CA1095265A - Process for clarifying iron ore slimes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Use of quaternized Mannich bases of low molecular weight poly-acrylamides is highly effective in clarification of iron are slimes.

Description

This invention relates to a secondary recovery pro--~ cess ln the settling of mineral ores. More particularly, this invention relates to such a process wherein fines arlsing in mineral treatment waters are recovered by use of a low mole-cular weight quaternized dimethylaminomethyl acrylamlde polymer.
Recent developments ~n the field of water~soluble ; polymers have led to materials that are effective in water~
treatment to remove undesLrable materia1 suspended th~reln.
The separation of suspended particles from aqueous suspenslons ~;; 10 thereof is generally referred to as "flocculation". Such general term can lnclude ~ wide range of aqueous ~ystems varying from a minor amount of lnorganic solids in ~queous suspension, such as raw water, to high concentratlons of or-ganic wastes in aqueous suspenslon, such as sewage sludges.
Because of this widely diverse n~ture of the various solids~
-water systems~ the agents provided for such utllity are gen-. . ~
erally provlde~ in a fo~m that offers vers~tile per~ormance, i.e., suitable for use with a wide variety of solld-water systems.
For certain 301ids-water systems, such as raw waters, these polymerlc agents are used to clarify the water by removal of inorganic solids suspended therein. For .; other solids-water systemsJ such as sewage sludges, the poly-meric agents are used primarily to dewa~er the sludge so that the sollds may be readlly dlsposed o~ without prohlblt-~; ive amounts of water being associated therew1th~ The~e dis-;i tinct applications of the polymerlc aKents gi~e ri6e to dif-; ferent requirem~n~s a~ to the nature o~ the agents employed~
One teaching wi th respect to certain prior art flocculants is that, in general, increased ef~ectlvene&~
arlses with increased m~lecular weigh~ of the polymeric agenk .~
em~loyed, see U.~. Patent 3,738,945 for example. A~ther ,~

5;~6~;j teaching with respect to certain other prior art flocculants is that there is ~ certain high mol0cular weight value at which maximum ef~ectiveness occurs and above which e~ective-ness remains essentially unchanged, see U.S. Patent 3,897,~33 for example~ AccordlnglyJ one seeking an effective flocculant for the various solids-water systems contemplated by such application of polymerlc agents would provide such agent ln high molecular weight range.
Typically, polymeric agents that are used in ~loc-ulation applications have molecular weights in excess of about 200J OOOJ usually ln the range of about 500,000 to several millionJ and in difficult solid-water systems, such a8 sewage sludgesJ ~requently higherJ depending upon the chemical nature oY the polymerlc agent. Most products that have been available for commercial use have been in the high molecular weight, range so a6 to provlde ver~atile utillty in the wide variety o~ applications in which they are useful.
Al~hough the co~mercial products po~se88 ~ome degree o~
versatility ~s to u~age, they do not n~cessarily provide the optimum p0rformance in any given appllcation.
Certain polymeric flocculanta can be made dlrectly ~rom suitable re~ctant~, ~uch a~ reaction product~ of epi-chlorohydrin and dimethylamine or ~ree radic~l polymeriza-tion product~ of ~uch monomers aR diallyld~methylammonium chloride. Other polymeric flocculants may be made by pre-p~ring a polymer ~rom a re~ctive monomer not containlng certain deslred ~unctionalities and ~ub3equently mo~i~ying the pre-formed polymer to provide the iunction~litie~ des-ired. In th1s procedure, the ~unctlonality o~ the pre-~0 formed polymer can be varied in a number of re~pects but the degree o~ polymeriæation as Lt a~ect~ molecular weight o~ the modi~led polym~Y i3 determlned by the polymer pre~
-~ormed r

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Acrylamide is a highly reactlve monomer that is widely used to provide pre-formed polymers that can be readily modlfied chemically to provlde alternative or additional functional~ty for speclfic end-uses. Thus, acrylamlde poly~
mers may be controllably hydrolyzed to provide acrylic acid functions on the polymer structure and provide an anlonic polymer. Alternatively9 formaldehyde and dimethylamlne can be reac~ed wlth the amlde group~ of the polymer to provide substltuent dimsthylaminomethyl functionality thereo~ and provide a catlonic polymer. Because of the high reactivlty of acrylamide monomer, however, the pre-forme~ polyacryl-amide used for subsequent chemical modlfication is usually in ~he molecular weight range of about 200~000 to 5, OOOJ 000~
since such is the degree o~ polymerization normally obtained.
~o obtain polyacrylamide of molecular weight out~ide this range, special preparatlve procedure~ are n~cessary. For higher molecular we~ght polyacr~lamides, for example, highly purified monomer is required. hlthough procedures for obtain-ing lower molecular weight polyacrylamides are available, uee of such t0chniques is not ~enerally considered with respect to ~locculation applications becau~e o~ the preference for high molecular welght polymers.
The intrinsic viscosity of` a polymer is obtained by measuring the viscoslty o~ varying concentrations of the polymer in a specific solvent and extrapolating to avalue at zero concentration3whlch ls the valledesignated as "lntrins~c viscosit~'~ The vlscosity i~ the resistance of the liquid ~rm~
o~ the polymer to flow and ls a characteristlc property measur~
ing the combined effects of adhesion and cohesionO From the ln--~o trlnsic viscosity can be calculated the molecular ~elght ofa polymer by use of appropriate equations. As is apparen~,the intrin~ic viscosity~molecular wei~ht relationshlp of one poly-mer type ~ill dlffer from that ofanother polym~r typeO Accord-;2~

ingly, the intrinsic viscosity of a polyacrylamide of a specific degree of polymerization will differ ~rom that of a chemically-modified polyacrylamide of the same degree of polymerization. The f'act remains, however~ that as the mole-cular weight, or degree of polymerization, of a polymer in-creases, the intrinsic viscosity thereof also increases in any particular series.
A quaternized dimethylaminomethyl polyacrylamide ha~ been previously disclo~ed for the treatment of sewage sludges~ see U.S, Patent 3,897,333~ The use~ul polymer dis-closed 1~ one stated to have an intrinslc visco~ity of at lea~t 0.5 declllters per gram and the examples used to illus-trate the invention employ polymers having intrinsic viscos~
ities o~ 1~0 and 2.5 deciliters per gram. For ~ quaterniæed dlmethylaminomethyl polyacrylamlde containing at least 50 mole percent of such quaternized groups to have an intrinsic vis-coslty of at least 0, 5 decillter~ per gram, the pre-formed polyac~ylamide mu~t ha~e a molecular welght of about 1309000 as a minlmum and to con~orm to the exemplifled species must have a molecular weight of about 350J 000 to l,500,0000 The degree of' polymerization ~or such polymers would be at least 1,800 and~ as exempli~ied~ from about 5,000 to 20,000. At this range o~ degrees of polymerization, the polymers of the reference are said to exhlbit equivalent performance in de-watering of sewage æludges, regardless o~ the actual degree o~ polymerization in ~uch range, Absent any further teaching by the reference, one would be led to believe that the same range of lntrinslc vi8cos~ ties would be the mo~t ef~ectiYe ~or other ~locculation operation3.
3o In accordance with the present invention, there is provided a process for clarifying ore slimes containing up to about 100,000 part~ per milllon of suspended ~norganic solids with a particle ~lze of up to about 2 mlcrons which ,. . , ~ . .. ... .. ~

comprises mixing wlth said ~limes from about 0.1 to 1,000 parts per million, based on the ~olids content of said sllmes, of a polyacrylamide havlng a content of at least about 50 mol percent of amide groups chemically-modifled to contain dl-methylaminomethyl groups9 the dimethylaminomethyl groups being further modified by quaternization with an alkylating agent, the chemically-modified polyacrylamide having an intrinsic viscosity in the range of about Ool to 0.5 deciliters per gram measured in 3 molar NaCl at 30C, to form suspendible f]ocs ~rom a portion of the solids presentJ maintainlng said SU8-pendible flocs in suspension in said water until a substantial portion of the remaining solids are adsorbed thereto; and thereafter settling the resulting flocs formed.
The process of the present lnvention employs a poly-acrylamide chemically modified to contain certain quaternlzed dimethyl~minomethyl groups and of low molecular weight Un-expectedly, such polymer type exhlbits lmproved perform~nce in clarifying ore slimes at lower molecular weight values than do other polymer types and o~fer advantages over higher 29 molecular weight polymers of the same type. Because the hLghly effective polym~rs of the present lnvention are of low molecular weight, numerous-advan-tages arL~e, which lnclude the following:
1, The polymers used ln the process of the present in-vention develop maximum effectiveness in ore sllme clarifi-catlon at low molecular weight, thus eliminatin~ disadvantages associated w~th prov~ding high molecular weight polymers, 2. Because preparation of low molecular weight polymers t~kes less time than does preparation of h-lgh molecular weight polymers 9 greater productivity is obtalned for a reactor of given capacity in a specific time period.
~. Because low molecular weight polymer~ provide low solution viscosity, chemical modification can be achieved at ~ 5 --6~i higher polymer concentrations than in the case of high molecular weight p~lymers, 4, Because chemic~l modification can be achieved at high polymer concentration chemical modlflcation is more readily and completely effected.
5. Because the polymer of t,he present invention is pro~
vided at high polymer concentration, shlpping costs per unit weight of polymer are reduced, 5, The low molecular weight polymers of the present in-vention provide smaIler absorbent flocs which adsorb addit-ional suspended solids of the ore slimes and provide greater clariflcation than do high molecular weight polymers which ; provide larger, non-absorbent flocs.
7, The polymers of the present invention offer cost--performance advantages over other polymeric fl.occulants because of their processing advant~ges, .1 The polymor~ use~ul in the proces~ of the present invention i5 a polyacrylamide chemically-modified to provide ' a polymer consisting essentially of repeating units o~ the ~-~ 20 . structure:

:: f F CHa - CH -- ~ ~H2 - CH - _ 1=0 ~=0 ( I HD ~ I _ NHZ
LC~3--~--R .A~
x n ; ~
wherein A~ is an anion, R ls alkyl o~ 1-3 carbons or ~: ~0 hydroxyalkyl of 2-3 carbons, x is a mol ~raction of at -. least 50 percent~ y is a mol fraction of up to about 50 percent and represents unmodified acrylamide unitsJ and n is an integer in the range of about 100 to about 2,000 5~

to provide the chemically~modifled polyacrylamide ~lth an intrinsic vi3coslty ln the range of about a 1 to 0~ 5 decl-llters per gram.
In order to prepare the polymers useful in the pro-cess of the present lnvention, it is ~lrst necessary to pre-pare a low molecular welght polyacrylamide ~n aqueou~ solut-ion. By "polyacrylamide" is meant a polymer whlch consists essentially of repeating units of acrylamide. Although it is generally prefered to employ a homopolymer of acrylamide ~or optimum results in use, it is also possible to replace part of the acrylamide units with another monomer in amounts which do not inter~ere wlth the advantageous perfo~mance of the poly-mer in ore slimes clarl~ication. Other monomers that may re-~, place part of the acrylamide monomer include acrylonitrlle, methyl methacrylate, styrene, diallyldimethylammonium chloride, methacrylamide, N,N'-dimethylacrylamide, and acrylic acid. If ~ an acidic monomer is used, it should constltute le~s than 10 i~ mol percent o~ the polymer. It ls generally pre~er~ble to introduce a high degree of chemical modi~ication in the poly-acrylamide and, therefore, the amount of comonomer employed should be mlnimized ~n ordar to achieve ~uch preference. The .. . .
polyacrylamide, accordingly, will consist essentially of ~t least 50 mol percent o~ acrylamide groups that have been chem-ically modified to provide quaternized dimethylaminomethyl ~` 25 groups thereon and preferably the balance of unmodlfied acryl-amide groups or of comonomer units that do not adversely af-Pect the performance of the polymer in the clarificatlon of ore slimes. Both unmodlfied acrylamide units and units de rived ~rom another comonomer m~y be present with the required content of quaternized dimethylamlnomethyl acrylamlde groups.
In preparing ~he polyacrylamlde, an ~queous ~olution of about 10 to 505 preferably 15 to 30, more p~e~erably 20 to ` ", "`' ' ' ` ", ' ` ~

s ?5 welght percent of acrylamide9 or monomer mixture9 is em-ployed. A number of techniques are known which can be em-ployed to provide the deslred low molecular weight polymer~
Use o~ initiator contents of at least about 0,1 percent are e~fective. The use of high reaction temperature such as at least 50C,, preferably about 70C 9 to 100C,, is also e~
~ective using the initlator content as sta-ted. A chaln trans-fer agent, such as i~opropanol, ls also effective but is not necessary, In instances ~herein an impurity, such a~ ionic copper, is presentJ a chelating agent, such as ethylenediamine tetraacetic acid may ~e used to combine with this impurity.
However, the presence o~ lmpurities and use of chelatin~ agent~
is not necessary to prepare the low molecular weight polymer.
Free radical initiators useful at the concentration speci~led include, for example, ammonium persul~ate, potassium persulf`ate, benzoyl peroxide, bromobenæoyl peroxide, t~butyl hydroperoxide, and hydrogen peroxide in the presence o~ fer-rous ion, As indicatedy the inltiated polymer solution is heat~
ed to 50C,, or hlgher~ and held at the selected temperature until a polymer o~ desired molecular weight is obtained, The polyacrylamide should have a degree of polymerization ln the range o~ about 100 to 29000. In the case o~ a homopolymer o~
; acrylamide, -this will correspond to a molecular weight o~about 7~000 to 140,000. After the de~ired polyacrylamide is provlded9 t,he reaction solution is cooled to about, 40C~ to e~ect chem~cal modificatlon with ~ormaldehyde and dimethyl~
amine.
E`o ~aldehyde may be used as a 20 to 60 weight per-cent aqueous ~olution and dimethylamine is used as a 20 to 55 weight percent aqueous solutlon, The molar amount of ~ormalde-hyde employed must be sufficient to chemically modi~y enough acrylamide groups to provide at lea~t 50 mol percent of modi-.

2~

fied acr~lam~de groups in the final polymer but the amount of formaldehyde used may be su~ficient to provide a polymer con-sisting essentially of modified acrylamide groups~ preferably a polymer containing 60-90 mol percent of modified ae~ylamide groups~ The amount of dimethylamine employed ln the chemlcal modification of the acrylamide groups will constitute the mol-ar equivalent amount of dimethylaminè plus about a 1 to 10 mol percent e~cess, preferably about 5 mol percent e~cess.
The reaction to provide chemical modl~ication ls preferably conducted at about 40C., ~or suf~icient time to complete the reaction; generally in about two hours, Temperature and ap-`~ propriate time modlfications may be made in accordance wlth conventional procedures for providing this chemical modi~lcat-ion, which is also called Mannich base formation.
Qfter the reaction with ~ormaldeh~de and dimethyl-amine i~ completei the reaction product is quaternized with an alkylating agent to a pH in the range of about ~ to 7O Pre-f0rred alkylating agents are dlmethyl sulfate, and meth~l chlo~ide but other alkylatlng agents may be usedO The qu~ter-niæation is preferably c~rrled out to involve e~centially all of the dimethylaminomethyl groups provided b~ complete re-action 1~ not required so long as the minimum quantity of ; quaternized groups is provided. In the event that all of the dimethylaminomethyl groups are not quaternized, the unquater-ni~ed dlmethylamlnomethyl acrylamide will repre~ent a part o~
the polymer composition. With respect to the indlvidual steps o~ polymer preparation, chemica! ~odific~tion of the poly acrylamide to provide Mannich base modification and quaterniz~
ation of the reactlon product~ the conditions of reaction and useful reactants are known~ The process of the pre~ent in-vention requires that the molecular weight of the lnitlal polyacrylamide be in the low specified molecular weight range.

_ g _ , ' - ~ '- ' ,- ~,,.

~ss~s The polymer obtained by the above descri.bed process is a stable product which contains from about 50 to lO0 mol percent of quaternized dimethylaminomethyl acrylamide groups.
The degree of polymerization of the chemically-modified poly-acrylamide will be substantially the same as that of the start-ing poly~crylamide slnce no increase in polymer backbone mole-cular weight is known to occur as a result of the chemical modification effected. Accordlngly, the degree o~ polymeriza-; tion of the polymer will range from about lO0 to 2,000. As a.result of the chemical modification oP the polyacrylamide, the molecular weight of the repeating unlts will be increased dep-endin~ upon the extent to which chemical modification is e~fect-ed and, accordingly, the product polymer will have a higher molecular weight than the starting polyacrylamide although the degree of polymeriza-tion is unchan~ed. Also, as a r~sult o~
the chemical modification of the polyacrylamide, the result-ing product wlll have dlfferent rheological properties from those of the starting polyacrylamide and consequently the in-trinsic viscosity va.lues of the starting and product polymers will differ. The intrinsic viscosity of the polymer used in the process of the present inventi.on ~hould be in the range of about 0.1 to 0.5, pre~erably about 0,3 to 0,5 deciliters per gram when measured in ~ molar sodium chloride at 30C.
The ore slimes which are effectively clarifled by the polymers of the present invention are those which contaln up to about 100, 000 parts per million of suspended inorganic solids of a particle size of up to about 2 mlcrons. Such ore ~ slimes arise as effluents from processing ores to separate .` valuable minerals there~rom The slimes will contaln small portions of the desired mineral values and gangue materlals.
~ Any ore sllme that responds to clari~ication with a cationic; polymeric flocculant may be processed by the process of the 35~6~

present lnventlon~ The process of the present invention has been found to be particularly effective in the clarification of iron ore slimes.
In processing the ore slimes9 two advantages arise.
Such processing recovers additional ore values that would otherwiqe be lost and reduces the suspended solids of the effluent water tha+ must be discharged. The process o~ the present ~nvention by providing improved clarlfication of the ore sllmes increases the amo~mt of mineral value~ recovered from the slimes, thus provlding an increased yield thereo~
and reduces ecological problems arising from discharge of the effluents from ore processing~
In carryin~ out clarification of ~ ore ~lime as de-fined, an ePfective amo~nt of' a polymer of the present invent-ion is mlxed with the slime to be clarified~ By "an effective amount" is meant that amount which produces a desirable clari-fLcatlon of the slime belng treated. Such amount will vary widely depending upon the nature of the slime being cl~ri~ied~
the nature of the chemicall~-modified polymer employed, the &pecl~ic degree of clarification desired~ and tha like. A~ a general rule, clarification agent~ ma~ be used Ln the range of' about 0~1 to 1,000 part~ per million (ppm) based on the solids content of sllme being proce~sed~ The polymers of the present invention have ~enerally been ~ound to be e~ective ln the r~,nge o~ about 0,5 to 100 ppm, same basls.
A~ter the chemically-modi~ied polymer ha~ been mixed with the slime being treated, ~ma~' absorbent floc~ in~olvlng part of the suspended solidæ will immediately fo~m. These flocs, because of their natureJ can be kept in suspension by 3o application of suitable agitation~ usually slow speed~ and whlle in suspension will ad~orb additional suspended sollds to e~ect a greater degree of clariflcatiGn than would be the . .

case lf the initial ~locs were immediately settled and the supernatant liquor separated. The duration o~ time over which the lnitial flocs are maintained in suspension will ~ary wlde~
ly dependlng upon the n~ture of the slimes being clarified and the content of solids thereinJ the particular polymer em-ployed in clarif`ication, the e~tent to which clarlflcatlon ls deslr~d, and the l~keO It i~ generally desired to remov2 a 3ubstantial amount of the suspended solids remalnlng ln the slimes being clari~ied by adsorption by the inltial ~locs formed. Preferably, the suspendible flocs are maintained in suspen~ion until the turbidity of the treated water ~s ~ufflc-iently clarlfled to provide a residual Jackson turbidity value o~ leæs than about 350~
- A~ter the su~pendlble floc~ have adsorbed a suitable amount of the remaining ~olids in ~uspension, the resulting flocs are allowed to settle3 thus provlding supernatant clari~
fied water and a sediment of flocculated inorganic solids.
The clarlfied water may be decanted or otherwise recovered from the sedlment in accordance with conventional procedures involving the processing equlpment employed. The water ob-tained by use of the clarification process o~ the present in~
vention will have a lower residual turbidity than water clari fled by equal amounts of other polymèric flocculants~ an equal residual turbidit~ at a lower dosage of polymerlc ~loccu].ant than requlred with other commercially available polymeric floc- ' culants or the cost-per~ormance requiremRn-ts for the desired level of clarification will be substantlally lower ~or the process of the present invention than for other processes.
The ~nvention is more ~ully illustrated in the exam~
ples which follow wherein all parts and percentages are by weight unless otherwise specified, The examples are not to be construed as llmitations on the scope of the claims.

:
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In evaluating a posslble candidate for use ~s a clarifying agent for ore slimes or tailings, there are several procedures that may be employed. A convenlent method involves a laboratory procedure that is convenlently per~ormed andJ when conducted in con~unction with agents known to be ef-fective, can be used to ~uggest agents ~or ~urther testing under actual use conditions. Alternatively~ the agents can be tested directly under use condltion~g but such testlng requires large quantities of test agents and can lead to un-success~ul results wlth large quantities of slimes that would require additional treatment for proper dl~charge into the enviro2~nent or for recycle in processing. Therefore, lt is generally desirable ~o run laboratory screening tests to en~
sure at least some degree o~ success in an actual run under use conditions.
The tests given in the example~ which follow are o~
; the laboratory scree~ing type but the results obtained in act-ual use trials correlate well with the screening results, best results in the labora~ory belng conslst~ntly confirmed in actual u~e, The tests are described below under des-crlptlve headings.
STATIC TEST
In this test9 a speci~ic amount of the clari~yi.ng ~gent ls added to lOQ0 milliliters of the ore slime ln a graduated cyllnder and the contents are rapidly mlxed by in-verting the cylinder quickly several times. Then the cylin-der is set uprlght ln a stationary position and a timer startedO The contents o~ the graduate are watched as a solids level ~ppears below a clarlfied supern~tant llquor~
A line of demarcation will appear above whlch the clarl~ied liquor forms. Timing 1~ continued until the line o~ demarc-ation drops to the 500 ml. mark or such other mark as ma~ be deslgnated. The time' required to reach the sp~cl~ied level ~9~65 is recorded ~s the settlin~ rate for the given level and the clarity o~ the supernatant is then dete~mined. These tests are generally run using various dosages of test agent and from the results can be determined the minimum resldual turbidity associated with a test agent and the do~age required ror a particular resldual turbidit~ or a given ~ettling tlme can be obtained.
The statlc test indica~es two properties of a clari-fying agent, the rate at whlch it eff~cts settling and the ex-tent to which it e~ects clarl~icationO The ideal clarlfying agent would be one which provides the maximum clarificatlon in the minimum settling time. However, in practlce it is gen-erally ~ound that those agents that provide the ~astest set-tling rates provLde somewhat less than maximum clarity. As a result it is generally necessary to comprise between fastest settling rate and ma~imum clarlty. I~ clarl~ier c~pacity is limited, a compromiæe in clarity is generally made to obtain faster settling rate. If clari~ier capacity 1~ adequate, a compromise ~n settllng rate i~ generally made to obtain max-imum clarity, DY~AMIC TEST
~ .
In thls test~ the act~on o~ a commercial clar:Lfier is simulated, The ore slime is placed in a contalner supplied w~.th agltation to stir the slime. A given do~age of clarify-ing agent is added to the sllme and agitatlon at 100 revolut~
ions per minute 19 carried out ~or 45 secondsp after which agitatlon is reduced to 30 rpm and malntalned for 3 minutes.
After agitation, settling is conducted for 15 minutes. A~ter settling is ^~mplete, the clarity o~ the supernatant llquor is det,ermined~ The clarlty i~ indicated by the residual tur~
bidity remaining after clarifying using a Hach Turbidimeter and i3 expressed ln Jack~on Turbldity Unlts (JoToUo )~

- 14 _ ., The test is run using various dosages of the test clar~ying agent and from the resul"t~ the minimum turbidity remain:Lng is established as well as the dosage required to achleve such value. The effectiveness o~ a test agent is generally expressed in terms relatlve to a standard commerclal clari~ying agent.
In the dynamic tests which are illustrated herein, ~he standard clarifying agent was ~he reaction product o~
dimethylamlne and epichlorohydrin havlng a molecular weigh~
o~ 75J000. The mlnimum turbidity value reached with this agent ~or the ore slime evaluated was 8.o JTU and was achleved at a dosage of 4 ppm based on the solids of the slime. For comparlson purposesJ the dosage required to provlde a minimum turbid~ty that is 8 ~ of that of the standard agentJ i.e,, 6,4 JTU, was determined and the dosage given is converted to a relative value, assigning the dosage of the standard agent a value o~ 1.0~
E~AMPLE 1 The following example illustrates a process for manufacturing a polymer contalning aminomethylated acrylamlde groups quaternL~ed wlth dimethylsulfate, 226 pQunds o~ deionlzed waterJ 0,087 pounds of ethylene diaminc tetraacetlc acid, disodium dihydrate salt . and 0.87 pounds of i~opropyl alcohol are charged to a clean reactor which iP then sealed. Agitation is started and th@
charge iq heated to 70~ 2~C~ under a stream o~ nitrogen. At 70C,, a 5c15 weight percent aqueous solution o~ ammonium persulfate (i~e., 15,000 ppm b~sed on acrylamide) 1B added as rapldly as possible, the temperature is read~usted t~ 70~C, 3o if necessaryy and then a 50 weight percent aqueous acrylamide solution is metered in during 2 hours~ while maintainlng the temperature at 70 2CJ The amount of ac~ylamide charg~d is ;

. ~ 15 ~; I
. .

calculated to give a 20 we~gh~ percen~ ~queOU~ po~ymer ~olut-lon, After all the ac~ylamide h~ been added, the batch 1 held at 70C. for ~nother hour ln order to complete the poly~
merization, then the nitrogen flow 1~ ~topped and 1 opropyl alcohol i~ di~t~lled o~f at a batch temperature of 70-75C~
and a pre~sure of 225 mm. Hg, Di~tilli~g o~ 0.8 to 0~9 weight percent o~ the b~tch load remo~e~ gO-95 weight percent of the i~opropyl alcohol a~ a ~2:w~1gh~ percent.~aqueou~ sol-~ , ution (Sp. Gr. 0.967).~ A~ter~reducing the batch to a tempcra-: 10 ture below 50C., the batch weight iR ad~usted by adding an amount of delonlzed water equal to the weight of i~opropyl alcohol ~olution removed during ~trippingc Then a premixed solution of 100 mole percent each of ~ormaldeh~de and dimethyl-amlne based on the am~unt o~ acrylamlde contalning 5 mole pcr-cent exceBa dim~thyl~m~ne~ dd~d as r~pl~ly~a~ po~ible.
The dlmethylamlne-~or~aldehyde ~alution shou~a be premlxed :
and cooled below 40C, A~ter holdlng for two hours; the batch temperature i~ readJu~ted to 35C~ and then 100 mole percent of ~ ;:
dimethylsulfate ba~ed on the ~mourlt o:f dimethylamirle i3 pumped ~n as rapidly a~ pos~lble ~hll~ maintain~ he ~tch a~ 35 to 40C. to a ~inal pH o~ 6,.û--~0,:~, A~t;er the dimethylaul~ate .
haa been added and.the pH ie ~table at pH 6"C~0.2, the batch i~ drummed o:E f`.
EX~MPLE 2 ~ ~:
The following example lll~ tra~es ~nother proces~
:for manu~acturing a polym~r of' thl~ vent$on wlthout the use ~ ....Or a ehain tran~rer~a~ent and~withou~purglng the reactor wlth nitrogen.
, A. Preparatlon oY the Polyac~rlamide Backbone 3o 738 lb. delonized wa~er and 0.38 lb. EDTA (di~odium di-hydrate9 1000 ppm on monc~er3 ar~ e~rged ~ ~ cle~n re~tor and thz pH i~ ad~u~ted to 4~ 5 with 10% ~ul~urlc acid ~olution.

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The r~actor is ~ealed and the batch is heated to reflux during 1 hour. A~ter 1 hour, 0.22 lb. of ammonium pe~sul-fate initlator is added and then 2~02 lb. o. the lnitiator and 941 lb. of ~9~7~ acrylamide monomer solution (at pH 4.~) are metered in slmultaneously during 90 mins, while maintain-ing ~teady reflux, A~ter th~ monomer and inltiator solutions have been added the batch is held at re~lux ~or 30 minutes to complete the polymerization and then the b~tch temperRture is reduced to 35~40~C~
B. Preparation of the Amlnomethyl~ted Polyacrylamide Quate mized Polymer.
At 35C,, a premixed ~olution of 532375 lbu of a 37 weight percent ~ormaldehyde solution and 779.88 lb. of a 40 weight percent dlmethylamine ~olution (1:1:1.05 mole 15 ~ ratio o~ amide: formald0hyde: am~ne) is ~dded a~ rapidly as possible wlth no cooling, The ba~ch is held 3 hours. Then the batch temperature is reduced to 20C. and 698 lbs. of dimethylsulfate i~ metered in at a temperature of' 35~C, untll the pH is reduced to ~0~5. ~fter the dimethylsul~ate has been added and the p~ is stable the batch may be drummed off.

An iron ore slime containlng mostly colloidal silica and clay and having a 2 3~ solids content was employed to . compare settling rates and supernatant turbid~ties oi a poly-mer o~ the invention and a highly ef~ective pri~r art ~loc-culant~ To one liter ~amples o~ the sllme in separate one--lit~r graduated cylinders wer~ mi~ed either 2 or 4 milligram~
; o~ the polymer of te~t. The tims for the ~uspended solids to settle below the 500 milliliter mark of the ~yllnder was determined along with the Jackson turbidity value of the sup-ernatant liquor. The polymer o~ the present invention wa~
made by the procedure of Ex~mple 1 and had an intrinsic Vi8-.
~ . .. .

~IILC~95~S

cosity of OA25 declliters per gram at 30C, in 3M NaCl which corresponds to a polyacrylamide of molecular weight 45,000 as the ~tarting polymer. The prior art polymer 1B de~cribed in U,S, Patent 3,894,947 and i~ th~ reaction product o~ di-methylamine and epichloroh~drln havin~ a molecular wsight of 45,000. The result~ are glven ln Table I.
TABLE I
':
SettlAng Su~ernata~t ~ Ra~
10 Example 1 2mg/1 138 320 Example 1 4mg/1 85 390 Prior Art 2mg~1 ~44 330 Prior Art 4mg/1 97 3 Notes: 0 Second~ to 500 ml mark ~ Jackson Turbidity Unit~
The re8ult9 show that polymera o~ the present in-ventlon provide fa~ter se~tling rate~ at the ~ame or reduced supernatant turbidlty than do the prlor art polymer~.

:
In this example, a serie~ oP runs w~re made follow-ing the procedure of ~cample 3 but using polymers of higher molecular weight~. The polymer o~ the invention was again prepared by the proce~s of Example 1 but had an intrinsic visco~i~y of 0~34 decillters per gram at 30C. in 3M NaCl . whlch corresponds to a polyacrylamide o~ molecular weight 75JOOO a~ the starting polymer, The prlor art polymer was as in Example 3 except that it had a molecular we1ght o~
75, 000. In the varlous run~, a serle~ of concentrations o~ :~
: each of the two polymers was evaluated to determlne the ~ettling time ~or the su~pended solids to reach the 500 ml mark and the supernatant clarity achieved~ From the var:Lou~
data obtained, the relative doses o~ the two polymers neces-sary to a~hieve equal ~ttling time to the ~00 ml mark and ~ .
. .

` ~\

6~;

a supernatant turbid~ty of 190 JTU was determined, The re-sults are given in Table II~
TABLE II
RELATIVE POLYMER DOSAGES
______ Relative Dosa~es For Equal Settling 190 JTU Super-Polymer Example 1 1,O 1.O
Prior Art 1,7 200 The results again show that the polymers of ~he present inventlo~ are sup~rlor to the prior art polymer ln dosage requirements for a gi~en settling rate or a given supe matant turbidity.
EXA
In this example, a s0ries o~ polymers dif~ering only in molecular weight were evaluated Ln clarlfying iron ore slimes obtained ~rom an iron mlne in Michlgan. In ~ each instance the polymer was obtalned by the proce~s of Exam-; ple 1 except that the molecular waight o~ the intermedlate jpolyac~rlamlde di~fered, In e~ch test, the pclymer was em~
ploy~d at 50 parts p~r million part~ o~ suspended solids.

The results obtained and the polymer viscosities ~re given in Table III.
: TABLE III

Polymer Ir~rinsic Settling Ti~e Supe matant ViscosltY _ _(dl ~ml ~ Clarity (JTU) 0.28 3.~0 43 0.51 2.77 57 0,75 2.45 ~0 1.53 2~00 84 2.00~ 1.80 120 Notes: determined ln 3M NaCl at 30C~
8 precise v~lue not available ~L~95~

These results show that as the intrinsic viscoslty o~ the polymer increases 9 the ~ettling tlme decrea~es whlle the supernatant clarity increase6. The~e results demonstrate that the fastest settllng time leaves much to be de~ired with respect to supernatant clarity.

In thls series o:~ runs7 the Dynamic T~ t was fol lowed as described. As the standard flocculant was employed the reactlon product of dimethylamine and epichlorohydrin havlng ~ molecular weight of 75~000~ As test agents were used polymers prepared according to Example 1 except that the mole-cular weight o~ the intermediate polyacrylamide varied. The standard polymer was used at a dosage of 4 parts per million parts of suspended solids and provided a re~idual t~rbidity o~ 8 J~ToU~ measured with a Hach turbidimeter a~ the minimum value, The test agent~ were run at various dosageæ and from theæe ~uns the dosage~ required to provide a residual turbid-lty that wa~ 80~ of that of the standard agent were determined.
This repre~ent~ an actual turb$dlty o~ 5.4 JTU ~nd an improve ment o~ 125~ compared to the standard. The vari~u~ reBults and pertinent data are given in Table IV.
., I'ABLE IV
CLARIFICATION OF I R ON ORE SLIMES
Intrlnsic Relative Supernatant ~ er ~ c~ Dv~age ; 25 Standard ~ 1~00 8,0 Example 1 .22 .~ 6.4 9 .15 ~.4 ~41 .19 5~4 '.' ,4~ 604 ,54 .21 514 Note: ~ dl/g. mea~ured in ~M NaCl at ~O~C, :

5~iS

These results show that polymers of the present invent-lon provlde a lower supernatant clarity than the prior art polymer and provlde such clarity at a small fraction of the dosage requirements o~ the prlor art clarifying agentO It can be see~ that greatest efficiency o~ the polymer type o~
the invention is below an intrinslc viscosity of about 0.5 dl/l, .

; 30 ' . ~ . ;
. .. . .

Claims (5)

CLAIMS:

1. A process for clarifying iron ore slimes con-taining up to about 100,000 parts per million of suspended inorganic solids with a particle size of up to about 2 microns which comprises mixing with said slimes from about 0.1 to 1,000 parts per million, based on the solids content of said slimes, of a polyacrylamide having a content of at least about 50 mol percent of amide groups chemically-modi-fied to contain dimethylaminomethyl groups, the dimethyl-aminomethyl groups being further modified by quaternization with an alkylating agent, the chemically-modified polyacryl-amide having an intrinsic viscosity in the range of about 0.1 to 0.5 deciliters per gram measured in 3M NaCl at 30°C
to form suspendible flocs from a portion of the solids present, maintaining said suspendible flocs in suspension in said water until a substantial portion of the remaining solids are adsorbed thereto; and thereafter settling the resulting flocs formed.

2. The process of Claim 1 wherein said polyacryl-amide contains at least 50-90 mol percent of modified acryl-amide groups.

3. The process of Claim 1 wherein the dimethyl-aminomethyl groups are modified by quaternization with di-methyl sulfate.

4. The process of Claim 1 wherein the intrinsic viscosity of said chemically-modified polyacrylamide is in the range of about 0.3 to 0.5 dl./g.

5. The process of Claim 1 wherein from 0.5 to 100 ppm of said chemically modified polyacrylamide are mixed with said slimes.