RE: extraction of aluminae from Saudi Arabia Jeanlouis, alumina extraction trials from clays has been around for a very, very long time. Trouble is, they are uneconomic. From page 37 of the report:
Below a calcination temperature of 450ºC
represent a negligible extraction zone exist. An active zone exists
between 500 and 600ºC and another inert zone exists after about 650ºC.
The alumina extraction yields increase from 17.02% to 62.94% over the
range of 400 to 600ºC
this is an uneconomic process because:
1. calcination temperatures of 450-600C are required to produce maximum yields of 62.94%
Orbite process uses temperatures below 270C, to yield over 87% extraction.
Clearly, the Orbite process is superior and has the added benefit of being able to extract other metals and also to recycle the hydrochloric acid.