Electrolysis: processes – compositions used therein – and methods – Electrolytic material treatment
Reexamination Certificate
1999-06-30
2001-05-08
Phasge, Arun S. (Department: 1741)
Electrolysis: processes, compositions used therein, and methods
Electrolytic material treatment
C205S480000, C205S770000, C423S431000
Reexamination Certificate
active
06228249
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a product and a process for its preparation. More particularly, the present invention relates to a process for purifying calcium carbonate by removing metal contaminants. Even more particularly, the present invention relates to a process for lowering metal contaminants in calcium carbonate products by electrochemically treating the precursors that are subsequently used for producing calcium carbonate.
BACKGROUND OF INVENTION
Many limestone quarries contain some level of metal contaminants, such as iron, aluminum, magnesium, manganese, lead and tin in the calcium carbonate. The metal contaminants are usually in the form of oxides. For example, the presence of iron, in any form, is considered a contaminant in specialty markets, such as food products and pharmaceutical applications. Furthermore, the presence of other metal contaminants in calcium carbonate diminishes the economic value of products, such as paper, plastics, and paints that are produced containing these metal contaminants.
Several physical and chemical processes have been suggested to remove iron from calcium carbonate. Physical removal typically requires grinding the calcium carbonate to such fineness so that the iron can be removed by screening, classification, magnetic separation or floatation. Chemical removal typically requires leaching or bleaching the ground calcium carbonate with solvents followed by filtration. However, these physical and chemical processes for the removal of iron from calcium carbonate are complex, difficult to apply, and the results are erratic and unreliable. There is a need for reliable ways to remove iron and other metal contaminants from calcium carbonate.
The use of electrolytic techniques to remove metal contaminants such as lead and other metals is described in a number of systems. Acar Y. B., “J of Geo-technical Engineering,” Vol. 122 No. 3, pps. 175-185, describes an electrolytic technique for the removal of metal contaminants from soil. Dudek F. J.; Morgan, W. A. International Symposium on the Extraction and Applications of Zinc and Lead, Sendai, Japan, May 22-24, 1995, describes an electrolytic technique for reclaiming zinc from steel scrap. Flett D. S.; Covington, J. W.; Winter, D. G.; Spring 1988 Proceedings of the Electrochemical Society Meeting, Volume 88-1, describes a method for removing lead contaminants from zinc solutions. All these techniques describe electrolysis as a method for purifying various systems but none describes using this technique for purifying calcium carbonate.
U.S. Pat. No.5,690,897 describes a method of lowering the iron content of calcium carbonate by using chelating agents. Mahanti, H. S., Barnes, R. M., “Application Spectroscopy,” 1983, Vol.37,155.4, and as Golley, C. R. L. and European Patent Application 88304211 describes, purification through the use of floatation. All these techniques provide processes for purifying calcium carbonate. However, none of the techniques make use of the electrolytic process of the present invention.
What has been found to be novel and unanticipated by the prior art is an electrolytic process for reducing the metal contaminants in calcium carbonate, including the reduction of metal contaminants in precursors that are subsequently used in calcium carbonate production.
It is therefore an object of the present invention to provide a process for the removal of metal contaminants from calcium carbonate. Another object of the present invention is to provide a process for the removal of metal contaminants from precursors that are subsequently used in the production of calcium products. Still a further object of the present invention is to provide calcium carbonate products that are free of metal contaminants. Still another object of the present invention is to produce calcium carbonate products that are of sufficient purity such that they find particularly use in market applications where purity of the final product is required.
SUMMARY OF INVENTION
The present invention provides an electrochemical process for reducing metal contaminants in calcium carbonate materials by solubilizing the calcium carbonate material containing the metal contaminant in an aqueous solution and then removing the metal contaminant by passing an electrical current through the aqueous solution containing the solubilized metal contaminant to produce a high purity calcium carbonate product.
In another aspect of the present invention, an electrochemical process is used to treat any calcium carbonate precursors that are subsequently used in the production of calcium carbonate products having lower metal contaminants.
Calcium carbonate produced according to the process of this invention is particularly suitable for use as food or pharmaceutical additives. The calcium carbonate is also suitable for use in papermaking process as fillers, or coatings, or as additives in the production of plastics, paints, adhesive products, or any other application where high purity calcium carbonate products are required.
DETAIL DESCRIPTION OF THE INVENTION
In one aspect, the present invention provides an electrochemical process for removing metal contaminants such as, for example, iron, aluminum, magnesium, manganese, lead, and tin and the like, from calcium carbonate. The metal content of the final product was substantially reduced, and in some instances, complete extraction of the contaminant occurred.
In another aspect of the present invention, an electrochemical process was used to lower metal contaminants in chemical species that are used as precursors for the subsequent production of calcium carbonate. The electrochemical process of the present invention may be used for reducing metal contaminants in calcium carbonate products that are destined for use in USP grade products, food grade products, and in paper products as fillers and coatings, and in the production of plastics, paints and adhesive products. Uses of high purity calcium carbonate include, but not limited to, catalysts and catalyst supports, electrical/semiconductor applications, florescent lighting, and optical/laser applications.
The electrochemical process of the present invention is useful in lowering the metal contaminants in calcium carbonate minerals, such as, for example, limestone, chalk, dolomite and synthetically produced precipitated calcium carbonate (PCC). Additionally, the process is also applicable to the treatment of chemical species that are used as precursors from which calcium carbonate products are produced.
The electrochemical process for removing metal contaminants from calcium carbonate is applicable during the production of calcium carbonate. The process may be practiced during the slaking stage, during the carbonation stage or during the heat aging stages to produce high purity calcium carbonate products.
In order to practice the electrochemical process during the slaking operation, all chemical species, such as, the calcium ions, the carbonate ions and other metal ions are preferably in a uniformly dispersed solution. A uniformly dispersed solution is one having no particulate matter present prior to the precipitation of calcium carbonate. The uniformly dispersed solution is prepared by dissolving enough calcium oxide (lime) into water to produce from about zero 0 weight percent to about 2.0 weight percent calcium hydroxide solution, based on the weight of the calcium hydroxide solution. The preferred weight of the calcium hydroxide is from about 0.11 weight percent to about 1.5 weight percent calcium hydroxide solution, based on the weight of the calcium hydroxide solution. Before carbonating the calcium hydroxide, an electrical current of from about zero 0 volts to about 10 volts is passed through the calcium hydroxide solution to remove metal contaminants. The preferred voltage is from about 3 volts to about 7 volts. The subsequent carbonation of the calcium hydroxide produces the high purity calcium carbonate product of the present invention.
In order to practice the electrochemical process during the carbonation o
Minerals Technologies Inc.
Morris Terry B.
Phasge Arun S,.
Powell Marvin J.
LandOfFree
Electrolytic purification of calcium carbonate does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrolytic purification of calcium carbonate, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrolytic purification of calcium carbonate will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2535472