Rapid Thermal Decomposition Of Pyrite Under Protective Atmosphere And Its Effect On The Immobilization Of Heavy Metals

In N₂ atmosphere the common pyrite?Py?and colloidal pyrite?CPy?in tube furnace and muffle furnace could be thermal decomposed.When the temperature reached 650 OC,two kinds of pyrite could be changed to monoclinic pyrrhotite?MPyr?and colloidal monoclinic pyrrhotite?CMPyr?,and the magnetization rate of MPyr and CMPyr reached a high level.The macroscopic results showed that the adsorption of Eu???on MPyr was independent of ionic strength,indicating that inner-sphere surface complexation predominated their adsorption.The kinetic adsorption process was well described by pseudo-second-order model?R2>0.999?.The maximum adsorption capacity of Eu???on MPyr calculated from Langmuir model was 10.03mg?g-1 at p H5.0 and 293 K.The thermodynamic parameters suggested that the adsorption of Eu???on MPyr was a spontaneous and endothermic processes.According to XPS analysis,the adsorption of Eu???on MPyr was mainly dominated by ion exchange and inner-sphere surface complexation at low p H and high p H conditions,respectively.The removal efficiency of Cd???by MPyr and CMPyr in the solution of no dissolved oxygen were high at p H 2⁶,which indicated that the removal efficiency of Cd???was less affected by p H.Moreover,surface oxidation of CMPyr could restrain the interaction between CMPyr and Cd???.The kinetic adsorption process was well described by pseudo-second-order model with high correlation coefficient.The influence of p H,change of concentration of Fe???and SO42-showed that the adsorption of Cd???on MPyr and CMPyr was mainly dominated by ion exchange and surface complexation.The removal of U???on Py and MPyr significantly decreased with increasing ionic strength from 0.001 to 0.1 mol?L-1 at p H 2.0⁶.0.The maximum removal capacity of U???on Py and MPyr calculated from Langmuir model was 10.20 and21.34 mg?g-1at p H 4.0 and 333 K,respectively.The XPS analysis indicated the U???was primarily adsorbed on MPyr and Py,then partly U???were reduced to U???by MPyr after 20 days,the reduction of Py is weak.Based on the XANES analysis,theadsorption edge of uranium-containing MPyr located between UIVO2?s?and U?O22+spectra.The EXAFS analysis demonstrated the inner-sphere surface com-plexation of U???on MPyr due to the occurrence of U-S shell.The surface com-plexation modeling showed that outer-and inner-surface complexation dominated the U???removalat p H < 4 and p H > 5.0,respectively.Fe_1-x S can be used as precipitant,adsorbent and reductant to remove heavy metals in water under various conditions...