Environmental Technologies for Contaminated Solids, Soils and Sediments
2nd cohort

Nang Htay Yin

Contribution of Isotopic Techniques to the Study of Metallurgical Slags Bio/weathering

Primary smelting slags, known as Lead Blast Furnace (LBF) and Imperial Smelting Furnace (ISF), are generated by the former pyrometallurgical industries located in Noyelles-Godault, Northern France. Following its closure in 2003, 4 million tons of primary slags have been landfilled as a heap in the vicinity of the Deûle River, near the industrial basin of Nord-Pas-de-Calais. These slag materials are often enriched in toxic elements, in particular metals (Pb, Zn) that can be released into the environment through alteration processes and leaching. Metals leaching from slag dumping sites may have deleterious effects on the environment and lead to the contamination of soils and water bodies.

Many biological and chemical processes are known to take place within these tailings and thus affect significantly the slag weathering. Predicting the environmental impact of these wastes requires an understanding of the mineral-water interactions as well as the influence of the biological activities (the involvement of microorganisms). Thus, this research is designed to simulate the natural weathering of slag by simulating different weathering conditions with or without the involvement of the microorganisms as well as by varying several chemical parameters.

Chemical weathering of both LBF and ISF slags was studied by as a function of pHs (4, 5.5, 7, 8.5 and 10) as well as under two atmospheres (open air and nitrogen). On the other hand, bioweathering of both slags was studied in the presence of a pure heterotrophic bacterial strain (Pseudomonas aeruginosa) in a bioreactor with leachate stagnant conditon as well as in a semi-flow through reactor intermittent leachate renewal conditions. The evolution of leachate chemistry, slag composition and texture were monitored during the experiments and the leaching results were coupled with a geochemical model; Visual MINTEQ version 3.0. In addition, the fractionation of Zn isotopes was studied during chemical and biological weathering of slags and, whether or not, it is possible to use Zn isotopes to trace the processes involved in weathering.

Last but not the least, Scanning Electron Microscopy (SEM) with Energy Dispersive X-Ray Analysis (EDS), Transmission Electron Microscopy (TEM) analysis, and X-ray Photoelectron Spectroscopy (XPS) analysis were used to characterize fresh and altered slags in order to give insights regarding the mechanisms of alteration, surface morphology of slags and the formation of secondary mineral phases.

Keywords: Slag, chemical, biological weathering, leaching, pH dependent, atmospheres, Zn isotopes, fractionation, secondary precipitates