Application de la spectrométrie de fluorescence X à l'analyse in situ des métaux dans les sols contaminés

Abstract

Contaminated sites, particularly in urban areas, represent a great challenge for the public sector as well as private holders. This issue takes on more and more importance given the shortage of land, common to most of cities nowadays. Indeed, in 2010, approximately 8000 contaminated sites had been identified in 17 administrative regions of the Province of Quebec, from which approximately 1500 are in Montreal. The regions of Montreal and Montérégie represent 45% of the total number on contaminated sites in Quebec. The main objective for the actors concerned is the reuse of these sites by their re-integration in the economic and social development. This requires the remediation of these contaminated lands. The first step in the remediation process is an environmental assessment to identify the risks of potential contamination. Then site characterization is performed to determine with precision the nature, the mobility and the extent of the contamination. Finally, remediation is conducted using in situ or ex-situ soil treatment techniques (biological, chemical or thermal) followed by the redevelopment of the site. In order to carry out this remediation process, and more specifically site characterization, representative sampling procedures and efficient analytical techniques are required. The device used in this project is the XRF (X-ray fluorescence spectrometry). This device allows the analysis of metals in the soil and may be used both in the laboratory and on the field. Its use in situ could reduce time and money constraints during site characterization, given that a very large number of measures can be carried out with a minimum of sample preparation. The amount of sample preparation could affect the accuracy of the measurements made by the device by mitigating of the effects of interferences such as moisture and particle size. The objective of this project was to study the use of XRF in situ. To do this, an evaluation of two interferences cited above and their influences on the accuracy of the measures, has been made. The results obtained showed that the increase in the water content of the soil leads to the decrease of the concentration measured. The results for six selected heavy metals are presented in this report: As, Cu , Ni, Pb , Sn and Zn. Globally, a 10% increase in water content, corresponded to a decrease of 15% in the measured concentration. Similarly, 20% and 30% increases in water content corresponded to decreases of 26% and 30% respectively in the measured concentrations. Regarding the influence of particle size, the results have shown that for most of the metals analyzed, grinding the soil lead to a decrease in the measured concentration. The latter has decreased by an average of 29% when the soil was ground to a particle size smaller than 2 mm and 31%, when it was ground to a particle size smaller than 200 μm. Nevertheless, nickel (Ni) and tin (Sn) showed an opposite trend, with an increase in the measured concentrations following grinding. Three scenarios for the preparation of soil samples for XRF analysis were studied in this project. For most of the metals, drying the soil and grinding it to a particle size smaller than 2 mm gave results closer to those obtained by the conventional ICP analytical technique.

Date	16 Aug 2016
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Jean-Sébastien Dubé (Supervisor)