dso~pt 1 on on soli d subst rates have recently beenrevi~ by several luthors (1-3). Although co~s1d.r.ble progress hasbeen made 1" theoretfca1 developments. experiMental verificatfon ofthe MOdels has been difficu1t because of the unavailability ofsu1table instru.entlt1on.t~.

%~

~..,

~

.wI

V4

:rom (613) 998-2606 Order' 02563887DPO1991445: i ic .

Sat Feb 23 00:28:37 2002 Page 3 of 9

592 FI.oo."'1.JI.ATI

Order' 02563887DPO1991445

;i:::

Sat Feb 23 00:28:37 2002 Page 4 of 9

ISOI.TDA110~ R. M. A~gil a."1d P. Soma$undaran 593

sedimentation balance and to est1.ate the floG size from thesedi~ntation t1me measurements (8-11). Photographic techniquQshave been employed to measure floc sizes (8. 12). De~sities ofthe flacs produced were estimated from simultaneous measurementsof f1oc size and free sett11ng velocity i" a suspending fluid.Further researth in experi~"tal te~hntques is needed to obtainmore conclusive results rega~ing these properties.f!:

',::I ~: :!:-

"i

Ii

conformation of theI region fs expected to:le distance and,Applications of tech-

. infrared spectro..19~etic resonance. andrtion regarding shape

a function of t1~ is'actical p01nt of viewItered 1 n realIn studying the

flo, Structure: In agg~egation of anisotropi, particles it isexpected that orie"tation of the particles will influence theaggregate structure and propert1es such as shear strength. One ofthe _jar difficulties in studying structure of particle aggre..gates using Microscopic ~thods has been introduction of artificesdue to the saqple preparatio~ techniques. For example, prepa-ration of samples for SEM/TEM ~alysis involves evacuation ofsamples under high vacuum, and ca" change the arrange.ent of theparticles in the aggregates, thus altering its structure. Thisproblem is 81ni.ized in a recently developed freeze fracturetechnique whIch ensures that the floc structure is not mod1f1ed toa significant extent during the sanlple preparation stage (12-16). This has been accomp11shed by freezing the samples at ratesthat are considerably h1gher than the rotational and translationaldiffusion of the particles whiclt deterllines particle displacementin the suspending medium. Besides obtaining a reliable micro.graph, the quantification of orientation of particles is necessaryto evaluate the effects of relevant parameters on the structure.Attempts have been made to obtain quantitative estimates oforientation of particles in two dimensions but further work isneeded to deve10p theories to quantify orientation in threeri1inensfons so that the results can be applied to the real systems.

locculatfon) 1s a'owth and sizeto develop thepartly due toevant parameters,

I ' ';,

it:

~ considered to be'a) adsorptfon ofla1 char1ges in the~en po lymer--coatedlregates (7). At, the rate of, depend on a number of:in9 the problell evenadso~ptfo". and tomentally. }t)wever.~f polymer~ress 1n theoreticallev1 sing llethods to

E12c~tt~ar St!:~!!g~~: It has bee" reportec! that flocs produced bybridging mechanisM usually eKhibit a higher strength than those byelectrostatfc patch model or cha~ge neutralization (18). A1so.floc breakage in bridging flocculation is often irreversiblewhereas in the other two cases it is reversible (18. 19). In theearly stages of floc

From (613) 998-2606 Order' 02563887DPO1991445

A~~'

! fr 594

Sat Feb 23 00:28:37 2002 Page 5 of 9

FI,occuLATION. SEDI~fENTA11ON AND CONSOUDA'nON

~culat10f1~onso1idation Research

..Flocculation of fine particle suspensions can reduce the t1~

required for sedimentation and conso11datfon processes. Effects offlocculation in consolidation. Which sc.etiaes occur over severalyears. have not been studied syste.at1cally. Since po1ymer employedfor floccu1ation will degrade in a ~tter of weeks or months. it isimportant that the1r effect on particle packing is investigated toachieve optimum consol1datfon of the settled mass.

The major limitation involving long-terln consolidation studies onthe laboratory scale so far has been the duration of testing.However. development of centrifuge modeling techni~ues and simulationof consolidatfon processes using bench sca1e centrifuges have made itpossible to screen reagent and i~ortant f1occulation para8etersrelevant to the conso1idation procass (24-28).

It should be noted that conso1idation of fine particlesuspensions, especially of clays, is limited by particle size and lowself-wefght conso11dltion forces. Attempts nave been made to usecoarse particles of sand. with or without flocculants. to achievegreater consoiidation (27,28). The addition of coarse part1cles,which can either be .ixed N1th the clay mass or spread over it.increases the consolidation forces. Bench scale and field scaleeva1uations are in progress to establish the technical and e

From (613) 998-2606 Page 6 of 9Order # 02563887DPO1991445 Sat Feb 23 00:28:37 2002

I i~'!"KmATJON

R. M. Moudgil aDd P. SomlI5undar8J\ m

1n the flocculation process. Synthesis of polymers which are not1tnear. such as blo,k and branch copolyners and their effectivenessin flocculatlon need to be evaluated.

I~::

[~:,:~:I ~

't".;

tJ::::~:~~

~I~"'*

.~

ii"~;t

:~~~j{ ~;.~.""

",,*:

l

:

.;,:.~~~.~:

~~~~"'l'i[:

It

can reduce the time~cesses. Effects ofoccur over several1nce polyller employedeks or ~ntns. it isis investigated to

Gnsolidation studies onGn Of testing.hniques and simulationntrifuges have made it1ation parameters

Multi-C~ponent Flocculatj~-

In practice, suspensions of fine particles of different surfacechemical properties and physical properties are encounte~ed. Forexample, waste produced in tar sand operation contains organ1c siltsand fine sand-clay IIlxtures. The synergistic effect of variousconstituents in such cases may require different approaches to achievethe desired aggregation. Most of the research efforts rel~ted tonMJlt1-.compcnent flocculation so far have been emp1r1cal. In order tomeet futu~ challenges in the waste disposal area further work inunderstanding the floccuiation of mixed inorganic and organic materialis required.

~-AQueous Dis~si9n/F'occulat.i.onfne particleparttc1e size and low

e been made to useulants. to achievef coarse part1clei.spread over it.

e and field scalechnical and ~ooOl1lfc

Dispersion and aggregation of fine ~rticles in non-aqueous mediahas acquired added importance because of applfcations in hightechno1ogy areas. e.g. in e1ectrophoret1c display dev1ces. depositionof coat;ngs. e1ectrophoretic deve1opment of latent 1mages and removalof particulates from non-aqueous media. The basic mechan1sms ofcharge developments in non-aqueous media and the role of additives inmodifying surface chemica' characteristics of partfcles are not yetcomplete1y understood. further work is requ;red in develop;ngunderstanding of the role of surface charge in dispersion of particlesin non-aqeuous ~dia.

r predict1ngIJt for theirQ the consolidat;onIllining the role of. further work,chemical parameters.enhance the

0, the centrifugeIJnt thec r-elevant~stem.

~l~~.!!e Flocculatio!!.

Selective f1occulat1on techniques for solid-solid separationinvolves aggregation of only the desired ~ompon@nt leaving the otherconstituents dispersed in the suspension. The second ~st importantr-equ1re.ent next to good dispersion of all the constituents is these1ective aggregation of the particles by polymers. Several reviewshave discussed the principles under-lying the selective flocculationprocess (29.30). However-. cO8l\er-c1al applications of this techniqueare li.ited because of lack of basic 1nfonlation about the polymer-adsor-ption and flocculation processes. In achieving the selectivityin flocculation a1most aT' past atte~pts have relied ~ selectiveadsorption of the polymers on the substrate. A l18ited effort hasbeen made to achieve the desired $e1ectivity by selective desorptionof the species from the surface (31). It is suggested that-tnlS routebe investigated further- because of the flexibility it can pr-ovide inselective adsor-ption of the polymers on the solid sur-face.

v

"

-ide distribution of~e.1 is probably most~mer n.>lecules undert the adsorption and9gregation process. As should enhance then polymer synthecsis.f1arr-ow 1IM>1ecular

As discussed earlier. factors governing the aggregate propertiesneed to be established to obtain flocs of desired structure andproperties.

1y exhibit a flexibleonlation is availableand their effectiveness

It is not uncommon to identify suitable conditions for sele~tivef1occulation on the basis of single co~onent tests. However. mostoften the selectivity is lost when mult1 component tests are

,,:, ~.;:""..

:rom (613) 998-2606 Order # 02563887DPO1991445"~j: ~

1 : ~

Page 7 of 9Sat Feb 23 00:28:37 2002

S% ~wa.~LATK)N. SEDIMrNrATK>N AND CONSOI.mATJON

tonducted. Partly the loss of selectivity, at least in salt type!linera1!;, can be attributed to the effect of dissolved tons (32-34).The rea$ons for the loss of selectivity 1" salt type lIinerals andother systems need to be established 1n order to realize the fullpoter\tial of the selective fioccu'lation techf1ique.

Scale Consideration!;

.~~~I.;,., !I

The role of ag1tation intensity and mode of agitation infloccu1at1on process cannot be over88phasized. In the case of dilutesuspensions flash mixing of c;hemic;als. sORletimes in line. ispracticed. On the other hand. mixing of polymers under more gentleconditions is des;red in dilute suspens;or;s. It is reported thatrecycling of previously flocculated so'ids will invariably result inreduction in the pol)mer dosage (35). With more c;oncentratedsuspensions of solids. stage1ltise addition of the pol}'fter. therefore.may result in better dispersion. In cases Where a combination ofi no~anic and organic species are used. the fonner 1 s added prior tothe organic reagents. Most of these observat~ons lack scientificbasis. For design and scale up of tlt.e equflJl'ent 8Iptoy~ in floc-culation and sedimentation processes it is important that theunderlying mechanisms are understood.Ij~:~ACKNOWLEOOEMEHT~

The ituthor~ iic.knowledge partial financial support of thi~ wrk bythe Florida Institute of Phosphate Research (FIPR Contract 182-02-023(8tf4) a~d '84-02-037R (PS)). ~e of the authors (Btt4) alsoacknowledges additional support by NSF-PVI Award (CPE '8352125). Anyopinions, findings, and conclusions or recOMmendations expressed inthis publication are those of the authors and do not nec~$$arilyreflect t~ views of tr.e Florida Institute of A1osphate Research.

~ \.~ .!. . I ., ~ ,; ~:

f . ~;.! . "

REFER!

1. Vincent. 8. and S. "'ittingtcn in Surface and Colloid Science. E.Matijevic. ed.. Vol. 12. John Wiley I Sons. ~ York. 1981.fleer. G. J. and J. l,yk18la in ~sorption f,.~ Solution~~~Sol id/liquid Interface. G. D. Pii';f1tt and C. H. ~c~ster. eds..kadfSifc-Press-. .-w York. 1983.

2.I'

II

3. tessel1nk. F. Th. in Mscrption fr~ Sol ut10ns at theSol id/li~Interf.ce;-~. D. parfitt and C. H. ~ster. eds..~-aa_fCPress:~Ycrk. 1983.

4. Glasgow. l.. A. and .J. O. Hsu. AIChE Journal.]!!.. 779 (1982).Hog9. R.. J. Colloid Interface Sci.. !Q.?. 1232 (1984).

.099. R.. in .~~!! 1cj_s_~~£

5.6.

I

~

From (613) 998-2606 Order' 02563887DPO1991445 Sat Feb 23 00:28:37 2002 Page 8 of 9

OOLmAnON Ii 8. M. M,"w~il HI1d P. Soma...unt1Hnm meast in sa1t typesolved ions (32~34).type minerals andrealize the full

1

8.~e90ry, J. and I. St1e1hin. British Pol,y11er J.. .! 41 (1974).Klillpel. R. C.. C. Diri(:an and R. .k>g9. "~asur~nts ofAgglc-.erate ~nS1t1es in Flocculated Fine Partic1e Suspens1onst"presented at the 15th Annual ~eting. Fine Particle Society.Oriando. FL (1984). Submitted for publication to ParticulateSC1ence arK! Technology.

t ' . ~. ~

] ~i ~

9.

10.

~I

agitation inIn the case of dIlutein line, is

s under more gentleis reported that

invariably result inconcentratedpo1Y1fter-, therefore.it combination of

er is added prior tos lack scientific:

8Iployed in floc-tant that the

11.

Dirican, C., "The Structure and ~owth of Jggregates inFlocculat1on,- M. S. Thesis, The Pennsylv~n1a State \tt1versity,l)1iversity Park, PA (1981).

Kl illpel, R. C., -The Structure of .JQg108erates in Fl occul ation ,"M. S. Thesis, The Pennsylvania State (k\fversfty, lkIiversfty Park,PA (1981).

Ray, D. T., "AgglCJRerate Breakage in Flocculated Suspensions," M.S. Thesis, The Pennsylvania State 1k11versfty. \ttiversity Park, PA(1985) .

~udg1l, B. M.. "Aggregation of ~osphatfc Clay,- in Proc.Consolid.tio_~_~~n~ l:ewatering of Fine Particles, U. S.aureau ofMines, Tuscaloosa, Al (198Z).,.."

I~i .i ~ :~

! ~

.~

ii~

I~I

;:

:j

.;

I

I ~::

iij!~,,~"

~~~,~

ji[i

13. ~udg1l, B. M. and B. ft)ghoogh1, "A Freeze-Fracture Technique forStudying (),1entation of Particles in Flocs," presented at the 5thInternational Conf~ren'e 0/\ Surface and Colloid Science and 59thColioid and Surface Science S}'Dposilm, Clarkson University,Potsdam, NY, June 24..28. 1985.

upport of th1s work byR Contract 182-02-023(BMM) al $0(CPf '8352125). MY

ations expre$sed innot necessar;1y

osphate Re$earch.

14. It>ghooghf, B., "Flocculation of Palygorskite Suspensions and theOrientation of Particles in Flocs," M. S. Thesis, lkIivers1tyofflorid~, Gainesville, FL. 1985.

15. Stewart. R. F and D. Sutton. Chem. Ind.. May. 373 (1984).

16,d Colloid Science. E.

Pew York. 1981 rCJI So1ut1ons at the

. H". ~c,;eSier-.*-eas.-. ,7.

Stewart, R. F. and D. Sutton in Solfd-lfq\Afd Separation. J.Gregory. ed.. Ellis Harwood. Inc-:;-crrrc-nester. U. t.. III (1984).

Buscall. R.. R. F. Stewart and D. SlAtton. Filtration andSeparat1on, ~. 183 (1984).

18. Ditter, W., J. E1senlauer and D. Ibrn in The Effect of ~lymersin Dispersion Properties. '!}I. F. Tadros. ea., ~ad8R1c-'p;.ess';"""london (1982).-

ons at the:. H. ~cheste;r, eds

19. Stratton, R. A.. Toppi J..~. 141 (1983).

20. Hsu. J. P. and l.. A. Glasgow. Chem. Engrg. Ca."nications. 28.127 (1984). --Jeffrey. D. J. and A. krivos. AIChE J..1.?:.. 417 (1976).

. .~., 779 (1982).232 (1984).

ion Stability, E. D.--sefies-"NI). ~40,:. (1984).

21.

22. Kao. S. v.. l. E. Nielsen and C. T. Hill. J. Co11oid InterfaceSc.i...E. 358 (1975).

:~ (613) 998-2606 Order' 02563887DPO1991445.1; ,"""--: ~: ': ; j,

. : ' :,

Sat Feb 23 00:28:37 2002 Page 9 of 9

598 FLO