U.S. patent application number 09/818693 was filed with the patent office on 2001-09-20 for process for removing impurities from kaolin clays.
Invention is credited to Nagaraj, D. R., Rothenberg, Alan S., Ryles, Roderick G..
Application Number | 20010022282 09/818693 |
Document ID | / |
Family ID | 21961577 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010022282 |
Kind Code |
A1 |
Nagaraj, D. R. ; et
al. |
September 20, 2001 |
Process for removing impurities from kaolin clays
Abstract
An improved process for the selective flocculation of impurities
from clays is disclosed. The process comprises blunging the clay in
the presence of dispersing agents, conditioning the blunged clay
with aliphatic or aromatic hydroxamic acids, or salts thereof,
flocculating the impurities with a high molecular weight polymeric
flocculant, particularly polymers containing hydroxamate groups,
and removing the flocculated impurities from the unflocculated
clay. The use of hydroxamic conditioning agents improves the
removal of impurities from the clay, thereby providing a clay
product having high brightness and low level impurities. The
hydroxamic acid conditioning agents may advantageously be used in
combination with other conditioning additives and with a wide
variety of polymeric flocculating agents.
Inventors: |
Nagaraj, D. R.; (Stamford,
CT) ; Ryles, Roderick G.; (Milford, CT) ;
Rothenberg, Alan S.; (Wilton, CT) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
21961577 |
Appl. No.: |
09/818693 |
Filed: |
March 27, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09818693 |
Mar 27, 2001 |
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09618463 |
Jul 18, 2000 |
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09618463 |
Jul 18, 2000 |
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09049761 |
Mar 27, 1998 |
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Current U.S.
Class: |
209/5 ; 209/3;
210/723; 423/69 |
Current CPC
Class: |
C01P 2006/60 20130101;
B03B 1/04 20130101; C09C 1/42 20130101; C01P 2006/80 20130101; B03D
3/06 20130101 |
Class at
Publication: |
209/5 ; 209/3;
423/69; 210/723 |
International
Class: |
B03B 001/00 |
Claims
We claim:
1. A process for removing colored impurities from clay comprising
the steps of: a) blunging the clay with a dispersing agent, or a
combination of dispersing agents, in water to form an aqueous clay
dispersion; b) forming a conditioned dispersion by treating the
aqueous clay dispersion with a conditioning agent, or a mixture of
conditioning agents, represented by the formula: R-C(=O)N(R")-OM
wherein R is linear or branched C.sub.2-C.sub.18 alkyl, linear or
branched C.sub.2-C.sub.18 alkenyl, C.sub.6-C.sub.20 aryl,
substituted aryl, C.sub.7-C.sub.26 aralkyl or substituted aralkyl;
R" is H, C.sub.1-C.sub.12 alkyl or aralkyl; and M is hydrogen, an
alkali metal or ammonium, wherein the substituted aryl or
substituted aralkyl are substituted on aryl with hydroxy,
C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl, to form a
conditioned dispersion; c) treating the conditioned dispersion with
a flocculating agent comprising a water soluble or water
dispersible organic polymer to flocculate the impurities; and d)
removing the flocculated impurities to form a purified clay
dispersion.
2. The process according to claim 1, wherein the clay is a kaolin
clay.
3. The process according to claim 1, wherein the dispersing agent
is selected from the group consisting of sodium silicate, sodium
polyacrylate, and sodium carbonate.
4. The process according to claim 1, comprising blunging the clay
with a dispersing agent, or combination of dispersing agents, and a
pH modifying agent, in water.
5. The process according to claim 1, wherein the pH modifying agent
is sodium hydroxide or ammonium hydroxide.
6. The process according to claim 1, wherein the conditioning agent
is a hydroxamic acid, or salt thereof, or a mixture of hydroxamic
acids, or salts thereof, represented by the formula:
R-C(=O)N(R")-OM wherein R is an aralkyl moiety selected from the
group consisting of (R'-phenyl), (R'-hydroxy-phenyl),
(R'-naphthyl), or (R'-hydroxy-naphthyl), wherein R' is linear or
branched C.sub.1-C.sub.12 alkyl, or linear or branched
C.sub.2-C.sub.12 alkenyl.
7. The process according to claim 1, wherein the conditioning agent
is a hydroxamic acid, or salt thereof, or a mixture of hydroxamic
acids, or salts thereof, represented by the formula: R-C(=O)NH-OM
wherein R is linear or branched C.sub.8-C.sub.12 alkyl or linear,
branched C.sub.8-C.sub.12 alkenyl, C.sub.6-C.sub.20 aryl, or
substituted aryl, and M is hydrogen, an alkali metal or ammonium,
wherein the substituted aryl is substituted with hydroxy,
C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl.
8. The process according to claim 1, wherein the water soluble or
water dispersible organic polymer is an anionic or a non-ionic
polymer having a molecular weight in the range of about 0.5 million
to about 30 million.
9. The process according to claim 1, wherein the water soluble or
water dispersible organic polymer is an anionic or a non-ionic
polymer having a molecular weight in the range of about 1 million
to about 20 million.
10. The process according to claim 1, wherein the water soluble or
water dispersible organic polymer contains at lease one hydroxamic
acid moiety, or salts thereof.
11. The process according to claim 1, comprising forming a
conditioned dispersion by treating the aqueous clay dispersion with
a conditioning agent, or a mixture of conditioning agents, and at
least one conditioning additive, wherein said conditioning additive
is selected from the group consisting of an aliphatic alcohol, a
hydrocarbon oil, a carboxylic acid ester oil, and a fatty acid
having the formula: R-C(=O)OM wherein R is a C.sub.10-C.sub.18
alkyl, C.sub.6-C.sub.20 aryl, substituted aryl, C.sub.7-C.sub.26
aralkyl or substituted aralkyl, and M is hydrogen, an alkali metal
or ammonium, wherein the substituted aryl or substituted aralkyl
are substituted on aryl with hydroxy, C.sub.1-C.sub.6 alkoxy, or
C.sub.1-C.sub.6 alkyl.
12. The process according to claim 11, wherein the aliphatic
alcohol is decanol or dodecanol.
13. The process according to claim 1, further comprising the step
of treating the aqueous clay dispersion with a salt containing a
polyvalent metal cation.
14. The process according to claim 13, wherein the salt is calcium
chloride.
15. A process for removing colored impurities from clay comprising
the steps of: a) blunging the clay with a dispersing agent, or a
combination of dispersing agents, in water to form an aqueous clay
dispersion; b) treating the aqueous clay dispersion with a
conditioning composition comprising at least one conditioning agent
and at least one conditioning additive, wherein (i) the at least
one conditioning agent is represented by the formula:
R-C(=O)N(R")-OM wherein R is linear or branched C.sub.2-C.sub.18
alkyl, linear or branched C.sub.2-C.sub.18 alkenyl,
C.sub.6-C.sub.20 aryl, substituted aryl, C.sub.7-C.sub.26 aralkyl
or substituted aralkyl; R" is H, C.sub.1-C.sub.12 alkyl or aralkyl;
and M is hydrogen, an alkali metal or ammonium, wherein the
substituted aryl or substituted aralkyl are substituted on aryl
with hydroxy, C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl, to
form a conditioned dispersion; and (ii) the at least one
conditioning additive is a fatty acid represented by the formula:
R-C(=O)OM wherein R is a C.sub.10-C.sub.18 alkyl, C.sub.6-C.sub.20
aryl, substituted aryl, C.sub.7-C.sub.26 aralkyl or substituted
aralkyl, and M is hydrogen, an alkali metal or ammonium, wherein
the substituted aryl or substituted aralkyl are substituted on aryl
with hydroxy, C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl, to
form a conditioned clay dispersion; c) flocculating the conditioned
clay dispersion by treatment with a flocculating agent comprising a
water dispersible organic polymer, to form flocculated impurities;
and d) removing the flocculated impurities to form a purified clay
dispersion.
16. The process according to claim 15, wherein the clay is a kaolin
clay.
17. The process according to claim 15, wherein the dispersing agent
is selected from the group consisting of sodium silicate, sodium
polyacrylate, and sodium carbonate.
18. The process according to claim 15, comprising blunging the clay
with a dispersing agent, or combination of dispersing agents, and a
pH modifying agent, in water.
19. The process according to claim 15, wherein the pH modifying
agent is sodium hydroxide or ammonium hydroxide.
20. The process according to claim 15, wherein the conditioning
agent is a hydroxamic acid, or salt thereof, or a mixture of
hydroxamic acids, or salts thereof, represented by the formula:
R-C(=O)N(R")-OM wherein R is an aralkyl moiety selected from the
group consisting of (R'-phenyl), (R'-hydroxy-phenyl),
(R'-naphthyl), or (R'-hydroxy-naphthyl), wherein R' is linear or
branched C.sub.1-C.sub.12 alkyl, or linear or branched
C.sub.2-C.sub.12 alkenyl.
21. The process according to claim 15, wherein the conditioning
agent is a hydroxamic acid, or salt thereof, or a mixture of
hydroxamic acids, or salts thereof, represented by the formula:
R-C(=O)NH-OM wherein R is linear or branched C.sub.8-C.sub.12 alkyl
or linear, branched C.sub.8-C.sub.12 alkenyl, C.sub.6-C.sub.20
aryl, or substituted aryl, and M is hydrogen, an alkali metal or
ammonium, wherein the substituted aryl is substituted with hydroxy,
C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl.
22. The process according to claim 15, wherein the fatty acid is a
compound represented by the formula: R-C(=O)OM wherein R is a
C.sub.16-C.sub.18 alkyl, C.sub.6-C.sub.20 aryl, substituted aryl,
C.sub.7-C.sub.26 aralkyl or substituted aralkyl, and M is hydrogen,
an alkali metal or ammonium, wherein the substituted aryl or
substituted aralkyl are substituted on aryl with hydroxy,
C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl.
23. The process according to claim 15, wherein the fatty acid is
oleic acid.
24. The process according to claim 15, comprising treating the
aqueous clay dispersion with at least two conditioning additives,
wherein the second conditioning additive is selected from the group
consisting of an aliphatic alcohol, a hydrocarbon oil and a
carboxylic acid ester oil.
25. The process according to claim 24, wherein the aliphatic
alcohol is decanol or dodecanol.
26. The process according to claim 15, further comprising the step
of treating the aqueous clay dispersion with a salt containing a
polyvalent metal cation.
27. The process according to claim 26, wherein the salt is calcium
chloride.
28. The process according to claim 15, wherein the water soluble or
water dispersible organic polymer is an anionic or a non-ionic
polymer having a molecular weight in the range of about 0.5 million
to about 30 million.
29. The process according to claim 15, wherein the water soluble or
water dispersible organic polymer is an anionic or a non-ionic
polymer having a molecular weight in the range of about 1 million
to about 20 million.
30. The process according to claim 15, wherein the water soluble or
water dispersible organic polymer contains at lease one hydroxamic
acid moiety, or salts thereof.
31. A process for removing colored impurities from clay comprising
the steps of: a) blunging the clay with a dispersing agent, or a
combination of dispersing agents, in water to form an aqueous clay
dispersion; b) treating the aqueous clay dispersion with a
conditioning agent represented by the formula: R-C(=O)OM wherein R
is C.sub.10-C.sub.18 alkyl, C.sub.6-C.sub.20 aryl, substituted
aryl, C.sub.7-C.sub.26 aralkyl or substituted aralkyl, and M is
hydrogen, an alkali metal or ammonium, wherein the substituted aryl
or substituted aralkyl are substituted on aryl with hydroxy,
C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl; c) flocculating
the conditioned clay dispersion by treatment with a flocculating
agent comprising a water soluble or water dispersible organic
polymer containing hydroxamic acid groups or salts thereof, to form
flocculated impurities; and d) removing the flocculated impurities
to form a purified clay dispersion.
32. The process according to claim 31, wherein the clay is a kaolin
clay.
33. The process according to claim 31, wherein the dispersing agent
is selected from sodium silicate, sodium polyacrylate, and sodium
carbonate.
34. The process according to claim 31, wherein the water soluble or
water dispersible flocculant is an organic polymer containing
hydroxamic acid groups or salts thereof having a molecular weight
in the range of about 0.5 million to about 30 million.
35. The process according to claim 31, wherein the water soluble or
water dispersible flocculant is an organic polymer containing
hydroxamic acid groups or salts thereof having a molecular weight
in the range of about 1 million to about 20 million.
36. The process according to claim 31, further comprising treating
the clay dispersion with at least one conditioning additive
selected from the group consisting of an aliphatic alcohol, a
hydrocarbon oil and a carboxylic acid ester oil.
37. The process according to claim 31, wherein the additive is
decanol or dodecanol.
38. The process according to claim 31, further comprising the step
of treating the aqueous clay dispersion with a salt containing a
polyvalent metal cation.
39. The process according to claim 31, wherein the salt containing
a polyvalent metal cation is calcium chloride.
40. A process for removing colored impurities from clay comprising
the following steps: a) blunging the clay with sodium silicate and
sodium polyacrylate in water to form an aqueous clay dispersion; b)
treating the aqueous clay dispersion with a oleic acid fatty acid
and calcium chloride, c) flocculating the conditioned clay
dispersion by treatment with hydroxamated polyacrylamide of
molecular weight of about 10-20 million, to form flocculated
impurities; and d) removing the flocculated impurities to form a
purified clay dispersion.
41. The process according to claim 40, wherein the conditioning
agent further comprises an additive selected from aliphatic
alcohol, hydrocarbon oil or a carboxylic acid ester oil.
42. The process according to claim 41, wherein the additive is
decanol or dodecanol.
43. The process according to claim 40, further comprising the step
of treating the aqueous clay dispersion with a salt containing a
polyvalent metal cation.
44. The process according to claim 43, wherein the salt containing
a polyvalent metal cation is calcium chloride.
45. A process for removing colored impurities from kaolin clay
comprising the following steps: a) blunging the clay with sodium
silicate and sodium polyacrylate in water to form an aqueous clay
dispersion; b) treating the aqueous clay dispersion with a mixture
of C.sub.8-C.sub.10 hydroxamic acid and C.sub.12 alcohol; c)
flocculating the conditioned clay dispersion by treatment with
hydroxamated polyacrylamide of molecular weight of about 10-20
million, to form flocculated impurities; and d) removing the
flocculated impurities to form a purified clay dispersion.
46. The process according to claim 45, further comprising blunging
the clay with sodium hydroxide or ammonium hydroxide.
47. The process according to claim 45, further comprising treating
the aqueous clay dispersion with oleic acid.
48. The process according to claim 45, further comprising treating
the aqueous clay dispersion with calcium chloride.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an improved selective flocculation
process for the separation of impurities from clay. The selective
flocculation process of this invention is particularly useful for
separating colored impurities from kaolin clays.
[0003] 2. Background of the Invention
[0004] Crude clays often contain well dispersed mineral impurities
that must be removed from the clay prior to use. For example,
naturally occurring kaolin clays are contaminated with highly
colored impurities composed of iron oxides and titanium oxides
(rutile, anatase) and mixtures thereof. Purified kaolin clay is
generally white and is suitable for many industrial uses,
particularly as a pigment or filler in the paper industry. The
technique chosen for the purification of crude clays is often
determined by the type of clay (e.g. clays having different
particle size distributions and/or different mean particle sizes)
and the quantity and identity of the impurities that are to be
removed from the clay. The most commonly used purification
techniques include chemical bleaching, magnetic separation, froth
flotation and selective flocculation. Chemical bleaching is
generally used to remove iron impurities, but is not always
effective. Chemical bleaching is generally ineffective at removing
titanium impurities. Magnetic separation has proven useful for
removing titanium impurities from some clays, but it is not useful
for purifying clays containing very fine titanium particulates, as
found in the ultra-fine kaolin clays mined from the eastern part of
Georgia. Froth flotation and selective flocculation processes have
proven to be the most useful techniques for the purification of
these fine clays. Accordingly, many attempts to improve the
efficiency of these processes for producing clays having higher
purity have been made.
[0005] For example, U.S. Pat. No. 4,629,556 describes a froth
flotation process using alkyl, aryl or alkylaryl hydroxamates as
collectors for the removal of colored impurities. U.S. Pat. No.
4,871,466 describes a collector composition comprising alkyl or
alkaryl hydroxamic acids, or salts thereof, and an aliphatic
alcohol for the flotation of colored impurities. U.S. Pat. No.
5,522,986 describes a froth flotation process using a combination
of a fatty acid and an alkyl hydroxamate compound, as a collector,
to remove impurities in the form of a froth from a coarse grained
kaolin clay dispersion. U.S. Pat. No. 3,138,550 discloses another
froth flotation process for metallic minerals comprising adding an
anionic polymeric flocculating agent to a mineral pulp already
conditioned with a fatty acid, as a collector. The success of a
froth flotation operation depends on the ability of the collector
to effectively bind the impurities and to form a froth. Whereas the
froth flotation process is generally effective with coarse grained
clays, it has limited effectiveness with very fine clays. For this
reason, many non-flotation processes, such as selective
flocculation, have been developed as alternatives to flotation.
[0006] For example, U.S. Pat. Nos. 3,701,417 and 3,862,027,
describe a selective flocculation process using a soluble source of
polyvalent cations, specifically calcium chloride, and an anionic
organic polyelectrolyte to selectively flocculate and remove
impurities from an aqueous kaolin clay dispersion. Other related
processes are described in U.S. Pat. Nos. 3,837,482 and 3,371,988.
The foremost problem associated with the use of polyvalent cationic
reagents is that these reagents bind to clay particles as well as
to the impurities. These reagent-bound clay particles flocculate
together with the impurities, which results in reduced recovery of
the purified clay. It is often difficult to quantitate the amount
of polyvalent cationic reagent required to purify a given clay
sample without reducing clay recovery. Accordingly, balancing clay
purity against clay recovery is a constant problem.
[0007] To overcome the problems encountered with the use of
polyvalent cationic reagents, monovalent cation conditioning
agents, such as ammonium salts, are used in the process described
in U.S. Pat. No. 4,604,369. U.S. Pat. No. 3,837,482 describes a
reverse flocculation process for purifying clay wherein the clay
particles are flocculated, leaving the impurities dispersed in the
aqueous suspension. The clay particles are flocculated by addition
of an anionic polymeric flocculant. While such a process may be
effective, its cost would be very disadvantageous. Instead of
selectively flocculating the relatively small amount of impurities,
typically 2-4% by weight of crude clay, this process selectively
flocculates the clay itself, typically 80-95% by weight of crude
clay. Ravishanker et al. (Bull. Mater. Sci., Vol. 10, No. 5, August
1988, pp. 423-433) describe selective flocculation of iron oxide
from a 1:1 synthetic mixture of iron oxide and kaolin using
hydroxamated polyacrylamide. Clauss et al. (Intl. J. Miner.
Process., Vol. 3, 1976, p.27) describe selective flocculation of
cassiterite using a modified polyacrylamide flocculant containing
hydroxamate functional groups.
[0008] U.S. Pat. No. 5,535,890 describes a recent improvement to
the selective flocculation process using a conditioning agent
composition composed of a water soluble source of polyvalent
cations and a fatty acid. Both the polyvalent cation source and the
fatty acid are used in quantities insufficient to flocculate the
clay particles. Separation of the impurities from clay is
accomplished using a highly anionic, high molecular weight
copolymer of polyacrylamide and acrylic acid.
[0009] Despite the many attempts described above to improve the
traditional clay purification processes, there remains a need for a
highly efficient, high through-put process that can produce
purified clays of varying particle size at low cost.
SUMMARY OF THE INVENTION
[0010] This invention is directed to an improved process for the
selective flocculation of impurities from clay, particularly,
kaolin clay. The process comprises blunging the clay in the
presence of dispersing agents, treating the blunged clay with a
conditioning agent, or a mixture of conditioning agents, composed
of aliphatic or aromatic hydroxamic acids, or salts thereof,
flocculating the impurities with a high molecular weight organic
polymeric flocculant, and separating the flocculated impurities
from the unflocculated clay. The use of hydroxamic acid
conditioning agents improves the removal of impurities from the
clay, thereby providing a clay product having high brightness and
low level impurities. The hydroxamic acid conditioning agents may
advantageously be used in combination with other conditioning
additives, including alcohols, fatty acids, hydrocarbon oils, and
carboxylic acid esters, or with salts containing polyvalent
cations. Additionally, the conditioning agents of the present
invention are useful with a wide variety of anionic and non-ionic
water soluble or water-dispersible polymeric flocculating agents,
particularly polymers containing pendant hydroxamate groups. A
further embodiment of this invention is the use of a
hydroxamate-containing polymeric flocculant to selectively
flocculate impurities from clay slurries which have been treated
with a fatty acid and a polyvalent metal salt as conditioning
agents.
DETAILED DESCRIPTION OF THE INVENTION
[0011] The improved process of this invention utilizes selective
flocculation of mineral impurities from an aqueous crude clay
dispersion using alkyl or aryl hydroxamic acids, or salts thereof,
as conditioning agents. This process is particularly useful for
selective flocculation of impurities found in ultra-fine kaolin
clays, which are not readily purified using conventional
techniques, such as froth flotation. The clay dispersion is treated
with an alkyl, aryl or aralkyl hydroxamate conditioning agent, or a
mixture of hydroxamate conditioning agents, that selectively binds
to the mineral impurities commonly found in the crude clays.
Flocculation, and subsequent separation of the conditioned clay
impurities, is accomplished by addition of high molecular weight
organic polymeric flocculating agents. In the prior art, strongly
anionic polymeric flocculating agents have been commonly used. It
has been found that the use of alkyl, aryl or aralkyl hydroxamate
conditioning agents in the process of this invention,
advantageously allows for the step of flocculation to be performed
using either anionic or non-ionic high molecular weight
flocculating agents, and particularly polymeric flocculants
containing hydroxamate groups. Furthermore, it has been found that
polymers containing hydroxamate groups may be advantageously used
when the clay dispersion is treated with fatty acids as
conditioning agents. After addition of the flocculating agent to
the conditioned dispersion, flocculation of the impurities occurs
rapidly to form a two phase mixture having an upper phase
containing the purified milky-white clay suspension, and a lower
phase containing the impurity-rich flocculated material. Separation
of the two layers may be accomplished by any of the techniques
conventionally used in flocculation operations.
[0012] The process of the present invention is flexible and may be
used to effectively purify different types of clays containing a
variety of different impurities. With appropriate modifications,
which are readily accomplished by those skilled in the art, the
present process may be advantageously used to separate a wide
variety of minerals from one another. For example, iron oxides may
be readily separated from silica or silicates, or cassiterite (tin
oxide) may be separated from gangue in ores, ore concentrates or
ore pre-concentrates. Significantly, effective removal of
impurities may be obtained using the process of the present
invention without the use of polyvalent cationic salts, although
these salts may be used in conjunction with alkyl hydroxamic acids
and other conditioning aids, such as fatty acids, to enhance the
purity of the clay.
[0013] Use of the selective flocculation process of the present
invention provides additional benefits. For example, fine kaolin
clays generally contain grit, composed of +325 mesh (U.S. Sieve)
particles, which generally must be separated from the crude clay
prior to the purification process. This additional separation step
may be eliminated using the selective flocculation process of this
invention because the grit may simply be removed with the
flocculated impurities.
[0014] The aqueous clay dispersion is prepared by blunging, or
mixing, the clay in water to form a finely dispersed mixture having
a milk-like consistency. This clay dispersion is also called a
slip. The objective in forming the aqueous clay dispersion is to
form a clay composition wherein the crude clay particles are not
aggregated with each other, but are uniformly dispersed. The
concentration of the dry crude clay in the aqueous clay dispersion
is generally about 50% to about 70% by weight of the total weight
of the dispersion. In the art, this concentration is described as
about 50% "solids" to about 70% "solids".
[0015] Advantageously, in the method of this invention, at least
one dispersing agent is added during the blunging step, to increase
the dispersibility of the clay in water. As used herein, a
dispersing agent is a material that is used to impart a highly
negative overall charge onto the surface of the clay particles,
thereby inducing particle-particle repulsion and preventing
particle aggregation. Exemplary dispersing agents that may be
useful for preparing a well-dispersed aqueous clay dispersion
include sodium silicate, sodium metasilicate, sodium carbonate,
sodium or ammonium polyacrylate, hexametaphosphate or the like.
Preferred dispersing agents include, for example, sodium silicate,
soda ash, and sodium polyacrylate.
[0016] The dispersing agent may be added as a solid, or may be
pre-dissolved in water and added in an aqueous solution. The amount
of dispersing agent used to form a finely dispersed clay mixture
will vary from sample to sample and for each type of clay, but is
generally in the range of about 0.05 to about 10 kilogram (kg) of
the dispersing agent per ton of crude clay (on a dry solids basis)
depending on the type of dispersing agent and type of clay crude
used. The concentration of the dispersing agent(s) is selected to
provide enhanced dispersion of the clay in the clay dispersion
which consequently provides enhanced separation of the colored
impurities from the clay. Reduction of the viscosity of the
dispersed clay dispersion is frequently used as a guide for
obtaining a well dispersed clay slip, but ultimately the preferred
dispersion is judged by the separation obtained between colored
impurities and clay.
[0017] Combinations of two or more dispersing agents may be used to
improve the formation of the aqueous clay dispersion and the
efficiency of the overall purification process. Effective
dispersing agent combinations include, for example, soda ash and
low molecular weight sodium polyacrylate (molecular weight in the
range of 1000-20,000), or sodium silicate and sodium polyacrylate,
or a combination of sodium carbonate, sodium silicate and sodium
polyacrylate. Preferably, sodium or ammonium polyacrylate are used
as one of the dispersing agents. Polyacrylate dispersing agents are
commercially available from many suppliers under different trade
names, for example, Cyanamer P70.RTM. (sodium polyacrylate) sold by
Cytec Industries Inc., West Paterson, N.J. When a combination of
dispersing agents is used, the agents comprising the combination
may be added to the clay dispersion either sequentially or
simultaneously. The preferred addition method and the individual
use rates for each dispersing agent may be established without
undue by experimentation by those skilled in the art. Generally,
the use rates for the dispersing agents are in the range of about 1
to about 5 kilograms/ton of clay for sodium silicates, preferably
about 2 to about 4 kilograms/ton; in the range of about 0.05 to
about 1.0 kilograms/ton for polyacrylates, preferably, about 0.2 to
about 0.4 kilograms/ton; and in the range of about 0.25 to about
2.5 kilograms/ton for sodium carbonate, preferably about 0.5 to
about 1.5 kilograms/ton. The use rates are dictated by the type of
crude clay being treated and the overall separation efficiency
between colored impurities and the clay. Statistical experimental
designs, such as two- or three-factor, three-level factorial
designs, may be useful in determining the use rates, when
combinations of dispersing agents are used. See generally,
Statistics for Experimenters, by Box, Hunter and Hunter, John Wiley
& Sons, Inc., 1978.
[0018] "Conditioning" of the clay dispersion is a conventional
process wherein the clay dispersion is mixed with a conditioning
agent to develop dissimilar surfaces between the dispersed clay
particles and the impurities, to thereby promote the subsequent
separation process. Conditioning is accomplished by treatment of
the well-dispersed clay slip with a conditioning agent, or a
mixture of conditioning agents, comprising compounds that are
N-hydroxy derivatives of amides, or hydroxamic acid derivatives.
These compounds are referred to herein as "hydroxamate conditioning
agents". The hydroxamate conditioning agent, or a mixture of
hydroxamate conditioning agents, used herein are represented by the
formula:
R-C(=O)N(R")-OM
[0019] wherein R is linear or branched C.sub.2-C.sub.18 alkyl,
linear or branched C.sub.2-C.sub.18 alkenyl, C.sub.6-C.sub.20 aryl,
substituted aryl, C7-C.sub.26 aralkyl or substituted aralkyl; R" is
H, C.sub.1-C.sub.12 alkyl or C.sub.7-C.sub.26 aralkyl; and M is
hydrogen, an alkali metal or ammonium (NH.sub.3), wherein the
substituted aryl or substituted aralkyl are substituted on aryl
with hydroxy, C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl. As
used herein, aralkyl represents a moiety comprising an alkyl moiety
bonded at either R, R", or both, of R-C(=O)N(R")-OM, wherein the
alkyl moiety possesses an aryl, or a substituted aryl substituent.
Exemplary aralkyl moieties include benzyl, salicyl, and the like.
Preferably, aryl is phenyl or naphthyl. More preferably, the
hydroxamate conditioning agents are alkyl hydroxamic acids, or
salts thereof, wherein R is linear or branched C.sub.8-C.sub.12
alkyl, linear or branched C.sub.8-C.sub.12 alkenyl, aryl or
substituted aryl; R" is hydrogen; and M is selected from hydrogen,
sodium, potassium or ammonium.
[0020] The hydroxamate conditioning agent, or the mixture of
hydroxamate conditioning agents, may be added as a solid, a liquid,
or as a solution or a dispersion in water. Although the amount of
hydroxamate conditioning agent required for purification of a given
clay sample will vary depending on the type of clay and the amount
of impurities to be removed, the hydroxamate conditioning agents
may generally be used in the process of the present invention in an
amount of about 250 grams/ton of clay to about 2,000 grams /ton of
clay. The hydroxamate conditioning agent, or mixtures thereof, may
be used alone or may be optionally used in combination with other
conditioning additives. The conditioning treatment described herein
comprises treatment of the aqueous clay dispersion with a
hydroxamate conditioning agent and a conditioning additive, either
simultaneously or sequentially.
[0021] Optionally, a conditioning agent composition may be used to
condition the clay sample. The conditioning agent composition of
this invention is comprised of the hydroxamate conditioning agent,
or mixtures thereof, in combination with at least one conditioning
additive selected from an alkyl or aralkyl alcohol, hydrocarbon
oil, carboxylic acid ester, or fatty acid represented by the
formula:
R-C(=O)OM
[0022] wherein R is a C.sub.10-C.sub.18 alkyl, C.sub.6-C.sub.20
aryl, substituted aryl, C.sub.7-C.sub.26 aralkyl or substituted
aralkyl, and M is hydrogen, an alkali metal or ammonium (NH.sub.3),
wherein the substituted aryl or substituted aralkyl are substituted
on aryl with hydroxy, C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6
alkyl. Preferably, R is C.sub.16-C.sub.18 alkyl, C.sub.6-C20 aryl,
substituted aryl, C.sub.7-C.sub.26 aralkyl or substituted aralkyl,
and M is hydrogen, an alkali metal or ammonium, wherein the
substituted aryl or substituted aralkyl are substituted on aryl
with hydroxy, C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl.
Conditioning additives are lipophilic materials that have low water
solubility in water that enhance the conditioning of the slurry
with the conditioning agent and the subsequent separation
process.
[0023] Alcohol conditioning additives that may be useful in the
process of this invention include long chain branched or linear
C.sub.10 to C.sub.22 alkyl alcohols, preferably C.sub.12 to
C.sub.16 alkyl alcohols, or C.sub.7-C.sub.26 aralkyl alcohols.
Preferably, decanol or dodecanol may be used as conditioning
additives. Useful hydrocarbon oil conditioning additives are
composed of branched or linear C.sub.12 to C.sub.32 alkanes or
alkenes, preferably C.sub.12 to C.sub.20 alkanes or alkenes. Useful
carboxylic acid ester conditioning additives comprise branched or
linear C.sub.9 to C.sub.22 hydrocarbon moieties, comprising
alkanes, alkenes, or aryl moieties. The hydroxamate conditioning
agent, or mixtures thereof, may be advantageously pre-dissolved or
pre-dispersed in the alkyl alcohol or hydrocarbon oil and added
directly to the aqueous clay dispersion. The conditioning additives
typically may be used in an amount of about 50% to about 200% by
weight, relative to the amount by weight of alkyl hydroxamate
conditioning agent.
[0024] Useful fatty acid conditioning additives are comprised of
C.sub.12-C.sub.18 alkyl, C.sub.6-C.sub.20 aryl, substituted aryl,
C.sub.7-C.sub.26 aralkyl or substituted aralkyl acids or salts
thereof. Preferably, oleic acid is used as a fatty acid
conditioning agent. The aqueous clay dispersion may be conditioned
with the hydroxamate conditioning agents and the optional fatty
acid conditioning additive, sequentially, in any order, or
simultaneously. The fatty acid and hydroxamate may be added
directly to the aqueous clay dispersion as neat oils, or may be
added as a dispersion in water. The fatty acid may be
advantageously used in an amount of about 500 grams/ton to about
3,000 grams/ton of crude clay, although that amount may vary
depending on the type of clay and the amount of impurities to be
removed from the clay.
[0025] Optionally, the process of this invention may also include
the use of a salt containing a polyvalent metal cation,
particularly the alkaline earth metal salts of calcium, magnesium
and barium. Incorporation of a polyvalent cationic salt, a critical
component in many of the prior art process, is not required for
effective purification of clays using the process of this
invention, and may be substantially absent. These salts, however,
may be optionally added to further improve the overall process.
Salts that are useful as conditioning additives are well known, and
are generally water soluble salts that may be added directly to the
aqueous clay dispersion as a solid or in solution. A preferred
polyvalent metal cation containing salt is calcium chloride. The
salts may be added simultaneously with, or prior to, the addition
of the hydroxamate conditioning agent, or mixtures thereof, in
combination with any of the conditioning additives described above.
The salt may be added in an amount generally in the range of about
0 grams/ton to about 1,000 grams/ton of crude clay, and preferably
at about 250 grams/ton of crude clay, depending on the type of clay
and the amount of impurities to be removed from the particular clay
sample.
[0026] During processing, the clay dispersion, conditioned with
hydroxamate and other additives, if any, may be transferred from a
blunging/conditioning vessel, such as a mixing tank, or a blender
pitcher, to another vessel that would permit subsequent removal of
the flocculated impurities, e.g., a settling vessel. The density or
% solids of the clay dispersion may be adjusted by addition of
water, as necessary, for enhanced flocculation and separation.
Typically, the clay concentration in the clay dispersion is reduced
such that the clay concentration is in the range of about 10% to
about 30% solids, prior to addition of the flocculating agent.
Alternatively, the density of the clay dispersion may be adjusted
upon addition of the polymer solution. Selective flocculation of
the impurities may be accomplished by adding a dilute solution of
the polymer, typically, at about 0.01% to about 0.1% by weight,
with low shear mixing.
[0027] Optionally, the stability of the dispersion and the
effectiveness of subsequent impurity separation may be enhanced by
the addition of a pH modifying agent. A pH modifying agent is a
material having a basic pH (greater than 7.0) that is capable of
maintaining the pH of the aqueous clay dispersion in the range of
7.5-10.5, and preferably in the range of 8.0-9.5. Useful pH
modifying agents include, without limitation, water soluble agents
such as ammonia or ammonium hydroxide, sodium or potassium
hydroxide and sodium carbonate. The preferred pH modifying agents
include, for example, sodium hydroxide or ammonium hydroxide.
Optionally, the amount of the pH modifying agent added to the clay
dispersion will be that amount necessary to adjust the pH of the
aqueous clay dispersion to about 7.5 to about 10.5. The pH
modifying agent is commonly added during the blunging step,
generally as a solid, but it may be pre-dissolved in water and
added as a aqueous solution.
[0028] The impurities in the clay dispersion are flocculated (e.g.
aggregated and precipitated) from the dispersion by addition of a
flocculating agent. The flocculating agent may be added to the
conditioned clay dispersion as a dilute water solution. In the
process of this invention, useful flocculating agents are high
molecular weight organic polymers that are anionic or non-ionic
water soluble or water-dispersible organic polymers, having a
molecular weight in the range of about 0.5 million to about 30
million, and preferably a molecular weight in the range of about
1.0 million to about 20 million. Examples of useful organic
polymeric flocculants include, but are not limited to hydrolyzed
polyacrylamides, co-polymers of acrylamide and acrylic acid,
copolymers of acrylamide and acrylamidomethylpropanesulfoni- c
acid, vinyl sulfonic acids, carboxymethyl cellulose, polystyrene
sulfonic acids, water soluble polymers containing pendant
hydroxamic acid functionality, and salts there of, such as
hydroxamated polyacrylamides or polyacrylates, water-soluble or
dispersible polyethylene oxide polymers, and other non-ionic water
soluble or water-dispersible polymers such as polyacrylamides and
polyvinyl alcohols. Preferred polymeric flocculants of this
invention are hydroxamated polyacrylamides and hydroxamated
polyacrylates.
[0029] An additional feature of this invention is that hydroxamated
polyacrylamides and hydroxamated polyacrylates may be used to
selectively flocculate impurities from clays that have been treated
with conditioning agents comprising fatty acids and alkaline earth
metal salts. This process comprises the steps of forming an aqueous
clay dispersion by blunging the clay with a dispersing agent, or a
combination of dispersing agents, in water; treating the aqueous
clay dispersion with a conditioning agent represented by the
formula:
R-C(=O)OM
[0030] wherein R is C.sub.10-C.sub.18 alkyl, C.sub.6-C.sub.20 aryl,
substituted aryl, C.sub.7-C.sub.26 aralkyl or substituted aralkyl,
and M is hydrogen, an alkali metal or ammonium, wherein the
substituted aryl or substituted aralkyl are substituted on aryl
with hydroxy, C.sub.1-C.sub.6 alkoxy, or C.sub.1-C.sub.6 alkyl;
flocculating the conditioned clay dispersion by treatment with a
water soluble or water dispersible organic polymer containing
hydroxamic acid groups or salts thereof, and removing the
flocculated impurities to form a purified clay dispersion. The
amount of polymeric flocculant used to purify a clay sample will
vary depending upon the type of clay used and the amount of
impurity to be flocculated from the particular clay sample.
However, the general use rates of the polymeric flocculant in the
process of the present invention are in the range of about 20
grams/ton to about 200 grams/ton of crude clay. Advantageously, the
aqueous clay dispersion may be also treated with a salt containing
a polyvalent metal cation. Preferably, the salt is calcium
chloride. Optionally, the clay dispersion is also treated with at
least one conditioning additive selected from an aliphatic alcohol,
a hydrocarbon oil or a carboxylic acid ester oil. Preferably, the
conditioning additive may be decanol or dodecanol. Useful
dispersing agents include sodium silicate, sodium polyacrylate, or
sodium carbonate.
[0031] Rapid flocculation of the colored impurities in the aqueous
clay dispersion generally occurs upon addition of the polymeric
flocculating agent. The flocculated impurities settle to form a
highly colored lower layer, leaving a milky-white upper layer of
purified clay.
[0032] This upper clay layer may be isolated from the lower
impurity-containing layer by any of the conventional processes used
in selective flocculation operations which are well known to those
skilled in the art. The upper layer may be decanted away from the
lower layer, or alternatively, the lower layer may be drained off
from the bottom. Other apparatus, such as a drag box or a low shear
centrifugal device, may also be used to separate the lower
impurity-containing layer from the purified upper clay layer.
[0033] The purified clay produced by the process of this invention
possesses high brightness and low levels of impurities. The purity
of this product may be further improved by using the conventional
techniques of magnetic separation or chemical bleaching.
[0034] The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied. All quantities are reported on a dry
weight basis unless otherwise indicated. The crude kaolin clay used
in these Examples was obtained from a mine in the eastern part of
Georgia, USA, having a titanium oxide concentration of about 3.0%
by weight. The crude clay possessed a particle size distribution of
80-90% finer than 2 microns.
EXAMPLE 1
[0035] A 60% solids dispersion of kaolin clay was prepared by
blunging (mixing) 386 g. of the crude clay (approximately 330 g. of
clay on a dry weight basis) containing 3.0% TiO.sub.2 with 500
grams/ton sodium carbonate, 3000 grams/ton sodium metasilicate, 250
grams/ton of sodium polyacrylate, and 400 grams/ton of sodium
hydroxide (to obtain a blunged slurry having a pH of approximately
8.5-9) in water for 5 minutes using a Waring laboratory blender at
high speed. At the end of blunging, 1200 grams/ton of Aero
6493.RTM. (a mixture of alkyl hydroxamates, sold by Cytec
Industries Inc., West Paterson, N.J.), a conditioning agent, was
added to the clay slurry, and the resulting mixture was mixed, or
conditioned, in the blender at high speed, for 5 minutes. The
conditioned slurry was then divided into three equal portions, each
of which was transferred to a 500 ml graduated cylinder. A
different selective flocculation polymer was added to each
cylinder, at a use rate of 30 grams/ton, to induce flocculation.
After addition of a dilute solution (0.01 or 0.03% by weight) of
the flocculation polymer, the concentration of the clay in the
dispersion was reduced to about 20% by weight by addition of water.
The clay slurry was mixed gently using a stainless steel plunger
with holes, typically used in flocculation tests. The mixture was
allowed to stand for 30 min. during which time the physical
attributes of the selective flocculation process, such as floc
formation, the appearance of flocs, and the rate of settling, were
observed. The volumes of settled and suspended phases were noted,
and samples from each phase were analyzed for Ti content, using
x-ray fluorescence (see Table 1).
[0036] Comparative tests were performed using the procedure
described above, but without addition of any conditioning agent(s)
prior to flocculant addition. The prior art selective flocculation
process was conducted using oleic acid as a fatty acid at 2500
grams/ton in combination with calcium chloride at 385 grams/ton.
The dispersing agents used in this test were 2600 grams/ton of
sodium metasilicate and 300 grams/ton of sodium polyacrylate.
1TABLE 1 % TiO2 in Clay Conditioning Test Flocculation Agents
Agents Agent A* Agent B* Agent C* None (Control) 2.01 2.11 2.13
Fatty Acid + CaCl.sub.2 1.00 -- -- (Prior art) Aero 6493 .RTM. 0.73
0.76 0.75 Fatty Acid + CaCl.sub.2 -- -- 1.06 *Flocculation Agent A:
95% acrylic acid, 5% acrylamide; molecular weight >10 million.
*Flocculation Agent B: Hydroxamated polyacrylamide, 8% hydroxamate
functionality, 72% acrylate functionality; # molecular weight
>10 million. *Flocculation Agent C: Hydroxamated polyacrylamide,
18% hydroxamate functionality, 62% acrylate functionality; #
molecular weight >10 million.
[0037] In the control test with no conditioning agent the TiO.sub.2
content in the clay product is reduced from about 3% by weight in
the crude clay to about 2.1% by weight, i.e. a reduction of 0.9%.
Use of alkyl hydroxamic acid as the conditioning agent, reduced the
TiO.sub.2 content in the clay product by more than 1.3%, relative
to the control where no conditioning agent was used, or by about
2.2%, relative to the crude clay. The TiO.sub.2 content in the clay
product is reduced by about 0.25% relative to the prior art process
using fatty acid, CaCl.sub.2 and a highly charged, high molecular
weight copolymer of acrylic acid and acrylamide.
EXAMPLE 2
[0038] A solids dispersion was prepared according to the procedure
set forth in Example 1, except that 1000 grams/ton sodium
carbonate, 2000 grams/ton of sodium metasilicate, 175 grams/ton of
sodium polyacrylate, and only 600 grams/ton of Aero 6493.RTM. were
blunged with the kaolin clay. The TiO.sub.2 concentration of the
clay, after selective flocculation follows: 1.17% for Polymer A
(use rate 30 grams/ton), 1.02% for Polymer B (6.5 grams/ton), and
1.00% for Polymer C (18 grams/ton).
EXAMPLE 3
[0039] A solids dispersion was prepared according to the procedure
set forth in Example 1, except that the conditioning agent was a
mixture of C.sub.8-C.sub.10 alkyl hydroxamic acids. The reduction
in TiO.sub.2 concentration in the clay product was substantially
similar to that observed for Aero 6493.RTM., as reported in Table
1.
EXAMPLE 4
[0040] A solids dispersion was prepared according to the procedure
set forth in Example 2, except that a conditioning agent
combination, consisting of a mixture of C.sub.8-C.sub.10 alkyl
hydroxamic acids (conditioning agent) and a oleic acid
(conditioning additive), was used to condition the clay dispersion.
The conditioning agent combination was added simultaneously with
the calcium chloride to the blunged clay dispersion. The reduction
in TiO.sub.2 concentration in the clay product was substantially
similar to that observed for Aero 6493.RTM., as reported in Table
1.
EXAMPLE 5
[0041] A solids dispersion was prepared according to the procedure
set forth in Example 3, except that the conditioning agent
combination consisted of a mixture of C.sub.8-C.sub.10 alkyl
hydroxamic acids (conditioning agent) and a hydrocarbon oil
(conditioning additive). The reduction in TiO.sub.2 concentration
in the clay product was substantially similar to that observed for
Aero 6493.RTM., as reported in Table 1.
EXAMPLE 6
[0042] A solids dispersion was prepared according to the procedure
set forth in Example 3, except that the conditioning agent
combination consisted of a mixture of C.sub.8-C.sub.10 alkyl
hydroxamic acids (conditioning agent) and methyl palmitate ester
oil (conditioning additive). The reduction in TiO.sub.2
concentration in the clay product was substantially similar to that
observed for Aero 6493.RTM., as reported in Table 1.
EXAMPLE 7
[0043] A solids dispersion was prepared according to the procedure
set forth in Example 4, except that the conditioning agent
combination, consisting of a mixture of C.sub.8-C.sub.10 alkyl
hydroxamic acids (conditioning agent) and a oleic acid
(conditioning additive), was used in combination with calcium
chloride to condition the clay dispersion. The conditioning agent
combination was added simultaneously with the calcium chloride to
the blunged clay dispersion. The reduction in TiO.sub.2
concentration in the clay product was substantially similar to that
observed for Aero 6493.RTM., as reported in Table 1.
EXAMPLE 8
[0044] A solids dispersion was prepared according to the procedure
set forth in Example 1, except that the flocculant was a
polyethylene oxide. The reduction in TiO.sub.2 concentration in the
clay product was substantially similar to that observed for Aero
6493.RTM., as reported in Table 1.
[0045] Other variations or modifications, which will be obvious to
those skilled in the art, are within the scope and teachings of
this invention. This invention is not to be limited except as set
forth in the following claims.
* * * * *