Relationship between cation distribution with electrochemical and flotation properties of calcic amphiboles

• The crystal structure of amphiboles defined their surface properties.
• The isoelectric points of monoclinic calcic amphiboles were achieved at pH < 4.
• The floatability of amphiboles was very sensitive to the amine surface coverage.
• The density of Mg surface centres played a key role in the adsorption of starch.

Reverse cationic flotation is a very efficient method of beneficiation of oxidised iron ores when you need to separate hematite and quartz. This method can be also applied to reduce silica content in the magnetite concentrates obtained by wet low-intensity magnetic separation. However, cationic flotation in this case is less effective due to the presence of Fe–Mg–Al-bearing silicates as amphiboles in magnetite ores. These silicates are concentrated in magnetic products and determine the difficulties of their separation from iron oxides when amines and starches are used as collectors and depressants, respectively. The recalculation of the results of the electron microprobe analysis of five calcic Fe–Mg–Al-bearing amphiboles used to characterise cation distributions in structural units and to obtain structural formulae in accord with stoichiometric limits was conducted. The Mössbauer spectroscopy was used to examine the validity of the empirical estimation of cation distributions in amphiboles. The studied samples are metamorphic pargasite, ferrotschermakite and magnesiohornblende and volcanic kaersutite and magnesiohornblende. The crystallographic analyses of the amphibole samples exhibited their heterogeneous surfaces explaining worse floatability of amphiboles with amines at pH 10. The electrokinetic measurements showed that the position of the isoelectric point of amphiboles is related to a substitution of Al3 + for Si4 + in tetrahedral sites and to an amount of Mg2 + cations in octahedral sites. Thus, the amine adsorption onto amphiboles through electrostatic interactions is mainly affected by a distribution of these cations in tetrahedral and octahedral sites of amphiboles. In addition, the effect of starch on the depression of Fe–Mg–Al-bearing amphiboles during flotation can be attributed to the presence of metal ions on the amphibole surface, which are capable of forming strong chemical complexes with starch molecules.

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