An investigation into a bentonite clay based geosynthetic liner in a caustic refinery environment

Abstract

Bauxite residue (red mud) management is a major environmental issue for alumina refineries. The global average for residue storage can cover in excess of 2.1 million square metres per refinery and is increasing annually by 300 to 400 thousand square metres. Residue has the potential to damage surface and groundwater quality due to the residue’s high alkalinity. Bauxite residue drying areas (RDAs) need to be designed in a manner that is safe for the population and the natural environment. Currently, RDA construction practice relies on the placement of a minimum of two clay lifts, a constructed low permeability base and an embankment seal that is at least equivalent to a 0.5m depth of mechanically compacted clay with a permeability coefficient of less than 10-9m/sec. This is overlain with a high-density polyethylene (HDPE) geomembrane, as the primary seal against seepage of caustic liquor. In Western Australia it is becoming increasingly difficult to source sufficient clay for future RDA constructionTo continue to meet and improve on current community and environmental standards, this investigation proposes an alternative to the clay lining system. A factory prehydrated geosynthetic liner (GCL) was evaluated in terms of its feasibility and its use in the design of a RDA, which would reduce the dependency on the sourcing of mass volumes of high quality clay from potentially long distances. The investigation also reviews the use of the GCL in a structural application, utilising it as a secondary containment measure under concrete bunds containing alumina process tanks.