Migration and transformation of heavy metals during pyrolysis of printing and dyeing sludge

The effects of pyrolysis conditions and sludge water content on the distribution of heavy metals, Cr and Cu, in the pyrolysis residues of printing and dyeing sludge were studied through the horizontal tube furnace pyrolysis experiments, and the release trend of heavy metals in the pyrolysis residues was discussed. Experiments show that under N₂ atmosphere, the release rate of Cr in the sludge is basically not released with the increase of temperature, but the form of chromium in the printing and dyeing sludge can be converted to more stable Cr³⁺ due to the reducing atmosphere provided by it. In the simulated dry flue gas atmosphere containing oxygen, the chromium in the printing and dyeing sludge was oxidized, so that the release was promoted. The copper in the printing and dyeing sludge has a very low pyrolysis volatilization under N₂ atmosphere, while in dry flue gas, the CO₂ generated by CO₂ pyrolysis reduces Cu to form CuCl, which increases the release of copper. At the same time, the increase of sludge water content is conducive to the fixation of the two heavy metals in the coke. The inhibition of Cr release by water is mainly achieved by providing a reducing atmosphere; while for copper, water can promote the chlorine in the sludge to generate HCl, thereby reducing the Volatilization of CuCl.