Arsenic partitioning behavior during sludge co-combustion: Thermodynamic equilibrium simulation

Abstract

Using the computation method of thermodynamic equilibrium, effects of sewage sludge (SS) co-combustion conditions and interactions with Fe2O3, SiO2, CaO and Al2O3 on migration and transformation of arsenic (As) were simulated in oxy-fuel (CO2/O-2) and air (N-2/O-2) atmospheres. Arsenic mainly existed as As(s), As-4(g), As2O5(s), As4O6(g) and AsO(g) and volatilized more easily in reducing than oxidizing atmosphere. Increased O-2 concentration slowed down the formation rate of AsO(g), thus reducing the volatilization rate of As. With the increased pressure, the conversion rate of As2O5(s) into As4O6(g) accelerated. In the multi-chemical system of SiO2, Al2O3 and CaO, As reacted with CaO and Al2O3 to form AlAsO4(s) and Ca-3(AsO4)(2)(s) which inhibited As volatilization. SiO2 prevented As from reacting with CaO to generate Ca-3(AsO4)(2)(s). Fe2O3 affected reactions between Al2O3(CaO) and As which inhibited As volatilization. In the whole SS co-combustion system, As reacted with O-2 but had a weak affinity with Cl and with no arsenic chlorides observed.