Environmental evaluation of dredged sediment submitted to a solidification stabilization process using hydraulic binders.

Polluted soils are a serious environmental risk worldwide and consist of millions of tons of mineral waste to be treated. In order to ensure their sustainable management, various remediation options must be considered. Hydraulic binder treatment is one option that may allow a stabilisation of pollution and thus offer a valorisation as secondary raw materials rather than considering them as waste. In this study, we focused on sulphate-polluted soil and tested the effectiveness of several experimental hydraulic binders. The aim was to transform gypsum into ettringite, a much less soluble sulphate, and therefore to restrict the potential for sulphate pollutant release. The environmental assessment of five formulations using hydraulic binders was compared to the gypsiferous soil before treatment (contaminated in sulphate). The approach was to combine leaching tests with mineralogical quantifications using among others thermogravimetric and XRD methods. In the original soil and in the five formulations, leaching tests indicate sulphate release above environmental standards. However, hydraulic binders promote ettringite formation, as well as a gypsum content reduction as observed by SEM. The stabilisation of sulphates is, however, insufficient, probably as a result of the very high content of gypsum in the unusual soil used. The mineralogical reactions highlighted during the hydration of hydraulic binders are promising; they could pave the way for the development of new industrial mixtures that would have a positive environmental impact by allowing reuse of soils that would otherwise be classified as waste.

Release of arsenic from cyanidation tailings

Release dynamic process identification for a cement based material in various leaching conditions. Part I. Influence of leaching conditions on the release amount

Co-pyrolysis with pine sawdust reduces the environmental risks of copper and zinc in dredged sediment and improves its adsorption capacity for cadmium

Stabilisation/solidification of APC residues from MSW incineration with hydraulic binders and chemical additives

The aim of this study was to examine the use of calcined clay (CC), which is a pozzolanic material, as a substitute for 10% by weight of the amount of cement, for the stabilization/solidification (S/S) of hazardous waste using a hydraulic binder. For comparison, an ordinary Portland cement was used. The standard toxicity characteristic leaching procedure (TCLP) test showed that the average concentrations of heavy metals in the raw hazardous waste far exceeded those of the required standards. Leaching of heavy metals from the mortar was evaluated by the monolithic leaching test (MLT) under dynamic leaching conditions for 64 days in sulfated and neutral media. Tests of compressive strength, setting times, and X-ray diffraction were carried out. The addition of CC considerably improved the strength of the mortar specimens containing hazardous waste. Following the MLT test, CC cement-made mortar was more efficient in the S/S of heavy metals than mortar made without CC.

Long-term prediction of the leaching behavior of pollutants from solidified wastes

Landfill deposits of contaminated, dredged sediments are subject to chemical alteration and especially to oxidation processes. Accordingly, sulphides are gradually oxidized leading to the formation of secondary phases and associated metals could become mobile and redistributed among the sediment components, such as carbonates, clay and freshly precipitated (hydr)oxides. Once mobilised, metals could represent a hazard for the environment and especially for drinking water supply facilities. In the present study, leaching experiments have been carried out on a dredged sediment to study metal mobilisation after 5 years of field aging. First, kinetic batch tests allowed one to evaluate the impact of solid-liquid contact time and to determine the kinetic parameters. Secondly, two types of dynamic experiments have been conducted: dynamic flush reactor and column leach test to evaluate the impact of solution renewing by excluding or not excluding the transport processes, respectively. In order to evaluate the impact of calcium on the metal mobilisation, the column leaching test is conducted with pure water and Ca(NO3)2 solution, at the beginning and at the end of the injection, respectively. Geochemical and reactive transport modelling of the experiments was performed using the geochemical code CHESS and the reactive transport model HYTEC. The studied sediment is complex with numerous reactive phases such as sulphides, (hydr)oxides, organic matter, phyllosilicates. All leaching tests highlight that zinc and cadmium are mobilised in significant concentrations and lead remains insoluble. A conceptual geochemical model of the sediment has been built to allow simulations of the whole experiments, based on a single, coherent phase description and parameter set. Simulations of the batch, flush and column experiments were performed taking into account the major reaction-controlling mechanisms including, among others, pH buffering, kinetic dissolution (carbonates, silicates) and ion exchange between calcium and exchangeable metals (Cd, Zn and Mn). The simulation results are in good agreements with the results obtained from the experiments. The experiments showed that zinc and cadmium are reversibly bound to the sediment and underline the importance of calcium concentration with respect to their mobility. Modelling confirms that ionic exchange is the main mechanism involved in metal mobilisation for this sediment. Metals can be retained as cation exchange species due to the high quantity of clays and organic matter present in dredged sediments. Cation exchange is a reversible mechanism and subsequent remobilisation of metals can be expected during oxidation and leaching phases. To quantify the mobilisation potential of polluted sediment, it is recommended to characterize the CEC properties of the sediment and calcium availability. Indeed, dissolution of minerals such as gypsum during rain events lead to metal mobilisation due to the increase of calcium concentration even for well-buffered sediments.

The substantial volumes of tailings produced during ore beneficiation present significant challenges for sustainable management due to potential public health hazards, particularly from metal leaching. The risk associated with tailings varies greatly depending on their mineralogical composition and climatic conditions. If tailings are classified as a non-hazardous by-product, they may serve as secondary raw materials, offering a sustainable alternative to the reliance on non-renewable primary resources. In this study, the recycling feasibility of tailings from an active copper mine was assessed through mineralogical characterization, environmental tests (e.g., static, kinetic, and leaching tests), and geochemical modeling. This multi-faceted approach aimed to predict the geochemical behavior and reactivity of tailings under varying conditions. Results from the static tests indicated that the tailings were non-acid generating. Weathering cell tests revealed circumneutral pH conditions (6.5–7.8), low sulfide oxidation rates, and low instantaneous metal concentrations (<1 mg/L), except for copper (0.6–3.5 mg/L) and iron (0.4–1.4 mg/L). These conditions are attributed to the low abundance of sulfide minerals, such as pyrite, chalcopyrite, bornite, covellite (<0.1 wt.%), and chalcocite (0.2 wt.%), which are effectively encapsulated within gangue minerals. Additionally, the presence of neutralizing minerals, specifically dolomite (27.4 wt.%) and calcite (2.4 wt.%), further stabilizes pH and promotes metal sequestration in secondary mineral forms. The Toxicity Characteristic Leaching Procedure (TCLP) test confirmed low leachability, classifying the tailings as non-hazardous.

Effect of hydraulic binders’ addition on trace metals stabilization in the S/S process of dredged sediments

This study has focused on the dam sediments and marble waste reuse as subgrade materials for road construction, with the overarching goals of reducing greenhouse gas emissions and conserving natural resources. Different mixtures were prepared based on sediments and marble waste, and treated with hydraulic binders. The first mixture consisted solely of raw sediment, while the second mixture combined 50 % dredged sediments with 50 % marble waste. Additionally, this mixture was treated with 1 % aerial hydrated lime and hydraulic road binder to enhance its properties. The experimental study focused on assessing both the short-term and long-term mechanical properties of the prepared mixtures. Results highlighted that the mixtures containing dam sediments and marble waste were highly suitable for road subgrade construction. These mixtures satisfied the criteria for trafficability (UCS), wetting resistance (UCSI), freezing resistance (ITS), and overall mechanical strength. Furthermore, a comprehensive analysis of the mixtures' microstructure and their environmental impact was conducted. A significant relationship was observed between CaO/SiO2 ratio and the mechanical properties of the treated mix. The research contributes to the growing body of knowledge regarding sustainable construction practices by highlighting the viability of utilizing dredged sediments and marble waste as valuable resources in road subgrade construction. The study showed that recovering 20 % of sediment and marble waste to replace natural materials would reduce energy consumption and greenhouse gas emissions by at least 40 % and 28 % respectively.

Contaminant release from massive copper metallurgical slags: Insights from long-term monolithic leaching tests

This paper investigates the leaching potential of heavy metals present in stabilised/solidified (S/S) electric arc furnace dust (EAFD). Granular leaching test results showed that Mo was effectively stabilised by Portland cement type I (CEMI) and MgO at 1:2:7 and 3:12:35 ratios. Monolithic leaching test results showed that pulverised fuel ash (PFA) stabilised Zn and Pb but not Mo and Cl. MgO was highly effective in reducing Zn leaching. X-ray diffraction analysis revealed the presence of zinc ferrite in the solidified EAFD products which explains the excellent immobilisation of Zn. The leaching mechanisms analysis demonstrated that few S/S samples exhibited a leaching behaviour dominated by diffusion with the majority displaying a leaching mode dominated by depletion. Although the monoliths’ physical integrity was maintained, Pb, Cl and Mo were not effectively immobilised with PFA and MgO-based systems based on the current granular and monolith leaching test protocols.

The aim of the present paper is to investigate the effect of the water/cement ratio (w/c) (0.4 and 0.6) and the amount of hazardous waste (W/c) (10, 20, 25, 30, and 45%) incorporated on the leaching of heavy metals from a cementitious solidified materials. Mechanical strength of the S/S materials was evaluated at 28 days of cure. Specimens that have shown a good mechanical strength for the two water/cement ratios were used to make this study succeed. XRD analysis has shown the presence of heavy metals within the structure of S/S materials which explains immobilization of heavy metals contained in the waste by the S/S process. Amount of heavy metals released to the environment was evaluated by several leaching tests, namely, TCLP (toxicity characteristic leaching procedure), pore water (PW) and maximum mobile fraction (MMF), and monolithic leaching test (MLT). Monolithic specimens were evaluated under dynamic leaching conditions for 64 days with periodic leachant renewal on two aggressive media, sulfatic attack and in demineralized water. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 93–103, 2017

With the increase in environmental awareness, in combination with a more restrictive legislation, traditional solutions to the management of dredged sediments, such as dumping at sea or disposal to landfills, become more and more inadequate. In order to improve the management of dredged marine sediments, alternative solutions such as beneficial use in civil engineering, manufacture or agriculture have been proposed. Reuse solutions have to fulfil economical, technical and environmental criteria. At present, the proposed solutions are relatively costly and not adaptable to all types of sediments. In particular, fine sediments are difficult to reuse in comparison to sands because of their high water content, the presence of organic matters, their mechanical behaviour and the presence of pollutants in some cases. In this context, this study aims to design a road material that includes dredged fine sediments from a harbour in the north of France. With an initial water content higher than 100%, the first operation consisted in preparing the dredged sediments by reducing its initial water content and, as a consequence, the content of dissolved salts. Then the sediments were characterized and finally a material with the required properties was designed. This material included fine marine sediments, traditional granular materials and hydraulic binders. This paper focuses on the methodology used to design the road material.