Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Instrumented column testing and numerical modelling of evaporation induced salt accumulation and precipitation from underlying bauxite residue to soil cover under natural weather conditions (422)

Chenming Zhang 1 , David Williams 1 , Wenqiang Zhang 1 , Ximing Lei 1 , Mike O’Neill 2
  1. School of Civil Engineering, the University of Queensland, Brisbane, QLD, Australia
  2. Queensland Aluminium Limited, Gladstone, QLD, Australia

The best cover design for mine rehabilitation is to effectively minimise the salt uptake from mine tailings from uplifting by evaporation, so that the cover can provide healthy accommodation for vegetation. An instrumented column was constructed to test the evaporation-driven uptake of salts from compacted red mud into an overlying cover material. The PVC column is 1.2 m in length, with a 200 mm internal diameter. The top 0.6 m was filled by compacted bauxite residue with a salinity of 35 part per thousand (PPT) and the top 0.6m was covered by sandy loam material. The column was instrumented with 10 of each of moisture, suction, salinity and temperature sensors, designed and manufactured in-house at The University of Queensland (UQ). The instrumented and filled column was installed on a building roof at UQ, alongside weather stations, and was subjected to the prevailing weather conditions for two years. Numerical modelling was carried out to simulate the evapo-concentration and precipitation, and associated transport of liquid water, water vapour, salt and heat. Both the modelling and column testing results indicate when water table could be maintained in the cover material, the water table acts as a barrier layer to prevent salt uptake during evaporation. However, if water table fell in to the bauxite result, the salt in the tailings would eventually transport to the cover and deteriorate the pore water quality in the cover material. This testing and modelling results provide key physical insight on salt dynamics in the unsaturated zone and cover design criteria.