Molecular modelling of reagents for flotation processes

It has long been recognized that the selectivity of froth flotation processes is highly influenced by the specificity of interactions between minerals and reagents that are used to control the hydrophobic/hydrophilic character of the mineral/water interfaces. We have modelled mineral surfaces (hydroxy-apatite, calcite) and molecules of two polysaccharides (starch, ethyl-cellulose) which are candidates as depressing agents for calcite. A special parameter named “Total Fitting Number” (Ft) was developed to assess the steric compatibility between the structure of both minerals and polysaccharide species. The calculation of Ft was based on measurements of OH-OH distances that exist at reagent molecular structures versus Ca---Ca distances that exist along the most common crystallographic orientations (hkl) exhibited by mineral particles.Higher values of Ft were found for the interaction calcite/starch than calcite/ethyl-cellulose. This finding suggests that starch is a more effective depressant for calcite than ethyl-cellulose. However, low values of Ft were found for the interaction apatite/starch and apatite/ethyl-cellulose. This fact means that both substances are unlikely to act as depressants for apatite. Microflotation response of apatite and calcite with sodium oleate (pH = 10.2) in the presence of both polysaccharides corroborates the model.