Interaction effects of chlorine and phosphorus on thermochemical behaviors of heavy metals during incineration of sulfur-rich textile dyeing sludge

Sulfur (S)-rich textile dyeing sludge (TDSS) with different chlorine (Cl) and phosphorus (P) contents was incinerated at 900 degrees C to determine interaction effects of Cl and P on the distributions and transformations of the seven heavy metals (Ni, Pb, Cr, Cu, Zn, Mn, and Cd). The volatilizations of the heavy metals were adversely affected by the P addition. The Cl addition in low concentrations offset the negative effects of P on the Ni, Cr and Mn volatilizations. An interaction effect between Cl and P was found on the Pb and Cd volatilizations. Up to certain Cl and P concentrations, their synergistic effect restrained the Ni, Cu, Mn and Cr volatilizations but promoted the Zn volatilization. The addition of Cl/P in different ratios changed the distributions of Cu, Mn, Pb, and Cd. The addition of over 1% NH4Cl and NH4H2PO4 together decreased the residual fractions mainly transformed into oxidizable forms (6.5-19.7%) which in turn raised their potential toxicity and bioavailability. With the decreased Cl and S contents of the bottom ash, the volatilization rate of Cl was higher than that of S. The NH4H2PO4 addition increased the Ca content on the surface but decreased the Cl and S contents. S emissions were mainly in the forms of SO2, SO3, COS, CS2, and H2SO4, with Cl emission in the form of HCl. The increased P content was correlated with the Cl volatilization positively and the S volatilization negatively. The increased P content decreased the S volatilization by 11.2-17.0% with the addition of up to 1% Cl.