Use of cyclonic ashes to remediate metal-contaminated soils

Abstract

Cyclonic ashes, consisting of modified aluminosilicates, were compared to other soil additives used for in-situ remediation of metal-contaminated soils. The effectiveness to reduce bioavailability of metals was evaluated in a pot experiment. The additives cyclonic ashes with or without steel shots, lime, phosphate rock and red mud were added to control soil and to four Zn-, Cd- and Pb-contaminated soils. Three of these soils were from an industrial site and one was a garden soil. Lettuce and ryegrass were grown on the treated soils. These plants could not grow on the untreated industrial soils from Maatheide and Joplin. This was also found when phosphate rock and red mud were added. The lime and cyclonic ash (± steel shots) treatments were most efficient in promoting plant growth and reducing Zn and Cd concentration in pore water of the different soils. When detectable, also Pb decreased but less spectacularly. In the plants, only accumulation of Zn was systematically lower when these soil additives were applied. Cd was reduced in a few cases and to a lower extent. Pb in leaves was often higher in the treated soils, in particular with lime additions. The treatments with cyclonic ashes were slightly better than the lime treatments in the Joplin soil and addition of steels shots seemed to reduce Pb transfer into shoots. Also column percolation experiments and long-term results (12 years) of application of cyclonic ashes in the field will be discussed.