Evaluation of the use of a sequential extraction procedure for the characterization and treatment of metal containing solid waste

Metal containing wastes like MSWI fly ashes and blast furnace sludge form a major environmental problem as they are polluted with heavy metals. The as h has to be landfilled or can be used as a construction material, but a pre treatment is in general necessary. Washing of the ashes with water in order to dissolve soluble salts or extracting the heavy metals with chemicals ar e possibilities. Blast furnace sludge contains large quantities of iron and carbon and could be recycled in the blast furnace, if the zinc content wer e not that high. Using a hydrometallurgical process the zinc can be removed from the sludge particles. In order to evaluate such treatment methods kno wledge of the leaching behaviour of the studied material is very important. One of the factors influencing the leaching behaviour is the composition a nd mineralogy of the solids. A sequential extraction procedure, whereby the material is sequentially leached with different leaching solutions, can be used as an aid to characterize the material and to determine which chemica l conditions are needed to obtain a sufficient extraction efficiency. To ve rify the accuracy of the sequential extraction procedure, a method is teste d on MSWI fly ash and evaluated by comparing the results with those of leac hing experiments whereby the final pH of the leaching solutions is varied o ver a wide range. Based upon this evaluation some suggestions for the use o f the sequential extraction procedure are made and an adapted procedure is suggested, and applied to a blast furnace sludge. (C) 2001 Elsevier Science Ltd. All rights reserved.