Flotation machine

Abstract

A flotation machine comprising a flotation cell having therein an air inlet pipe for introducing air into the liquid being treated, a rotating body for agitating said liquid, and a dispersing unit having a plurality of guide vanes, characterized by the improvement that the outer end of the external periphery of each guide vane in the dispersing unit is positioned circumferentially forwardly of an imaginary straight line connecting the center of the dispersing unit to the inner end of the trailing side of the adjacent leading guide vane in the direction of rotation of the rotating body.

Parent Case Text

This is a continuation, of application Ser. No. 341,269, filed Mar. 14, 1973, now abandoned.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flotation machine in which a dispersing unit equipped with a plurality of improved guide vanes is installed in the flotation cell.

DESCRIPTION OF THE PRIOR ART

A flotation machine is required to provide the function of generating bubbles in the liquid, or slurry of solids and liquid, being treated therein. The material desired to be separated from the flotation liquid adheres to the bubbles so that it rises to the surface of the tank or cell with the bubbles. Therefore a large amount of bubbles must be generated and at the same time the bubbles must be caused to contact the flotation liquid as intimately as possible.

In general, the amount of bubbles that is generated depends on the amount of air that is introduced into the cell. Methods have heretofore been employed for vigorously agitating the flotation liquid, for example, by increasing the speed of rotation of the rotating body, such as an impeller or a rotor, used for effecting agitation of the flotation liquid in order to increase the amount of air sucked into the cell, or by blowing a large amount of the air progressively into the cell of the flotation machine. However, these techniques have drawbacks. When the speed of rotation of the rotating body of the flotation machine is increased and the amount of air sucked in is increased, not only does the consumption of power, for example, electric power, increase, but also an increased amount of wear of the rotating body and its supporting mechanical structure is caused. And, when the method of progressively flowing air into the cell of the flotation machine is employed, there is a drawback that extra equipment and power for preparation and supply of the pressurized air are required.

SUMMARY OF THE INVENTION

The present invention is intended to provide an improved flotation machine in which the bubbles of air are caused to contact the flotation liquid more effectively, without increasing the amount of air sucked in.

The inventor has discovered, as a result of numerous studies, that the opportunities for contact of the generated air bubbles and the flotation liquid can be increased, by employing a flotation machine in which an air suction pipe, such as a stand pipe or a hollow shaft, is positioned in parallel with the vertical axis of the flotation cell. The flotation machine has a rotating body for agitating the flotation liquid and a dispersing unit consisting of a plurality of guide vanes at the bottom of the flotation cell. According to the invention, when the direction of flow of the flotation liquid from the center of the cell through the dispersing unit and thence toward the internal wall of the cell, caused by the rotating body, is directed tangentially and in parallel with the bottom surface of the flotation cell, the opportunities for contact between the flotation liquid and the bubbles are increased. As a consequence the separation efficiency is substantially and unexpectedly increased even though the total amount of air is not greatly different from the amounts conventionally employed.

The present invention is based on this discovery.

The present invention will be further described in detail with reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cut away perspective view showing the inside of the cell according to the present invention;

FIG. 2 is a sectional view along the line II--II of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The construction of the cell, except the specific construction and arrangement of the guide vanes (6, 7) of the dispersing unit (5), of the flotation machine as shown in the drawings is generally similar to a conventional flotation machine and it will be described only briefly.

The apparatus comprises a flotation cell 1 having a rotating body or impeller 2 for drawing air into the cell and circulating the liquid through the cell. The impeller 2 is rotated by a shaft 3. An air inlet pipe 4 encircles and is spaced from the shaft 3. A stationary dispersing unit 5 is mounted on the lower end of the pipe 4. The dispersing unit 5 has a series of guide vanes, such as the guide vanes 6 and 7. A froth discharging trough 8 is provided in the side wall of the cell at the upper end thereof. The vanes are mounted on support rings 9 and 10.

When the impeller 2 is rotated by shaft 3 in the direction of the arrow (FIG. 1), after feeding the flotation liquid into the flotation cell 1, air is sucked into the cell through the inlet pipe 4. This air flows to the inside of the dispersing unit 5 is moved, together with the flotation liquid, toward the side wall of the flotation cell by rotation of the impeller 2. The liquid and the air are dispersed through the gaps between the guide vanes 6, 7 of the stationary dispersing unit 5.

In the conventional dispersing unit, the outer end of the external peripheral side of each guide vane, such as vane 6, is positioned so that it trails or is spaced circumferentially rearwardly of an imaginary straight line connecting the end point A of the trailing side of the inner end of the adjacent leading vane, and the center point O of the dispersing unit. For example, in the conventional dispersing unit, the outer end of a given vane 6 is set at a position in the vicinity of the point C of FIG. 2 relative to its adjacent leading vane 7. All of the guide vanes of the dispersing unit are arranged similarly. For this reason, it has been observed that the flotation liquid and air bubbles are directed in the non-tangential direction in the flotation cell. There is a large tendency for splashing to occur, and the opportunities for smooth uniform contact of the bubbles and the flotation liquid and/or the contacting time thereof is reduced, and this causes a drop of the flotation efficiency.

According to the present invention, the flotation liquid and the air bubbles circulated by the impeller 2 are caused to move in a more nearly circumferential direction and in parallel with the bottom surface of the flotation cell. This advantageous flow pattern is attained by shaping the guide vanes with a greater curvature than is customary so that the outer end (B) of the external peripheral side of each of the guide vanes of the dispersing unit is positioned so that it is located forwardly (in the direction of rotation) of the imaginary line of O - A as shown in FIG. 2. The bubbles are thereby caused to float from the broad surface or the layer at a position close to the bottom surface of the cell and the contacting opportunity of the bubbles and the flotation liquid is enhanced.

In other words, as shown in FIGS. 1 and 2, the end point B of the external peripheral side of the first guide vane 6, which point is positioned between the support elements 9 and 10 of the dispersing unit 5, is positioned at a location forwardly of the imaginary straight radial line connecting the center O point of the dispersing unit to the end point A of the trailing side of the inner end of the adjacent leading guide vane 7. All of the guide vanes are arranged in like fashion. The contacting opportunity of the air bubbles and the flotation liquid is thereby enhanced.

In the flotation machine equipped with the dispersing unit as described in the foregoing, the flow of the flotation liquid caused by the rotating impeller is directed in a substantially circumferential direction and horizontally relative to the bottom of the cell without being moved in an aslant upper direction in the flotation cell. Also the introduced bubbles are capable of floating to the upper part of the cell. According to the present invention, a concentrated bubble layer is formed which is nearly parallel with the bottom wall of the cell and between the external peripheral portion of the dispersing unit 5 and the side wall of the flotation cell 1. The floating distance of the bubbles from the said layer to the upper surface of the liquid in the cell is considerably extended as compared with the case of the conventional flotation machine. Therefore, the contacting opportunity of the bubbles and the flotation liquid becomes remarkably enhanced.

Accordingly, the opportunity for adherence of the bubbles to the material being floated out of the liquid is enhanced, and the amount of mass transfer per unit time of the valuable substance to the froth which is discharged from the froth discharging trough 8 is also increased, whereby the flotation efficiency is increased.

The dispersing unit according to the present invention may be installed not only in a cylindrical flotation cell, as illustrated, but also in any type of flotation cell, and in both cases, a similar effect can be obtained.

The invention will be further described with reference to the following illustrative example.

Example

Using a flotation machine (a) according to the present invention, as illustrated in FIGS. 1 and 2 in which point B of each guide vane of the dispersing unit is forwardly of the imaginary line O - A and a comparative flotation machine (b) having a similar structure except that the end of each guide vane of the dispersing unit is positioned at point C, flotations were effected under identical conditions. An industrial waste water having a Cu.sup.+.sup.+ concentration of 30 ppm was supplied to each flotation machine and furthermore, ethyl xanthate and a frother were added thereto to form precipitates of Cu xanthate. Flotation was effected for 10 minutes. The floating conditions of each flotation machine (temperature, speed of rotation of impeller) were made identical. The results were as shown in the following table.

Table 1 ______________________________________ Performance Cu concentration Distribution ratio Flotation in tailings after of CU (%) machine flotation (ppm) tailings froth ______________________________________ (a) flotation 0.8 2.7 97.3 machine according to the present invention (b) comparative flotation machine 2.0 6.7 93.3 ______________________________________

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A froth flotation machine comprising a flotation cell having an air inlet pipe for introducing air into the flotation liquid close to the bottom of the cell, froth removal means for removing froth from the upper end of the cell, a rotatable impeller disposed close to the bottom of the cell for mixing the flotation liquid with the air supplied by the pipe and circulating the mixture along the bottom of the cell, an annular stationary dispersing unit mounted on the lower end of said air inlet pipe and adjacent to the bottom wall of the cell, said impeller being disposed within the central opening of said dispersing unit and said dispersing unit being coaxial with the axis of rotation of said impeller, said dispersing unit comprising two coaxial, vertically spaced, imperforate, annular supports, a series of substantially uniformly spaced guide vanes mounted on and extending between said supports and located in the path of flow of said mixture from said impeller and being forwardly curved in the direction of rotation of the impeller for directing the liquid in a direction substantially tangential to the side wall of the cell and substantially parallel to the bottom wall of the cell, with the radially outer edge of each guide vane being positioned forwardly of its radially inner edge in the direction of rotation of said impeller, each pair of adjacent guide vanes defining a discharge passage for said mixture, said discharge passage having an inlet at the radially inner end thereof and an outlet at the radially outer end thereof, said outer edge of each guide vane also being positioned circumferentially forwardly of said inner edge of the adjacent leading guide vane in the direction of rotation of said impeller, the entirety of the outlet of each discharge passage being disposed circumferentially forwardly of the entirety of the inlet of the same discharge passage in the direction of rotation of said impeller, and the radially outer edge of said upper annular support is located substantially at and directly above the outer edges of said guide vanes.