The jarosite residue is a harmful byproduct of the zinc hydrometallurgical process and has been classified as hazardous waste due to its high content of heavy metals and poor stability. In this work, the recovery of valuable metals by synergistic disposal of jarosite residue with cement kiln has been investigated. A series of investigations were undertaken to assess the effect of amount of jarosite residue, roasting time, and the addition of CaCl₂ on phase transformation and migration of valuable elements in the cement clinker. When 25% of jarosite residue was added to the raw cement materials and roasted at 1400 °C for 30 min, the silicate content in the cement clinker reached 54.4%. In the presence of CaCl₂ as the mineralizer, the volatilization rates of Pb and Zn were 93% and 75%, respectively. The results indicated that jarosite residue can be used as the cement additive and valuable metals of Pb and Zn can be recovered simultaneously during the roasting process.

Ultrasound is introduced into the gold adsorption process by activated carbon to improve the adsorption efficiency. The effects of ultrasonic equipment, initial pH value, amount of activated carbon, initial CN⁻ concentration, and temperature on the Au(CN${)}_2^{-}$ adsorption onto activated carbon were investigated. The adsorption results show that the water bath ultrasonic generator is more beneficial to promote the gold adsorption onto activated carbon than the probe ultrasonic equipment. With the introduction of ultrasound, the gold adsorption capacity of activated carbon is obviously improved, and the gold balance loading is increased by about 37%. The Freundlich model can describe well the adsorption behavior of Au(CN${)}_2^{-}$ onto activated carbon with or without ultrasound, which indicates that the Au(CN${)}_2^{-}$ adsorption onto activated carbon belongs to multi-molecular chemisorption. Compared with the pseudo-first-order equation and intra-particle diffusion equation, the pseudo-second-order equation can better fit dynamic data. Through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FT-IR), BET specific surface area, SEM, and particle size distribution analysis, it is proved that the enhancement of the gold adsorption onto activated carbon by ultrasound is due to the continuous action of ultrasound, which reduces the particle size and ultrasonication increases specific surface area through physical fragmentation effects and improves active site accessibility by reducing mass transfer resistance of activated carbon, rather than changing the adsorption mechanism of gold onto activated carbon.

As a pioneering exploration of gallium nitride (GaN) as reinforcement in metal matrix composites, this study systematically investigated the mechanical–electrical property evolution in copper matrix composites through controlled GaN incorporation—a research gap scarcely addressed previously. GaN-Cu composites with tailored GaN contents were successfully synthesized by precisely controlled mechanical alloying and powder metallurgical processing and exhibited exceptional mechanical–electrical synergies. Advanced microstructural characterization via X-ray diffraction and electron microscopy revealed the homogeneous dispersion of GaN nanoparticles within the Cu matrix, forming coherent interfacial structures. The characterization results show that GaN-Cu composites could be successfully prepared by mechanical alloying and powder metallurgy methods, and it was confirmed that GaN nanoparticles could improve the mechanical properties of metal matrix composites as reinforcement; with an exponential increase in GaN content, the decrease in conductivity became very slow. With an increase in GaN content, the electrical conductivity decreased in an “L” shape, while the hardness first increased and then decreased, but the hardness could reach up to 128.66 HV, which is about 130% higher than that of the substrate.