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Fresh Water Leaching of Alkaline Bauxite Residue after Sea Water Neutralization
Author(s) -
Menzies Neal W.,
Fulton Ian M.,
Kopittke Rosemary A.,
Kopittke Peter M.
Publication year - 2009
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2008.0511
Subject(s) - bauxite , leaching (pedology) , chemistry , leachate , dissolution , salinity , phosphogypsum , red mud , environmental chemistry , soil salinity , soil water , environmental science , geology , soil science , raw material , oceanography , organic chemistry
Processing of bauxite to extract alumina produces a strongly alkaline waste, bauxite refining residue, which is commonly stored in engineered structures. Once full, these waste dumps must be revegetated. In many alumina refineries, the waste is separated into fine‐textured red mud and coarse‐textured residue sand (RS). The sand component has physical characteristics that make it a suitable plant growth medium, provided the adverse chemical characteristics can be addressed. Neutralization of the highly saline‐sodic RS with sea water lowers pH, reduces Na saturation, and adds plant nutrients. However, sea water–neutralized RS remains saline sodic and needs fresh water leaching before use as a plant growth medium. Columns containing sea water–neutralized RS were leached with 30 m depth‐equivalent of fresh water to evaluate the effects of rainfall on the RS and its leachate. Entrained cations were rapidly displaced by the fresh water, lowering salinity to non–plant‐limiting levels (≤0.3 dS m −1 ). The percentage of the effective cation exchange capacity (ECEC) saturated by Na decreased from 71 to 62% due to a reduction in soil solution ionic strength (causing a decrease in the ECEC) and the preferential displacement of Na + (and K + ) from the exchange. Fresh water leaching increased pH (leachate pH increased from 8.0 to 10.1). This pH increase is attributed to the slow dissolution of the Na‐containing mineral sodalite. Under the current experimental conditions, the application of 30 m depth‐equivalent of leaching reduced the total RS sodalite content by <10%.