The need of light weight alloys for future transportation industry puts Sc and Ti under a sudden demand. While these metals can bring unique and desired properties to alloys, lack of reliable sources brought forth a supply problem which can be solved by valorization of the secondary resources. Bauxite residue (red mud), with considerable Ti and Sc content, is a promising resource for secure supply of these metals. Due to drawbacks of the direct leaching route from bauxite residue, such as silica gel formation and low selectivity towards these valuable metals, a novel leaching process based on oxidative leaching conditions, aiming more efficient and selective leaching but also considering environmental aspects via lower acid consumption, was investigated in this study. Combination of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4) was utilized as the leaching solution, where various acid concentrations, solid-to-liquid ratios, leaching temperatures and times were examined in a comparative manner. Leaching with 2.5 M H2O2: 2.5 M H2SO4 mixture at 90 °C for 30 min was observed to be the best leaching conditions with suppressed silica gel formation and the highest reported leaching efficiency with high S/L ratio for Sc and Ti; 68% and 91%; respectively.

Due to its alkalinity, red mud produced by the Bayer process may affect both the environment and human health. For this reason, its further utilization instead of disposal is of great importance. Numerous methods have already been studied for hydrometallurgical treatment of red mud, especially for the recovery of various metallic components such as iron, aluminum, titanium or rare earth elements. This study focuses on the extraction of titanium from red mud and in particular the mineralogical changes, induced by leaching. Sulfuric acid, hydrochloric acid and their combination have been utilized as leaching agents with the same leaching parameters. It has been determined that sulfuric acid is the best candidate for the red mud treatment in terms of titanium leaching efficiency at the end of 2 h with a value of 67.3%. Moreover, samples from intermediate times of reaction revealed that leaching of Ti exhibit various reaction rates at different times of reaction depending on acid type. In order to explain differences, X-ray Diffraction (XRD), scanning electron microscope (SEM) and QEMSCAN techniques were utilized. Beside titanium oxide (TiO 2 ) with available free surface area, a certain amount of the TiO 2 was detected as entrapped in Fe dominating oxide. These associations between Ti and Fe phases were used to explain different leaching reaction rates and a reaction mechanism was proposed to open a process window.

This article explains the mechanism of the metal/oxide core-shell Ag/TiO 2 and Au/TiO 2 nanoparticle formation via one-step ultrasonic spray pyrolysis (USP) by establishing a new model. The general knowledge on the standard "droplet-to-particle" (DTP) mechanism, nucleation, and growth processes of noble metals, as well as physical and chemical properties of core and shell materials and experimental knowledge, were utilized with the purpose of the construction of this new model. This hypothesis was assessed on silver (Ag)/titanium oxide (TiO 2 ) and gold (Au) TiO 2 binary complex nanoparticles' experimental findings revealed by scanning electron microscopy (SEM), focused ion beam (FIB), high-resolution transmission electron microscopy (HRTEM), and simulation of crystal lattices. It was seen that two mechanisms run as proposed in the new model. However, there were some variations in size, morphology, and distribution of Ag and Au through the TiO 2 core particle and these variations could be explained by the inherent physical and chemical property differences of Ag and Au.Keywords: ultrasonic spray pyrolysis; core shell nanostructure; formation mechanism; TiO 2 ; Ag; Au Motivation and BackgroundCore shell complex nanostructures comprised of binary systems have been the focus of great interest due to their high functionality [1,2]. Preserving the core material's properties and modifying the surface with another material multiplies properties and, owing to the core/shell interface, superior performance has been introduced to a system that cannot be achieved by a single constituent. In recent studies, it was seen that thin surface layers on fine particles affect various properties substantially, such as chemical and thermal stability [3], catalytic activity [4], optical, magnetic, and electrical properties [5][6][7][8].Among various combinations of materials that have been utilized as core-shell systems this study targets on inorganic-inorganic group of Ag/TiO 2 and Au/TiO 2 . TiO 2 is proposed as a core material due to its inertness, chemical stability, and non-toxic nature [9]. It is a crystalline material with three polymorphic phases; anatase (tetragonal), rutile (tetragonal), brookite (orthorhombic), with an order of enthalpy of formation as; ∆H f (rutile) < ∆H f (brookite) < ∆H f (anatase) [10,11]. Regarding the energetics of three polymorphs, rutile is the most stable phase, thermodynamically. However, these three compounds have a surface energy order as; Abstract: This article explains the mechanism of the metal/oxide core-shell Ag/TiO2 and Au/TiO2 nanoparticle formation via one-step ultrasonic spray pyrolysis (USP) by establishing a new model. The general knowledge on the standard "droplet-to-particle" (DTP) mechanism, nucleation, and growth processes of noble metals, as well as physical and chemical properties of core and shell materials and experimental knowledge, were utilized with the purpose of the construction of this new model. This hypothesis was assessed on silver (Ag)/titanium oxide (TiO2)...

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Synthesis and characterisation of spherical core-shell Ag/ZnO nanocomposites using single and two -steps ultrasonic spray pyrolysis (USP)