Reduction of bischofite transport costs

Abstract

The present invention relates to a method for reducing costs associated with the transportation of magnesium chloride hexahydrate (6·H2O·MgCl2), known as bischofite.

Description

[0001] REDUCTION OF TRANSPORTATION COSTS OF BISCHOFITA

[0002] DESCRIPTIVE MEMORANDUM

[0003] Technical field

[0004] The present invention, in general terms, relates to the reduction of the transport cost of magnesium chloride hexahydrate (6 H2O MgCl2), known as Bischofite, which is a derivative of lithium extraction.

[0005] The proposed methodology consists of reducing the weight of Bischofite by heating it to separate its water molecules, thus lowering its transport cost.

[0006] Background

[0007] Magnesium chloride hexahydrate (MgCl2 → 6 H2O), also known as bischofite, is the most widely used dust suppressant and road stabilizer in Chile. This is due to its good performance in dry weather conditions and its low cost, as it is a waste material from the lithium industry.

[0008] Bischofite is a magnesium chloride hexahydrate mineral belonging to the halides and is a concentrated marine salt from the Permian Period. It is an ecologically pure, natural magnesium polyunsaturated mineral with a unique composition. This salt is used as a chemical stabilizer for road surfaces and as a dust control treatment for unpaved roads in low-humidity environments. The moisture content increases with the dosage of Bischofite. Magnesium chloride can be synthesized by reacting magnesium carbonate or magnesium hydroxide with hydrochloric acid and subjecting the resulting salt to successive evaporations. The fundamental property of Bischofite is its hygroscopic nature, meaning it has the ability to absorb and / or retain water from the environment.Therefore, when incorporated into granular materials, roads are able to maintain a moist surface with apparent cohesion, which considerably reduces the amount of particulate material emitted by passing vehicles and increases the road's service level and durability. Unpaved roads experience more accelerated deterioration than paved roads. This is because the fine particles, when mixed with the coarse aggregates and exposed to the environment, lose moisture. Combined with the abrasive action of vehicular traffic, this causes surface disintegration of the material, turning it into dust and leading to defects such as potholes, undulations, and scaling, resulting in a loss of comfort, safety, and durability.

[0009] The primary use of bischofite today is as a dust suppressant and chemical stabilizer for unpaved roads, as it requires less maintenance and repairs than asphalt pavements. It retains moisture in the base, forming a layer that is resistant to the wear and tear of vehicles and heavy machinery. This allows for the passage of heavy vehicles at moderate speeds and extends the lifespan of the road surface.

[0010] Preparing the Bischofite liquid solution is one of the first steps to achieving high-impact results. Bischofite, being a salt, has an optimal dissolution and saturation point with the water it is mixed with; this translates to achieving an average density of 1.25 ton / m³. 3in the solution or brine. Its properties include, among others, binding fine particles and stabilizing the road surface, the ability to absorb moisture from the environment (hygroscopy), the property of dissolving in the absorbed moisture (deliquescence), resistance to evaporation, reducing the water evaporation rate by up to 3 times, lowering the freezing point (-32°C), and, in addition, it is water-soluble.

[0011] Bischofite is produced in the Atacama Salt Flat, so to be used it must be transported for hundreds, even thousands of kilometers.

[0012] Therefore, the biggest limitation of using Bischofite is its high transportation cost when moving it to points far from the place of extraction.

[0013] The proposed methodology involves reducing the weight of Bischofite by heating it to separate its water molecules, obtaining a dehydrated Bischofite powder. This significantly reduces its transport costs and weight, making Bischofite more competitive and allowing it to reach markets where it is not currently present.

[0014] The solution proposed in this patent application consists of heating Bischofite to a level at which the six water molecules (6 H₂O) separate from the Magnesium Chloride (MgCl₂). This loss corresponds to approximately 50% of the weight of Bischofite obtained naturally, according to chemical calculations and measurements carried out in the Materials Laboratory of the Department of Construction Engineering and Management, School of Engineering, Pontifical Catholic University of Chile. An economic evaluation was performed, including the heating costs using a heating drum like those used in asphalt plants.

[0015] The asphalt result considered the cost of Bischofite at the source, the cost of transport per ton, and the cost of heating using data from asphalt plants that have a heating drum.

[0016] The results of the analysis show that for a transport distance of 800 km it is already more economical to dry Bischofite.

[0017] Currently, Bischofite is even used in the Araucanía Region (southern Chile), that is, it travels a distance of more than 2,000 kilometers from the extraction center, yet it is still profitable due to its low production cost.

[0018] Preliminary calculations indicate that if 50,000 tons per year, which are transported on average for 1,500 kilometers, were dried, savings of more than $500,000 per year would be produced.

[0019] One improvement relates to CO2 emissions, considered a greenhouse gas (GHG), which were found to be directly proportional to the weight transported. In other words, by dehydrating the Bischofite, its weight is reduced, and so are CO2 emissions. Specifically, if dehydration reduces the weight to 50% of the total, CO2 emissions will be reduced by the same percentage.

[0020] Furthermore, there is another improvement implicit in the economic benefits, namely fuel savings beyond a certain mileage (considering the diesel used to heat the Bischofite). Since less material needs to be transported, the number of trucks required for this activity will undoubtedly also be reduced. Therefore, using the same example of 50,000 tons dried and transported over 1,500 kilometers, and considering that a cargo truck consumes 35 liters of diesel per 100 kilometers, the annual fuel savings would amount to approximately 875,000 liters.

[0021] Finally, although there is no precise calculation, an improvement is observed in the environmental field, since the use of Bischofite involves the use of waste from the mining industry, generating positive environmental impacts due to the good management of said waste, since its useful life is extended.

[0022] However, obtaining magnesium chloride as dehydrated Bischofite can be observed in the state of the art.

[0023] CN107500319 describes a method for preparing anhydrous magnesium chloride. This document teaches a preparation method comprising the steps of mixing bischofite with ammonium chloride to obtain a dehydrating raw material. The dehydrating raw material is then subjected to primary dehydration at 180-240 °C and secondary dehydration at 250-300 °C to obtain anhydrous magnesium chloride crude product. The anhydrous magnesium chloride crude product is heated to a temperature above 250 °C under a protective atmosphere after the white smoke surrounding the product disappears, and the heat is held for at least 2 hours to obtain anhydrous magnesium chloride. Ammonia gas can be used to replace water molecules in the hydrated magnesium chloride to further facilitate the production of anhydrous magnesium chloride.The use of high temperatures to dehydrate Bischofite is evident, which implies a large energy expenditure.

[0024] CN1429770 describes a method for preparing anhydrous magnesium chloride by dehydrating Bischofite comprising the following steps: (1) dehydrating Bischofite containing water adsorbed onto hydrated magnesium chloride hexahydrate with hot air at 60-100°C as the fluidizing medium; (2) dehydrating Bischofite to magnesium chloride dihydrate through the first stage; (3) dehydrating magnesium chloride dihydrate to anhydrous magnesium chloride through the second stage; (4) after the gas in the previous step (3) is cooled to 50-120°C, it enters the tail gas recovery fluidized bed containing adsorbent to remove moisture; (5) the adsorbent that has absorbed moisture is sent back to the dehydration fluidized bed of the first stage for dehydration to magnesium chloride dihydrate, which can be reused.

[0025] This method involves several steps, which makes the process inefficient.

[0026] The document “Study of Industrial Waste Used as Thermochemical Energy Storage Materials” describes the study by Essen et al., which characterized the dehydration of the hydrated salt MgCl₂·6H₂O for seasonal thermochemical energy storage applications using a TGA-DSC instrument and a fixed-bed reactor. The reversible reaction was successfully carried out. However, due to the high hygroscopicity of this material, a gel-like material formed during hydration, possibly due to melting, which caused a problem with subsequent water absorption. In the present invention, the gelation phenomenon does not occur, as far as has been observed. The dehydrated product is placed in water and dissolves.

[0027] In the invention under study, the temperature used allows for the dehydration of Bischofite in such a way that its water reabsorption properties are not lost. This means that when the Bischofite is rehydrated with water, there are no differences compared to a sample of Bischofite at room temperature (25°C) hydrated with water.

[0028] The dehydrated product is then used in the hydration process, where dried Bischofite and water are used together to allow the complete dilution of the Bischofite into liquid form, thus allowing its application as a dust suppressant.

[0029] In the state of the art, it is not observed that the raw material used is a remnant compound derived from lithium extraction, nor does it teach the rehydration of the compounds at the same time.

[0030] The solution proposed in this patent application is aimed at companies that currently produce Bischofite. Due to the lithium boom, more companies are expected to enter the market in the future. Currently, over 150,000 tons of Bischofite are produced annually.

[0031] The beneficiaries will be the mining companies that exploit Lithium and the consumers, who will be able to obtain this product at a lower cost.

[0032] Currently, this solution does not exist, so it cannot be compared to a direct competitor; therefore, a solution is needed that provides both economic benefits and waste management benefits for the mining industry.

[0033] Summary of the invention

[0034] The present invention relates to the handling of magnesium chloride hexahydrate (6 H2O MgCl2), Bischofite, with the aim of reducing transportation costs and using mining waste to lower the environmental impact produced by the lithium extraction company.

[0035] This invention focuses on dehydrating Bischofite for transport and rehydration at the destination.

[0036] Description of the figures

[0037] Figure 1: Thermogravimetric tests (DSC-TGA) with an air environment.

[0038] Figure 2: Drying of Bischofita at 150°C.

[0039] Figure 3: Preparation of test specimens.

[0040] Figure 4: Results of tests on specimens without Bischofite, with Bischofite at room temperature and Bischofite dehydrated at 100°C and rehydrated.

[0041] Figure 4.a shows the detailed comparison of the Bischofites [at room temperature and dried at 100 o ]

[0042] Figure 5: Depth of application.

[0043] DETAILED DESCRIPTION OF THE INVENTION

[0044] To demonstrate the effect of heating, Thermogravimetric Analysis (DSC-TGA) tests were performed in an air environment. Figure 1 shows that raising the temperature to approximately 250 °C results in a loss of about 50% of the initial weight.

[0045] Similarly, tests were carried out in the conventional oven. Figure 2 shows the drying at 150°C. It can be observed that a mass loss of approximately 50% occurs on the first day of drying.

[0046] Figure 3 shows the solubilized Bischofite and two test specimens used for subsequent tests.

[0047] Figure 4 shows the emission of particulate matter 10 (PM10) over time. It illustrates the behavior of three different samples: a control soil sample without added dust suppressants, bischofite at room temperature as a dust suppressant, and dehydrated bischofite at 100°C applied as a dust suppressant.

[0048] Figure 5 shows a comparison of moisture penetration in ambient Bischofite and Bischofite dried at 100°C. Figure A shows the moisture penetration in the specimen made with Bischofite dried at 100°C. Figure B shows the moisture penetration in the specimen made with ambient Bischofite.

[0049] The process for producing Bischofite is described below:

[0050] Collection of Bischofite from the Atacama Salt Flat as waste material from the lithium industry using heavy collection machinery,

[0051] Reduction of the weight of Bischofite by heating itself to generate the separation of magnesium chloride hexahydrate,

[0052] Heating will separate 6 water molecules from the magnesium chloride. The heating temperature will vary between 80 and 120 °C, since at that temperature Bischofite does not lose its ability to recover its hygroscopic characteristics, that is, it does not lose its absorption capacity, and will allow the total weight to be reduced by 40 to 60%, which implies a decrease in transport costs, since less material is transported.

[0053] The heating should be carried out in a drying drum like those used in asphalt plants, as these allow for the efficient application of heat.

[0054] The dehydrated magnesium chloride will be transported to the destination by truck.

[0055] Dehydrated magnesium chloride must be rehydrated at the application site to return to its initial composition.

[0056] The dehydrated Bischofite (in solid state) will be rehydrated by incorporating it into the water pools that are already prepared on site.

[0057] In a first embodiment, a procedure is described to reduce costs associated with the transport of Bischofite, CHARACTERIZED in that it comprises: a) Providing magnesium chloride hexahydrate (6 H2O MgCl2), Bischofite, b) separating Bischofite from the material from which it comes, c) heating the Bischofite to reduce its weight, d) obtaining dehydrated magnesium chloride from heating the Bischofite, e) transporting the dehydrated magnesium chloride to the destination place, f) rehydrating the magnesium chloride to obtain magnesium chloride hexahydrate (6 H2O MgCl2).

[0058] In one embodiment of the invention, in step a), Bischofite is collected from a salt flat where there is a waste extraction operation of the lithium industry with heavy collection machinery.

[0059] In another embodiment of the invention, in step c), the Bischofite is subjected to a temperature between 80 and 120°C and is carried out in a drying drum.

[0060] In another embodiment of the invention, step c) is carried out until the Bischofite reduces its weight by between 40 and 60%.

[0061] In another embodiment of the invention, step e) is performed in trucks.

[0062] In yet another embodiment of the invention, in step f), the dehydrated Bischofite (in solid state) will be rehydrated by incorporating it into the water pools that are already prepared on site.

[0063] In yet another form of the invention, the use of rehydrated Bischofite is defined as described in the process described above, which serves to reduce the cost of transporting it.

[0064] Experimental design

[0065] The inventors have carried out tests that show that rehydrated Bischofite has a virtually identical behavior to that of Bischofite in its natural state.

[0066] They have also surprisingly discovered that bischofite does not need to be heated to very high temperatures, but rather to around 100-120°C. This can reduce HCl emissions and the energy consumption of the solution, which are the biggest problems encountered in the current state of the art when rehydrating bischofite.

[0067] The following test measured the dust suppressant capacity of applied Bischofite. A comparison was made of particulate matter 10 (PM10) emissions between a control soil (without dust suppressant) and two soils treated with Bischofite. One of these two soils was treated with undehydrated Bischofite (conventional Bischofite), and the other with Bischofite dehydrated at 100°C and subsequently rehydrated.

[0068] Testing procedure

[0069] Bischofite was heated to 100°C to dehydrate it. The percentages of mass loss are shown in Table 1.

[0070] Table 1: Percentage of mass loss per unit of time at 100°C.

[0071] Next, a sample of dehydrated bischofite was taken to obtain magnesium chloride hexahydrate, or rehydrated bischofite. For this purpose, the dehydrated bischofite was dissolved in water. Subsequently, to compare the effectiveness of undehydrated bischofite with that which was dehydrated and then rehydrated, soil samples were prepared from compacted soil. Bischofite was applied to the surface of these samples as a dust suppressant, at an irrigation rate similar to that used in the field. A control soil sample without dust suppressant was also prepared. All samples then underwent controlled surface abrasion using rubber wheels rotating at a known speed via a mechanism. This surface abrasion generated particulate matter, which was measured using a laser sensor in units of particles per cubic centimeter (particles per cubic centimeter) for a particle size of 10 microns (MP10).The test results are presented in Table 2.

[0072] Table 2. Results of particulate matter measurements

[0073] The results in Table 2 indicate that PM10 emissions in the untreated or control soil are considerably higher than those in the soils treated with Bischofite. Furthermore, and most importantly, PM10 emissions from Bischofite dried at 100 °C and rehydrated are similar to those of Bischofite without rehydration.

[0074] The details of the results in Table 2 are reflected in Figure 4, which graphs PM10 emissions over time for: the sample with control soil (blue line), the sample treated with undehydrated Bischofite (orange line), and the sample with Bischofite dried at 100°C and rehydrated (gray line). The results indicate that the effectiveness in dust suppression is practically the same for both Bischofite samples. This suggests that the Bischofite dehydration process does not diminish its ability to suppress dust; in fact, it shows similar performance to conventional Bischofite.

[0075] The method used to test the specimens was as follows:

[0076] 1. Placement of previously prepared test specimen with / without application of dust suppressant.

[0077] 2. Attach the hose for particulate matter measurement at a distance no greater than 3 centimeters. The hose connects to a DustMate device (laser sensor for particulate matter measurement).

[0078] 3. Start of measurement with DustMate equipment.

[0079] 4. After starting the equipment, begin moving the rubber wheels at the desired speed to produce surface wear [2.3 Km / h].

[0080] 5. Average trial duration: 20 minutes.

[0081] The results can be seen in Figure 4, where the behavior of the specimens is observed when Bischofite is used at room temperature and dried at 100°C and rehydrated.

[0082] The absorption capacity of the treated Bischofite was measured at 100°C. Figure 5 clearly shows the difference between the two samples. Comparing the soil penetration capacity reveals that the dehydrated Bischofite has lower penetration than the untreated sample. The data are summarized in Table 3.

[0083] The explanation for this difference in soil penetration lies in the fact that the dehydrated Bischofite was rehydrated with the same amount of water used to prepare the 'standard' Bischofite (undehydrated or at room temperature). Therefore, the brine from the dehydrated and rehydrated Bischofite has a lower total water content than the brine from the 'standard' Bischofite. Consequently, the viscosity of the 'standard' Bischofite brine is lower, facilitating soil penetration. The difference could also be due to gelation, but this was not evident in the experiments with this technology.

[0084] Table 3: Comparison of application depth between Bischofita Ambiente and

[0085] Drying (Results observable in figure 5)

[0086] These tests have led to the following conclusions:

[0087] • Bischofite dried at 100°C has water losses in the range of 35-40% but these water losses do not represent losses in the suppressive action exerted by the dehydrated Bischofite.

[0088] • When comparing soil penetration capacity, it is observed that dehydrated bischofite has lower penetration than untreated bischofite. This is due to viscosity, as dehydrated bischofite has a lower water content than untreated bischofite.

[0089] In view of the foregoing, those skilled in the art will understand that changes can be made to the specific aspects described and still achieve the same or a similar result without departing from the spirit and scope of the invention. Therefore, the specific functional and structural details described herein should not be interpreted as exhaustive. It should be understood that the full description of each reference cited herein is incorporated within the description of this application.

[0090] While this invention has been described in the embodiments indicated above, it might seem obvious that other alternatives, modifications, or variations would yield the same results. However, we have established that the subject matter described in this application is fundamental to the success of the invention described herein. Consequently, the embodiments of the invention are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.

[0091] All patents, patent applications, scientific articles and other public documents that, to the applicant's knowledge, constitute the state of the art, have been duly cited in this application.

Claims

CLAIMS 1. A process for reducing costs associated with the transport of Bischofite, CHARACTERIZED in that it comprises: a) Providing magnesium chloride hexahydrate (6 H2O MgCl2), Bischofite, b) separating Bischofite from the material from which it comes, c) heating the Bischofite to reduce its weight, d) obtaining dehydrated magnesium chloride from heating the Bischofite, e) transporting the dehydrated magnesium chloride to the destination, f) rehydrating the magnesium chloride to obtain magnesium chloride hexahydrate (6 H2O MgCl2).

2. The procedure described in claim 1, CHARACTERIZED in that in step a), the Bischofite is collected from a salt flat where there is a waste extraction operation of the lithium industry with heavy collection machinery.

3. The process described in claim 1, CHARACTERIZED in that in step c), the Bischofite is subjected to a temperature between 80 and 120°C and is carried out in a drying drum.

4. The procedure described in claim 1, CHARACTERIZED in that step c) is carried out until the Bischofite reduces its weight by between 40 and 60%.

5. The procedure described in claim 1, CHARACTERIZED in that step e) is performed on 4-axle trucks.

6. The process described in claim 1, CHARACTERIZED in that in step f), the dehydrated Bischofite (in solid state) will be rehydrated by incorporating it into the water pools that are already prepared on site.

7. Rehydrated Bischofite CHARACTERIZED in that it is obtained according to the procedure described in claim 1.

8. The use of the rehydrated Bischofite described in claim 7, CHARACTERIZED because it serves to reduce the cost of transporting it.

9. The use of the rehydrated Bischofite described in claim 7, CHARACTERIZED in that it serves to reduce CO2 emissions.

Images