Roast-reaction method

The reaction equations of the cycle using liquid Pb are shown in Table IV. As a means of preparing Pb from PbS, the roast-reaction or air-reduction method is well-known in nonferrous extractive metallurgy. The reactions for this method can be presented as follows ... 

The method chosen to reduce the metal ion to the free metal, a process called smelting, depends on the affinity of the metal ion for electrons. Some metals are good enough oxidizing agents that the free metal is produced in the roasting process. For example, the roasting reaction for cinnabar is... 

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). 

As seen in the above equations, the aqueous oxidation processes convert sulfur in the feed to dissolved sulfate, while arsenic is oxidized and precipitated as ferric arsenate compounds. So, problems of the emission of sulfur and arsenic oxides caused by roasting are avoided in the aqueous oxidation processes. The two different industrial methods which achieve the oxidation reactions are pressure oxidation and biological oxidation. 

Among the methods for extracting metals from their ores are (i) roasting a metal sulfide, (ii) chemical reduc-tion of a metal oxide, and (iii) electrolysis. The preferred method depends on the E° value for the reduction half-reaction Mn+(aq) + ne —> M(s). 

Many individual flavor chemicals which were isolated and identified from Maillard "side reactions" have been reported in the patent literature. It is evident from these patents that much work has been done to glean specific flavor chemicals from the complexities of the Maillard reaction. 3-Furyl alkyl sulfide, disulfide, and 0-chalcogenalkyl sulfide derivatives are claimed to provide bloody, meaty, and roasted notes to beef broth and beef products (64-66). 3-Methylcyclopent-2-en-l-one was declared for its flavor eiiEancement of beef bouillon (67). Firmenich claimed 2,6-dimethyl-2-octenal and its analogs as possessing meat flavor qualities (68). A method to produce disulfides for application to meat and savory flavors was patented (69). 

Reaction of an aqueous solution of cystine with thiamin, glutamate, and ascorbic acid produces a complex mixture of compounds with an overall flavor resembling that of roasted meat. The reaction was carried out at 120 C for 0.5h at pH 5.0 in a closed system. The aroma compounds were isolated by means of the simultaneous steam distillation/solvent extraction method. The flavor concentrate was pre-separated by liquid chromatography on silica gel and subsequently analysed by GC and GC/MS. Unknown flavor components were... 

The traditional equilibrium method of flavor release study mentioned above is extremely time consuming, and several weeks are commonly needed to obtain full release profiles of flavors from powders. Recently, thanks to the pioneering work of Dronen and Reineccius (2003), proton transfer reaction mass spectrometry (PTR-MS) has been used as a rapid analysis to measure the release time-courses of flavors from spray-dried powders. The PTR-MS method has been applied extensively to analyze the release kinetics of volatile organic compounds from roasted and ground coffee beans. The release profiles could then be mathematically analyzed by means of Equation 1.1 to obtain the release kinetic parameters, A and n (Mateus et al., 2007). 

These topics are discussed in detail in monographs and reviews (NAS 1975, IPCS 1991, Barceloux 1999, Mastromatteo 1986, Sunderman 1984, 2001a). Nickel constitutes less than 0.008% of the Earth s crust. The world s nickel production is obtained primarily from sulfide ores (e.g., pentlandite and nickeliferous pyrrhotite) and, to lesser extent, from oxides ores (e.g., laterite). Nickel sulfide ores, usually mined underground, are crushed and ground, concentrated by physical methods, converted to nickel subsulfide matte, and roasted to nickel oxide. The nickel oxide may be refined electrolytically to yield nickel cathodes or refined by the Mond process, which involves reduction with hydrogen, reaction with carbon monoxide to yield nickel carbonyl, and thermal decomposition to deposit pure nickel. Nickel oxide ores, usually mined in open pits, are smelted to produce ferronickel for use in stainless steel. 

One method of preparing elemental mercury involves roasting cinnabar (HgS) in quicklime (CaO) at 600.°C followed by condensation of the mercury vapor. Given the heat of vaporization of mercury (296 J/g) and the vapor pressure of mercury at 25.0°C (2.56 X 10 torr), what is the vapor pressure of the condensed mercury at 300.°C How many atoms of mercury are present in the mercury vapor at 300.°C if the reaction is conducted in a closed 15.0-L container ... 

An alternative method that has been used to prepare ferrite particles in a single step is the evaporative decomposition of the solutions, or spray-roasting (Ruthner, 1977). The solutions were mixed and atomised, and the droplets fell through a reaction chamber at 900-1050 °C. The solvent evaporated and the salts decomposed to oxides. The process took 3-5 s. By using a roasting furnace for industrial production, agglomerates of 40-200 pm containing 1 pm ferrite particles were obtained. The furnace feedstock was an aqueous suspension of the oxides, carbonates or hydroxides of the desired composition. However, the residence time was insufficient and complete transformation to the desired ferrite was not achieved. 

Cu2(0H)2C03). Polished malachite is widely used for decorative purposes. Traditional Cu production involves roasting chalcopyrite in a limited air supply to give CU2S and FeO the latter is removed by combination with silica to form a slag, and CU2S is converted to Cu by reaction 22.6. However, over the last two decades, methods which avoid SO2 emissions have been introduced (Box 22.2). 

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