Mechanochemical Synthesis of Nanocrystalline CdS in a Laboratory and Industrial Mill

Nanocrystalline materials have been of interest of more than 20 years and this interest is still increasing. The preparation and characterization of different chalcogenides have attracted a considerable attention due to their important nonlinear properties, luminiscent properties and other important physical and chemical properties. The main cause is in their unusual properties based on the high concentration of atoms in interfacial structures and the relatively simple ways of their preparation. Nanoparticles of semiconductors have many potential applications in the area of advanced materials. These materials can be synthesized via solid state reactions where the recovery degree can be strongly enhanced by the intervention of mechanical activation. Mechanochemical synthesis belongs among the synthesis route which can effectively control and regulate the course of solid state reactions.This paper describes structural and surface properties of cadmium sulphide nanoparticles synthesized in a planetary mill and in an eccentric vibratory mill. The main aim of this paper was to illustrate the potential of this technique for the large-scale production of CdS nanopowder.CdS nanoparticles were successfully synthesized by the mechanochemical route from the cadmium acetate and natrium sulphide. Structure properties of the as-prepared products were characterized by X-ray powder diffraction. X-ray diffraction patterns reveal the crystalline nature of CdS nanoparticles. Hexagonal ¿-CdS greenockite together with cubic hawleyite À-CdS are present among the products of mechanochemical synthesis. The methods of SEM, particle size analysis and low temperature nitrogen sorption were used to analyze the surface composition. The SEM measurements show the aggregates of small nanocrystals in which particle sizes of 5-9 nm were estimated by ScherrerLs formula.The cadmium sulphide nanoparticles are obtained in the simple step, making the process attractive for industrial applications. Industrial ball mills capable of processing large quantities are readily available, consequently the scaling up of the mechanochemical process is possible. The presented solid-state reaction opens its application also for the engineering area of advanced materials synthesi

Leaching of gold, silver and accompanying metals from circuit boards (PCBs) waste

Au-Ag noble metal wastes represent a wide range of waste types and forms, with various accompanying metallic elements.The presented leaching strategy for Au-Ag contained in circuit boards (PCBs) aims at gaining gold and silver in the metallic form.Application of the proposed ammonium thiosulphate leaching process for the treatment of the above mentioned Au-Ag containing wastesrepresents a practical, economic and at the same time an ecological solution. The ammonium thiosulphate based leaching of gold and silverfrom PCBs waste, using crushing as a pretreatment, was investigated. It was possible to achieve 98 % gold and 93 % silver recovery within48 hours of ammonium thiosulphate leaching. This type of leaching is a better leaching procedure for recovery of gold and silver from PCBwaste than the classical toxic cyanide leaching. 84 % Cu, 82 % Fe, 77 % Al, 76 % Zn, 70 % Ni, 90 % Pd, 88 % Pb and 83 % Sn recovery ofthe accompanying metals was achieved, using sulphuric acid with hydrogen peroxide, sodium chloride and aqua regia. A four steps leachingprocess gave a very satisfactory yield and a more rapid kinetics for all observed metals solubilization than other technologies

A processing method of the goldsmith’s and electronic Au-Ag-containing wastes

Veľké množstvá odpadov z elektrických a elektronických zariadení sa hromadia v celej Európe. Každý spotrebiteľ vyprodukuje priemerne 16 kg tohto odpadu za rok, čo v Európe predstavuje celkovo šesť miliónov ton za rok. Ide o obrovské plytvanie zdrojmi. Znamená to taktiež veľké ekologické nebezpečenstvo, keďže elektrické spotrebiče a elektronické zariadenia obsahujú vysoko toxické ťažké kovy a organické znečisťujúce látky. Podľa nových predpisov EÚ budú musieť výrobcovia odteraz platiť za zber a likvidáciu týchto výrobkov. Odpady ušľachtilých kovov Au-Ag predstavujú širokú škálu typov a foriem odpadov s rôznymi balastnými prvkami aj zložkami. Problematika spracovania odpadov s obsahom Au a Ag je vysoko aktuálnou v celosvetovom meradle z hľadiska hodnoty a špecifických vlastností týchto kovov ako aj ich nenahraditeľnosti v oblasti bankovníctva, zdravotníctva, priemyslu a v neposlednom rade aj v samotnej výrobe a predaji zlatníckych výrobkov. Predkladaný návrh možnosti spracovania Au-Ag zlatníckych a elektronických odpadov si kladie za cieľ získať zlato a striebro v kovovej forme. Aplikácia navrhovaného procesu spracovania uvedených Au-Ag odpadov predstavuje pre spoločnosť praktický, ekonomický a zároveň ekologický význam pri ich spracovávaní. Získavanie zlata, resp. striebra z Au-Ag odpadov je mimoriadne dôležité v podmienkach inflačného vývoja, kedy tieto ušľachtilé kovy sú stabilným zdrojom pokrývania potrieb spoločnosti

Aluminothermic Production of Titanium Alloys (Part 2): Impact of Activated Rutile on Process Sustainability

The aluminothermic process provides a cost-reduced production method for titanium and titanium alloys by reduction of TiO2 with subsequent refining by electroslag remelting The aluminothermy involves high heating rates, high temperatures and short reactions times combined with a self-propagating behaviour of the reaction. By co-reduction of TiO2 and oxides of alloying elements such as vanadium pentoxide, direct synthesis of a titanium alloy is possible. The use of rutile ore concentrates causes a further reduction of process steps. In order to charge rutile ore complex thermodynamic calculations are required taking enthalpy input of various bycomponents into account. The aluminothermic reduction is conventionally enhanced by a highly heatproviding reaction based on the reduction of KClO4. In order to minimize the use of chlorine-based products extensive studies are made to investigate the feasibility of using mechanically activated rutile as input material for the aluminothermic process. Due to the mechanical activation the intrinsic enthalpy of the reaction is increased thus facilitates a process with reduced amount of KClO4. A major challenge represents the determination of a compromise between low activation duration and reduced KClO4 amount. In order to define the process window parameters like intrinsic chemical energy (enthalpy of the reaction mixture), equilibrium temperature and physical properties (particle size and mixing degree) were optimized. After adjusting the process parameters it is possible to save up to 42 % KClO4 for the ATR reaction with 2h activated input material. This reduction of KClO4 material affects a decrease of the produced gaseous compounds and the subsequent off-gas cleaning system

Aluminothermic Production of Titanium Alloys (Part 1): Synthesis of TiO2 as Input Material

This article reports on the hydrometallurgical production of synthetic anatase from ilmenite. Mechanical activation followed by pressure leaching facilitates the leaching of ilmenite and the separation of titanium/iron by means of the synchronous hydrolysis of anatase. At 95% TiO2, the produced synthetic anatase fulfills the requirements for the aluminothermic production of titanium alloys