In the present paper, an improved solidification/stabilization (S/S) process for the production of cement-based granular
materials from contaminated soils is described. The presented method is based on the use of Portland cement as a
binder and superplasticizers (SPs). The effectiveness of this process on the immobilization of inorganic hazardous
wastes has been tested on a contaminated soil from an industrial site, showing high levels of several heavy metals and metalloids such as copper, zinc, arsenic and lead.
At first, a characterization of the contamination was carried out. The nature and distribution of contaminants have been
investigated in detail by means of SEM-EDS (scanning electron microscopy with energy dispersive spectroscopy) and
micro-PIXE (particle-induced X-ray emission) chemical mapping, both in the original soil and in the cement grains
after the S/S treatment. The coupling of the high imaging capabilities of SEM with the excellent detection limits of
micro-PIXE, allowed the identification of several metal-bearing phases in the investigated samples. The analyses
showed that the main source of pollution is related to the presence of \u3bcm- to mm-sized particles of inorganic
compounds, employed as pigments or additives by the glass production plant formerly operating at the studied area.
In a second stage, the physico-chemical properties of the granular S/S materials were evaluated by means of
mechanical and leaching tests. In particular, the attention was focused on the role played by superplasticizers in the S/S
process. For this purpose, the performances of samples produced following the presented method have been compared with those of similar grains prepared without the addition of superplasticizers. Due to the lower demand of mixing
water, the samples produced using superplasticizers showed a general improvement of performances in terms of
decreased porosity, reduced leaching of contaminants and improved mechanical properties. The laboratory tests that
were carried out showed that the granular materials produced with this improved S/S technique may be suitable for an in-situ re-use as filler or concrete aggregate and may be employed in several other large scale applications
