Surface contaminants on cassiterite recovered from an industrial concentrator

Abstract

The industrial flotation of cassiterite can vary significantly from that which might be expected from most surface chemical and micro-flotation studies. Metal hydroxides adsorbed on minerals in plant pulps were thought to be contributing to this variation because most cassiterite collectors can interact chemically with heavy metal ions. Two techniques for the examination of solid surfaces (X-ray photoelectron spectroscopy - XPS; secondary ionization mass spectroscopy - SIMS) were used to examine cassiterite grains recovered from the tin concentrator of Renison Limited (Australia). These analyses showed that the amount of iron on the surface of the grains exceeded the iron concentration in the cassiterite lattice but there was no evidence of a disproportionate accumulation of iron on the surface by migration from the interior of the mineral. The data were consistent with ferric sols being adsorbed on the surface of the cassiterite before the test work. These sols are derived in Renison pulps from ferrous ions produced by the oxidation of grinding media during comminution, by the oxidation of pyrite and pyrrhotite in the ore and by the dissolution of siderite. At the pH of flotation, aeration of pulps results in the oxidation of ferrous ion to ferric hydroxide. The electrokinetic properties of the cassiterite, after drying, were found to be unchanged by the iron contamination contrasting with the behaviour of oxides on which metal hydroxides have freshly precipitated.