Refining metals

Reduction of metal oxides with hydrogen is of interest in the metals refining industry (94,95) (see Metallurgy). Hydrogen is also used to reduce sulfites to sulfides in one step in the removal of SO2 pollutants (see Airpollution) (96). Hydrogen reacts directiy with SO2 under catalytic conditions to produce elemental sulfur and H2S (97—98). Under certain conditions, hydrogen reacts with nitric oxide, an atmospheric poUutant and contributor to photochemical smog, to produce N2 ... 

Dead-burned magnesia, characterized by large crystaUite size and very low chemical reactivity, is resistant to the basic slags employed in the metals refining industry. It reacts very slowly with strong acids, and does not readily hydrate or react with carbon dioxide unless finely pulverized. 

There are no fumes or effluents generated in the processing of powders and the requirements of state and federal environmental protection agencies are met without difficulty. However, the production of powders has been subjected to the same concerns as most other metal refining and smelting operations. 

A. H. Leigh, "Precious Metal Refining Practice," in D. J. I. Evan and R. S. Shoemaker, eds.. International Symposium on Hydrometallurgy, AIME, New York, 1973. 

Cyanohydrins are used primarily as intermediates in the production of other chemicals. Manufacture of methyl methacrylate, used to make acrylic mol ding resins and clear sheet, eg, Plexiglas acrylic sheet, from acetone cyanohydrin is the most economically important cyanohydrin process (see Methacrylic polymers). Cyanohydrins are also used as solvents in appHcations including fiber-spinning and metals refining. Cyanohydrins and derivatives reportedly act as antiknock agents in fuel oil and motor fuels and serve as electrolytes in electrolytic capacitors. 

Acetone cyanohydrin is used as a raw material for insecticides manufacture and also to produce ethyl a-hydroxyisobutryate [80-55-7], a pharmaceutical intermediate. It has been used as a complexing agent for metals refining and separation. Acetone cyanohydrin complexes can be used to separate, Cu , , 7x5, Cd , or Fe from Mg , , Ca , Na , or on strongly basic ion-exchange resins (31). Acetone cyanohydrin is... 

Despite low collection efficiencies, settling chambers have been used extensively in the past. The metals refining industries have used settling chambers to collect large particles, such as arsenic trioxide from the smelting of copper ore. 

Miscellaneous Refinery catalyst regenerator Municipal incinerators Apartment incinerators Spray drying Precious metal refining... 

Blick-feld, n. field of vision, -gold, n. refined gold still containing silver. -silber, n. (Metal.) refined silver still containing impurities. 

Fein-arbeit, /. fine or delicate work (Metal.) refining, -aufspaltung, /. fine separation, -bau, m. fine structure, -bewegung, /. (Micros., etc.) slow motion, fine adjustment, feinblasig, a. having minute bubbles or blisters. Fein-blech, n. (Metal.) thin plate, sheet. 

Fein-probe, /. delicate test, -prozess, m. refining process, -puddeln, n. (Metal.) refining puddling. 

Gar-heit, /. finished state (Metal.) refined state, -herd, m. refining hearth. 

Pauschal-. total, lump (sum, etc.), pauscheu, v.t. swell (Metal.) refine. 

Treiber, m. driver propeller beater Metal) refiner. 

Eventually all catalysts become spent. At this stage they can be discarded, itself sometimes a problem, or returned to a refiner for recovery of metal values. In commercial use, noble-metal catalysts are always returned to a refiner. At the refinery, the catalyst is destroyed and the noble metals are recovered and converted to high-purity metal. In a loop system, the pure metal is converted to a suitable salt and again used for catalyst manufacture. In the entire loop, some metal will be lost and must be replaced with fresh metal. Refining is nowadays very efficient, and most metal loss will occur in the process itself, The total cost of a catalyst used in a loop is accordingly given by ... 

For the noble metals used in oxidation, the loading is about 0.1 oz per car, with calls for a million ounces per year. The current world production rates of platinum, palladium, and rhodium are 1.9, 1.6, and 0.076 million ounces respectively the current U,S. demand for platinum, palladium, rhodium, and ruthenium are 0.52, 0.72, 0.045, and 0.017 million ounces respectively (72, 73). The supply problem would double if NO reduction requires an equal amount of noble metal. Pollution conscious Japan has adopted a set of automobile emission rules that are the same as the U.S., and Western Europe may follow this creates a demand for new car catalysts approaching the U.S. total. The bulk of world production and potential new mines are in the Soviet Union and South Africa. The importation of these metals, assuming the current price of platinum at 155/oz and palladium at 78/oz, would pose a balance of payment problem. The recovery of platinum contained in spent catalysts delivered to the door of precious metal refiners should be above 95% the value of platinum in spent catalysts is greater than the value of lead in old batteries, and should provide a sufficient incentive for scavengers. 

Potential sources of carbon monoxide hazards include metal-refining processes, in which it is formed as a byproduct and used as a fuel (LEL 12.5%), and running vehicle engines (particularly petrol-driven) or gas-fired heaters in poorly ventilated confined spaces. It is also a feedstock in the manufacture of a variety of chemicals, e.g. methanol, acetic acid, phosgene and oxo-alcohols. 

The process objectives defined earlier must relate to the process routes. A process route essentially consists of several sequential steps with the ultimate aim of achieving the process objective. There are one or more of basic objectives, namely, separation, production of a compound intermediate, metal reduction, and metal refining. With a given starting source material the four basic objectives can be pursued singly or in combination to arrive at the ultimate aim. For example, if the ultimate aim is to prepare a concentrate for the market then it is only the separation that is required for reaching to the product. If, on the other hand, purified metal production is the ultimate aim then possibly all the four objectives have to be fulfilled. 

Various pollution prevention case histories have been documented for nonferrous metals refining industries. In particular, the actions of the AMPCO Metal Manufacturing Company, Inc., typify industry efforts to simultaneously lessen the impact of the industrial process on the environment, reduce energy consumption, and lower production costs.1... 

Precious metal catalysts on carbon are often used. The entire cycle of catalyst manufacture, use, removal, and metal refining (recovery) typically loses 20-25% of the metal when the process operates well. 

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