Study of factors involved in the gravimetric separation process to treat soil contaminated by municipal solid waste.

The current research investigated the effectiveness of a gravimetric process (shaking table) to treat soil contaminated by municipal solid waste. A detailed characterization of the inorganic pollutants was performed, followed by concentrating the metals within smaller volumes using the shaking table technology. The densimetric examination of the 1-2 mm and 0.250-1 mm fractions of the contaminated soil showed that lead (Pb), copper (Cu), and tin (Sn) were mostly concentrated in the heavy fraction (metal removals > 50%). Scanning electron microscopy coupled with elemental analysis indicated the relevance of using gravimetric processes to treat this soil sample. The influence of shaking table parameters was determined using a Box-Behnken design. The tilt and washing water flow demonstrated significant effects on the motion of the 1-2 mm soil fraction and on the removal of Pb, Cu, and Sn. The results obtained under the optimal settings of the shaking table defined using the Box-Behnken methodology when treating the 1-2 mm fraction were close to those obtained when using dense media separation. The recovered mass of the concentrate was approximately 20.8% (w.w-1) of the total mass. The removals of Pb, Cu, and Sn were estimated to be 67.3%, 54.5% and 54.6% respectively. The predicted and experimental mass distributions of the medium (1-2 mm) and fine-sized (0.250-1 mm) particles were compared successively under some selected conditions. The mass distribution of both fractions showed similar tendencies in response to the forces applied by each condition. However, lowering the forces induced by the bumping action and the flowing film was recommended so as to efficiently treat the fine fraction (0.250-1 mm). The recovered mass of the concentrate (10%) was slightly lower than that obtained by dense media separation (13%). However, satisfactory removal yields were obtained for Pb, Cu, and Sn (42.7%, 23.6%, and 35% respectively).

Effect of pCO2 on direct flue gas mineral carbonation at pilot scale.

Concerns about global warming phenomena induced the development of research about the control of anthropogenic greenhouse gases emissions. The current work studies on the scaling up of aqueous mineral carbonation route to reduce the CO2 emissions at the chimney of industrial emitters. The reactivity of serpentinite in a stirred tank reactor was studied for several partial pressures of CO2 (pCO2) (0.4, 0.7, 1.3 and 1.6 bar). Prior to carbonation, the feedstock was finely grinded and dehydroxyled at 650 °C by a thermal treatment. The major content of magnetite was removed (7.5 wt% · total weight-1). Experiments were carried out under batch mode at room temperature using real cement plant flue gas (14-18 vol% CO2) and open pit drainage water. The effect of the raw water and the pCO2 on the carbonation efficiency was measured. First, the main results showed a positive effect of the quarry water as a slight enhancement of the Mg leaching in comparison with distilled water. Secondly, a pCO2 of 1.3 bar was the optimal working pressure which provided the highest efficiency of the carbonation reaction (0.8 gCO2 · g residue-1). Precipitation rates of dissolved CO2 ranged from 7% to 33%. Pure precipitate was obtained and essentially composed of Nesquehonite. At a pCO2 of 1.3 bar, additional physical retreatment of the solid material after being contacted with 6 batches of gas enhanced considerably mineral carbonation efficiency (0.17 gCO2 · g residue-1.).

Prediction of physical separation of metals from soils contaminated with municipal solid waste ashes and metallurgical residues.

Environmental legislation is forcing industrialized countries to rehabilitate contaminated lands. Expensive solutions are available to treat soils contaminated by metals (e.g., solidification, stabilization, and landfilling). Physical remediation techniques, which are less expensive, are able to efficiently separate metals from contaminated soils under specific physical conditions. In the current study, densimetric and mineralogical characterization of fractions of soil between 0.25 and 4 mm contaminated by municipal solid waste (MSW) ashes and metallurgical waste was performed. This characterization confirmed the usefulness of the jig and wet shaking table for separating the metal contaminants from the soil. Mineralogical characterization allowed the prediction of treatment efficiencies and potential limits. The jig performance was optimized based on densimetric characterization. Water washing coupled with ferrous material extraction using magnetic separation, and, attrition scrubbing coupled with the jig and wet shaking table, led to a removal yield varying from 42.1% to 83.4% for Ba, Cu, Pb, Sn, and Zn from the fraction of soil >0.25 mm contaminated by MSW ashes. The recovered treated mass varied from 57.1% to 73.4% (by weight). For the fraction of soil >0.25 mm contaminated with metallurgical residues, Cu and Zn removal yields were higher than 57.5%. The recovered treated mass from this soil fraction corresponded to 64.8% (by weight). Depending on the level and leachability of contaminants, the soil fractions <0.25 mm were recommended for appropriate treatments (solidification or stabilization) or for safe disposal via landfills.