Flotation machines

In mineral processing plant ,Flotation machines are designed to ensure flow of the pulp into good, active contact of particles with bubbles and levitation of mineral-laden air bubbles to the top of the cell, allowing entrapped particles to be removed. In addition, some laboratory machines are also designed to allow study of the physicochemical principles involved in flotation subprocesses. Different attempts to meet these requirements have resulted in many designs.

Essentially, flotation machines for production are divided into two types depending on the mechanisms by which air is introduced into the cell. Many variations of these types are seen, allowingdifferent intensity of agitation and different flow patterns in equipment with a variety of sizes and shapes. The two main types are pneumatic and mechanical machines. In pneumatic machines, air entering the turbulent pulp is dispersed into bubbles by baffles or perforated bases, ensuring maximum opportunity for contact with the mineral particles. Dispersion of the pulp itself is achieved by agitation caused by compressed air. These cells have essentially disappeared, except for the “apatite” machine manufactured in the USSR. A variation of this machine is used in the Davcra air cell, in which feed enters through a nozzle at the bottom of the cell and impacts on a baffle where sufficient turbulence is created to provide dispersion of bubbles and contact with particles. Although these cells are mechanically simpler than other designs because they lack many moving parts, they also give less effective performance. The mechanical machines, on the other hand, achieve dispersion of the pulp through agitation by a mechanically driven impeller. Mechanical machines employ one of two types of pulp flow and aeration systems: cell-to-cell flow with adjustable wiers between cells or open flow without the wiers and air intake via suction resulting from the rotation of the impeller or an external blower.

Manufacturers offer many types of cell and impeller geometries, each with its aims and claims. Cell shapes vary from rectangular to truncated rectangular to U-shaped, and impeller components vary from simple flat turbine set to cylindrical finger set to propellers (Figures 1 and 2). The position of the impellers relative to the cell bottom and the type and placement of the stator also vary to achieve the desired pulp suspension and circulation.

Aker’s impeller consists of a flat turbine. Air is charged through the impeller shaft and delivered through slots behind the impeller. Booth, on the other hand, uses a truncated shallow rectangular tank and impellers significantly above the tank bottom. Agitation at the bottom is achieved with the help of a propeller mounted below the impeller. The Denver D-R cell is an open tank type with vertical recirculation enhanced by means of a well that directs pulp to the impeller region. In contrast to the D-R cell, the Denver subaeration cell has adjustable wiers between cells that reduce chances for back mixing and also allow control of pulp level in each cell. The Agitair cell uses an impeller consisting of a horizontal disk with cylindrical fingers extending toward the bottom. Air blown in through the hollow shaft is mixed with pulp via a secondary pump on the disk and a stator. In contrast to all these designs, the Outokumpu cell is characterized by teacup-shaped impeller blades with tapered slots between the blades for air passage from the hollow shaft. Flotation of the impeller causes pulp to be drawn from the bottom toward the slots and expelled toward the periphery. This machine claims better suspension and lower power consumption. The Wedag design for coal, on the other hand, uses a shallow self-aerating impeller with blades at the periphery under a horizontal hood with a stator projecting downward at the periphery. This design permits stratification of the pulp because of minimum vertical circulation dispersing air into finer bubbles, according to claims, and floating finer particles more efficiently than other models.
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