The wide application of concrete prepared with coal gangue (CG) as an aggregate (CPCGA) is limited because of the low mechanical strength and strong water absorption capacity of CG. This paper used silica fume (SF) to improve the performance of the interfacial transition zone (ITZ) in CPCGA and revealed the enhancement mechanism. The results showed that the compressive strength of CPCGA prepared with cement replaced by a suitable amount of SF at the age of 28 days increased by more than 30%, and the flexural strength increased by over 20%. The SF could effectively reduce the porosity and micropore size in the ITZ of CPCGA, and the porosity of the ITZ in CPCGA added with 7.50% SF decreased by 44.22, 46.16, and 24.46% at distances from the aggregate surface of 10, 50, and 100 μm, respectively, compared with CPCGA without SF. Further research showed that Ca(OH)₂ (CH) generated in the cement hydration reaction reacted with a large amount of active SiO₂ in SF to restrain the formation of coarse CH in the ITZ of CPCGA, and the calcium silicate hydrate (C-S-H) gel generated filled the ITZ micropores to reduce the ITZ porosity further. Moreover, the reaction of SF and CH helped to promote the hydration reaction of cement to proceed thoroughly in CPCGA, thus improving CPCGA performance.

Open stockpiling and the continual production of industrial solid wastes such as red mud (RM) and yellow phosphorus slag (YPS) have caused serious environmental pollution issues. Additionally, concrete prepared easily and with high strength is a widely applied building material. Therefore, replacing part or all of the cement for preparing concrete with RM and YPS will greatly reduce this kind of solid waste and, thus, decrease environmental pressures. This study investigated the best ratio for the replacement of concrete with RM and YPS, testing the mechanical properties as well as the morphology, material composition, and microporous structure of the interface transition zone (ITZ). The results showed for the concrete prepared with ordinary Portland cement replaced by 10.00 wt.% RM and 18 wt.% YPS, compared to ordinary Portland cement concrete, the compressive strength of concrete with basalt aggregate and dolomite aggregate increased by 25.04% and 27.27%, respectively, when the concrete was cured with steam for 28 days. Furthermore, it had a smaller average pore diameter and crystal size in the ITZ. The aggregate and matrix were more closely intertwined. This was because RM had a low cementitious activity and mainly had a filling effect when added to concrete, while the highly active silica in YPS could react with the Ca(OH)₂ crystal (CH) produced from cement hydration to form calcium silicate hydrate (CSH) gel, improving the mechanical properties and microstructure of the concrete.

Gold is mainly present in the form of [Au(CN)₂]⁻ during the cyanide leaching process, and this [Au(CN)₂]⁻ can be adsorbed by graphite in carbonaceous gold ore resulting in preg-robbing gold. In order to clarify the adsorption mechanism between the [Au(CN)₂]⁻ and graphite, the interaction between the [Au(CN)₂]⁻ and graphite (0001) surface was studied using density functional theory (DFT). The distance between [Au(CN)₂]⁻ and graphite (0001) decreased from (4.298–4.440 Å) to (3.123–3.343 Å) after optimization, and the shape of [Au(CN)₂]⁻ and graphite (0001) obviously changed from straight to curved, which indicated that the [Au(CN)₂]⁻ had been adsorbed on the graphite (0001) surface. A partial densities of state (PDOS) analysis revealed that there was little change in the delocalization and locality of the PDOS on the graphite (0001) surface after adsorption. However, the valence bands of the Au 5d orbital, C 2p orbital, and N 2p orbital near the Fermi level moved slightly towards lower energy levels; therefore, the adsorption configuration was stable. An analysis of the Mulliken charge population indicated that the Au, N, and C in [Au(CN)₂]⁻ obtained 0.26, 0.18, 0.04 electrons after adsorption, respectively, while C(surf) lost 0.03 electrons. [Au(CN)₂]⁻ changed to a conductor from an insulator after adsorption. Taking into account the surface electrical properties of [Au(CN)₂]⁻ and graphite (0001), there was still a slight electrostatic adsorption between them. The analysis of adsorption energy, electronic structure, PDOS, electron density, Mulliken charge population, and Mulliken bond population revealed that [Au(CN)₂]⁻ could be adsorbed to the graphite (0001) surface; the adsorption was a type of physical adsorption (including electrostatic adsorption) and mainly occurred on the two C≡N. These results contributed to the understanding of the mechanisms involved in preg-robbing gold formation by graphite and the optimization of this process during cyanide leaching.

Serious environmental pollution issues caused by the storage and exposure of large amounts of red mud (RM) and yellow phosphorus slag (YPS) have raised significant concerns. Red mud-yellow phosphorous slag-cement concrete (RM-YPS-CC) is prepared with 25% yellow phosphorus slag content (YPSC) and 10% red mud content (RMC) to replace a portion of the cement at the age of 28 days and was found in this study to satisfy the mechanical property requirements. More ettringite and portlandite were generated with the RM-YPS-CC than with the yellow phosphorous slag-cement concrete (YPS-CC). In addition, the cementitious materials were more interlaced, and there was more disorder in the crystals of the RM-YPS-CC, which formed a more complex spatial structure than the YPS-CC did. Without RM, the initial cracking strength on the surface of the concrete was 5–6 MPa, the maximum crack width was 3.96 mm, and the crack number was 8. However, the cracking strength was 26.5–27 MPa with RMC5, the maximum crack width was 0.66 mm with RMC15, and the crack number was 3 with RMC15. Moreover, studies using the digital image correlation (DIC) method indicated that the displacement distribution and evolution of the first crack area changed quickly at 10 MPa in either horizontal or vertical direction, and a similar trend was maintained from 10 MPa to 27.1 MPa for the YPS-CC. However, with a small distribution and evolution of horizontal or vertical displacement from 5 MPa to 25 MPa, the evolution would change rapidly when reaching 30 MPa for RM-YPS-CC. This study aims to provide new insights into the wide application of YPS and RM for saving energy and reducing emissions and to develop a new method to study the fracture behavior of concrete.