Process for recovering alumina from red mud by mixing it with soda ash (Na₂CO₃) and ground limestone, and sintering in a rotary kiln at temperatures of 1,800 to 2,000 degrees F (980 to 1,090 degrees C). This breaks up the sodium aluminum silicate and forms an insoluble calcium silicate and sodium aluminate. The sinter is leached with water to recover the sodium silicate, which is then treated in the same way as in the standard Bayer process.