Development of a Suitable Slag Practice for Valorization of Fluorine-Containing Slags

Abstract

A submerged N2–H2O gas-injection technique was used to measure the rates of F and Na removal from complex industrial slags containing Al2O3, CaO, FeO x , MgO, MnO, Na2O, SiO2, and F at temperatures between 1125 and 1250 °C. The results show that for a given slag chemistry, the rate of F removal is proportional to the gas flow rate and the square root of the water vapor partial pressure. The rate of F removal was also found to increase with silica concentration in the slag. The Na loss was generally low (<1%) and decreased as the silica content increased. There were no detectable losses of Si and Al. To test the environmental soundness of the slag, a series of fluxed slags were melted at 1250 °C and then water granulated. The slags contained 4% F, between 13 and 17% Na2O, and SiO2 varying from 16 to 45%. The granulated slags were crushed and subjected to the Australian Standard Bottle Leaching Procedure. With less than 20% SiO2 in the slag, the leachate contained over 10 ppm F. Increasing SiO2 above 20% in the slag produced a dramatic reduction of the F content in the leachate, to <2 ppm, and the F content decreased further as the SiO2 content in the slag increased. The slags containing 25% SiO2 or more passed the leaching procedure and were classified as nonhazardous.