ABSTRACT
The basic purpose of depressants is to improve the selectivity of separation by preventing flotation of unwanted minerals. Since a reagent can prevent flotation by acting on a mineral surface or by reacting with the collector in bulk solution, depressants are specific to a mineral-collector-activator system. This chapter discusses the conditions under which various inorganic reagents act as depressants. The thermodynamic and kinetic information considered valuable in the selection of depressants, the design of flotation separations, and the interpretation of results is included, where possible. Pourbaix diagrams may be used to represent the thermodynamic conditions in which sulfide minerals oxidize. It is generally accepted that oxidation/reduction reactions are important in flotation separation of sulfide minerals with sulfhydral collectors. Several investigators have demonstrated that reducing conditions lead to depression of sulfide minerals. Strong oxidizing conditions also lead to the depression of sulfide minerals. The action of sodium sulfide as a depressant for sulfide minerals is strongly time-dependent.
