CA2236043A1 - Hydroxamated polymers in the bayer process - Google Patents

Abstract

The filtration rate of Bayer Process primary settler feed and/or the flocculation in the initial stages of the washer train in the Bayer Process are improved by contacting the settler feed stream or the feed stream to the first stages of the washer train first with a) a lower molecular weight polymer which contains hydroxamic acid and/or salt groups and then with b) a mixture of an anionic polymer and a second, higher molecular weight polymer which contains hydroxamic acid groups.

Description

w ~ 97/16378 PCTrUS96/17250 REMOVING SUSPENDED SOLIDS BY ADDITION OF HYDROXAMATED POLYMERS
IN THE BAYER PROCESS

The ~r~:se"l invention is cli.~c~ed to a p,ucess of alumina manufacture via the Bayer 5 r,~,cess. More particularly it is col~ce",ed with improvements in the Bayeralumina p,ucess by the improved removal of sus~e"ded solids from the settler overflow and/or the washer train feed stream by CGI ,lacting the settler feed stream or the stream to the first stages of the washer train first with a) a lower molecular weight polymer which contains hyd~o~~
acid groups or salts thereof and then with b) a blend of an anionic polymer flocculant and 10 a second higher mc ~ J~--weight polymerwhich contains hydlux~lli~ acid groups orsalts thereof.

The almost universally used p,~cess for the manufacture of alumina is the Bayer Process. In a typical commercial Bayer Process raw bauxite is pulverized to a finely divided state. The pulverized ore is then fed to a slurry mixer where a 50% solids slurry i5 prepared using spent liquor and added caustic. This bauxite slurry is then diluted and sent through a series of digesters where at about 300 800~~. and 100-2000 p.s.i. 98% of 20 the total available alumina is extracted from the ore which may contain both trihydrate and monohydrate forrrls of alumina. The effluent from the digesters passes through a series of flash or blow-off tanks or wherein heat and condensate are recovered as the digested slurry is cooled to about 230~F. and brought to atmospheric pressure. The aluminate liquor leaving the flashing operation co,llai.1s about 1-20% solids which consist of the insoluble 25 residues that remain after reaction between the bauxite ore and basic material used to digest the ore and the insoluble co",poner,l~ which precipitate during digestion. The coa,aer solid particles are generally removed with a "sand trap" cyclone. To separate the finer solid particles from the liquor the slurry is nommally fed to the center well of a mud settler (also called a decanter. a residue thickener or a raking ll~ e,) where it is treated 30 with a flocculant such as a polyacrylate polymer. As the mud settles clarified sodium aluminate solution referred tc as "green" or "~,~y"a"l liquor overflows a weir at the top of the mud settling tank and is passed to subsequent processing steps. The settled solids ("red mud") are withdrawn from the bottom of the mud settler and passed through a countercurrent washing circuit (called "the washer train") for further recovery of sodium 35 aluminate and soda. Aluminate liquor overFlowing the settler still coll~ s typically 50 to -W O 97/16378 PCT~US96/17250 aiuminate and soda. Aluminate liquor ove,~lo.1 ;. ,g the settler still conL~. ,s typically 50 to 200 mg of sus~n~eci solids per liter. This liquor is then generally further claliried by filtration to give a filtrate with 10 mg. suspel-d~d solids per liter of liquor. Alumina, in relatively pure fomm, is then pl~-;p ~ d from the filtrate as alumina trihydrate crystals. The 5 remaining liquid phase or spent liquor is retumed to the initiai digestion step and e."r'~yed as a dige~lant of additionai ore after being recorctitln~d with aJ-lilional caustic. After pA-~sas~e through the fill-dlio-- step, the level of sus~ended solids should be suri-ic;onlly low to provide an aiumina product from the p,~;~ un step which meets ail of the industry standards.
The aforementioned insoluble cc""ponerlt~ are p~2re~dbly separated from the slurry at a relatively fast rate so as to make the overall Bayer Process efficient. This is generally accomplished in large settlers, decanters, residue ll.:~k~ne.~ etc, as mer,lioned above. The separdlion itself should be clean and COIl F!~ ~ with but minimal amounts of residue remaining as a ~ pe,~ed phase in the solubilized aluminate liquor. The settlers, decante~s, residue (or raking) II. ':ene,~- (all of which are her~,:.-drler referred to as "setter(s)" may exceed 49m in diameter. Some are of a multideck configuration, ho.Ycvcr, single-deck units are almost exclusively used at the present time. In operdlion, the settler(s) feed liquor is fed at the center of the settler(s) and clarified solution overflows at the perimeter. The settler feed liquor is added to the settler(s) via a feedpipe which exits into a ree~w_ll centrally located at the top of the settler. As the solution flows radially across the seKler, the l1orku.,lal and vertical velocities become very low and the solids i.e. red mud, sink to the bottom because the specific gravity thereof is higher than the solution. The faster the settling rate, the more material which can be processed in the settler(s). The solution overflowing the seKler(s) contains very few solids whereas the unde,~lu./ can contain up to 35% solids. However, the overflow contains the majority of the Al203 to be recovered as product. A rotating mechan;s", with plows mounted at an angle, slowly moves the settled solids across the bottom of the settler(s) to a discharge cone usu~lly located in the bottom center thereof. The fine solids of the seKler feed liquor settle very slowly unless accele. dl.eli by the addition of flocculants which act to bind the fine solids into flocs that often are several millimeters in diarneter. The ratio of mass to drag forces is thereby i"~;,based causing the flocs to settle more rapidly. The settled solids from the settler(s) are treated in the counter-current washing circuit (washer train) discussed above, to further remove the red mud II~e,~r~o", by washing. Decanlaliol1 systems are employed for this purpose using washing thickeners similar in design to the settler(s). The washing operation isaccol"~' hed in as many as ten (10) stages, the solids moving counter-current to the wash W O 97/16378 PCT~US96/17250 stream to recover solubles and the overflow being recycled back from each stage of the washer train to its p~dec~sor. Flocculant addition to the stages of the washer train i, ~l~ases the solids separ~iùn, it being generally known to utilize different floccu'~nts in the - earlier stages from those used in the latter stages see for example U.S. Pat. No.
4,678,585 hereby inco"Jordled herein by ~~f~ ce. The settler~s) overflow must becla,i~ied in order to recover as pure a product as possible. The overFlow is SU~8 H '~ to what is called polish fill,dlion (so",eli",es l~felled to as clear pr~ssi,lg) whereby the solids r~maining are removed. Slationary filters are also used for this purpose. It is nommal to allt~ l to reduce the solids to below about 0.5 mg/L to enable product purity to be as high as possible since the ultimate product is used for applications where purity is ess~nlial e.g.toc~tl "~asle.
The reduction of the amount of sl,spendedl solids in the stream co",prising the Bayer Process settler(s) overfiow and that which proceeds to the initial stages of the washer train ie. the first separalion stages to which the red mud slurry from the last settler are introduced has been a majo! pn~t e " for many years.
Among the methods of overcoming the above p,.t ~ ~,s and materially speeding up sepa,i~lion of sus~nded solids from Bayer Process ~lr~"s as well as effecting a cleaner separation of the constituents, is that di~closed in U.S. Patent No. 4 767,~40, issued on August 30 1988. In this patent there is ~lisc~osed the addition of a water-soluble polymer colllai.lil,g ~endanl h~dluA~ll;c acid or salt groups to Bayer Process ~ a",s alone or in conjunction with an anionic flocculant. The polymer containing hyd,u,~a",ic acid groups may be added into the Bayer Process caustic aluminate process stream alone subsequent to followed by or in A~soc:~liol1 with the anionic flocculent e.g. a conventional polyacrylate polymen This treatment is shown to ~educe levels of suspended solids in the prucess stream as compared to then existing state-of-the-art prucesses.
Said U.S. 4 767 540 ho.vevcr does not di~l~e the use of a lower m~P~ r weight hyd,u,~"ated polymer followed by a blend of an anionic flocculant and a highe m"o-ec~ r weight h~nl~u,ca",ated polymer in acco,dance with the present invention.

SUMMARY OF THF INVFNTION
~ It has now been found to be une)t~,ecledly advant~geou-s when treating the feed to frt~m the primary seKler~s) (or digester blow-off) of the Bayer Process and/or the feed to the J initial stages of the washer train to contact said feed liquor first with A) a lower mc e l~r weight polymer containing the pendant h~dlu,cdll,ic acid groups and/or hyclro,~dl"ic acid salt W O 97/16378 PCT~US96/17250 groups f~"~ued by B) a blend of an anionic flwculant and a second, higher ",c~e~ nr weight polymer containing hyd~uAd-- ~~ acid or sait groups.
This sequence of aduii~ion of additives results in a clearer settler overflow as indicated by a higher rillldliun rate and/or more ~Ire~t;~,c flocc-~'-'ion of the red mud in the washer 5 train.

D~TAII FD DF~CRIPTION OF THF INVFNTION
According to the present invention, there is provided a p~cess for improving thefiltration rate of the settler overflow and/or the floccu'~lon in the initiai stages of the washer 10 train in the Bayer Process u,he,~by there is added to the feed to the settler or to the feed to the initiai stages of the washer train, a) a water-soluble, lowem~ cl~ r weight polymer containing hyci~uAdr ,ic acid groups or saits thereof followed by b) a blend of an anionic flocculant and a second, higher lll~2cUI~'r weight, water-soluble polymer containing hydl.~xd",ic acid or sait groups and removing the resultant filtered solids.
1~ The anionic flocculant used in the prucess of the present invention is preferably a ho",opolymer of an acryiic acid or a copolymer of an acrylic acid conLai,l ~g at least 80 molar percent of the acrylic acid or the aikaii metal, aikaiine earth metal or a~ on:urn sait thereof, or a combination of any of the foregoing. Examples of acrylic acids which may be used include acrylic acid, methacrylic acid etc. Copolyrners and terpolymers of said acrylic 20 acids with copolymerizable monoethylenically unsaturated co",ono",e,s such as acrylamide, methacrylamide etc. may be used. Pr~:~erdbly, the anionic flocculant is a ho",opolymer or copolymer of an acrylic acid salt.
Both the water-soluble anionic, flocculant and water-solubie, hydroxamated polymers to be e" F'cycd in the present invention should be sufficiently stable to be effective under 25 the Bayer Process conditions used, e.g. high temperatures and strong caustic conditions typically, 185-225~F, and 80~0009./1. total alkali content (~A~u,~:ssed as sodium ca,l~onale equivalent).
Any water-soluble h)~dluAdlll c acid or hyd,u,~d-, c acid salt group-conlai";.,g polymer may be used in the p~cess of the present invention. The useful polymers can best be 30 eAe~ll F' 'ied by those collld;.. ~9 pendanl groups of the Fommula (I);
O
Il - C - NH- OR (I) W O 97/16378 PCTrUS96/17250 ~ :.er~:., R is hydrogen or a cation. These polyiners are well known in the art and can be derived from polymers containing pend~,l estel; amide, anhydride, nitrile, etc., groups by the ~~action thereof with a hydroxylamine or its salt.
E~e,..~,lary of the polymers which may be hy(J~uAdllldled for use in the ~n,cess of the 5 prese.,l invention are acrylic, methyacrylic, ~-ul(n- etc., acid ester polymers such as polymers produced from the poly...e.i,dlion of methyl acrylate, ethyl acrylate, t-butyl acrylate, methyl ~--eU,acrylate, ethyl ~I,eU-aclylate, cyclohexyl ~,--:II,acrylate, dimethyl ~-.;.,oetl,yl methacrylate, dimethyl aminoethyl "-~:ll,acrylate, dimethyl aminoethyl acrylate, methyl c~londle, etc.; polymers of maleic anhydlride and esters thereof, and the like; nitrile 10 polymers such as those pr~duced from acrylon-- ile etc; amide polymers such as those produced from acrylamide, m~tl ,acrylamide and the like.
H~d~u~d",ated polymers are well known to those skilled in the art and are specifically di;,closed, as are methods for their production, in the above U.S. Patent No. 4,767,540, hereby inco,,uordled he~ein by r~er~nce. Generally, these hy~-uxd..,aled polymers may be 15 produced by reacting the polymer containing the pen~,l reactive group, in solution, with a hydroxylamine or its salt at a te",perdlure ranging from about 10~C to 100~C for several hours. In addition to ,~actiùn of hydroxylamine or its salt with a polymer solution, it has been found that a polymer latex may be reacted directly with the hydroxylamine or its salt.
Tl1e latex may be, e.g. a copolymer of acrylarnide and methyl acrylate, a copolymer of 20 acrylic acid and methyl acrylate etc. In these cases, the hydroxylamine or its salt reacts primarily with the ester groups to fomm h~ dll c acid groups.
Also, it has been found that inverse emulsions made of, for ~,~cd~ e, aqueous polyacrylamide or acr~amide/acrylic acid copolymers dispersed in oil can be reacted directly with hydroxylamine or its salt to give very I ;igh molecular weight polymers containing 25 hy~l~u~ lic acid groups, all of which function efflciently in the prwess of the present invention.
The degree of hyd.u,~"alion, i.e., the concenl,dlion of Fommula I units in the polymers useful herein, may range from about 1 to about 100 mole percent, plt:~erdbly from about 15 to about 90 mole percent and, most pr~ferdbly, from about 20 to about 80 mole percent 30 of the polymer.
Suitable hydroxylamine salts include the su~f~tes, sulfites, phospl1ales, perchlorates, hyd,~l,'ondes, ~e~les, prl r ~nales and the like. The pH of the solution of the polymer - to be h~d,o,~dn,ated is adjusted to over about 6.0, pr~fe,dbly over about 10.0, beforehand.
Any water-soluble polymer may be used in the present pr~ess which, after 35 hyd,u~"ation, perfomms to settle suspended solids. Thus, homopolymers, copolymers, O 97/16378 PCT~US96/17250 terpolymers, etc. of the above eAe"" ~ unumel~ may be used. .SI~ -~'e co,-,ono",e,:, which, by copol~",eri~dlion, may form, for exarnple, up to about 95 mole percent of the polymers useful herein can include acylic acid, sodium acrylate""~lhac~ylic acid, maleic anhydride, vinyi ~r-et~ts, vinyl pyrrolidone, butadiene, styrene as well as others of the above enl""erdled esters, amides an/or nitriles and the like as is known in the art and is set forth in the above-i"co"~,aled patents as long as such copolymers, terpolymers etc., are water- '' soluble after hydl xdlll-dlion. The weight average ",c'e~ r weight of the hycl,u~,,aled polymers useful in the p,ucess of the present invention range from about 1 x 10~ to about 3x10'. Thema'e~u'~-weightofthehy~l~o~dledpolymerisbestcc",l,."o~'bycontrolling the molecular weight of the polymer to be hyd,u~,,ated, such by the use of chain-length regulators, e.g. ~"erudplans, during pol~,",e,i~dlion.
The water-soluble polymer containing h~,dlu~ll;c acid and/or salt groups which is first added to the settler(s) feed and/or the feed to the initial washer stages of the Bayer process in accor~ance with the present invention must have a Ill~ r weight lower than that of the hyd,uxd",ic acid and/or s~t group containing polymer which fomms part of the blend which is added thereafter. Although any polymer having a molecular weight within the above range may be used, it is preferred that the first added h)~d,u,~d,,,aled polymer have a molecular weight of below about 7 million, most pr~fer~bly below about 3 million.
Preferably, the hyd,u,td,,,ated polymer which constitutes part of the blend with the anionic flocculant will have a mslecu'~r weight over about 7 million, most pr~t7rably over about 10 million, hu.vevcr, the specific m~ r ~ r weight of either additive is critical only to the extent that the h~n~uxa~aled polymer of the blend has a m~tec,J'~r weight higher than that of the hydroxamated polymer added individually, i.e., the lower molecular weight polymer.
The blend of the anionic flocculant and the higher ",c'e ~ weight polymer containing hydroxamic acid and/or salt groups should be co",p,ised of from about 10 to about 90 weight percent of the higher molecular weight polymer and about 90 to about 10 weight percent of the anionic floca~' nt, p,~r~r~bly about 80 to about 20 c.nd about 20 to about 80, same basis, l~spe-;lively, most pr~fer~l~ about 70 to about 30 and about 30 to about 70, same basis, respectively.
The blend can be added to the stream being treated as a single dose or via a series of dos~ges, it being pr~ei,~ that the blend be added in at least 2 dos~ges for purposes L' of insuring co,-lr'--te admixture with the stream.
The anionic flocculant and the water-soluble, h~d,u,tdl,,ated polymers used in the present invention are e",, '~yed by adding them, i.e., the lower molecular weight polymer and/or the blend, in the fomm of aqueous solutions, to the feed to the settler(s) containing -W O 97/16378 PCTrUS96/17250 solubilized alumina and s~Jspended solids di~pel:jed throughout, and/or the feeds to the initial stages of the washer train, in an amount at least sufficient to settle suspended solids Il ,er~,u"~ Generally, for best results, at least about 0.1 mg, of the lower m- 'e u~- r weight hyd~A~.,-dled polymer, per liter of the settler(s) and/or washer train stage feeds should be 5 employed. More prt:tt:ld~ly, at least 1.0 mg, of the lower ,- ~ 'e~ r weight hy.JIuAdlllated polymer, per liter of the settler(s) andlor washer stage feeds should be e" ~'~ycd. The blend of the anionic flocculant hydluAdllldled polymer may be added in amounts ranging fnDm about 0.01 to about 40 Ibs. of blend solids per ton of solids to be settled.
It is unde,:,lood, that higher amounts than those above stated may be ell f ' jcd 10 without depa,li"~ from the scope of the invention, although generally a point is reached in which ad.Jilional amounts of blend and/or h~-J~x~lldled lower m~e ~ weight polymer do not improve the separation rate over already achieved maximum rates. Thus, it is uneconomical to use eAcessive amounts of either additive when this point is reached.
The addition of the water-solub!e, lower m~e ul~r weight hy~rùA0~aled polymer 1~ should precede the ad~lilion of the blend ~y sufficient time such as to enable the lower molecular weight polymer to at least begin to perfomm. Thus, for ~example, when both additives are added to the settler fccd there must be sufficient time allowed between the individual additions to enable the lower molecular weight h~,u~d",ated polymer to at least begin to flocculate the susperlded solids. The same applies to diffe,~-"l addition points of 20 ths initial washer train stages.
The r~ ..,;. ,9 examples are set forth for purposes of illu:,l,dlion only and are not to be construed as lir"i~alions on the present invention except as set forth in the ap,vended claims, All parts are by weight unless otherwise specified.

r YS-m~7les 1-2~
To a vessel containing a settler feed from a commercial Bayer Process alumina plant is added, as set forth in Table 1, below, an 80 mole percent hy~JIuAdlllaled polymer containing 10 mole percent of acrylic acid units and 10 mole percent of acrylamide units and having a weight average molecular weight of about 350,000 (identified as A). A
commercially available ammonium polyacrylate flocculant having a nurnber average" ~'e-u!~r weight of about 10-15 million (ide,ltified as B) is added alone (cc""pardlive) and as a 70/30 blend, ~~spe~,1ively, with a second polymer containing 18 mole percent hyd,ux~"ate groups, ~2 mole percent of acry~ic acid units and 30 mole percent acrylamide units and having a weight average molecular weight of 12-20 million (ider,lified as C).

W O 97/16378 PCT~US96/17250 The additives are added as indicated with mixing betwecn each addilion such as to simulate the mixing in the plant. The results are set forth in Table 1, below.
All additives are made up to 0.1% with 10 gpl caustic in water. The till-~lion volume is 100 ml.
Exd",r'es 1-14 employ one settler feed stream, Exdll, 'es 15-17 employ another dirr~,enl settler feed stream and Examples 18-29 employ a third settler feed strearn.

W O 97/16378 PCT~US96/172~0 TABI Fl r;itl dliOn FXAMPI F ~nD. #1 ~nD. #? ~nD #3 mls #1 mls#2 mls #3 ~
a~ /hr/rrl~) 51 X - B B - 3.0 3.04.386 2X - B B - 2.0 2.02,819 3X - B B - 2.5 2.56,579 4X A B B 0.5 2.0 2.05,639 5X A B B 1.0 2.0 2.05.639 106X A B B 2.0 2.0 2.05,263 7X A B B 0.25 2.0 2.0 7,894 8X - B B - 2.0 2.04,644 9X - C C - 3.0 3.07,177 1 OX - C C - 2.5 2.56,C73 1511 A C C 0.5 2.0 2.08,772 12 A C C 0.5 2.0 2.011,287 13 A C C 0.5 2.0 2.09,288 1 4X - C C - 2.0 2.04,644 1 5X - C C - 4.0 4.01,338 2016 A C C 2.0 4.0 4.01,925 17 A C C 2.0 4.0 4.01,925 1 8X - C C - 3.0 3.01,462 19 A C C 0.5 3.0 3.03,036 A C C 1.0 3.0 3.03,759 2521 A C C 1.5 3.0 3.03,588 22X - B B - 3.0 3.00,897 23X A B B 0.5 3.0 3.01,974 24X A B B 1.0 3.0 3.03,289 25X A B B 1.5 3.0 3.03,759 3026 A~ C C 0.05 3.0 3.0 3,588 27 A C C 5.0 3.0 3.03,588 28X - C C - 3.0 3.01,925 29 A~ C C 0.02 3.0 3.0 3.432 ADD = additive 35~12% solution X = comparative W O 97/16378 PCT~US96/17250 As can be readily app,~ciale~ the results of Table I show that an overall superior effect is obtained dS cv;denced by the higher fill,alion rate when the blend of the anionic flooal'~nt and the higher ",~ weight h~ Adlll~ted polymer is used suhsequent to the ac~-~ition of the lower molecular weight h~lUA0lldl~ polyrner.

FYI~MPI FS 30-39 F_ r,i.l~ the testing procedure of Examples 1-29, a series of lower molecular weight hy(J~w~dllldled polymers are e" ~'cyed in the treatment of a settlcr feed stream from a ccj"""er~ial Bayer Process plant. The same blend of EA~IIII, '~S 1-29, i.e., that desiy"aled as C, is then added. The results are shown in Table ll, below.
Polymer D = 80% hydluAdl~laled, M.W. 220,000 Polymer E = 60% h~nlluAdlllale~J M.W. 350 000 Polymer F = 100% h~J,uAa.,,ated; M.W. 350 000 Polymer G = 80% h~luAdlllated; M.W. 700,000 Polymer H = 20% h~ ùAdlllated; M.W. 350,000 Polymer I = 25% h~ll UAdl I Id~ M.W. 10 million Polyrner J = 80% h~ uAdrl lated; M.W. 100 000 rlll, dliUn FXAMpl F ~nD. #1 ADD. #~ ~nD. #3 mls #1 mls #2 mls #3 ~lhrtrr~) 30X - C C - 3.0 3.0 1,650 31 A C C 1.0 3.0 3.0 1,925 32 D C C 1.0 3.0 3.0 1,754 33 E C C 1.0 3.0 3.0 2 134 34X - C C - 3.0 3.0 1 645 F C C 1.0 3.0 3.0 2,392 36 G C C 1.0 3.0 3.0 3,158 37 H C C 1.0 3.0 3.0 2,256 38 I C C 1.0 3.0 3.0 3,298 39 J C C 1.0 3.0 3.0 2,392 X = comparative These data clea~y show that variation of the degre!e of h~ uAdilldlion and the ",c ecu'~- weight of the lower m~'e l-' r weight hyd~Ad",ated polymer still results in a superior i"c,ease in the overflow lill,dlion rate.

FY~Mpl ~ 40 Fc ~ ing the procedure of Example 12 except that the anionic floccu'-nt of the blend is a ~ re:~l co---~er~;ia',ly available polyacrylate having a number average l-l~ ~cu'~
weight of about 1~15 million similar results are ach;eved.

FY~MPI 1- 41 The anionic flocculant of Example 40 is replaced by a 90/10 sodium acrylate/acry~amide copolymer. Similar results are achieved.

FY~MPI F 42 Replacement of the h~d,uA~",ated polymer of blend C of Example 13 with a polymerwhich is 25% hycdloAdillated and has a weight average m~ o ul~r weight of a~out 12 million results in a similar incf~ased filtration rate.

t5 FYI~MPI 1~ 43 Again fo~ ;ny the procedure of Example 12 except that the anionic flocculant is a ho",l)polymer of sodium acry,ate similar results are obse,-ved.

FXAMpl F~ 44-72 When Exd",Pec 1-29 are again followed individually using the additives of Table 1 except that a feed to the first stage of the washer train of a commercial Bayer Prwess a,umina plant is used as the charge medium an overall improvement in floccl~'~tion is shown by those eAa",r'es representative of the instant ir,vention as compared to the other comparative exd",r es

Claims (13)

CLAIMS:

1. In the Bayer alumina process wherein there is produced a settler feed stream and streams containing suspended solids flowing into initial stages of a washer train, the improvement which comprises 1) admixing with either or both of said streams an effective amount of A) a first, water-soluble polymer containing pendant hydroxamic acid or salt groups and having a molecular weight below about 7,000,000 and then B) an effective amount of a blend of i) an anionic water-soluble, acrylic flocculant and ii) a second water-soluble polymer containing pendant hydroxamic acid or salt groups and having a molecular weight higher than said first polymer to flocculate the suspended solids, wherein the blend comprises from about 10 to about 90 weight percent of the second polymer and about 90 to about 10 weight percent of the anionic flocculant and 2) removing the resulting flocculated suspended solids from the stream or streams.

2. A process according to Claim 1 wherein A) and B) are added to the settler feed stream.

3. A process of Claim 1 wherein said hydroxamic acid or salt group containing polymers are derived from polymers containing pendant ester amide anhydride or nitrile groups.

4. A process of Claim 1 wherein the degree of hydroxamation of said first polymer ranges from about 1 to about 100 mole percent.

5. A process according to Claim 1 wherein said anionic flocculant is an acrylatepolymer.

6. A process according to Claim 2 wherein said anionic flocculant is an acrylatepolymer.

7. A process according to Claim 1 wherein said anionic flocculant is an acrylatepolymer and said hydroxamic acid or salt group containing polymers are derived from a polymer containing pendant ester, amide, anhydride or nitrile groups.

8. A process according to Claim 7 wherein said anionic flocculant is an acrylatepolymer and said hydroxamic acid or salt group containing polymers are derived from an amide polymer.

9. A process according to Claim 8 wherein said acrylate polymer is a polymer of an acrylic acid and said amide polymer is a polymer of acrylamide.

10. A process according to Claim 1 wherein A) and B) are added to any streams flowing into the initial stages of the washer train.

11. A process according to Claim 10 wherein said flocculant is an acrylate polymer.

12. A process according to Claim 10 wherein said hydroxamic acid or salt group containing polymers are derived from a polymer containing pendant ester, amide, anhydride or nitrile groups.

13. A process according to Claim 10 wherein said flocculant is an acrylate polymer and said hydroxamic acid or salt groups containing polymers are derived from a polymer of acrylamide.