Thermal behaviour of chrome shavings and of sludges recovered after digestion of tanned solid wastes with calcium hydroxide

摘要

The thermal behaviour of chrome shavings and of sludges recovered after digestion of tanned wastes with Ca(OH)_2 was studied. Ashes obtained after incineration of wastes at various temperatures were analysed by X-ray diffraction and EDX method. The main crystallized phases present in the ash obtained at 600 deg C are Cr_2O_3 and NaCl. The diffractograms revealed an increase in the intensities of the chromium oxide peaks and a very notable decrease of the amount of sodium chloride at 1100 deg C. EDX analysis revealed a total disappearance of the chlorine peak at this temperature. Scanning electron micrographs show that the waste lost its fibrous aspect when the temperature increases. Formation of aggregates was noted after 550 deg C. Combustion of organic matters and decarbonation phenomenon are the main stages observed on GTA and DTA curves of sludges. These phenomena are, respectively, exothermic and endo-thermic. The diffractogram of sludges recorded at 550 deg C, in the presence of a constant oxygen surplus, revealed the presence of CaCrO_4 and CaCO_3.