Assessment of heavy metals released into the air from the cement kilns co-burning waste: Case of Oujda cement manufacturing (Northeast Morocco)

Abstract

The metallic contents released into the air from cement kilns of Oujda cement plant have been investigated. Heavy metal (HM) concentrations of kiln gas emissions were evaluated and compared to Moroccan standards. The analyzes revealed the presence of various trace metals, i.e., mercury (Hg), cadmium (Cd), thallium (Tl), cobalt (Co), antimony (Sb), arsenic (As), lead (Pb), tin (Sn), selenium (Se), tellurium (Te), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), vanadium (V) and zinc (Zn) in atmospheric emissions of the cement kiln. Analysis of emitted gas revealed that emissions originated from cement kiln #1 were generally in the same order of magnitude as those released from the cement kiln #2. Concentrations of the HMs were found to be higher when the raw mill was not in operation compared to those during operation. Gas emissions remained always below the National Regulation Limit Values (RLV). For the period 2008–2009, results showed that the average values of the metallic abundance were in the order Zn > Mn > Se > Te > Sb > As > Cr > Tl > Pb > Ni > Sn > Cu > Hg > Cd > Co > V, for the cement kiln #1. In addition, Oujda cement plant emissions were assessed over the period 2010 to 2015. The annual average values of HMs were successfully measured, regardless of whether the raw mill was on or off. Therefore, our results suggest that the metal contents from Oujda cement kilns co-burning waste were well below the RLV.