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A new process for Al 2 O 3 production from low‐grade diasporic bauxite based on reactive silica dissolution and stabilization in NaOH‐NaAl(OH) 4 media
Author(s) -
Ma Jiayu,
Li Zhibao,
Xiao Qinggui
Publication year - 2012
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.12722
Subject(s) - dissolution , bauxite , leaching (pedology) , bayer process , aluminium , chemistry , precipitation , inorganic chemistry , chemical engineering , nuclear chemistry , organic chemistry , geology , physics , meteorology , soil science , engineering , soil water
Abstract A new process of Al 2 O 3 production from low‐grade diasporic bauxite based on the reactive silica dissolution and stabilization in concentrated NaOH‐NaAl(OH) 4 solutions is proposed and proved feasible. NaOH and Al 2 O 3 concentrations and leaching temperature were found to be the main factors affecting the leaching process of reactive silica. The A / S (mass ratio of Al 2 O 3 /SiO 2 ) of diasporic bauxite was enhanced from 5.4 to 15 by reactive silica removal under the optimum operation conditions. Two obvious steps control the whole leaching process of reactive silica in NaOH‐NaAl(OH) 4 media: reactive silica dissolution and desilication products (DSPs) precipitation. The kinetics data of two controlling steps fit a shrinking core model based on the calculation of OH − activity with the aid of OLI platform and an empirical kinetic model well, respectively. Apparent activation energies of reactive silica leaching in the temperature range from 80 to 110 °C are 101.91 and 58.65 kJ mol −1 for the two steps, respectively. The stabilization mechanism of reactive silica in concentrated NaOH‐NaAl(OH) 4 solution was also elucidated based on the complexation of aluminum‐bearing species and the calculation of supersaturation to DSP. It was found that the concentration of OH − sharply decreases due to the formation of Al(OH) 4 −species with increasing aluminum concentration, suppressing greatly DSP precipitation. This proposed process paves the way for Al 2 O 3 production from low‐grade diasporic bauxite with high‐reactive silica content. © 2011 American Institute of Chemical Engineers AIChE J, 2012