Assessment of chemical sensitivity of Waelz slag

In the recycling industry, the recuperation of zinc from electric are furna ce dust by the Waelz process generates important quantities of slag. This s lag presents good mechanical properties, and for the most siliceous slag, a high stability that would enable its use by total or partial substitution of certain granulates in civil engineering. Our study (within the framework of a European program, co-funded by the European Commission - DGXII) conce rns the physico-chemical and mineralogical characterization and leaching be haviour of several types of Waelz slag. The leaching tests used are regulat ory tests and specific characterization tests of leaching behaviour. They t ake into account the influence of several main parameters of the valorizati on scenarios envisaged for the slag (e.g. pH, Redox potential, chemical nat ure of the leachant, type of contact - liquid/solid etc). The influence of the chemical nature of the alkaline leachant (lime or NaOH) is particularly important in the case of release of lead (strongly leached by a lime solut ion), of zinc and of arsenic. The agreement between ANC test results and co ntrolled pH test results can be noted. Leachability is largely controlled b y pH in solution. Alkaline slags are more sensitive to the influence of pH. The low buffer capacity of the silica-rich slags implies that application or disposal of untreated slag in acid environments (pH 4-6) should avoided. To optimize integration of slags in materials, it will be necessary to ori ent research towards less alkaline binders than classical OP cements. A con crete with low limestone content where the alkalinity in the porewater woul d have a less corrosive effect on the vitreous phases of slags would seem m ore appropriate. (C) 2000 Elsevier Science Ltd. All rights reserved.