Classifying – separating – and assorting solids – Fluid suspension – Liquid
Reexamination Certificate
2000-11-30
2002-04-30
Lithgow, Thomas M. (Department: 1724)
Classifying, separating, and assorting solids
Fluid suspension
Liquid
C106S486000, C501S148000
Reexamination Certificate
active
06378703
ABSTRACT:
FIELD OF THE INVENTION
This invention relates an improved method for purifying titania contaminated kaolin clay by froth flotation which features the use an hydroxamate flotation collector at a neutral or mildly alkaline pH wherein a slurry of the impure clay is conditioned for the flotation step in a baffled conditioning apparatus provided with mean for imparting sufficient mechanical energy of a dispersed slurry of the impure clay before flotation.
BACKGROUND OF THE INVENTION
Froth flotation has been widely used on an industrial scale to separate various mineral particles from other particles in an aqueous mineral pulp based on differences in mineral species. The processing generally depends upon adding reagents that selectively attach to mineral particles to be floated, whereby the particles with attached reagent(s) have a greater affinity for air bubbles than other particles and can be removed as a froth. The step conventionally used in the art to describe the step(s) prior to aeration and, hence, flotation, is referred to as “conditioning” Material(s) added to selectively attach to a desired species is referred to as the “collector.” In the case of oxide and/or silicate minerals, the collector is usually anionic, exemplified by, but not limited to, fatty and/or resin acids. In many cases of oxide and/or silicate flotation, polyvalent ions, usually calcium are used to promote “collector coating” of the mineral to be floated. Frequently, frothers are added. Obviously pH control must be applied. Since the products processed by froth flotation are frequently industrial minerals, the economics of the processing is of prime significance. Economics is affected, among other factors, by the sharpness of separation, the extent of recovery of valued mineral and energy requirements, including but not limited to costs incurred during removal of water.
When froth flotation is applied to separate large oxide or silicate mineral particles, e.g., particles large than 20 microns, the processing can be relatively straight forward. However, when froth flotation is used with “slimed” ore pulps, i.e., ore pulps that contain sub-micron size particles, the processing becomes more difficult. Among other reasons, slimes tend to attach to particles to be floated and the desired selectively is relatively difficult to achieve. A prime example of a slimed ore pulp that presents unique difficulties in practicing froth flotation is the flotation purification of kaolin clay wherein the objective is to remove a colored, anatase (titania) impurity from the kaolin clay, resulting in a purified kaolin product of materially increased brightness value. In such case, the flotation of coarse particle size fractions of kaolin clay ores was readily achieved over 50 years ago by simple anionic (negative ion) flotation using a fatty acid collector and selected sulfate salts. However, when slimes were present, as they were when using whole kaolin crudes or fine particles size fractions of crudes, the desired selectivity for titania flotation, achieved at a commercially feasible recovery of purified clay, was difficult to achieve. Among the reasons for the difficulty, was the necessity to physically separate the mineral particles before the aeration and flotation step. This necessitated the use of controlled amounts of clay dispersants to assure physical separation of slimed particles from other particles. However, reagents used as aids to collector coating, such as sources of polyvalent cations, e.g., calcium ions, tended to conflict with operation of clay dispersants. On the other hand, clay dispersants that were too powerful (for example, condensed phosphate salts) tended to interfere with the action of collectors and adjuvant flotation oils. The generation of froths that were sufficiently strong to endure the mechanical forces of aeration and flotation also presented technical obstacles.
Thus, while the froth flotation purification of kaolin clays is one of the most widely practiced industrial mineral operations, there has been an ongoing need to improve the effectiveness and economics of the operation. Among the prime inventions heretofore utilized to purify kaolin clay on a commercial basis is the “Ultraflotation” process described in U.S. Pat. No. 2,990,958, Greene et al, commonly assigned. Briefly, a particulate calcite reagent was employed with a fatty acid and selected flotation oils to remove titania from a dispersed pulp of a fine fraction the impure clay. A characteristic of the processing was that the purified kaolin was recovered as a dilute, e.g., 10% solids aqueous pulp, that was subsequently dewatered. Another commercially practiced process is referred to as “TREP” (an acronym for “titania removal and extraction process”). In this process, conditioning was conducted in a “squirrel cage” conditioner using a fatty acid collector and a calcium or iron salt. This was followed by addition of an acrylate salt dispersant. Reference is made to U.S. Pat. No. 4,492,628, Young et al. Conditioning was carried out in a baffled, high intensity mill referred to as “squirrel cage.” See U.S. Pat. No. 4,483,624 Bacon et al. A drawback of TREP is that the high intensity conditioning is time intensive and adds significantly to the cost of the processing. Also, equipment wear adds to costs. Efforts to reduce conditioning time have resulted in inadequate purification and/or undesirably low recovery of purified kaolin clay.
In addition to fatty acids used as anionic collectors for oxide flotation, anionic hydroxamates have been advocated. The use of hydroxamate in clay flotation is described in U.S. Pat. No. 4,629,559, Yoon et al and allegedly has the advantage of not requiring the use of salt activators such as calcium salts. Initial attempts to substitute an hydroxamate for the fatty acid/salt activator system used commercially in practice of the TREP process were not promising. The low recovery and less than desired degree of purification was due to foaminess resulting probably from high pH (9-10) and excessive temperatures (200° F. or higher) generated during conditioning. Initially, it was speculated that the hydroxamate reagent would not be stable at the high temperatures used in TREP flotation.
SUMMARY OF THE INVENTION
An object of the present invention is to improve TREP flotation of kaolin clay.
In accordance with this invention an anionic hydroxamate collector is used in TREP flotation to remove selectively the titania impurity from kaolin clay. Operation of the process of the invention, while making use of an hydroxamate collector, necessitates significant departures from parameters advocated in the prior art for flotation purification of kaolin using an hydroxamate collector. Specifically, the pH of the flotation pulp is significantly lower than those advocated in the prior art. Much more energy is used in the conditioning step when practicing conventional TREP flotation using a fatty acid collector.
The substitution of hydroxamate for the oleic acid-calcium chloride reagents of the prior art led to unexpected results. The most surprising result was that the anatase removal improved with decreasing pH, in contrast to the prior art directed to the use of hydroxamate collector. The optimum pH for attachment of the hydroxamate to titania has been reported to be at least pH 8.5 in the prior art. At pH 7.0 titania removal does occur but not to the optimum level as at pH 10.0 recommended by Yoon et al (U.S. Pat. No. 4,629,556). There was substantial removal of anatase at pH 7.0 compared to pH 10.0 with increase in conditioning time. Another novel aspect of hydroxamate conditioning using the TREP conditioner is that the temperature generated can be as high as 170° F. without adversely affecting the flotation performance.
It was also observed that the conditioning time could be reduced by 75% by substituting the Ca-oleic acid reagent system with hydroxamate in the TREP process. With 35% conditioning solids the residence time in the TREP conditioner with hydroxamate is about 20 minutes compared to 80 minutes with the C
Brooks Ronnie E.
Finch Ernest M.
Mathur Sharad
Engelhard Corporation
Lithgow Thomas M.
Miller Stephen I.
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