No abstract

In the work described in this paper, partially zeolitised coal¯y ash from a Spanish power station has been studied as the immobilising agent of an arc furnace dust waste (s-WA). s-WA is a dust coming from the collecting systems of particulate material in a carbon±steel electric arc furnace (EAF). The hazardous metals normally found in this kind of waste are lead, cadmium, and chromium. In addition, the dust usually has a high zinc content resulting from the use of galvanised scrap. Because of its heavy metal content, s-WA is classi®ed as hazardous waste, according to Spanish regulations. Different zeolitisation procedures, depending on the treatment of the¯y ash with NaOH and KOH alkaline solutions, using re¯ux heating and different times of attack were tested. The zeolitised products were studied using XRD in order to characterise the solid phases produced. The solidi®-cation/stabilisation (S/S) trials of s-WA were carried out using the zeolitised ashes, as well as the original coal¯y ash, in mixtures containing 20% (w/w) of ordinary Portland cement. To evaluate the ef®ciency of the immobilisation process, some speci®c criteria were de®ned, with regard to some physical (compressive strength) and chemical (pH and metal concentrations in TCLP leachates) characterists of the S/S solids. Finally, comparisons among the stabilising mixtures were made and the role of the zeolitisation of¯y ash in the S/S process was evaluated.

This article describes the stabilization/solidification (S/S) of a steel industry waste, using a common type-F fly ash from a coal power station as the main binder. The waste, which contains hazardous levels of metals, may be stabilized by a conventional S/S to achieve permissible Pb, Cd, and Zn concentrations in the Toxicity Characteristic Leaching Procedure (TCLP) leachates of S/S solids. On the other hand, the stabilization of Cr(VI), also present in the waste, requires a reducing pretreatment stage with ferrous sulfate to attain TCLP leachates within limits. A bibliographic study on the stabilization of Cr(VI)-containing wastes is included in the paper, along with a discussion on the lowest Cr concentration in TCLP and aqueous (DIN) leachates.

No abstract

Fly ash (FA) is a by-product of coal combustion in power plants whose characteristics depend on the type of combustion process and coal properties. A large proportion of FA is used by the cement and concrete industries, but most is disposed to land®ll, potentially causing environmental problems. The main objective of the CEFYR project was to study new ®re-proof products (FPP) in the laboratory and at the pilot level, employing FA from a pulverized coal combustion power station and other industrial wastes and cellulosic derivatives. As a result of the project, new FPP have been developed and manufactured as panels or as sprayed surfaces. In this paper is described one such product: panels formed by simple compaction or by vacuum ®ltration using coal¯y ash, waste paper and other industrial wastes. After thermal treatment to eliminate the cellulosic matrix and produce high porosity products, their stability at high temperatures was assessed. The results show that the developed FPP are stable and have acceptable physical and mechanical properties. In addition, the insulating capacity of the products was assessed by submitting one of the panel faces to heat according to standard ®re resistance tests, and measuring the temperature rise on the cold face. The results indicate that some of the manufactured FPP have better insulating properties than other commercial ®re-resistant products, and consequently, that it is possible to produce FPP using FA and other residues as raw materials, using simple, cost-effective processing methods.