Selectivity Vs. Recovery
Columns are often discounted as roughers because of the beliefs that a) mechanical cells will provide a
higher level of recovery, and, b) higher recovery provides more revenue than higher grades. For simple ores, this is
may be true. For more complex ores containing impurities which translate into additional treatment and refining
charges, or for mines located in very remote regions, the benefit of being able to produce high grade concentrates
even at the expense of a slight reduction in recovery, may make economic sense.
The magnitude of economic benefits including the savings in capital and operating costs can vary significantly
from project to project and will depend on a number of factors. Some of the most important factors are listed
For some processes, the use of column flotation has been shown to provide higher levels of recovery or
better concentrate grades, thus contributing significantly to the economic viability of the project.
Reduced Capital Costs
The savings in capital cost will depend on the size and complexity of the circuit, the location of the plant and
to a lesser degree the level of automation desired. Typical savings can range from 10% to 40%. For small and
simple plants, the relative cost of the flotation plant is small in comparison to other sections of the concentrator and
therefore the savings in capital cost may insignificant. For large projects the savings in capital can be substantial. Not
only is the cost of the equipment less, but the costs of ancillary equipment, electrical services and building size are
also reduced. In subtropical climates, it may be possible to eliminate a building entirely.
When comparing the cost of a column plant versus a conventional plant care should be taken to evaluate the
level of instrumentation that is being proposed. Column cells generally have a greater degree of automation than
conventional cells. The level of automation can be classified into two basic categories; stabilizing controls and
optimization controls. The control system should be matched to the duty that the column will be performing. It is
generally recommended to begin with a good basic control system and to add optimizing controls as the need arises.
Operating Cost Savings
Operating cost savings can be realized from reduced power requirements, reduced maintenance costs and in
some cases reduced reagent consumption.
· Power costs are typically 50% lower than an equivalent mechanical flotation circuit.
· Column cells have very low maintenance requirements and low inventory requirements.
· Reagent savings depend on the nature of the ore being treated and the reagent scheme being utilized.
The most significant reductions usually occur with depressants, where it is possible to use wash water to
lower impurity levels.
ANALYSIS OF TECHNICAL RISK VERSUS ECONOMIC BENEFITS
Assuming that all of the selection criteria have been satisfied, the technical risk of using columns in rougher applications will be low. In any event, it is prudent to conduct some sensitivity analysis on the economic effects that variations in grade and recovery would have in relation to the derived benefits. This type of analysis is more applicable to cases were columns are being considered as part of a plant expansion or modernization rather than a new project since accurate production data are available for comparison.
Industrial Column Rougher Circuits Column roughers are being used successfully in a number of plants around the world. Descriptions of various applications in zinc, fluorspar, phosphate, copper, lead, iron ore and glass sand have been documented.
The following examples describe two processes where column cells have been successfully implemented as
roughers. For both of these plants, column cells are the only type of flotation cells being used.
Example 1 - Reverse Silica Flotation From Iron Ore
High grade hematite ore is crushed and classified into three main product categories; lump ore, pellet ore and sinter feed.
Until about five years ago, the fine iron was routinely discarded.
Example 2 - Phosphate Flotation
A project in which an entire concentrator was converted from mechanical
flotation cells to column flotation cells over a period of 2 years as part of a program to reduce plant operating costs.
For complete details, download the paper below Industrial Applications of Column Cells as Roughers