Classifying – separating – and assorting solids – Fluid suspension – Liquid
Reexamination Certificate
2003-09-19
2004-08-10
Lithgow, Thomas M. (Department: 1724)
Classifying, separating, and assorting solids
Fluid suspension
Liquid
C261S087000, C209S164000
Reexamination Certificate
active
06772885
ABSTRACT:
The present invention relates to a rotor used in the flotation mechanism in the concentration of ores. According to the invention, upper part of the rotor chambers under the rotor cover are formed to be downward inclined from the outer edge of the chambers into the core so that they form an angle between 5 to 70 degrees with the horizontal plane. In addition the upper surface of the rotor cover can be inclined upwards raising from around the rotor shaft towards the outer edge at an angle between 5-70 degrees. With the means inside and above the rotor the slurry is directed upwards through the stator of the flotation mechanism. The developed rotor improves the suspension of coarse particles with high specific gravity within a flotation machine. The invention relates also to a method for inverting the material flow discharging from the rotor.
Flotation is essentially a three phase process involving the mixing of finely ground solids, and air to concentrate valuable minerals from gangue by floating one away from the other. Upstream to this process, water is added to the ore and fed to a comminution circuit whereby the ore is broken down and reduced in size to form a finely ground solid/liquid mixture called a slurry or pulp. The slurry is then further processed through a group or bank of flotation devices which have flotation mechanisms suitable for keeping the slurry mixture suspended while at the same time air is induced through the mechanism and dispersed evenly throughout the cell.
Suitable reagents are also added to the process that are capable of coating the surfaces of the valuable minerals to make their surfaces hydrophobic and so promote bubble/particle attachment. Once the valuable mineral particles attach to an air bubble they slowly rise to the cell surface to form a stable froth zone. This froth containing the valuable minerals is then recovered via a launder system to complete the flotation process.
For those who are experienced in the art it is generally accepted that a flotation device can be broken down into the following zones:1) a mixing zone, 2) a quiescent zone, 3) an enrichment zone and 4) a froth zone.
The mixing zone is located in the lower region of the flotation device where there is a significant zone of turbulence created by the high velocity pulp flows exiting the flotation mechanism. The quiescent zone is directly above the mixing zone and is a region where the secondary pulp (slurry) flows are of a much lower velocity and promote the upward movement of valuable mineral particles attached to air bubbles. The enrichment zone is directly under the froth zone and can extend 4 to 6 inches below the froth/pulp interface.
As the secondary pulp flows move across the cell directly underneath the enrichment zone these air bubbles together with their mineral load get the opportunity to rise up due to their inherent buoyancy and transfer into the enrichment zone before the pulp flow is redirected downwards and back into the mixing zone to repeat the cycle. Once these valuable mineral particles attached to air bubbles enter the enrichment zone the probability is high that these particles will continue to rise into the froth zone and be recovered via the launder system. However, some “dropback” of valuable mineral does occur and as a consequence these particles return into the secondary flows to repeat the process if they do not collide and reattach themselves to another air bubble in the meantime.
While it is accepted that the froth zone, quiescent zone and enrichment zone are also important regions within a flotation cell it goes without saying that the mixing zone is the most important region within a flotation device for it is in this region that particle suspension and air dispersion takes place. If the flotation mechanism fails to properly disperse the air throughout the cell or if the solids suspension is inadequate then the flotation process suffers and the overall recovery of the desired minerals will be less.
A very common type of flotation mechanism consists of a rotating rotor and stator blades around the rotor. Air is fed near the rotor for example through the rotor shaft. As a result of flotation, valuable mineral particles attach to air bubbles and accumulate in a froth In the upper part of the flotation cell and is discharged through a launder of the cell. Tailings of the slurry are directed to the next separation step.
In the U.S. Pat. No. 4,078,026 there is described a rotor-stator mechanism where the rotor has both slurry and air slots separately. The main idea of the mechanism is that the rotor creates a dynamic pressure that compensates for the hydrostatic pressure developed across the height of the rotor so that the total pressure caused by the slurry to the dispersion surface is substantially equal over said surface. The main type of said mechanism is so-called OK-rotor, whose form in vertical section is downward tapered and in which vertical rotor blades are so arranged that they form separate slurry slots and air slots between the blades. Air is pumped through the hollow rotor shaft into the air slots. The rotor has a horizontal cover plate above the blades which deflects both the slurry and air flows exiting the slots in a predominantly horizontal direction. Stator vanes are predominantly vertical and help eliminate the rotational component of the flow from the rotor.
Another flotation mechanism is described in U.S. Pat. No. 4,800,017 which seems very similar to the above-mentioned system except that the function of the slots is different. The rotor body includes a horizontal top plate and a plurality of vertically oriented rotor blades which form pump chambers. Air is pumped to each chamber for aerating the pulp of the flotation cell. The stator blades are deflected outwardly from their upper part, the lower part being vertical. The discharge of the slurry flow exiting the rotor is predominantly horizontal. However, the stator incorporates a deflector vane which effectively deflects this flow downwards at approximately 15 degrees.
In the EP patent 844 911 the rotor has a horizontal barrier in the middle of the pumping chambers which again deflects both the upward and downward flows entering the rotor in a predominantly horizontal direction when discharged.
It is also know before a flotation machine which has a plurality of vertical oriented plates which form the pumping chambers. Air is pumped to each chamber via a vertical downcomer which also incorporates and supports a horizontal shroud directly above the rotor. This shroud also supports the vertical stator blades. While the slurry flow entering the rotor is initially deflected upwards as it exits the rotor pumping slots it is deflected horizontally by the overhung shroud and is pumped radially outwards through the stator blades.
In all the mechanisms described above the slurry and air flow is directed horizontally from the rotor towards the stator blades. The mechanisms are effective in the flotation of normal size particles which means that their size is less than P
80
=180 &mgr;m (80% of the material passes a sieve of 180 &mgr;m). However their performance deteriorates as the particle size and specific gravity of the mineral particles to be floated increases past this point It is also difficult to suspend particles whose specific gravity is above 3.5 t/m
3
. It is the object of the present invention to overcome or substantially ameliorate drawbacks of the prior art and to achieve a flotation machine whereby coarse and high specific gravity material can be effectively suspended within the mixing zone using a new style of rotor that is capable of varying the mixing flow patterns within the cell.
A new type rotor of a flotation mechanism is now developed especially for a material which is coarse and has a high specific gravity. It has been proved that a vertical section downward tapered rotor which is equipped with means to direct the slurry flow upwards instead of horizontal direction allows the rotor to vary the mixing flow patterns within the machine and without interferin
Lithgow Thomas M.
Morgan & Finnegan , LLP
Outokumpu Oyj
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