Jacques Méhu

Leaching behavior of pollutants in stabilized/solidified wastes

The objective of the study is to characterize pollutant retention in wastes solidified with hydraulic binders in order to predict the long term leaching behavior. The stabilized/solidified wastes are APC MSW (air pollution control residues from municipal solid waste incineration), lead secondary smelting slag and different salts. The binders used are ordinary Portland cement (OPC 55) or blast furnace slag cement (CLK 45) and additives, such as metakaolin. Leaching tests are used in the characterization procedure. Modelling of the observed leaching behavior is conducted to improve the description of the physical and chemical phenomena involved in the release of soluble species. The main results of the study allow a distinction to be made between the species whose solubility is not sensitive to the chemical context of the porewater, and the other species, such as amphoteric metals, whose solubility is sensitive to the context (especially the pH). In the first case, a diffusion or shrinking front model is appropriate. In the second case, a coupled solubilization/diffusion model must be developed in order to describe the leaching behavior of heavy metals (lead, etc.) contained in the stabilized/solidified wastes.

Pollutants leaching behaviour from solidified wastes : A selection of adapted various models.

Leaching tests are essential in the environmental assessment of stabilized wastes. Research programmes were conducted on their interpretation in order to develop tools for the evaluation of long term release of pollutants contained in solidified wastes. Models for the leaching of porous materials are discussed in this paper according to the specificity of the chemical species (i.e. transport model with total dissolution of species-diffusional model; transport model with progressive dissolution of species due to limitation of solubility-shrinking core model; and the model coupling transport and chemical phenomena). The leaching behaviour of pollutants (i.e. lead) solidified in a cement matrix was studied under different chemical conditions. Results have shown that the release of species whose solubilities depend on the physico-chemical conditions, and especially the pH (e.g. amphoteric metals), is governed by the solubility of the species in the pore water at local conditions and by the pH evolution within the matrix. A coupled dissolution/diffusion model was developed to describe the release of chemically complex species contained in a porous medium in contact with water. Leaching tests of cement matrices and artificial porous matrices containing calcium hydroxide and pollutants were conducted in order to validate the coupled dissolution/diffusion model. A good assessment of the retention of some pollutants contained in cement matrices could then be obtained by the association of two tests: solubilization of the pollutants related to the chemical context (pH) under steady state conditions and monolithic long term dynamic leaching tests in order to characterize the evolution of the chemical context (pH) and consequently the release of pollutants. The objective is to integrate this approach in the standardization process (CEN TC 292- WG 6, in progress).

Assessment of chemical sensitivity of Waelz slag

Abstract In the recycling industry, the recuperation of zinc from electric arc furnace dust by the Waelz process generates important quantities of slag. This slag presents good mechanical properties, and for the most siliceous slag, a high stability that would enable its use by total or partial substitution of certain granulates in civil engineering. Our study (within the framework of a European program, co-funded by the European Commissionxa0— DGXII) concerns the physico-chemical and mineralogical characterization and leaching behaviour of several types of Waelz slag. The leaching tests used are regulatory tests and specific characterization tests of leaching behaviour. They take into account the influence of several main parameters of the valorization scenarios envisaged for the slag (e.g. pH, Redox potential, chemical nature of the leachant, type of contactxa0— liquid/solid etc). The influence of the chemical nature of the alkaline leachant (lime or NaOH) is particularly important in the case of release of lead (strongly leached by a lime solution), of zinc and of arsenic. The agreement between ANC test results and controlled pH test results can be noted. Leachability is largely controlled by pH in solution. Alkaline slags are more sensitive to the influence of pH. The low buffer capacity of the silica-rich slags implies that application or disposal of untreated slag in acid environments (pH 4–6) should avoided. To optimize integration of slags in materials, it will be necessary to orient research towards less alkaline binders than classical OP cements. A concrete with low limestone content where the alkalinity in the porewater would have a less corrosive effect on the vitreous phases of slags would seem more appropriate.

Models for Leaching of Porous Materials

Abstract The release of soluble species contained in solidified/stabilized wastes are assessed by leaching tests. Interpretation of experimental results must be supported by precise modeling of the different phenomena involved hydrodynamics, dissolution, chemical interaction, diffusive transport. The models are presented, which can apply according to the leaching scenario (with or without advection).n - solubilization shrinking core model, - diffusionnal model, - coupled dissolution/diffusion model.

French qualification procedure for solidification processes

Abstract In the framework of the new French technical and regulatory requirements of industrial waste landfilling, solidification/stabilization processes are expected to be one of the main tools to render wastes physically and chemically compatible with the Environment on the long term. Consequently, it appears necessary to propose a comprehensive qualification procedure to assess the real performances of the different industrial processes in front of the wide range of industrial wastes to stabilize. This paper presents the main steps of the procedure, proposed by ADEME (French Agency for the Environment and Energy Management) and designed by POLDEN and L.C.P.A.E.(INSA de Lyon).

Leaching behavior assessment of wastes solidified with hydraulic binders: critical study of diffusional approach

Abstract Leaching procedures of wastes solidified with hydraulic binders are expected to allow the assessment of the safety of the long term storage. The Dutch procedures (Availibility Test and Tank Leaching Test) or the Canadian one (close to ANS 16.1) are based on diffusion model and determine the two parameters De and Co from two different experiments : one on crushed materials and the other one on a monolithic sample. The present study, jointly conducted by a Dutch team (ECN) and a French one (POLDEN, LCPAE INSA Lyon), has been funded by RE.CO.R.D. Its two main aims were: - to point out the influence of the chemical properties of the binders and the wastes upon the release of the pollutants. - to define the application field of the diffusion model in order to predict the long term leaching behavior of the solidified products.

French Approach Towards the Evaluation of Monolithic and Solidified Waste:: Development of a New Leaching Procedure

I-Summary – Introduction In France the problem of landfill as a means of waste disposal and the delicate operation of setting criteria for waste qualification to landfill led the different partners concerned (authorities, industries, either producers or eliminators, research laboratories,⋯) to work together on processes that would firstly render pollutants as insoluble as possible, and secondly fix them in a mineral or organic matrix to ensure structural integrity and protection against leaching phenomena.

Assessment of Chemical Sensitivity of Waelz Slag

1. Abstract In the recycling industry, the recuperation of zinc from Electric Arc Furnace dust by the Waelz process generates important quantities of slag. This slag presents good mechanical properties, and for the most siliceous slag, a high stability which would enable its use by total or partial substitution of certain granulates in civil engineering. Our study (within the framework of a european programme, cofunded by the European Commission – DGXII) concerns the physico-chemical and mineralogical characterization and leaching behaviour of several types of Waelz slag. The leaching tests used are regulatory tests and specific characterization tests of leaching behaviour. They take into account the influence of several main parameters of the valorization scenarios envisaged for the slag (e.g. pH, Redox potential, chemical nature of the leachant, type of contact – liquid/solid etc).

Evolution of Regulations and Standards for Stabilized Hazardous Industrial Final Waste Management in France

The application (first partial then total) of the new regulation concerning Final Special Industrial Waste (SIW) landfilling has brought to light the radical increase in management costs (stabilization + landfillmg). This has led industry to reconsider waste generating processes (reduction at the source, pretreatment) to reduce either the quantity or the polluting character of the wastes (authorizing, for example, admission as they stand). In certain extreme cases, this has led to questioning the process itself, leading to the abandon of the considered waste. As far as management of the “unavoidable” Final SIW is concerned, 3 fields of reflection are now open to industry: (1) Delisting of the stabilized waste (either classified as “M” assimilated to household waste, allowing landfilling in class II sites, or potentially as “I” inert, allowing landfilling in class III sites). (2) Valorization of the stabilized waste, thereby economizing the cost of landfill and even fixing a sale price for the material. (3) Valorization of the waste as it stands, thereby economizing the cost of stabilization.