This application claims the benefit of U.S. Provisional Application No. 62/477,742, filed

03/28/2017

FIELD OF THE INVENTION

[001] The present invention is in the technical field of carbon materials, graphite materials and beneficiation of natural graphite. This invention describes an apparatus and method for removing gangue material and other impurities from graphite flakes by subjecting a mixture of graphite flakes and water to centrifugal acceleration. This invention provides an easy, simple, cost-effective, portable and eco-friendly approach to purification of graphite flakes. The solution offered by this invention can be used for purification of graphite ore in an ecologically friendly way, as does require any chemicals. Graphite purified by the method and apparatus offered by this invention contains low level of impurities. BACKGROUND OF THE INVENTION

[002] Graphite, as the most common polymorph of naturally occurring crystalline carbon, is required in production of many different goods, such as batteries, refractories, electrical products, and so on. Graphite is a unique material since, as a covalent substance, it should not conduct electricity, yet it does. Graphite is a carbon substance where three of its valence electrons are covalently bonded to three other carbon atoms. However, the fourth valence electron is left unbounded, and, therefore, can move freely. Such valence electrons allow electric currents to flow through graphite.

[003] Gangue material and other impurities present in graphite are natural insulators and do not conduct electricity as well as graphite does. Thus, as concentration of carbon increases and concertation of gangue material decreases, the electric conductivity of a graphite crystal increases as well due to graphite's superior conductivity over gangue material.

[004] Pure graphite is naturally hydrophobic on the cleavage planes due to the low surface energy. Thus, it is not surprising that the most popular industrial approach to graphite purification is by flotation. Despite graphite's natural floatability, however, the separation from gangue minerals, such as feldspar, quartz, mica, and carbonate, usually requires use of chemicals - surfactants and depressants - which makes the process more expensive and ecologically consequential. Furthermore, graphite can be upgraded by flotation to no more than 95% of carbon, and, after flotation, some of impurities are disseminated back into graphite scales. Other approaches to purify graphite involve acid leaching and caustic roasting, that are not only costly but may also cause environmental pollution.

[005] Therefore, production of high-grade graphite by technologies that are both energy- efficient and environmental benign is in great demand. In recent years, there has been a growing interest in graphite beneficiation through microwave heating. Microwave irradiation has many advantages too, as it allows for rapid and selective heating while also being environmentally benign. These approaches, however, require highly sophisticated equipment, and, therefore, are costly. Other separation techniques include gravity separation, two-liquid separation and film flotation. While those techniques are promising, they do require additional substantial research and significant investments. With the development of graphene, demand of graphite is constantly increasing. This fact has recently motivated the exploration of new graphite deposits. As these graphite deposits are typically of lower quality than those currently in production, there is a strong need for adopting new methods to retain graphite product quality while containing beneficiation process costs. [006] The method and apparatus described in the present invention provide for production of high purity graphite while keeping the costs low and with virtually no environmental impact. The main difference of the present invention from relevant prior art is the absence any chemicals or excipients. In addition, water - the only component used in this invention - can be re-used repeatedly and without recycling. The simplicity of the apparatus' design combined with low processing temperatures also contribute to the effectiveness of the described invention.

SUMMARY OF THE INVENTION

[007] The present invention directed at the apparatus and method for removal of gangue material and other impurities from graphite by applying centrifugal acceleration to a mixture of graphite flakes and water.

[008] The force generated by a plurality of rotating impellers is applied to the mixture or water and graphite flakes, which, in turn, causes build-up of high pressure and turbulence sufficient to wash out gangue material and other impurities from graphite.

[009] The method and apparatus described in this invention comprise: a) preparing a working mixture of water and natural graphite flakes; b) placing the working mixture into a flow reactor; c) circulating the working mixture in the flow reactor thus, causing centrifugal flows of the solution and subsequent collisions of the graphite flakes it contains; d) purifying graphite flakes through leaching and washing off gangue materials; and e) separating resulting high purity graphite flakes from the working mixture.

[0010] The method and apparatus described herein provides for a significant increase of carbon content in graphite treated by this invention. The effectiveness of the present invention has been confirmed by multiple tests observing spectral and elemental (purity) analysis. In addition, 30-40% increase of electrical conductivity in graphite purified by the disclosed method has been observed.

[0011] The disclosed invention purifies graphite in cost-effective and ecologically-friendly way. Furthermore, this invention does not require substantial sources of energy nor sophisticated equipment, it can be implemented in a field near graphite depositories, which, in turn, would reduce transportation costs and overall costs of production.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Detail features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings. We also provided purified graphite flake analysis results in order to prove advantage of this invented technology.

[0013] FIG. l is the apparatus for removing gangue materials and other impurities from graphite flakes through centrifugal acceleration.

[0014] FIG.2A and FIG.2B depict SEM (Scanning Electron Microscope) images of purified graphite.

[0015] FIG.3 shows Raman spectra of purified graphite.

[0016] FIG.4 demonstrates XRD (X-ray diffraction) pattern of purified graphite.

[0017] FIG.5 shows FTIR spectra of purified graphite.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The following is a detailed description of the invention provided to aid those skilled in the art in practicing in the field of the present invention. Those of ordinary skill in the art may make modifications and variations in the embodiments described herein without departing from the spirit or scope of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for describing particular embodiments only and is not intended to be limiting of the invention. All publications, patent applications, patents, figures and other references mentioned herein are expressly incorporated by reference in their entirety.

[0019] The present invention is directed at the apparatus and method for removing impurities from natural graphite by applying centrifugal acceleration to a mixture of graphite flakes and water.

[0020] The gist of the proposed method and apparatus is application of centrifugal forces to the mixture of water and graphite flakes placed into a flow reactor equipped with a plurality of rotating impellers. As said impellers rotate, they are causing the mixture to move with high linear velocity, which, in turn, is causing graphite flakes to collide with each other and leach gangue material off the collided flakes. In addition, high levels of centrifugal acceleration cause graphite flakes to swirl in the reactor resulting in higher levels of graphite-water friction, which, in turn, enhances effectiveness of removal of gangue material from graphite flakes.

[0021] In one exemplary embodiment depicted in FIG. l, the plurality of impellers 1 and 4 are rotated through a mechanical controller; thus, causing centrifugal acceleration and a plurality of streams of the working mixture, which streams collide at or about point of collision 2. The diameter of impellers 1 and 4 are substantially similar to the inner width of reactor 3, providing a gap of no more than 0.8 mm.

[0022] In other exemplary embodiment, the working mixture of water and graphite is prepared by mixing 15 kg of natural graphite with carbon content of 98% in 100 L of water. Said working mixture is then passed through the flow reactor at speeds of about 20 m/sec and temperatures in the range of 40-50 degrees Celsius. The foregoing process continues for about 15 minutes, after which the working mixture is separated into two fractions - small and large - using a generic centrifuge. Once the entire mixture is processed, the resulting aqueous paste is dehydrated and graphite flakes with high carbon content - up to 99.8 %, - are separated from the paste. Electric conductivity of the resulting graphite is increased by 30 - 35% comparing to the original graphite.

[0023] In other exemplary embodiments, the working solution may consist of 100 parts of water and 10 to 20 parts of graphite, and be subjected to centrifugal accelerations of up to 20g and linear velocities of up to 40 m/sec, reaching speeds in the range of 30-50 m/sec.

[0024] Yet in other exemplary embodiments the foregoing process occurs under pressure of 5- 15 bar with temperatures in the range of 40-65 degrees Celsius.

[0025] Based on the foregoing, the present invention provides for ecologically clean and inexpensive method of purification of graphite with carbon content of up to 99.8% and high electrical and thermal conductivity. The method and apparatus described herein use only one component - water - that can be re-used multiple times and without recycling. Moreover, because the present invention does not require substantial sources of energy nor sophisticated equipment, it can be implemented in a field near graphite depositories, which, in turn, reduces the cost of transportation and overall cost of production.

[0026] Referring now to FIG.2A and FIG.2B depicting SEM (Scanning Electron Microscope) images of purified graphite flakes. Different layers of graphite can be noticed. Each graphite flake comprises a plurality of near two-dimensional graphite layers called "graphene". Also noticeable is the absence of impurities on the graphite surface, which is indicative of graphite being free of impurities. [0027] Image FIG.2B shows of a single purified graphite flake. A plurality of graphene layers free of impurities is noticeable. A plurality of small and thin graphite flakes can be seen around a large graphite flake.

[0028] Referring now to FIG.3 showing Raman spectra of purified graphite. Raman spectra was collected by measuring bulk material of purified graphite. Raman analysis is used to identify graphite structure, level of crystallinity and extent of defects present in flakes. G peak is universal for all types of carbon based materials. The most characteristic peaks for graphite-like materials are D and 2D. D peak represents an extent of defects present in the graphitic structure. The lower the D peak's intensity the purer the material. It can be seen that D peak's intensity is lower comparing to other peaks, which means graphite has fewer defects. On the other hand, 2D peak's intensity is significantly higher and prominent, which means that graphite has crystalline and ordered structure. A 2D shoulder can be seen in the spectra, which corresponds to a standard multilayered graphitic structure.

[0029] Referring now to FIG.4 showing XRD (X-ray diffraction) pattern of purified graphite, which is comparable to the standard graphitic structure. Two main types of the graphitic structure are present in the spectra: (a) hexagonal (alpha) phase corresponding to the high intensity peak in the 2Θ range 25-30; and (b) rhombohedral (beta) phase corresponding to the peak in the 2Θ range 54-58. It is worth mentioning that the hexagonal structure is the most predominant.

[0030] Referring now to FIG.5, FTIR spectra of purified graphite is shown. FTIR analysis was performed in order to identify gangue materials and other impurities chemically or physically attached to the graphitic structure. It can be seen from the spectra that impurities are attached to the graphite surface, either physically or chemically. A prominent CO2 absorption peak can be seen, which is most likely of the atmospheric nature.

[0031] Elemental analysis of purified graphite was performed using quantitative XRF (X ray fluorescence spectroscopy) technique. The analysis showed that the concentration of carbon in purified graphite flakes was about 99.2%. The 0.7% oxygen content was detected, but this value is likely to be inaccurate. Chloride and potassium, most likely results of water contamination, were also detected.

[0032] TABLE 1 :

[0033] The description of the present embodiment has been presented for purposes of illustration, but is not intended to be exhaustive or to limit the invention to the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art.

[0034] Those of ordinary skill in the art will appreciate that the elements depicted herein may vary depending on the implementation. The depicted examples are not meant to imply architectural limitations with respect to the present invention.

[0035] Herein above, or in the following claims, the term "comprises" is synonymous with "includes." The use of terminology such as "X comprises A, B and C" is not intended to imply that A, B and C are necessarily the only components or most important components of X.

[0036] Unless clearly and explicitly stated, the claims that follow are not intended to imply any particular sequence of actions. The inclusion of labels, such as a), b), c) or 1), 2), 3) etc., for portions of the claims does not, by itself, imply any particular sequence, but rather is merely to facilitate reference to the portions.

[0037] To reiterate, the embodiments were chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention. Various other embodiments having various modifications may be suited to a particular use contemplated, but may be within the scope of the present invention