Thermal and XRD analysis of Egyptian galena

Galena is the principal ore mineral for lead industry and the production of lead and its alloys. The industrial processing of galena includes its oxidized roasting to lead oxide, followed by reduction smelting of lead oxide agglomerate with coke in the blast furnace to commercial lead. The present work reports a thermal analysis study of oxidized roasting of Egyptian galena using a derivatograph. The reaction products were identified microscopically and by using a Siemens Crystalloflex diffractometer. On roasting of galena (heating in the air flow), its oxidation to lead sulphate was shown by a wide and small exothermic DTA peak at 460 degrees C. The reaction between galena and lead sulphate, produced PbSO4 center dot PbO at 580 degrees C, is shown by a small exothermic peak. A large and sharp exothermic tripple maximum at 730, 740 and 765 degrees C was due to the intensive oxidation of galena, accompanied by an increase in mass (TG). This mass increase is attributed to the formation of different sulphates. The mass loss is observed at temperature higher than 900 degrees C due to the dissociation of the sulphates to lead oxide and evolution of sulphur dioxide. The standard free energy (Delta G degrees) and equilibrium constant (K) of the reaction of oxidation of galena to lead oxide at 800 degrees C are -167.102 kcal mol(-1) and 1.09 center dot 10(34), respectively. These values reflect the irreversibility of the reaction. The products of the oxidized roasting of galena are different, depending upon the temperature of roasting such as anglesite at 300 degrees C, basic lead sulphates of specified compositions: (PbSO4 center dot PbO at 600 degrees C, PbSO4 center dot 2PbO at 800 degrees C and PbSO4 center dot 4PbO at 900 degrees C) and lead oxide at 1000 degrees C.