Search

The revegetation of bauxite refining residue, red mud, produced from alumina refining is extremely difficult because of the high amount of Na in the residue especially in the desilication product (DSP). The high Na content imparts to red mud highly saline and sodic characteristics. The present study was to develop means to revegetate red mud through the control of Na release and the utilization of acidic and organic ameliorants together with tolerant plant species. Neutralization of red mud with HCl showed that the DSP, which was found to be a zeolite mineral akin to nosean, decomposed at pH between 5.4 and 7.0 and with a maximum Na release of 98.6 meq/100 g occurring at pH 5.4. At pH >7, the release of Na was due to the cation exchange between Na+ in red mud with H+ , and Ca2+ from dissolution of calcite. At pH between 5.4 to 7.0, Na release from the DSP was due to acid hydrolysis. The cation exchange capacity (CEC) obtained with monovalent cations was higher than with divalent cations. About 83 meq Na /100 g red mud could be displaced by K+ with repeated washings. Divalent cations could only displace about one third of the Na. The external CEC of red mud was estimated to be 15.4 meq/100 g while the internal CEC of red mud was 49.6 meq/100 g. A selectivity sequence for red mud was established: K > Li > NH4 > Ba ≥ Ca> Mg at a cation fraction on red mud ≥ 0.2. Four first-order reactions could be used to describe the release of Na from Na-K and Na-Ca exchanges in red mud with a total release of 61 and 31 meq/100 g red mud respectively. Sodium located in the external sites was released in about 6 h and 3 days for K and Ca exchange respectively. The final rates of Na desorption from the DSP were low for both exchanges. This indicates that the sodicity of red mud may increase with time. A glasshouse pot trial was used to investigate the effectiveness of copperas (FeSO4) and gypsum (CaSO4) for red mud reclamation. Copperas was effective in reducing the EC and Na content o

by Wong Woon-chung Jonathan., Bibliography: leaves 232-260, Thesis (M.Ph.)--Chinese University of Hong Kong, 1984, http://library.cuhk.edu.hk/record=b5885475, Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/)