Waste blast furnace slags as raw materials for the production of binders

Abstract

Problem. Industrial waste accumulating in dumps, in many cases, have valuable technical properties, so they can be considered as secondary resources. Тhe study of the properties and modification of slags under various conditions requires an integrated approach, including different analysis. Goal. Based on the selected experimental methods to justify the resource value of Zaporizhstal waste blast furnace slag.  Methodology. The methods of the study were X-ray diffraction, gamma-spectrometry, spectrographic analysis and electron-probe microanalysis. Results. X-ray phase analysis revealed the minerals of the blast-furnace slags in the crystalline state: rankinite 3CaO∙2SiO2, quartz SiO2, gehlenite 2CaO∙Al2O3∙SiO2, bredigit α-2CaO∙SiO2, okermanit 2CaO∙MgO∙2SiO2, pseudowollastonite α-CaO∙SiO2. The mass fraction of the glassy component is calculated, which is half the mass of Zaporizhstal blast furnace slag. The elemental composition of the slag, determined by electron probe microanalysis, made it possible to characterize its fractions from the standpoint of toxicity. The elements potassium, sodium, sulfur, chlorine, copper and titanium, which are not included in the composition of minerals, were recorded using a scanning electron microscope, which gives grounds for assuming that they are sorbed by the surface of mineral particles. Micrographs of the surface of the particles of blast furnace slag indicate a high degree of loosening with the presence of needle-like and plate-like crystals, which determines the sorption properties of the slag. The maximum content of potassium, sodium and titanium is characteristic of the 2.5–5 mm fraction. Slag contains an insignificant amount (<1 %) of compounds of metals Fe, Ti and Cu belonging to the 3rd hazard class of substances, which does not interfere with the further disposal of slag. The III hazard class of waste slag blast furnace slag has been determined. Gamma-spectrometric method determined the specific radioactivity and the effective specific activity of slag fractions. Natural radionuclides 40K, 226Ra and 232Th were detected. It is proved that slag and its separate fractions belong to the first class of radiation hazard and can be used in building industry without restriction. Originality. The minerals okermanit, bredigit, pseudovollastonite are technically valuable in the production of binding materials, since they have hydraulic activity. The presence of amorphous phases indicates increased sorption and chemical activity of slag, which is important from the standpoint of the use of slag in the production of binders. In the large slag fraction, the mass contribution of the amorphous state of the substance is slightly higher. Practical value. Zaporizhstal waste blast furnace slag can be recommended in the production of binders – Portland cement and slag Portland cement, according to a combination of chemical indicators: a high concentration of hydraulically active minerals and amorphous phase, highly developed surface of slag particles, the presence of sorption surface activity, attitude to moderately hazardous production waste and class I radiation danger