Amandine ANDERSON

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In this study, we determinate the concentration of different metals over time by ICP-AES and the shape, size and chemical composition of colloids by SEM-EDX.
Amandine ANDERSON*, Sylvie VILLAIN**, Pierre HENNEBERT*** and Patricia MERDY* * Laboratoire PROTEE, Université de Toulon -BP 20132 83957 La Garde Cedex ** Laboratoire IM2NP, Université de Toulon –BP 20132 83957 La Garde Cedex ***INERIS, Technopôle de l’Environnement Arbois Méditerrannée/Domaine du petit Arbois BP33 F-13545 Aix-en-Provence Cedex 04 E-mail contact: [email protected]

Different types of waste are extensively produced all over the world but after disposal, their fate is poorly known, especially when pollutant release occurs under colloidal form

European Union is aiming to promote sustainable long-term progressive reduction of contaminant discharges to the environment

5 different wastes 1- Bauxite residue 2- Marine sediments 3- Sludge of wastewater treatment plant 4- Domestic crushed wastes 5- Ashes from household incineration treatment plant 1-

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Thus, it is of great interest to evaluate the composition of metals under colloidal form present in waste leachates.

In this context, 5 different wastes were studied. Chemical composition of colloidal phase is obtained by ICP, and we used SEMEDX to specifically detect the phases bound to metals of colloidal size

Fractionation Batch leaching

Cut off : 0.45 µm  Microfiltrate Cut off : 2kDa  Ultrafiltrate MF- UF = Colloidal phase

Chemical composition SEM-EDX and ICP-AES

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In this study, we determinate the concentration of different metals over time by ICP-AES and the shape, size and chemical composition of colloids by SEM-EDX

ICP-AES results :

For ashes from household of treatment plant, the Al concentration decreases from around 20 000 µg/L to around 3000 µg/L on 81 days. For other metals Si, As, Cr, Ni and Pb there is not really tendency during three months but they are present under dissolved phase at the end of the experiment. For marine sediments, most of the metals are present under dissolved phase. For bauxite residue, Al and Si are under dissolved form at the beginning of the experiment but after 57 days, they are under colloidal phase and the concentration tends to increase especially for Al. Cr have also tendency to increase during the experiment. For sludge from wastewater of treatment plant, 6 metals are present in colloidal phase. Al concentration increases during the experiment from around 50 µg/L to around 2000 µg/L instead of Ni. Co concentration is constant. For domestic crushed wastes, 10 metals are present in colloidal phase. Al, Mo and Ti concentration are relatively constant during experiment. Zn concentration increases instead of Ni concentration.

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Concentration of different metals by ICP-AES in colloidal phase of ashes from household of treatment plant leachate over time

Photographies by SEM-EDX of ashes from household of treatment plant leachate

Concentration of different metals by ICP-AES in colloidal phase of marine sediment leachate over time

Photographies by SEM-EDX of marine sediment leachate

SEM-EDX results :

Concentration of different metals by ICP-AES in colloidal phase of bauxite residue leachate over time

Concentration of different metals by ICP-AES in colloidal phase of sludge from wastewater of treatment plant leachate over time

Concentration of different metals by ICP-AES in colloidal phase of domestic crushed wastes leachate over time

 Some metals are specifically bound to organic matter  Others are bound to minerals (such as oxides, alumina-silicates) Those typical features give them various pattern of stability over time.  SEM-EDX and ICP-AES are effective and complementary

For both samples, particles are agglomerated and it is difficult to see in SEM colloidal particles with a size between 0.45 µm and 1 nm. Moreover, C,N,O quantifications are overestimated so we used this technique to determinate the shape and what kind of phase (organic or mineral) metals are bound. For ashes from household of treatment plant, most of metallic particles (shining particles) are alumina-silicates and they are bound to organic matter matrix (more than 100 µm of diameter) and minerals (CaCl2, KCl, MgCl2, P and S). For marine sediments, the first photo obtained by SEM shows a 1 µm-agglomerate of metallic particles (Al, Si and Fe) combined to Mg. For bauxite residue, metallic particles (Alumina-silicates and Cr-rich) are combined to organic matter (more than 20 µm of diameter) and salts. For sludge, most of metallic particles are bound to organic matrix (photo 1) but some particles (photo 2) are combined to salts such as MgCl2, CaCl2. It is the same for domestic crushed wastes even if more different metals (Al, Si, Fe, Cr, Ni, Zn) are present in this sample.

Photographies by SEM-EDX of bauxite residue leachate

Photographies by SEM-EDX of sludge from wastewater of treatment plant leachate

Discussion:

For both samples, SEM-EDX and ICP-AES results are consistent. These techniques are complementary because SEM-EDX gives indications on the shape and the size of metallic particles and what kind of matrix metals are bound to. The drawbacks of SEM technique are the lack of representativeness of samples due to the low number of particles analyzed by samplee and the over-estimation quantification of light chemical element. The combination of these two techniques allowed to specifically identify the environmental risks brought by colloidal toxic metals leached from wastes deposited without caution in damp pits.

Photographies by SEM-EDX of domestic crushed wastes leachate

 Organic matter will be analysed by 3D fluorescence and carbon analysis to characterize it more precisely since its role in metal uptake has to be taken into account for environmental assessment.  The size of colloids will be measured by NTA and DLS simultaneously.