Leaching of High Kaolinite Content Gibbsite Bauxites with Aluminate Solutions with Various Caustic Moduli.

A study was made of the kinetics of the dissolution of silica and gibbsite from low-quality bauxite with a high kaolinite content during the leaching of the bauxite with aluminate solutions with various alumina contents. It was established that in every case gibbsite is completely dissolved after 30 to 40 minutes of leaching. During leaching with solutions with a high caustic modulus the silica content in the solution at first sharply increases, but then decreases, owing to the precipitaion of a sodium hydroaluminosilicate with the composition Na//2O multiplied by (times) Al//2O//3 multiplied by (times) 2SiO//2 multiplied by (times) nH//2O. During leaching with low-modulus solutions a different pattern is observed: the silica is dissolved more slowly and remains in solution longer.