Gypsum Compositions Modified with Metallurgical Wastes

The main results of the study of the influence of man-made products of the metallurgical industry on the properties and structure of gypsum binder are presented. It has been proved that the introduction of man-made modifiers, metallurgical dust, and slag leads to an increase in the strength properties and electric conductivity of the material, but, over time, the waste efficiency decreases. The use of Portland cement as an activator leads to the formation of amorphous hydration products based on calcium hydrosilicates, which bind calcium sulfate crystals and provide an increase in the physicomechanical characteristics and electric behavior of the gypsum composite.

Effect of galena contained in dust from Zn–Pb metallurgical processes on environment

This paper assesses the effect of galena emitted with dust from an electrostatic precipitator at Miasteczko Śląskie Zinc Smelting Plant (Poland) onto a soil and water environment. The Eh–pH diagrams plotted in the temperature range of − 3 to 25 °C serve to determine the conditions of PbS stability and conditions under which its decomposition may occur, resulting in the release of ionic forms of lead into the soil and water environment. Determination of the mobility of galena emitted with metallurgical dust is a current and important issue in view of the geochemistry of mineral components in the environment.

Comprehensive Processing of Fine Metallurgical Dust

The processing of fine metallurgical dust by pyrometallurgical methods leads to the accumulation of impurities and deterioration in the quality of blister copper. Fine dust contains copper, zinc, lead, arsenic and iron. A hydrometallurgical method for the separation of the main components into the following products is proposed: copper-zinc residue, iron-arsenic residue, lead residue. The hydrometallurgical scheme consists of three stages of leaching: neutral and using sulfuric and nitric acids. When processing metallurgical dust according to the proposed scheme, a solution containing copper, zinc, iron and arsenic is formed, as well as a lead containing precipitate. Arsenic and iron are removed from the solution in the form of iron (III) arsenate, after which zinc and copper are precipitated. Lead in sediment is in carbonated form. The developed technology allows the extraction of: 87% copper, 88% zinc, 83% iron, 83% arsenic, 99% lead in individual products. Keywords: metallurgical dust, arsenic removal, nitric acid leaching

Dioxins and furans’ behavior in the process of zinc and lead removing from EAF dust

The use of galvanized scrap as a charge material for electric steel-smelting production leads to formation of metallurgical dust suitable for extraction of non-ferrous metals. Chlorine and organic compounds content in metallurgical charge can lead to dioxins and furans formation in the process of electric smelting with their subsequent sedimentation on EAF dust. In the previous study we determined dioxins and furans content in dust at the level of 474 ng/kg of EAF dust. The methodology for conducting an experiment in a muffle furnace at temperatures of 300, 600, 900 and 1150 °Cwas developed for the study of dioxins and furans’ behavior during dust heating. Investigation of EAF dust chemical composition before and after the experiment made it possible to establish that desorption of dioxins and furans occurs during heating in the temperature range of 300 – 900 °C. In parallel with dioxins and furans’ desorption some chemical compounds evaporate indirectly and it is determined by calculation of changes in the content of C, Na, Cl, K, Pb, Zn in the sample. In the studied temperature range, the content of C, Na, Cl decreases to zero; K content is reduced by 81 %; Pb content is reduced by 83.5 %. Reduction of Zn content does not exceed 5 %. Change in content of the remaining components is insignificant. The obtained data confirm the predominant presence of chlorine in inorganic compounds in forms of NaCl and KCl, along with a slight presence in forms of ZnCl, PbCl, and PbCl2 . The study revealed the need of consideration of dioxins and furans’ presence during development of technologies aimed at metallurgical dust processing. It is proposed to perform high-temperature processing of dust (>850 °С) with the subsequent irrigation of exhaust gases with lime milk. The most rational ways to decrease dioxins and furans’ content in EAF dust are conducting afterburning of exhaust gases, followed by rapid cooling in order to avoid secondary synthesis of ecotoxicants or reducing the amount of chlorine-containing and conventional materials during pretreatment of metals.

Dioxins and furans in zinc-containing metallurgical dust: behavior and formation processes

The use of galvanized scrap as a charge material for electric steel-smelting production leads to the formation of metallurgical dust suitable for the extraction of non-ferrous metals. The issues related to the behavior of chlorine and its compounds in zinc and lead containing EAF-dust is not sufficiently studied. Current research exhibits the danger of chlorine and its compounds in charge and, consequently, in emissions of EAF. Chlorine and its compounds are considered to be the main components associated with the formation of highly toxic organic substances – dioxins and furans (D&F). D&F enter the environment not only in gaseous form, but also in the form of compounds adsorbed on the surface of dust particles. According to various data, D&F concentration is 5-500 ng / kg of dust and depends on the technological parameters of melting. Analysis of the formation processes of D&F in EAF and their behavior in the captured dust is given. It was found that at the studied chlorine content of 1.3% in EAF-dust from the charge materials, 99.9% of chlorine form relatively safe compounds, mainly chlorides, and a small amount goes to the formation of D&F. The amount of D&F adsorbed on the surface of captured dust particles was 474 ng / kg of dust. As strong toxicants, D&F increase the hazard category of dust from the 4th to the 3rd and above that must be considered at dust usage. In addition, the transport of D&F in the environment is due to solid particles that absorb poisons on their surface. Therefore, EAF dust, with D&F adsorbed on its surface, can provoke their entry into organisms. The ways of reducing D&F emission in the production of EAF-steel and the resource-saving and environmentally safe technologies of dust processing are considered. In particular, the possibility of using lime milk for the off-gases irrigation in the EAF gas flue was analyzed and it was shown that it allows to reduce the D&F content to acceptable limits. The efficiency of the proposed activities was evaluated.