Calcium aluminate cement as an alternative to ordinary Portland cement for the remediation of heavy metals contaminated soil: mechanisms and performance

Abstract

Purpose This work deals with the application of a solidification/stabilization process with the aim to obtain safe and reusable granular materials from a polluted soil and to elucidate the mechanisms involved in the retention of several heavy metals. Materials and methods The High Performance Solidification/Stabilization (HPSS®) process was applied to the selected contaminated soil by using both ordinary Portland cement and calcium aluminate cement, as well as several binders prepared by combining these two types of cement in different proportions. Leaching and mechanical tests were carried out to evaluate the performances of the proposed binders in the pellets produced by the HPSS® process, while XRD analysis and SEM/EDX imaging were used to investigate the phase composition and internal microstructure of the treated samples. Result and discussion The examination of the obtained granular materials revealed that the immobilization of Sb was mainly related to its inclusion within calcium silicate hydrates’ structure; the immobilization of Cr, Pb, Ni, Co, Zn and Tl was associated with the eluate pH and their incorporation within ettringite structure, while for Se, Cu, Ba and V, the main retention mechanism was physical encapsulation. In addition, the application of a wet conditioning process improved the materials’ performance, leading to granules always satisfying the Italian regulatory requirements for reuse. Conclusions The findings obtained in this study were useful to better elucidate the mechanisms involved in the retention of heavy metals by several binders, contributing to the development of sustainable management strategies for contaminated soils and sediments through their transformation into reusable materials. Graphical abstract

A multitechnique approach for the identification of multiple contamination sources near a polluted industrial site

“…Previous works (Calgaro et al, 2021; highlighted the presence of serious heavy metals' contamination in the industrial site of Bagnolo Mella located in Italy. In some detail, a soil sample was collected from the surface of a selected area to 1.5-m depth, showing both heavy metals' content (i.e., Pb, As, Se, Hg, and Sb), exceeding the Italian regulations for industrial use of soils and sediments (EMD, 2006), and the presence of mineralogical phases derived from anthropogenic activities (i.e., gypsum, anglesite, lithargite, jarosite, hematite, and amorphous iron oxides).…”

“…There is an agrarian consortium producing fertilizers near the SW border of the City, close to various smelting and steel manufacturing plants. The site includes installations dedicated to different industrial activities, from sulfuric acid production through pyrite roasting (lead chambers process) to fuel and mineral oil storage (Calgaro et al, 2021; Contessi, Calgaro, et al, 2020; Contessi, Dalconi, et al, 2020).…”

Maximize the use of municipal waste generated by the hydrogen peroxide industry in the production of high-quality refractory CAC

“…CAC was also utilized in the remediation of heavy metals contaminated soil and has shown a better performance than OPC 16 . Calgaro et al 16 , have investigated the performance of CAC and OPC in the treatment of contaminated soil with heavy metals (i.e. As, Ba, Be, Cu, Cd, Co, Cr, Hg, Tl, Ni, P b, Sn, Sb, Se, V, and Zn), using solidification/stabilization processes.…”

The validation of converting pyrite ash‐contaminated soil into End‐of‐Waste by the High‐Performance Solidification/Stabilization process application

“…In this context, this work reports on the first industrial‐scale application of the HPSS® (High‐Performance Solidification/Stabilization) technology to reclaim a metals‐contaminated soil to produce a cement‐based granular aggregate classified as EoW that can be used as filler for excavation or as a building material (Calgaro et al, 2021; Ferrari & Pellay, 2007; Scanferla et al, 2012). The HPSS® process is carried out in suitable mixing and granulation installations to obtain a hardened granular material by mixing a finely divided (≤2–6 mm) contaminated matrix with a hydraulic binder (typically Portland cement) and special additives.…”

“…In particular, several concerns have been raised regarding the most suitable methods to be used for the reclamation of contaminated soils and sediments. Considering the increasing problems caused by soil deterioration (e.g., worsening of water quality, biodiversity decline, ecosystem service degradation, and land use capability losses) (Thomas et al, 2013; UNCCD, 2014; C. Yang et al, 2020) the development and application of industrial‐scale technologies capable of obtaining safe and reusable materials starting from contaminated soil and sediments is fundamental (Calgaro et al, 2021; Contessi et al, 2020).…”