Thermodynamic Analysis on the Thermal Treatment of Electric Arc Furnace Dust-PVC Blends

Abstract

This work reports a thermodynamic assessment of EAFD chlorination products stem from thermal decomposition products of PVC. Upon PVC pyrolysis, HCl gas is liberated in conjunction with several volatile organic matters leaving solid carbonaceous residue. EAFD contains appreciable quantities of zinc, iron and lead oxides. These react with HCl to form metal chlorides, if EAFD is added to the PVC as a dechlorination agent. Selective chlorination of zinc and lead present in EAFD leaving iron in its oxide form is of an apparent commercial value. Detailed thermodynamic analysis of EAFD chlorination by HCl was performed considering the effects of several variables. These include temperature, amount of chlorination agent, presence of oxidizing agent and the effect of presence of other EAFD constituents such as sodium, potassium, calcium, silicon and sulfur. It was found that 100% recovery of both zinc and lead can be achieved for mixture containing 50% EAFD and 50% PVC when pyrolyzed under inert conditions, but contaminated with at least 20% of the iron chloride. However, when thermal treatment is performed in the presence of oxygen, the 100% zinc and lead recoveries were achieved at lower temperature with a minimal iron contamination (< 2.6%). Removal of sodium and potassium chloride from EAFD prior to pyrolysis by washing, under oxidizing condition, has also resulted in great selectivity in zinc and lead chlorination. The behavior of other elements during chlorination process was also discussed. The results obtained shall be instrumental in efforts aiming to achieve optimum recycling operations for both categories of pollutants.