The processing of high silica bauxites — Review of existing and potential processes

World reserves of bauxite include vast quantities of ore which at present are sub-economic due to high levels of reactive silica that cause expensive loss of caustic soda during Bayer processing. As the economic reserves of high grade ores diminish, attention is turning to how these lower grade ores may be processed at reasonable cost. This paper presents a review of existing and potential processes from the open literature that have been proposed for high silica bauxites. The processes have been divided into three strategies for reducing soda loss. These are (i) reduce the input of reactive silica into the process (ii) modify the process to produce a low soda residue and (iii) recover caustic soda by re-processing residue. For each of the processes considered, a description of the principle is given along with the current status and any hurdles (economic, environmental etc) to implementation.For each strategy the review identifies the most promising processes for future consideration.