Study On The Crystal Chemistry And Floatability Of Pyrrhotite

Usually, pyrrhotite exists in many non-ferrous metallic ores as an associated mineral with little industrial value, but it is the main resource of sulfur. Flotation is the most common method for the separation of pyrrhotite from other minerals. However, pyrrhotite is variable in the properties of crystal chemistry and easy to be oxidized, which usually has a great influence on flotation of the purpose minerals, and it also causes a big problem for the flotation separation of non-ferrous metal ores. Pyrrhotite is always presented in many non-ferrous metallic ores, so many mines have the problems of the interference of pyrrhotite on flotation process. The differences of crystal structure and electronic structure between monoclinic and hexagonal pyrrhotite were studied detailedly as well as the floatability differences of both minerals in this paper.The band structure, density of states and frontier orbital energy of ideal monoclinic and hexagonal pyrrhotite were calculated by CASTEP of Material Studio. The results show that hexagonal pyrrhotite is an indirect gap semiconductor while the monoclinic is a conductor mineral, and monoclinic pyrrhotite is easier to be oxided and react with oxygen and butyl xanthate than hexagonal pyrrhotite.The results of pure mineral flotation tests show that the relationships between flotation recovery of minerals and slurry pH are similar both for monoclinic and hexagonal pyrrhotite. However, monoclinic pyrrhotite is easier to be floated than hexagonal pyrrhotite, and it is more difficult to be depressed. Hexagonal pyrrhotite is easier to be activated by copper sulfate than monoclinic pyrrhotite in acidic solution. Lime has shown no inhibition on the non-activated monoclinic pyrrhotite, but it has a little inhibition effect on the non-activated hexagonal pyrrhotite. After activated by copper sulfate, the flotation recovery of hexagonal pyrrhotite is nearly close to monoclinic pyrrhotite in the weak acidic and neutral solution. The combined depressant, sodium humate and calcium chloride, has shown good inhibition on the activated monoclinic and hexagonal pyrrhotite by copper sulfate in the range of pH 2-12.5, but the depression of hexagonal pyrrhotite just needs less dosage of combined depressant.The surface electrical difference between monoclinic and hexagonal pyrrhotite was studied by the measurement of zeta potential. The results show that the PZC of monoclinic and hexagonal pyrrhotite are about 7.3 and 8.8, respectively. FTIR was applied to study the possible products produced by the reaction between reagents and both pyrrhotites. The results present that the products on both pyrrhotites are the same as dixanthogen after reacted with butyl xanthate. The different crystal structures lead to different molecular bonding force, so the absorption peaks of butyl xanthate on both pyrrhotites surface are different. By the analysis of Eh-pH diagrams of Fe-S-H2O system, the hydrophobic So could be generated on the surface of both pyrrhotites in the entire pH range if the Eh is appropriate. The optimal Eh range of monoclinic and hexagonal pyrrhotites for self-induced flotation is the same as the Eh range predicted by Eh-pH diagrams.