Solidification/stabilisation of Zn-contaminated soils using cement and soda residue

Soda residue is a by-product of sodium carbonate manufacturing and has a highly adsorptive capacity for heavy metal ions. Thus, this research intended to utilise soda residue to remediate zinc (Zn)-contaminated soil by partial replacement of cement based on the stabilisation/solidification (S/S) method. Then, the effectiveness of S/S based on cement blended with soda residue was evaluated through an unconfined compressive strength (UCS) test, an electrical resistivity test and the toxicity characteristic leaching procedure (TCLP). Results show that UCS increases with the increase in total binder content and curing time, while it decreases with the increase in zinc ion (Zn2+) concentration in the soil. The leached zinc ion concentration determined through TCLP decreases with increasing curing time. Increasing the curing time, mass ratio of cement to soda residue and total binder content results in an increase in the electrical resistivity of the specimen, while a reverse trend occurs with the increase in zinc ion concentration. Based on the results of X-ray diffraction analysis and scanning electron microscopy, the formation of hydrated products such as calcium silicate hydrate, calcium aluminate hydrate and ettringite can be detected, as well calcium zincate hydrate (CaZn2(OH)(6)H2O), which is responsible for zinc ion immobilisation.