Leaching titanium

Opa.nte. There are two methods used at various plants in Russia for loparite concentrate processing (12). The chlorination technique is carried out using gaseous chlorine at 800°C in the presence of carbon. The volatile chlorides are then separated from the calcium—sodium—rare-earth fused chloride, and the resultant cake dissolved in water. Alternatively, sulfuric acid digestion may be carried out using 85% sulfuric acid at 150—200°C in the presence of ammonium sulfate. The ensuing product is leached with water, while the double sulfates of the rare earths remain in the residue. The titanium, tantalum, and niobium sulfates transfer into the solution. The residue is converted to rare-earth carbonate, and then dissolved into nitric acid. 

Aluminum. All primary aluminum as of 1995 is produced by molten salt electrolysis, which requires a feed of high purity alumina to the reduction cell. The Bayer process is a chemical purification of the bauxite ore by selective leaching of aluminum according to equation 35. Other oxide constituents of the ore, namely siUca, iron oxide, and titanium oxide remain in the residue, known as red mud. No solution purification is required and pure aluminum hydroxide is obtained by precipitation after reversing reaction 35 through a change in temperature or hydroxide concentration the precipitate is calcined to yield pure alumina. 

The reaction of finely ground ores and an excess of carbon at high temperatures produces a mixture of metal carbides. The reaction of pyrochlore and carbon starts at 950°C and proceeds vigorously. After being heated to 1800—2000°C, the cooled friable mixture is acid-leached leaving an insoluble residue of carbides of niobium, tantalum, and titanium. These may be dissolved in HF or may be chlorinated or burned to oxides for further processing. 

A number of high temperature processes for the production of titanium carbide from ores have been reported (28,29). The aim is to manufacture a titanium carbide that can subsequently be chlorinated to yield titanium tetrachloride. In one process, a titanium-bearing ore is mixed with an alkah-metal chloride and carbonaceous material and heated to 2000°C to yield, ultimately, a highly pure TiC (28). Production of titanium carbide from ores, eg, ilmenite [12168-52-4], EeTiO, and perovskite [12194-71 -7], CaTiO, has been described (30). A mixture of perovskite and carbon was heated in an arc furnace at ca 2100°C, ground, and then leached with water to decompose the calcium carbide to acetjdene. The TiC was then separated from the aqueous slurry by elutriation. Approximately 72% of the titanium was recovered as the purified product. In the case of ilmenite, it was necessary to reduce the ilmenite carbothermaHy in the presence of lime at ca 1260°C. Molten iron was separated and the remaining CaTiO was then processed as perovskite. 

Extraction of Bertrandite. Bertrandite-containing tuff from the Spor Mountain deposits is wet milled to provide a thixotropic, pumpable slurry of below 840 p.m (—20 mesh) particles. This slurry is leached with sulfuric acid at temperatures near the boiling point. The resulting beryUium sulfate [13510-49-1] solution is separated from unreacted soflds by countercurrent decantation thickener operations. The solution contains 0.4—0.7 g/L Be, 4.7 g/L Al, 3—5 g/L Mg, and 1.5 g/L Fe, plus minor impurities including uranium [7440-61-1/, rare earths, zirconium [7440-67-7] titanium [7440-32-6] and zinc [7440-66-6]. Water conservation practices are essential in semiarid Utah, so the wash water introduced in the countercurrent decantation separation of beryUium solutions from soflds is utilized in the wet milling operation. 

Based on a comprehensive investigation, Welham [453] recommends the use of a strong acid or high fluoride concentration in order to achieve optimal leaching. Specifically, the use of hydrofluoric acid with a concentration > 18% or fluoride concentration > 0.5 mol/1 was indicated. It is also noted that leaching at elevated temperatures leads to the separation of titanium by hydrolytic precipitation from the solution. 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

Titanium sponge is separated from sodium chloride and excess sodium by leaching with water. 

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

The process is operated in heated, batch reactors under an inert atmosphere. Two companies (Deeside Titanium, North Wales, and New Metals Industries, Nihongi, Japan) operate a one-stage process. Reactive Metals Industries Company, Ashtabula, OH, operates a two-stage process in the first stage, at 230°C, the trichloride and dichloride are formed. In the second, more sodium is added and the temperature is raised to 1,000°C. The sponge product is mixed with sodium chloride, which is leached out with dilute hydrochloric acid. Based on the work by M. A. Hunter at Rensselaer Polytechnic, New York in 1910. See also Kroll. 

Sulphuric acid is the largest volume chemical in the world with an annual production of about 180 mill, t/year which is used primarily for phosphate fertilizers, petroleum alkylation, copper ore leaching and in smaller quantities for a number of other purposes (pulp and paper, other acids, aluminium, titanium dioxide, plastics, synthetic fibres, dyestuffs, sulphonation etc.). The major sulphur sources for sulphuric acid production are sulphur recovered from hydrocarbon processing in the refineries and from desulphurisation of natural gas, SO2 from metallurgical smelter operations, spent alkylation acid, and to a minor extent mined elemental sulphur and pyrites. A simplified flow sheet of a modem double-absorption plant for sulphuric acid production from sulphur is shown in Fig. 1. 

Although the titanium oxide layer at the surface of the nitinol is highly biocompatible and protects the underlying substrate from electrochemical corrosion, the titanium oxide layer itself is mechanically very brittle. Under mechanical stress, such as the shear of blood flow in the aorta or under the bending moments of aortic pulsations, the titanium oxide surface layer can fracture, exposing the underlying metal to corrosion. Not only is corrosion undesirable in terms of biocompatibility (i.e., leaching of nickel and its... 

The lag between the time that nitinol, was first produced and the time it was used commercially in medical devices was due in part to the fear that nickel would leach from the metal and not be tolerable as a human implant. As it turns out, with a correct understanding of the surface electrochemistry and subsequent processing, a passivating surface layer can be induced by an anodizing process to form on the nitinol surface. It is comprised of titanium oxide approximately 20 mn thick. This layer actually acts as a barrier to prevent the electrochemical corrosion of the nitinol itself. Without an appreciation for the electrochemistry at its surface, nitinol would not be an FDA-approved biocompatible metal and an entire generation of medical devices would not have evolved. This is really a tribute to the understanding of surface electrochemistry within the context of implanted medical devices. 

Mono(siloxy) metalhydrocarbyl species can be converted into bis- or tris(siloxy) metal hydrides by reaction with hydrogen, as shown for zirconium and tantalum. Such species are less susceptible to leaching and this route can be extended to titanium and hafnium surface species that are potential precatalysts for hydrogenolysis of C-C bonds, alkane metathesis and epoxidation reactions. 

Most HPLC equipment currently available has a high tolerance to most mobile-phase conditions that can be contemplated for use in RPC applications with peptides. If it is intended to use mobile phases containing halide salts in RPC separations of peptides with standard HPLC equipment made from type 316 stainless steel, it is essential that the equipment is properly flushed with neat water when not in operation to avoid corrosion by the residual halide ions, especially at low pH. Otherwise, the use of the less popular biocompatible metal-free HPLC equipment, marketed by several manufacturers, avoids potential problems of equipment malfunction due to corrosion of the stainless steel or the contamination of peptide samples by low levels of leached metal ions. With such metal-free HPLC equipment, titanium, glass, or perfluoro-polymeric components have been used to replace any wettable stainless steel components. 

Transition metals and their complexes can be immobilized in the mesopores or incorporated in the structure to make silica-supported metal catalysts. For instance, titanium catalysts for selective oxidation can be formed by modifying the mesoporous structure with either Ti grafted on the surface (Tif MCM-41) or Ti substituted into the framework (Ti->MCM-41). The grafted version makes the better catalyst for the epoxidation of alkenes using peroxides, and has good resistance to leaching of the metal. 

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