Influence of leaching conditions on the release kinetics of lead, chromium and nickel from solidified/stabilized cementitious materials

Abstract

In this work, we investigate, on a laboratory scale, the influence of the leaching conditions on the release of various chemical elements from a cementitious material obtained by solidification of PbO, Ni ₂O₃ and Cr₂O₃ with blended cement (CEMII-B32.5, according to European Standards). The pH effects on the pollutants release and the composition of the initial pore solution (target elements: chloride, sulfate, sodium, potassium, calcium, lead, chromium and nickel) were assessed through an experimental procedure consisting of two equilibrium leaching tests [the acid neutralization capacity (ANC) and the pore water (PW) tests] and the maximum mobile fraction (MMF) text. Samples of the same material were submitted in parallel to dynamic leaching tests in order to assess the influence of the boundary conditions (instantaneous liquid/solid (L/S) ratio, solution renewal) on the leaching kinetics of the target elements. The comparison criteria were the leachate saturation state, the released cumulative quantities and the leaching flux. Generally, leachate quantities obtained by the ANC, PW and MMF tests were important. However, the lowest released amount was observed for the monolith leaching test, and leachate saturation slowed down the dynamic release. Finally, experimental results highlighted another important parameter: the influence of the liquid/solid contact type on leaching kinetics.

Keywords:

• solidified/stabilized waste
• heavy metals
• cement-based materials
• leaching phenomena
• pollutant release