TABLE OF CONTENTS Dispersion, selective coagulation and flocculation are the major accessories of the mineral engineering field. The organic and inorganic chemicals used in these functions belong to a group of modifiers. A number of chemicals used as dispersants are also used as depressants and activators. The organic polymers used as depressants are also used as flocculants, when their chemical structure is altered. In a number of applications, dispersants and flocculants are used together where selective flocculation is required.
The dispersing modifiers are used to prevent fine particle from aggregating, and in many cases, to reduce pulp viscosity. Aggregation or the slime coating phenomenon is common where slimes are present in the pulp, and has a negative effect on flotation. Dispersion is also used in various hydrometallurgical processes as well as in selective flocculation where gangue minerals are dispersed while valuable minerals are flocculated.
The action of dispersing agents in mineral processing is therefore to (a) improve flotability of the mineral by preventing slime coating on the mineral particles and (b) disperse fines or gangue minerals during selective flocculation.
The flocculation process is opposite to dispersion. In a dispersed system, particles of all species can be aggregated into larger structures by several mechanisms. Aggregation, based on reducing inter-particle repulsion forces, is known as coagulation and the aggregates are called coagula. If coagulation is induced by a polymer-bridging action, the process is called flocculation and the aggregates are called flocs. When aggregation is achieved as a result of the action of an...
