These two factors affect negatively gold recovery by flotation and leaching. Tarnished particles were obtained during the geological formation of the deposit by oxidation, dissolution, reduction, and precipitation processes. For example, some stains of iron oxides could be detected on sulphides particles. Then, there are two effects, first part of the particle is readily floatable and other not. This is a competition between the hydrophobic and hydrophilic areas on the same particle.
Smeared particles are obtained during the ore processing. The main source of these stains is the grinding process. Ball mill operates under different conditions, but there is a common problem, the production of iron compounds. Basically, sulphide minerals and free gold particles react with reagents in flotation and cyanidation. The efficiency of the process is influenced by particle surface changes resulting from the reaction of the grinding media and dissolved gases. In this way, gold recovery is governed by oxidation-reduction reactions in the slurry, although there is some doubt as to whether it is the oxidizing conditions or the oxidant which affect both processes. The level of oxidation of the particles is significant when flotation is performed with xanthates. This condition affects flotation.
It is well known that sulphide minerals are not stable in the presence of water and air and the condition of their surfaces, after primary grind, not only depends if the equilibrium was achieved, else on the oxidation rate. Typically, metallurgists and operators have not considered the effect of the grinding environment on the recovery process.
Nowadays it is possible to know the different types of compound deposited on mineral surfaces and how they were formed. Also, when there are detailed studies, the metallurgist can establish the relationship between pH and pulp potential in order to know the conditions that favor this problem.