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.

This article presents the results of the study of the morphological composition of municipal solid waste (MSW) from the landfill of Atyrau city, and the waste’s energy characteristics and presence of microorganisms, including bacteria, fungi and viruses. This study was carried out under a government order to determine the feasibility of recycling accumulated and incoming waste into electricity and its hazard to the environment and the workers involved in handling it. At the moment, there is no MSW recycling in Kazakhstan, which has led to the accumulation of more than 125 million tons of waste with an annual increase of 5 million tons. The research included four major cities (Almaty, Shymkent, Atyrau and Astana), which were selected not only on the basis of population, but also because the cities were located in different climatic zones. Samples were collected at the city landfills: 10 samples with an average distance of 100 m from each other were collected to provide a maximum coverage of both recently received waste and long-time stored waste. The research showed that neither climatic conditions nor the population size had a significant impact on MSW density, the values of which ranged from 120.1 kg/m³ to 145.4 kg/m³, as this indicator directly depends on the quality of life. The mass of the combustible fraction ranged from 39.41% to 54.62% and was mainly represented by plastic, textile and paper waste. The average value for the four cities was 50.30%. The higher calorific value fell in the range of 24.22–30.49 MJ/kg, with an average value of 26.71 MJ/kg. Microbiological studies showed little difference in average composition regardless of climatic conditions. Thus, no sharp differences in MSW composition, its energy characteristics and microbiological composition were found. The results of this study may be useful for optimising MSW recycling and disposal processes, as well as for developing measures to reduce their negative impact on the environment and human health.

The presence of iron(II) impurities hinders the leaching and purification of magnesium ores. The most viable technological solution is to oxidise Fe²⁺ to Fe³⁺, which then precipitates as goethite. However, this process requires the development of new catalysts for use in highly acidic media. This study demonstrates that the Pt^0.25/CeO₂⁵/TiO₂ catalyst is highly effective at oxidising Fe²⁺ in 0.3 M HNO₃, outperforming samples supported on pure titanium dioxide or cerium dioxide. The rate constant is 0.304 L/(mol·min) at room temperature. Notably, the activation energy is only 10.7 kJ/mol, which is over five times lower than that of the non-catalytic process. This result was achieved by selectively depositing platinum particles onto highly dispersed cerium dioxide particles (average size ~5 nm), synthesised using the sol–gel method, and then depositing them onto titanium dioxide. Using a hybrid mixed oxide support ensures a high density of oxygen vacancies at the interface between the platinum (Pt) and mixed cerium and titanium dioxide phases. The formation of abundant adsorbed oxygen species enhances the catalytic activity of the Pt^0.25/CeO₂⁵/TiO₂ catalyst. The catalyst Pt^0.25/CeO₂⁵/TiO₂ also reaches a plateau in terms of efficiency after a durability experiment, which is the highest among the other samples.