Note: Descriptions are shown in the official language in which they were submitted.
339
INTRODUCTION
This invention relates to an improved method for prepar-
ing readily disposable waste products from tailings obtained in the
mining and processing of minerals and ores. This is accomplished by
taking a thickener underflow containing a slurry of mineral tailings
~sludge) which is difficult to settle, and adding to this ma~erial a
polypolar polymer followed by adding the thus treated material to a
vibrating screen having placed thereon coarse mineral refuse, operating
the vibrating scre0n, and then recovering a semi-solid waste composite
which can be disposed of in land fills or the like.
One of the problems faced currently by the mineral processing
industries and especially the coal industry is the disposal of finely
divided tailings obtained from the mining and processing of the mineral.
These finely divided materials are often difficult to settle and
commercially, most of such tailings are currently being treated by pumping
it as an aqueous suspension to holding ponds where it is allowed to settle
over a long period of time.
Problems have arisen using this technique, including the con-
tamination of ground water supplies by the seepage of this material
through the soil, dam breaks causîng large quantities of this tailing
waste ~o enter streams and rivers killing substantial numbers of fish and
wild Iife as well as damage to human property and life; and of course, the
amount of land which must be expended to maintain the settling ponds.
The mineral tailings, consisting largely of clay-like materials,
have not been satisfactorily treated by conventional methods such as the
.
use of flocculation or coagulation or by filtration techniques since these
particles tend to be so fine as to take an unduly long period to settle
; even with the aid of chemical treatment and t~eir small size gives them
.
the ability to clog filter media. As witnessed by the prior art, the
settling of thls type of ma~erial~has been a problem for quite some time.
Booth et al, U.S. 3,418,237, discloses a method for settling
minerals which are predominantly non-argillacous in nature from water
- 2 - ~
. . . ~ .. . :
~7~39
suspensions by the use oE a water soluble acrylate polymer. ~hile this
method has gained some success and involves the use of conventional type
thickeners or clarifiers and while producing a pulp oE largely mineral
slimes or tailings still does not dewater these materials suf~iciently
to enable the disposal of these materials as solid, it is pointed out
that this reference specifically deals with the problems which the
instant invention seeks to remedy; that is, gravity or sedimentation
techniques are slow and inefficient and that ~iltration is difficult due
to the tine nature of these materials.
Dajan; et al, U.S. 3,~08,293, assigned to the Nalco Chemical
Company discloses a method for the clarification of coal slurries,
specifically relating to the clarification of aqueous waste containing
coal fines and clay products as a by-product and coal washing or process-
ing techniques. Again, while this method has gained some acceptance in
the art, it deals with conventional clarification techniques using a
thickener or clarifier and produces waste which must be pumped to lagoons
or ponds for evaporation of the water or settling of ~he fines so that
a high quality waste water can be discharged.
Booth, U.S. 3,524,682 discloses a method for improving the
20 pumpability of the coal by the addition of a water soluble polyelectrolyte
so as to suspend the fine materials and thus allow further treatment.
Priesing et al, U.S. 3,259,570 and U.S. 3~300J~07, disclose
methods for the dewatering of aqueous suspension of organic solids, again
using conventional techniques, i.e. the use of a clarifier or thickener
and again producing a floc or sedimentation product which must be ~urther
treated to enable disposal as a solid when only these methods are used.
~hile Priesing does use a vacuum filter in several of his examples, this
method would be difficult at best with mineral tailings due to the fine
nature of the particulates and thus would not be applicable to a process
such as that of the instant invention.
Spoerle et al, U.S. 3,790~476, discloses a method for thickening
OT dewatering solids from industrial wastes including coal mining slurries
~- ~ 3
. . . .. .. .. . . . ..
3L33g~
using various acrylamide type polymers again using con~entional clarifiers
for sedimentation of the floc to produce a wet material which is not
readily disposable as a solid, but must be dried by other means before
solids disposal can take place.
We have now found a simple and inexpensive technique using
readily available mechanical equipment for rendering the Eloc produced
in clarifiers and thickeners, consisting largely of mineral tailings,
semi-solid and non-sticky allowing for their immediate disposal in land
fills and the like thus eliminating the need or use of settling ponds or
expensive and time consuming mechanical operations such as vacuum filtration.
This is accomplished by separating the tailings first by using a conven-
tional clarifier or thickener, adding to this waste floc ~rom 1 - ~,000
ppm of a water soluble polypolar polymer and adding this material to a
vibrating screen having a layer thereon of a coarse refuse, subjecting
the screen to vibratory motion and then dîsposing of the waste as a semi-
solid non-sticky composite waste in land fills or the like.
It is pointed out that while parts of the process as described
above will vary greatly, it will be seen by those skilled in the art that
the general jist of our invention is to treat sludge produced in mineral
tailings on a vibrating screen using a bed of coarse particulate matter
as essentially a filter aid and then recovering a solid disposable
material.
Thus the present invention seeks to provide a method for the
disposal and reclaimation of mineral tailings as a semi-solid non-sticky
waste.
Alternatively, the invention seeks to provide a method for the
disposal and reclaimation of sludges produced in mineral processing
operations by the addition of a polypolar polymer to the sludge and
the addition of the treated sludge to a vibrating screen having placed
. .
thereon a layer of a coarse refuse, subjecting the screen to vibratory
mo~ion and then recovering a disposable semi-solid material.
~7~L33~
This i.nvention also provides a method for maintaining a closed
water system and the elimination of holding ponds or lagoons or the like
used to settle mineral tailings ~y the addltion of from 1 - 4,000 ppm of
a water soluble polypolar polymer to the waste sludge prepared from the
initial clarification of mineral processing waste waters followed by
adding the so treated sludge to a vibrating screen having a layer
thereon of a coarse refuse screened out of the waste water prior to
the initial coagulation or flocculation, subjecting the vibrating screen
to vibratory motion and then recovering a semi-solid non-sticky waste
10 composite which is readily disposed of.
THE INVE~TION ;.
The method of our invention for the recovery of a solid waste
from aqueous mineral processing waste which contains coarse particulate
, refuse and finely divided suspended tailings generally comprises the
steps of:
A. Separating the coarse particulate re-fuse from the finely
- divided suspended tailings to provide a solid mass of coarse particulate
refuse and an aqueous suspension of finely divided suspended tailings;
B. Flocculating the aqueous suspension of the finely divided
~ 2~ tailings to form a concentrated aqueous suspension of the finely divided
:. tailings;
C. Treating the concentrated aqueous suspension of the finely
divided tailings with from 1 - 4,000 ppm of a polypolar water soluble
polymer wherein the concentrated aqueous suspension is flocculated to form
. a semi-solid non-sticky material;
D. Adding the semi-solid non-sticky material formed in Step C
to the solid mass of coarse particulate refuse formed in Step A to provide
- a composite solid waste; and then
~. Disposing the composite solid waste.
~ More specï.ficallyl the method of our invention for the recovery .
of solid waste from aqueous mineral solid waste comprises the steps of:
: _ 5 _
!. p~ ,.:
~ ~ ~J ~: ~
,'~ . ~ :
.;
~7133g
A. Separating the coarse particulate refuse from the finely
divided suspended tailings to provide a solid mass of coarse particulate
refuse and an aqueous suspension of finely divided suspended tailings;
B. Flocculating the aqueous suspension of the finely divided
tailings to form a concentrated aqueous suspension of the finely divided
tailings;
C. Treating the concentrated aqueous suspension of the finely
divided tailings with from 1 - 4,000 ppm of a polypolar water soluble
polymer wherein the concentrated aqueous suspension is flocculated to
form a semi-solid non-sticky material;
D, Adding a layer of the coarse particulate refuse of Step A
to a vibrating screen so as to remove water from said coarse particulate
refuse;
E. Maintaining said coarse particulate refuse on the vibrating
screen;
F. Adding to the coarse particulate refuse on the vibrating
; screen a layer of the semi-solid non-sticky material formed in Step C to
provide a composite solid waste;
G. Retaining said composite solid refuse on the vibrating
screen for a period of time necessary to reduce the water content of the
composi~e solid waste to below 50%, and then,
H. Disposing of the composite solid waste.
BRIEF DESCRIPTION OF THE DRAWING
.,
Figure 1 shows a typical waste treatment plant in a mineral
processing operation encompassing the improvement of our invention. The
diagram is schematic and shows basically mineral processing waste water
. .
entering the plant through line 2 going through line 4 to a thickener
generally designated as 8. Clear water 18 leaves the thickener while
the sludge produced consisting of mineral tailings 20 is pumped through
line 22 by pump 24 eventually ~inding up in line 32 to ~e deposited upon
vibrating screen generally designated as 44. Coarse particulate matter
from other operations within the mineral processing plant enters through
::
,. , , : : " . - ,:
~07~L339
line 34 and flows into hopper generally des~gnated as 38 ~here it is
deposited onto the vibrating screen in an even layer. In the drawing
shown, the scr~en shown is slightly inclined downward to the right as
shown by arrow 54 causing the flow of the material to progress in that
direction as ~he screen is vibra~ing. It is also within the scope of our
invention to have the screen level, or inclined upward, the vibratory
motion of the screen being sufficient to propel the material contained
upon the scr~en to the end of the screen. Sludge 20 is then deposited
as a layer upon the coarse material on vibrating screen 44, vibrating is
continued producing a solid non-sticky waste composite which can be
readily disposed of by trucks or other means.
D~IAIL~ CRIPIION OF TH RAWING
As stated above, Figure 1 shows a schematic diagram of a waste
water plant treating mineral processing kailings. Water hav;ng had coarse
particulate matter screened out through means not shown, enters the plant
through line 2. Line 2 merges with line 4 and empties into the thickener
generally designated as 6. Thickener 6 has sides 8 and bottom 10, influent
well 12 and a water level generall~ designated as 14. In the sedimentation
step within the thickener, water is clarified with clear water rising to
.
the surface passing through wiers 1~ and exiting the thickener through
line 18 for disposal or recycle. Mineral tailings sludge 20 settles to
; the bottom of the thickener and is then pumped through line 22 by pump 24
into line 26. From line 26~ mineral processing sludge 20 containing the
fm ely divided tailings enters line 32 and is deposited upon a layer of
coarse refuse on the vibrating screen 44. Coarse particulate refuse
enters through line 34. Line 34 passes into hopper 38 at point 36 and
leaves the hopper 38 at point 40 where it is deposi~ed upon the vibra~ing
screen 44 in an even layer. Vibrating screen 44 basically consists of a
screen 4~, sides 48 and 50. It i5 powered by means 52 which causf_s it to
vibrate in either a vertical or horizontal direction or both. While in
the drawing the screen shown is inclined downward as shown by arrow 549
in actual practice the screen may be level or inclined downward and
~ 7
..~, ,.. ~, f
-
~6~7~1L3~9
the flow will thus be governed by the vi~ratory motion imparted to the
screen by means 52. The rate at which material passes off the screen is
governed by the feed rate of coarse refuse and tailings as well as the
incline and intensity and character of the vibrations. Coarse refuse
deposited through line 40 moves downward along the screen and at point 33
has added to its surface the concentrated aqueous suspension of finely
divided tailings.
Vibrating is continued while the material loses water which
drains through the screen 46 and flows into drain 56. Drain 56 while
shown at one end of the vibrating screen in the drawing may in actual
practice by anyl~here underneath the vibrating screen~ and the method
chosen for water removal wi]l be readily apparent to those skilled in
the art.
Upon reaching the end of the screen 50, the now semi-solid
non-sticky material composite solid waste flows into hopper 60 having
sides 62 and then flows through line 64, shut-off 66 and line 68 to a
waiting refuse truclc not shown or to a conveyer belt not shown which will
take the material to a land fill, strip mine, mine shaft, etc. for disposal.
; Water removed from the material flows through drain 56, enters line 58 and
then flows into line 4 re-depositing the water into thickener 6 for further
clarification.
The coarse refuse deposited upon screen 44 through pipe 40 is
generally deposited in a depth of from .01 - 2 inches. Preferably, this
coarse refuse is deposited on the screen at a depth of from .01 - 1 inch.
This allows the coarse refuse to act as a filter aid to hold the small
particulate matter to be deposited on the screen through line 32 but not
at such a depth as to retain water itself.
The size of coarse refuse may range from 1 inch to .001 inch
and is prefera~ly from 3/4 inch to .01 inch. Most preferably the coarse
refuse is sized from 3/8 mch to .1 inch. As a further description, the
screen 44 should have a mesh 46 sufficient -to retain substantially all
of the particles of the coarse refuse on the screen. Thè aqueous
. ~ .
-- 8 --
1 ~ .
;~, ~.,., ~ .
- .:
~L~?7~33~
suspension of finely divided tailings being deposited -upon the layer of
coarse refuse through line 32 at point 33 is generally depasited as
unifor~ly as possible at a depth of from n.s - lO inches. Preferably this
material is deposited at a depth of from 1 - 8 inches and most preferably
from 2 to 6 inches. This material generall~ contains approximately 50 -
80% by weight water and resembles a mud or sludge of sorts.
Of course, the relative size of the equipment pictured and details
of the construction ~ill vary from plant to plan~ depending upon location,
pump and siæe. It is pointed out also that while one particular design of
thickener 6 is shown, other designs will perform adequately. The plant
waste water entering clarifier 6 may or may not be treated by chemicals
to settle out the flock faster and it is unimportant ~lithin the scope of
our invention whether this occurs sv long as a floc is formed.
The polypolar polymers of our invention are generally added to
, the aqueous suspension of the finely divided tailings at a point somewhere
- along line 26 and before the finely divided taîlings contact the coarse ~`
refuse on the vibrating screen. Referring again to the drawing, polymer
storage tank 70 containing a water soluble polypolar polym~r travels
through line 74 and into valve and meter 76. ~alve and meter 76 should
be capable of adjustment and ~ay in fact be two separate devices so long
as polymer is sufficiently metered into the system through point 78 to
insure a quantity to form 1 - 4,000 ppm by weight of acti~e polymer
present in the aqueous suspension of tailings.
Optionally, two or more different types of polypolar polymers may
be useful and as such a second polymer container 80 connected by line 84
to valve and meter 86 feeds polymer into line 26 at point 88. This allows
for treatment as necessary with both a cationic and anionic polypolar
polymer as th~ tailings so warrant ~o achieve adequate de~atering.
Polymer container 70 and 80 may be of any conventional construction and
should be resistant to attack from the polymers contained therein. We
have generally ~ound that suficient mixing of the polypolar polymers in
line 26 with the aqueous suspension of the concentrated tailings wîll
- g _
~i~
~7~33g
occur by the simple flow prior to their contact with the coarse refuse on
t~e vibrating screen. It should be seen and will be obvious to those
skilled in the art that methods for the injection of polypolar polymer
into the system at approximately these points are well known and thus
further discussion of suitable valves, flow meters, measuring devices
and pumps is unnecessary.
The coarse refuse entering the system through line 34 and
being fed onto the screen through hopper 38 at point ~0 is generally
carried to the screen as an aqueous dispersion or suspension. This
material is generally obtained by separating the mineral species desired
from the coarse refuse by gravity or size separation such as by jigs,
screens or the like. This material generally contains small particles of ~
stone, gravel, or the like having been crushed or processed earlier to ~-
remove the desired mineral. The aqueous suspension of the concentration
tailings 20 generally consist largely of clay, soils, or finely divided
particles of minerals such as coal or the like. These tailings are often
the by-product generally of a gravity separation of a heavier tailing -
from the generally less dense desired material as in the case of the
removal of coal from clay.
Processes for which our invention is applicable include the
disposal of clay tailings from coal preparation pIants, phosphate slimes
resulting from the washing or leaching of phosphate, rock, waste from the
mining of ferrous and non-ferrous metals, and more generally any time a
finely divided solid must be removed and dried from an aqueous slurry or
suspension. It is pointed out that prior to this invention, the finely
divided tailings 20 were generally sent to a sludge lagoon and/or pond
to settle, there~y creating the problems discussed earlier.
Ideally with the process of our invention, a con~posite solid
waste having a moisture content ~elow 50% is formed. Preferably, and by
3Q the careful selection of operational parameters, moisture content o~ ;
composite prepared ~y the instant inventlon may be lowered to below ~0%,
i.e. greater than 60% solids. The composite waste so formed is readily
-- 10 --
~i7~L33~
handleable, non-sticky, and may be disposed in land fills or the like
alleviating the necessity for sludge lagoons or other complicated,
expensive, drying or dewatering processes.
THE WATER SOLUBLE POLYPOLAR POLYMERS
The water soluble polypolar polymers whïch are useful in
the invention may be either cationically and/or anionically charged.
These ionic polymers generally have molecular weights of at least 10,000
and should be water soluble. By the term "polypolar" is meant having a
multitude of either cationically or anionically charges on the polymer.
It is important within the scope of this invention that the polymer
generally no~ contain both charges at the same time.
Cationic Polymers
As is discerned from the discussion above, a wide variety of
cationic polypolar treating agents may be suitably employed in the
; invention. Generally, such materials usually have sufficient strength
of ionization to form salts with alkali cations in aqueous media. The ~-~
following materials are just a few of the typical cationic substances
which may be suitably employed în practice of the invention.
One preferred cationic class of materials is a polymeric
polyamine subs~ance. Generally, these polymers have molecular weights
in excess of 1,000 and more preferably in excess of 2,000~ The most
preferred polymers of this type have molecular weight ranges of 2,000 -
50,000. Such above polymeric polyamines may be formed by a wide variety `
of reactions such as by the reaction of alkylene polyamines and
; difunctional alkyl materials.
A greatly preferred class of polyamine polymers are condensation
polymers of alkylene polyamines and halohydrins.
The alkylene polyamines which are reacted with the poly-
functional halohydrin for the purpose of the invention are well-known
compounds having the general formula:
H2N ~CnH2nNH) XH
~here n is an integer from 1 to 4 and x is one or more. Preferably, n
- 11 -
33g~
is 2 and x ranges from 1 to 5 to give the preferred polyethylene poly-
amine class. Examples of alkylene polyamines useful in the invention
are the alkylene diamines, such as ethylene-diamine, 1,2-propylene
diamine, 1,3-propylene diamine, and the polyalkylene polyamines, such
as, for example, diethylene triamine, triethylene tetramine, tetraethylene
pentamine, pentaethylene hexamine, dipropylene triamine, and the similar
polypropylene polyamines and polybutylene polyamines. Mixtures of any
of the above may also be used and often times commercial sources of
these compounds contain two or more of any of the above alkylene polyamines.
Some commercial amine products may contain mixtures of as many as five
separate compounds.
Yet another species of polyamines falling within the above
class is formed by reaction of an alkylene dihalide and an amine.
Preferred amine reactants include ammonia, ethylene diamine, diethylene
triamine, tetraethylene pentamine and triethylene pentamine and dimethyl-
amine methyl amine. Of these, the most preferable due to excellent
reactivity, low cost and availability is ammonia. The alkylene dihalide
reactant may be chosen from a wide variety of difunctional organics
including ethylene dichloride and 1,2-propylene dichloride. Of these
the most preferred is ethylene dichloride. One excellent cationic
polymer for use in the instant invention is formed by reaction of ammonia
and ethylene dichloride under super-atmospheric pressures and with heating.
A greatly preferred class of polyamine polymers are condensa-
tion polymers of alkyl polyamines and halohydrins. Exemplary of
polymers of this type are those disclosed in Green, United States
2,969,302 and Kekish United States 3,174,928. Other useful polyamines
in this same class include the condensation reaction of epihalohydrins
with dimethylamine as disclosed in Panzer, United States 3,738,945,
United States 3,725,312 and United States 3,741,8~1. Other useful
polyamines for th~ practlce of this invention include polyalkylene
polyamines such as those prepared by the reaction of a lo~er alkyl
amine such as ethylene diamine, propyl diamine, methyl amine,
- 12 - ;
-'IJ ~ :
.. . . .. . ... . .
~L~7~L33~
dimethylamine, trimethyl amine and ammonia with a lower alkyl dihalide
such as ethylene dichloride. Polymers of these types are disclosed in
the following United States Patents, United States 3,372,12~; United
States 3,751,474; and United States 3,928,448.
Other useful polypolar cationic polymers for use in this
invention include those disclosed in United States 3,248,353; United
States 3,~94,502 and United States 2,494,775.
While the above enumerated cationic polypolar polymers find
great utility in our invention, the above description encompasses only
- 10 those polymers prepared by condensation reactions. Other polypolar
cationic water soluble polymers prepared by vinyl addition polymerizations
also find usefulness within the scope of this invention.
Examples of cationic polymers useful in our invention which
are polymerizaed by a vinyl addition technique include water soluble
acrylamide polymers and copolymers containing at least 50, preferably 10
and most preferably 20 percent by weight of diallyl dimethyl ammonium
chloride, polydiallyl dimethyl ammonium chloride, polyacrylamide which
has undergone a Mannich reaction and may or ~ay not be quaternized,
dimethylamino ethyl methacrylate and its corresponding water soluble
homologues and quaternary derivatives. Other useful polymers produced
by this method may include those prepared from other water soluble monomers
which have an active nitrogen which need not be elaborated on here, it is
sufficient to say any cationic water soluble vinyl addition polymer,
having at least 5 weight percent of a cationic water soluble monomer
may be employed in our invention.
Anionic Polymers
Polypolar polymers falling within the anionic class are those
consisting of substances which in an aqueous medium will form organic
anions having a measurable negative electric charge. Greatly preferred
anionic materials are those substances polymeric in nature having a
substantial number of negative electrical charges distributed at a
~- plurality of positions on the polymer. These polymeric anionic substances
'
:, : . . :
~ 107~339
which generally have a molecular weight of at least 100,000 when formed as
addition-type polymers or copolymers are derived by polymerization of at
least one mo~o-olefinlc compound through an allphatïc unsaturated group.
These polymers should be water-dispersible or water soluble and have a
structure substantially free of cross linkage and are therefore available
for solubiliziation or dispersion in the particular aqueous turbid liquid
~eing treated. Preferred anionic substances found to be especially
effective for the purpose of the invention are water dispersible synthetic
polymers having a linear hydrocarbon structure and containing in a side
chain a hydrophilic group selected from the class consisting of carboxylic
acid, carboxylic acid anhydride, carboxylic acid salt groups, and copolymers
of any of the foregoing. Typical water-dispersible synthetic organic
polymers, anionic in nature~ which have these characteristic groupings
are listed below. These have been found to be effective for the
practice of the invention.
No. NameCharacteristic Grouping
1 Polyacrylate sodium salt. - CH2- fH -
COO ~ - )
Na(+)
2 Polymethacrylic acid-
sodium salt. ICH3
CH2 lC
COO(-)
Na(+)
3 Maleic anhydride-vinyl
acetate copolymer. - fH - CH2 - fH - CH
O O = C C = O ::
\ /
CH3C = O O
Polyvinyl methyl ether-
maleic anhydride co- - CH - CH2 - CH CH -
polymer. I I
OCH3 O = C\ / ;
.~
3L339
No. Name Characteristic Grouping
Me~hacrylic acid- CH CH
acrylamide copolymer. 1 3 1 3
--CH2C--CH2-- lC
COO(-) CONH2
H~+)
6 Polyacrylic acid - CH2 - CH -
' I ' '
COO ( - )
H(+)
7 Isopropenyl acetate-maleic CH
anhydride sodium salt. 1 3
CH2 - C - CH - CH
o C = O Ç = O
I
CH2C = O 0(-) O~-) :
Na(~) Na(+)
8 Itaconic acid-vinyl
acetate. COO(-)H(+)
- f - CH2 - CH2 - CH -
CH2 COO ( - )
H(+) CH3C O
9 a-methyl styrene-maleic CH
anhydride sodium salt. 1 3
C ~ CH CH CH
.' 11 1 COO(-) COO~-)
~ Na(+) Na(~)
Styrene-maleic anhydride - CH - CH2 - CH CH -
sodium salt.
~/~ COO(-) COO(-) ' ,-
Na(~) Na(+)
. -.
- 15 -
~ ' , .:
~ ~ ,
.~. '.
.. .. ......
~7~;~3~
No. Name Characteriskic Grouping
llMethylmethacrylate-maleic Cll
anhydride sodium salt. 1 3
- C - CH - CH - CH -
1 2
COOCH3 COO(-) COO~-)
Na(-~) Na~)
12Acrylic acid-styrene - CH - CH2 - CH CH~ -
copoly~er. ¦ ¦
~q COO~-) '
¦l I H~
~ .
A suitable anionic copolymer may be derived from a poly-
carboxylic acid monomer and at least one other monomer copolymerizable
therewith. The polycarboxylic acid may be maleic anhydride, acrylic acid,
maleic acid, fumaric acid, itaconic acid, aconitic acid, citraconic acid,
etc., which may be copolymerized with the amides of these acids, the
alkali metal derivatives (e.g., sodium, potassium and lithium), the
alkaline earth metal derivatives ~e.g., magnesium, calcium, barium and
strontium~, and ammonium salts of these acids, the par~ial alkyl esters
: ~e.g., methyl, ethyl, proyyl~ butyl, mono es~ers), the salts of said
partial alkyl esters, and the substituted amides of these polycarboxylic
acids or a variety of other different monomers. Where a hydrophilic ~ ;
polycarboxylic acid such as maleic acid is used as one of the starting
components to form the copolymer, a hydrophobic comonomer may be used, as :
for example, styrene, alpha-methylstyrene, vinyl toluene, chlorostyrene,
: -
- vinyl acetate, vinyl formate, vinyl alkyl ethers, alkyl acrylates, alkyl
methacrylates, ethylene, propylene, and/or isobutylene. The foregoing ~
; synthetic copolymers are prefeTably~obtained by reacting equimolar ~; :
~ ~ proportions of a polycarboxylic acld and at least one other monomer.
;~ However, certain of the unsaturated polycarboxylic acids can be polymerized
in less than equimolar proportions ~ith some of the less ~ydrophobic
comonomers.
- 16 -
..
7~
A variety of other anionic polymeric substances ~ay be employed
such as hydroly~ed polyacrylonitrile-sodium salt thereof, sodium carboxy-
me~hyl cellulose, the sodium salt of an acid-ester of starch, the sodium
salt of a sulfonated polystyrene, phosphorylate starches, such as those
obtained by treating corn starch with phosphorous oxychloride in
pyridine, anionic polysaccharides, and combinations of any of the above
or other anionic coagulant materials.
Another class of anionic materials particularly suitable in the
practice of the invention are copolymers of sodium acrylate and acrylamide.
The most preferred copolymers of this type comprise 5 - 95% by weight of
sodium polyacrylate and 5 - 95% by weight of polyacrylamide and have a
molecular weight in excess of 100,000. Other polymers or copolymers of
acrylic acid ~ypes are particularly preferred and are typified by those
obtained by vinyl polymerizat~on of acrylic acid, methacrylic acid,
sulfoethyl acrylate, carboxyethyl acrylate or salts thereof or copolymers
thereof of the acids or salts obtained by suitable copolymerization with
monomers such as acrylamide, methacrylamide, acrylonitrile, methacryloni-
trile, lower alkyl esters, alkyl esters of the acrylic acids, vinyl
alkyl ethers, and the like. Also useful is an anionically modified poly-
acrylamide such as that prepared by sulfomethylating polyacrylamide.
Another greatly preferred class of anionic polymers is a linear
high molecular weight polymer or copolymer of a vinyl aryl hydrocarbon,
such as styrene, vinyl toluene, alpha-methylstyrene, vinyl xylene or the
like, which are polymerized and then sulfonated under controlled conditions
to produce a water-soluble substantially linear polymer sulfonate.
As mentioned above, one of the most preferred anionic coagulants
falling within the scope of the invention are copolymers of polyacrylate
sodium salt and polyacrylamide of varying proportions of the respective -
~ .
- monomers.
~ 30
i - 17 -
~7 1
~7~L339
THE AD~ITION OF THE POLYPOLAR POLY~R
TO THE MINERAL TAILINGS
The addition of the polypolar polymer to the finely divided
mineral tailings generally, two modes of addition may be used in the
practice of our invention.
In the first practice when an aqueous suspension of mineral
tailings having a lo~ net charge, that is, approaching the iso-electric
paint, is being treated, anionic polymer alone is generally sufficient to
cause sufficient coagulation of the aqueous suspens;on prior to the aqueous
suspension of the mineral tailings beïng deposited onto the coarse refuse
on the vibrating screen. The anionic polymer in this instance is generally
added at a level of from 1.0 - 4,000 ppm by weight and preferably from
1.0 - 2,000 ppm. Most preferably, from 1.0 - 1,000 ppm by weight of the
anionic polymer is added to the aqueous suspension of the mineral tailings
prior to its contact with the refuse on the vibrating screen.
The polymer employed should be injected into the stream as a
dilute aqueous liquid, or should form a dilute aqueous liquid on contact
with the tailings, so as to 1nsure proper mixing ~ith the aqueous suspen-
sion of the tailings. The polymer content of the aqueous solution so used
may range from Q.25 to 40% or higher by weight.
In a preferred practlce of our invention, a water-in-oil emulsion
of the anionic polymer such as those disclosed in United States 3,624,019
and United States 3,790,476 is mixed with a suitable hydrophillic sur-
factant to render the emulsion self-inverting. This emulsion by itself ~ -
may then be injected into the line containing the aqueous dispersion or
suspension of the mineral tailings, the turbulence of the pumping in the
line being sufficient to cause the polymer to invert thus solubilizing the
polymer contained within the emulsion and giving the benefits of our
invention. Water-in-oil emulsions of the type above described are
generally acrylamide-sodium acrylate polymers and are available from ~ -
several commercial sources.
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An additionally preferred method involves the use of water-in-
oil emulsions of water soluble vinyl addition polymers such as those
described in Anderson et al U.S. 3,624~019 and U.S. 3,790,476, and
involves inverting these emulsions into water so as to form a water
soluble polymer and then injecting this into the system by the methods
described above. The procedure for inverting these types of polymers
is well designated in the Anderson reference listed above.
When the aqueous waste suspension of tailings to be treated is
of a mixed or anionic nature, that is containing both cationic and
anionic materials or anionic materials alone, it is often times desirable
to use both a cationic and anionic polymer. While the anionic polymers
have been described above with the use of both polymer systems, it is
important that the cationic polymer be injected into the concentrated
aqueous suspension of the finely divided tailings prior to the addition
of the anionic polypolar polymer. When using both types of polymers,
from 1 - 2,000 ppm of each or a total of 4,000 ppm of polymer is all that
is generally required. The addition of the cationic polymer in line to
the aqueous slurry of mineral tailings prior to the point of injection
of the anionic polymer generally provides sufficient time and mixing for
the coagulation of clays etc. before the anionic polymer is added.
In order to show ~he benefits of our invention, tlle following
; examples are presented:
EXAMPLE I
A large West Virginia coal mine operated a plant water
purification similar to that shown on Figure 1. A thickener underflow
being pumped to refuse located on the vibrating screen contained 40%
solids. Upon leaving the vibrating screen, the aqueous slurry of the
suspended mineral tailings in conjunction with the coarse refuse had a
combined total of 48% solids. Wa~er passing through the screen and
being returned to the thickener contained 36% solids, largely as clay
~ fines and the llke.
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,
~7~3;~
XAMPLE II
The same system as that described in Example I had added to it
20 ppm of an acrylamide sodium acrylate copolymer. This polymer was
prepared according to the teachings of U.S. 3,624J019 and in latex form
before inversion contained 28% polymer, the polymer contained 36% sodium
acrylate and 64% acrylamide~ and had an intrinsic viscosity of approximately
21 in 0.1 N NaN03. The polymer was added to the aqueous slurry of the
suspended mineral tailings immediately prior to its contact with the
coarse refuse located on the vibrating screen. The thickener lmderflow
which originally contained ~0~ by weight of finely divided mineral tailings
in water was treated in this manner to obtain a semi-solid non-sticky
composite waste containing 66% solids. Water filtering through the screen
contained 0.7% solids and was r0cycled back to the thickener. A visual
observation of the composite waste showed that it was wet, but could
; easily be handled by shovels, tractors, and the like in a land fill or
other similar disposal arrangement. The material was agglomerated, and
was not sticky or paste like.
; ~ EXAMPLE III -~
The same system as described in Example I was treated with 15 ppm
of the polymer described in Example II. The thickener underflow containing
40% solids was treated to prepare a composite solid waste product being of
a non-sticky semi-solid character containing 63% solids. The water which
passed through the screen during this process contained 0.6% solids and
was recycled through the thickener. This composite waste material prepared
in this manner was also suitable for applying to land fills, etc.
EXAMPLE IV
Another coal plant operating a water treatment plant similar to
that shown in Figure 1 had been pumping its thickener underflow to settling
ponds and lagoons. This created a serious ecological problem and took up
costly land as well as created a problem in recovering the solid waste
product. Thickener underflow contained 35% finely di~ided mineral tailings
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~7~33~
in water. This material was treated prior to contact with the vibrating
screen having a layer thereon of fine gravel with 2~ ppm of an epichloro-
hydrin-dimethylamine polymer. The polymer had an approximate intrinsic
viscosity of 0.16 in 0.1 N NaN03. Following this addition and several
feet from this point of addition~ 15 ppm of ~he acrylamide-sodium acrylate
polymer discussed in Examples II and III above was added. The resulting
semi-solid non-sti.cky waste composite leaving the vibrating screen
contained 70% solids and was useful as a land fill ingredient. The
composite waste could be handled easily by conventional techniques.
Water passing through the screen contained 0.5% solids and was returned
to the plant thickener for further clarification and treatment.
It is thus seen ~hat with the application of our invention,
waste treatment and mineral processing facilities can be greatly improved.
A method of our invention allows for the disposal of a solid waste product
and the return of water removed from the waste to be recycled in the
plant.
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