SUITMA 2005 Cairo - Stabilization of residual metallic pollution of industrial polluted soils by soil reconstitution

Soils of Urban, Industrial, Traffic, Mining and Military Areas
SUITMA 2005 Cairo

Stabilization of residual metallic pollution of industrial polluted soils by soil reconstitution

SUITMA

This abstract is about one of the papers of the Cycling of city fluids and solid refuse theme of the SUITMA 2005 symposium.

Clémence Lefort,i	Geoffroy Séré,i,ii
Stéphanie Ouvrard,i	Christophe Schwartz,i
Jean-Louis Morel.i

• i - Laboratoire sols et environnement (LSE), ENSAIA, Université de Lorraine - INRA, Nancy, France

• ii - 2TVD Centre d’Affaires, Clairs Chênes, Chavigny, France.

As a consequence of the increase of the industrial brownfields and the reinforcement of environmental legislation, the requalification of these degraded sites becomes necessary. One of the major steps of the reclamation is the treatment of polluted soils. Among the numerous available treatment processes, most of them are dedicated to the thermal degradation of organic pollutants, and do not often deal with heavy metals. Therefore, the stabilization of the residual metallic pollution by containment appears as a low cost solution for site managers. This work aims to assess a new in situ reclamation process to stabilize heavy metals in industrial soils. This process is based on a soil reconstitution through the incorporation of urban wastes and industrial by-products. It uses technic materials such as composts, paper sludge and treated industrials soils combined and placed in superposed layers to form a soil profile over in situ derelict substrates. Two types of material associations are tested. Modality I represents a classic reclamation practice, consisting of an upper layer of compost placed above a layer of treated industrial soil. Modality II is a more complex reconstituted soil profile, where the industrial treated soil is replaced by a mixture of industrial treated soil with paper sludge (50/50 v/v). This work is based on a pilot-scale experimental set-up consisting in two in situ lysimetric plots (10m x 10m). This study presents the impacts of leachates from the reconstituted soil on the mobilization of metals contained in the underlying industrial soils. Batch experiments are conducted with four solutions: water, CaCl₂ (10^-2 M), leachates sampled under the reconstituted soil from modality I (L1), leachates sampled under the reconstituted soil from modality II (L2). Selective extractions are carried out with those four solutions on four contrasted metal polluted industrial soils. The effect of the leachates on the mobilization of metals is compared to the effect of two model solutions: water and CaCl₂. The solutions are added to each soil in a 1:5 ratio (g soil dry matter/ml solution) and agitated for 24 hours. The suspensions are filtrated on a 0.45 µm membrane and the solutions are analyzed for major elements (Ca²⁺, K⁺, Mg²⁺, Na⁺, NH₄⁺, Cl^-, NO₃^-, PO₄^3-, SO₄^2-), heavy metals (Cd, Pb, Zn), C_organic, carbonates, N and pH. Results show that Zn contents are in the same range for extractions with water, CaCl₂ and L1. They are significantly reduced with L2, due its high carbonates content (buffering capacity). Moreover, Pb behavior seems to be correlated to C_organic concentration. Pb extraction decreases as organic matter content increases in the solutions (water = CaCl₂ < L1 < L2). Thus, this innovative process of soil reconstitution could be an interesting and efficient alternative way to residual heavy metallic pollution stabilization.