Roast reduction process

Rdst-posten, m. roasting charge, -probe, /. calcination assay or test, -produkt, n. = Rosterzeugnis. -prozess, m. roasting process, calcination process, -reduktionsarbeit, /. (Metal.) roast reduction process, rostrein, a. rust-free. 

The roast-reduction process using Dwight-Lloyd sinter machine and blast furnace operation is still the basis for the majority of the lead produced in primary smelters. Since the last survey (1), however, the total number of smelters based on this conventional technology has been remarkably reduced. 

After the ore is concentrated, the metal must be reduced from the compound containing it. Production of several metals will be discussed in later chapters of this book. However, a reduction process that has been used for thousands of years will be discussed briefly here. Several reduction techniques are now available, but the original procedure involved reduction of metals using carbon in the form of charcoal. When ores containing metal sulfides are heated in air (known as roasting the ore), they are converted to the metal oxides. In the case of copper sulfide, the reaction is... 

Appiying Concepts The processes used to remove metals from their ores usually involve a reduction process. For example, mercury may be obtained by roasting the ore mercury(II) sulfide with calcium oxide to produce mercury metal, calcium sulfide, and calcium sulfate. Write and balance the redox equation for this process. 

Because metals in their combined forms always have positive oxidation numbers, the production of a free metal is always a reduction process. Preliminary operations may be necessary to convert the ore to a chemical state more suitable for reduction. For example, an ore may be roasted to drive off volatile impurities and at the same time to convert the carbonates and sulfides to the corresponding oxides, which can be reduced more conveniently to yield the pure metals ... 

An oxidised ore is generally mixed up with the roasted sulphide for the reduction process and any ore, when sulphuretted, is worked together with antimony glance. 

The working expenses of the roasting and reduction process are less than those of the precipitation method, and hence it is suitable for the working of poorer ores and liquation residues, while the latter can only be adopted—and even then very rarely—when ore is rich, but coal and labour cheap. 

Mathematical modeling of the roasting reduction-smelting reduction process using comprehensive sets of such raw data should be the goal for optimization of the metallurgical method. 

In some operations, particularly for those processing lump feed, the roast-reduction cycle was repeated a number of times, with the temperature raised for each cycle. In this situation silver tended to concentrate in the first ran lead bullion, and could be four times the silver content of the final lead ran. This was a useful approach to handling high silver ores, so as to reduce the effort required in silver recovery by the Pattinson Process or by cupellation. 

The reduction process with chromium oxide comprises of, first, mixing chromite, soda ash (Na2C03) and slaked lime (Ca(OH)2) in a rotary kiln, and roasting them to give sodium chromate (Na2Cr04) (eq. (13.1)). Sulfuric acid is added to the... 

The roasting of a more active metal produces the metal oxide, which must be reduced to obtain the free metal. The most common reducing agents are coke (impure carbon), carbon monoxide, and hydrogen. The following are some common examples of the reduction process ... 

J. S. Anderson, The primary reactions in roasting and reduction processes, Discuss. Faraday Soc. 4, 163-173 (1948). 

It is made from manganese dioxide ores through a reductive roasting process (31—33). 

When a potential is appHed across the ceU, the sodum and other cations are transported across the membrane to the catholyte compartment. Sodium hydroxide is formed in the catholyte compartment, because of the rise in pH caused by the reduction of water. Any polyvalent cations are precipitated and removed. The purified NaOH may be combined with the sodium bicarbonate from the sodium dichromate process to produce soda ash for the roasting operation. In the anolyte compartment, the pH falls because of the oxidation of water. The increase in acidity results in the formation of chromic acid. When an appropriate concentration of the acid is obtained, the Hquid from the anolyte is sent to the crystallizer, the crystals are removed, and the mother Hquor is recycled to the anolyte compartment of the ceU. The electrolysis is not allowed to completely convert sodium dichromate to chromic acid (76). Patents have been granted for more electrolytic membrane processes for chromic acid and dichromates manufacture (86). 

Lateritic Ores. The process used at the Nicaro plant in Cuba requires that the dried ore be roasted in a reducing atmosphere of carbon monoxide at 760°C for 90 minutes. The reduced ore is cooled and discharged into an ammoniacal leaching solution. Nickel and cobalt are held in solution until the soflds are precipitated. The solution is then thickened, filtered, and steam heated to eliminate the ammonia. Nickel and cobalt are precipitated from solution as carbonates and sulfates. This method (8) has several disadvantages (/) a relatively high reduction temperature and a long reaction time (2) formation of nickel oxides (J) a low recovery of nickel and the contamination of nickel with cobalt and (4) low cobalt recovery. Modifications to this process have been proposed but all include the undesirable high 760°C reduction temperature (9). 

In the blast furnace reduction slag-making materials are also added together with a small amount of iron, the function of which is to reduce any sulphide which remains, to the product of the roasting operation to produce a sinter. The sinter is then reduced with coke in a vertical shaft blast furnace in which air is blown tluough tuyeres at the bottom of tire shaft. The temperature in the heartlr where metal is produced must be controlled to avoid the vaporization of any zinc oxide in the sinter. The products of tlris process are normally quite complex, and can be separated into four phases. Typical compositions of these are shown in Table 13.1. 

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