Speciation of chromium in swarf during pyrolysis

Abstract

Speciation of chromium in swarf wastes pyrolyzed at 673–873 K has been studied by X-ray absorption spectroscopy in the present work. The least-square fitted X-ray absorption near edge structural (XANES) spectrum shows that Cr 3C 2 (84%) was the main chromium species in the untreated swarf. A small amount of CrO 3 and Cr 2O 3 was also found. During pyrolysis at 673–873 K, Cr (35%) and FeCr 2O 4 (24%) were formed with disappearance of about 43% of Cr 3C 2 in the swarf. By extended X-ray absorption fine structural (EXAFS) spectroscopy, we found that metallic Cr (with Cr Cr bond distances of 2.56–2.59 Å) was formed during pyrolysis. At least two reaction paths might be involved during pyrolysis at 673–873 K: (1) reduction of Cr 3C 2 to metallic Cr and (2) formation of FeCr 2O 4 via reactions of chromium oxides and iron oxides.