Soda Ash Recovery from Soda Slag

Abstract

Recently, the demand for production of high quality steel ([P]≤0.010% and [S]≤0.0010%) and for cost saving of steelmaking has been increasing. Especially, in the new refining process for steelmaking using soda ash, soda recovery from soda slag is an important subject. So, we studied and developed new type soda ash recovery process. Our method is characterized as follows.
(1) NaHCO₃ crystallization is reactionary crystallization with lowering pH 11 to 9 and decreasing temperature 80°C to 40°C.
(2) Reflux method of Na₂O solution can decrease water-slag ratio in extracting stage, and as the result, the new process does not need vaporization stage in soda crystallization.
(3) Contaminative components Si, P, and S in solution can be removed (simultaneously) by addition of lime and (small quantity of) magnesia in extraction stage.
(4) Filtrating character of residue is very good by formation of CaCO₃.
(5) The crystal size of recovered sodium bicarbonate is 200μ and over, and its purity is about 97%.