This invention relates in general to flotation devices and flotation methods used in mineral separation. More specifically, the present invention relates to a method of and an apparatus for flotation of slurry that contains mineral particles or oil sands.
At flotation plants, it is common practice to arrange several flotation cells in line to achieve desired efficiency in the recovery of valuable ingredients. A conventional flotation cell includes a tank for receiving and containing slurry from a grinding circuit, a flotation mechanism comprising a rotor and a stator disposed within the tank, and an aeration system for direct dispersing gas into the flotation mechanism. The gas bubbles dispersed in the slurry rise toward the surface of the slurry and carry with them floatable, hydrophobic particles which form a froth layer on the surface of the slurry. The froth is withdrawn from the cell via a froth launder system. Gangue particles and particles not recovered by flotation are discharged from the cell through a bottom outlet and led to succeeding flotation cell or elsewhere for further processing. The bottom outlet control is often provided with a dart or pinch valve, which is opened to allow the remaining slurry to progress under gravity feed to downstream treatment process, and allow the froth-slurry interface to be kept at even non-fluctuating condition.
Suitable flotation reagents are added to the feed of a flotation cell to improve the desired properties of valuable and gangue particles in the slurry. The reagents for instance cover the surfaces of the particles within the slurry to make the particles hydrophobic and thereby to promote bubble to particle attachment. The slurry contains both relatively coarse particles and relatively fine particles. The fine particles have a total surface area much greater than that of the coarse particles. Accordingly, when flotation reagents are added to the slurry, majority of it tends to be absorbed by the fine particles portion from the distribution of particles. Consequently, the coarse valuable particles do not receive sufficient amount of flotation reagents to reach adequate hydrophobicity. It is a well-known fact that flotation process can be made more efficient where coarse and fine particles are treated separately. Classifying devices, such as hydrocyclones and spiral separators have been used to separate a flotation feed stream into two discrete streams for separate processing. However, the equipment of the prior art methods is often uneconomical due to a very high capital investment, operating costs as well as maintenance downtime, loss in production.
The object of this invention is to provide a flotation circuit for recovering valuable ingredients from mineral slurry efficiently and with low capital and operating costs. Another object of this invention is to produce an improved method of floating slurry with wide range of particles size.
In mineral processing, a conventional flotation circuit comprises one or several banks of flotation cells. One bank of cells is formed of cells arranged in series. Cell arrangements are established either in series or in parallel flow. The banks of cells are arranged in parallel when flows are too large for a single series line.
Now a novel type of flotation circuit for separating concentrates from mineral or oil sand slurry is introduced, where the flotation circuit comprises a flotation cell lines arranged in series or in parallel and a flotation cell system is arranged to receive a feed of mineral containing slurry from a grinding circuit with a flotation cell that is capable of classifying the slurry and that is provided with at least two outlet openings for discharging tailings with different particle size distributions and means of particle sizes. Adjacent to said flotation cell system, at least two parallel flotation cell lines are arranged to receive a flow of tailings from the output opening of the flotation cell system and adapted to process slurries with certain particle size distributions.
Also the present invention is a novel method of floating mineral slurry produced in a grinding circuit wherein the slurry is fed into a flotation circuit for recovering mineral concentrate and tailings. The mineral slurry is divided at least into two tailings flows having different means of particle sizes in a flotation cell system, that is arranged to receive the slurry from the grinding circuit and adapted to classify the slurry. The different tailings flows are fed for further flotation in banks of flotation cells arranged in parallel.
According to the invention at least two tailing flows are withdrawn via outlet openings arranged on different vertical levels of the classifying flotation cell of the flotation cell system.
In a grinding circuit, ore is grinded and slurry, that contains mineral particles, is produced for further processing in a flotation circuit. A typical solid content of such a slurry prepared for a flotation circuit is between 20 and 45%, in some special cases even lower or higher.
The classifying flotation cell system of the flotation circuit of the present invention is adapted to classify the slurry by particle size and pulp density. The flotation cell system may comprise several flotation cells arranged in series, but essential feature of the classifying cell system is that one of the cells in the system is capable of classifying the slurry into different slurry fractions and that the cell is provided with at least two outlet openings for withdrawing the different slurry fractions.
According to one preferred embodiment of the present invention, the classifying flotation cell system comprises one flotation cell that is a receiving cell that the slurry enters after the grinding circuit. The receiving cell has relatively high volume for the slurry. The pulp density on the bottom of the receiving cell is around the same as the density of the feed. The pulp density is gradually decreasing from the bottom of the cell to the pulp level. The pulp density may be around 10-20% on the top surface of the pulp. The classifying property of the receiving cell is realized with selecting suitable dimensions for the cell. The volume and the height of the cell are essential factors. The volume of the cell may range between 5 and even 5,000 m3, preferably between 5 and 500 m3 and most preferably between 5 and 380 m3.
The outlet openings of the receiving cell are arranged on different pulp levels of the cell. One of the outlet openings may be a conventional bottom outlet opening, when the outlet is arranged below or at the same level with the gas flotation mechanism of the cell.
According to another embodiment of the invention, in the flotation circuit, the flotation cell system comprises two flotation cells arranged in series and the downstream cell is capable of classifying the slurry and is provided with said outlet opening for withdrawing the slurry fraction and the upstream functions as a receiving cell.
These above mentioned objects are achieved by an apparatus and a method described later in the independent claims. Other advantageous embodiments of the invention are presented in the dependent claims. The apparatus and the method are suitable especially for metal and industrial minerals slurries. Furthermore, it may have advantages in special processes like oil and bitumen separation from sand or water.
The invention is described in more details referring to following drawings, where
Feed 11 of the flotation circuit of the present invention is produced in a grinding circuit, where ore is grinded for example in a SAG ball mill circuit. The particle size distribution of the in the slurry of the feed may be rather wide. The solid content of the feed 11 is typically between 20 and 45%. The feed enters the flotation circuit via a receiving cell 10. The receiving cell 10 is a flotation cell that comprises a flotation mechanism and froth launder system for recovering mineral rich froth. The receiving cell produces concentrate flow 25. Tailings 15, 16 of the receiving cell 10 are withdrawn via outlet openings arranged at different vertical position on the cell wall. The number of withdrawn tailings flows is at least two. In
According to one preferred embodiment of the present invention the receiving cell comprises two outlet openings for withdrawing two different tailings flows.
While the invention has been described with reference to its preferred embodiments, it is to be understood that modifications and variations will occur to those skilled in the art. Such modifications and variations are intended to fall within the scope of the appended claims.
Number | Date | Country | Kind |
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20050239 | Mar 2005 | FI | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FI06/00074 | 3/6/2006 | WO | 00 | 8/22/2007 |