METHOD FOR REUSING WHITE SILICA AND GRAY SILICA AS A FILTRATION AID IN INDUSTRIAL EFFLUENT TREATMENT SYSTEMS

Description

1 / 17 METHOD FOR REUSING WHITE SILICA AND GRAY SILICA AS A FILTRATION AID IN INDUSTRIAL EFFLUENT TREATMENT SYSTEMS FIELD OF APPLICATION

[001] The present invention applies to the field of waste management. More precisely, the invention proposes a method for the reuse of white silica and gray silica waste. The waste has properties and characteristics similar to those of the inputs used as a filtration aid in the wastewater treatment process. Thus, the method seeks to replace perlite and diatomite with white silica or gray silica in the industrial wastewater treatment process, also forming an aspect directly associated with the circular economy of materials. FUNDAMENTALS OF THE INVENTION

[002] Silica is commonly used for the preservation of electronic equipment, finished chemical products, and for stabilization in the storage of sensitive products. However, after its use, silica is discarded without being applied to reuse processes.

[003] During the coin production process, for example, it was observed that the current generation of silica waste occurs mainly in the Coins and Medals Department of the Brazilian Mint, where the silica is used to preserve the raw material for coin production. After use, the material is disposed of in a sanitary landfill duly licensed by the competent Environmental Agency.

[004] The material generated, called silica waste, can be divided into two categories: silica waste Petition 870240108734, dated 12 / 19 / 2024, page 9 / 33 2 / 17 white and gray silica residue, the details of each material being presented below.

[005] White silica can also be found under the synonyms: anhydrous synthetic silicon dioxide; amorphous synthetic silica and silicon dioxide. It is an inert material that is extremely efficient, simple to use, non-toxic and low cost, recommended for the protection of various products, objects and materials.

[006] Grey silica is a clay mineral, belonging to a family of clays with similar properties. This clay mineral can be calcic or sodic and has a very peculiar physical characteristic, as it expands several times its volume when in contact with water.

[007] The average annual quantity generated by the Brazilian Mint has the following behavior: white silica - 2200 kg and gray silica - 600 kg.

[008] Given this scenario, the need arose to reuse these residues. Thus, the inventors, in search of a reuse process, found that the properties of these silicas have characteristics similar to two inputs used in the treatment of industrial effluents: perlite and diatomite.

[009] These inputs are used as filtration aids during the filtration process of effluents generated by manufacturing processes, and the characteristics of these inputs are presented below.

[0010] Diatomite is a porous clay formed by the accumulation of seaweed skeletons containing 81-93% silica SiO2, with significant amounts of alumina, Al2O3, and iron oxide, Fe2O3. Petition 870240108734, dated 12 / 19 / 2024, page 10 / 33 3 / 17

[0011] Perlite originates from expanded volcanic rock and consists basically of a mineral from the silica group, thus this material has approximately 73.59% silicon oxide (SiO2), 14.88% aluminum oxide (Al2O3) in addition to other components in smaller proportions such as potassium (K), iron (Fe), sodium (Na), etc.

[0012] Given the urgent need to develop solutions related to the circular economy of waste and also the similarity between silica waste and the inputs used in the industrial effluent treatment process, tests were proposed to assess the feasibility of replacing the input with the waste. That is, silica waste (white silica and gray silica) was tested as a filtration aid to replace perlite and diatomite inputs.

[0013] Perlite and diatomite are used in the industrial wastewater treatment process, more specifically in the stage prior to filtration, where this material acts as a filtration aid. The filtration aid has the function of forming a pre-layer in the filters that retains the finest particles, thus reducing the compressibility of the filter cake (filter residue composed of metals in their precipitated form). The annual consumption of these inputs is 2880 kg for perlite and 2630 kg for diatomite.

[0014] Notably, in addition to the direct economic impact, this method has an extremely relevant environmental premise, since a waste product becomes an input within the same production chain, mitigating mineral exploration for new materials, greenhouse gas emissions from the logistics of receiving inputs and disposing of waste. Petition 870240108734, dated 12 / 19 / 2024, page 11 / 33 4 / 17 waste, as well as the reduction of waste sent to landfills.

[0015] The method of the present invention for the reuse of silica waste was based on steps of theoretical study of the materials involved, characterization of the silica waste, grinding of the silica waste, granulometric analysis of the silica waste in comparison to the inputs perlite and diatomite and testing in the laboratory and in an industrial effluent treatment plant.

[0016] Consequently, the result was no change in the concentrations of metals in the effluent, that is, the behavior of silicas as a filtration aid is the same as when perlite and diatomite are used, in addition to improving the filterability of the effluent, resulting in retained material (ink sludge) with less moisture and better mesh detachment during filter opening.

[0017] The method of the present invention also has at its core issues related to environmental sustainability, that is, a sustainable innovation was developed by reusing a waste product (silica residue) as a substitute for production inputs (perlite and diatomite), since the proposal meets sustainable premises considering the economy of natural resources and the reuse of materials. STATE OF THE ART

[0018] Patent document EP3887310B1 addresses the bleaching and / or filtration of oily liquids using amorphous silica combined with two other types of minerals, culminating in a combination of 3 different minerals. This design is compared with the present invention. Petition 870240108734, dated 12 / 19 / 2024, page 12 / 33 5 / 17 differs in the following points:

[0019] The filtration aid material proposed by the present invention is a silica residue, that is, a material that has already been used in another production process and would be disposed of in landfills. In document EP3887310B1 it is understood that the material used for bleaching and / or filtration is a material originating from the commercial market of mineral-based filtration aids, however, the material used in the method of the present invention is a material originating from reuse that would be discarded after its use.

[0020] The present method proposes the filtration of general industrial effluents using only one material, silica residue, as a filtration aid. Document EP3887310B1 uses a consortium of 3 different minerals, including amorphous silica, differing from the present method, which uses only one silica-based filtration aid originating from a recycling process.

[0021] It is important to highlight that the use of mineral-based filtration elements is something that has already been developed. However, the present method proposes the reuse of a material that would be discarded (silica residue) in substitution of perlite and diatomite (filtration aids consolidated in the market), mitigating mineral exploration of new materials, greenhouse gas emissions from logistics (receipt of inputs and disposal of waste), as well as reducing waste sent to landfills, in addition to reducing internal costs with savings in the purchase of inputs (perlite and Petition 870240108734, dated 12 / 19 / 2024, page 13 / 33 6 / 17 diatomite).

[0022] Document EP1609842B1 discusses the process of treating liquid media containing hydrocarbons or petroleum derivatives, where diatomite and other types of silica are used in the preparation of a sorbent for the adsorption of impurities. Once the sorbent to be used is chosen, a binder is added, which can be common mineral or synthetic materials such as clays (kaolinite, bentonite, montmorillonite, attapulgite, smectite, etc.), silica, alumina, alumina hydroxide, alumina trihydroxide, aluminosilicates, cements, etc., forming the adsorbent-catalyst. This adsorbent-catalyst is used for the oxidation process in the treatment of liquid media. This design, in comparison with the present invention, differs in the following points:

[0023] The filtration aid material proposed by the present invention is a silica residue, that is, a material that has already been used in another production process and would be discarded in landfills. In document EP1609842B1 it is understood that the materials used for the treatment of liquid media with hydrocarbons or petroleum derivatives originate from the commercial market of mineral-based filtration aids, however, the material used in the method of the present invention is a recycled material that would be discarded after its use.

[0024] The method of the present invention relates to the filtration of general industrial effluents, using only one material, silica residue, as a filtration aid. Document EP1609842B1 makes use of a consortium of 2 Petition 870240108734, dated 12 / 19 / 2024, page 14 / 33 7 / 17 different minerals, including diatomite, silica, zeolite, among others, for the formation of an adsorbent-catalyst aimed at the oxidation of effluents with hydrocarbons and / or petroleum derivatives. This project differs from the present invention, which uses only a silica-based filtration aid originating from a recycling process.

[0025] In addition to the processes being distinct, in document EP1609842B1 the materials used (minerals, clay and other compounds) form a catalyst with an oxidative chemical function, while in the present method the recycled silicas are used as a filtration aid with a physical function.

[0026] Document JP2016203034A uses silica as an adsorbent, where it is understood that a membrane is formed from silica or other materials for the purpose of adsorbing contaminants. However, the method of the present invention uses silica as a filtration aid, that is, the silica acts in conjunction with the filter mesh creating a containment barrier in order to improve the efficiency of the filters.

[0027] Document US6833075B2 addresses the filtration and / or purification of fluids, water, or other solutions containing microbiological and chemical contaminants. This process involves a composite of materials including carbon, metal phosphates, metal oxides, reduced metals, silicates, metal sulfates, metal carbonates, metal hydroxides, or combinations thereof, in the form of loose particles or fibers, or with material binders. This composite may or may not require a binding agent. Document US6833075B2 differs from the method of the present invention in the following points: Petition 870240108734, dated 12 / 19 / 2024, page 15 / 33 8 / 17

[0028] US patent 6833075B2 utilizes silicon-based compounds (silicates) along with other materials for the composite formation process aimed at filtering and purifying fluids. This composite acts as a filter, which is different in the present method, since the silica residue is used as a filtration aid in the filters, acting in conjunction with the filter mesh to create a containment barrier in order to improve filtration efficiency.

[0029] Thus, it can be concluded that the present invention differs from the prior art documents presented here, since none of them refers to a method for reusing silica, which would otherwise be discarded, in an effluent filtration process. SUMMARY OF THE INVENTION

[0030] The present invention applies to the field of waste management and presents a method involving the replacement of perlite and diatomite with white silica or gray silica as filtration aids in wastewater treatment plants. The method aims to increase filtration efficiency, resulting in less moisture in the retained ink sludge and better detachment of the filter mesh, while maintaining the cleaning frequency of when perlite and diatomite were used. The method supports the circular economy by reusing silica waste, resulting in economic gains and reducing the need for new materials, greenhouse gas emissions from logistics, and waste sent to landfills. BRIEF DESCRIPTION OF THE FIGURES

[0031] The invention may be better understood Petition 870240108734, dated 12 / 19 / 2024, page 16 / 33 9 / 17 through the brief description of the following figures:

[0032] Figure 1 illustrates silicas in different physical forms: The first sample consists of the raw material, i.e., white silica grain in the upper left and granulated gray silica in the upper right; the second sample consists of white silica and gray silica ground to the ideal particle size for use as a filtration aid; and at the bottom are the inputs perlite (left) and diatomite (right);

[0033] Figures 2 and 3 illustrate a rod mill at the Mineral Technology Center - CETEM / UFRJ;

[0034] Figure 4 illustrates funnels with filters, in each of which synthetic effluent with white silica and gray silica was added;

[0035] Figure 5 illustrates beakers with filtered synthetic effluent;

[0036] Figure 6 illustrates funnels with filters, in which the actual effluent with white silica and gray silica was added to each of them;

[0037] Figures 7 and 8 illustrate beakers with actual filtered effluent from Tank 1;

[0038] Figures 9 and 10 illustrate beakers with actual filtered effluent from Tank 2;

[0039] Figure 11 illustrates the table with the results of the chemical analyses of the collected samples. DETAILED DESCRIPTION OF THE INVENTION

[0040] The invention can be better understood through the following detailed description, in accordance with the attached figures.

[0041] Silica residue is generated from Petition 870240108734, dated 12 / 19 / 2024, page 17 / 33 10 / 17 manufacturing processes that use silica for preservation. Usually, these residues are white silica and gray silica and are in the form of grains, with an average diameter of approximately 4 mm.

[0042] For the material to be a substitute for filtration aids in the wastewater treatment process, it must have powder characteristics with a diameter of 0.053 mm to 0.074 mm. Thus, the silica residue is ground until it reaches a diameter of 0.053 mm to 0.074 mm, as illustrated in Figure 1.

[0043] After grinding, the silica residue is mixed with the effluent in a proportion of 2% white silica relative to the effluent volume (e.g., 2.4 g of white silica per 120 ml of effluent) or 1% gray silica relative to the effluent volume (e.g., 1.2 g of gray silica per 120 ml of effluent). The tank where the filter aid is added, in this case, white silica or gray silica, has an agitation system to disperse the filter aid in the effluent.

[0044] After mixing, the effluent with silica passes through a filter, preferably a filter press. At this stage, all suspended material is retained in the mesh, as the silica forms a pre-layer in the filter, allowing for greater particle retention and resulting in greater efficiency in the formation of the retained compound, known as paint cake or paint sludge.

[0045] After passing through the filter, the filtered effluent is obtained, with characteristics similar to the effluent filtered by the traditional route with filtration aids. Petition 870240108734, dated 12 / 19 / 2024, page 18 / 33 11 / 17 TESTS AND RESULTS

[0046] The silica waste used was generated in the Coins and Medals Department - DEMOM of the Brazilian Mint - CMB.

[0047] To make the tests feasible, it was necessary to grind the silica residue in partnership with the Federal University of Rio de Janeiro - UFRJ through the Mineral Technology Center - CETEM. In the CETEM laboratory, a 10 kg capacity rod mill was used, as shown in Figures 2 and 3. The transformation of silicas into the ideal particle size for use as a filtration aid can be done using any equipment that can grind the material to the standard particle size range.

[0048] The laboratory test was carried out at SELAB in the chemical laboratory of the Brazilian Mint. The test simulated the filtration process using silica residues (white and gray) in synthetic effluent and in real effluent extracted from the industrial wastewater treatment plant.

[0049] Below are detailed all the materials used during the laboratory tests: - 25 mm filter; - 150 ml beaker; - Funnel; - Precision Scale; Glass rod; Deionized water; Barium chloride; - Anhydrous Sodium Sulfate; White silica; - Gray silica. Petition 870240108734, dated 12 / 19 / 2024, page 19 / 33 12 / 17

[0050] The tests carried out aimed to reproduce the filtration process as it occurs in the wastewater treatment process at the treatment plant. Thus, 4 funnels were prepared (numbered 1 to 4, as shown in Figure 4) with 4 filters, and 120 ml of synthetic effluent and real effluent with white silica or gray silica was added to each one, in order to use these materials as a filtration aid.

[0051] Test with synthetic effluent in the laboratory:

[0052] Funnel 1 — without filtration aid

[0053] Funnel 2 - 1.2 g of white silica

[0054] Funnel 3 - 1.2 g of gray silica

[0055] Funnel 4 - 2.4 g of white silica

[0056] It was observed in this first test, as Figures 4 and 5 show that the silicas (white and gray) used as filtration aids have particle retention properties, with filtration being more effective when 2.4g or 2% of the synthetic effluent volume (120 ml) is used for white silica, and for gray silica, 1% or 1.2g is sufficient for satisfactory filtration. Laboratory effluent test:

[0057] Filtration tests with real effluent (Figures 6 to 10) were performed using effluents from two distinct processes, i.e., originating from two locations where filtration occurs at the industrial effluent treatment plant of the Brazilian Mint. We will adopt the tank nomenclature to differentiate the effluent origins, Tank 1 and Tank 2.

[0058] Test with Effluent Tank 1 Petition 870240108734, dated 12 / 19 / 2024, page 20 / 33 13 / 17

[0059] Funnel 1 - without filtration aid

[0060] Funnel 2 - 1.2 g of white silica

[0061] Funnel 3 - 2.4 g of white silica

[0062] Funnel 4 - 1.2 g of gray silica

[0063] Figure 8 shows 5 beakers with actual effluent filtered in Tank 1. In beaker 1, no filtration aid was used, therefore, the result is a The filtrate was quite yellowish. In beaker 2, 1.2 g of white silica was used, and an improvement in color was observed compared to beaker 1. In beaker 3, with 2.4 g of white silica, the color of the filtrate was not very different from beaker 2 (with 1.2 g of white silica). In beaker 4, with 1.2 g of gray silica, a considerable reduction in color was observed compared to beakers 1, 2, and 3. Beaker 5 was used to compare the laboratory tests with the actual effluent treatment process; that is, this filtrate (beaker 5) was extracted from the Wastewater Treatment Plant after the industrial effluent filtration process.

[0064] Thus, through visual analysis of the results, it is concluded that both white silica and gray silica have the property of acting as a filtration aid, and that for this specific effluent (Tank 1), gray silica has greater efficiency.

[0065] Test with Effluent Tank 2:

[0066] Funnel 1 - without filtration aid

[0067] Funnel 2 - 1.2 g of white silica

[0068] Funnel 3 - 2.4 g of white silica

[0069] Funnel 4 - 1.2 g of grey silica

[0070] Funnel 5 - 2.4 g of grey silica

[0071] The result of this test in Tank 2, according Petition 870240108734, dated 12 / 19 / 2024, page 21 / 33 14 / 17 Figures 9 and 10 showed that white silica (beaker 2 - 1.2g and beaker 3 - 2.4g) and gray silica (beaker 4 - 1.2g and beaker 5 - 2.4g) aided in effluent filtration, obtaining a clearer filtrate compared to beaker 1 without filtration aid. However, for the effluent from Tank 2, white silica showed better effectiveness. Practical Test - Wastewater Treatment Plant:

[0072] Full-scale tests were conducted at the Wastewater Treatment Plant. The test / process steps and their respective peculiarities are detailed below:

[0073] Tank 1 / Tank 2 - Tank 1 has a volume of 5000 liters and Tank 2 has a capacity of 4000 liters. In this stage, which precedes filtration, the effluent is already fully prepared with the ideal physicochemical characteristics: adjusted pH (between 9.5 and 10.5) and particles agglomerated with polyelectrolyte. It is at this stage that the filtration aid is added to the effluent.

[0074] In the test, 4.5 kg of white silica was used in Tank 2 with 4000 liters of effluent and 4.5 kg of gray silica for Tank 1 with 5000 liters of effluent, replacing the perlite and diatomite inputs, respectively. After the addition of the filtration aid, the tank is agitated so that the material mixes with the effluent and then filtration begins.

[0075] Filtration - This is the process by which the effluent passes through the filter press and all suspended material is retained in the mesh. It is at this stage that the filtration aid plays its role, forming a pre-layer in the filter, allowing for greater retention of particles and Petition 870240108734, dated 12 / 19 / 2024, page 22 / 33 15 / 17 resulting in greater efficiency in the formation of the retained compound, internally referred to as paint cake or paint sludge.

[0076] Sample Collection - After the effluent passed through the filter press, samples were collected for laboratory analysis, where the parameters copper, chromium, aluminum, iron, zinc, silver, cobalt, manganese, nickel, lead, and tin were analyzed in the internal laboratory of the Brazilian Mint.

[0077] The table in Figure 11 shows the results of the chemical analyses of the samples collected on the day of the practical test (using white silica or gray silica as a filtration aid) compared with other results from the process operating using the standard filtration aids, perlite and diatomite. Analysis of the results:

[0078] As shown in the table in Figure 11 Analytical Results, the use of white silica or gray silica did not alter the concentrations of metals in the effluent, that is, the behavior of silicas as a filtration aid is the same as when perlite and diatomite are used.

[0079] It is important to highlight that, for the copper parameter in Tank 2, the analytical result showed a lower concentration than when compared to analyses using perlite as a filtration aid. Another positive factor in relation to the practical tests performed is that, due to the improvement in the effluent's filterability, the ink sludge generated in the filters (retained material) showed lower moisture content and better mesh detachment, also contributing positively. Petition 870240108734, dated 12 / 19 / 2024, p. 23 / 33 16 / 17 for the filter opening stage, and the subsequent cleaning, obtaining the same frequency of opening and cleaning as when using perlite and diatomite inputs.

[0080] The fact that the retained material had lower moisture content is a substantial benefit to the process, since the residue generated when using traditional perlite and diatomite inputs has high moisture content, requiring water removal before final disposal, which could take 3 to 5 days.

[0081] Therefore, it can be concluded that the present invention, with the proposal to reuse white silica and gray silica waste as a substitute for perlite and diatomite inputs, is a viable alternative for implementation in the wastewater treatment process, considering the results presented in this report.

[0082] Table 1 presents the financial result obtained by replacing the inputs perlite and diatomite with white silica or gray silica. Table 1 - Financial result Using current silica generation with current capacity Material Cost / Kg Quantity Annual (kg) Annual Cost Perlite 7.95 2880.0 R$22,896.00 Diatomite 17.28 2630.0 R$45,446.40 Total 5510.0 R$68,342.40

[0083] The Brazilian Mint consumes 2880kg of perlite and 2630kg of diatomite annually. This means that by replacing these inputs with the residue, the Brazilian Mint achieves annual savings of R$ 68,342.40, considering the lowest prices offered by suppliers. REFERENCES Petition 870240108734, dated 12 / 19 / 2024, page 24 / 33 17 / 17

[0084] LUZ, Adão; OLIVEIRA, Cristiano. 10. Bentonite. Industrial Rocks and Minerals. Cetem, 2005. Available at:<http: / / mineralis.cetem.gov.br / bitstream / cetem / 1046 / 1 / 10.Ar gila-BENTONITA%20ok.pdf> .

[0085] PERFILTRA. Perlite. Available at: <http: / / www.perfiltra.com / por / pages / display / perlita> .

[0086] PERFILTRA. DIATOMITE. Available at: <http: / / www.perfiltra.com / por / pages / display / diatomita> .

[0087] ROSSETTO, Enéderson; BERALDIN, Rosa, et al. Characterization of bentonite and diatomite clays and their application as adsorbents. Sciello, 2009. Available at:<https: / / www.scielo.br / j / qn / a / Qy5fC4fXdY5xQGsLTJP8Nht / > .

[0088] Severino H. da Silva Filho; Paloma Vinaches; Sibele BC Pergher. STRUCTURAL CHARACTERIZATION OF EXPANDED PERLITE. Available at<https: / / www.uricer.edu.br / site / pdfs / perspectiva / 155_638.pd f> . Petition 870240108734, dated 12 / 19 / 2024, page 25 / 33

Claims

1 / 2 CLAIMS 1. Method for reusing white silica as a filtration aid CHARACTERIZED by comprising the following steps: grinding the silica residue; mixing the white silica residue with the effluent, wherein the white silica residue and the effluent are mixed in a proportion of 2% white silica in relation to the volume of the effluent; and filtering the effluent with silica, wherein the mixed material in suspension is retained in the mesh, forming a pre-layer in the filter, so as to obtain the filtered effluent.

2. Method for reusing grey silica as a filtration aid CHARACTERIZED by comprising the following steps: grinding the grey silica residue; mixing the grey silica residue with the effluent, wherein the silica residue and the effluent are mixed in a proportion of 1% grey silica relative to the volume of the effluent; and filtering the effluent with silica, wherein the mixed material in suspension is retained in the mesh, forming a pre-layer in the filter, in order to obtain the filtered effluent.

3. Method, according to claim 1 or 2, CHARACTERIZED in that the silica residue is ground until it reaches a diameter of 0.053 mm to 0.074 mm.

4. Method, according to claim 1 or 2, CHARACTERIZED in that the silica residue is mixed with the effluent through an agitation system to disperse the silica residue in the effluent. Petition 870240108734, dated 12 / 19 / 2024, page 26 / 33 2 / 2 5. Method, according to claim 1 or 2, CHARACTERIZED in that the effluent containing silica is filtered through a filter press. Petition 870240108734, dated 12 / 19 / 2024, p. 27 / 33

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