The use of tank cells over the years has provided a means for low cost, space efficient, extra capacity in existing flotation circuits. In some cases, new plants have selected tank cells as the machine of choice. Typical tank cells use high efficiency impellers for mixing, which results in low power draw. Unfortunately, these mixers have poor aerating characteristics that compromise metallurgical performance. This has all changed with Outokumpu’s new flotation concepts.

Objectives

The objective of any froth flotation circuit is to maximise recovery and selectivity. The successful performance of any flotation circuit depends on the ability of operators to efficiently use the flotation volume available. Traditionally, rougher/scavenger, cleaner, and re-cleaner circuits, among others, have been the mechanical “tools” used to realize the main objective. Combined with the use of reagents (including air) it is truly amazing how successful mineral separations using froth flotation have been.

The Tools

Bubble Particle Contact

Certain sizes of particles are easy to float in most processes. These particles are easily maintained in suspension and have sufficient mass to ensure collision with, and subsequent attachment to, a bubble. It is not so easy to float the coarse and fine end of the particle size spectrum (See Figure 1) .

Froth Handling

The froth crowders or “boosters,” as they are called, extend free deep in the cell near the rotor toward the froth lip reducing the area available for froth formation.

Outokumpu HG Flotation Cell

The Outokumpu HG or High-Grade flotation cell was introduced in 1990 after extensive field trials at Outokumpu concentrators. The main characteristics of this cell are:

• High selectivity
• High recovery
• Simple Construction and installation
• Simple operation and control

The “Virtual Column” Concept

Consider Figure 4 below. The height of a simple cylindrical column can easily be calculated as:

H = V/A………………………………………………………………………..(1)

where H = Actual height
V = Total Volume
A = Surface Area of Froth

 

Calculated according to equation (2) below:

Hv = V/A……………………………………………………………………………(2)

where Hv = “Virtual” height
V = Total Volume
A = Surface Area of Froth

Taking this one step further, we can also determine the diameter of the column and a corresponding Dv or “Virtual Diameter” for the HG Tank Cell:

Dv = √A/N x 2………………………………………………………………..(3)

 

Example 1

Installation:

1500 tpd copper flotation circuit.

The OK-HG-16 produces final grade at 30% overall recovery. Performance is a vast improvement over the older type tank cell. The older cell is now being retrofitted with an OK-28 mechanism and booster assembly.

Example 2

Installation:

Les Resources Aur Inc. Division Aurbel

1500 stpd gold mill floating pyrite/gold.

The cell is recovering more than 75% of final concentrate at final grade. Overall recovery has improved.