Rare Earth Elements (REE) are considered to be highly "critical" by the European Commission because the concentration of global supply and their use in a wide range of emerging technologies (e.g. smart phones, electric cars and wind turbines) and this at a time of increasing geopolitical tensions. According to the European Commission’s assessment, the demand for rare earth elements is expected to increase more than fivefold by 2030. Today, Europe is dependent on imports of these minerals, where China completely dominates the market, a factor which increases the vulnerability of European industry. Alternative sources of REE in Europe, such as recovery of quarrying and processing waste, are being considered.This research, part of an italian project NODES, wich has received funding (PNRR) from the EU, about circular economy and recovery of mineral waste, focuses on the possibility to recover REE from extractive waste. The investigated area cover Piedmont Region in northern Italy. Waste materials from gneisses and granites (ranging from blocks up to residual sludge) used as dimension stones were characterized for volume, chemistry, mineralogy, and texture.Based on the first analyses carried out, the most interesting contexts are those related to gneisses in Luserna Stone and Verbano Cusio Ossola quarrying area and to quartzites of Monte Bracco quarrying area.Thanks to a proper treatment activity (grinding, screening and magnetic separation), these materials, present in past extractive waste facilities and in extractive waste coming from exploitation and working activities, could be used to recovery of REE. After the first phase, connected to “waste” characterisation, the following activities will be linked to processing of the richest samples to exploit (at Laboratory level) REE, and to economic issues.An additional step will include leaching extraction tests (always at laboratory scale) to identify the best and most sustainable technique to extract and separate REE from the sampled extractive waste. Key words: Rare Earth Elements, Critical Raw Materials, Supply-chain, extractive waste, mining waste, leaching, magnetic separation.

Conventional explosive welding is performed in the atmosphere. In addition to causing many hazardous effects (air shock wave, vibration, and noise), air medium also affects the welding quality. To study the influence of the vacuum environment on the above problems, this study conducted CP-Ti/Q235 explosive welding in the vacuum (0.1 atm), and set another experiment in the atmospheric environment as a reference. The results showed that the vacuum environment significantly reduced the hazardous effects. Compared with the atmospheric environment, the low density of the gas medium attenuated the shock wave (69.27%) during the explosive welding, resulting in reduced levels of vibration (74.46%) and noise (45.31%). Microstructure analysis found that in both environments, the wavelength and amplitude of the waveform interface were remarkably different at the end portion, and the overall waveform obtained in the vacuum was more uniform than that in the atmosphere. Through the two-step simulation, the pressures of the interstitial gas shock wave were respectively 15.4 and 1.66 MPa under the atmospheric and vacuum environments. Therefore, the interstitial gas shock wave affected the movement of the flyer plate, causing welding instability, especially in the atmosphere. Furthermore, the participation of the gas during the wave formation led to the appearance of the pores and microcracks. In contrast, the vacuum environment effectively decreased the micro-defects of the bonding interface, improving the welding quality. This study revealed the detailed advantages of the vacuum environment and provided a reference for explosive welding in urban areas.

To explore the optimal method for simulating impact welding, we compared detailedly the smoothed particle hydrodynamics (SPH) and structured arbitrary Lagrangian-Eulerian (S-ALE) methods in predicting bonding interface. Based on the experimental results of Cu-Q235 steel atmospheric explosive welding, an in-depth analysis was presented. The results show that the SPH and S-ALE methods converged at element sizes of 2.5 and 2 mu m, respectively. When the element size was further reduced to 0.5 % of the wavelength, the errors of both methods were less than 5 %. Benefiting from the gradient mesh, the efficiency of the S-ALE method was 2-4 times that of the SPH method at the same element size. With the addition of the gas medium, the S-ALE method derived the formation mechanism of the gap gas shockwave and indicated that the pressure distribution is not uniform. Furthermore, the local high pressure of the gas shockwave prevents the vortex closure during the wave formation, generating the pore. The calculated pressure and velocity of the wavefront were 20 MPa and 3500 m s- 1, respectively. In conclusion, the SPH is suitable for fast previewing waveform interfaces, while the S-ALE method has the advantage of capturing fine waveform structures under various environmental conditions.

In order to reduce critical impact velocity and enlarge weldability window of aluminium/steel explosive welding, a chemical copper plating layer as interlayer was proposed to carry out aluminium/steel explosive welding. The results showed that the interface of the 1060/Q235 composite plate had good bonding performance, and no obvious defects such as cracks and pores were found. Copper plating as intermediate layer could enlarge aluminium/steel weldability window. The thickness of solidified melt was much thicker than that of diffusion zone. The molten copper particles participated in the formation of re-entry jet, which rotated under the action of initial jet. The presence of the Cu layer reduces the occurrence of excessive melting during welding and improves the properties of the interface.

Keywords: Fatigue crack propagation; Welding residual stress; Plastic re-distribution; Stress ratio effect

Ti/Fe clad plate had attracted extensive attention because of its important application. In order to reduce the titanium layer thickness, the explosive welding of TA1 titanium foil to Q235 steel plate was carried out. The interfacial bonding performance was analyzed by micromorphology analysis and mechanical property test, and the formation process of interfacial wave and molten block in the vortex was simulated by smoothed particle hydrodynamics (SPH) method. The results showed that salt as pressure transfer layer used in explosive welding could play a good buffer effect on the collision between flyer and base layers. Regular waveforms were formed on the bonding interface, and the titanium foil/steel clad plate exhibited good welding quality and bonding property. The crest of the observed interfacial wave moved 200 μm from the beginning to the final formation, and it was important of jet on the formation of interfacial waveform. The interface was mainly bonded in the form of molten layer, and the grains near the interface were streamlined. Molten block containing intermetallic compounds and metal oxides appeared in the vortex of wave crest.

Smooth particle hydrodynamics (SPH) is often adopted to simulate the waveform interface, which has a crucial effect on the bonding quality in explosive welding (EXW). However, owing to the nature of the SPH method, it is difficult to evaluate the influence of the air medium and calculate detailed waveform structure. In this study, a Cu-Q235 steel EXW model containing air medium was established using a structured arbitrary Lagrangian-Eulerian (S-ALE) method. A full-size 2D model was first performed to acquire welding parameters, which were set to the initial conditions for the next oblique collision method. Subsequently, the experiment was conducted to verify the accuracy of the simulations. The results show that the S-ALE method can effectively predict the waveform and acquire the detailed process of the EXW. With the addition of an air medium, the calculated velocity and pressure of the shock wavefront were approximately 3300 m center dot s(-1) and 15 MPa, respectively. Despite the limited effect of the gas shockwave on the overall waveform, the influence on the large-scale or thin plates cannot be ignored. Furthermore, the simulation indicates that the participation of the air during the wave formation led to the generation of the pore in the vortex zone. The proposed method could predict the waveform structure and optimize the manufacturing process of composite plates in the atmospheric EXW.

Coal seam deformation due to gas adsorption affects the stability of the underground structure. Natural coal blocks of the Shanxi Formation were selected to study the dynamic adsorption characteristics of coal samples subjected to CO2, CH4, and N2 gas injections under coaxial pressure and confining pressure (7 MPa), as well as the displacement of CH4 with CO2 and N2 under the same conditions. The results show that, under the same conditions, the strain in the coal samples first increased, followed by a rapid increase along with the increase in pressure, with the transverse strain being always higher than the axial strain. The amount of gas adsorption varied from high to low as CO2 > CH4 > N2, and the final adsorption strains and equilibrium times were different for each gas. Based on the increase in gas pressure, the gas adsorption strain curve can be divided into two stages. The displacement of N2 only uses partial pressure to achieve the desorption of CH4 in the coal sample, leading to shrinkage deformation of the coal sample. In contrast, the displacement of CO2 has the dual effects of competitive adsorption and partial pressure reduction on CH4, leading to the swelling deformation of the coal sample.

To avoid support crushing again under the similar conditions of working face No. 1202( 3) by improving upper limit in Gubei Coal Mine of Huainan, based on fracture characteristics of overlying strata, a structural mechanics model of overlying strata with the natural arch is established. The theoretical formula of the arch rise for both the low the high caving arches are deduced. Firstly, the influence of fracture location of the roof on the support load is studied. Then, the overlying strata loads under conditions of loose aquifer inside and outside the natural arch are calculated. Moreover, the criteria of support crushing for sliding instability and squash instability are determined. This study shows that it is easy to form the structure of high caving arch when the working face of improving upper limit is influenced by the water of loose aquifer. The volume weight of loose aquifer inside the high caving arch increases, and the contact forces between hinged rocks decrease. Additionally, the key layer is influenced by the water pressure of loose aquifer, which increase loads on the supports sharply. Therefore, the working face of improving upper limit easily leads to support crushing. However, the influencing factors of support crushing belong to both geological factors and mining technology factor. It should be mentioned that the blindly increasing working resistance of supports is not necessary to reduce the risk of support crushing, but the support cost is inevitable to increase rapidly. Based on the above analysis, the dimensionless sensitivity index is defined, and then the sensitivity of influencing factors of support crushing is analyzed. It aims at investigating the influencing factors of high sensitivity and preventing countermeasures of support crushing, such as controlling an appropriate mining height, forced caving for the roof of open-off cut, preventing an immediate roof suspending, hydrophobic step-down before mining, strengthening the rib of working face, improving support force, selecting reasonable equipment, and guaranteeing reasonable advance speed of working face. These measures provide some theoretical guidance for safe mining under the similar conditions of working face No. 1202(3).