Kazakhstan’s asbestos industry produces over 3 million tons of waste annually. The primary component of asbestos ore waste (AOW) is magnesium rich minerals. In this study, the extraction of magnesium from AOW with nitric acid (HNO₃) was for the first time systematically studied. A series of experiments were conducted to optimize acid concentration (300–600 g/L), leaching temperature (55–95 °C), leaching time (60–180 min), solid-to-liquid ratio (1:3–1:7), and particle size, with the overall goal of maximizing magnesium extraction and cost efficiency. Our results provide dependence of magnesium extraction in the order of acid concentration > temperature > time > solid-to-liquid ratio, while particle size was found to be negligible. The cost-efficiency optimization demonstrated the positive impact of the relatively low acid concentrations (< 450 g/L) and temperatures between 65 and 85 °C, while the Protodyakonov model validated a linear dependence of the extraction rate on temperature and acid concentration. Our model demonstrates that extraction efficiencies of up to 90% can be achieved while reducing reagent use and lowering the overall cost of magnesium production. Leaching of magnesium by HNO₃ also opens a pathway to a closed-cycle process, due to the formation of magnesium nitrate. The thermal decomposition of Mg(NO₃)₂ provides valuable products such as MgO and NO₂ reused in HNO₃ regeneration for subsequent cycles. The proposed model predicts magnesium extraction from asbestos ore depending on leaching parameters with reasonable accuracy.

Zirconium-based conversion coatings were prepared on unpolished ST20LS mild steel by conventional immersion and cathodic polarization in aqueous H₂ZrF₆ solutions. Five-factor experimental designs were used to examine the effects of pH, temperature, deposition time, H₂ZrF₆ concentration, drying temperature/applied cathodic potential for both methods. The Zr conversion coatings were characterized by SEM/EDS, Raman spectroscopy, and XPS. Their protective properties were evaluated by neutral salt-spray testing, potentiodynamic polarization, and gravimetric testing in an oil–water emulsion. Cracks were observed in the Zr conversion coating prepared by the immersion method. The coating prepared at pH 4.0 decreased the salt-spray corrosion rate from 6.00 to 3.07 mm·year⁻¹. Cathodic polarization promoted coating formation on the rough steel surface, and the results showed that solution pH and applied potential affected the corrosion protection performance. Among the samples selected for detailed electrochemical analysis, the coating deposited at pH 6 and −1.2 V versus Ag/AgCl showed the strongest overall protection. Its polarization resistance reached 1310 Ω·cm², compared with 232 Ω·cm² for uncoated steel, while the corrosion current density decreased from 5.431 to 0.305 μA·cm⁻², corresponding to a protection efficiency of 94.5%. Raman and XPS results supported the formation of a poorly crystalline zirconium oxide/oxyhydroxide-containing layer. The results suggest that cathodically generated OH⁻ promotes interfacial hydrolysis and condensation of zirconium complexes, improving conversion-coating formation on rough mild-steel surfaces.