OA16593A - Process for improving the flow rate of an aqueous dispersion. - Google Patents

Abstract

A process for improving the flow rate of an aqueous dispersion which comprises adding a natural polymer to said aqueous system and then adding a synthetic polymer to the aqueous system.

Description

PROCESS FOR IMPROVING THE FLOW RATE OF AN AQUEOUS DISPERSION

BACKGROUND OF THE INVENTION

Field ofthe Invention [0001] Processes for improving the flow rate of an aqueous System comprising adding naturel polymer to the aqueous System, and then adding a synthetic polymer to the aqueous System. The natural polymer may be a polysaccharide, such as dextran. The Related Art [0002] In the production of valuable metals and minerais in mining, ore bodies are typically ground, dispersed in aqueous solutions, treated with agents, and subjected to various processing conditions (température, pH, pressure, shear rate). The intended resuit ofthe mining operation is to generate aqueous dispersions thatwill undergo isolation, séparation, or purification of the valuable portion of the ore, whether it is a 10 métal or minerai.

[0003] Aqueous dispersions that resuit from the subject mining operations are comprised of mixtures ofwater, solids, and other materials. Examples ofthe types of solids typically found in the aqueous dispersions from minerai operations indude minerais, metals, métal oxides, métal sulfides, métal hydroxides, salts, organic matter, ¹⁵ and other inorganic matter. Aqueous dispersions that are comprised of ores, concentrâtes, tailings and the like, which may contain partides that hâve morphologies that are not conducive for rapid sédimentation or pumping are of particular interest. The pumped concentrated aqueous dispersions may contain valuable minerais or metals or waste residues. Valuable resources found in the aqueous dispersions may include minerais (bauxites, latherites, or sulfides), metals (such as iron, base metals, p recio us metals, light metals, and uranium), coal and the like. The waste streams consist of gangue minerais and other constituants with little or no value. Typically, aqueous dispersions are processed by treatment with flocculating or coagulating agents to initiate liquid-solid séparation that concentrâtes the solids portion of the aqueous dispersion in appropriate séparation processes, e.g. centrifuging, concentrating, sédimentation, dewatering, fittering and the like.

[0004] Liquid-solid séparations facilitated by the use of coagulating and/or flocculating agents are required to further concentrate the aqueous dispersions to reduce the process costs associated with transport, calcination, séparation, digestion, or storage. Liquid-solid séparations are now more challenging because ore bodies that are processed today contain lower concentrations of the valuable minerais and metals and higher concentration of gangue minerais. Gangue comprises that portion of ore bodies that is unusable or of low value, and gangue typically consiste of fine particles of irregular shape. Liquid-solid séparations are accelerated by the use of synthetic or natural palymers prior to transportlng the aqueous dispersion from where it is found or generated to the facility where it is stored, calclned, separated, or transported. Due to the size and shape of the gangue particles, gangue minerais are more difficult to agglomerate; therefore, higher dosages of synthetic or natural polymer flocculants are required to achieve the same sédimentation rates necessary to maintain desired mil) flow rates. What makes the transport of the concentrated aqueous dispersions even more challenging is that the chemicals used to coagulate or fiocculate the solids of the aqueous dispersions promote higher rheological parameters, such as higher viscosity or higher yield stress for the concentrated solids and make the solide even more difficult to pump.

[0005] Use of high molecular weight, synthetic polymer flocculants imparts higher rheological characte ris tics making pumping of the aqueous dispersions more difficult, as 5 a conséquence operating cost and profitability are negatlvely impacted. Preferably, concentrated aqueous dispersions should exhibit low yield stresses to allow pumping at low threshold energy levels. Additionally, concentrated aqueous dispersions should possess low viscosities, which should resuit in fast flow rates through mining processes for improved efficiency, productivity, and lower energy costs at the mills or refineries. In 10 order for mining companies to remain profitable, there is a need for mining operations to be able to process concentrated aqueous dispersions efficiently by reducing the rheological properties of the substrates.

SUMMARY OF THE INVENTION [0006] The disclosure relates to a process for improving the flow rate of an aqueous dispersion which comprises (a) adding a natural polymer to the aqueous dispersion, and (b) then adding a synthetic polymer to the aqueous dispersion.

[0007] By using the defined process it was discovered that the yield stress of the aqueous dispersion was reduced. The réduction of the yield stress of the aqueous dispersion is important because aqueous slurries having a lower yield stress can be transported through pipelines and other equipment more rapidly and efficiently, which results in increased productivity and energy savings. The process is of partlcular significance because the yield stress is reduced without adversely affecting the sédimentation rate or compaction of the solids in the aqueous dispersion. The conséquence is that the amount of flocculating agent needed to promote the sédimentation of the solids can be reduced thereby saving expenses on the flocculating agent. The process is particularly useful when the aqueous dispersion contains high amounts of gangue and/or when the shapes of the particles of the solids in the aqueous 5 dispersion are fine and/or of irregular shapes.

[0008] The following définitions and abbreviations shall hâve the following meanings and définitions as set forth in this spécification, including the drawings and examples. [0009] AA shall mean and refer to acrylic acid.

[0010] AM shall mean and refer to acrylamide.

[0011 ] AMPS shall mean and refer to 2-acrylamido 2-methylpropane sulfonic acid.

[0012] Aspect ratio is defined by the ratio of the minimum to the maximum Feret diameter as measured by x-ray diffraction. The aspect ratio provides an indication of the élongation and sphericity of a particle, where the sphericity of the particle is inversely proportional to the aspect ratio.

[0013] Mn is the number average molecular weight as determined by SEC-MALLS analysis.

[0014] Mw is the weight average molecular weight as determined by SEC-MALLS analysis.

[0015] MALLS shall mean and refer to multl-angular laser llght scattering.

[0016] SEC-MALLS shall mean and refer to a size exclusion chromatography technique using MALLS to détermine Mw and Mn.

[0017] PDI shall mean and refer to the polydispersibility index, which is a measure of the distribution of molecular mass in a given polymer sample and is Mw divided by the number average molecular weight (Mn), which represents the distribution of molécules of various of molecular weights.

[0018] Pa is Pascals, a measure of pressure.

[0019] Polysaccharide A shall mean and refer to a dextran having Mw of <50,000.

[0020] Polysaccharide B shall mean and refer to a dextran having Mw of 713,000.

[0021] Polysaccharide C shall mean and refer to a dextran having Mw of 2,150,000. [0022] Polysaccharide D shall mean and refer to a dextran having Mw of 4,370,000. [0023] Polysaccharide E shall mean and refer to dextran having Mw of 8,870,000. [0024] Polysaccharide F shall mean and refer to a dextran having Mw of 9,860,000.

[0025]Synthetic Polymer A is an anionic copolymer available under the trade name PRAESTOL® 2640 from Ashland Inc., Wilmington, Delaware, U.S A (“Ashland) where Mw is about 1,270,000, which is prepared by the free radical polymerization of AA and AM, such that the mole ratio of AA to AM is about 2:3.

[0026] Synthetic Polymer B is an anionic copolymer available under the trade name

FLOMIN® AL80EH from SNF Floerger, Andrézieu, France where Mw is about

1,760,000, which is prepared by the free radical polymerization of AA and AM, such that the mole ratio of AA to AM is about 4:1.

[0027] Synthetic Polymer C is an anionic copolymer available under the trade name PRAESTOL® 2740 from Ashland where Mw is about 1,080,000, which is prepared by the free radical polymerization of AA and AMPS, such that the mole ratio of AA to AMPS is about 5:1.

[0028] Synthetic Polymer D is an anionic copolymer, Photafloc 1143.5, available from Neutron Products, Inc., Dickerson, Maryland, U.S.A. which is prepared by the free radical polymerization of AM and AMPS, such that the mole ratio of AM to AMPS is about 4:1 [0029] Yield stress means and refers to the amount of energy required to start a solids moving as measured by vane rheometry,

DESCRIPTION OF THE DRAWINGS [0030] Fig. 1 is a graphie depiction showing the effect of the ratio of polysaccharide dosage to synthetic polymer dosage on the yield stress of an aqueous dispersion containing phosphate ore where a polysaccharide and synthetic polymer were used.

[0031] Fig. 2 is a bar graph showing how yield stress is affected by the order of addition ofthe polysaccharide and synthetic polymer in an aqueous dispersion containing copper tailings.

[0032] Fig. 3 is a graphie depiction showing how flow rate is affected by the addition of the polysaccharide and synthetic polymer in an aqueous

I dispersion containing phosphate ore.

DETAILED DESCRIPTION OF THE INVENTION [0033] Among the natural polymers that can be used in the process are polysaccharides, such as potato starch, xanthan gums, guara, dextran, cellulose dérivatives and glycosaminoglycans, as well as lignosulfonates.

[0034] Preferably, the natural polymer used in the subject invention is the polysaccharide dextran. Dextran is generally available from various suppliera including Dextran Products Limited, Toronto, Ontario, Canada and USB Corp., Cleveland, Ohio, U.S.A. Typically used as the polysaccharide is a dextran having a Mwoffrom about

5,000 to about 40,000,000, preferably from about 50,000 to about 25,000,000 and more preferably from about 200,000 to about 10,000,000. Typically, the PDI of the polysaccharide is from about 1.0 to about 10.0, more typically from about 1.1 to about 9.0, and most typically from about 1.2 to about 8.0. Persons of ordinary skill in these arts, aller reading this disclosure, will appreciate that ali ranges and values within these explicitly stated ranges are contemplated.

[0035] Synthetic polymers that can be used in the process include water-soluble anionic, cationic, nonionic polymers, and amphoteric polymers. For purpose of this disclosure, synthetic polymer shall include copolymers and terpolymers, as well as to homopolymers. Typically the synthetic polymer used has a Mw of from about 500,000 to about 25,000,000, preferably from about 750,000 to about 20,000,000, and more preferably from about 1,000,000 to about 18,000,000. The synthetic polymers may be linear, branched, or cross-linked. Persons of ordinary skill in these arts, aller reading this disclosure, will appreciate that ail ranges and values within these explicitly stated _1S ranges are contemplated.

[0036] Nonionic polymers include polymers formed from one or more water soluble ethylenlcally unsaturated nonionic monomers, for instance acrylamide, methacrylamide, hydroxyethyl acrylate and N-vinylpyrrolidone, preferably acrylamide. Nonionic polymers also include alkoxylated muitifunctlonal alcohols.

₂₀ [0037] Cationic polymers are formed from one or more ethylenically unsaturated cationic monomers optionally with one or more of the nonionic monomers mentioned previously. The cationic polymer may also be amphoteric provided that there are predominantly more cationic groups than anionic groups. The cationic monomers include dialkylamino alkyl (meth) acrylates, dialkylamino alkyl (meth) acrylamides, including acid addition and quaternary ammonium salts thereof, diallyl di methyl ammonium chloride. Typical cationic monomers include the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate and dimethyl aminoethyl méthacrylate. Of particular interest are the copolymer of acrylamide with the methyl chloride quaternary ammonium salts of dimethylamino ethyl acrylate (ADAME); the copolymer of acrylamide and acrylamidopropyl trimethyl ammonium chloride (APTAC); and the copolymer of acrylamide and acryloloxyethyl trimethyl ammonium chloride (AETAC); and the copolymer of epichlorohydrin and dimethylamine.

[0038] Anionic polymers are formed from one or more ethylenically unsaturated anionic monomers or a blend of one or more anionic monomers with one or more of the nonionic monomers mentioned previously. The anionic monomers include acrylic acid, methacrylic acid, maleîc acid, crotonic acid, itaconic acid, vinyl sulfonic acid, allyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylamide, mixtures thereof, and salts thereof.

[0039] Of particular interest are copolymers and/or terpolymers of monomers selected from the group consisting of acrylamide, 2-acrylamido 2-methylpropane sulfonic acid (AMPS), acrylic acid, and (meth)acrylic acid. For example, the anionic polymer may be selected from the group consisting of copolymers derived from 2-acrylamido 2methylpropane sulfonic acid, copolymers of acrylic acid and acrylamide, homopolymers of acrylic acid, homopolymers of acrylamide, and combinations thereof. Typically used as anionic polymer are the copolymer of sodium acrylate and acrylamide and the copolymer of acrylic acid and acrylamide.

[0040] In certain mining segments whereby the pH range is approximately between about 5 and about 10, of particular interest are copolymers of AMPS and acrylamide wherein the mole percent of AMPS is from about 10 mole percent to about 25 mole percent, and terpolymers of AMPS, acrylamide, and acrylic acid wherein the mole percent of AMPS is from about 10 mole percent to about 30 mole percent, the mole percent of acrylamide is from about 40 mole percent to about 60 mole percent, and the mole percent of acrylic acid is from about 20 mole percent to about 40 mole percent. Otherwise, homopolymers of acrylic acid or copolymers of acrylic acid and acrylamide are of particular interest.

[0041 ] The synthetic polymer can be prepared by polymerization of a water soluble monomer or water soluble monomer blend according to methods well known in the art. The water soluble monomers typically are water soluble monomers or water soluble monomer blend that having a solubility in water of at least 5 g in 100 ml of water.

[0042] The natural polymer is first added to the aqueous dispersion and this is followed ₁₅ by the addition of the synthetic polymer to the aqueous dispersion. Although not critical, the synthetic polymer is typically added to the aqueous dispersion within a minute, or even seconds, after the natural polymer is added to the aqueous dispersion.

[0043] The amount of natural polymer required to promote lower rheological properties such as yield stress or viscosity will be dépendent on the characteristic properties of the ₂₀ natural polymer, the morphology of the particles in the aqueous dispersion, and the concentration of the aqueous dispersion during liquid-solid séparation. The weight ratio of natural polymer to synthetic polymer is a ratio that effectively reduces the yield stress of the aqueous dispersion is generally is a ratio is from about 4:1 to about 1:4, and typically ranges from about 0.10:1.0 to about 1.0:1 0, preferably from about 0.25:1.0 to about 0.75:1.0, and more preferably from about 0.25:1.0 to about 0.50:1.0. The total amount of natural polymer and synthetic polymer used to treat the aqueous System varies over wide ranges but typically ranges from about 1.0 to about 1000 grams per metric ton of aqueous System treated, preferably from about 5.0 to about 500 grams per metric ton, and more preferably from about 10.0 to about 100 grams per metric ton. [0044] The total solids found in the aqueous dispersion can vary over wide ranges, but typically ranges from about 25 g/liter to about 2,000 g/liter, such as about 50 g/iiter to 2,000 g/liter. The process is particularly useful in reducing the yield stress of the aqueous dispersion where the aspect ratio of the solids is less than about 1.0, more particularly when the aspect ratio is less than about 0.5, and/or the solids If the aqueous dispersion contains a substantial amount of gangue.

EXAMPLES [0045] In ail of the examples, unless otherwise noted, the polysaccharide dextran was used as the natural polymer and anionic copolymers were used as the synthetic polymers. In each set of examples, a comparative example was run using only a synthetic polymer, Le., no natural polymer was used. Mw values for the polysaccharides were determined by SEC-MALLS analyses.

[0046] Unless otherwise indicated, the yield stress of the tested aqueous dispersion was determined by adding 1000 mL of an aqueous dispersion to a graduated cylînder, where it was first treated by adding natural polymer to the aqueous dispersion, tamping the natural polymer into the dispersion three fîmes with a plunger having perforated holes.

Then, the synthetic polymer was added to the aqueous dispersion using the same mixing technique and number of tamps.

[0047] The rate at which the liquid-solîd séparation occurred was established by starting a timer at the point where the liquid-solid interface reached the 1000 milliiiter mark in the graduated cylinder and then recording the time at which the liquid-solid interface reached each additional 50 milliliters down to the 700 milliiiter mark. The sédimentation rate was calculated by subtracting the time recorded at the 900 milliiiter mark from the time recorded at the 700 milliiiter mark.

[0048] A compaction value was recorded after 18 hours. The subséquent measurements of yield stress were taken after the 24 hour mark. To préparé the samples for analysis the liquid was siphoned out of the 1000 milliiiter graduated cylinders until there were only concentrated solids left in the cylinders. The resulting slurries were quantitatively transfarred into appropriately sized beakers. The slurries in the beakers were allowed to restfor an additional 4 hours prier to conducting the yield stress measurements.

[0049] The yield stress (in Pa) was measured with a Brookfield HBDVIII Ultra rheometer or Brookfield RVDVIII Ultra rheometer using vane spindles. The tested aqueous dispersion was placed in an appropriately sized beaker for the vane spindle used. The sélection of the spindle or rheometer depended on the magnitude of range of yield stress measured. The vane spindle was lowered down into the aqueous dispersion to the vane spindle's primary mark. RHEOCALC ® software was used to calculais the yield stress utilizing either the Bingham model or the Casson model where noted. [0050] Descriptions of the polysaccharides used in the examples are setforth in Table I.

; Table I. I
iReagent	ÎMw(g/mol)	PDI (Mw/Mn) ;
Polysaccharide A	j <50,000	1.01 !
Polysaccharide B	713,000	3.62 !
Polysaccharide c	2,150,000	2.09 I
Polysaccharide D	4,370,000	1.08 j
.Pp.lyssccharide E	8,870,000	. 1.01 I
Polysaccharide F	9,860,000	1.30

Exemples 1-3 and comparative example A [0051] These examples illustrate the use of polysaccharides of Table I with a synthetic polymer (Synthetic Polymer B) to concentrate the solide of an aqueous dispersion containing alumina tailings, known in the alumina industry as red mud, and how this affects the yield stress of the concentrated aqueous dispersion. Comparative example 5 A used only Synthetic Polymer B as the polymer treatment [0052] In these examples, the dextran polysaccharides of varying molecular weight, were added first followed by the addition of Synthetic Polymer B, an anionic copolymer. The amount of solids in the aqueous dispersion was 50 grams per liter. The dosage of dextran plus Synthetic Polymer B in the examples ranged from 250 grams per ton to 400 grams per ton, with a constant synthetic polymer dosage of 200 grams per ton. The dextrans used and the percent dosage of dextran to Synthetic Polymer B are set forth in Table II. The yield stress values of the aqueous dispersions were then measured and the résulta are also set forth in Table 11.

tim il.

i ; Polysaccharide Dcaete at Percentega of Synthetic Polymer Dosage,

' Brample ·	SutHtnte	'StMldt (t/u	Ressentis)	0	25	333 37.3	se : ».7	.100 !	300
A	.Alu mina TalUr>f»_	w	Synthetic Polymer B (1).____ i 10,21	-	•	- - :		____
1	Alumine Talllnes	50	Polysaccharide A plue Synthetic Polymer B		641	- . -	3.33 1 -	2.94
2	Alumine Talllnf»	»	PolyiMchirld. D plu· Synth.tlt Polym·.		«3.	; 1 *	s. ta	m aa	-
3	Alumine Tellings	50	Polysaccharide F plu» SyntheticPolymer B	-,	9.28		1X00 .	10.40	_
B	Fhoaphate Or*	130	Synthetic Polymer A	104.1					-
	Phosphate Or*	130	Polysaccharide B plu»5yntheticPolymerA		-	36-8	60.9	52.7	*
S	Phosphate Or*	130	Polyiwxharlde C plu» SynlheUcPolymer A		1	- ! 12-1	54.0 >	59-1 .	-
6	Phosphate Ore	130	. Polysaccharide 0 plusSynthetlC Polymer A	-		- 1 Κβ.9	TM. |. ς..	54.4 '	-
c	Gold Cancanent*	L...»...	Synthetic Polymer A	444.2		- -	• 1 -	-
7	Gold Concentrât*	UO	PolyiKchirld. B plutS^ntheticPolymer A		339.4	- 1 -	295.8 ’	276.5 '	-
B	Go IdConcentrât*	180	Polysaccharide C plus Synthetic Polymer A		415.fi		394.5 -	4S5.1
«	Gcld Concentrât·	.»0 .	. Polysaccharide 0 plu» Synthetic Polymer A				419.7 -	410.4 1400.8
D	CopperTalHne»		Synthetic Polymer A	33B.1	-	T·.—
10	Copper Tailings	.. 90	Polysaccharide B plu» Synthetic Polymer A	-	197.1	i	2δί_6	2547
11	Copper Tailings	90	PolyiKChwtPe C plus Synthetic Polymer A		1M.9		361.5	248.
12	Copper Tailings a	90	^Polyteccharld· Dplua SyntheticPolymer A			: -	316	177.1	-
13	CoppcrTallInge	90	Polysaccharide E plus SyntheticPolymer A		252.9		233.6	196.5
t	Copper ΓιΙΙΙηρ	isa	Synthetic Polymer C	537.9		- -	- t .	-	-
M_____	Copper Tailings	.. i?·..	_ Polysaccharide B plu» Synthetic Polymer C		-_____		.. x... roc.3	.7»·? I	____
15	CopperTalllnp	-	P.ohfMjxhiirltle ç plu» Synthetic Pommer Ç			1427 i ·	. ’. ; 214.3	29B '
16	CopparTalllMs	138	PolyiKCharld* 0 plia Synthetic Polymer C		•	««L -	--JW.	371.4 ·	-
F	Copper Tailings	59	Synthetic Polyma r A (1)	3.1		Ί -	• r ·	- 1	•
17 iCopoerTalIlHii	sa	Polysaccharide B pkA Synthetic Pôîyme r A (2]		-	-	. ! -	114 1	-J
______G_____	CopperTelllnp_____		Synthetic Polymer A plu» Polysaccharide a (2,3)			...:...1..-..	a “Γ\’	i» ;

Note* . ... __ ., _ '{1) Yield tkhBMvalue I» eyerige of twoMrnple».

(3) Yteldstr*» value»wer* calcul atad wltbÇMion modal. |3J Synthetic polymer added prier to polysaccharide., _ .

[0053] The data in Table II demonstrate that the yield stress values for the aqueous dispersions containing the afumina tailings decreased when the dextran was used in conjunction with Synthetic Polymer B. The data show that the yield stress was reduced as the proportion of polysaccharide dosage to synthetic polymer dosage increased to an optimal ratio. The data also indicate that the yield stress decreased If the ratio of polysaccharide to Synthetic Polymer B was less than or equal to about 1:2 for polysaccharides A and D, and the yield stress decreased if the ratio of polysaccharide to Synthetic Polymer B was less than or equal to about 1:4 for polysaccharide F.

Moreover, the data suggest that the lower molecular weight polysaccharides require lower dosages to achieve lower yield stress values.

Examples 4-6 and comparative example B [0054] Examples 4-6 and comparative example B were conducted using an aqueous dispersion containing phosphate ore. In these examples, the dextran polysaccharides of varying molecular weight were added first followed by the addition of Synthetic Polymer A, an anlonic copolymer. The amount of solids in the aqueous dispersion was 5 130 grams per liter and the dosage of dextran plus Synthetic Polymer A in the examples ranged from 77 grams per ton to 108 grams per ton with a constant synthetic polymer dosage of 62 grams per ton. The dextrans used and the percent dosage of dextran to Synthetic Polymer A are set forth In Table II. The yield stress values of the aqueous dispersions were then measured and the results are also set forth in Table II and in Fig.

1.

₁₀ [0055] The data in Table II demonstrate that the yield stress values for the aqueous dispersions containing phosphate ore decreased when the dextran was used in conjunction with Synthetic Polymer A. The data show that the yield stress was reduced as the proportion of polysaccharide dosage to synthetic polymer dosage increased to an optimal ratio. The data indicate that the yield stress decreased if the ratio of polysaccharide to Synthetic Polymer A was less than or equal to about 1:4 for polysaccharide B and C, and yield stress decreases if the ratio of polysaccharide to Synthetic Polymer A was greater than equal to about 1:4 for polysaccharide D.

Moreover, the data also suggest that lower molecular weight polysaccharides utilize lower dosages to achieve lower yield stress values.

Examples 7-9 and comparative example C [0056] Examples 7-9 and comparative example C were conducted using an aqueous dispersion containing gold, sulfides, carbonaceous minerais, and other materials. The amount of solids in the aqueous dispersion was 180 grams per Iiter and the dosage of dextran plus Synthetic Polymer A in the examples ranged from 17 grams per ton to 35 grams per ton with the synthetic polymer dosage remaining constant at 12 grams per ton. The dextrans used and the percent dosage of dextran to Synthetic Polymer A are set forth in Table II. The yield stress values of the aqueous dispersions were then measured and the résulta are also set forlh In Table II.

[0057] The data in Table II demonstrate that the yield stress values for the aqueous dispersions containing gold concentrate decreased when the dextran was used in conjunction with Synthetic Polymer A. The data show that the yield stress decreases most significantly if the ratio of polysaccharide to Synthetic Polymer A is less than or equal to about 1:2 for polysaccharide. The data indicate that the yield stress for the aqueous dispersion containing gold ore decreases if the dextran is used in conjunction with Synthetic Polymer A. Moreover, the data also suggest that lower molecular weight polysaccharides require lower dosages to achleve lower yield stress values.

Examples 10-13 and comparative example D [0058] Examples 10-13 and comparative example D were conducted using an aqueous dispersion containing copper, sulfides, tailings, and other materials. In addition, polysaccharide E was also tested. The amount of solids in the aqueous dispersion was

grams per liter and the dosage of dextran plus Synthetic Polymer A in the examples ranged from about 21 grams per ton to 34 grams per ton with the synthetic polymer dosage remaining constant at 17 grams per ton. The dextrans used and the percent dosage of dextran to Synthetic Polymer A are set forth in Table II. The yield stress values of the aqueous dispersions were then measured and the results are also set forth in Table II.

[0059] The data in Table II demonstrate that the yield stress for the aqueous dispersion containlng copper tailings and other materials decreased when the dextran was used In conjunction with Synthetic Polymer A. The data show that the yield stress decreases if 10 the ratio of polysaccharide to Synthetic Polymer A is less than or equal to about 2:3 for polysaccharide B and C, and D. Moreover, the data suggest that lower molecular weight polysaccharides require lower dosages to achieve lower yield stress values.

Exemples 14-16 and comparative example E [0060] Examples 14-16 and comparative exampte E were conducted using an aqueous dispersion containing copper, sulfates, tailings, and other materials. The amount of solids in the aqueous dispersion was 198 grams per liter and the dosage of dextran plus Synthetic Polymer C in the examples ranged from 18 grams per ton to 27 grams per ton with the synthetic polymer dosage remaining constant at 14 grams per ton. The dextrans used and the weight percent of dextran and Synthetic Polymer C (dosage ratio) are set forth in Table II. The yield stress of the aqueous dispersion was then measured and the results are also set forth in Table II.

[0061] The data in Table II demonstrate that the yield stress for the aqueous dispersions containing copper tailings and other materials decreased when the dextran was used in conjunction with Synthetic Polymer C. The data indicate that the yield stress decreases if the ratio of polysaccharide to Synthetic Polymer C is less than or equal to about 2:3 for polysaccharide B, C, and D.

[0062] Examples 1-16 lllustrate that the yield stress value exhiblted by an aqueous dispersion is reduced by adding a dextran to the aqueous dispersion followed by anionic copolymer, particulariy for certain naturel polymers with an appropriate Mw and for particular weight ratios of naturel polymer to synthetic polymer. This discovery is important because reducing the yield stress of the aqueous dispersion means that the initial energy required to begin pumping the dispersion is reduced. Reducing yield stress results in cost savings and increased flow rates when the aqueous dispersion is pumped through the pipes that transport the aqueous dispersion to the facility where valuable resources are separated from the solids of the aqueous dispersion and when the aqueous dispersion is pumped through the equîpment used to separate valuable resources from the solids in the aqueous dispersion. This can be accomplished without significantly increasing the sédimentation rate of the solids in the aqueous dispersion.

Example 17 and comparative examples F, and G [0063] For Example 17, the procedure of Examples 10-13 was repeated using an aqueous dispersion containing copper, sulfides, tailings, and other materials. However, in comparative example F, only Synthetic Polymer A was used, and in comparative example G, the order of addition was reversed, i.e. the synthetic polymer was added

before the natural polymer. The amount of solids in the aqueous dispersion was 59 grams per liter. The dosage of dextran plus Synthetic Polymer A in the examples remained constant at 34 grame per ton with the synthetic polymer dosage remalnlng constant at 17 grams per ton. The yield stress values of the aqueous dispersions were 5 then measured and the results are set forth in Table II.

[0064] The data in Table It demonstrate that the yield stress values for the aqueous dispersions containing copper tailings, and other materials decreased when the dextran was used in conjunction with Synthetic Polymer A. Fig. 2 indicates that the yield stress decreases if the polysaccharide is added first followed by the addition of synthetic ₁₀ polymer.

Comparative Examples H, I, J, and K [0065] The procedure of Example 1 was repeated using an aqueous dispersion containing alumina tailings, red mud, and other materials, but only Synthetic Polymer B was used to détermina the effect on yield stress if no natural polymer was used. The amount of solids in the aqueous dispersion was about 50 grams per liter and the dosage of the Synthetic Polymer B in the examples ranged from 54 grams per ton to 200 grams per ton. The yield stress of the aqueous dispersion was then measured and the results are set forth in Table III.

Table III.

Example Substrat* ; Solids (g/L) I______Reagent_______[ j H_ ; AluminaTalllngs ^{* 1} 47 (Synthetic Polymer B I j I ÎAlumlnaTalllngs ] 47 'Synthetic Polymer B ( ;____J jAluminaTalllngs j 50 ___Synthetic Polymer B I

K Alumina Talllngs ;_____50_____[Synthetic Polymer B j

Synthetic Polymer Dosage (g/T) Yleld Stress (Pa) ~54 107 ί 2ÛÛ 2ÔÔ

------^μ ~ ------I 4,97 -9.22 _!_____

J_.io.60 ^f ‘ .. J.. ! .9-.82.

[0066] The data in Table III demonstrate that the yield stress values for the aqueous dispersions containing alumina tailings and other materials increased when the dosage of Synthetic Polymer B was increased. This is just the opposite from ail previous examples where the naturel polymer was added first and then followed by the addition of synthetic polymer.

Examples 18-19 and comparative example L

I [0067] Examples 18-19 and comparative example L were conducted using an aqueous dispersion containing phosphate ore. In these examples, the dextran polysaccharides of varying molecular weight were added first followed by the addition of Synthetic Polymer D, an anionic copoiymer. The amount of solids in the aqueous dispersion was 1099 grams per liter and the dosage of dextran plus Synthetic Polymer D in the examples ranged from 50 grams per ton to 75 grams per ton with a constant synthetic polymer dosage of 100 grams per ton. The dextran used and the percent dosage of dextran to Synthetic Polymer C are set forth in Table IV. The flow rate values for the aqueous dispersions at given pump potentials were then measured and the results are also set forth in Table IV and Fig. 3.

[0068] The data in Table IV demonstratas that the matériel flow rates values for the aqueous dispersions containing phosphate ore increased when the dextran was used in conjunction with Synthetîc Polymer D. The data show that the flow rate was increased as the proportion of polysaccharide dosage to synthetîc polymer dosage increased.

Table IV.
Substrate	Sollds (k/L)	Ireatment / Pump Meules
Phosphate Ore	1099	Naiural Polymer	Flow	Potentiel	Current
Exemple N	Reagent	Percent Dosage (K)	(GPM)	(volts)	(amps)
L	Synthetîc Polymer D Only	......Q.._ ......	.....3?.....	... .»L.„	r..A8.....
L	Synthetîc Polymer D Only	0	34	477	3,3...
[ L	Synthetîc Polymer 0 Only	0	....	319	28
L	Synthetîc Polymer 0 Only	0	Γ 35 ...	475	3.3
I 18 ______	. PelysacçhgrideC.plusSynthetîcPolymer0,.^	_______50_______.	30	253	2-’
18	Polysaccharide C plus Synthetîc Polymer D	50	40	363	3.0

j____Polysaccharide C plus Synthetîc Polymer O

Polysaccharide C plus Synthetîc Polymer D j Polysaccharide C plus Synthetîc Polymer D__;

' Polysaccharide C plus Synthetîc Polymer D Polysaccharide C plus Synthetîc Polymer D ..P?tys?cdiarlde Ç plusSynthetlc Polymer D

Claims (20)

1. We claim:

   1. A procès s for improving the flow rate of an aqueous dispersion comprising (a) adding a natural polymer to the aqueous dispersion, and (b) then adding a synthetic polymer to the aqueous dispersion, wherein the natural polymer and the synthetic polymer is an amount effective to Increase the flow rate of the aqueous dispersion.
2. 2. The process of Claim 1 wherein the natural polymer is a polysaccharide.
3. 3. The process of Claim 2 wherein the polysaccharide is a dextran.
4. 4. The process of Claim 3 wherein the synthetic polymer is selected from the group consisting of water soluble anionic polymère, cationic polymère, amphoteric polymère, nonionic polymère, and mixtures thereof.
5. 5. The process of Claim 4 wherein the synthetic polymer is an anionic polymer.
6. 6. The process of Claim 5 wherein the anionic polymer is selected from the group consisting of copolymers derived from 2-acrylamido 2-methylpropane sulfonic acid, copolymers of acrylic acid and acrylamide, homopolymers of acrylic acid, homopolymers of acrylamide, and combinations thereof.
7. 7. The process of Claim 5 wherein the anionic polymer comprises a copolymer of sodium acrylate and acrylamide or a copolymer of acrylic acid and acrylamide.
8. 8. The process of Claim 5 wherein the pH of the anionic polymer is about 5 to about

   10.
9. 9. The process of Claim 5 wherein Mw of the dextran is about 5,000 to about 40,000,0000.
10. 10. The process of Claim 9 wherein Mw of the anionic polymer is about 500,000 to about 25,000,000.
11. 11. The process of Claim 10 wherein the PDI of the dextran is about 1.0 to about 10.0.
12. 12. The process of Claim 11 wherein weight ratio of natural polymer and synthetic polymer is a ratio effective to increase the flow rate of the aqueous dispersion.
13. 13. The process of Claim 12 wherein weight ratio of natural polymer and synthetic polymer is about 4:1 to about 1:4.
14. 14. The process of Claim 13 wherein the weight ratio is about 0.10:1.0 to about 1.0:1.0.
15. 15. The process of Claim 13 wherein the total solids in the aqueous dispersion is about 25 grams per liter to about 2,000 grams per liter.
16. 16. The process of Claim 15 wherein the aspect ratio of the solids is less than about 1.0.
17. 17. The process of Claim 16 wherein the majority of the solids by weight comprises an ore containing phosphate, copper, gold, or other minerais.
18. 18. The process of Claim 16 wherein the majority of the solids by weight comprises gangue.
19. 19. The process of Claim 2 wherein the polysaccharide is selected from the group consisting of potato starch, xanthan gums, guars, cellulose dérivatives and glycosaminoglycans.
20. 20. A process for improving the flow rate of an aqueous dispersion comprising (a) adding a lignosulfonate to the aqueous dispersion, and (b) then adding a synthetic polymer to the aqueous dispersion, wherein the lignosulfonate and the synthetic polymer is an amount effective to increase the flow rate of the aqueous dispersion.