Mechanical and leaching behaviour of slag-cement and lime-activated slag stabilised/solidified contaminated soil

Stabilisation/solidification (S/S) is an effective technique for reducing the leachability of contaminants in soils. Very few studies have investigated the use of ground granulated blast furnace slag (GGBS) for S/S treatment of contaminated soils, although it has been shown to be effective in ground improvement. This study sought to investigate the potential of GGBS activated by cement and lime for S/S treatment of a mixed contaminated soil. A sandy soil spiked with 3000 mg/kg each of a cocktail of heavy metals (Cd, Ni, Zn, Cu and Pb) and 10,000 mg/kg of diesel was treated with binder blends of one part hydrated lime to four parts GGBS (lime-slag), and one part cement to nine parts GGBS (slag-cement). Three binder dosages, 5, 10 and 20% (m/m) were used and contaminated soil–cement samples were compacted to their optimum water contents. The effectiveness of the treatment was assessed using unconfined compressive strength (UCS), permeability and acid neutralisation capacity (ANC) tests with determination of contaminant leachability at the different acid additions. UCS values of up to 800 kPa were recorded at 28 days. The lowest coefficient of permeability recorded was 5 × 10− 9 m/s. With up to 20% binder dosage, the leachability of the contaminants was reduced to meet relevant environmental quality standards and landfill waste acceptance criteria. The pH-dependent leachability of the metals decreased over time. The results show that GGBS activated by cement and lime would be effective in reducing the leachability of contaminants in contaminated soils.

Research Highlights
► Cement and lime activated slag were used for treatment of a mixed contaminated soil.
► The performance of the treated soil was assessed by mechanical and leaching tests.
► There was significant reduction in the leachability of heavy metals and organics.
► The treatment reduced the pH-dependent leachability of some heavy metals over time.
► Hence, treated soils could be put to beneficial uses without threat to human health.