The type and concentration of species present on the surface of sphale
rite as a function of pH both in the presence and absence of ferrous i
ons were predicted from zeta potential measurements using a model of t
he electrical double layer. A qualitative description is given of the
method which involves simultaneously solving surface and solution equi
libria including charge and mass balances. The significance of the spe
cies in terms of flotation is discussed.