Metal purification process

In addition there are two principle metal purification processes ... 

Alumina trihydrate (ATH) is made from waste generated by the almninum metal purification process. It has high brightness but low refi active index. At low levels of substitution for Ti02, 25% or less, optical properties can be maintained. Like the synthetic silicas, ATH can be used as a paper brightning pigment when opacity is not as important. ATH is used in NCR (no carbon required) papers where it favorably affects the special dyes used in the paper. ATH is also known for its flame retardant properties. ATH retards bmming by the release of water at rather low temperatures. It is added to impart flame retardance to certain specialty papers. 

As a result of the development of electronic applications for NF, higher purities of NF have been required, and considerable work has been done to improve the existing manufacturing and purification processes (29). N2F2 is removed by pyrolysis over heated metal (30) or metal fluoride (31). This purification step is carried out at temperatures between 200—300°C which is below the temperature at which NF is converted to N2F4. Moisture, N2O, and CO2 are removed by adsorption on 2eohtes (29,32). The removal of CF from NF, a particularly difficult separation owing to the similar physical and chemical properties of these two compounds, has been described (33,34). 

Because of the development of electronic appHcations for WF, higher purities of WF have been required, and considerable work has been done to improve the existing manufacturing and purification processes (20). Most metal contaminants and gaseous impurities are removed from WF by... 

The initial step of production is carried out in a titanium reactor (34) because of the high corrosivity of maleic acid to most metals under the drastic reaction conditions used. The other steps are performed in stainless steel equipment. Improved purification processes for malic acid have been patented (37,38). 

Electrorefining. Electrolytic refining is a purification process in which an impure metal anode is dissolved electrochemicaHy in a solution of a salt of the metal to be refined, and then recovered as a pure cathodic deposit. Electrorefining is a more efficient purification process than other chemical methods because of its selectivity. In particular, for metals such as copper, silver, gold, and lead, which exhibit Htfle irreversibHity, the operating electrode potential is close to the reversible potential, and a sharp separation can be accompHshed, both at the anode where more noble metals do not dissolve and at the cathode where more active metals do not deposit. 

Amoco Purification Process. The Amoco process is used to purify terephthaHc acid produced by the brornine-promoted air oxidation of Nxylene. The main impurity in the oxidation product is 4-formylbenzoic acid] [619-66-9] and the Amoco process removes this to less than 25 ppm. Metals and colored organic impurities are also almost completely removed by the purification. 

Examination of the metallic product (regulus) of such aluminothermically produced vanadium metal reveals the presence of oxide phases in the metal matrix. This suggests that there is a decreasing solubiHty for aluminum and oxygen below the melting point. To date, no purification processes have been developed that take advantage of the purification potential of this phenomenon. 

MWCNT was first discovered by arc-discharge method of pure carbon and successive discovery of SWCNT was also based on the same method in which carbon is co-evaporated with metallic element. Optimisation of such metallic catalyst has recently been performed. Although these electric arc methods can produce gram quantity of MWCNT and SWCNT, the raw product requires rather tedious purification process. 

It must be emphasised that under the optimised preparation conditions, no byproducts, such as carbon nanoparticles or amorphous carbon fragments are formed. Thus this preparation method for PCNTs is promising for large-scale synthesis of MWCNTs, since apart from removal of the metal catalyst tedious purification processes are avoided. 

Pyroredox. This is a three-step plutonium purification process ( 3). Impure plutonium metal is reacted with ZnCl2 in a solvent salt of KC1-CaCl 2 > as follows ... 

The basic electrorefining process is now being used on a production scale for the purification of non-specification plutonium metal. The technology is sufficiently well developed to permit 24-hour unattended operation of the electrorefining cells, and the quality of the product metal is highly consistent. This technology is rapidly replacing aqueous chemistry for plutonium metal purification. 

Recent process development efforts have been devoted to more expeditious and less costly pyrochemical reprocessing of residues created by the metal preparation and purification process. We intend to establish an internal recycle which yields either reusable or discardable residues and recovers all plutonium for feed to the electrorefining purification system. This internal recycle is to be performed in a more timely and less costly operation than in the present reprocessing mode. 

The first step of NCA polymerization is usually accomplished by the use of nucleophilic initiators. These initiators can be alkoxides, alcohols, amines, transition metals, and even water [53,54]. In order to synthesize a copolymer diblock, the polymerization of the second block and its connection to the previously formed block are performed in a single process. This is achieved by initiating the polymerization of the second NCA monomer using the first homopolypeptide as a macroinitiator. Precipitation and purification processes follow to isolate the... 

When a melt-zone is moved through a long crystal, an impurity concentration builds up in the melt zone due to rejection by the crystal as it resolidifies. We can also say that the distribution coefficient favors a purification process, i.e.- k 1. Another reason (at least where metals are concerned) is that a solid-solution between impurity and host ions exists. It has been observed that the following situation, as shown in the following diagram, occurs ... 

This process of metal purification is of particular interest in that it involves the application of principles of both chemistry and chemical engineering and necessitates the cost evaluation of alternatives. 

Metal complexation — One of the most insidious and widely occurrent sources of analytical variation in IEC is product complexation with metal ions. Most proteins can form complexes with metals, regardless of whether or not they are metalloproteins.1 Participant metal ions can derive from the cell culture production process, purification process buffers, or even stainless steel chromatography systems. Complexation can alter retention times, create aberrant peaks, and substantially increase peak width. To the extent that metal contamination of your sample is uncontrolled, so too will be the performance of your assay. 

Rhodium is recovered from platinum and other ores by refining and purification processes that start by dissolving the other platinum group metals and related impurities with strong acids that do not affect the rhodium itself Any remaining platinum group elements are removed by oxidation and bathing the mixture in chlorine and ammonia. 

For drug substances from plants, examples of contaminant impurities could be herbicides, for example, diquat and glyphosate, or pesticides, for example, carbofuran and endrin, sprayed in the environment. Additionally, heavy metals or polycyclic aromatic hydrocarbons, if present in the soil, may be absorbed through the root systems of the plants. Polycyclic aromatic hydrocarbons, if present in the air, may be absorbed through the leaves of the plant. These contaminants will be present as residues in the drug substance if the selection, cleaning, extraction, and purification processes do not reduce or eliminate them. 

There are several processes for extracting and refining niobium from its ores. (Payton, P.H. 1981. Niobium and Niobium Compounds. In Kirk-Othmer Encyclopedia of Chemical Technology, 3 . ed., Vol, 15, pp. 820-827. New York Wiley Interscience). The process of choice depends on nature of the ore and end use intended for the metal. Some common steps in these recovery processes involve ore preconcentration, breaking or opening the ore, obtaining pure niobium compounds, reduction of niobium compounds to niobium metal, purification or refining metal and fabrication. If niobium is extracted from a niobium-tantalum ore, the most important step is separation of niobium from tantalum, both of which are chemically very similar. 

In Japan, there is a project aimed at capturing the considerable volume of hydrogen gas which can be obtained as a by-product steel production. R D will focus on the purification process of fuel from coke oven gas to an acceptable level for fuel cell utilisation. METI, the Japan Research and Development Centre for Metals and Nippon Steel are working on the project with a 2003 budget allocation of 549 million. Japan also operates the 4C/.f project which aimsto develop an optimum coal gasifier for fuel cells and the establishment of gas clean-up system for purification of coal gas to the acceptable level for utilisation for MCFC and SOFC. The budget allocations for 2000-2003 total 4.6 billion. 

According to the vendor, liqnid-liquid extraction (LLX) provides recovery, separation, purification, and concentration of metals in one unit process. By use of the proper extractant, metals can be reduced in process or waste streams to the low parts per million (ppm) level. The metals concentrated by the process can often be reused. When appropriate, specific metals can be recovered selectively in the presence of other metals or process stream components. Alternatively, broad-spectrum metal recovery is achievable with the properly selected extractant or process. 

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