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Flotation

Flotation Chemistry

Background

The creation of a favourable chemical environment is critical to the overall success of the flotation process. One of the most important chemical factors that determine the flotation response of a pulp is the reagent suite that is added. This includes those that have specific roles, such as collectors, activators, frothers, pH modifiers and depressants. Other factors are those that could be modified if there was enough metallurgical or economic incentive, such as water quality or milling media. A third category of chemical factors is those that are fixed and are inherently part of the system, such as the nature of the desired minerals and gangue in the ore. Before the pulp chemistry of a plant can be optimised, it is necessary to elucidate the role of each of these factors in the process. The primary objective of the flotation chemistry research programme is to develop an understanding of the chemical aspects of flotation and to explain the roles and interactions of the various chemical factors to establish their influence on the overall process. The Reagent Research Group (RRG), an industry collaboration between the flotation chemistry research team and selected South African Platinum producers, currently; Anglo American Platinum, Impala Platinum and Lonmin Platinum, was established in 1999 as the Depressant Research Facility (DRF) with the aim to establish a centre for the characterisation and research of polymeric depressants in flotation. However, the effects of depressant action cannot be studied in isolation. Thus, the DRF was rebranded in 2008 to the Reagent Research Group (RRG) to investigate interactions of the major reagents (collectors, depressants, frothers) in the flotation circuit in an integrated manner.

Research Themes

Particle preparation: This research considers the chemistry within the grinding stage. Although most comminution practices focus on particle size reduction, the fact that the majority of theseprocesses make use of a slurry implies that the chemistry can be monitored and/or manipulated to improve flotation outcomes.

Pulp phase chemistry: This research focusses on the various parameters that affect the interaction of reagents and minerals within the pulp phase. The conditions within the pulp phase will determine the species of the reagents present as well as the availability of the mineral surface for interaction. Chemical parameters such as redox potential, dissolved oxygen and pH are the primary focus of this research.

Reagent interactions at interfaces: Flotation behaviour depends on the complex interactions of reagents at the solid-liquid and air-liquid interfaces. These interactions may be synergistic or antagonistic and this research seeks to decouple and interpret the effects of individual reagents and reagent mixtures. It does this by understanding adsorption behaviour and the resultant effect of the adsorption on flotation sub-process, such as the altered wettability of particles, bubble-particle interaction and froth behaviour.

Water in flotation: While water is most often considered as a transport medium in minerals processing, this research considers water as a reagent. Restrictions around water usage are becoming more and more stringent forcing operations to reduce, reuse and recycle where possible. This adds complexity to the chemistry of the system which needs to be understood in order that changing water qualities are not detrimental to the recoveries and grades of the values.

Froth phase chemistry: This research focusses on the various parameters that affect stability of the froth phase, which in turn affects recovery, grade and mass pull. Various bench-scale froth characterisation devices have been designed and manufactured to allow for characterisation of the froth and research efforts continue to focus on tying these characterisation measurements to a prediction of full scale operational outputs.

Activities Supporting Research Themes

Electrochemistry: Measurements such as rest potential and cyclic voltammetry allow for consideration of the reactions occurring at the mineral surface under different pulp chemical conditions. Through electrochemical studies the reagent species at the mineral surface can be considered and correlated with the flotation outcomes observed.

Comminution: While in most flotation studies the grinding of the ore is kept constant, different particle preparation methods will impact on the flotation outcomes owing to the impact they have on the chemistry of the slurry and the particle morphology produced.

Microcalorimetry: This is the measurement of the thermochemical changes that occur with chemical reactions. It is used to measure the affinity of reagents for mineral surfaces and for the measurement of the wettability of mineral surfaces as an alternative to powder contact angle
techniques.

Mineralogy: An understanding of the composition of the ore samples is paramount to being able to determine suitable flotation chemistry conditions.