Influence of Gypsum Addition and Hydrothermal Treatment on Dissolution Behavior of Fluorine in Hot Metal Pretreatment Slags.

Abstract

Immobilization of fluorine by using calcium aluminate, calcium silicate, calcium aluminum silicate and secondary refining slag as a stabilizing agent has been studied by focusing on the effect of gypsum addition on fluorine dissolution from hot metal pretreatment slags in shaking test. When gypsum is added to aqueous solution in which calcium aluminate or secondary refining slag with low contents of both SiO 2 and total Fe are present, fluorine immobilization does not occur due to the formation of ettringite and monosulfate on particle surface of added stabilizing agent. In the case of the mixture of calcium silicate and gypsum, calcium aluminum silicate or secondary refining slag with high SiO 2 and low total Fe contents, fluorine ion in solution can be immobilized through the formation of C-S-H-F-SO 4 gel, Ca 10 (SiO 4 ) 3 (SO 4 ) 3 (OH, F) 2 and Ca 5 [(Si, S)O 4 ] 3 (OH, F). It was found that fluorine is immobilized by hydrothermally treating the mixture of hot metal pretreatment slag, secondary refining slag with high SiO 2 and low total Fe contents and gypsum at 80°C for 3 h.