Patent Application
20130220894
The disclosure relates to a flotation apparatus having a stirrer as dispersion device and to a flotation method. A flotation apparatus known for example from DE 1 279 573 comprises a flotation chamber bounded by a sidewall and a base, a pulp infeed, a stirrer, an aeration device associated with the stirrer, and a foam-collecting device arranged in an upper region of the flotation chamber for the purpose of collecting a foam product formed during the flotation process.
Flotation is a physical separation method for separating a mixture of particles on the basis of differences in the particles' surface wettability. In such a method, utilized for example for separating ore minerals and gangue, a gas such as air or nitrogen is introduced with the aid of the aeration device into the particle mixture that is present in the form of an aqueous suspension, the pulp. In addition flotation chemicals for hydrophobizing the surface of the valuable particles, in other words the ore particles in the case of a crude ore, are added to the pulp. The gas bubbles present in the pulp adhere to the hydrophobic particles, thereby producing adducts, also called aeroflocs, which rise to the surface and accumulate as a foam product on the pulp and can be discharged from there.
In order to enable aeroflocs to form it is necessary to induce turbulences in the pulp with the aid of a mixing device, the aforementioned stirrer, so that the gas will be dispersed in the pulp and collisions are able to take place between gas bubbles and particles. However, not every collision leads to the formation of an aerofloc. Thus, forming an adduct from a small gas bubble with a small particle requires a collision taking place with relatively high kinetic energy, i.e. the particle must be accelerated to a high velocity by the mixing device. To achieve this with a stirrer, however, would necessitate at best high expenditure of energy and high material attrition, which would make the flotation process uneconomic. Flotation apparatuses with stirrer as mixing device are therefore operated with lower input of energy in such a way that the hydrodynamic conditions that become established favor the separation of particle fractions having diameters that are larger on average. Due to a lack of sufficient kinetic energy finer particles in this case form at best adducts on a smaller scale and remain behind in the residual pulp. In order to recover the fine fraction of the particles the residual pulp is conventionally treated further in other downstream flotation apparatuses, which is associated with corresponding process engineering and equipment overhead.
One embodiment provides a_flotation apparatus comprising a flotation chamber having a sidewall and a base and serving to contain a pulp, a foam-collecting device arranged in an upper region of the flotation chamber for the purpose of collecting a foam product formed during the flotation process, and a charge line for continuously charging the flotation chamber with pulp, wherein the charge line leads into the flotation chamber at a point located above the stirrer, wherein for the purpose of dispersing a gas in the pulp a first mixing device is present in the charge line and a second mixing device comprising a stirrer and a sparging device associated with the stirrer is present inside the flotation chamber.
In a further embodiment, a plurality of charge lines equipped with a first mixing device are present which are arranged on the flotation chamber in a mutually spaced relationship in the circumferential direction.
In a further embodiment, the sidewall of the flotation chamber has a circular cross-sectional shape.
In a further embodiment, an end section of the charge line connected to the flotation chamber is aligned tangentially with respect to the sidewall.
In a further embodiment, an inner chamber having a cylindrical sidewall and being open at top and bottom is arranged centrally in the flotation chamber with a radial clearance from the sidewall of the flotation chamber while leaving an annular space free.
In a further embodiment, a foam-collecting device arranged in an upper region of the inner chamber is present.
In a further embodiment, the charge line leads into the annular space.
In a further embodiment, the charge line leads into the inner chamber.
In a further embodiment, the inner chamber is height-adjustable.
In a further embodiment, a baffle with adjustable baffle opening is present at the lower end of the inner chamber.
In a further embodiment, the stirrer is encompassed laterally by a deflector plate which is in the form of a funnel opening toward the top and which covers a corner region of the flotation chamber formed by the lower end of the sidewall and the base.
In a further embodiment, the foam-collecting device is a collecting tank encompassing the flotation chamber or the inner chamber with a radial clearance.
In a further embodiment, the first mixing device is an ejector.
Another embodiment provides a flotation method which is performed in two flotation stages inside a pulp-containing flotation chamber of a flotation apparatus, wherein the dispersion of a gas in the pulp is accomplished with the aid of a first mixing device arranged inside a charge line serving to feed pulp into the flotation chamber in the first flotation stage and with the aid of a second mixing device comprising a stirrer and a sparging device associated therewith in the second flotation stage.
In a further embodiment, such flotation method is performed using a flotation apparatus as disclosed above.
Exemplary embodiments will be explained in more detail below based on the schematic drawings, wherein:
Embodiments of the present disclosure provide a flotation apparatus with stirrer and a flotation method which enable a flotation with improved yield.
For example, in some embodiments a flotation apparatus comprises a flotation chamber having a sidewall and a base and serving to contain a pulp, a foam-collecting device (5, 5a) arranged in an upper region of the flotation chamber for the purpose of collecting a foam product formed during the flotation process, and a charge line (6) for continuously charging the flotation chamber with pulp. The charge line leads into the flotation chamber at a point located above the stirrer. For the purpose of dispersing a gas in the pulp a first mixing device (M1) is present in the charge line and a second mixing device (M2) comprising a stirrer (3) and a sparging device (4) associated with the stirrer (3) is present in the flotation chamber (2).
Other embodiments provide a method in which the flotation is performed in two flotation stages inside a flotation chamber containing a pulp within a flotation apparatus, wherein a gas is dispersed in the pulp with the aid of a first mixing device arranged inside a charge line serving to feed pulp into the flotation chamber in the first flotation stage, and with the aid of a second mixing device comprising a stirrer and a sparging device (4) associated with said stirrer in the second flotation stage.
In some embodiments two mixing devices operating essentially independently of each other are present, by means of which a gas in the form of gas bubbles and particles can be dispersed in the pulp under high turbulence. In the process the respective turbulence zones are spatially separated from one another in such a way that mutual influencing of the adducts forming there due to the prevailing hydrodynamic conditions is practically excluded. It is therefore possible to realize a two-stage flotation process within one and the same flotation chamber, wherein the first flotation stage comprises one or more first mixing devices and the second flotation stage comprises the stirrer and its associated sparging device. Different hydrodynamic conditions can be created in the respective turbulence zones, thus affording the possibility in principle to recover different particle fractions simultaneously in one flotation apparatus and/or by means of a flotation method performed in a single flotation apparatus or, as the case may be, in the flotation chamber of the same. It is therefore possible to convert particles having a wider range of sizes into the foam product than in the case of the known flotation apparatus, with the result that proportionally higher yields can be achieved and subsequent flotation steps are rendered unnecessary or necessary only on a reduced scale.
An ejector may be employed as the first mixing device. Ejectors are known per se in the field of flotation technology and are described for example in European patent application no. EP 09171568.0. In this case the ejector is, as will be explained in more detail further below, an apparatus for dispersing a gas in a pulp, comprising—viewed sequentially in the flow direction of the suspension—a suspension nozzle tapering in the flow direction, a mixing chamber into which the suspension nozzle leads, and a mixing tube adjoining the mixing chamber and tapering in the flow direction. Also present is a gas supply line for feeding a gas into the mixing chamber. A large volume of gas can be introduced into the pulp with the aid of an ejector and distributed in the form of very many, predominantly small, gas bubbles. This increases the frequency of particle-bubble collisions, resulting in the formation of mainly adducts composed of small bubbles and particles tending to be of smaller size. The adducts rise upward in the flotation chamber without passing into the turbulence zone of the stirrer and being exposed to the danger of disintegrating again due to collision with a particle. Rather, they can float to the surface practically without a detrimental effect of said kind and be discharged with the aid of a foam-collecting device, e.g., a foam-collecting tank encompassing the flotation chamber with a radial clearance. Heavier particles which encounter rather unfavorable hydrodynamic conditions for forming aeroflocs in the ejector and consequently after passing through the ejector or after the pulp has entered the flotation vessel have not formed any aeroflocs sink toward the bottom and are caught up by the turbulence zone of the stirrer in which hydrodynamic conditions are present which favor the formation of particle-bubble adducts composed of larger bubbles and larger particles.
The flotation apparatus 1 shown in the diagrams according to
The charge lines 6 are arranged on the sidewall 8 of the flotation chamber 2 such that their end section 11 connected to the flotation chamber 2 and/or the flow direction 18 of a pulp flowing through the end sections 11 extend tangentially with respect to the flotation chamber 2 or to its cylindrical sidewall 8. The charge lines 6 lead into the flotation chamber 2 at a point 19 disposed above the stirrer 3 close to the upper edge 19 of the sidewall 8. A vertical distance is therefore present between the outlet of the charge lines 6 and the stirrer 3.
An ejector 7 comprises as essential component a nozzle, referred to hereinbelow as a suspension nozzle 25, from the outlet orifice of which the pulp is ejected at high velocity, a gas being introduced in the outlet region or, as the case may be, being ingested on account of a negative pressure that is present there. The gas enters the pulp stream exiting the suspension nozzle and is dispersed therein in the form of fine gas bubbles. The injector 7 represented schematically in
The above-described flotation apparatus 1 operates as follows: The flotation chamber 2 is filled with an aqueous pulp, for example a crude ore suspension. The rotating stirrer 3 of the second flotation stage creates a turbulence zone 34 indicated by the arrows 33. A gas is introduced into the flotation chamber 2 by way of the sparging device 4, which is formed substantially by the interior 35 of the hollow shaft 10 which is open at its bottom end, with gas bubbles being dispersed in the pulp, in particular in the turbulence zone 34, due to the rotational movement of the stirrer 3. A similar dispersion, albeit of smaller gas bubbles on average, takes place in the ejectors 7 of the first flotation stage. There, aeroflocs form from said gas bubbles and rather smaller particles. Said aeroflocs float to the top and accumulate as foam product in the foam-collecting tank 16, from which they are discharged by way of the discharge port 17. In contrast, heavier particles to which no gas bubble has adhered in the ejectors 7, sink toward the bottom—as indicated by the arrow 36—and enter the turbulence zone 34 of the stirrer 3. Corresponding collision events between particles and gas bubbles lead in turn to the formation of aeroflocs, though in this case such composed of larger particles and larger gas bubbles, which rise upward (indicated by the arrow 37) and likewise arrive as foam product in the foam-collecting tank 16. Because the turbulence zone 31 of the ejectors 7, which essentially corresponds to the mixing chamber 26 of an ejector 7, is arranged outside the flotation chamber 2 or separated off from the latter, aeroflocs ascending from the region of the stirrer 3 cannot pass into said zone, in which they could be destroyed again due to collision with high-energy particles.
In order for the ejectors 7 to be able to operate effectively they must always have passing through them a pulp stream which is sufficiently voluminous to ensure the hydrodynamic conditions necessary for forming aeroflocs. With this object in view it is beneficial if a return line 32 is provided which branches off from an outlet 42 serving to discharge residual pulp from the flotation chamber 2 and leading into at least one charge line 6. Part of the residual pulp stream can be ducted into an ejector 7 by way of the return line if it becomes necessary to restrict the supply of pulp for process control reasons.
The flotation chamber 2 of the flotation apparatus 1 shown in
An inner chamber 38 is similarly present in the variant of a flotation apparatus 1 shown in
In order to prevent a sedimentary deposition of particles in the corner regions 50 of the flotation chamber 2 that are formed by the lower end section of the sidewall 8 and the base 9, the corner regions are covered by a deflector plate 51 which is embodied in the form of a funnel opening toward the top and laterally encompassing the stirrer 3. A deflector plate of said type may be present in all of the variants of flotation apparatuses 1 described herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10189809.6 | Nov 2010 | EP | regional |
This application is a U.S. National Stage Application of International Application No. PCT/EP2011/068937 filed Oct. 28, 201, which designates the United States of America, and claims priority to EP Patent Application No. 10189809.6 filed Nov. 3, 2010 The contents of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/068937 | 10/28/2011 | WO | 00 | 5/3/2013 |
