CA1123309A - Destabilization of sludge with hydrolyzed starch flocculants - Google Patents

Abstract

DESTABILIZATION OF SLUDGE
WITH HYDROLYZED STARCH FLOCCULANTS

Abstract of the Invention Hydrolyzed corn and potato starches are effective as flocculants in destabilizing dilute as well as thick sludge suspensions. Potato starch flocculants are equal to, or better than, the synthetic polyacrylamide flocculants in destabilizing sludge suspensions, especially when clarity of the suspension is a significant consideration.
Among the potato starch flocculants which were found to be generally better than the corn starch flocculants, those containing A?PO4 were the best. Potato starch flocculants are equally effective on oil-removed and no-oil-removed sludge suspensions.

Description

Back~round of the Invention This invention relates to the hot ~.ater process for treating bituminous sands, such as Athabasca tar sands, and, more particularly, to the treatmcnt of the water and clay-containin~ efflucnt discharlged from the process.
Tar sands (~hich are also known as oil sands and bituminous sands) are sand deposits which are impregnatcd with dense, viscous petroleum. Tar sands are found through-out the world, often in thc same geographical area asconventional ~etroleum. The lar~est deposit, and thc only one of present commercial importance, is in the Athabasca arca in the northeast of the Province of Alberta, Canada.
This deposit is bclieved to contain over 700 billion barrels of bitumen For comparison, this is just about equal to the ~orld-wide reserves of conventional oil, Sn%
of which is found in the middl~ east.

330~
Athabasca tar sand is a thrce-component mixture of bitumen, mineral and water. Bitumen is the value for the extraction of which tar sands are mined and proccssed.
The bitumcn content is variableJ averaging 12 wt.~ of the deposit, but ranging from 0 to 18 wt.%. Water typically runs 3 to 6 wt.% of the mixture, increasing as bitumen content decreases. The mineral content is relatively constant ranging from 84 to 86 wt.%.
Several basic extraction methods have been known for many years for serarating the bitumen from the sands. In the so -called "cold water" method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in water. The combined mass is then subjectcd to a press~lre or gravity separation.
The hot water process for primary e~traction of bitumen from tar sands consists of three major process steps (a fourth step, final extraction, is used to clean up the recovered bitumcn for do~nstream processing.) In the first step, called conditiolling, tar sand is mixed with ~ater and heate~ with ol~en steam to form a pulp of 70 to 85 ~it.%
solids. Sodium hydroxidc or other reagents are added as required to maintain pl-l in the range 8.0 - 8.5. In the second stcp, called sepclration, the con~itioned pulp is diluted further so that settling can take place. l`he bulk of the sand-size mineral rapidly settles and is withdrawn as sand tailings. ~ost of the bitumen rapidly floats (settles upward) to form a coheTent mass known as froth which is reco~-ered b~ skimming the scttling vcsscl. A thir~
stream may be withdrawn from the settling vessel. This stream, callcd the middlin~s drag strcam, may be subjected to a third processing step, scavcnging. This step l~rovides incremental rccovery of suspendcd bitumcn and can bc accomplished by conventional froth flotation.
The mineral particle sizc distribution is particularly significant to operation of the hot watel process and to sludge accumulation. The terms sand, silt, clay, and fines are used in this specification as particle size designations wherein sand is siliceous material ~hich will not pass a 325 mesh screen. Silt will pass 325 mcsh, but is larger than 2 microns, and clay is material smaller than two microns including some siliceous material o~ that si~e.
Conditioning tar sands for the recovery of bitumen consists of heating the tar sancl/~.ater ecd mixture to process ten-perature (lS0-20nF), physical mixinS of the pulp to uniform composition and consistency, and the consumption (by cllemical reaction) of the caustic or other reagents added. Under these conditions, ~itumen is strip~ed from the individual sand grains and mi~ed into the pulp in the form oE discretc droplets of a partic]e si~e on the same order as that o tl~e sand grains. The same proccss conditions, it turns out, are also ide~l for accomplishing deflocculation of the cla~-s ~hich occur naturally in the tar sand feed. Deflocculation, or dispcrsion, mcans brca~ing down thc natural]y occurringaggregates of clay particlcs to producc a slurry of individual particlcs. Thus, during conditioning, a largc fraction of the clay particles bccome wcll dispcrscd and mixcd througllollt thc pu]p.

Those skilled in the art will thercfore understand that the conditioning process, which prepares the resource (bitumen) for efficient recovery d~lring the~ following process steps also prepares the clays to be the most difficult to deal with in the tailings disposal operations.
The second process step, called separation, is actually the bitumen recovery step, (the separation having already occur~ed during conditioning). The conditioned tar sand pul~ is screened to remove rocks and unconditionable lumps of tar sands and clay. The reject material,"screen oversize", is discarded. The screcned pulp is further dilutc~ with water to promot~ two settling processes: globules of bitumen, essentially mineral-free, settle ~float) u~ ard to form a coherent mass of froth on the surface of the separation cells;
and, at the same time, mineral particles, particularly the sand size mineral, settle down and are removed from the bottom of the separation cell as tailings. The medium through which thesc two settling processes ta~e place is called the middlings. ~liddlings consists primarily of l,~ater, ~ith suspendcd fine material and bitumen particles.
The particle si es and densitics of the sand and of the bitumen particlcs are rclatively fi~ed. Thc parameter whicll in~lucnces the settlillg l)rocesses most is the viscosit~
of thc middlings. Charactcristically, as the fines content rises above a certain threshold ~ hich varies according to t11e com~osition of the fines), viscosity rapidly acilieves high values ~ith the cffcct that tlle settling processes essentially stop. In this oper~ting condition, the separation cell is said to be "upset". ~ittle or no oil is rccovered, and all streams c~iting the ccll havc about the same composition as the fecd.

~ 3 0 ~ i As feed fines content increases, more water must be used in the process to maintain middlings viscosity within the operable range.
The third step of the hot water process is scavenging.
The feed fines content sets the process water requirement through the need to control middlings viscosity which, as noted above, is go~erned by the clay/water ratio. It is usuall~ necessary to withdraw a drag stream of middlings to maintain the se~aration cell material balance, and this stream of middlings can be scaYenged for recovery of incremental amounts of bitumen. Air flotation is an effective scavenging method for this middlings stream~
Final extraction or froth clean-up is usually accomplished by centrifugation. Froth from primary extraction is diluted with naptha, and the diluted froth is then subjected to a two stage centrifugation. This process yields an oil product of an essentially pure (diluted) bitumen. Water and mineral removed from the froth constitute an additional tailing stream which must be disposed of.
In the terminology of extractive processing, tailings is the throwa~a) ~aterial generated in the course of extract-ing the valuable material from an ore. In tar sands processing, tailings consist of the whole tar sand ore ~-ody plus net additions of process water less only the recovered bitumen product. Tar sand tailings can be subdivided into three categories; viz: (l) screen oversize,

(2) sand tailings ,~the fraction that~ settles rapidly), and

(3) tailings sludge ~the fraction that settles slowly).

.
., ~ . , ! .. .. ..

30g Screen oversi~e is typically collectcd and handled as a separate stream.
Tailings disposal is all the operations required to place the tailings in a final resting place. Onc obvious long-range goal of tailings disposal is to replace the tailings in the mined out area in a satisfactory forrn.
Thus, there are two main opcrating modcs for tailings disposal: (1) dike building-hydraulic conveying of tailings followed by mechanical compaction of the sand tailings fractionj and ~2) overboarding-hydraulic ~ransport with no mechanical compaction.

Recently, in view of the high level of ecological consciousncss in Canada and the United States, technical interest in tar sands operation has begun to focus on tailings disposal. The concept of tar sands tailings disposal is straightforward. Visuali-e mining one cubic foot of tar sands. This lea~res a one cubic foot hole in the ground. The ore is processed to reco~Jer the resource~bitumen) and the remainder, including both process matcrial and the gangue constitutes the tailings; tailings that are not valuable and are to be disposed of. In tar sands processing, thc main process material is water and the gangue is mostly s~nd with soole silt and clay. Physically, the tailings consists o a solid part (sand tailings) and a more or less fluid part ~sludge). The most satisfactory placc to dispose of these tailillgs is, of course, the existing one cubic foot hole in the groulld. It turns out, however, that the sand tailings from the one cubic foot of ore occupy just about one cubic foot. The amount of sludgc is a 33~)9 variable, de~endin~ on ore quality and process con~itions, but may run up to 0.3 cubic feet. The tailings simply will not fit into the hole in the ground.
The historical literature coverin~the hot water process for the recovery ol bitumen from tar sands contains little in the way of a recognition that a net accumulation of liquid tailings or slud~e would occur. Based on analysis of field test unit operations which led to the Great Canadian Oil Sands plant design near Ft. ~Ic~lurray, Alberta, the existence of sludge accumulation was predicted. This accumulation came to be called the "pond water problem".
Observations during start-up and early commercial operations at Ft. ~Ic~lurray (1967-6~) ~ere of insufficient precision to confirm the prediction. Since 1969, commerical operating data have confirmed the accumulation in GCOS' tailings disposal area of a layer of fine material and water (slud~e) which settles and compacts only ~!ery slowly, if at all.
~ t the GCCS plant, for dike building, tailillgs al~e conveyed hydraulically to the disposal area and discharged onto the top of a sand dike which is constr~lcted to serve as an impoundment for a pool oE liquid contained inside.
On the di~e, sand settles rapidly, and a slurr) of fines, hat~r, and minor amounts of bitumen ~lows into the pond interior. The settled sand is mecllanically compacted to build the dike to a higher level. The slurry which drains into the pond interior commences stratification ill settling over a time scale of mont}ls to years. As a result of this long-term settling, two layers form. Thc top 5 to 10 feet of the pool are a layer of relatively clear wrater containin~
30 0 to 5 wt. r/ sol i~s. Bclow this clcar water layer is a 11;~;3309 discontinuity in solids content. Over a matter of a few feet, solids content increases to 10-15 wt.~, and thereafter, solids content increases regularly toward the pond bottom.
In the deepest parts of the pond, solid contents of over 50 wt.% have been recorded. This second layer is called the sludge layer. The solids content of the sludge layer increases regularly from top to bottom by a factor of 4-5. The clay-water ratio in this layer increases also, but by a lo~er factor of 1.5 - 2.5. The clays, dispersed during processing, apparently have partially reflocculated into a very fragile gel network. Through this gel, fines of larger-than-clay sizes are slowly settling.
Overboarding is the operation in whic]l tailings are discharged over the top of the sand dike directly illtO the liquid pool. A rapid and slow settling process occur but their distinction is not as sharp as in dike building and no mechanical compaction is carri~d out. The sand portion of the tailings settles rapidly to form a gently sloping beach extending from the discharge ~oint to~ard the pond 2G interior. As the sand settles, fines and water drain into the pool and commence long-term settling.
In summary: ~1) tar sands cont~in clay minerals, ~2) in tl~e hot water e~traction ~rocess, most o the clays become dispersed in the process streams and tra-erse the circuit, exiting in the tailings, ~3) the amoullt of process water input is fixed by the clay content of the feed and the need to control viscosit~ of the middlings stream, ~4) the amount of l~ater required for middlings viscosity control represents a large volunle re~ative to the volume of the ore itself, and (5) u})on dis~osal, clays settle onl~ very very slowly; thus, the process water component of tailings is only partially available for reuse via recycle. That which can't be recycl~d re~resents a net accumulation of tailings sludge.
The pond ~ater problem is then: to devise long-term economically and ecolo~ically acceptable means to eliminate, minimize, or permanently dispose of) the accumulation of liquid tailings or sludge.
Flocculation of the drag stream in order to improve the settling characteristics theretohas been proposed and practiced in the prior art. In flocculation, individual particles (in this case clay particles) are united into rather loosely bound agglomerates or flocs. The degree of flocculation is controlled by the probability of collisions bett~een the clay particles and tlleir tendency to-~ard adhesion after collision. Agitation increases the probability of collision and adhesion tendency is increased by the additio of floccu]ants.
Reagents act as flocculants through one or a combination of threegeneral mechanis~ls: ~1) neutralization o the electrical repulsi~e forces surrounding the small particles whicll ena~les tl~e ~ander ~'aals collesive force to hold the particles togetiler once the~ have collided; (2) precipitation of voluminous flocs, such as metal hydroxides, that entrap fine particles; and t3) bridgin~ of particles by natural or synthetic, long-chain, high-molecular-~eight polymers.
T}lese polyelectrolytes are believed to act by adsorption (by ester formatioll or hydroRen bonding) of hydroxyl or amide groups on solid surfaces, each poly]l~er chain bridging hetl~een more tl~an one solid particle in the suspension.

3 3~9 Amon~ the various reagents which have been found useful for flocculating clay are: aluminum chloride, polyalk~lcne o~idcs, sucll as polyethylenc oxide, compounds of calcium such as calcium hydroxide, calcium oxidc, calcium chloride, calcium nitrate, calcium acid phosphate, calcium sul~ate, calcium tartrate, calcium citrate, calcium sulfonate, calcium ]actate, the calcium salt of ethylene diamine tetraacetate and similar or~anic sequestering agents. Also useful are quar flour or a high molecular weight acrylamide polymer such as polyacrylamide or a copolymcr of acrylamide and a copolymerizable carbo~ylic acid such as acrylic acid. Additional flocculants which ha~e been considered include the polymers of acrylic or methacrylic acid derivitives, for e~ample, acrylic acid, mcthacrylic acid, the alkali metal and ammonium salts of acrylic acid or metllaclylic acid, acTylamide methacrylamide, the aminoaklyl acrylates, the aminoal~yl acrylamides, the aminozklyl methacrylamides and the N-al~yl substituted aminoaklyl estcrs of either acrylic or methacrylic acids.
Those s~illed in the art ~ill understand that a satisfactory solution to the "pond ~ater problem" must be economically, as ~e].l as ecologically acce~tablc. Desp;te the considerable attclltion ~ ich has becn paicl to the llse of flocculants in the treatmcnt of tailillgs from the IIOt water e~traction process for tar sands, no flocculant, or flocculant family kno-m in the ~rior art has been able to mcet thcse fundamental criteria.

- 1()-Objects of the Invcntion .
It is thereforc a broad object of our invention to provide an effectivc flocculating agcnt for treatin~ tar sands tailing streams w}lich carly suspended clay particles.
I~ isanother object of our invention to provide such a flocculatin~, agent which is economical to prepare and employ in the treatnlent of tar sands tailin~ streams.
In another aspect, it is yet another object o~ our invention to provide such a flocculant ;hich is safe and easy to handle and which its~lf offers no ecologically undesirable side e~fects.
It is a still further object of our invention to pro~ide a flocculant ~-hich dces not require the prior removal of oil to be effective in flocculating sludge suspensions within the tailing stream from a hot l~atcr bitumen extraction process.
~rief Sur"mar~ of the ~n~ention Briefly, these and other objects of the invention are achieved by elnplo~ing synthesi~.ed flocculants comprising starches. Starches are polysaccllarides containing many mono.saccllarides joincd together in long chains, ~pon cor,~l)lcte h)~rolysis b~ chemical or en~ymatic mcans, starch ~-ie]ds monosaccharides. Ilydroly~ed COI`II and potato starc~cs arc e~fectivc ~s flocculants in destabili,ing d]lute as l~ell as thicX sllldge suspensions. Potato starch flocculants are gencrally superior to corn starch flocculants, and those potato st:arch ~locculants are equally effective on oil-removc~ and no-oil removed-sludge suspension~s .

Dcsc_ ~tion of thc nrawin~
Thc sub~cct matter of the invcntion is particularly pointed out and distinctly claimed in the concluding portion of the spccification. The invention, however, both as to the mallner in which the flocculants are prepared and the method of employing them, may best bc understood by reference to thc follo~in~ dcscriptiorl taken in connection ~ith the dra~ing of which the single figure is a schematic representation of a hot water extraction process whcrein the invention finds particular use.
Detailed Description of the In~ention Referring now to thc single figure, bituminous tar sands are fed into the system through a line 1 and pass to a conditioning drum or muller 18. Water and steam are introduced to the mullcr through another line 2. The total ~ater so introduced in liquid and vapor form is a minor amount based on the weight of the tar sand~ proccssed. The tar sands, conditioncd ~ith water, pass through a line 3 to the feed sump 1~ which servcs as a ZOIIC for diluting the pulp Wit]l additional ~ater bcrore ~assage to the separation zone 20.
The pulp tar sands are continuously flushed from the ~ced sump 19 tlllollgll a line 4 into a separator 20. The settling zone within thc separator 20 is relatively quiescent so that bituminous froth rises to the top and ;s witlldra~n via line 5 ~hile thc bulk of the sand settles to t11e bottom as a tailings layer which is withdrawn through line 6.
A middlings strealn is .~ithclrawn through linc 7 to be processed as describcd belo~.~. Anothcr middlings strcam, 33Qg which is relatively oil-rich compared to thc stream withdrawn throu~h line 7, is withdrawn from the cell via line 8 to a flot~tion scavenger zone 21. In this zone, an air flotation operation is conducted to cause the formation of additional oil froth which passes from the scaYenger zone through line 9 in mixture with the primary froth from the separator 20 to a froth settler 22. An oil-lean water stream is remo~ed from the bottom of the scavenger zone 21 through line 10 to be further processed as described below. In the settler zone 22, some further oil-lean water is withdral.n from the froth and removed through line 11 to be mixed with the oil lean water stream from the flotation scavenger zone, the sand tailings stream from the separation zone and a portion of the lower middlings withdrawn from the separation zone. The bitumen from the settler is removed through line 12 for further treatment.
The oil-lean water from the froth settler, the scavenger -one, and the scparator, and the tailings from the settler, all of ~hich ]na~e up an effluent discharge stream, are treated in the sand separation zone 20 by, for e~ample, a simple gravit~ s~ttil~g process. The sand is withdrawn by a line 13 and discarclcd, and a process wAter stream is withdrawn by a line 14 to thc 1Occulation zone 24.
In the flocculation zone 24, a substantial amount of clay suspended in the process water is coagulated, and a slurry of coagulated clay and process water is withdrawn in line 15 to a centrifuge zone 25. In the centrifuge zone, coagulated clay is separatcd from the process ~a~er and discarded via line 16. Watcr substantially rcduced in clay 330~

and sand content comp;lrcd to the efflucnt dischar~e is recovered from the centrifuge 7One ancl is recycled hy a line 17 to be mixecl with fresh water ancl charged into the hot water process.
As previously cliscussed, a substantia] amount of flocculants havc been invcstigated and none are known to have been both effecti~~e and economical when used in treating tailings from the hot water process Eor ex~racting bitumen from tar sands. Ho~cver, according to the present invention, it has been found that h~drolyzed starches synthesized from corn and potato starches can effectively meet these criteria. The major fraction of starch per se is ~ater insoluble. To prep?.re the h~droly~ed starch, a 20,000 ~pm stock solution ~as prepared by reflu~ing a mi~ture of the starch and an aqueous solution containing the requisite amount of electrolyte. The hydrolysis was considered complete ~hcn the insolublc starch was con~erted into a clear colloidal solution. Henceforth in this specification~ these l-)drol~ed starches will be referrecl to as starcll flocculallts. A sumTnaly of the preparecl starch flocculants is gi~en in T~ble 1 on the following page:

11~3309 TABLE 1. Sul[rnary of prepared starch flocculants from corn and potato starches SMRL Type of Starch Nature and Concentration of Lab. Flocculant Electrolyte Added Na starch 0.05 N NaOH
2 Ca starch 0.05 N CatOH)2 3 AQ starch 0.10 N A~C~3

4 Na AQ starch 0.05 N NaOH ~ 200 ppm AQ
Ca AQ starch 0.05 N Ca(OH2) + 200 ppm AQ
Na AQPO4 starch 0.05 N NaOH + 200 ppm AQ + 200 ppm PO4 7 Ca AQPO4 starch 0.05 N Ca(OH2) ~ 200 ppm AQ +200 ppm PO4 8 AQPO4 starch 0.1 AQCQ3 ~ 200 ppm PO4 * AQ was added using AQ2(SO4)3.1~ H2O
** PO~ was added using Na3PO4.12 H20 Thus, in accordance with the present teachings, a composition is provided which comprises a hydrolyzed corn or potato starch which is obtained by aqueous hydrolysis of starch in the presence of insoluble metal salts formed in situ. The salt which is employed may contain calcium, aluminum and phosphate ions with the salt being AlPO4 being preferred.
In order to test the effectiveness of synthesized starch flocculants, two sludge suspensions containing 5.5 and 17.3 wt. % solids, respectively, were employed. In addition, synthetic polyacrylamide flocculants were used for comparative purposes. Test criteria used were:
reflitration rates, self-settling and sedimentation upon centrifugation at a relative centrifugal force of 790g at the bottom of the tube for 30 minutes. The results of reflitration tests and preliminary tests on self-settling indicated that the starch flocculants prepared from potato 33~9 starch were superior to those prepared from corn starch;
therefore~ Table 2 presents only the sedimentation-upon-centrifugation studies done with potato starch flocculants.

-15a-'eLE 2. Sollds conccntration In cakc and supcrnatant upon scdimcntation by ccntrifugation using diffcrcnt flocc-llants.
.
Trcatment Flocculant Initlal Solids Final Solids Conc., ~(W/W) Typc Conccntrat;~n Conc., ~(W/~ Cake Su~crnatant Po!yacrylamldc_Flocculants 1 Nonc (untrcatcd sludgc~ 17.3 1I2.1 2.4 2 1820A(anionic) 200 ppm 17.3 39.9 1.1 3 573C ~cationic) 200 " 17~3 37.7 1.7 4 19n6N(non-ionic) 200 " 17.3 42.9 2.4 Pota~o Starch Floccu!ants Na Starch 200 ppm 17,3 36,6 o.o 6 AQ starch 200 " 17.3 35.8 0,o 7 Na A~ starch 200 " 17.3 37.o o.o ~ Ca ~ starch 200 " 17.3 36.3 o~o 9 Na A~P04 starch 200 " 17.3 41.7 o,o Ca ~QP04 starch 200 " 17.3 41.~ o,o 11 AQP04 starch 200 " 17.3 42.9 o.o 12 None (untreated sludge) 5.5 35,4 o.4 13 Na A~ starch 200 " 5.5 36.o 0.2 14 Ca A~ starch 200 " 5.5 35.6 0.2 , From thc data sct forth in table 2, it is evident that the starch Elocculants are decide~]y superior to the polyacrylamide flocculants vis-a-vis the quality of the resultant supernatant. ~or thosc in which no flocculants ~erc used or in which synthetic polyacrylamide flocculants were used, the su~ernatant had up to 2.4 wt.~ solids in it, wl~ereas the runs in which the starch flocculants were emp]oyed with a 17.3 wt.~ sludge concentration had no suspended solids in the supcTnatant at all. Among the starch flocculants, 30g it appcars that those starches containing A2P04 were thc best. Further, it was found that thc starch flocculants are c~lally cffective on no-oil-remov~d sludge as in treating oil-removed sludge whereas the polyacrylamide flocculants were more effective on oil-removed than on no-oil-removed slud~e suspensions.
The fines contained in the sludge suspension associated with the hot water process for extracting bitumen from tar sands consists of primary~ as well as secondary minerals.
Primary minerals, ~hich are mostly quartz and some feldspars, have very low specific surface areas and little of any kind of charge. In contrast, the secondary minerals, which are mostly ~aolinite and illite with some montmorillonite and intergrade mi~ed-layer minerals, have high specific surface areas and a substantial amount of negative charge.
There is also some positive charge, usually disnosed at the edges of the crystals of solids~
As previousl~ noted, starches are polysaccharides containing many monosaccharides joined together in long chains. Upon complete hydrolysis, b~ chemical or en7ymatic means, starch )ields monosacc}larides. Starch consists primarily of two components: amylose and amylol)c~ctin. The am)~lose flaction m~kes up from ]0 to 20% of the starch and is water soluble. The other portion, amylopectic, constitutes 80 to 90% of the starch and is water insoluble.
The molecular weig]lt of the starches varies from 10,000 to 1,000,000. Thc mechanism by which starch functions as a destabilizin~ agent for sludgc appears to be one where the free hydroxyl groups of the starch attach themselvcs onto the surfaces of solid particles, probably throu~h ~ 330~

hydrogen bonding. The clay particles with adsorbed starch polymers are then no longer able to attract water molecules as before, and hence, attrac~ each other and are flocculat~d~ The presence of electrolyte in the system enhances the effectiveness of the starch flocculants by reducing the repulsive forces between the electric double layers of the solid particles, thereby ma~ing it easier for thè starch polymer to adsord and form a floc. The presence of phosphate is notably helpful, because the starch polymers can readily interlink through this radical.
It may be noted that potato starch contains 0.07 to 0.13%
phosphate and has generally been considered as a better flocculant ~han those starches containing no phosphate.
Further, starches ~ith branched chains appear to be more effective than straight chain varieties.
While the principles of the in~ention have now been made clear in an illustrative embodiment, there ~ill be immedia~ely obvious to those skilled in the art many modifications of structure, arrangement, proportions, the elements, materials and componen~s used in the practice of the in~ention which are particularly adapted for specific environments and operat;ng retluirements Wit]lOut departing from those principles.

Claims (3)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising a hydrolyzed corn or potato starch obtained by the aqueous hydrolysis of starch in the presence of insoluble metal salts formed in situ.

2. The composition according to claim 1 wherein the salt is a salt containing calcium, aluminum and phosphate ions.

3. The composition according to claim 1 wherein the salt is AlPO4.