This study investigated the potential of low-grade gold deposits in modern mining, particularly in the context of declining high-grade resources. The primary method for processing these ores was gravity separation with the Knelson concentrator. A GRG test (gravity recoverable gold test) was conducted on two gold-bearing samples: a polymetallic Cu-Zn-Au ore from Zlaté Hory–Západ (Czech Republic) containing refractory gold and an ore with free gold from Kašperské Hory (Czech Republic). The study evaluated the effectiveness of the GRG test for gold recovery from these ores. The results showed that the Kašperské Hory sample predominantly contained relatively large gold grains, with recovery rates dropping significantly upon finer comminution. In the sample from the Zlaté Hory–Západ deposit, the greatest GRG release occurred in the first and last test stages, suggesting that larger sulfide grains with bound gold passed predominantly in the first stage, while fine gold with residual sulfides passed in the third. Both samples achieved high overall GRG recovery rates, with 64.2% for Kašperské Hory and more than 66% for Zlaté Hory–Západ, demonstrating the efficacy of centrifugal concentrators for both ores.

In the coming decades, mineral extraction will cease at several locations in the Czech Republic. This article examines the transformation of these sites into natural carbon storage reservoirs after mining has ceased. This innovative approach supports sustainable land use, helps mitigate climate change, and restores ecological landscape functions.

This article deals with the possibility of using a recycled aggregate from railway ballast and platforms for the production of cement composites with a full or partial replacement of natural aggregates. This study evaluates the physical and mechanical properties of fresh and hardened concrete, as well as its resistance to water pressure, microstructure, and environmental safety. Four concrete recipes using an aggregate at the end of its life cycle from railway ballast (0/25 mm) and from the layers under the asphalt covering of the platforms (0/32 mm) were designed, with a 100% replacement for 0/25, 55% replacement (coarse fraction) for 0/32, and 45% sand for 0/4. The results have shown a significant influence of the type of aggregate on the strength, bulk density, and watertightness of the concrete. At 28 days, the compressive strengths of mixes R250, R400, R250N, and R400N were approximately 8, 20, 30, and 35 MPa, respectively, while after 90 days they increased to 10, 22, 37, and 45 MPa. The corresponding fresh concrete bulk densities ranged from about 1.95 to 2.27 g/cm³, and the water penetration depths ranged between 16 mm (best) and 27 mm (worst) among the mixes. Analyses of aqueous leachates have confirmed that the cement matrix effectively stabilizes the contaminants contained in the recycled aggregate and that the resulting products comply with the legislative limits. This study shows that an aggregate at the end of its life cycle from railway ballast and platforms can be effectively used to produce sustainable cement composites (concrete) with suitable mechanical properties and minimal environmental risks.

The growing production of construction and demolition waste has been stimulating the need to look for sustainable alternatives to natural aggregate used in the production of cement composites. This study evaluates the potential use of recycled brick material as a substitute for natural coarse aggregate in terms of environmental safety, mechanical properties, the solidification effect of the cement matrix, and life cycle assessment (LCA). Recycled brick materials sourced from four recycling yards were characterized using physical, chemical, and leaching tests. Cement composites containing 50%, 70%, 80%, and 100% replacement of natural coarse aggregate with recycled brick material were subsequently designed. The results demonstrated significant variability in the environmental properties of the recycled materials depending on their origin. Compressive strength after 28 days ranged from 31.8 to 36.2 MPa, and all mixtures met the requirements for strength classes C20/25 to C25/30 according to ČSN EN 206+A2. At the same time, a significant solidification effect of the cement matrix was confirmed, leading to a reduction in the concentrations of dissolved substances by 68.0–80.1% and sulfates by 97.8–99.2% compared to the original recycled material. A life-cycle assessment demonstrated a gradual reduction in the environmental impacts as the proportion of recycled brick material increased, with the best results achieved by a mixture with 100% replacement of natural aggregate. The results confirm that recycled brick material can be safely used as a full-fledged substitute for natural coarse aggregate while maintaining the required mechanical properties and reducing environmental impacts.