Method for decontaminating acid mine water and installation for implementing same

Abstract

The present invention relates to a continuous vacuum evaporation method that reproduces a natural geological process of mineral salt formation in an industrial process. The process is suitable for the decontamination and economic valorisation of any type of acid mine water. Before starting the process, the water must be conditioned and homogenised to improve the efficiency and profitability of the process. The process yields two products: 1) decontaminated water and 2) a residue rich in critical raw materials and sulphates. The invention relates to a sequential process in which a pump feeds acid mine water to a vacuum evaporation machine. Of the total incoming mine water, 95% is evaporated, while the remaining 5%, which is concentrated in solids, passes to a vacuum crystalliser, where the solid fraction and decontaminated water are obtained.

Description

[0001] PROCEDURE FOR THE DECONTAMINATION OF ACID MINE WATERS AND INSTALLATION FOR ITS IMPLEMENTATION.

[0002] OBJECT OF THE INVENTION

[0003] The present invention relates to a procedure for the decontamination of acid mine waters, which is applicable in the field of decontamination of waters contaminated by different anthropogenic activities such as mining, industry, agriculture, etc.

[0004] The object of the invention is to provide a decontamination method that provides the following technical advantages:

[0005] • To offer a procedure that does not require reagents in the process of decontaminating acid mine waters.

[0006] • The solid residue obtained is rich in critical raw materials and sulfates which are economically valued as they are separated into marketable products and by-products with different uses in the industrial sector.

[0007] • It allows the recovery of contaminated bodies of water (rivers, lakes, aquifers, reservoirs) and their ecosystems.

[0008] The invention also relates to the installation for implementing the procedure.

[0009] BACKGROUND OF THE INVENTION The methods for decontaminating and treating acid mine waters are classified into two groups: active and passive.

[0010] Active wastewater treatment requires the continuous addition of chemicals and / or energy, oxidation by physical methods (e.g., cascade aeration) or chemical methods (e.g., H₂O₂), alkalinity generation, generally through the addition of chemicals (typically CaCO₃, Ca(OH)₂, NaOH, etc.), and precipitation of contaminants by various means. These methods are costly, especially when dealing with large volumes of water. Furthermore, they require monitoring and maintenance of the aeration and mixing systems, as well as proper storage of the resulting sludge containing metals, sulfates, and organic matter. The volume of sludge generated varies between 5% and 20% of the treated water volume.

[0011] In short, these types of processes offer the following advantages:

[0012] • Treatment of large flows.

[0013] • Longer lifespan.

[0014] • They are robust structures. Their size depends on the volume or flow rate to be treated.

[0015] On the contrary, they present the following disadvantages:

[0016] • Energy consumption.

[0017] • It generates a waste product that must be stored in a hazardous waste storage facility.

[0018] • Waste generated from the treatment of acid mine water is not recovered.

[0019] They consume reagents.

[0020] They require maintenance. Meanwhile, passive treatment methods are based on the construction of systems designed to enhance natural chemical and biological processes, so they do not require the continuous addition of chemical agents or energy, characteristic of active treatment methods, and are much cheaper and easier to maintain. Their main limitation or disadvantage is that they can only be used for small flow rates of less than 5 l / s.

[0021] Both methods currently available on the market generate hazardous waste that must be managed, which involves additional costs and environmental risks.

[0022] EXPLANATION OF THE INVENTION

[0023] The procedure of the present invention refers to an “active” procedure that, unlike existing procedures or methods of this type to date, does not require reagents in the process of decontaminating acid mine waters. The resulting solid residue is rich in critical raw materials and sulfates, which are economically valued as they are separated into marketable products and by-products with different uses in the industrial sector. In addition, it allows the recovery of contaminated water bodies (rivers, lakes, aquifers, reservoirs) and their ecosystems.

[0024] To this end, and more specifically, the invention process starts from a previous stage of conditioning and homogenizing the water, in order to improve its efficiency.

[0025] In the next stage, the homogenized water undergoes a continuous vacuum evaporation process. This process, when carried out at 40°C, has been shown to be 22% more energy efficient than existing systems on the market.

[0026] Unlike conventional technologies used for the decontamination of acid mine water, which rely on chemical reagents and generate hazardous waste with no economic value, the present invention offers a more efficient and economical solution. In the inventive process, no reagents are used, significantly reducing operating costs and preventing the generation of hazardous waste requiring storage in specialized facilities.

[0027] Instead, the procedure of the invention produces two valuable results: 1) decontaminated water that is condensed and recovered at the outlet of the vacuum evaporator, suitable for various uses, and 2) a residue rich in critical and strategic metals and sulfates, which can be economically valued, and which is subjected to a vacuum crystallization process, a process in which a small proportion of additional decontaminated water is recovered.

[0028] Thus, the process of the invention allows the decontamination of any type of acidic mine water and any contaminated water by vacuum evaporation with temperature ranges between 100 and 40°C, which implies a very significant energy saving.

[0029] This makes the decontamination and economic valorization of acid mine waters economically viable.

[0030] It should be noted that this type of water is not currently used for any purpose. The invention process can be developed in phases depending on the objectives of each specific project, and evaporation can be partial or total.

[0031] This requires an installation involving water pumps, a vacuum evaporation machine, an evaporator and vacuum crystallizers, tanks for contaminated water, decontaminated water and solid waste.

[0032] In addition, a continuous monitoring and control system has been planned where all the sensors are installed, including a sampling tank that allows the control of the physicochemical properties of the contaminated water and the decontaminated water.

[0033] Regarding the electronic interface, the installation has the possibility of jointly controlling the main environmental variables that affect the quality of the process, such as temperature, pH, electrical conductivity, vacuum pressure, etc.

[0034] It also includes an electronic control system with automatic recording: this allows for the continuous accumulation of all data generated by the different sensors at set time intervals. It generates a new file every 24 hours, ensuring data preservation in case of failure. The system is fully automated throughout all phases of vacuum evaporation. This automation reduces working time, improves the quality of results, and provides valuable information for validating various numerical methods for obtaining and estimating parameters. Its versatility allows for the control of a set of parameters that were previously studied and analyzed separately, all within a single test.The information obtained from the various sensors used to monitor the vacuum evaporation process in a decontamination procedure allows for the acquisition of parameters necessary to understand the evolution and changes in the characteristics of acid mine water. Having these parameters also allows for their use in predicting and monitoring the evolution of specific contamination processes occurring in acid mine water, depending on the type of mineral deposit and the metallurgical process employed.

[0035] DESCRIPTION OF THE DRAWINGS

[0036] To complement the description that follows and to aid in a better understanding of the characteristics of the invention, according to a preferred embodiment thereof, a set of drawings is included as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:

[0037] Figure 1 shows a schematic diagram of the installation for the implementation of a procedure for the decontamination and economic valuation of acid mine waters carried out in accordance with the object of the present invention.

[0038] Figure 2 shows, finally, a schematic diagram of the overall process.

[0039] PREFERRED EMBODIMENT OF THE INVENTION

[0040] Figure 2 shows a very schematic and generalized representation of the entire process of the invention, which begins with a watershed (15) affected by acid mine drainage. 100% of the water to be treated (12) is pumped to a vacuum evaporation plant (2). This plant returns approximately 95% of the decontaminated water (17) to the watershed (15), yielding approximately 5% liquid concentrate, which is then sent to a vacuum crystallizer (3) for separation of the raw materials through various processes.

[0041] More specifically, and in accordance with Figure 1, this figure shows an example of an installation for implementing the procedure that is the subject of the invention, capable of treating any type of acidic mine water with continuous vacuum evaporation.

[0042] In this case, it is a decontamination process where the characteristics of the incoming acidic mine water, the outgoing water, and the moisture content of the solid waste rich in critical raw materials are controlled.

[0043] To this end, and more specifically, the installation includes a reservoir, well, dam, lake, river, or aquifer containing the water to be treated (12), in which one or more water booster pumps (1) are installed. This pump is responsible for the continuous supply of water to the vacuum evaporation plant (2), and is made of titanium and is corrosion-resistant.

[0044] The vacuum evaporation plant (2) decontaminates acidic mine water at a temperature of forty degrees Celsius. It produces two products: decontaminated water and a liquid-solid concentrate, where the solid predominates over the liquid. The plant includes means of resisting corrosion and the formation of precipitates on its walls.

[0045] In this plant, the evaporated water, once condensed, is conveyed to a decontaminated water tank (10), while the non-evaporated byproduct or liquid-solid concentrate is conveyed through a second pump (T) to a vacuum crystallizer (3).

[0046] This equipment completes the evaporation of the water contained in the concentrate from the vacuum evaporation plant, yielding two products: decontaminated water and a crystallized or dehydrated solid, depending on the type of acidic mine water used in the process. It is the only crystallizer on the market that operates continuously.

[0047] Thus, in the vacuum crystallizer equipment (3), in which an evaporated water outlet is defined which, after passing through a condenser, communicates with the decontaminated water tank (10), and a waste outlet towards a solid waste tank (11).

[0048] The installation is complemented by an electronic interface or computer (5) to which pH (6), electrical conductivity (8), temperature (7) and redox potential sensors are connected, installed both in the decontaminated water tank (10) and in the tank, reservoir, well, dam, lake, river or aquifer of the water to be treated, computer (5) to which pressure sensors (4) are connected for measuring the vacuum both in the vacuum evaporation plant (2) and in the vacuum crystallizer equipment (3), including a humidity sensor (9) corresponding to the solid waste tank (11).

[0049] More specifically, the pressure sensors (4) monitor the vacuum pressure in the vacuum evaporation plant at a temperature of forty degrees and in the crystallizer. These sensors operate continuously, 24 hours a day, 365 days a year, sending their data to the cloud where it is stored and processed to track the spatiotemporal evolution of the decontamination process.

[0050] The computer (5) includes the electronic interface with the different sensors. The computer program performs the acquisition and storage of the data and displays the results of the measurements from the different sensors in real time, allowing for the correction of any deviations in the decontamination process and the economic valuation of acid mine water.

[0051] The pH sensors (6) monitor the pH of both the acidic incoming mine water and the decontaminated outgoing water in their storage tanks. These sensors operate continuously, 24 hours a day, 365 days a year, sending their data to the cloud where it is stored and processed to track the spatiotemporal evolution of the decontamination process.

[0052] Meanwhile, the temperature sensors (7) monitor the temperature of both the incoming acidic mine water and the decontaminated outgoing water in its storage tank. These sensors operate continuously, 24 hours a day, 365 days a year, sending their data to the cloud where it is stored and processed to track the spatiotemporal evolution of the decontamination process.

[0053] In parallel, the electrical conductivity meter (8) measures the electrical conductivity of the acidic mine water entering the vacuum evaporation chamber and the decontaminated water exiting. These sensors operate continuously, 24 hours a day, 365 days a year, sending their data to the cloud where it is stored and processed to observe the spatiotemporal evolution of the decontamination process.

[0054] In parallel, a volumetric water content meter (9) has been included to measure the volumetric water content in the solid waste. This sensor operates continuously, 24 hours a day, 365 days a year, sending its data to the cloud where it is stored and processed to track the spatiotemporal evolution of the decontamination process.

[0055] As for the decontaminated water tank (10), as previously stated, it stores the decontaminated water and controls the temperature, pH and electrical conductivity, for its subsequent conditioning (13) to the different industrial uses.

[0056] Meanwhile, in the solid waste deposit (11) the waste rich in critical raw materials for its economic valorization is stored and the volumetric content of water is controlled.

[0057] The installation may optionally include a solar concentrator that allows the drying (14) of the residue rich in critical raw materials.

[0058] Similarly, it may include a photovoltaic plant for energy generation: it is used for the generation of energy that powers the evaporation process, as well as a well for supplying the facility with geothermal energy materialized in a system that allows evaporation from geothermal energy through the use of hot water and steam.

[0059] Finally, the installation can also incorporate a muffle furnace for calcining the residue rich in critical raw materials: it allows the calcination of the mineral at temperatures exceeding 1000 degrees Celsius.

[0060] The experimental results demonstrated that the process is capable of continuously measuring vacuum pressure, temperature, physical and chemical properties of the inlet and decontaminated outlet waters, and the moisture content of the concentrate.

Claims

1 a - Procedure for the decontamination of acid mine water, characterized by a continuous process comprising the following operational phases: a) Conditioning and homogenization of the contaminated water to be treated. b) Evaporation of the water using vacuum evaporation equipment. c) Condensation and recovery of the evaporated and decontaminated water. d) Subjection of the byproducts not evaporated in the vacuum evaporation process to a vacuum crystallization process with recovery of evaporated water. e) Drying and separation of the metals and byproducts generated in the crystallization process. 2 a - Procedure for the decontamination of acidic mine waters, according to claim 1 a where the water enters the vacuum evaporator equipment at a temperature between 40 and 100°C. 3 a- Installation for the decontamination of acidic mine waters, characterized in that it includes a reservoir, well, dam, lake, river or aquifer of the waters to be treated, in which one or more pumps (1) are established to propel said waters towards a vacuum evaporation plant (2), in which the evaporated water, once condensed, is conveyed to a decontaminated water tank (10), and where the non-evaporated by-product is conveyed through a second pump (1') to a vacuum crystallizer (3), in which an evaporated water outlet is defined which, after passing through a condenser, communicates with the decontaminated water tank (10), and a solid waste outlet (11). 4 a - Installation for the decontamination of acid mine waters, according to claim 3 a , where the installation includes an electronic interface or computer (5) to which they are connected sensors of pH (6), electrical conductivity (8), temperature (7) and redox potential, installed both in the decontaminated water tank (10) and in the tank, reservoir, well, dam, lake, river or aquifer of the water to be treated, computer (5) to which pressure sensors (4) are connected for measuring the vacuum both in the vacuum evaporation plant (2) and in the vacuum crystallizer equipment (3), including a humidity sensor (9) corresponding to the solid waste tank (11). 5 a - Installation for the decontamination of acid mine waters, according to claim 3 a where the pumps materialize in corrosion-resistant titanium pumps. 6 a - Installation for the decontamination of acid mine waters, according to claim 3 a , where in correspondence with the solid waste outlet (11) a mineral drying system based on solar concentrators is installed. 7 a - Installation for the decontamination of acid mine waters, according to claim 3 a , where in correspondence with the solid waste outlet (11) a geothermal mineral drying system is installed.

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