Magnetic stability of power-plant fly ash in different soil solutions

Temporal stability of magnetic parameters of anthropogenic ferrimagnetics i n model soil conditions was studied. Fly ash from a power plant was used as original contaminant material, while soil reactive medium was modeled by d ifferent soil solutions. Changes in mass-specific magnetic susceptibility ( chi), percentage frequency dependent magnetic susceptibility (chi(FD)%), hy steresis parameters and thermomagnetic curves were measured for samples whi ch underwent different leaching time periods. Virtually constant magnetic s usceptibility values were obtained, independently on the soil medium (acid, neutral). On the other hand, the original highly non-stoichiometric maghem ite phase rapidly transformed to stable magnetite. In some cases (model of free-draining soils) further decrease of Curie temperature (T-c) to 550-560 degrees C is observed. (C) 2000 Elsevier Science Ltd. All rights reserved.