Process for the extraction of alumina from minerals, rocks and industrial by-products

A process for recovering alumina present in an alumina-bearing material selected from the group consisting of minerals, rocks, and industrial waste products derived from such minerals or rocks comprising the steps of:

• a. kneading particles of said alumina-bearing materials with lime and water to form a homogeneous plastic mass, said lime being present in an amount of 1 to 3 moles per mole of alumina in said alumina-bearing material;
• b. forming said homogeneous plastic mass into a plurality of shaped bodies;
• c. maintaining said shaped bodies under hydrothermal conditions at a temperature of up to 200.degree. C for a time sufficient for the bodies to harden by hydraulic setting and to solubilize the alumina in the bodies by reaction with said lime;
• d. comminuting the hardened bodies;
• and
• e. leaching the solubilized alumina from the comminuted hardened bodies.