Influence of FeCl3/Fe3(PO4)2/CaO in sludge on the migration pattern of heavy metals during coal slime combustion

The influence of minerals (FeCl3, Fe3(PO4)2, CaO) contained in SS(Sewage Sludge) on the migration and mechanism of Pb, As, Cu, Cr, Cd in CS(Coal Slime) during the co-combustion process was studied by electric heating tube furnace. Studies have shown that the interaction of minerals in SS with minerals and heavy metals in CS is an important factor affecting the migration of heavy metals in the co-combustion process of SS-CS. The heavy metals combine to form volatile heavy metal-Cl compounds. Compared with the single combustion of CS, the retention rates of Pb, As, Cu, and Cd are reduced by 89.6%, 45.1%, 70.4%, and 89.2% at 900 °C. When CS is blended with Fe3(PO4)2, Fe3(PO4)2 decomposes a large amount of Fe2O3 and P with the increase of combustion temperature to react with As, Cu, and Cr in CS, which makes the retention rate of the three heavy metals increase by 30.6%, 194.1%, and 1726.4% under the combustion condition of 900 °C compared with CS alone. When CS was burned with CaO, CaO had a competitive adsorption effect on Pb and Cd, which reduced the retention rate of Pb and Cd by 12.2% and 58.2% at 900 °C compared with CS alone. Meanwhile, CaO reacted with As, which increased the retention rate of As by 1.3% and 38.9% at 700 °C and 900 °C.The effects of Cl on the migration of Pb, Cu, Cr, and Cd were stronger than those of CaO and Fe3(PO4)2, and Fe2O3 and CaO had the greatest effect on the sequestration of As.