Gold Flotation with Nitrogen
Interaction of gold-bearing minerals, base metal sulphide minerals and native metals (e.g. gold, copper, silver) with reagents in flotation is largely determined by particle surface changes resulting from the action of the medium and dissolved gases. Sulphide minerals flotation is known to be affected by oxidation-reduction conditions in the pulp, although there is some doubt as to whether it is the oxidizing environment or the type of oxidant which influences flotation. The degree of oxidation of the surface is especially important when flotation is carried out with xanthates. The products formed affect flotation. Sulphides are unstable in the presence of water and air and the state of their surface, after grinding, not only depends on reaction equilibrium, else on reaction kinetic. Most of people have tended for many years to overlook the chemical environment in grinding mills and their effects during the flotation process. Nowadays it is possible to establish the relationship between pH and pulp potential of solutions in contact with sulphides minerals or ores.
It has been noted that the physicochemical conditions before flotation (i.e. crushing, grinding, conditioning) have an effect on the separation. Further, in the flotation process that follows, for a given set of preparation conditions, the separation that is achieved is dependent on the pulp potential that is obtained. Air is added usually as the flotation gas. Few times happen that the air set steady state pulp potential in a flotation circuit is sometimes suitable for the flotation process. Many times, the air set steady state pulp potential will no reached at the start of a flotation circuit, if reducing conditions existed during the grinding stage and air is added in an unexpected way during transportation from the grinding mill to the rougher flotation circuit. It is probable for the pulp potential to be less than the value needed for adequate collector adsorption, causing low flotation rates.
In some gold flotation plants, changes of the air set pulp potential to another value may give a more efficient flotation. The pulp potential can be changed by the use of oxidizing and reducing agents, by the use of nitrogen or nitrogen/air mixtures to halt the increase in pulp potential after leaving a reducing environment in a grinding mil containing mild steel balls, and by direct connection to a power supply. Employ an oxidizing or reducing agent and an appropriate gas can lower the addition rate of the agent needed to achieve a target pulp potential. Nitrogen is the gas that has been studied with more extension and its application in separations by froth flotation has been implanted like solution to many problems when there is a complex ore.