en fr

Selection of amendments to decrease the mobility and toxicity of inorganic pollutants (Pb, As, Ba, Zn) in a mine tailing for the development of a phytoremediation process

Sélection d'amendements pour diminuer la mobilité et la toxicité de polluants inorganiques (Pb, As, Ba, Zn) dans un déchet minier pour le développement d'un procédé de phytoremédiation

Abstract : In mining sites, the dispersion of solid particles of tailings, induces a risk of dispersion of toxic elements, in addition with potential pollution of groundwater and surface water through leaching. The development of a vegetal cover is one of the potential options to decrease the risks. However, the growth of plants on mine tailings is generally hampered by several parameters: acidity, lack of nutrients, poor texture and toxicity of metals and metalloids. Thus, amendments are necessary to overcome these limitations. A mine tailing material was sampled on a former silver and lead mining site. Chemical analysis indicated the following concentrations in pollutants: 26 432 mg.kg-1 Pb, 265 mg.kg-1 Zn, 1 063 mg.kg-1 Ba, 1134 mg.kg-1 As. The tailing is acidic, siliceous and coarse (76% of particles with size in the range of 315 µm - 2 mm). A cow manure and some ochre (iron oxide-hydroxide) material produced in the water treatment plant of a coal mine were tested, alone or in combination, to stabilize the most mobile toxic pollutant, Pb, while avoiding the mobilization of other toxic elements. Leaching and microcosm experiments were performed and showed that the Pb concentration in water, that was higher than 10 mg.L-1 with the not-amended tailing, was decreased by a factor ×100, while As, Zn and Ba concentration did not increase significantly. Ochre (added at 5% in weight/weight) allowed increasing pH and could adsorb some metals and metalloïds. The metabolic microbial diversity, evaluated using Ecolog® plates, was improved by all amendements after one month of incubation. Polymers were the most used substrates in the non-planted microcosms, after one month of incubation, suggesting a specialized microbial community. Planted microcosms revealed that the growth of ryegrass was significantly improved by the addition of ochre and manure : the biomass of ryegrass is 3.5 X (with 5% ochre and 2% manure) to 4.8 X (with 5% ochre and 0.15%) greater than in the condition of plants growing on unamended soil. The next experimental step will include the monitoring of phytostabilization at metric scale, in mesocosm, with a vegetal specie naturally present on Pontgibaud mine site, belonging to the Agrostis genus.