An investigation of the effects of water injection on froth flotation.
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Date
2014
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Abstract
The majority of platinum production in South Africa is from the UG-2 chromitite seam. Fine
grinding of this material followed by flotation has resulted in a chromite entrainment problem
which affects the efficiency of the downstream smelting furnace. Froth washing offers the
potential for selective removal of chromite and possible improvements in platinum grade and
recovery from the flotation concentrate.
This project was aimed at improving flotation efficiency using froth washing on a laboratory scale
and evaluating its application to various stages on a platinum flotation plant. A synthetic mixture
of minerals was chosen for the laboratory batch flotation test work to enable monitoring of the
flotation and entrainment of fully liberated particles. Smith and Warren (1989) described
entrainment as a function of water recovery. This simple model was used to compare the
entrainment factor for froth washing tests.
Subsequent work focused on mixtures of two components, i.e. limestone (gangue) and Alsil P
(floatable mineral) and the use of froth washing to reduce gangue entrainment. Several methods of
froth washing were investigated and the use of a submerged wash water bar was chosen. Variables
included the position for water injection, the rate of water addition, concentration of reagents and
the stage of flotation (rougher, cleaner and scavenger).
Results indicated that the effectiveness of froth washing was mostly dependent on the stage of
introduction and the positioning of the wash water. Laboratory tests found that the best positioning
for washing was 3cm from the lip of the cell. Although tests on the scavenger stage alone were
disappointing, froth washing from the start of flotation resulted in an increase in recovery of
floatable material of approximately 10 percent when comparing the same mass recovery.
The tests conducted at Lonmin Platinum showed that the concentrate grade was increased by
washing, but the flow of platinum (recovery) was reduced. Observations and results showed that
the positioning of the wash bar at the upper surface of the froth inhibited its flow. A few tests, with
the wash bar at the froth/pulp interface showed promise, although the mass flow decreased by
approximately 15 percent the PGM content increased by 19 percent.
Description
Master of Science in Chemical Engineering. University of KwaZulu-Natal, Howard College 2014.
Keywords
Water--Purification--Dissolved air flotation., Flotation reagents., Theses--Chemical engineering.