Titanium production via metallothermic reduction of TiCL4 in molten salt : problems and products

Industrial production of titanium occurs via the batch-wise reduction of titanium tetrachloride (TiCl4) with a reducing metal, being magnesium in the Kroll process, or sodium in the Hunter process. In the search for low cost titanium, the CSIR is developing a continuous process to produce titanium powder directly via metallothermic reduction of TiCl4 in molten salt, dubbed the CSIR-Ti process. The move to a continuous process has been attempted by a number of organizations, but was until now always met with failure, due in no small part to challenges inherent in the process chemistry. The reaction between TiCl4 and the reducing metal can occur directly, when TiCl4 or any titanium sub-chlorides present, comes into contact with suspended or dissolved reducing metal. The reaction can also occur indirectly, without any physical contact between the reacting species, via an electronically mediated mechanism. The reaction mechanism via electronic mediation can cause TiCl4 to react at the outlet of the feed port, rapidly causing blockages of the TiCl4 feed line. The electrical conductivity of the metal reactor can also cause the electronically mediated reaction to favour the formation of titanium sponge on the reactor walls and internals, rather than titanium powder. Various methods were investigated to overcome the problem of blockages in the TiCl4 feed line, e.g. mechanical removal, sonic velocities, dilution of the TiCl4 and the use of ceramic feed lines. This article discusses problems experienced with the continuous feeding of reagents, and various methods attempted are shown and discussed. Information is also given on the morphology, chemical composition and suitability of the final titanium powder for powder metallurgical application as presently produced by the CSIR-Ti process.http://www.saimm.co.za/ai201

Leachability of nitrided ilmenite in hydrochloric acid

Titanium nitride in upgraded nitrided ilmenite (bulk of iron removed) can selectively be chlorinated to produce titanium tetrachloride. Except for iron, most other components present during this low temperature (ca. 200°C) chlorination reaction will not react with chlorine. It is therefore necessary to remove as much iron as possible from the nitrided ilmenite. Hydrochloric acid leaching is a possible process route to remove metallic iron from nitrided ilmenite without excessive dissolution of species like titanium nitride and calcium oxide. Calcium oxide dissolution results in unrecoverable acid consumption. The leachability of nitrided ilmenite in hydrochloric acid was evaluated by determining the dissolution of species like aluminium, calcium, titanium and magnesium in a batch leach reactor for 60 minutes at 90°C under reflux conditions. The hydrochloric acid concentration (11%, 18% and 25%), initial acid-to-iron mole ratio (2:1, 2.5:1 and 3.3:1), and solid-to-liquid mass ratio (1:8.33 to 1:2.13) were varied. The results indicate that a hydrochloric acid concentration of 25 wt% supplied in a 2:1 acid-to-iron mole ratio would produce the most favourable upgraded nitrided ilmenite product. The dissolution of iron in this solution reached 97 per cent after only 60 minutes. The total dissolution of calcium and titanium species was 0.01 and 0.11 wt% respectively. Hydrochloric acid can therefore be used as lixiviant to remove metallic iron from nitrided ilmenite.http://www.saimm.co.za/ai201

The heterogeneous coagulation and flocculation of brewery wastewater using carbon nanotubes

Coagulation and flocculation treatment processes play a central role in the way wastewater effluents are managed. Their primary function is particle removal that can impart colour to a water source, create turbidity, and/or retain bacterial and viral organisms. This study was carried out to investigate whether carbon nanotubes (CNTs) can be used as heterogeneous coagulants and/or flocculants in the pretreatment of brewery wastewater. A series of experiments were conducted in which the efficiencies of pristine and functionalised CNTs were compared with the efficiency of traditional ferric chloride in a coagulation/flocculation process. Turbidity and chemical oxygen demand (COD), including the zeta potential were used to monitor the progress of the coagulation/flocculation process. Both pristine and functionalised CNTs demonstrated the ability to successfully coagulate colloidal particles in the brewery wastewater. Overall, ferric chloride was found to be a more effective coagulant than both the pristine and functionalised CNTshttp://www.elsevier.com/locate/watreshb2013ai201

Kinetic model of carbon nanotube production from carbon dioxide in a floating catalytic chemical vapour deposition reactor

The production of carbon nanostructures, including carbon nanotubes (CNTs), by chemical vapour deposition (CVD) occurs by thermally induced decomposition of carbon-containing precursors. The decomposition of the feedstock leading to intermediate reaction products is an important step, but rarely incorporated in rate equations, since it is generally assumed that carbon diffusion through or over the catalyst nanoparticles is the rate-limiting step in the production of CNTs. Furthermore, there is no kinetic model to date for the production of CNTs from carbon dioxide. These aspects are addressed in this study with the aid of a series of experiments conducted in a floating catalytic CVD reactor in which the effects of reactor temperature, concentration and flow rate of CO2 were investigated. A simple rate equation for the reductive adsorption of CO2 onto the catalyst surface followed by carbon diffusion leading to the production of CNTs is proposed as follows: d[CNT]/dt ¼ K[CO2], where K is proportional to the diffusion coefficient of carbon. The derived kinetic model is used to calculate the amount of CNTs for a given concentration of CO2, and the experimentally measured data fits the simple rate equation very well at low carbon dioxide concentration.The National Research Foundation (NRF) under South Africa NRF Focus Area, NRF Nanotechnology flagship programme, DST/ NRF Centre of Excellence and University of the Witwatersrand Staff Bursary.http://www.rsc.orgadvanceshb201