Instrumented column testing of salt uptake from compacted red mud into a cover

Mine waste facility liner and cover systems

Chenming Zhang

The University of Queensland

A cover of inert material overlain by topsoil is proposed over compacted, seawaterneutralised red mud, a waste product from the refining of bauxite to produce alumina, at Queensland Alumina Limited in Gladstone, Queensland, Australia. The cover is to be revegetated, and it is necessary to demonstrate that the potential evaporationdriven uptake of salts from the saline red mud will not impact the re-vegetation. The partially saturated compacted red mud would have a low unsaturated hydraulic conductivity, and it would be buried beneath the cover, limiting evaporative and evapotranspirative stresses at the top of the compacted red mud. Hence, the evapotranspirative uptake of salts from the compacted red mud into the cover would be expected to be minimal and slow.

An instrumented column has been constructed to assess the evaporation-driven uptake of salts from compacted red mud into an overlying cover material. The PVC column is 1.2 m in height, with a 200 mm internal diameter. The column is instrumented with 10 of each of moisture, suction, salinity and temperature sensors, designed and manufactured at The University of Queensland (UQ). The sensors are installed through the wall of the column at regular height intervals, with each set of sensors located at quarter points around the circumference of the column. Two pressure transducers are installed in the column to monitor the change of water level due to rainfall and evaporation. The column is filled with compacted red mud in its lower 600 mm and cover material in its upper 600 mm. The instrumented and filled column is installed on a building roof at UQ, alongside weather stations, and will be subjected to the prevailing weather conditions for up to 1 year in the first instance, during which time the weather conditions and sensor responses will be continuously monitored. This paper reports on the instrumented column set-up and the early results obtained from the test.

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