Classifying – separating – and assorting solids – Precedent preparation of items or materials to facilitate... – Selective differentiation
Reexamination Certificate
2000-07-18
2002-05-21
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Precedent preparation of items or materials to facilitate...
Selective differentiation
C209S003000, C423S023000, C423S069000, C423S155000, C210S723000
Reexamination Certificate
active
06390301
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Background of the Invention
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.
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.
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.
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.
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.
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
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
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 h
Nagaraj D. R.
Rothenberg Alan S.
Ryles Roderick G.
Cytec Industries Inc.
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Tuan N.
LandOfFree
Process for removing impurities from kaolin clays does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for removing impurities from kaolin clays, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for removing impurities from kaolin clays will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2853345