No abstract

With the aim to increase the recycling of fine sludge and dust disposed normally in landfill, cold bonded pelletizing of the sludge and dust using cement as binder was investigated in laboratory scale as well as in the pilot scale pelletizing plant. The influence of BF flue dust, BOF fine sludge and oily mill scale sludge on the cold strength, capacity and reduction degree of cold bond pellets was studied experimentally on the basis of a statistical procedure. With a coarser representative particle size, oily mill scale sludge has the greatest effect on the cold strength. BF flue dust has a negative effect for increasing both the cold strength and capacity for levels of over 25 % of the mixture. The BOF fine sludge has the positive effect on cold strength, while its interaction with BF flue dust has the negative effect on reduction degree.The results of pelletizing tests in pilot scale show that the maximum cold strength (TTH 94 %) and capacity (13-15 t/h) of products is obtained at the conditions given by the optimal mixture design and cure time. The industrial tests on charging cold bonded pellets as burden material in the BOF converter were described. The charging weight of cold bonded pellets varied from 0.5 to 2.5 tons. The results of industrial tests indicated that the converter process was not subject to any adverse disturbances due to the addition of 2.5 tons of cold bonded pellets.

No abstract

Large amounts of slag are generated by the Swedish steel industry each year. The Electric Arc Furnace process generates about 200 000 ton of slag per annum, from which approximately 40% is deposited. An alternative to deposit is to use slag as road construction material. However, leaching of metals from the slag can be a reason to limit slag use in road construction. The aim of this work was to investigate how stable these materials are when aged, in an environment open to seasonable weather conditions, with respect to leaching and mineralogy. Three different EAF-slags from domestic steel plants were used in this study. The materials were characterized after 0, 6, 12, 18, and 24 months to evaluate the ageing process. The analytical techniques that were used to evaluate the effect of ageing are scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and a standard test for leaching. The changes in ageing behavior differ between the three materials. The conductivity and the pH decreases with time for all samples. The leaching of calcium, chromium as well as aluminum decreases with time while the leaching of magnesium increases. CaCO 3 was formed on slag surfaces as CaO reacts with moisture and CO 2 from the air.

Ladle slag is an internal by‐product generated within the steelmaking industry during the refining of steel. The realisation of beneficial inherent properties of ladle slag as a binder supplement or substitute material is believed to be advantageous with respect to both economy and environment for steelmakers. For this reason, the current study has focused on highlighting the properties of ladle slag that are pertinent to the formation of calcium aluminate hydrates. Three fractions of ladle slag, two of which were based on different slag formers, have been characterised using XRF, XRD and calorimetric analysis. Commonly known hydraulic minerals such as mayenite, tricalcium aluminate and dicalcium silicate were detected during analysis. An important aspect in the utilisation of ladle slag is the slag handling methodology. Therefore, this study also highlights and discusses the need to reconsider slag handling procedures concerning unnecessary exposure to weathering and the possible need for further processing of the slag in order to better employ the inherent hydraulic properties of this material.