Covering and revegetation of red mud disposal sites is a complex engineering task,
due to the special conditions, such as the high pH and the high exchangeable sodium
content of red mud. The capillary barrier system introduced in this paper consists
of two layers, a capillary block layer and a capillary layer made from construction
waste such as crushed concrete and brick. The capillary block layer consists of a
coarse material that prevents upward capillary transport of the highly alkaline and
Na+ containing liquor from the red mud while the capillary layer comprises fine material
that withholds and stores the infiltrating water from precipitation. The function
and capacity of the capillary barrier system was tested and monitored in scaled-up
experimental series: 1. plastic vessels to test the waste materials (1−1.5 kg); 2.
microcosms (20 kg) for modelling the processes at a larger scale; 3. open-air lysimeters
(1.5 tonnes) for measuring the technological parameters under field conditions. We
characterized the waste materials of the capillary system by the integrated application
of physico-chemical analyses and environmental toxicity testing. Chemical analysis
showed that the applied materials do not contain mobile metals that might pose additional
risk. The environmental toxicity tests proved that the applied materials are non-toxic.
The results of the microcosm studies showed that crushed concrete of 30−50 mm particle
size can be used as capillary block layer, while both the 0−20 mm particle size crushed
concrete and the 0−6 mm particle size crushed brick can be used as capillary layer.