Surface and chemical properties of chlorite in relation to its flotation and depression

The chlorite group of minerals exhibit a wide range of surface charging properties in aqueous suspensions. A systematic review of the literature as it relates to the flotation, depression and surface properties of chlorite and related minerals was undertaken, with a view to using this information to help develop suitable reagent schemes which might allow the selective removal of chlorite from sulphide and oxide flotation systems. The surface charge on chlorite mineral particles originates from permanent charges on basal planes of the crystallites and pH dependent (amphoteric) charge on crystallite edges, typical of clay minerals. The net charge on chlorite particles depends upon the edge/face plane ratio (crystallite size), the solution pH and the presence of specifically adsorbing ions (principally Ca2+). Both cationic and anionic surfactants (collectors) are observed to adsorb on chlorite particles, over a wide range of pH conditions. This apparently contradictory behaviour is most likely due to the dual modes of surface charging and the effects of cation substitution into the chlorite lattice. In the case of anionic collectors, some specific (chemical) adsorption energy may also contribute to the adsorption properties. Chlorite depressants used in oxide and sulphide flotation are typical of those used for other silicate minerals. The most common of these depressants are sodium silicate (Na2SiO3), carboxymethylcellulose and fluoro compounds (hydrogen fluoride and sodium hexafluorosilicate). There have been no studies of the effects of the chlorite surface charging properties upon depressant selection, although it appears likely that the edge/face plane ratio will strongly influence the depressant adsorption behaviour.