Feasibility of Acid–Salt Processing of Alumina-Containing Raw Materials in a Closed-Loop Process

Acid methods for processing of bauxites and aluminosilicates with high silicon content become attractive in connection with the exhaustion of natural alumina-containing resources suitable for processing by standard procedures based on using alkalis. The main problems in using acid procedures are associated with organization of closed-loop processes with low consumption of chemicals and power. The acid–salt technologies suggested by now are based on using ammonium hydrosulfate in the whole cycle and are economically inferior to the classical Bayer alkaline procedure. This study demonstrates on the laboratory level good prospects for developing a new efficient technology for alumina production from low-grade raw materials in a closed-loop process with recuperation of the consumed salt reagent in each cycle. The process takes advantage of the relationships of the aluminum and iron distribution in the solid phases and equilibrium solutions, revealed by the authors. Another feature is the use of a special method of acid retardation in nanoporous media for separating the residual amounts of the acid and salt, which are returned to the head of the process, with substantial saving of the power and chemicals.