This article presents an experimental study of the effect of chromium (III) oxide, recovered from chromium-containing catalyst sludge, on the properties of grouting mortars used for well cementing in permafrost zones. The necessity of modifying grouting mortars to increase the strength of the cement stone for intervals in permafrost formations is justified. A method for reducing Cr(VI) to the stable form Cr(III) has been developed, and Cr₂O₃ has been obtained for use as an active mineral additive. Four grouting mixture compositions are considered: a base mixture, commonly used at sites, based on Portland cement with a setting accelerator; a mixture based on Portland cement; a mixture based on Portland cement with the addition of chromium (III) oxide; and a mixture based on Portland cement with calcium chloride and the addition of chromium (III) oxide. The experiments include testing of the four compositions at two water-to-solid ratios (W/S = 0.4 and 0.5) with an assessment of flowability, compressive and flexural strength, microstructure (microtomography, SEM) and phase composition (XRD) at normal and sub-zero temperatures, including cyclic temperature changes. The data obtained show that at W/S = 0.5, the addition of Cr₂O₃ increases the compressive and flexural strength of the cement stone; a reduction in the content of free Ca(OH)₂ is observed, the proportion of calcium silicate hydrates (CSH) increases, and a more homogeneous and dense microstructure is evident. This modification increases the flowability of the grout, which facilitates better replacement of the drilling fluid. The use of Cr₂O₃ to improve the durability and watertightness of support structures in cryolithozone conditions is clearly advisable.

The paper describes the issues associated with waste generated during steel production and processing, in particular the dust from electric arc furnaces (EAF). An effective solution for the disposal of such waste is its involvement in processing to obtain valuable products. This paper studies the physical and chemical properties of EAF dust produced during the smelting of metallized pellets and captured by the dust and gas cleaning system of the steel-smelting shop at the Oskol Electrometallurgical Combine, Belgorod Region. The results obtained in the study of the chemical and disperse compositions of dust, the microstructure of the surface made it possible to propose the use of dust as a raw material for coagulant production. The conditions of acid-thermal treatment of dust are determined, contributing to the partial dissolution of iron (II), (III), and aluminium compounds, which ensure the coagulation processes during wastewater treatment. Model solutions show high efficiency (> 95 %) of water treatment from heavy metal ions by modified EAF dust.

The development of a comprehensive approach to preventing the pollution of natural objects is necessary due to the high requirements of environmental legislation for the discharge of industrial wastewater. Adsorbents are used in various industries to extract heavy metals from wastewater. In this study the possibility of using saponite clay as a raw material for the production of sorbent for the extraction of copper ions Cu²⁺ from industrial wastewater is considered, a recipe and technology of sorbent production are developed, and its chemical composition is established. It has been established that the optimum temperature for heat treatment of the sorbent and corresponds to 550 ºC, since at this temperature saponite extrudates acquire strength (strength 34.1 kg/mm²) and textural properties (specific surface area of pellets 22.803 m²/g), allowing them to be used as sorbents. The kinetics of molecular adsorption was studied using model solutions of copper (II) sulfate. The extraction efficiency of copper (II) ions from the model solutions is 93 %. Extraction efficiency of copper (II) ions from copper plating wastewater reaches 94 %. SEM results confirm the presence of metal on the sorbent surface.