WO2011151484A1

WO2011151484A1 - System for the neutralisation of acid mine water and the recovery of the metal load therefrom

Info

Publication number: WO2011151484A1
Application number: PCT/ES2011/000173
Authority: WO
Inventors: José Manuel ANDUJAR MARQUEZ; José Antonio GRANDE GIL
Original assignee: Universidad De Huelva
Priority date: 2010-06-02
Filing date: 2011-06-01
Publication date: 2011-12-08
Also published as: ES2372246A1; ES2372246B1

Abstract

The invention relates to a system for the neutralisation of acid mine water and the recovery of the metal load therefrom, consisting in harnessing renewable energy in order to evaporate the acid water originating from the mine and recover the dehydrated mineral. The invention comprises at least (i) first energy generating means (18, 19, 20, 21); and (ii) second evaporator means (1, 3, 4, 5, 6, 7) for evaporating the water contaminated with AMD (2).

Description

SYSTEM FOR THE NEUTRALIZATION OF MINE ACID WATER AND RECOVERY OF ITS METAL LOAD

DESCRIPTION

The main object of the present invention is a system and a procedure for the neutralization of acidic waters from the mines and the recovery of their metallic charge, by means of energy obtained from renewable sources.

STATE OF THE PREVIOUS TECHNIQUE

Of all the causes of pollution of river courses, perhaps the acid mine drainage, AMD, is one of the most serious, due to its nature, extent and difficulty of resolution. The rivers affected by this type of pollution are characterized by their acidity, as well as the high sulfate and heavy metal content of their waters.

This type of contamination originates when a sulphurous mineral comes into contact with oxygen and atmospheric moisture; on the surface of the mineral begins a complex mechanism that begins with the oxidation of sulfides, very insoluble, transforming them into sulfates with acid production. The kinetics of this oxygen oxidation is very slow, between 1.08.10-15 to 1.8. 10-14 mol / (cm2. S), being able to increase its speed up to one hundred times by the presence of ferric ion and by the action of catalytic bacteria. Together with the oxidation of pyrite, finally, secondary reactions occur between the products of the previous reactions and the remaining minerals present in the rock, the final result being a set of soluble pollutants deposited on the mineral, which are subsequently dissolved and dragged by rainwater or runoff, producing a polluting liquid flow that takes its acidity, sulfates and heavy metals to the water courses. Contamination of metallic origin in aquatic environments has very high chances of occurrence, since of the 106 known elements, 84 are classified as metals. Within these 84 metals, those whose specific weight is greater than 4 or 5 g / cm3 are considered heavy metals, the most common being iron, copper, zinc, lead, manganese, chromium, nickel, arsenic, mercury and cadmium. The toxicity of certain heavy metals at certain concentrations has caused numerous incidents. Heavy metal contamination of a water is serious based on three fundamental reasons:

a) Unlike organic matter, heavy metals are not biodegradable, so they remain in the contaminated environment indefinitely, except for transport processes to other media.

b) Heavy metals, once the microorganisms and the microflora incorporate them, can be retained by the tissues of the organism, producing the phenomenon of bioaccumulation. Thus, in filter organisms, concentration factors of 290,000 have been found for zinc, 100,000 for lead, 35,000 for copper and 500 and 100 for chromium and nickel respectively. The accumulated metals can be transmitted to other species located at a higher level of the trophic chain, producing the phenomenon known as biomagnification. Through bioaccumulation and biomagnification, much higher values are achieved than those found in the liquid medium.

c) Heavy metals, from the point of view of their influence on animal physiology, can be classified as essential and non-essential; Thus, certain heavy metals such as copper, zinc and manganese are essential micronutrients for plants and animals, and only become lethal in high concentrations. The organism needs them within an optimal range, below which deficiency states occur and toxicity above. Similarly, non-essential heavy metals have a value for each individual, below which it is tolerable and above toxic. The entry into force of regulations governing the chemical composition of mining spills has caused severe restrictions for mining companies that have resulted in millionaire restoration costs and have caused the closure of numerous sulphide farms. Of more than one hundred open mines in the Southwest of the Iberian Peninsula in the middle of the last century, there were barely three in operation at the end of it. On the other hand, the current price of copper, in clear process of increase, caused, in large part, by the great demand from Asian countries, is allowing, under severe restrictions, and with high costs of prevention and restoration of water pollution, the expected resurgence of metal mining in Europe.

The preventive and corrective techniques that are summarized are being used in different facilities, there is no common pattern, and depending on the choice of each correction system of different factors such as, requirements imposed by national, regional and local regulations, type of mineral, size of the holdings, flow and chemical composition of the effluent to be treated.

Techniques used as preventive measures include barrier methods, chemical methods and bacterial inhibition methods, all of them conducive to water pollution.

Once the water is contaminated, the techniques most frequently used as corrective measures to remedy or alleviate the process are, among others, chemical neutralization plants, neutralization with uncontaminated water, reverse osmosis, ion exchange, treatments biological and in marshes, anoxic limestone traps, bioleaching of debris, electrocoagulation, and a host of variants and combinations of the above. The common denominator of all of them can be summed up in a high cost of installation and maintenance, in the case of those that really achieve as a final result a water of discharge that complies with the regulations, or a low yield for others, cheaper, that cause spills with undesirable residual contaminants.

EXPLANATION OF THE INVENTION To avoid the problems described, the system and method for the neutralization of acid mine waters and metal charge recovery has been developed, object of the present invention and which is of the type that consists of harnessing a renewable energy to evaporate acidic water from the mine and recover the dried ore, and which comprises at least

(i) first means of generating renewable energy; Y

(ii) second evaporating means of water contaminated by AMD and extraction of its metallic charge, and characterized in that (a) it comprises a mainland evaporator of water contaminated by AMD until it is brought to its boiling point, for which a heater through which a high temperature thermal fluid passes through said fluid coming from the first means of power generation and a plurality of ejectors or vacuum pumps configured to lower the boiling point of acidic water by generating vacuum inside the evaporator; and (b) once the water contaminated by AMD becomes steam, all the polluting materials that were dissolved in it precipitate to the bottom of the evaporator, being moved by a stirrer; and because when the level of the deposited material reaches a height predetermined by the plant's own operation, a sliding gate operated by a motor slides at the bottom of the evaporator, which allows the evaporator to be emptied with a closed filling valve; and where once the evaporator has been emptied, the gate closes, the valve opens and a new fill-evaporation-empty cycle begins. Throughout the description and the claims the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in the art, other objects, advantages and features of the invention will be derived partly from the description and partly from the practice of the invention. The following examples and drawings are provided by way of illustration, and are not intended to be limiting of the present invention. In addition, the present invention covers all possible combinations of particular and preferred embodiments indicated herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a scheme of principle of one of the modules (the others up to the necessary number N - depending on the treatment flow - of the installation would be all similar) that form the acid mine neutralization plant and recovery of its metallic load .

FIG. 2 shows a field of renewable energy utilization systems, solar energy, that provide the necessary electrical energy for the systems that need it present in the scheme of FIG.l.

DETAILED EXHIBITION OF EMBODIMENTS AND EXAMPLES

The object of the invention is to take advantage of renewable energy, such as solar energy, to evaporate acidic water from the mine and recover the dried ore. A diagram of the principle of one of the modules is shown in Figure 1 (the others up to the necessary N number - depending on the treatment flow - of the installation would be all similar) that form the acid mine and recovery water neutralization plant of its metallic load. The process consists of heating in an evaporator (1) the water contaminated by AMD (2) until it is brought to its boiling point, for which a heater (3) is used, through which a thermal fluid flows at a high temperature (approx. 400 ° C). The boiling point of acidic water can be drastically lowered (up to around 40 ° C) by vacuuming inside the evaporator (1); for this, steam ejectors or vacuum pumps can be used (not drawn in the scheme in Figure 1).

Once the water contaminated by AMD becomes steam, all the polluting materials that were dissolved in it precipitate to the bottom (4) of the evaporator (1). In order that the precipitated material is not caked, the evaporator (1) has inside it an agitator (5) moved by a motor. When the level of the deposited material reaches a height predetermined by the plant's own operation, at the bottom of the evaporator (1) a sliding gate driven by a motor (6) slides, which allows the emptying of the evaporator (1) . If necessary - not drawn in Figure 1- the evaporator base can be equipped with a shake table driven by an eccentric cam, the shaking movement being initiated at the time of opening to favor the fall of the decanted material outwards of the evaporator (1). During the process of emptying it, the filling valve (7) must be closed. Once the evaporator is empty, the gate (6) closes, the valve (7) opens and a new cycle begins.

In general, a complete installation will consist of N evaporators analogous to that described and schematized in Figure 1, so that the processes of filling with water contaminated by AMD and emptying of the materials dissolved in them, will be done in a synchronized manner, in order to that there are no waiting times; for this, the appropriate control system will be implemented.

The contaminants extracted from each of the N evaporators go to a conveyor belt (8) that runs through them everybody. This is continuously depositing the transported material (9) to the trays or containers enabled for it (10). Regarding the steam produced (11), it has 3 fundamental tasks. The greatest amount of steam will go, through a condenser (12) and already liquefied, to a cooling tower (13) for cooling. This cooled and clean water will go, in a small part to feed (14) the condenser and, to a large extent, to the pipe (15) that feeds the channel or channels of the environment. The second task of the steam produced will be to generate a steam line, of adequate pressure, for the entire installation (16). The last task of the steam generated will be that a small part of it is injected (17) into the evaporator jacket (this must have been built with this characteristic), which will cause it to preheat and, as a consequence, greater energy efficiency of process . The possible unwanted "drag" of particulate matter potentially transported by the steam at the exit of each evaporator, can be collected in a siphon or other element retaining particles before being incorporated into the steam circuits.

In order to make the entire process completely renewable and clean, the energy necessary for the heater (3) to raise the temperature of the water contaminated by AMD (2) to its boiling point, will be obtained according to the following practical examples.

Example 1: the system works only by day and is 100% renewable.

In this case there is a field of parabolic trough reflectors (18) in number M according to the energy needs of the installation. The main components of the parabolic trough reflector are: the specular surface (19) The parabolic cylinder is achieved through films of silver or aluminum deposited on a support that gives it sufficient rigidity. This surface reflects the sun's rays on an absorber tube (20) by heating it. The absorber tube consists of two concentric tubes separated by a vacuum layer. The interior, through which the thermal fluid that is heated (an oil for example) circulates, is metallic, and the exterior is glass. In order to optimize the operation of the parabolic cylinder so that it is always facing the sun along its horizon, the system consists of a solar tracker (21), a device that rotates the parabolic trough reflectors of the collector around A shaft Finally, the mechanical structure (22) of the collector is intended to stiffen the set of elements that compose it.

In daytime operation the valves (23) are closed and the recirculation of the thermal fluid occurs through the parabolic cylinder reflector, so that the heated fluid (up to 400 ° C) is driven by a pump (25) to the heater ( 3) to cause the boiling of water contaminated by AMD. The cooled fluid (26) returns, by driving a pump (27) to the parabolic trough reflector to be heated again. The circuit also includes an expansion vessel (28) in order to absorb the dilations and changes in volumes that originate, so that they are not created on pressures.

Example 2: the system works day and night continuously and is 100% renewable.

During the day the process is already described, however, when sunlight falls from a certain level, the thermal fluid no longer reaches the proper temperature, which prevents the passage to the parabolic trough reflector (closing the valves ( 29)) and is forced, by opening the valves (23), to circulate through an electric heater (30). This heater can be external to the evaporator (1) or internal, concentric with the one that houses (3) the thermal fluid. Of course, in order to make the system renewable, the necessary electrical energy is also generated in a clean and non-polluting way. The procedure to do this is explained in Figure 2.

Figure 2 shows a field of solar panels that, during the day, provides the necessary electrical energy for the systems that need it present in the scheme of Figure 1 (depending on the degree of automation given to the plant, they will be fundamentally instrumentation and control systems, as well as motors and pumps). In addition to the above, the panel field feeds an electrolyzer, which generates hydrogen from water and is stored in a tank. During the day, the steam from the installation circuit (16 in Figure 1) feeds a turbine that, together with the panels, generates electrical energy in a non-polluting way. In the event that the electricity generated is greater than that demanded by the installation, it can be sold to the electricity grid.

During the night, when solar panels and parabolic trough reflectors do not work, the hydrogen generated during the day serves to fuel a high temperature fuel cell (> 400 ° C). This generates electricity by hydrogen without producing polluting waste and, the exothermic reaction it produces, allows cogeneration, which feeds the steam line that moves the turbine.

The battery bank (Figure 2) is a backup system only, in order to maintain critical systems in the event of any failure and guarantee the necessary electrical energy to start the battery (its electromechanical systems), since when it is running it supplies itself . Example 3: the system works day or night and is partly renewable.

The circumstance may arise that, depending on the type of operation or the needs of the operating company, the possibility of installing a mixed renewable system / power grid or with a support boiler fueled by any fuel is considered. In this case the scheme in Figure 1 would be maintained in its entirety. However, in Figure 2 they would no longer be: solar panel field, electrolyser, hydrogen tank and fuel cell. That is, the energy needs of the plant during the day and night (greater, since the field of parabolic trough reflectors does not work) should be met by connection to the power grid or by own means, such as a boiler that generates Enough steam to move a turbine.

Claims

1. - System for neutralization of acidic mine waters and recovery of metallic cargo of the type that consists of using renewable energy to evaporate acidic water from the mine and recover the dried ore, and which comprises at least (i) first means of power generation; and (ii) second evaporating means of water contaminated by AMD and characterized in that

(a) comprises an evaporator (1) continent of the water contaminated by AMD (2) until it is brought to its boiling point, for which a heater (3) is used, through which a thermal fluid flows at a high temperature, said fluid coming from the first means of power generation (18,19,20,21); and a plurality of ejectors or vacuum pumps configured to lower the boiling point of acidic water by generating vacuum inside the evaporator (1);

(b) and where once the water contaminated by AMD becomes steam, all the polluting materials that were dissolved in it precipitate to the bottom (4) of the evaporator (1), being moved by an agitator (5); and because when the level of the deposited material reaches a height predetermined by the plant's own operation, at the bottom of the evaporator (1) a sliding gate operated by a motor (6) slides, which allows the emptying of the evaporator ( 1) with a filling valve (7) closed;

and where once the evaporator (1) has been emptied, the gate (6) is closed, the valve (7) is opened and a new filling-evaporation-emptying cycle begins.

2. - System according to claim 1 characterized in that the base of the evaporator (1) comprises a shaking table driven by an eccentric cam, the shaking movement being initiated at the time of opening to favor the fall of the decanted material towards out of evaporator

3. - System according to claims 1 and 2 characterized in that it comprises a plurality of evaporators (1) where the processes of filling with water contaminated by AMD and emptying of the materials dissolved therein, will be done in a synchronized manner, with so that there are no waiting times.

4. - System according to the preceding claims characterized in that the contaminants extracted from each of the evaporators go to a conveyor belt (8) that runs all of them, and where it continuously deposits the transported material ( 9) to the buckets or containers enabled for it (10).

5. - System according to the preceding claims characterized in that the steam produced (11) will go, through a condenser (12) and already liquefied, to a cooling tower (13) for cooling, where this water is cooled and clean will go, in part to feed the condenser (14) and, in part, to the pipe (15) that feeds the channel or channels of the environment.

6. System according to the preceding claims characterized in that the steam produced (11) will go to a steam line, of adequate pressure, for the entire installation (16).

7. System according to the preceding claims characterized in that the steam produced (11) will be injected (17) into the evaporator jacket (1), which will cause it to preheat.

8. System according to the preceding claims characterized in that the possible "unwanted" dragging of particulate matter potentially transported by the steam (11) of water at the exit of each evaporator (1) _{/ they} are collected in a siphon or other element retaining particles before they are incorporated into the steam circuits (12,16,17).

9. - System according to the preceding claims characterized in that the first means of power generation comprise a field of parabolic trough reflectors (18) in number M, at least one for each evaporator (1).

10. - System according to the preceding claims characterized in that when sunlight falls from a certain level, the thermal fluid no longer reaches the appropriate temperature, thereby preventing the passage to the parabolic trough reflector (19), closing the valves (29) and being forced, opening the valves (23), to circulate through an electric heater (30) powered by renewable energy.

11. - Procedure for neutralization of acidic mine waters and recovery of metallic cargo of the type that consists of using renewable energy to evaporate acidic water from the mine and recover the dried ore, implemented in the system of claims 1 to 10 characterized in that it comprises the stages of

(i) heating in an evaporator (1) the water contaminated by AMD (2) until it is brought to its boiling point, for which a heater (3) is used, through which a thermal fluid from a means of generating energy (18,19,20,21);

(ii) drastically lower the boiling point of acidic water (2) by vacuuming inside the evaporator (1); for this, steam ejectors or vacuum pumps can be used;

(iii) once the water contaminated by AMD becomes steam, all the polluting materials that were dissolved in it they precipitate at the bottom (4) of the evaporator (1), stirring to avoid caking, so that when the level of the deposited material reaches a height predetermined by the plant's own operation, at the bottom of the evaporator (1) a sliding gate is driven by a motor (6), which allows the emptying of the evaporator (1); Y

(iv) where once the evaporator is empty, the gate (6) closes, the valve (7) opens and a new fill-evaporation-emptying cycle begins.