An experimental study of the reaction of sulfur dioxide with pyrrhotite produced by pyrolysis of pyrite

摘要

Recovery of sulfur dioxide from flue gases of non-ferrous smelters is a pressing environmental issue.Flue Gas De-sulfurisation(FGD) processes which produce elemental sulfur are attractive but existing technology using carbon based reductants is costly.This paper describes a reaction between pyrrhotite (produced by pyrolysis of pyrite) and sulfur dioxide which could be the basis for a FGD process.In the past the reactions between iron sulfides and sulfur dioxide have been extensively studied at temperatures above 600 deg C, where the products are magnetite and sulfur,but the thermodynamics and kinetics are unfavourable.The reaction at temperatures below about 600 deg C, where the products include pyrite and magnetite,however,is not well understood. A laboratory kinetic study was undertaken in which pyrite was pyrolysed to pyrrhotite and the pyrrhotite then reacted with sulfur dioxide.Pyrolysis conditions at 650 to 825 deg C produced porous hexagonal pyrrhotites of compositions FeS_1.11 to FeS_1.06 Reaction of these with sulfur dioxide produced monoclinic pyrrhotite and magnetite at 300 to 350 deg C, magnetite and pyrite at 375 to 550 deg C,and magnetite and sulfur vapor above 550 deg C.The greatest conversion (to pyrite and magnetite) occurred at 450 deg C and the reaction was effectively complete in an hour in pure SO_2; the rate and conversion decreased with decreasing sulphur dioxide concentration.A mechanism for the reaction was hypothesised which involved the conversion of initial pyrrhotite to an iron-deficient iron sulfide through diffusion of iron out of the crystal lattice to the gas - solid interface and reaction with sulfur dioxide to produce magnetite and sulfur.