With the addition of urea as an inhibitor,four groups of reducing dioxin emission experiments in sintering pot were conducted.The results show that,adding 0.05%,0.1% and 0.5%(mass fraction) urea,the emission concentrations of dioxin are 0.287,0.258 and 0.217 ng-TEQ/m3,respectively,The dioxin emission rates drop substantially compared to 0.777 ng-TEQ/m3 free of urea.With an increase of the urea content,the concentration of SO2 emission reduces sharply.(NH4)2SO4,formed by the reaction of SO2 and NH3,goes into the dust and part of NH3 is released before reaction with the emission of exhaust gas.The NOx emission presents an increasing trend because the reaction of NH3 and O2 at high temperature produces NOx.Based on the consideration of factors such as the effect of reducing dioxin emission,and the chemical composition of exhaust gas,0.05% is the optimum adding content of urea.
Chromium slag(CS)has become one of the most hazardous solid waste containing chromium and iron.Based on its characteristics,the technology of reduction roasting and magnetic separation was employed to treat CS.The major impurity element of CS is magnesium and it exists in magnesium ferrite phase,which is hard to recover iron in the absence of additives.During reduction roasting,additives(Al2O3and CaF2)could destroy the structure of magnesium ferrite and improve the iron grade and recovery.The final product,i.e.chromium-iron powder,contains 72.54% Fe and 13.56% Cr,with the iron recovery of 80.34% and chromium recovery of 80.70%.
Hong-ming LONGQing-min MENGPing WANGTie-jun CHUNYong-lin YAO
