Durability of stabilised galvanic sewage sludge against the impact of sea water and sulfate solutions

Abstract

Solidification of industrial sludge in concrete matrices has been examined. The concrete mixes in which galvanic sewage sludge was immobilised were prepared with the use of two binder types: Portland-fly ash cement CEM II/B-V, and a binder composed of Portland cement (60%) and fly ash obtained from fluidized bed combustion of fuels (40%). Leaching of heavy metals (Cr, Cd, Zn, Ni, Cu, Pb, V) was observed from solidification matrices which had been exposed to various aqueous media (distilled water, sea water, sulfate solution) over a long period of time. Features of concrete were also studied which could directly influence the release of heavy metals, i.e. their microstructures and microporosity. Moreover, the effect of sewage sludge addition was shown on physical and mechanical properties of concrete, i.e. compression strength, water absorbability and water penetration depth were analysed. The research programme covered the periods of 1 year and 2 years, during which the concrete samples were stored in various aqueous environments. The stability parameters of the matrix which contained fly-ash from fluidized bed combustion of fuels were found not to be much different from the parameters for the matrix which was based on the Portland-fly ash cement. Leachability of heavy metals was demonstrated to increase in the aggressive aqueous medium as compared to the level obtained when the samples were stored in distilled water.