Alenka Rastovčan-Mioč

EAF Steel Slag Application Posibilities in Croatian Asphalt Mixture Production

This paper demonstrates the results of testing basic physical and chemical properties of steel slag generated in the steel mill of CMC Sisak d.o.o., Croatia, with the purpose of its characterization as the type of waste, i.e. by- product intended for recycling in other industries. Special attention has been directed at investigating the possibilities of it being used as substitute for natural mineral aggregates when producing asphalt mixtures. The results which were obtained by testing geometric, physical-mechanical properties, as well as the properties of duration on the specimen of electric arc furnace steel slag, have satisfied the conditions for manufacturing mixtures of the tested steel slag and natural aggregate which can be used in asphalt production. In comparison to the natural carbonate and silicate aggregates which are used in asphalt mixtures on highways and roads with heavy traffic, the examined steel slag has equally good physical-mechanical properties. Within the framework of this project, test fields have recently been constructed. The existing wearing course was replaced by an AC 11 type of asphalt, in one lane with conventional natural carbonate aggregate and in the other two lanes with slag aggregate from CMC Sisak (0/4, 4/8, 8/11). The results of measurements of skid resistance on the section constructed using natural aggregate, and the section made using steel slag aggregate, were comparable. By means of laboratory analyses and in situ monitoring it should be possible to prove that asphalt composites containing slag have sufficient durability, and can achieve and maintain the required surface characteristics for road traffic safety.

Leaching properties of electric arc furnace dust prior/following alkaline extraction

This study was carried out to determine the appropriate treatment of electric arc furnace (EAF) dust prior to permanent disposal. The total heavy metal content as well as heavy metal leaching from EAF dust was investigated in five composite samples obtained from three Croatian and Slovenian steelworks. In order to recover zinc and reduce its leaching from the dust, all five samples were submitted to alkaline extraction with 10 M NaOH. Reduction of Cr (VI) to Cr(III) was conducted using FeSO4· 7H2O solution. The elements Mn, Fe, Cu, Ni, and notably Zn and Pb, exhibited highest mobility during toxicity characteristic leaching procedure (TCLP). Comparing to TCLP extracts of initial EAF dust, zinc was found to be over 15 times lower and lead over 200 times lower in TCLP extracts of EAF dust processed by the alkaline leaching method. Since Cr (VI) exceeded its permissible level in the DIN 38414-S4 extracts of both initial and alkaline digested dust, its reduction to Cr (III) prior to permanent disposal is necessary. The recovery of zinc from EAF dust treated with alkaline agent ranged from 50.3% to 73.2%. According to phase analysis, recovery yield showed dependence on zincite/franklinite ratio. The results of the study indicate that permanent disposal of EAF dust require the following procedure: alkaline digestion (followed by leachate purification and alkaline zinc electrolyses), chromate reduction (if necessary), solidification of leaching residue and its testing using the leaching analyses.

Elution of Foundry Sand and Mould Mixture in Water

Abstract Over 90% of iron alloy castings are made in disposable moulds, i.e. in raw synthetic moulds. Raw mould mixture is applied in all production process types. Mould mixture is composed of sand as the basic component, binding material, water, and additives. Sand particles take up 70 to 95% of the total mould material in the mixture. The most frequently used sands include quartz sand, chromite sand, and olivine sand. Preliminary study of elution of foundry sand and mould mixture in distilled water has been studied through electrical conductivity measurements, complemented by measurements of the leaching concentrations of Cr3%, Al3%, Si4%, Ca2%, Mg2%, Fe3, and the pH value in eluates after the leaching process.