A method and a water purification apparatus for purifying acidic wastewater from a mining process, and use of the water purification apparatus

Abstract

A method for purifying acidic wastewater from a mining process, the method comprising pretreating (12) the acidic wastewater to obtain pretreated wastewater (16), providing a water purification apparatus (30) comprising an electrolytic cell (14) comprising a substantially vertical tube connected to a source of electric power (13) and comprising one or more first electrode(s) (2) comprising one or more iron and / or aluminum electrode(s), and one or more inert second electrode(s) (4), and a substantially vertical separator tower (20) arranged in a flow connection with the electrolytic cell, applying the pretreated wastewater (16) to the electrolytic cell (14), operating the electrolytic cell (14) to produce iron hydroxide and / or aluminum hydroxide (3) acting as molecular sieve capable of trapping impurities, such as comprising sulphates and any remaining solids, and to produce hydrogen causing the molecular sieve with the trapped impurities to raise in the vertical tube as an accumulating floc, conveying the raising floc into the separator tower (20), wherein the floc (5, 19) is separated by expelling from the top of the separator tower (15), and obtaining first purified water (W1) from the separator tower (20) from below the raising floc. A water purification apparatus (30) and use of the water purification apparatus.

Description

[0001] A method and a water purification apparatus for purifying acidic wastewater from a mining process, and use of the water purification apparatus

[0002] Field of the application

[0003] The present application relates to a method and to a water purification apparatus for purifying acidic wastewater from a mining process. The present application also relates to use of the water purification apparatus for purifying acidic wastewater from a mining process.

[0004] Background

[0005] Wastewaters produced in processes of mining industries have adverse effects on the ecosystem. Therefore, it is essential to treat the wastewaters before discharging them into the environment. The mining wastewaters are acidic and contain a high amount of toxic or harmful substances, such as metal sulfides, metal oxides, metal sulphates, chemicals, particles and the like substances, which may be remains from treatment processes carried out at the mining site.

[0006] In prior art the mining wastewaters have been treated by methods such as evaporation and crystallization, calcium carbonate precipitation, biological processes, ion exchange, desalination, flocculation, clarification, and membrane separation. However, these methods cannot effectively remove all the substances from the wastewaters, and they may have high maintenance costs and high energy consumption, they may be slow, and / or they may generate toxic or harmful residues. The water obtained from the processes may not be useful for most purposes and cannot be released to the environment. However even stored mining wastewaters and other mining wastes from both active but also from closed mines may release harmful substances to the environment over a longer period of time thus contaminating natural waters including surface waters and groundwaters. There is a need to treat such wastes.

[0007] One widely used prior art method for treating mine waters is calcium hydroxide precipitation, which produces a basic gypsum precipitate also including metal hydroxides formed in the processes. The yield of valuable minerals is poor. The gypsum precipitate is a serious environmental problem, and also part of the valuable minerals is discarded into waste fraction, wherefrom they will be released and thus will contaminate natural waters.

[0008] Mines may suffer from acute lack of water, and there is a need to recycle purified wastewater.

[0009] There is a need for methods and systems for treating wastewaters from mining processes in a simple and economical way. Especially there is a need to find better alternatives to the prior art methods producing harmful waste, which also contain valuable minerals. It is desired to efficiently recover the valuable minerals present in the wastewaters. It is also desired to treat practically any type of mining wastewater at practically any location, and to produce water, which is pure or substantially pure and which can be recycled.

[0010] Summary

[0011] The present method and apparatus enable overcoming drawbacks of prior art. In the present invention it was found out how to treat challenging sulphate-containing acidic wastewaters from mining processes with a simple and economical system and to produce pure water, which can be used or released to the environment. The present solution is sustainable, can be implemented as a portable system and can be run continuously. Metals can be recovered from the process as solid minerals. The present solutions eliminate risks on site and to environment and to public health. The present solution can overcome for example issues associated with calcium hydroxide precipitation. The yield of valuable metals is increased, costs are decreased, and adverse effects to environment can be avoided.

[0012] The present application provides a method for purifying acidic wastewater from a mining process, the method comprising

[0013] -providing acidic wastewater form a mining process,

[0014] -pretreating the acidic wastewater to obtain pretreated wastewater having:

[0015] • total solids in the range of 0-3% by weight,

[0016] • pH in the range of 6.0-9.0,

[0017] • conductivity in the range of 0.3-3.0 mS / cm, and

[0018] • temperature in the range of 0-99.9°C,

[0019] -providing a water purification apparatus comprising

[0020] • an electrolytic cell comprising a substantially vertical tube connected to a source of DC electric power and comprising one or more first electrode(s) comprising one or more iron and / or aluminum electrode(s), and one or more inert second electrode(s) having a higher electronegativity compared to the first electrode(s),

[0021] • a substantially vertical separator tower arranged in a flow connection with the upper part of the electrolytic cell,

[0022] -applying the pretreated wastewater to the electrolytic cell,

[0023] -operating the electrolytic cell to produce iron hydroxide and / or aluminum hydroxide acting as molecular sieve capable of trapping impurities, such as comprising sulphates and any remaining solids, and to produce hydrogen causing the molecular sieve with the trapped impurities to raise in the vertical tube as an accumulating floc,

[0024] -conveying the raising floc into the separator tower, wherein the floc is separated by expelling from the top of the separator tower, and

[0025] -obtaining first purified water from the separator tower at a point below the raising and / or expelled floc.

[0026] The present application also provides a water purification apparatus for purifying acidic wastewater from a mining process, the water purification apparatus comprising

[0027] -an electrolytic cell comprising a substantially vertical tube connected to a source of electric power and comprising

[0028] • one or more first electrode(s) comprising one or more iron and / or aluminum electrode(s), preferably in a form of cylinder(s), and

[0029] • one or more inert second electrode(s) having a higher electronegativity compared to the first electrode(s), preferably in a form of cylinder(s) inside the cylinder(s) of the one or more first electrode(s),

[0030] -a substantially vertical separator tower arranged in a flow connection with the upper part of the electrolytic cell,

[0031] -a source of pretreated wastewater obtained from a pretreatment step of acidic wastewater from a mining process, the source of pretreated wastewater being arranged to be conveyed to the electrolytic cell,

[0032] -an outlet for expelled floc at top of the separator tower,

[0033] -an outlet for first purified water at a lower part of the separator tower,

[0034] -an electronic controlling means,

[0035] -one or more means for controlling the flow of liquids in the apparatus, the means being operatively connected to the electronic controlling means, wherein the electronic controlling means is arranged to control the source of electric power applied to the electrolytic cell and preferably the one or more means for controlling the flow of one or more liquids in the apparatus.

[0036] The present application provides use of the water purification apparatus for purifying acidic wastewater from a mining process.

[0037] The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments and examples disclosed herein are mutually freely combinable unless otherwise explicitly stated. The embodiments and examples not in the scope of the claims are embodiments and examples not part of the invention, but useful for understanding the invention.

[0038] Brief description of the figures

[0039] Figure 1 shows a flowchart of the present method.

[0040] Figure 2 shows an example of a setup of the present apparatus.

[0041] Figure 3 shows examples of the electrolytic cell and the separator tower.

[0042] Figure 4 shows the first step of precipitating metals for the Windows of tolerance for Step 1 of Example 1 .

[0043] Figure 5 shows the second step of precipitating metals for the Windows of tolerance for Step 1 of Example 1 .

[0044] Figure 6 shows separation of sulphate and pure water from effluent of step 1 .

[0045] Figure 7 shows direct purification of mine water without precipitation as pretreatment.

[0046] Detailed description

[0047] In this specification, percentage values, unless specifically indicated otherwise, are based on weight (w / w, by weight, or wt%). In specific examples the embodiments and examples specified with the open term “comprise” may be further limited with a closed term “consisting of”.

[0048] The diameters disclosed herein, unless specifically indicated otherwise, may refer to the smallest diameter, and may be presented as average or number-average diameter. The diameter may be also presented as equivalent spherical diameter. The diameter may be determined microscopically or by other optical methods, which may comprise using a camera, and / or by sieve analysis.

[0049] The present disclosure provides a method for purifying acidic and / or sulphate- containing wastewater 10 from a mining process, as shown in Figure 1. The mining process may be any suitable process of mining industry, which produces wastewaters, which are herein also called mining waters. Mining waters differ significantly from other wastewaters and are in general substantially more challenging, so method and devices used for purifying other wastewaters are not usually directly applicable to mining waters. The mining may refer to any mining process, wherein valuable substances, such as metals, minerals, battery materials and the like are obtained from a mine. The mining waters may contain valuable substances and / or substances considered as waste and / or harmful.

[0050] The wastewater may be originated from one or more treatment steps of mining waters, such as treatment with acids, treatment with flocculants, which may be harmful and contain flocculating agents such as xanthates or the like, treatment with other agents, wherein the wastewaters may contain toxic or harmful residues, remains of flocs, and / or solids. The wastewaters may be characterized as acidic mining waters, which may comprise soluble alkali and earth alkali metal sulfates as well as heavy metal sulfates in aqueous acidic solution, i.e. the wastewaters may be sulphate-containing wastewaters. The mining waters may comprise substantial amounts of valuable metals, which may be separated and recovered by the present method and system. The present method can be considered as an alternative to the calcium hydroxide precipitation, which produces harmful gypsum precipitate waste containing valuable minerals. The wastewater 10 may have been treated or may have not been treated with one or more of the prior art methods, such as by the calcium hydroxide precipitation.

[0051] In the present method metals may be separated from acidic wastewater by precipitating quantitatively as metal hydroxides by neutralizing the wastewater with alkali, such as with sodium hydroxide. The remaining filtrate contains sulfates which can be precipitated as iron and / or aluminum sulfates by using the present apparatus and method. With the method carried out with the apparatus harmful substances left in the filtrate are coprecipitated and separated and purified water is obtained. Metals and sulfates can be recovered and further processed.

[0052] The method comprises providing the acidic wastewater form a mining process 10, wherein the wastewater 10 may be directly conveyed, for example pumped through a pipeline, from a container, a basin, a pond or the like reservoir at the mining site, or the wastewater may have been transported to the site of treatment in a container or via a pipeline. The site of treatment may refer to a site or location, wherein the present pretreatment and / or purification treatment is / are carried out. The present apparatus 30 may be provided at the site of treatment. The apparatus 30 can also be transported to the mining site, and it can be implemented as a portable / transportable apparatus.

[0053] However, it was found that most wastewaters from mining processes cannot be directly treated with the apparatus 30 in an efficient manner. For example, too high conductivity was found to interfere with the formation of the floc essential for the process. The process requires specific conditions in order to be able to efficiently treat the challenging mine waters and to recover soluble substances, such as valuable metals, from the mine water. Merely conveying the mining waters as such to the apparatus was found unsuccessful.

[0054] After numerous trials it was found out that the properties of the wastewater 10 to be treated with the apparatus 30 must be in the window of tolerance including total solids in the range of 0-3% by weight, pH in the range of 6.0-9.0, conductivity in the range of 0.3-3.0 mS / cm, and temperature in the range of 0-99.9°C. The desired properties are obtained in a pretreatment step 12. The pretreatment may be run as a batch mode or as continuously.

[0055] The method comprises pretreating 12 the acidic wastewater to obtain pretreated wastewater 16 having:

[0056] • total solids in the range of 0-3% by weight, such as 0-2% by weight,

[0057] • pH in the range of 6.0-9.0, such as pH in the range of 7.0-8.8, for example about 8.3,

[0058] • conductivity in the range of 0.3-3.0 mS / cm, such as 0.3-2.5 mS / cm, and

[0059] • temperature in the range of 0-99.9°C. In one embodiment the pretreating 12 comprises adjusting the pH of the wastewater with alkali, such as alkali solution comprising NaOH. The optimal pH was found to be in the range of 6.5-8.5, wherein pH of about 8.3 was found most suitable for the process also in term of general efficiency. The pH depends also on ionic strength. The wastewater 10 can be neutralized with NaOH to obtain desired pH value. As the mining water practically has no buffering capacity, even a small amount of NaOH is enough to adjust the pH. NaOH solution with a suitable concentration, such as 2-50% by weight, such as 2-10% by weight, or as solid, may be used. For example, about 3.5% (w / v) NaOH solution was found suitable for adjusting the pH value.

[0060] Soluble metallic elements in the acidic wastewater may be first removed by chemical precipitation to decrease conductivity and to increase pH from acidic to more neutral range. Total solids have to be less than 3% but the percentage depends on the ratio between Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) and the surface charges of the suspended particles.

[0061] In one embodiment the pretreating 12 comprises precipitating solids, preferably as metal hydroxides, and / or filtering. The system may comprise a solid separator, which is used for separating the solids. Solids from the wastewater may be precipitated in a precipitation tank or the like container. However, due to the effectiveness of the present method and apparatus to remove sulphates there is no need to precipitate sulphates or convert them into sulfides in the pre-treatment. Thus, the pretreated water can contain soluble sulphates.

[0062] In one embodiment the pretreating 12 comprises diluting the wastewater. This may be carried out to obtain the desired conductivity. The diluting water may comprise tap water and / or it may comprise purified water obtained from the subsequent process, such as the first purified water (W1 ) or the second purified water (W2). The present method and apparatus allow total recycling of the purified water with no need to increase water from outside of the purification process once the process is running. Tap water may be added in an initial step, after which purified water is obtained from the process and can be used. The conductivity can be measured by using a conductivity meter and / or sensor, such as by providing one or more conductivity sensors arranged to measure the conductivity of the wastewater and / or pretreated water. The conductivity sensors may be connected to controlling means, which may be arranged to provide diluting water to the wastewater to adjust the conductivity as feedback to measured conductivity to obtain conductivity in the range of 0.3-3.0 mS / cm.

[0063] The present method and apparatus can be used to efficiently treat dilute solutions, which makes it possible to pretreat the wastewater simply by dilution to adjust the properties suitable for the pretreated wastewater to be processed. The present method and apparatus were found to efficiently recover substantially or almost all soluble substances from the solution.

[0064] The present method and apparatus require liquid aqueous solutions but is feasible between 0 to 99.9°C having optimal temperatures specific for most solutions. It is desired not to allow the aqueous solution to boil or freeze. The temperature of the pretreated wastewater may be for example in the range of 5-80°C for practicality and safety.

[0065] The pretreatment may be carried out in a specific pretreatment 12 system, apparatus and / or arrangement, which may be a part of the present apparatus 30 or a system comprising the apparatus 30, or which may be separate. The pretreatment system may comprise one or more containers for the acidic wastewater, and one or more means for dosing chemicals to the wastewater solution, such as alkali solution and / or precipitating agents, one or more means for adjusting the temperature of the wastewater solution, such as heater(s) and / or cooler(s), one or more means for diluting the wastewater, one or more sensors for detecting the properties of the pretreated wastewater, means for separating solids, such as one or more filters and / or other solid separator devices and / or containers, and / or one or more further means required for carrying out the pretreatment and / or controlling thereof. The pretreatment system or the means and / or other parts thereof may be operatively connected to electronic controlling means 24, and the pretreatment may be controlled by the electronic controlling means. Separated solids may be arranged to be expelled and / or recovered from the pretreatment system and discarded and / or further treated, so that valuable metals can be recovered and used in further applications. The solid dried sulfate precipitate can be treated into non-soluble form.

[0066] The method comprises providing a water purification apparatus 30 comprising

[0067] • an electrolytic cell 14 comprising a substantially vertical tube connected to a source of electric power 13 and comprising one or more first electrode(s) 32 comprising one or more iron and / or aluminum electrode(s), and one or more inert second electrode(s) 34 having a higher electronegativity compared to the first electrode(s),

[0068] • a substantially vertical separator tower 20 arranged in a flow connection with the upper part of the electrolytic cell.

[0069] An example of the water purification apparatus is shown in Figure 2. Examples of the electrolytic cell 14 connected to the separator tower 20 are shown in Figures 2 and 3. The water purification apparatus 30, as used herein, may refer to a system, a setup or a device arrangement comprising the apparatus and optionally other devices and / or setups, such as disclosed herein. The system or device arrangement may be arranged in the same setup or at the same location and / or plant.

[0070] The water purification apparatus 30 may comprise

[0071] -an electrolytic cell 14 comprising a substantially vertical tube connected to a source of electric power 13 and comprising

[0072] • one or more first electrode(s) 32 comprising one or more iron and / or aluminum electrode(s), and

[0073] • one or more inert second electrode(s) 34,

[0074] -a substantially vertical separator tower 20 arranged in a flow connection with the upper part of the electrolytic cell 14,

[0075] -a source of pretreated wastewater 16 obtained from a pretreatment step 12, such as from a pretreatment system, of acidic wastewater 10 from a mining process, the source of pretreated wastewater 16 being arranged to be conveyed to the electrolytic cell 14,

[0076] -an outlet 15 for expelled floc 19 at the top of the separator tower 20,

[0077] -an outlet 18 for first purified water W1 at a lower part of the separator tower 20, such as at the bottom of the separator tower and / or at below the point and / or level whereto the flow from the electrolytic cell is connected and / or arranged in or to the separator tower, preferably at a lower position than the outlet 15 for expelled floc 19,

[0078] -electronic controlling means 24, such as an electronic control unit,

[0079] -one or more means for controlling the flow of liquids in the apparatus 22a,b,c,d,e,f,g,h,i, such as one or more controllable pumps and / or valves, the means being operatively connected to the electronic controlling means 24, -preferably one or more sensors for detecting pH, temperature, and / or conductivity connected to the electronic controlling means, wherein the electronic controlling means 24 is arranged to control the source of electric power 13 applied to the electrolytic cell 14 and the one or more means for controlling the flow of one or more liquids in the apparatus 22a, b,c,d,e,f,g,h, i.

[0080] The method comprises applying the pretreated wastewater 16 to the electrolytic cell 14, such as by pumping. The electrolytic cell may be installed in a substantially vertical position, wherein the first end of the electrolytic cell points down and the second end points up. The first end comprises an inlet 31 for incoming liquid (pretreated wastewater), such as an aperture and / or a connector for the liquid, preferably for a tube or pipeline for the liquid. The second end comprises an outlet for outgoing liquid and floc, and the second end / outlet is in a flow connection with the separator tower, for example the electrolytic cell 14 and the separator tower 20 are connected together at their ends as shown in Figure 3, of the flow from the electrolytic cell 14 is conveyed to a point in the separator tower 20 between the ends of the separator tower, such as substantially at the center of the separator tower as shown in Figure 2, or at the lower part of the separator tower. In general, the outcoming liquid and floc from the electrolytic cell 14 are provided to the separator tower at a point between the ends of the separator tower so that pure water can be obtained below the point and the floc can be expelled above the point. In this way the floc and the purified water can be efficiently separated.

[0081] The one or more first electrode(s) 32 comprising one or more iron and / or aluminum electrode(s) are preferably in a form of cylinder, which defines a flow channel for the solution. The first electrode(s) 32 is / are worn in the process.

[0082] The one or more inert second electrode(s) 34 are preferably inner electrode(s), which preferably is / are in a form of cylinder inside the cylinder of the first electrode. Therefore, between the first electrode 32 and the second electrode 34 a channel is formed, whereto the pretreated wastewater may be conveyed. The cylinder of the second electrode 34 may be longer than the cylinder of the first electrode 32, which enables for example using the second electrode 34 as a pipeline for conveying treated flow from the electrolytic cell 14 to a next step and / or to a specific point / level in the separator tower 20.

[0083] In one example an apparatus 30 or a system comprising the apparatus is provided comprising, as disclosed in Figure 3, an electrolytic cell 14 comprising a vertical tube connected to a source of DC electric power 13 and comprising a first electrode 32 comprising a cylindrical outer iron electrode, and a cylindrical inner inert second electrode 34 comprising precious metal, such as platinum, having a higher electronegativity compared to the first electrode. A vertical separator tower 20 is connected to the upper part of the electrolytic cell so that the flow raising from the cell is conveyed to the separator tower substantially at the middle of the separator tower. The total height h of the combination disclosed in Figure 3 may be in the range of 2-10 meter, for example about 4 meters. Each of the electrolytic cell 14 and the separator tower 20 may have a height in the range of 1-6 meters, for example. The system may comprise one or more of electrolytic cells 14 and one or more of separator towers 20, or combinations thereof, which may be arranged in series and / or in parallel, and / or as a cascade.

[0084] The pretreated water 16 in Figure 3 is pumped into the electrolytic cell 14 with a suitable flow rate via inlet 31 at the first end of the electrolytic cell to between the first electrode 32 and the second electrode 34. In the example of Figure 3 the electrodes 32, 34 are in the form of cylinders, but electrodes in other forms may be applied as well.

[0085] In general, the first electrode is fed with positive current releasing iron ions and electrons. The electrons are conducted to the second electrode. The iron ions react with hydroxides from the water making iron hydroxide 33. Iron hydroxide forms a molecular sieve that captures impurities from the water but allows water molecules to pass through. A floc begins to evolve. The electrons react with hydrogen ions from water creating hydrogen gas. This lifts the iron hydroxide with trapped impurities, i.e. the floc, up to the separating tower. The situation would be similar if aluminum electrode was used, in which case aluminum ions would react with hydroxides from the water making aluminum hydroxide, which forms similar molecular sieve. However, the molecular sieve formed by iron hydroxide is substantially denser and can bind substances more efficiently.

[0086] In one example the second cylindrical electrode of precious metal 34 conducts the electrons from the cylindrical iron electrode 32 by negative current. The precious metal cylinder comprises a plurality of small holes or apertures. Jetting water from the holes, by the effect of electrolytic reactions, cleans the surface of the iron cylinder so iron ions can form readily. Wash water 22d may be provided to the electrolytic cell, such as inside the second cylindrical electrode, to facilitate the jetting flow shown by arrows in Figure 3. The second electrode 34 may be cylindrical and it may form a tube which is connected to the separator tower, as shown in Figure 3. The raising impurities in the forming floc, and the purifying water, raise inside the cylinder 34. The second electrode may comprise (larger) holes or apertures 26, which allow impurities and clean water to enter and escape up in the system. The cylinder 34 may continue inside the separator tower 20, and purified water may be separated from the tower 20 below the level / point of the second end of the cylinder 34, or an end of a tube continuing from the second end of the cylinder 34. This will ensure that the floc is properly separated from the purified water.

[0087] The method comprises operating the electrolytic cell 14, i.e. providing suitable and / or controlled electric current to the cell, to produce iron hydroxide and / or aluminum hydroxide 33 acting as molecular sieve capable of trapping impurities, and to produce hydrogen causing the molecular sieve with the trapped impurities to raise in the vertical tube as an accumulating floc. The electric current can be controlled to obtain desired reaction rate, such as desired degree of formation of the floc. The flow rate of the pretreated wastewater may be also controlled so that a desired reaction efficiency can be obtained. The controlling can be carried out by the electronic controlling means 24, which may be operatively connected to the pulp controlling the flow rate and to the source of electric current 13.

[0088] Typically, the electrolytic cell may be operated or run with a direct current (DC) in the range of 10-100 A and a voltage in the range of 10-100 V. In one example the voltage may be about 10 V and the current may be about 40-50 A. In another example, the voltage may be about 50 V and the current may be about 20-30 A. These parameters can be controlled by the electronic controlling means 24 to obtain desired reaction rate and for example adjust the electrolytic reactions to adapt to the currently used wastewater content and / or flow rate.

[0089] The network of metal hydroxides tends to self-set as globular or spherical structures. The metal hydroxides are oxidized by the oxygen present in the solution into oxides, i.e. iron oxides and / or aluminum oxides 33, which are solid minerals containing no water. During the formation thereof a solid shell is formed in the floc, which holds everything inside, except water. Thus, when the floc spheres raise at accelerating speed up while the hydrostatic pressure decreases, the gas inside the spheres expands thus forming buoyant force, which in turn accelerates the separation of the floc thus resulting in very efficient separation of the floc / im purities from the purified water. The impurities may comprise substances such as sulphates and / or other compounds, and any remaining solids, flocs and / or the like contaminants, which may have been originated from previous treatments of the mining water. For example, remains of harmful flocculants and / or other aids, such as xanthates, used in some processes can be recovered and removed by the present apparatus and method. Valuable metals or other substances of interest are also included in the floc and can be recovered later.

[0090] The floc comprising the iron hydroxide with impurities is lifted up towards the surface and / or the top / upper part 15 of the separator tower 20. The top of the separator tower, which may refer to the upper part and / or second end thereof, comprises an outlet 15 for the expelled or separated floc, which may comprise a pipe or chute sloping downwards, as shown in Figures 2 and 3. The floc, which is self-drying, falls from the outlet to a decanter by gravity.

[0091] The method comprises conveying the raising floc into the separator tower 20, wherein the floc 19 is separated by expelling and / or separating from the top / upper part of the separator tower 20, and / or from an outlet 15 for the floc.

[0092] The separated floc can be collected to a container positioned below the outlet or chute. The floc may be allowed to dry, or it may be dried. The floc may be further processed, such as disposed and / or it may be treated to recover any valuable substances, such as metals.

[0093] The method comprises obtaining first purified water W1 from the separator tower 20 from below the raising floc and / or from below the end of the tube or pipe connecting the electrolytic cell 14 with the separator tower 20. The point of withdrawing the water shall be selected in such way that the forming and raising floc cannot be included to the separated water fraction. In general, the floc and the purified water move to opposite directions, which facilitates the separation of purified water, especially when the purified water is withdrawn below the level of the raising floc. The first purified water W1 is separated at a point, position or level, such as via an outlet 18, which is below the aperture of the outlet 15 for expelled floc 19 in the separator tower 20, as shown in Figure 3. The first purified water W1 is withdrawn from an outlet 18 for the first purified water W1 , which may be at the bottom (first end) of the separator tower 20, as shown in Figure 2, or at any other suitable point / level. The first purified water W1 may be conveyed to a buffer tank 25 and / or for other use and / or treatment from the outlet 18. The flow of the first purified water W1 may be controlled by controlling means, such as wherein the means comprise a valve 22i. The pump controlling the flow rate of incoming pretreated wastewater may also control the flow rate of the whole apparatus, such as the flow rate of outcoming purified water.

[0094] The first purified water W1 contains iron, which may provide a red color to the water. It may be desired to remove iron from the first purified water.

[0095] The water purification apparatus 30, or a system or device arrangement comprising the water purification apparatus 30, may comprise an iron oxidizing device 17, wherein the first purified water W1 is arranged to be conveyed to the iron oxidizing device 17 to oxidize and to separate iron from the first purified water W1 to obtain second purified water W2. The iron oxidizing device 17 may comprise an outlet 23 for the second purified water W2, which outlet may be controlled by controlling means to obtain desired flow of the second purified water W2.

[0096] In one example an iron oxidizing device 17 comprises one or more pressurized containers, such as cylinders, such as made form stainless steel. The container(s) may be arranged in series, as shown in Figure 2. The container(s) is / are filled with limestone, which set pH of the water to about 8.3, which is the pH value wherein iron will be oxidized in optimal way into iron trioxide (hematite). The device is operated at an elevated pressure, such as at a pressure in the range of 3-5 bar, wherein the increased partial pressure of oxygen accelerates the oxidizing reactions. The container(s) may be pressurized with means for pressurizing the containers, such as a pump. On the limestone there are layers of silica sand, such as first a layer with a rough grain size, and subsequently layers having increasing liner grain sizes towards the surface. As the silica sand is piezoelectric, i.e. there is a voltage between the ends of crystals, electrolysis is obtained in the water. The silica sand thus catalyzes the oxidation of iron compounds into non-soluble form hematite. Hematite is bright red mineral, which will be precipitated on the surface of the silica sand layer, wherefrom it is washed / rinsed by backwash method and is conveyed back to feed container and / or out from the process as harmless mineral. While oxidizing, the iron coprecipitates oxidizing minerals such as arsenic, manganese and the like, if present in the first purified water W1. Aluminum hydroxide will be oxidized into aluminum trioxide (bauxite) and can be removed in similar manner by backwash. If drinking water is to be prepared, the purified water W1 , W2 can be treated with active carbon.

[0097] The method may comprise treating the recovered first purified water W1 by oxidizing iron and removing oxidized iron to obtain second purified water W2. This can be done by using the iron oxidizing device 17.

[0098] The method may comprise using the first purified water 18, W1 as washing water and / or as diluent. The method may comprise using the second purified water W2, which may be obtained from outlet 23, as washing water and / or as diluent, such as in the pretreatment system.

[0099] The method may comprise using the second purified water W2 as influent water 22a for applying to the electrolytic cell.

[0100] The method may comprise treating the recovered first purified water W1 and / or the second purified water with active carbon. The apparatus or the system may comprise an active carbon filter or the like flow-through container or column comprising active carbon, through which the purified water W1 , W2 may be conveyed.

[0101] The method may comprise adding one or more polyelectrolytic polymers 22c to the formed floc to stabilize the floc, preferably after the electrolytic cell 14 and / or before the separator tower 20.

[0102] In one embodiment the acidic wastewater from a mining process has a pH of 5 or less, such as pH of 4 or less, and / or a sulphate content of 50 g SO427I or less.

[0103] In one embodiment part of the second purified water W2 is arranged to be controllably conveyed as influent water 22a to the electrolytic cell 14.

[0104] The apparatus and related parts may be made of material(s), which can tolerate the conditions, such as used pressures, temperatures, liquids and reagents, such as stainless steel, plastic, glass, and / or silicone. Parts of the apparatus may be made transparent, such as the separator tower or part thereof may comprise a transparent tube and / or a transparent tube may be connected to the electrolytic cell, which enable monitoring the process visually, for example the formation of the floc. The apparatus 30 or the system may be electronically controllable, thus comprising one or more electronic controlling means 24, which may comprise an electronic control unit. The apparatus or the system may be automated or semiautomated. The controlling means may be programmable, preferably comprising one or more processors, memory, and software configured, when executed with a processor in the control unit, to carry out one or more operations to implement the method or part thereof, for example to adjust the voltage, current, temperature, pressure, dosing of one or more reagent(s), diluting water, and / or flow of liquids by controlling and / or adjusting any of the operating components of the apparatus or the system. The controlling means may be arranged to maintain one or more of said parameters in a desired range. The controlling means may be arranged, such as programmed, to monitor one or more properties from the apparatus or the system, for example as a function of time, and as feedback to the monitored properties carry out one or more control actions in the apparatus or the system to adjust the function of the apparatus to carry out the present method or a part thereof.

[0105] The electronic controlling means 24 may be arranged to control the flow and / or dosing of liquids and / or chemicals in the apparatus to carry out the method or any part thereof. For example, the electronic controlling means may be arranged to carry out one or more controlling actions to provide the pretreated water 16 from the pretreatment step 12, such as from the pretreatment system.

[0106] In one embodiment the electronic controlling means / the electronic control unit 24 is arranged to control the flow and / or dosing of liquids in the apparatus selected from one or more of

[0107] -incoming pretreated wastewater 16 from a mining process,

[0108] -outcoming separated floc 19 from the separator tower, -outcoming first purified water from the separator tower, -outcoming first purified water W1 from the separator tower to washing of the floc 19 expelled / separated from the separator tower 20,

[0109] -outcoming first purified water W1 to the iron oxidizing device of claim 10, -outcoming first purified water W1 as dilution water to pretreatment 12, -outcoming second purified water W2 from the iron oxidizing device 17 as dilution water to pretreatment 12, and

[0110] -outcoming second purified water W2 from the iron oxidizing device 17 as influent water 22a to the electrolytic cell 14. In one embodiment the one or more inert second electrode(s) 34 comprise precious metal, such as platinum, and / or stainless steel, nickel, chromium, or an alloy thereof.

[0111] In one embodiment the one or more inert second electrode(s) 34 comprise a plurality of apertures causing jetting water from the apertures during operation of the electrolytic cell. The apertures may have a small diameter, such as 2 mm or less, for example in the range of 0.1 -2.0 mm.

[0112] In one embodiment the electronic controlling means 24 is connected to means, such as one or more sensors, for detecting from incoming wastewater from the pretreatment step 12 and / or the pretreatment system one or more of conditions: -total solids in the range of 0-3% by weight,

[0113] -pH in the range of 6.0-9.0, such as pH in the range of 7.0-8.8, for example about 8.3,

[0114] -conductivity in the range of 0.3-3.0 mS / cm, and

[0115] -temperature in the range of 0-99.9°C, wherein the electronic controlling means 24 is arranged to convey the incoming wastewater 12, such as from the pretreatment system, as pretreated wastewater 16 to the electrolytic cell 14 only if the conditions are fulfilled.

[0116] The sensor(s) may comprise one or more of a pH sensor, a conductivity sensor, an optical sensor, for example a turbidity sensor or a spectrophotometric sensor, a camera, a flow sensor, a temperature sensor and / or any other sensor required to detect and / or monitor one or more properties from the apparatus, system, or any of the liquids discussed herein, such as wastewaters, purified waters and any other liquids or materials. The sensors may be connected to the electronic controlling means, which may be arranged to carry out one or more controlling actions to adjust one or more properties of the wastewater, pretreated water, the system and / or part thereof to carry out the present method.

[0117] The apparatus or the system may comprise one or more actuators or other means, such as valves, pumps, mixers, temperature controlling means, such as heating and / or cooling means, means for dosing one or more chemicals, and / or the like controllable means, which may be operatively connected to the electronic controlling means. The electronic controlling means may be configured to operate one or more of these means to carry out one or more controlling actions, preferably to carry out one or more steps of the method. The apparatus or the system may also comprise one or more pipes, tubes or other means for conveying one or more liquids, and the like parts necessary in such apparatuses and systems, and / or cooling means, heating means, washing means, conveying means such as one or more pumps, and / or the like means, which can be used in a controllable manner and can be controlled by the electronic controlling means.

[0118] The electronic controlling means 24 may be connected to means for providing diluent water to the incoming wastewater 12, such as to the pretreatment system, and arranged to control the flow and / or dosing of the diluent water to obtain conductivity in the range of 0.3-3.0 mS / cm in the diluted wastewater, preferably to obtain pretreated wastewater 16. Purified water obtained from the process can be arranged to be used as the diluent water, such as arranged to be conveyed, preferably in a controlled manner, to the pretreatment step 12 and / or to the pretreatment system, such as by using one or more controllable pump(s), valve(s) and / or the like means.

[0119] In one embodiment the first purified water W1 and / or the second purified water W2 is arranged to be conveyed to the pretreatment step 12 of acidic wastewater 10 to dilute the acidic wastewater. This is done controllably to obtain one or more of the properties of the pretreated water 16, and / or to obtain pretreated water, such as to obtain conductivity in the range of 0.3-3.0 mS / cm. The conveying of the first purified water (W1 ) and / or the second purified water (W2) may be controlled by the electronic controlling means operatively connected to one or more means for providing flow of water, such as means for providing diluent water to the incoming wastewater 12, for example by operating one or more of pumps, valves and / or other means.

[0120] In one embodiment the electronic controlling means 24 is connected to means for providing first purified water W1 and / or to means for providing second purified water W2 as diluent water to the pretreatment step 12 of acidic wastewater 10. The electronic controlling means may be arranged to control the flow and / or dosing of the first purified water W1 and / or the flow of the second purified water W2 to obtain conductivity in the range of 0.3-3.0 mS / cm in the diluted acidic wastewater 10, preferably to obtain pretreated wastewater 16. The means for providing first purified water W1 and the means for providing second purified water W2 may comprise one or more of outlets for the purified water, valves, pumps, pipes, tubes, and / or the like parts, actuators connected to the parts, wherein the means and associated parts may be operatively connected to the controlling means. For example, the means for providing first purified water W1 may comprise an outlet 18 for first purified water (W1 ) and / or a valve 22i, wherein the outlet and / or the flow of the water may be controlled by the controlling means. Similarly, the means for providing second purified water W2 may comprise an outlet 23 for second purified water and / or a valve, wherein the outlet and / or the flow of the water may be controlled by the controlling means.

[0121] The present disclosure provides use of the water purification apparatus 30 disclosed herein for purifying acidic wastewater from a mining process, preferably with the method disclosed herein.

[0122] Examples

[0123] Step 1

[0124] Water from a copper mine was used for tests. The pH of the mine water was 2.42, the conductivity was 24.7 mS / cm, and the total solids content was 79.6 g / l. The mine water was turbid and had red color, and it could not be efficiently purified with the water purification apparatus disclosed herein.

[0125] After the first chemical analysis of mine water (BW) it was evident that a pretreatment is required to get it through the Window of the Tolerance of the present water purifier as described in Step 1 (Figure 4). Therefore, the high concentrations of the soluble metallic elements in acidic solution were first removed by chemical precipitation to decrease conductivity and to increase pH from acidic to almost neutral.

[0126] It was found out that total solids have to be less than 3% but the percentage depends on the ratio between Total Dissolved Solids (TDS) and Total Suspended Solids (TSS) and the surface charges of the suspended particles.

[0127] However, due to the effectiveness of the present method to remove sulphates there is no need to precipitate sulphates or convert them into sulfides in the pretreatment of Step 1 . (Figure 4)

[0128] The system 30 disclosed in Figure 2 was provided comprising an electrolytic cell 20 comprising a vertical tube connected to a source of electric power 13 and comprising a first electrode 2 comprising a cylindrical outer iron electrode, and a cylindrical inner inert second (SS) electrode 4. A vertical separator tower 20 was connected to the upper part of electrolytic cell so that the flow raising from the cell is conveyed to the separator tower at the middle of the separator tower. The apparatus was run as described in the detailed description. In the examples the apparatus is called as MUST water purifier simulator. The present method is referred to as Molecular Unique Separation Technology.

[0129] In the first step, no attention was paid yet to the total volume of the Internal Loop but rather a volume was used which was big enough to run the first tests through the MUST water purifier simulator, which is the present water purification apparatus as shown in Figure 2. Therefore, the first bucket (20 L) of BW was mixed into 510 L of tap water as one-time seed water. Later on, it was noticed that BW in different buckets varied in volumes (17-20 L) and greatly in conductivity (20-27 mS / cm). Therefore, the rest of the buckets of BW were pooled and repacked to buckets, exactly 20 L in each (PDBP).

[0130] By neutralization (NaOH, 3.5% w / v) both conductivity and pH were close to the Window of Tolerance as 2.35 mS / cm and pH 7.5, respectively. This was achieved by adding 245 g of NaOH in 7 liters of water which was mixed with 530 L of diluted BW solution. Therefore, the total volume in the first step was 510 + 20 + 7 = 537 liters. The final process volumes were confirmed by remeasurements of the process chambers. Max possible variation of volume was measured for the total process of pre-treatment as less than + / - 2 % or + / - 10 liters. This variation has little effect on the final results compared to the errors of the chemical analysis which typically were more than + / - 10% and in some cases up to + / -20 %.

[0131] Total Material Balance

[0132] The very first calculations of the Material Balance were based on the analysis of Total Solids (TS). Normally, due to the ease of the method to analyze TS, the results should be the most reliable ones.

[0133] The total volume in the pre-treatment which simulates the first step for optimizing the Internal Loop was 537 liters in the settling tank. Without any intervention the settling tank left a clear effluent of 457 liters on top of the yellowish loose precipitation (of 80 L) after a day (practical rather than optimized time). (Figures 4 and 5) This effluent served for the base of the Internal Loop in the second step through the simulator (Figure 2). From the simulator the pure water is recycled back to the first step of pre-treatment in the settling tank and from there back to simulator for continuous purification again and again.

[0134] Therefore, the first addition of 510 L of tap water is only a one-time operation. Also, any amount of water from the settling and drying processes is recycled in the Internal Loop.

[0135] Because pH of the purified water from the simulator process is always over 8.0 the amount of recycled water for Step 1 will be less than the amount of tap water used in this preliminary test.

[0136] In this experiment it means that almost the total volume (ca 99.5 %) is recycling in the Internal Loop. However, for practical reasons samples were taken from both effluent and dry precipitate and from intermediate steps (Figures 4 and 5) as will be indicated in the following material balance calculations for total solids (TS) and for each element which were analyzed. (Tables 1-25)

[0137] Due to the wide variation in the quality of the used tap water and the very small concentrations of the analyzed ions and elements in the effluent of Mine Water, the internal errors in lab results combined may cause variation up to + / -20 %.

[0138] However, most analysis and material balance calculations prove almost quantitative recovery of elements.

[0139] Material Balance Calculation on Total Solids (TS) was analyzed down to primary effluent and primary wet precipitate. It was calculated that 96.9% of TS of PDB, based on primary wet precipitate (Table 1 ). Variation was high due to the variable quality of tap water, which was remarkable. Table 1. Material balance based on wet precipitate

[0140] Conductance has the lowest practical limit at ca 0.3 mS / cm, typical for pure water.

[0141] If conductance was higher than 2 mS / cm the conductivity was found to be too high for optimal production of floc. Conductance is also related to pH and Ionic Strength.

[0142] Total Material Balance based on Total Solids (TS) was analyzed down to Total Effluent and Dry Precipitate. It was calculated that 87.1% of TS of PDB was recovered based on dry precipitate (Table 2). Recovery of ~87 % is lower than from wet precipitate (96.9%). Some amount of material is missing from analysis mainly due to the drying process of the precipitate.

[0143] Table 2. Material balance based on dry precipitate

[0144] Total Solids (TS) MATERIAL BALANCE Material Balances per Elements

[0145] The Material Balance calculations per elements and sulfate ion were based on precipitation process and expressed as percentage of recovery in dry precipitate. In this Step 1 , metals were removed out of BW purposely by precipitating them as metal hydroxides. This simple and cheap precipitation process leaves all sulfate ions in the effluent (Table 14).

[0146] Metals can be removed from BW as metal sulfides, but our main task was to demonstrate how to remove sulfates from BW. Reducing sulfates to sulfides did not allow us to prove that sulfates can be removed in Step 2 by the present Molecular Sieve Separation Method through the simulator. Therefore, we used hydroxide precipitation.

[0147] Material Balance of Copper (Cu)

[0148] Recovery of Copper into dry precipitate was 84.1 %. In spite of the possible analytical errors, which apply to any of these results, we can speculate that there is some Copper left in the effluent even if Not Detected (ND). (Table 3.)

[0149] There was also an exceptionally high amount of copper in the tap water (0.511 mg / L, Sample 11-1 ) used to initialize the Sulfate removal experiment.

[0150] The other reason for a relatively low recovery is an obvious absorption of copper hydroxide into the filter media.

[0151] Table 3. Material Balance of Copper Material Balance of Manganese (Mn)

[0152] Manganese was quantitatively recovered (102.0%). High recovery is obvious because almost all was left into the effluent as a soluble compound (Table 4).

[0153] Table 4. Material Balance of Manganese

[0154] Mn (Manganese) MATERIAL BALANCE

[0155] Material Balance of Aluminum (Al)

[0156] An abundant amount of aluminum was quantitatively recovered (103.6%) even if a small amount was left in the effluent. The wet precipitate gave a much lower recovery but was most probably due to a rapid settling and therefore a difficult sampling procedure (Table 5).

[0157] Table 5. Material Balance of Aluminum

[0158] Al (Aluminium) MATERIAL BALANCE Material Balance of Zinc (Zn)

[0159] Zinc is abundant in BW and only a residual amount (0.063 mg / L) was left in the effluent (Table 6).

[0160] Table 6. Material Balance of Zinc

[0161] Zn (Zinc) MATERIAL BALANCE

[0162] Material Balance of Iron (Fe)

[0163] Iron was quantitatively removed from effluent (ND) even it was not expected from solution having pH less than 8.0 (Table 7).

[0164] Table 7. Material Balance of Iron

[0165] Fe (Iron) MATERIAL BALANCE

[0166] Material Balance of Nickel (Ni)

[0167] Small concentration of Nickel in BW (5.96 mg / L) was also quantitatively removed from effluent (ND) (Table 8). Table 8. Material Balance of Nickel

[0168] Ni (Nickel) MATERIAL BALANCE

[0169] Material Balance of Cobalt (Co) Cobalt was enriched into dry precipitate (90.1 % recovered) leaving trace amount into effluent (0.02 mg / L) (Table 9).

[0170] Table 9. Material Balance of Cobalt

[0171] Co (Cobalt) MATERIAL BALANCE Material Balance of Radio Isotopes of Uranium

[0172] The concentration of Uranium in BWwas relatively high (2.16 mg / L) and according to the analysis was totally recovered into wet precipitate (111.9%). Uranium was not analyzed in dry precipitate, but was obviously recovered into dry precipitate due to a residual amount in the effluent (0.004 mg / L) (Table 10). Table 10. Material Balance of Radio Isotopes of Uranium

[0173] Material Balance of Calcium (Ca) Calcium hydroxide is soluble and will stay in the effluent (87 mg / L). There is also a lot of calcium in tap water (77 mg / L). Therefore, the recovery percentage (111.7 %) is more or less inaccurate (Table 11).

[0174] Table 11. Material Balance of Ca

[0175] Ca (Calcium) MATERIAL BALANCE

[0176] Material Balance of Magnesium (Mg)

[0177] The concentration of magnesium is high in BW (2900 mg / L) and will appear in the effluent (132 mg / L) at a distinctly higher concentration than in tap water (29 mg / L). Recovery of 102.4% proves the accuracy of the material balance within statistical errors (Table 12). Table 12. Material Balance of Magnesium

[0178] Mg (Magnesium) MATERIAL BALANCE

[0179] Material Balance of Sodium (Na) Almost all NaOH added as precipitant was found in the effluent. Some amount was found concentrated in dry precipitate. Recovery of 91.3% is lower than expected but fits within the limits of analytical errors (Table 13).

[0180] Table 13. Material Balance of Sodium

[0181] Na (Sodium) MATERIAL BALANCE

[0182] Material Balance of Sulfate

[0183] The concentration of the sulfate ion was the highest among the analyzed elements and ions in BW (36.700 mg / L). The analysis of sulfate appeared to be rather erroneous as well. In the two independent measurements of the parallel samples, the results were distinctly different having a difference of more than 15%. The cumulative error of 4 samples is seen in the too high recovery of 116.5%. This however reveals the opportunity to remove the sulfate ion from the effluent (1580 mg / L) and therefore from BW (36700 mg / L) in Step 2.

[0184] In the sense of material balance calculations, there is 734.000 mg of sulfate in BW and in the effluent 846.880 mg / L, thus at least all Sulfate was staying in the effluent for recovering in Step 2. (Table 14.)

[0185] Table 14. Material Balance of Sulfate

[0186] Step 2: Separation of Sulfate and Pure Water from Effluent of STEP 1

[0187] Figure 6 shows separation of sulfate from Mine Water (PDB) by Molecular Unique Separation Technology water purification apparatus 30.

[0188] Separation through A1 Reactor Cell

[0189] The molecular Sieve Separation Method is the most effective one when iron (Fe) is used as the positive electrode (A1 ). All the other parameters in the experiment were not optimized.

[0190] Water Balance

[0191] The Internal Loop, as described in Figure 6, dilutes the original BW (PDB) by a factor of ca 50 for appropriate removal of sulfate. However, the total recovery of PDB in volumes was considered as 100 %. The net outcome of volume is ca 18 L / 20 L or 90 % (in the first step). The rest of the volume (PDB) went with the dry precipitate. The net pure water of 39.4 L includes the net input of the volume of the flocculent (PO) and the losses are due to evaporation in the drying processes (7.3 I). The recovery of the input volumes is therefore 84.4 % (100x39.4 / 46.7) and the final dilution factor only 2.34.

[0192] Total Material Balance

[0193] Because there was no reliable sulfate measurement from floc, we used COD to calculate the material balance between input and output as shown in Table 15. COD value of 1700 mg / L was measured in the volume of 33 L of floc (PDB1WS) and 52 mg / L in the processed mixture of 1096.1 L of the Effluent (PDB1WX). The recovery of COD in the floc was 99.1 % and proves that the material balance in Step 2 is correct.

[0194] Material balance calculations per element were not carried out due to the quantitative metal removal in Step 1.

[0195] Table 15. Material Balance based on COD

[0196] Chemical Oxygen Demand (COD) MATERIAL BALANCE (PDB)

[0197] Material Balance of Sulfate

[0198] The clear effluent having high sulfate concentration (1580 mg / L) did not floc easily as is. Therefore, a small amount (2.4 % v / v) of hydrocarbons containing flocculation aid was added to the 1 :1 diluted effluent. By doing this we decreased conductance from 2.35 mS to 1.75 mS and increased pH from 7.5 to 8.0 (Figure 6).

[0199] This helped the formation of compact floc with accelerated speed upwards to the surface of the purified water. We also added (17 % v / v) a low concentration polymer solution into the flocculating mixture before it entered into the floc separator. The ratio of polymer solution to the mixture of sulfate (PDB1WX) was determined by the capacities of the pumps and the volumes in use rather than optimized processes.

[0200] However, a compact floc was separated from pure water (PDB1 WW) which had a very low concentration of sulfate (36 mg / L). Compared to PDB (36700 mg / L) the total reduction of the concentration of sulfate through Step 1 and Step 2 was therefore 99.9 %. (Table 16.)

[0201] When effluent was mixed (PDB1WX) for Molecular Sieve Separation, the reduction of 95.8 % of sulfate concentration was achieved. The material Balance of sulfate proved the reduction in total amounts of 93.9 % and 95.2 % of sulfate compared to the original (PDB) sample and dilution of Internal Loop (PDB1WX), respectively (Table 16).

[0202] Table 16. Material Balance of Sulfate

[0203] Energy Balance

[0204] Regarding the energy consumption we measured and estimated that the total electric power used in this 2-step process for sulfate removal was ca. 1 .5 kWh / m3 / 1 .0 kg of sulfate.

[0205] Preliminary laboratory protocol in one step for Mine Water (BW)

[0206] One Step Separation of Sulfate and Purified Water

[0207] Separation through A1 Reactor Cell The molecular Sieve Separation Method is the most effective one when iron (Fe) is used as the positive electrode (A1 ). All the other parameters in the experiment were not optimized. There are alternative cells for testing in the second trial to complete the protocol.

[0208] Water Balance

[0209] Another experiment was carried out in a small volume to reveal the potentiality to reduce the dilution factor of the Internal Loop from 50 to 2. The final dilution factor was 1 and the final recovery 91 % (100 x (18.2 / 20.0 L)). At the same time the sulfate reduction was studied. Figure 7 shows direct purification of Mine Water without precipitation as pretreatment.

[0210] In this last experiment the pooled BW (PDBP) was diluted 1 :1 with tap water and 10% of hydrocarbon containing flocculent (PO) was added to mix a sample for Molecular Sieve Separation through the water purification apparatus 30.

[0211] Total Material Balance

[0212] Material balances were calculated based on TDS and COD analysis. Both parameters were reduced to the same level of 92 %. (Tables 17 and 18) All the rest of the materials were collected into floc, but not analyzed.

[0213] Table 17. Material Balance based on TDS

[0214] Total Dissolved Solids (TDS) MATERIAL BALANCE Table 18. Material Balance based on COD

[0215] Total Dissolved Solids (TPS) MATERIAL BALANCE

[0216] Reductions of Elements

[0217] Cobalt and nickel were reduced from 92 to 93 % and Cu, Al, Fe and Zn up to ca.

[0218] 99.6 % (Tables 19-24). However, the residual concentrations left in the purified water were distinctly higher when using the larger Internal Loop described above.

[0219] Reduction of Copper 99.5 %

[0220] Reduction of copper was 99.5 % even with the residual concentration of 0.2 mg / l, but less than in tap water (0.5 mg / l).

[0221] Table 19. Material Balance of Copper

[0222] Reduction of Aluminum 99.6 %

[0223] A trace amount of aluminum was left in purified water (2.8 mg / l), but somewhat bigger than in the effluent after precipitation in Step 1 even if the reduction was 99.6 %. Table 20. Material Balance of Aluminum

[0224] Al (Aluminum) MATERIAL BALANCE

[0225] Reduction of Cobalt 92.3 % The direct separation through the cell left 10 times more cobalt in the purified water (0.3 mg / l) than the chemical precipitation 0.02 mg / l).

[0226] Table 21. Material Balance of Cobalt

[0227] Co (Cobalt) MATERIAL BALANCE Reduction of Iron 99.6 %

[0228] Reduction of iron left 1 ,1 mg / l in the purified water; a remarkably low concentration that does not need of any further removal by oxidation. Table 22. Material Balance of Iron

[0229] Fe (Iron) MATERIAL BALANCE Reduction of Nickel 93.0 %

[0230] Nickel is in small concentration in pooled mine water with a tiny amount left in the purified water (0.2 mg / l). The effluent after chemical precipitation had no detectable amount of nickel.

[0231] Table 23. Material Balance of Nickel

[0232] Ni (Nickel) MATERIAL BALANCE

[0233] Reduction of Zinc 97.8 %

[0234] In spite of high reduction, some zinc was left in the purified water, but this quantity will be removed in the second cell of the cascade if used.

[0235] Table 24. Material Balance of Zinc 97.8 %

[0236] Zn (Zinc) MATERIAL BALANCE

[0237] Material Balance of Sulfate 95.8 %

[0238] Reduction of sulfate from this highly concentrated mixture of pooled BW (the calculated concentration of sulfate was ca. 20700 mg / L in dilution) was 95.8 % down to the level of 1730 mg / L. Compared to the original concentration of sulfate of 41400 mg / L. (Table 25.) Introducing this purified water (PDB2W) through the second cell of the cascade we could expect to reduce sulfate from 1730 mg / L down to the same level or less than 40 mg / L as in the first trial. Almost the same concentration of sulfate in the Effluent (1580 mg / L) was achieved after the precipitation in Step 1. This means that the total dilution factor in the first Internal Loop is less than 3 instead of ca. 50.

[0239] Due to the recycling of the purified water, there is no total dilution effect regarding the first cell of the cascade, and less than 10 % of the purified water is lost with the floc. In the second cell of the cascade the dilution factor could be less than two.

[0240] Table 25. Reduction of Sulfate 95.8 %

[0241] The Energy Balance

[0242] Regarding the energy consumption we measured and estimated that the total electric power used could be almost the same in this cascade sulfate removal process, as it was in the two-step approach with chemical precipitation ca. 1.5 kWh / m3 / 1 .0 kg of sulfates.

[0243] Preliminary laboratory protocol for another mine water (SW)

[0244] A screening process was carried out for SW, too. It indicated that the sulfate reduction behaves in the same way as PDB did. A more comprehensive testing with larger volumes than in the preliminary trial will be commenced to create the final protocol for Sulfate removal of SW.

[0245] Conclusion

[0246] The two alternative processes in the preliminary study were:

[0247] 1 ) Precipitation as pretreatment and use of large Internal Loop or

[0248] 2) The small Internal Loop and the cascade in two steps. Reduction of Sulfate from Mine Water at the level of 99.9 % in concentration in the first alternative is in accordance with the other protocols for wastewater purifications. The reduction of sulfate from production water of oil drilling was 100 % and from pulp process water 99.5 % (from 1900 mg / L to 8.9 mg / L), par example.

[0249] In the second alternative the reduction of sulfate was 95.8% and the expected reduction after the second step in cascade 99.9%. This allows the total recycling of the purified water in both Internal Loops with no need to increase water from outside of the purification process.

[0250] The energy consumption and other operating related expenses seemed to be reasonable and competitive.

Claims

Claims1. A method for purifying acidic wastewater from a mining process, the method comprising-providing acidic wastewater form a mining process (10), -pretreating (12) the acidic wastewater to obtain pretreated wastewater (16) having:• total solids in the range of 0-3% by weight,• pH in the range of 6.0-9.0, such as pH in the range of 7.0-8.8, for example about 8.3,• conductivity in the range of 0.3-3.0 mS / cm, such as 0.3-2.5 mS / cm, and• temperature in the range of 0-99.9°C,-providing a water purification apparatus (30) comprising• an electrolytic cell (14) comprising a substantially vertical tube connected to a source of DC electric power (13) and comprising one or more first electrode(s) (32) comprising one or more iron and / or aluminum electrode(s), and one or more inert second electrode(s) (34) having a higher electronegativity compared to the first electrode(s), and• a substantially vertical separator tower (20) arranged in a flow connection with the upper part of the electrolytic cell (14),-applying the pretreated wastewater (16) to the electrolytic cell (14),-operating the electrolytic cell (14) to produce iron hydroxide and / or aluminum hydroxide (3) acting as molecular sieve capable of trapping impurities, such as comprising sulphates and any remaining solids, and to produce hydrogen causing the molecular sieve with the trapped impurities to raise in the vertical tube as an accumulating floc,-conveying the raising floc into the separator tower (20), wherein the floc (19) is separated by expelling from the top of the separator tower (15), and-obtaining first purified water (W1 ) from the separator tower (20) at a point below the raising and / or expelled floc.

2. The method of claim 1 , wherein the pretreating (12) comprises adjusting the pH of the acidic wastewater with NaOH.

3. The method of claim 1 or 2, wherein the pretreating (12) comprises precipitating solids, preferably as metal hydroxides, and / or filtering.

4. The method of any of preceding claims, wherein the pretreating (12) comprises diluting the wastewater.

5. The method of any of preceding claims, comprising treating the recovered first purified water (W1 ) by oxidizing iron and removing oxidized iron to obtain second purified water (W2).

6. The method of any of preceding claims, comprising using the first purified water (18, W1) and / or the second purified water (W2) as washing water and / or as diluent.

7. The method of claim 5 or 6, comprising using the second purified water (W2) as influent water (22a) for applying to the electrolytic cell.

8. The method of any of preceding claims, comprising adding one or more polyelectrolytic polymers (22c) to the formed floc to stabilize the floc, preferably after the electrolytic cell (14) and / or before the separator tower (20).

9. The method of any of preceding claims, wherein the acidic wastewater from a mining process has a pH of 5 or less, and / or a sulphate content of 50 g SO427I or less.

10. A water purification apparatus (30) for purifying acidic wastewater from a mining process, the water purification apparatus comprising-an electrolytic cell (14) comprising a substantially vertical tube connected to a source of DC electric power (13) and comprising• one or more first electrode(s) (32) comprising one or more iron and / or aluminum electrode(s), preferably in a form of cylinder(s), and• one or more inert second electrode(s) (34) having a higher electronegativity compared to the first electrode(s), preferably in a form of cylinder(s) inside the cylinder(s) of the one or more first electrode(s),-a substantially vertical separator tower (20) arranged in a flow connection with the upper part of the electrolytic cell (14),-a source of pretreated wastewater (16) obtained from a pretreatment step (12), such as from a pretreatment system, of acidic wastewater (10) from a mining process, the source of pretreated wastewater (16) being arranged to be conveyed to the electrolytic cell (14),-an outlet (15) for expelled floc (19) at the top of the separator tower (20),-an outlet (18) for first purified water (W1 ) at a lower part of the separator tower (20), preferably at a lower position than the outlet (15) for expelled floc (19), -an electronic controlling means (24), such as an electronic control unit,-one or more means for controlling the flow of liquids in the apparatus (22a,b,c,d,e,f,g,h,i), such as one or more controllable pumps and / or valves, the means being operatively connected to the electronic controlling means (24), -preferably one or more sensors for detecting pH, temperature, and / or conductivity connected to the electronic controlling means, wherein the electronic controlling means (24) is arranged to control the source of DC electric power (13) applied to the electrolytic cell (14) and preferably the one or more means for controlling the flow of one or more liquids in the apparatus (22a,b,c,d,e,f,g,h,i).11 . The method of any of claims 1-9 or the water purification apparatus of claim 10, wherein the water purification apparatus comprises an iron oxidizing device (17), wherein the first purified water (W1 ) is arranged to be conveyed to the iron oxidizing device (17) to oxidize and to separate iron from the first purified water (W1 ) to obtain second purified water (W2), preferably the iron oxidizing device (17) comprising an outlet (23) for the second purified water (W2).

12. The method of claim 11 or the water purification apparatus of claim 11 , wherein part of the second purified water (W2) is arranged to be controllably conveyed as influent water (22a) to the electrolytic cell (14).

13. The method of any of claims 1-9 or the water purification apparatus of any of claims 10-12, wherein the electronic controlling means (24) is arranged to control the flow and / or dosing of liquids in the apparatus selected from one or more of-incoming pretreated wastewater (16) from a mining process, -outcoming separated floc (19) from the separator tower, -outcoming first purified water from the separator tower,-outcoming first purified water (W1 ) from the separator tower to washing of the floc (19) expelled from the separator tower (20),-outcoming first purified water (18, W1 ) to the iron oxidizing device (17) of claim 10,-outcoming first purified water (18, W1) as dilution water to pretreatment (12), -outcoming second purified water (W2) from the iron oxidizing device (17) as dilution water to pretreatment (12), and-outcoming second purified water (W2) from the iron oxidizing device (17) as influent water (22a) to the electrolytic cell (14) of claim 12, preferably wherein the electronic controlling means (24) is arranged to control the flow of liquids in the apparatus to carry out the method of any of claims 1-9.

14. The method of any of claims 1-9 or the water purification apparatus of any of claims 10-13, wherein the one or more inert second electrode(s) (34) comprise precious metal, such as platinum, and / or stainless steel, nickel, chromium, or an alloy thereof.

15. The method of any of claims 1-9 or the water purification apparatus of any of claims 10-14, wherein the one or more inert second electrode(s) (34) comprise a plurality of apertures causing jetting water from the apertures during the operation of the electrolytic cell.

16. The water purification apparatus of any of claims 10-15, wherein the electronic controlling means (24) is connected to means, such as one or more sensors, for detecting from incoming wastewater from the pretreatment step (16) one or more of conditions:-total solids in the range of 0-3% by weight,-pH in the range of 6.0-9.0, such as pH in the range of 7.0-8.8, for example about 8.3,-conductivity in the range of 0.3-3.0 mS / cm, and-temperature in the range of 0-99.9°C, wherein the electronic controlling means (24) is arranged to convey the incoming wastewater (12) as pretreated wastewater to the electrolytic cell (14) only if the conditions are fulfilled.

17. The water purification apparatus of any of claims 10-16, wherein the first purified water (W1 ) and / or the second purified water (W2) is arranged to be conveyed to the pretreatment step (12) of the acidic wastewater (10) to dilute the acidic wastewater, preferably to obtain conductivity in the range of 0.3-3.0 mS / cm.

18. The water purification apparatus of any of claims 10-17, wherein the electronic controlling means (24) is connected to means for providing first purified water (W1 ) and / or to means for providing second purified water (W2) as diluent water to the pretreatment step (12) of acidic wastewater (10) and arranged to control the flow and / or dosing of the first purified water (W1 ) and / or the flow of thesecond purified water (W2) to obtain conductivity in the range of 0.3-3.0 mS / cm in the diluted acidic wastewater, preferably to obtain pretreated wastewater (16).

19. Use of the water purification apparatus (30) of any of claims 10-18 for purifying acidic wastewater from a mining process, preferably with the method of any of claims 1-9.

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