Feed Launders

The center-drive mechanism and feed launder are usually supported by a walkway that extends across one-half or the whole diameter of the basin. Devices having drive mechanisms and rakes supported by a tmss across the diameter of the thickener are referred to as bridge machines. The bridge thickeners usually do not exceed 25—45 m in diameter. In thickeners with larger diameters, the drive mechanism is supported by a central column or pier and the rates are driven and supported by a drive cage. The sediment is discharged into an aimular trench around the bottom of the column. 

Feed Launders for M/s. Hindustan Dorr-Oliver Ltd, India... 

Iron ore with a solid content of 25%-30% in water was being handled in these feed launders. The velocity of the slurry was 2 ft per second. A 6 mm thick soft natural rubber compound of hardness 40°A was found to be well suited for this application. 

Thickener, single compartment, concrete with 3 m walls, overflow weir, launder excluding central rake, excavation, site preparation, piping feed launder, overflow pump. PM cost = 400000 for a surface area = 100 m with n = 0.38 for the range 80-2000. L-i-M = 3.1. L/M = 0.4. Alloy cost factors c/s X 0.7, concrete X 1.0 rubber lined for acid-leach mineral processing X 1.22. 

Static bath mode. Feed enters at one end of the dmm and the floats exit from the other end. The sink product is removed continuously from the rotating dmm through the use of lifters attached to the dmm which empty into a launder as they move to the top. A modification of the simple dmm separator is the two-compartment dmm separator which allows a two-stage separation. In the cone-type separator (up to 6.1 m in dia and 450 t/h) feed is introduced at the top. The medium in the cone is kept in suspension by gentle agitation. The sink product is removed from the bottom of the cone either directly or by airlift in the center of the cone. The maximum particle size that can be separated is limited to 10 cm. Other separators include the Drewboy bath and the Norwaltbath (2). 

A thickener has several basic components a tank to contain the slurry, feed piping and a feedwell to allow the feed stream to enter the tank, a rake mechanism to assist in moving the concentrated sohds to the withdrawal points, an underflow solids-withdrawal system, and an overflow launder. The basic design of a bridge-supported thickener mechanism is illustrated in Fig. 18-86. 

The Humphreys spiral concentrator is a spirally shaped channel or launder with a modified semicircular cross section, as illustrated in Fig. 19-30. The standard spiral consists of five complete turns, but three-turn units are used in some instances when an unusually rapid and clean separation takes place, as in second-stage or cleaner spirals. There is a drop of 0.34 m (13.5 in)/turn as the flowing pulp progresses from the top to the bottom of the spiral. One spiral concentrator occupies about 0.37 m" (4 ft") of floor space and about 2.1 m (7 ft) of headroom measured from feed to discharge box. The optimum particle-size range of feed particles for spirals is about 10 to 200 mesh (2 to 0.074 mm). 

Drum Separators Very coarse solids, up to 0.3 m (12 in), are often processed in a drum separator of the type shown in Fig. 19-32. This is similar to a ball-mill shell with hfters permanently attached to the wall. Medium and feed enter at one end, and the float product flows out through the discharge trunnion, while the sink is lifted by the rotation of the drum to a stationaiy launder, through which it is flushed out. Modifications of this type include division of the shell into two compartments, which permits simultaneous operation at two different piup densities resulting in various grades of products. The two-compartment revolving drum is illustrated in Fig. 19-32. 

Mechanical Cells. Figure 19-73 presents a schematic representation of a typical mechanical device commonly known as a flotation cell. It is characterized by a cubic or cylindrical shape, equipped with an impeller surrounded by baffles with provisions for introduction of the feed slurry and removal of froth overflow and tailings underflow. The machines receive the supply of air through a concentric pipe surrounding the impeller shaft, either by self-aeration due to the pressure drop created by the rotating impeller or by air injection by means of an external blower. In a typical installation, a number of flotation cells are connected in series such that each cell outputs froth into a launder and the underflow from one cell goes to the next one. The cell design may be such that the flow of slurry from one cell to another can either be restricted by weirs or unrestricted. 

Continuous Cone.—As shown in Fig. 8 the stream of material enters the feed. spout A and, after passing through the truncated cone the water and solid particles which it is desired to remove flow upward and out into the overflow launder. The heavy particles settle in the cone and form the basin. When the settled material reaches the outlet of B it obstructs it so that the water rises in B lifting the float C, thereby lowering the ball G from the spigot by means of the lever D, the link E and the valve arm F. Once the cone is filled up a balance will be obtained and the settled solids will flow out in a continuous stream but the... 

---