Dissolution kinetics of ulexite in ammonia solutions saturated with CO 2

Abstract

The dissolution kinetics of ulexite in ammonia solutions saturated with carbon dioxide were investigated. Experiments investigating the following parameters: concentration of ammonia; particle size; stirring speed; solid to liquid ratio; reaction temperature; and carbon dioxide flow rate; showed that ulexite can be dissolved completely in solutions of carbonic acid at atmospheric conditions. It was found that the dissolution rate increased with increasing ammonia concentration, reaction temperature and calcination temperature, and with decreasing particle size and solid to liquid ratio. It was observed that the flow rate of carbon dioxide and stirring speed have almost no effect on the dissolution rate. It was determined that the dissolution rate of ulexite can be described by a first-order pseudo-homogeneous reaction model and an empirical equation for the process was developed: −1 n(1−X)=1.0×10 5(C A) 0.22(d) −0.92( S L ) −0.54 exp( 6600 T −t) where C A is the ammonia concentration, d the initial particle size and ( S L ) the solid to liquid ratio. The activation energy for the process was found to be approximately 55 kJ mol −1.