Method for preparing bauxite samples

Abstract

The present invention relates to a method for preparing mineral bauxite samples for the analysis of reactive silica and available alumina parameters by fluorescence, using an X-ray device for samples in a liquid medium. The method can be applied in a laboratory setting or on-site at a mining or metallurgical industry location.

Description

METHOD OF PREPARING BAUXITE SAMPLES FIELD OF THE INVENTION

[0001] The present invention relates to the field of mineral research and analysis, particularly bauxite, by determining its chemical or physical properties. It is more specifically focused on the preparation of specimens and samples for research through automated analysis. In this context, the present invention relates to a method for preparing bauxite samples from the mining process for analysis of reactive silica and usable alumina by X-ray fluorescence in a liquid medium in a faster, more portable, and more efficient manner, which can be applied in the laboratory or on-site at the mining or metallurgical industry site. BACKGROUND OF THE INVENTION

[0002] In the bauxite market, it is estimated that global reserves of this mineral represent approximately 32 billion tons, of which 72.5% are distributed among five countries: 7.4 billion tons in Guinea; 5.8 billion in Vietnam; 5.3 billion in Australia; 2.7 billion in Brazil; and 2 billion in Jamaica. Thus, Brazil currently holds the fourth largest bauxite reserve in the world, accounting for approximately 8.5% of total global reserves [1].

[0003] In Brazil, the main bauxite reserves are concentrated mainly in Pará, Minas Gerais and Goiás. These three territories concentrate reserves that total, respectively, approximately 2.23 billion tons, approximately 342 million tons and approximately 76.2 million tons. Together, the reserves of these three states represent around 98.9% of all national bauxite deposits [2].

[0004] According to the Brazilian Aluminum Association [3], bauxite mining is carried out following three basic steps. First, vegetation and organic soil are removed in a planned manner. Then, The surface layers of the soil (clays and laterites) are removed. Finally, the ore is processed through crushing to reduce the size of the rock, washing with water to reduce the silica content, and drying. To be considered economically viable, bauxite must have a minimum aluminum oxide (AI2O3) content of 30%, which is assessed using various analytical techniques.

[0005] The quality control of bauxite used in the metallurgical industry is basically carried out by two chemical parameters, namely: (i) usable alumina (AVA12OS) and (ii) reactive silica (RxSiO2). Both parameters are, in general, determined according to procedures that simulate conventional Bayer digestion on a laboratory scale [4, 5].

[0006] In gibbsitic bauxites, for example, usable alumina and reactive silica are generally and respectively associated with the gibbsite and kaolinite mineral contents.

[0007] The deleterious mineral kaolinite is undesirable in the bauxite beneficiation process, since, considering conventional Bayer digestion conditions, it reacts with sodium hydroxide (NaOH - leaching agent) to form Bayer sodalite. This reaction results in irreversible losses of NaOH, considerably increasing the operational cost of beneficiation and requiring control of this mineral in the gibbsite purification process [5, 6].

[0008] Bayer sodalite is a sodium aluminosilicate, insoluble under Bayer digestion conditions and therefore discarded together with the other insoluble gangue minerals in the red mud (insoluble solid residue from the Bayer process).

[0009] Developed in 1880 by Karl Bayer, the Bayer process is the primary route for obtaining metallurgical alumina from bauxite. The process is based on the high solubility of aluminum hydroxides in soda. caustic under moderate temperatures.

[0010] The ore is necessarily reduced in size by crushing, followed by grinding in beneficiation plants. The digestion process is carried out under moderate temperature and pressure, and the resulting insoluble residue is separated by decantation. The sodium aluminate-rich liquor is cooled, followed by the induced precipitation of the gibbsite phase through the addition of gibbsite seeds (A1(OH)3). The resulting gibbsite is then separated into two fractions: the coarse fraction, which is calcined to form the alumina used in aluminum production, and the fine fraction, which is reused in the process to induce the nucleation of new gibbsite crystals.

[0011] The highly alkaline, insoluble residue generated in this process (red mud) is composed primarily of iron oxides and hydroxides (goethite, hematite), titanium oxides (anatase and rutile), and sodalite. The mud is washed to recover rich liquor and then discarded.

[0012] When the kaolinite concentration in the ore is high, this means that caustic soda (NaOH) consumption will increase, since, under typical Bayer process conditions, the reaction of kaolinite with NaOH forms sodalite. Furthermore, critical parameters during alumina extraction include the content and morphology of aluminum minerals, as well as mineral impurities with different solubilities in NaOH.

[0013] Equations 1 and 2 below present, respectively, the kaolinite dissolution and sodalite formation reactions. Initially, kaolinite is leached by caustic soda and dissolved in the liquor, a process that is undesirable for obtaining metallurgical alumina. The dissolved silica then precipitates as sodium aluminum silicate, Bayer sodalite, also known as desicalization product (DSP) 3Al2Si2O5(OH)4+ 18NaOH 6Na2SiO3+ 6NaAl(OH)4+ 3H2O (1) 6Na2SiO3+ 6NaAl(OH)4+ Na2X Na6[Al6Si6O24].Na2X + 12NaOH + 6H2O (2) where X can be selected from the group comprising anions of sulfates, chlorides, aluminates, among others [6].

[0014] In general, gibbsitic bauxites are the most attractive for alumina production using the Bayer process because they consume less energy. The higher the gibbsite concentration, the less energy is required for digestion [7, 8].

[0015] In this sense, the purity of the final product, caustic soda losses in the digestion process and energy consumption are variables that govern the production and costs of the bauxite beneficiation process, these variables being governed by two fundamental parameters, namely, the usable alumina content (AVA12O3) and the reactive silica content (RxSiO2).

[0016] Such parameters are of fundamental importance for the quality control of alumina refining, both to estimate the percentage of alumina and to control the leaching agent consumed in the process [5, 9].

[0017] In this context, the Alcan method is one of the oldest methods used to measure such parameters. The methodology is based on a laboratory-scale simulation of the Bayer digestion process, in which usable alumina (AVA12O3) is determined by titration (titrimetry) from the rich liquor. The method is a wet process and is widely known as the EDTA method.

[0018] Reactive silica (RxSiO2) is determined from the acidic dissolution of sodalite and subsequently measured in atomic absorption spectrometry (AAS), atomic emission spectrometry (AES), or UV-VIS equipment and in some cases by gravimetry.

[0019] The method for determining RxSiO2 is mainly composed of two stages: (i) firstly, the dissolution of sodalite in an acidic medium from the insoluble residue derived from alkaline digestion using caustic soda in order to transfer the analyte from the solid phase to the liquid phase; and (ii) in a second step, the RxSiCh measurement is performed, now transferred to the liquid phase, using one of the analysis techniques described previously, with the sodalite dissolution step in an acidic medium being considered a sample preparation step for the RxSiC measurement.

[0020] Considering that the measurement of reactive silica is an indirect measurement of kaolinite, and that kaolinite is converted into sodalite during the digestion process, it is necessary to dissolve the sodalite-type desicalization product (DSP) present in the red mud for this determination.

[0021] The standard method uses 30 mL of HCl, followed by homogenization, and a reaction time of approximately 30 minutes. After this established period, an aliquot is removed to determine the Si content. This method has already been studied for its effectiveness in fully opening the phase and dissolution time by Paz (2017a) [5], confirming that the amount of acid used and the reaction time are certainly sufficient for opening the reactive silica phase, in which all the sodalite is decomposed in a period of approximately 3 minutes. More specifically, "opening the reactive silica phase" consists of depositing a sample on a hot plate to be solubilized in an appropriate reagent (in this case, HCl). The sample (solid) will be solubilized in the presence of the reagent (liquid), forming a liquid solution containing the decomposed solid phase, which is understood as the concept for phase opening.

[0022] When it comes to the dissolution reaction of sodalite in an acidic medium, inorganic acids are commonly used to dissolve sodalite, whether in the form of scale or DSP. Hydrochloric (HC1) and sulfuric (H2SO4) acids are the most commonly used in industry for the dissolution of the phase in question. HCl is a strong, non-oxidizing acid that easily promotes the dissolution of sodalite (equation 3), and is used in the Alcan method for the dissolution of DSP [5, 10]. Na6[AlSiO4]62NaOH + 26HC1 8NaCl + 6A1C13+ 6H2SiO3+ 8H2O (3)

[0023] For complete dissolution, hydrochloric acid, which is monoprotic, requires 26 moles of acid for each mole of Bayer sodalite. The products formed in the dissociation of sodalite with HCl are sodium and aluminum chlorides, silicic acid, and water. It is worth noting that the formation of silicic acid in the reaction is expected, and this substance is characterized by instability in aqueous media, which can lead to the formation of less soluble species such as silica gel or colloidal silica.

[0024] Desicalization products (DSPs) or Bayer sodalite are formed in the Bayer process due to the dissolution of soluble clays (of which kaolinite is the most common) that react with sodium aluminate in the rich liquor to form less soluble crystalline aluminosilicates. These tend to be zeolitic minerals of the Bayer liquor sodalite type, containing cavities with different anions bound to them

[0011] .

[0025] Considering the qualitative importance of determining usable alumina (AVA12O3) and reactive silica (RxSiO2) in bauxite mineral, and considering the context of new instrumental analytical techniques, X-ray fluorescence spectrometry (XRF) has made significant progress. Thus, the advancement and dissemination of XRF analysis techniques can be considered due to their ability to determine several chemical elements simultaneously, generally quickly, with minimal sample preparation, without destroying the matrix, and at low operating costs.

[0026] Thus, X-ray fluorescence (XRF) has proven to be a highly versatile technique, which can be applied to multiple samples, including samples in solid and liquid states, without require exhaustive treatment for their preparation, and in a portable manner using compact equipment.

[0027] Furthermore, XRF analyses offer advantages over conventional atomic emission and absorption spectrometric techniques, particularly in the analysis of liquid samples. Although it does not achieve detection limits comparable to those achieved by atomic emission and absorption techniques, XRF presents low analysis costs, low reagent and glassware consumption, in general, and generates little or no waste, which also makes it ideal and viable for implementing routine analysis methodologies [12, 13].

[0028] However, atomic absorption and emission methods are still the most widely used in the analysis of bauxite samples. It is important to note that, unlike the precision of usable alumina (AVA12OS) measurements using the titrimetric method, the accuracy and quality of RxSiO2 measurements vary greatly depending on the analytical technique used, which can pose a problem for quality control.

[0029] Document CN101718707 (A), for example, refers to a method for determining reactive SiO2 in gibbsitic bauxite, which participates in the alumina dissolution reaction, providing data support for optimizing the alumina production process and simultaneously complementing the traditional test method. According to the document, bauxite is dissolved in an alkaline solution so that the silicon mineral kaolinite reacts with the alkaline solution to form hydrated sodium aluminosilicate and precipitates. In the sample preparation process, bauxite samples with a particle size of less than 150 μm are weighed and placed in a reactor, and then an alkaline NaO solution (180 g / L) is added. The temperature is maintained at 140-280°C (oil bath) for 30-120 min, and a filtrate and a filter residue are obtained, after which the filter residue is dried to obtain a weight of at least 0.25g of red mud.

[0030] Subsequently, 0.25g of red mud is weighed into a 250mL beaker, 100mL of dilute hydrochloric acid (0.1mol / L) is added, stirred immediately (to avoid agglomeration), and the system is sealed with a watch glass. The system is then heated in a water bath at a constant temperature of 100°C for 15 minutes, stirring every 5 minutes. The contents are transferred to a 250mL volumetric flask, diluted to the meniscus with hydrochloric acid and stirred, followed by filtration and drying. A 5.00 mL - 10.00 mL aliquot of the above filtrate is pipetted into a 100 mL volumetric flask, diluted to 70 mL with hydrochloric acid (0.1 mol / L), 5 mL of ammonium molybdate solution (100 g / L) are added and shaken. The solution is allowed to stand for color development, and 5 mL of tartaric acid solution (300 g / L), 5 mL of ascorbic acid solution (20 g / L) are added, and diluted to the mark with hydrochloric acid (0.1 mol / L).Finally, the amount of acid-soluble SiO2 is measured in a spectrophotometer. Therefore, the percentage (B) of SiO2 in the red mud is analyzed by a molybdenum blue light fluorometric method.

[0031] Document CN104111207 (A) discloses a method for detecting the silica fume content in bauxite. The method comprises the steps of: processing a bauxite sample using a microwave digestion method; placing the processed bauxite sample in a beaker; filtering; adding residual slag containing substances insoluble in hydrochloric acid for immersion and combining with a previous filtrate; evaporating the mixture on an electric hotplate; adding perchloric acid for desiccation; filtering again; and burning at a high temperature. Subsequently, the mass fraction of silica fume in the bauxite is estimated by indirect calculation relative to the mass variation of the sample, without the use of any electron emission / absorption or X-ray fluorescence analysis instrument.

[0032] Document CN106769300 (A) refers to a method for determining usable (effective) alumina and reactive silica in gibbsitic bauxite. To this end, the method includes in its procedure the weighing of 0.5000 g of sample in the microwave digestion apparatus with the addition of 10.0 mL of 90 g / L NaOH solution. After stirring, the digestion process is applied at 145 °C for 30 min.

[0033] Once the solution was digested, the contents were transferred to a 250 mL beaker containing 100.0 mL of 0.6 mol / L HCl, where it was heated for 5 min to gently boil and dissolve the hydrated sodium aluminosilicate. After cooling, the solution was then transferred to a 250 mL volumetric flask and diluted with distilled water to constant volume, followed by homogenization. After clarification, 10 mL of the solution was added to a 100 mL volumetric flask along with 10 mL of 6 mol / L HCl, brought to volume with distilled water, and then homogenized again. The supernatant was then analyzed using inductively coupled plasma atomic emission spectrometry to simultaneously determine the usable (effective) alumina and reactive silica content.

[0034] Therefore, the need for a methodology for preparing bauxite samples for analysis of reactive silica and usable alumina by X-ray fluorescence in liquid medium remains in the state of the art, which is capable of replacing conventional analyses by atomic absorption and emission in a faster, more portable and efficient manner, and which can be applied both in the laboratory and on-site at the mining site or metallurgical industry. SUMMARY OF THE INVENTION

[0035] The objective of the present invention is to provide a method for preparing the Bayer liquor that makes up the bauxite samples originating from the mining process for optimized analysis of reactive silica and alumina. usable by X-ray fluorescence in liquid medium in a faster, more portable and efficient way.

[0036] This specific methodology promotes proper aliquot opening and preparation through a series of optimized steps that include sample weighing, digestion in an alkaline medium, decantation and separation of the desired phases, and analysis of the aliquot in a portable X-ray device to read the desired parameters. Therefore, this methodology enables the use of benchtop X-ray fluorescence equipment, which prior to the development of this technology could not be used for bauxite ore, thus improving the quality analysis of bauxite ore under evaluation in various locations and points of the production process, beyond the laboratory. BRIEF DESCRIPTION OF THE FIGURES

[0037] Figure 1 shows a simplified flowchart of the methodology that is the object of the present invention as applied under preferred conditions.

[0038] Figure 2 shows a comparative graph for the usable alumina ranges (95% confidence interval (CI) for the mean) between titrimetric and liquid-based X-ray fluorescence analyses using the benchtop equipment (Epsilon 4). Individual standard deviations were used to calculate the ranges.

[0039] Figure 3 shows a comparative graph for the reactive silica ranges (95% confidence interval (CI) for the mean) between analyses by calculation from usable alumina (AA) and by X-ray fluorescence in liquid medium using the benchtop equipment (Epsilon 4). Individual standard deviations were used to calculate the ranges. DETAILED DESCRIPTION OF THE INVENTION

[0040] In view of the need for adequate and accurate analysis of the chemical-qualitative parameters of the mineral bauxite intended for metallurgy and aluminum production, the present invention has as its first objective to provide a method for preparing bauxite samples (100) composed of Bayer liquor for optimized analysis of reactive silica and usable alumina by X-ray fluorescence in a liquid medium (200). Such method (100) comprises the steps of: weighing the bauxite sample (100); addition of alkali (120); digestion of the sample (130); transfer of the sample to a container (140); addition of concentrated acid solution and flocculant (150a, 150b); addition of H2O and homogenization (160); decantation of the system (170); withdrawal of a liquid aliquot of the sample supernatant (180); and adding said liquid aliquot to the containers of an X-ray equipment (190) suitable for analysis by X-ray fluorescence (XRF) in a liquid medium.

[0041] The bauxite samples (A) are received previously pulverized so as to obtain a homogeneous granulometry, in which the average particle size varies from about 100 pm to about 400 pm, preferably about 150 pm to 270 pm, more preferably about 200 pm. The samples are then separated into individual aliquots and weighed. In a particular laboratory application of the invention, the weighing (110) is carried out on an analytical balance in weights ranging from about 2.5 g to about 5.0 g, preferably between about 3.0 g and about 4.0 g, more preferably about 3.25 g.

[0042] Each sample, after weighing, is then transferred to a conventional digestion pump, usually a Parr type pump. In then, an alkali (120) is added to the digestion bomb containing the pulverized bauxite sample using a dispenser. The alkali is a strong base generally selected from the group comprising at least one alkali metal hydroxide, preferably sodium hydroxide (NaOH) and potassium hydroxide (KOH), more preferably sodium hydroxide (NaOH). Also in this sense, considering the laboratory application modality of the invention, the volume of alkali added varies between about 10 mL and about 50 mL, preferably about 15 mL and about 30 mL, more preferably about 25 mL.

[0043] After the addition of alkali (120) is complete, the digestion pump is hermetically sealed and the system is homogenized. The digestion pumps are then placed in a rotating digestion block where they remain at an operating temperature of about 100°C to about 200°C, preferably about 120°C to about 160°C, more preferably about 150°C; for a digestion period of about 20 min to about 40 min, preferably about 30 min. After digestion (130), the sampled digestion pumps are removed from the digestion block and cooled in running water to room temperature.

[0044] After cooling, all bombs are placed in a suitable polyethylene container, taking care not to turn them over. In this way, the samples from each bomb are subsequently transferred (140) to an intermediate container. Again, when considering a laboratory application embodiment of the invention, the intermediate container is a glass item, such as a volumetric flask of about 100 mL to about 500 mL, preferably about 150 mL to about 250 mL, more preferably about 200 mL, properly labeled.

[0045] A concentrated acid solution (150a) selected from concentrated hydrochloric acid (HC1) and / or concentrated sulfuric acid (H2SO4), preferably hydrochloric acid (HC1) is added to the container. concentrated. The volume of concentrated acid in one embodiment of the invention ranges from about 15 mL to about 40 mL, preferably about 30 mL, to which a flocculant (150b) is additionally introduced, preferably an anionic organic flocculant for analytical use. In one embodiment of the invention, the flocculant is added in a volume of about 5 mL to about 15 mL, preferably 10 mL, and then about 15 minutes are waited for the system to cool down and then deionized / distilled water (160) is added to the system. In one embodiment of the invention, the amount of water added corresponds to the volume and calibration of the intermediate container, ranging up to a volume of about 100 mL to about 500 mL, preferably about 150 mL to about 250 mL, more preferably about 200 mL. Subsequently, the contents of the container are homogenized (160) at least three (3) times until a single phase is obtained.

[0046] The container is then placed under refrigeration at temperatures ranging from about 15°C to about 25°C, more preferably about 21°C for decantation (170) for a period of about 12 h to about 32 h, more preferably about 24 h until obtaining the two distinct phases (Bayer liquor and red mud). Then, an aliquot of the sample supernatant (180) is removed. In a laboratory application embodiment of the invention, the aliquot is removed, for example, with a volumetric pipette of about 5 mL to about 15 mL, preferably about 10 mL.

[0047] Finally, the sample is deposited in the cup of the appropriate X-ray apparatus (190) to perform the analysis by X-ray fluorescence (XRF) in liquid medium (200). EXAMPLE 1

[0048] In an exemplary process of the method of preparing bauxite samples on a laboratory scale, 3.2500 g (± 0.0004 g) of the pulverized bauxite sample were weighed on an analytical balance with the aid of boat and steel spatula. The weighed sample was then transferred to a digestion pump. The digestion pump containing the pulverized bauxite sample was then added with 25 mL of 10% (m / v) sodium hydroxide (NaOH) solution using a dispenser.

[0049] After completing the NaOH addition, the digestion pump was hermetically sealed with a ratchet wrench, and the system was homogenized. The digestion pumps were then placed in the rotating digestion block with a 1 / 4" (19.05 mm) wrench and held at 150°C for 30 minutes. After digestion, the digestion pumps were removed from the digestion block with a 1 / 4" (19.05 mm) wrench, a stainless steel PARR pump hook, and Brastorno pump removal pliers. The digestion pumps and sample were then cooled in running water to room temperature.

[0050] The digestion pumps were opened using a ratchet wrench, and each pump was placed in a 600 mL polyethylene beaker, taking care not to tip it over. The samples from each pump were then transferred to a properly labeled 200 mL volumetric flask using a spray bottle filled with distilled water.

[0051] 30 mL of hydrochloric acid (HCl) PA (37% m / v) and 10 mL of Separan® AP-30 flocculant from Dow Chemical Canada Limited were added to the volumetric flask. The system was allowed to cool for 15 minutes and then the volumetric flask was filled and adjusted with deionized / distilled water to a volume of 200 mL. Subsequently, the contents of the flask were homogenized three (3) times until a single phase was obtained.

[0052] The flask was then refrigerated at 21 °C for decantation for 24 h until two distinct phases (Bayer liquor and red mud) were obtained. Next, 10 mL of the sample supernatant was pipetted and deposited in a sample holder with Thim-Film mylar. (3.6 micron - 2.5" (63.5 mm) diameter). Finally, the sample holder containing the aliquot was placed in the cup of the Epsilon 4 benchtop X-ray apparatus to perform X-ray fluorescence (XRF) analysis.

[0053] Therefore, the present invention has the following main advantages: (1) An efficient and low-cost methodology for opening the reactive silica phase and, consequently, for adequate bauxite sample preparation.

[0054] (2) To have a fast, simplified, robust, reproducible, easily scalable, controllable analysis method that does not require the use of complex and expensive equipment, since it requires portable equipment, thus enabling the application of a route that makes it possible to use benchtop X-ray fluorescence equipment, which before the development of this technology could not be used for bauxite ore.

[0055] Typically, sample preparation according to the methodology and subsequent analysis do not require complex laboratory facilities and can be applied in situ at the production plant or mining site. Figures 2 and 3 show graphs comparing the accuracy of the analytical method described here with the conventional analysis method, which is already widespread and widely known in the state of the art.

[0056] After laboratory investigations applying a range of combinations and protocols, the inventors attributed the improved performance of the methodology to specific parameters, such as volumetric flask volume, decantation time, and Bayer liquor readings on a benchtop X-ray fluorescence equipment. In this regard, the inventors observed that reducing the volumetric flask volume from 500 mE to 200 mL resulted in an optimal / synergistic increase in analyte concentration combined with a reduction in solution volume within the decantation time. of about 12 h to about 32 h, more preferably about 24 h, in which the readings of usable alumina and reactive silica by X-ray fluorescence in liquid medium were more accurate.

[0057] As can be seen from the data and details provided, the present invention advantageously provides a method of preparing bauxite samples that can be surprisingly used in the analysis of reactive silica and usable alumina by X-ray fluorescence in liquid media, being capable of providing a fast, accurate and portable analysis.

[0058] When introducing the elements of this disclosure or the preferred embodiment(s) thereof, the articles "a," "an," and "said" are intended to indicate that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than those listed. While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any invention or what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features described in this specification, in the context of separate embodiments, may also be implemented in combination within a single embodiment.Conversely, multiple features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as operating in certain combinations, and even initially claimed as such, one or more features of a claimed combination may in some cases be removed from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination. REFERENCES

[0059] [1] BRAY, EL Bauxite and Alumina. In: US GEOLOGICAL SURVEY. Mineral Commodity Summaries. [Denver]: USGS, Jan. 2022.

[0060] [2] MONTEIRO, C. C; SILVA, JPA da. Aluminum. In: NATIONAL MINING AGENCY (ANM). Brazilian Mineral Summary 2018. Brasília, DF: ANM, 2021.

[0061] [3] BRAZILIAN ALUMINUM ASSOCIATION (ABAL). Alumínio: cadeia primária. São Paulo,

[2019] .

[0062] [4] OSTAP, S. Control of silica in the Bayer process used for alumina production. Can. Metall., Q. 25: 101-106, 1986.

[0063] [5] PAZ, S.P.A., ANGÉLICA, R.S., KAHN, H. Optimization of the reactive silica quantification method applied to Paragominas-type gibbsitic bauxites. International Journal of Mineral Processing, 162:48-57, 2017a.

[0064] [6] SMITH, P. The processing of high silica bauxites — Review of existing and potential processes. Hydrometallurgy, Perth, 98:162- 167, 2009.

[0065] [7] AUTHIER-MARTIN, M. et al. The Mineralogy of Bauxite for Producing Smelter-Grade Alumina. Mineralogy Overview, Quebec, 5 (8): 36-40, 2001.

[0066] [8] CONSTANTINO, VRL et al. Preparation of aluminum compounds from bauxite: considerations on some aspects involved in a didactic experiment. Química Nova, São Paulo, 25(3): 490-498, 2002.

[0067] [9] PAZ, SPA Development and optimization of quality control methods and beneficiation process for Paragominas-type gibbsitic bauxites. PhD Thesis, Mineral Engineering Course, Polytechnic School of the University of São Paulo, São Paulo, 204 p, 2016.

[0068]

[0010] CHESTER, H. A study of scale formed in the Bayer process. PhD Thesis, Philosophy, Loughborough University, Loughborough, 86 p, 2003.

[0069]

[0011] RADOMIROVIC, T. et al. Crystallization of sodalite particles under Bayer-type conditions. Hydrometallurgy, 50(137): 84-91, 2013.

[0070]

[0012] SANTOS, ES et al. X-ray fluorescence spectrometry in the determination of chemical species. Encyclopedia Biosfera, Goiânia, 9(17):3413-3432, 2013.

[0071]

[0013] KALLITHRAKAS-KONTOS, N. et al. A robust X-rayfluorescence technique for multielemental analysis of solid samples. Environmental monitoring and assessment, 188 (2): 188-120, 2016.

Claims

CLAIMS 1. Method of preparing bauxite samples for analysis of usable alumina (AVA12OS) and reactive silica (RxSiO2), characterized by the fact that it comprises the steps of: weighing the bauxite sample; addition of alkali; digestion of the sample; transfer of the sample to a container; addition of concentrated acid solution and flocculant; addition of H2O and homogenization; decantation of the system; removal of a liquid aliquot from the sample supernatant; and addition of said liquid aliquot to the containers of an X-ray equipment suitable for analysis by X-ray fluorescence (XRF) in liquid medium.

2. Method according to claim 1, characterized in that the bauxite is previously pulverized and has particle sizes ranging from about 100 pm to about 400 pm, preferably about 150 pm to 270 pm, more preferably about 200 pm.

3. Method according to claim 1 or 2, characterized in that the sample weighs between about 2.5 g and about 5.0 g, preferably between about 3.0 g and about 4.0 g, more preferably about 3.25 g.

4. Method according to any one of claims 1 to 3, characterized in that the alkali is a strong base selected from the group comprising at least one alkali metal hydroxide, preferably sodium hydroxide (NaOH) and potassium hydroxide (KOH), more preferably sodium hydroxide (NaOH).

5. Method according to claim 1 or 4, characterized in that the volume of alkali added ranges from about 10 mL to about 50 mL, preferably from about 15 mL to about 30 mL, more preferably about 25 mL.

6. Method according to any one of claims 1 to 5, characterized in that the digestion of the sample is carried out in a rotary digestion pump.

7. The method of claim 6, wherein the digester pump operates at a temperature of about 100°C to about 200°C, preferably about 120°C to about 160°C, more preferably about 150°C; for a digestion period of about 20 min to about 40 min, preferably about 30 min.

8. The method of claim 1, wherein the container is a volumetric flask with a volume ranging from about 100 mL to about 500 mL, preferably about 150 mL to about 250 mL, more preferably about 200 mL.

9. Method according to claim 1, characterized in that the added concentrated acid solution is selected from concentrated hydrochloric acid (HC1) and / or concentrated sulfuric acid (H2SO4), preferably concentrated hydrochloric acid (HC1).

10. Method according to claim 9, characterized in that the volume of concentrated acid ranges from about 15 mL to about 40 mL, preferably about 30 mL.

11. Method according to claim 1, characterized in that the flocculant is an anionic organic flocculant.

12. Method according to claim 11, characterized in that the flocculant is added in a volume of about 5 mL to about 15 mL, preferably 10 mL.

13. Method according to claim 1, characterized in that the decantation occurs for a period of about 12 h to about 32 h, more preferably about 24 h under refrigeration at temperatures ranging from about 15°C to about 25°C, more preferably about 21°C.

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