Patent Application
20190169709
The present invention relates to a process for the depression of iron sulphides and other disposable elements, mainly although not exclusively pyrite, in the concentration of mineral by flotation. Likewise, it relates to an electrochemical reactor.
Said process, as well as the reactor, replace, minimise, optimise or compliment the use of depressants and other chemical reagents during the depression of iron sulphides and other disposable elements such as arsenic, antimony, bismuth, mercury and lead. This invention is particularly relevant to the flotation of sulphide minerals of all types.
The field of the invention mainly applies to nickel, copper, zinc and lead ores.
Flotation is used to concentrate or separate mineral species through the selective adhesion of mineral particles of each species to air bubbles. These bubbles float up to the surface of the liquid, forming foam that is collected as the product of said process. The adhesion of the particles to the bubbles happens mainly as a function of the hydrophobicity of the mineral surface. The most hydrophobic particles tend to adhere to the bubbles, thereby floating, while the more hydrophilic ones tend to get surrounded by liquid, thereby being depressed. To modulate the hydrophobicity and consequent flotation of the different mineral species, typically, chemical reagents are added, such as collectors, depressors, activators, inhibitors, foaming agents or modifiers [11].
In the flotation of sulphides, for example nickel, copper, zinc and lead ores, a main objective of concentrating the mineral/s of interest consists of the selective depression of pyrite (sulphur and iron mineral), as trading iron is rarely profitable. In addition, pyrite and other sulphides can be associated with or contain elements that are of no interest or that are harmful, which can be penalised at a commercial level, such as arsenic, antimony, bismuth, mercury and lead. Therefore, upon eliminating/reducing said elements from the concentrate, the penalties for said elements can be reduced. Usually, the depression of pyrite and other sulphides to be discarded is achieved by modifying the pH by means of the addition of chemical depressants, typically cyanide or sodium metabisulphite [10].
Several ways of depressing pyrite have been devised. The main methods are as follows:
Even though these are used at an industrial level in the plants for concentration of minerals by flotation, the conventional methods for the depression of pyrite and other sulphides through the addition of chemical depressants have several disadvantages. Firstly, these entail relatively high costs of consumables, as well as of the water treatment process in order to clean and adapt it for reutilisation in the flotation circuits. Moreover, the use of certain depressants such as cyanide is increasingly restricted, due to its toxicity and associated environmental risk [9].
The process object of the present invention entails a great advantage compared to the conventional methods, given that it makes it possible to save on chemical reagents, which currently represent a significant cost. Specifically, the proposed process and reactor represent an electrochemical method for the depression of pyrite and other disposable sulphides, which does not necessarily employ chemical depressants.
The choice of electric potential enables any potential value to be use, unlike with chemical reagents, which are limited to discrete potential values. In addition, it enables the pH and the electrochemical potential to be independently varied, not just at a macro level but also at a local level. Consequently, this process enables a higher specificity in the depression action, increasing the resolution in the differential flotation between the minerals of interest and the unwanted sulphides. Therefore, it enables the grade-recovery relationship of the metals of interest to be optimised, offering greater benefits starting from the same input ore. Furthermore, not only is the treatment of the minerals introduced into the plant optimised; but the improvement in the quality of the concentrate can entail the reclassification of certain minerals, previously considered sterile due to not making the quality cut, resulting in the in-plant treatment of minerals that would otherwise be discarded. On the one hand, this could entail important savings, as less mineral would be moved to generate the same product; on the other hand, this could simplify the logistics of the mine, due to the fact it is no longer necessary to avoid or blast and discard certain areas that are currently considered sterile. Likewise, the blending of better and worse concentrates in order to obtain certain quality levels could be prevented or minimised.
Another advantage is the speed in changing the electric potential, which enables a fast response (virtually instantaneous) by the flotation process control system, which is relatively slow (typically minutes or hours) in the current system, as it depends on the concentration and flow of chemical reagents, which can remain recirculating in the system during relatively long periods of time.
Likewise, this process allows for a greater versatility in the flotation circuits, given that the process water is not chemically conditioned as it currently is, it being possible to vary the flotation conditions with greater ease in a modular manner, within the same circuit, line or treatment plant.
The present invention concerns a process according to claim 1, and an electrochemical reactor, according to claim 13, for the depression of iron sulphides and other disposable elements, mainly although not exclusively pyrite, in the concentration of mineral by flotation, which replaces, minimises, optimises or compliments the use of depressants and other chemical reagents. This invention is particularly relevant for the flotation of sulphide minerals of all types.
The process is based on the application of electric potential by at least one electrode, in order to simulate the electrochemical effect that the chemical depressants and other reagents have on the mineral particles. Therefore, through direct contact between the electrode and mineral particles, altering the surface of the mineral that are to be depressed is attained, such that it's hydrophilic character is increased, thus preventing the adhesion thereof to the bubbles, resulting in the depression thereof. This is an electrochemical alteration of the surface of the mineral particles, for which reason it translates into an improved selectivity in the separation by flotation. It does not, however, refer to electrostatically attracting towards the electrode(s) or repulsing from the electrodes the mineral particles (or mineral-bubble complexes).
As mentioned, the process consists of the application of potential, by means of a working electrode, in situ or ex situ, directly or indirectly, on the mineral particles in the pulp. Said application requires either direct contact between the electrode and the mineral, which is more likely to happen if the particles are in movement, for example by stirring, or by the transference of potential by means of electrochemical mediators.
In the process, which is typically electrolytic, although it can also be galvanic, the working electrode is polarised to certain potential values. These values are chosen in order to condition the surface of the pyrite species or other sulphides to be discarded, with the aim of increasing the hydrophilic character of said surface. Typically, the intention is to catalyse the selective formation of hydroxides on the surface of the pyrite. For which reason, the potential of choice is usually positive; the working electrode acts as an anode. Furthermore, said potential would typically lie below the potential of electrolysis of water, so that bubbles are not generated on the surface of the electrode and the pH does not change. It is worth mentioning that the application of potential is a pH-independent variable, at least at the macro level (although it would be possible to modify the pH at a macro level, any changes in pH would typically occur at a local level), which enables a higher resolution in the differential flotation of the minerals in question. The altering of the pH at the local level can be carried out by using the potential(s) necessary for generating or consuming hydroxyl protons/ions, e.g. acidification of the medium as a consequence of water hydrolysis, upon generating protons. Said pH alteration occurs in the local surroundings of the electrode, without affecting the pH of the general medium, when the influence of the electrochemical reactions carried out by the electrode is limited, in relation to those determining parameters, such as relatively high volumes and flows and/or relatively short residence times, which mask the pH changes generated by the electrode(s). It is most normal for the pH to be altered at the local level. However, altering the pH would be possible at a macro/general level, upon the electrochemical reactions carried out by the electrodes having an important influence on the pH of the medium, in relation to determining parameters, such as relatively low volumes and flows and/or relatively long residence times, which allow for extending, at the macro level, the changes in pH originally generated at the local level in the surface of the electrode(s).
The process is based on the use of an electrochemical cell in the mineral pulp circuit, at any point thereof, be it in the flotation cells or in conditioning or passing tanks or pipes upstream of, downstream of or intercalated in the process, whether pre-existing or added.
The electrochemical reactor may take any form, from a simple reactor with two parallel, flat electrodes, to more complex apparatus, such as column, packed bed and/or multi-tubular reactors, and/or that constitute or take advantage of at least part of the elements of the mineral treatment line, such as, for example, the flotation cells, containers or passages of pulp and mills, including any structure or element in the plant or line/circuit of treatment, the electrodes (at least partially) being submerged in liquid/pulp (at least while they are in operation). For example, the following may be coated and/or used as electrode/s: deflectors, pipes, passages, conditioning tanks, thickeners/cyclones, air or mineral dispersers, stirrers, false floors, sieves/filters, linings or elements of the mills such as the balls and rods.
The electrodes may be made of any conductor or semiconductor material, and they can be treated, for example, in order to modify the affinity with the pulp and/or mineral species and/or liquid(s), for example, through (pre)treatment/s to increase the hydrophobicity or hydrophilicity of the surface, as well as modified/treated/impregnated/associated/doped with catalysts or modifiers of potential, activation energy or other energetic or thermodynamic considerations. Likewise, the electrodes may be magnets or be magnetised, optionally to preferably attract or repel certain mineral species. Typically, electrodes made of stainless steel 316L would be used (alloy of iron, nickel, chrome, molybdenum and carbon), in order to prevent the rusting of the electrode given the medium and the potentials used.
Said electrodes may take any form, from flat sheets (smooth, perforated or articulated), to the shape of existing structures from the line/s of treatment (or lining of these). In addition, the surface can be maximised or modulated by the use of electrodes with three-dimensional surfaces, perforated surfaces or surfaces of particular roughness. The electrodes may be assisted by systems, in situ or ex situ, for their cleaning and/or maximising/modifying of the current efficiency, for example mechanical systems to maintain the surface clean, prevent/correct/minimise/act on impurities or aggregates, such as for example brushes or vibration/ultrasound systems for the release of particles/adhered species, and/or systems to prevent/correct/mitigate/act on physicochemical inconveniencies, such as for example programs to vary the potential/s against passivation layers formed on or from the electrode/s or chemical treatment systems. The electrochemical reactor may be assisted by washing systems such as hoses/vehicle washers/other water cleaning systems, which operate manually/semi-automatically/automatically, optionally in conjunction with systems to move said cleaning elements or reactor elements, such as hoists, or to empty/fill the tank housed by the reactor. The electrochemical reactor as well as the elements that house it may have security systems to prevent, mitigate or act in the event of electric discharge or short circuit, such as separators, rubber coatings, insulating coatings, ground wires, fuses and smart systems to guarantee safety. Likewise, the reactor may have mechanical supports suitable for the correct anchoring of the components thereof.
The process has two main modalities. In the first one, the potential is conferred to the mineral directly by the electrode. This requires direct contact between the mineral and the electrode. In the second modality, the potential is conferred to the mineral by means of chemical/electrochemical mediators, typically dissolved in the medium, added or already present in the medium (for example thiosalts), although they can also be conductor or semiconductor solids, again being added or already present (for example mineral particles), or a combination of these. Likewise, the process allows for the combination of the two modalities, both simultaneously, sequentially, in series and/or in parallel, using the same reactor or different reactors.
In the case of requiring direct contact between the electrode and the mineral, the electrochemical reactor may be assisted by additional mechanisms in order to promote/maximise/force said contact. These mechanisms may for example be stirrers and/or pumping and/or mixing and/or aeration and/or bubbling and/or vibration systems to promote/maximise the contact, and/or press filters and/or other types of presses and/or filters to force said contact or physicochemical methods to modulate the affinity between the electrode and the mineral, for example the modulation of hydrophobicity or the magnetising of the electrode, optionally to selectively foster the affinity (or lack thereof) with certain mineral species.
By means of the process object of this invention, several objectives may be attained:
Finally, the ideal industrial configuration would be the implementation of the process both in a passage (for example a pipe or expansion/compartment that houses the reactor in question, optionally by means of perforated or ring-shaped electrodes or of favourable configurations at the hydrodynamic level) or a conditioning tank prior to the rougher flotation, or in a passage like the one previously described or in a conditioning tank prior to any stage of the cleaner flotation and/or scavenger flotation. The reactor may be configured as a combination and/or matrix of the morphological unit(s).
The reactor may be installed parallel to the walls of the tank or compartment containing the pulp or through which the pulp passes, and/or constituting/taking advantage of at least part of these, and/or arranged in any way, for example in such a way as to maximise the electrode surface per volume of pulp, optionally using mosaics of reactors, column and/or bed configurations (e.g. packed, percolating, slurry phase and/or bubbling), (multi) tubular configurations, sieving, and/or to promote/modulate the hydrodynamics in the tanks or passages, optionally taking advantage of or acting as deflector(s). The reactor may take any shape, from a simple configuration with two parallel, flat electrodes, to more complex apparatus, such as a reactor that constitutes and/or takes advantage of at least part of the structures and/or elements of the mineral treatment line(s), such as the flotation cells, tanks, containers or passages of pulp, including any element in the plant or treatment line/circuit, such as pipes, conditioning tanks, elements such as, for example, air dispersers, stirrers, false floors, deflectors, linings and/or structures, and/or elements of the mills such as the balls, the rods and/or structures.
Mechanical/physical, electrical and/or chemical parameters of the system may be controlled by smart control systems, optionally remotely, in order to monitor and adjust the reactor, optionally in relation to process data for example from a laboratory/Courier data/mechanical or physicochemical parameters. In addition, automated transport systems can be used for processes such as the distribution of mineral to the electrode, the recirculation of the pulp, liquid/medium and/or solids, and/or extraction/cleaning/replacement/movement/modification/regeneration of electrodes or other elements of the reactor. Furthermore, the reactor design could allow for changing the separator/s, electrodes and/or other constituting elements without the need for disassembly.
To complement this description and with the aim of aiding a better understanding of the characteristics of the invention, in accordance with an example of preferred embodiment, this description is accompanied, as an integral part thereof, by a set of figures where, by way of illustration and not limitation, the following is represented:
The present invention relates to a process for the depression of iron sulphides and other disposable elements in the flotation of mineral particles in liquid, which would typically take place after the stages of extraction, crushing, grinding and suspension in liquid of the mineral.
An example of said processing for copper ores is presented below, illustrated in
The next step would be a grinding stage, either in a rod mill or a ball mill, in order to produce particles with a diameter less than 0.2 mm. The next step would be the stirring of the mineral pulp in a conditioning tank prior to the rougher flotation, which would be an ideal moment for the application of electric potential. In this way, the particles could be conditioned before the first flotation. The product of the rougher flotation is the rougher concentrate, the main objective of which is to eliminate most of the gangue (mainly silicates), as well as part of the iron sulphides (specifically pyrite).
The product of the rougher flotation would be subjected to a regrinding stage, where the diameter of the particles would be reduced from less than 0.2 mm down to less than 0.05 mm. Subsequently, the mineral pulp is stirred in a conditioning tank, before the three cleaner flotations and the scavenger flotation. Again, said tank could be used for the application of electric potential, with the aim of conditioning the mineral before the cleaner flotations. Likewise, conditioning tanks or intermediate passages where electric potential would be applied could be introduced, for example between the first and second cleaner flotations, as well as between the second and third cleaner flotations. The product of the flotation process, after thickening and filtration stages, is the final concentrate, which would typically be composed of copper sulphides such as chalcopyrite and chalcocite, containing at least 20% copper.
The previously described process incorporates at least a reactor for the application of electric potential. Said reactor can have different configurations. Below, some of the possible reactor configurations are cited. In all of the reactor configurations, the mineral may or may not come into contact with the electrode, although the first option is the preferred one. As mentioned, the option of contact consists of the particles touching the electrode, which can be achieved by stirring or moving the pulp, thereby guaranteeing the contact, at least during an instant. In the configuration without contact or the indirect configuration, an electrochemical mediator is used, whether present or added, to transfer the electric potential from the electrode to the mineral particles. In this case, the direct contact between the mineral and the electrode is not necessary. In any case, if an electrochemical mediator is used, it will also be possible to use a reactor with direct contact, although in that case it would not be necessary to guarantee the contact from a hydrodynamic point of view. Other options would be to use an ex situ reactor or to coat the electrode of interest with a separator in order to prevent direct contact with the mineral. Typically, a relatively low potential, from 0 to 12 volts, difference is used between the anode and the cathode.
The first reactor configuration is a simple electrochemical cell. Said cell, illustrated in
The second reactor configuration is a simple electrochemical cell, where at least one of the electrodes is, partially or totally, isolated from the pulp medium and/or other electrode(s) and/or liquid by a separator/s. This arrangement, which prevents contact between the counter electrode and the mineral particles by means of a physical separator, is the most favourable process configuration. Said cell, illustrated in
The third reactor configuration is a variation of the first configuration. Said cell, illustrated in
The fourth reactor configuration is a combination of the second and third configurations. Said cell, illustrated in
The fifth reactor configuration is a variation of the third configuration. Said cell, illustrated in
The sixth reactor configuration is a combination of the second and fifth configurations. Said cell, illustrated in
The reactor of any configuration uses at least one anode and at least one cathode, and is electro-assisted by applying and/or controlling a source of electric energy, to control and/or measure and/or modulate one or more of (i) cell potential(s), (ii) partial and/or relative and/or half-cell anodic potential(s), (iii) partial and/or relative and/or half-cell cathodic potential(s), (iv) medium potential(s), (v) partial potential(s) of species in solution, (vii) pulp potential(s) and (viii) zeta or mineral particle surface potential(s).
A simple example of use, as illustrated in
For example, the process could be used in the conditioning tank prior to the rougher flotation. In this tank, it would be normal for around 800 to 1,200 tons of mineral to enter every hour, at 20-40% by weight/volume in water. If it is copper ore, the input mineral would typically contain between 0.4 and 2% copper, between 2 and 30% sulphur, between 1 and 20% iron, between 0.1 and 5% zinc as well as gangue (typically silicates) and other elements in lower quantities.
The input mineral into the tank typically has a D80 between 100 and 250 μm. It is stirred for about 2 to 5 minutes in this tank, before flowing into the rougher flotation. After the application of potential in said conditioning stage, for example between 1 and 12 V between the anode and the cathode, the copper grade of the concentrate could be increased several points (e.g. from 20% to 24% copper without and with the reactor, respectively), as well as increasing the recovery of copper in several points (e.g. from 86% to 88% without and with the reactor, respectively). A lower pH could also be used in the rougher flotation, maintaining the same grade (for example 20%) but increasing the recovery (e.g. an increase between 4 and 6%). Usually, this would not be possible without using the reactor, given that upon lowering the pH, the copper grade in the concentrate would decrease. On the one hand, the use of a lower pH in the rougher flotation (e.g. pH 10 instead of pH 11.5) would allow for important savings in lime (typically several tons of lime per day), while at the same time obtaining greater benefit from the same input ore or mineral that is introduced into the plant and that is to be treated (typically with 1% copper, which is concentrated up to 20%), given that less copper would be discarded. On the other hand, if we used this process to increase the copper grade in the concentrate, the use of depressors such as sodium metabisulphite (e.g. 400 g/tons of reground mineral) could be reduced or even completely eliminated. Another example of use, illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 16382382.6 | Aug 2016 | EP | regional |
| P201730450 | Mar 2017 | ES | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/ES2017/070563 | 8/2/2017 | WO | 00 |
