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1. WO2020109861 - NOUVEAU PROCÉDÉ DE PRODUCTION DE SABLE CÉRAMIQUE LÉGER SYNTHÉTIQUE ET SES UTILISATIONS

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

DESCRIPTION

TITLE: A NOVEL METHOD OF PRODUCING SYNTHETIC LIGHTWEIGHT CERAMIC SAND AND USES THEREOF.

TECHNICAL FIELD OF INVENTION:

[0001] The present invention relates to a method of fabricating lightweight ceramic sand. The present invention particularly relates to a novel method of manufacturing sintered synthetic lightweight ceramic sand particulates directly from moist bauxite residue cake and fly ash as a secondary raw material. The said synthetic lightweight ceramic sand can be used as a building material. The said synthetic sand can also be used as a lightweight sand in hydraulic fracking for shale gas recovery. The novel feature of the invention is to manufacture low cost lightweight sand at high throughput to compete against the fast depleting natural sand and frat sand.

BACKGROUND ART:

[0002] Environmental compliance requirements cost alumina refineries 5-10% of alumina production cost for the sustainable disposal of bauxite residue.

Bauxite residue is produced from the Bayer process in converting bauxite ore into alumina. Currently, about 125 million tonnes of bauxite residue are produced worldwide. On average less than 3% of the bauxite residue produced is utilized, while most of the remaining 97% is dumped into mud ponds (lagoons), increasing the threat to the local environment. Bauxite residue presents a huge problem as it takes up large land areas which can neither be built on nor farmed - even when dry. An adequate storage and disposal solution for bauxite residue is very costly. As additional environmental legislation and industrial restrictions develop, the costs for adequate storage and disposal solutions continue to increase.

[0003] Fly ash is a by-product obtained by burning coal in coal fired power stations. Currently, about 1 ,100 million tonnes of fly ash is produced worldwide. On average about 55% of the fly ash produced is utilized, while most of the remaining 45% is dumped into ash ponds (lagoons) and dry stacking, increasing the threat to the local environment. While trying to minimize the environmental impact by production of fly ash as wastage, various uses of fly ash have been contemplated to both aid in fly ash disposal and to obtain some viable utility and economic return from the same.

[0004] The global demand for good quality sand in construction and other industries is applying increasing pressure on the dwindling natural sand sources. Annual production and consumption of sand outstrips nature's ability to generate sand by a factor of two. Particulates like sand are a high-volume consumption building material and an essential component of the construction industry. Currently, 40 billion tonnes of sand consumed worldwide of which 30 billion tonnes are used in the concrete and mortars production. The rapid urbanization puts growing pressure for supply from natural sand deposits in mostly ecologically fragile environments. Natural sand takes millions of years to form and is fast depleting. The extreme high consumption of sand has endangered coastal lines and 30 islands disappearance in the south east Asia.

[0005] There is an urgent need to address the issue from disposal of bauxite residue and fly ash. At the same time we are facing tremendous scarcity of natural sand due to heavy demand in ever growing construction activities which has forced research and development to find a suitable substitute.

[0006] One of the desirable is bauxite residue cake to convert it into ceramic sand as replacements for natural sand, manufactured sand, fine aggregates and lightweight fine aggregates to produce concrete, mortars, plasters, bricks, blocks and tiles. The other desirable bauxite residue cake is to convert it into intermediate strength lightweight sand as a replacement of frac-sand in hydraulic fracking to improve gas recovery. Frac sand is used in hydraulic fracking to hold fissures or cracks open so that petroleum from the shale can flow up to the surface.

[0007] The reasons favoring this approach are: (1 ) bauxite residue constitutes between 50-95 wt% and fly ash between 50-5 wt% of the total synthetic particulates weight (2) the natural resources (like sand and fine aggregates) is fast depleting (3) demand for ecological and green products is continuing to increase and (4) addressing the need of sustainable management of natural resources and circular economy.

[0008] Based on the fact that major component in the present invention is waste by-products, i.e, bauxite residue and fly ash, the raw material are inexpensive making the man made ceramic sand competitive and thus helps alleviate a waste disposal problem. Therefore, successful and economical manufacture of particulates from mixture of bauxite residue cake and fly ash will not only reduce the impact of bauxite residue and fly ash disposals on the environment but also provide a great benefit to the economy.

[0009] The present invention involves fabricating lightweight ceramic sand from a mixture of industrial wastes. The said fabricating process is a novel process for manufacturing synthetic lightweight ceramic sand. Substitution of natural sand with lightweight ceramic sand produced from two different industrial wastes i.e., bauxite residue and fly ash, supports protection of these habitats where natural sand is sourced.

[0010] In CN 101575503A, another attempt to use red mud as starting material for the production of propellants is described. Herein, red mud in a quantity between 1 -20 wt% is used in combination with other waste components like ceramic roller waste material or fly ash.

[0011] Tian, X. et al describe in CN 101085914 A and in "The exploration of making acid proof fracturing propellants using red mud" (JOURNAL OF HAZARDOUS MATERIALS, ELSEVIER, AMSTERDAM, NL, vol. 160, no. 2-3, 30 December 2008 (2008-12-30), pages 589-593) the making of propellants using red mud. Beside red mud, which is present in a quantity between 20-60%, refractory waste is used in order to increase the aluminium content of the resulting product. Furthermore, other essential additives like kaolin and barium carbonate or calcium fluoride are used in order to obtain the required properties of the resulting propellants.

[0012] In CN103396784A, attempt has been made to produce low-density and high-strength proppant prepared from mixture of red mud (40-70wt%), fly ash (0-30wt%), bauxite (5-30wt%) and auxiliary additives (1 -15wt%). The purpose of using bauxite and auxiliary additives is to achieve high strength proppant with the minimum closing pressure of 7,500 psi (52MPa). Herein, in order to achieve homogenous mixing red mud is oven dried prior to mixing with other ingredients and the final mixture are grind to 325 mesh fine before pelletization. Drying red mud is not only practically difficult but also costlier making it commercially unviable.

[0013] In CN101575503A, attempt has been made to produce high-strength proppant for coarse oil prepared from mixture of red mud (1 -20wt%), fly ash (0-20wt%), ceramic roller waste (60-85wt%), manganese oxide or barium carbonate (0-5wt%), dolomite (5-10wt%) and ceramic clay (5-10wt%). Herein, in order to achieve homogenous mixing red mud is oven dried prior to mixing with other ingredients and the final mixture are grind to fine powder before pelletization. Though the author claims the preparation method is simple and feasible, however, the practically difficult to emulate in industrial scale specially to find ceramic rollers with consistent chemical composition, making it impractical method.

[0014] In CN103304253A, attempt has been made to produce porous ceramic from red mud, fly ash and pore forming agent. The porous ceramic comprises 40-70wt% of red mud, 5-40wt% of coal ash, 10-30wt% of a pore-forming agent, 1 -5wt% of an additive, and water which is 10-20% of the total weight of the materials. Again, for uniformly mixing the process involves drying red mud and re-adding water. The mixture then formed a shape, dried and roasted to prepare the porous ceramic material. The resulting ceramic material has high porosity with high bending resistance and open pore structure.

[0015] One of the closest invention is CN105294142B. Here the author made attempt to produce lightweight aggregates from mixture of red mud, fly ash, gangue, silica fume, alkaline agent, nitration agent, carbonaceous pore former and granulating binder. Again, for uniformly mixing of all ingredients red mud must be dried, prior to mixing, blending and granulation. Furthermore, the invention involves usage of complex formulation involving expensive ingredients. It is a costlier, complex and impractical industrial/commercial approach making it commercially unviable.

[0016] Huifen, Y. et al describe in the article,“Utilization of Red Mud for the Preparation of Lightweight Aggregates” describes method to produce lightweight aggregates using red mud. Besides red mud other essential raw materials were glass waste and bentonite. Herein, to achieve homogenous mixing red mud is dried prior to mixing with other ingredients and the final mixture are finely grind before pelletization.

[0017] None of the above said prior arts mentions about the semi-lightweight sand particulates or lightweight sand particulates being produced which is a key feature of the present invention.

[0018] The present invention overcomes the above problems through one step manufacturing process which involves dry spraying of moist bauxite residue cake eliminating the need of drying of bauxite residue cake. Drying moist bauxite residue cake is not only complex but also makes finished products often unviable. It is a no surprise that despite hundreds of publications and patents there is not a single commercial technology which practically offers a solution to bauxite residue utilization.

[0019] The lightweight sand produced in the present invention offers the best alternative to natural sand, manufactured sand, lightweight fine aggregates and frac sand.

OBJECT OF THE INVENTION

[0020] The key objective of the invention is to provide a novel, simple and economical method of engineered well-defined ceramic lightweight sand from combination of different industrial wastes.

[0021] Another objective of the invention is to provide an alternative way of substituting natural sand, manufactured sand (also known as crushed stones), light fine aggregates to produce concrete, plasters, mortars, renders and roof tiles.

[0022] Yet another objective of the invention is to provide an alternative way of substituting frac-sand to recover shale gas.

[0023] Still another objective of the present invention is to manufacture the said product using mixture of moist bauxite residue cake and fly ash which are an undesirable by-product and/or wastage.

[0024] Other objective of the present invention is to manufacture size graded fine particulates at high throughput and at lowest manufacturing cost without the need of drying residue bauxite cake.

[0025] Other objective of the present invention is to manufacture lightweight ceramic sand.

SUMMARY OF THE INVENTION

[0026] In one aspect, the present invention discloses a novel, simple and economic process for manufacturing lightweight ceramic sand.

[0027] In another aspect, the aforementioned product is produced from industrial wastes, wherein the major raw material is moist bauxite residue cake and fly ash.

[0028] In yet another aspect, the present invention relates to fabrication of fine particulates at high throughput and at very low manufacturing cost to compete against the fast depleting natural sand including crushed stones and lightweight fine aggregates produced from expanded clay, expanded glass and volcanic activities.

[0029] In still another aspect, the present invention provides a novel method of manufacturing lightweight fine particulates comprising the steps of:-

1. dry spraying of fly ash into moist bauxite residue cake while rotor and pan both are rotating;

2. formation of granules using high intensity shear-mixer;

3. fine particulates with sand graded size gradation with sub-round shapes are produced;

4. particulates are dried using fluidized bed drying process;

5. particulates of desired size gradation, shapes and strength are sintered at high temperature (1 ,015-1 ,275°C).

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of the present invention and together with the description serve to explain the principle of the invention. In the drawings,

[0031] Figure 1 illustrates the schematic process flow diagram to fabricate sintered fine particulates from moist bauxite residue cake and fly ash in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] The present invention may be understood more readily by reference to the following detailed description of the invention taken in connection with the accompanying drawing figures, which forms a part of this disclosure. It is to be understood that this invention is not limited to the specific devices, methods, conditions or parameters described and/or shown herein and that the terminology used herein is for the example only and is not intended to be limiting of the claimed invention. Also, as used in the specification including the appended claims, the singular forms‘a’,‘an’, and‘the’ include the plural, and references to a particular numerical value includes at least that particular value unless the content clearly directs otherwise. Ranges may be expressed herein as from‘about’ or‘approximately’ another particular value when such a range is expressed another embodiment. Also, it will be understood that unless otherwise indicated, dimensions and material characteristics stated herein are by way of example rather than limitation, and are for better understanding of sample embodiment of suitable utility, and variations outside of the stated

values may also be within the scope of the invention depending upon the particular application.

[0033] Embodiments will now be described in detail with reference to the accompanying drawings. To avoid unnecessarily obscuring the present disclosure, well-known features may not be described or substantially the same elements may not be redundantly described, for example. This is for ease of understanding.

[0034] The drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure and are in no way intended to limit the scope of the present disclosure as set forth in the appended claims.

[0035] In order to achieve a better understanding of the nature of the present invention a preferred embodiment of a method of fabricating lightweight ceramic sand will now be explained.

[0036] In one embodiment, the present invention discloses a novel process of the present invention involves dry spray of fly ash into moist bauxite residue cake. The said process allows mixing of moist bauxite residue cake in the range of 50-95 wt% and fly ash in the range of 50-5 wt%. Granules are formed using highly intensity shear-mixer and dried between 150-300 Deg C. Dried granules are sintered at high temperature in the range of about 1 ,015-1 ,275°C. The resultant product conforms size gradation as per harmonized DIN 13139 (sand for mortars) and DIN 12620 (fine aggregates for concrete). Simultaneously, the product also conform DIN 13055 (lightweight aggregates for concrete and mortars). Interestingly, the product also conforms minimum crush strength (2,000 psi) as per crush stress guideline ISO 13503-2 for proppant sand.

[0037] In another embodiment, the aforementioned method of manufacturing lightweight ceramic sand comprises the steps as follows:

(a) dry spraying of fly ash into moist bauxite residue cake to form granules;

(b) drying said granules to obtain dried granules

(c) high temperature sintering of said dried granules thereby obtaining said lightweight ceramic sand.

[0038] In another embodiment, the aforementioned method utilises moist bauxite residue cake is preferably between 50-95 wt% and fly ash between 50-5 wt%. Further, bentonite may be added to the fly ash or to the moist bauxite residue cake, before forming granules. In addition, the moist bauxite residue cake may range between 50-95 wt%, fly ash 45-5 wt% and bentonite between

5-0%.

[0039] In another embodiment, the aforementioned method may further include the addition of fine silica to the fly ash or to the moist bauxite residue cake, before forming granules. The aforementioned moist bauxite residue cake may range between 50-95 wt%, fly ash between 40-5 wt% and fine silica between 10-0 wt%.

[0040] In another embodiment, the aforementioned method comprises a drying step wherein said drying is fluidized bed drying between 150-300°C.

[0041] In another embodiment, the aforementioned method may further involve a step of high temperature sintering wherein the temperature may range between 1 ,015-1 ,275°C.

[0042] In another embodiment, the aforementioned method involves light weight ceramic wherein the size of said lightweight ceramic sand may range between bit not limited to 0.075 mm to 3 mm. Further, the size of said lightweight ceramic sand conforms to size gradation as per harmonized DIN 13139 (sand for plaster). Furthermore, the size of said lightweight ceramic sand conforms to size gradation as per harmonised DIN 12620 (fine aggregates for concrete). In addition, the size of said lightweight ceramic sand conforms to lightweight aggregates definition as per harmonized DIN 13055:2016.

[0043] In another embodiment, the bulk density of said lightweight ceramic sand is between but not limited to 1 ,010 kg/m3 to 1 ,180 kg/m3. Further, said lightweight ceramic sand had crush strength between but not limited to 10-40 MPa for mesh 20/40. In addition, lightweight ceramic sand had crush strength preferably between 25-35 MPa for mesh 20/40.

EXPERIMENTAL DESCRIPTION

[0044] The below experimental details are provided to illustrate the working of the invention, and it should not be construed to limit the scope of the invention in any way.

[0045] Bauxite residue samples were supplied by Rio Tinto and Alteo. Fly ash samples were supplied by Vattenfall. Before dry spray process bauxite residue mixed with water in 30:70 solid-to-liquid ratio. Dewatering of slurry carried out using filter press resulting moist bauxite residue cake having water content between 25-35 wt%. The resultant cake then transferred into high intensity shear mixture. Dry fly ash sprayed into the moveable cake while both rotor and pan are rotating.

[0046] The ratio of the said combination for moist bauxite residue cake 50-95 wt%, for fly ash is 50-5 wt%, for fine silica 10-0 wt% and for bentonite is 5-0 wt%. The mixture improves green body strength. The formulations are prepared as indicated in Table 1 .

Table 1


[0047] Bauxite residue cake disposed into the high intensity shear-mixer. Fly ash, bentonite, and/or fine silica added to the cake both rotor and pan are rotating. The blending and mixing carried out for up to 60 seconds to ensure homogeneous mixing. If the mixture is too dried due to high fly ash content, then water up to 20 wt% added to the mixture. This addition of water is done under rotating condition of both rotor and pan. The rotation is carried out for 3-6 minutes. During the rotation procedure plurality of granules/spheres is formed. The granules thus obtained are herein referred to as sand precursor.

[0048] The moistened sand precursors are then dried using fluidized bed dryer. The residence time of fine particulates in the dryer depends upon several factors such as dryer’s length, drying temperature, drying duration and air flow. For the experiment temperature of the dryer used in the range of about 150-300°C and air feed between 750-1 ,500 m3/h and drying duration 4-8 minutes.

[0049] Dried sand precursors which has moisture between 1-5 wt% are fired in rotary kiln. The residence time of sand precursors in the kiln depends on several factors such as kiln length, temperature of the kiln which is in the range of about 1 ,015-1 ,275°C, chemical composition, particulate size, throughput and temperature of sand precursors. The size of lightweight sand particles produced are typically between 0.075 mm to 3 mm. The bulk density of these lightweight sand particulates is between 1 ,010 kg/m3 to 1 ,180 kg/m3.