Reductions process

The complete reduction of zinc oxide is favoured by a small value of K. i.e. when log,u A, > log,o X,. Figure 3.5 shows plots of logio Xi, and logio X2 against 1/T where the two graphs intersect log)o X for the reduction process is zero and hence X = 1. 

This can be prepared by the controlled reduction of a nitrite (nitrate(lll)) or nitrate. Cautious heating of ammonium nitrate gives dinitrogen oxide by an internal oxidation-reduction process ... 

Although the reduction process is not always a reversible one, oxidation and reduction potential values can be sometimes related to the Hiickel energies of the highest and lowest filled molecular orbital of the dye (108). 

The oxidation-reduction process that connects hydroqumone and benzoquinone involves two 1 electron transfers... 

Redox reactions, such as that shown in equation 6.22, can be divided into separate half-reactions that individually describe the oxidation and the reduction processes. 

Equivalent mechanical behavior can be achieved by either time (or frequency) or temperature manipulation. As noted in Sec. 3.2, results measured at different temperatures can be reduced to a common temperature to describe response over a wide range of times. We shall consider data reduced to a common temperature in this chapter and discuss the reduction process in Chap. 4. 

Sandolase Sandopan DTC Sandopan KST Sandopart Sandoptal Sandostatin Sandoz SF7810F Sandpaper Sandpapering Sand reduction process Sandstone... 

The first commercial production of fatty alcohol ia the 1930s employed the sodium reduction process usiug a methyl ester feedstock. The process was used ia plants constmcted up to about 1950, but it was expensive, hazardous, and complex. By about 1960 most of the sodium reduction plants had been replaced by those employing the catalytic hydrogenolysis process. Catalytic hydrogenation processes were investigated as early as the 1930s by a number of workers one of these is described ia reference 26. 

Direct Reduction. Direct reduction processes are distinguished from other ironmaking processes in that iron oxide is converted to metallic iron without melting. Because this product, called direct reduced iron (DRI), is soHd, it is most suitable for melting in an electric arc furnace (EAF) as a substitute for scrap (see Furnaces, electric). The briquetted form of DRI, hot briquetted iron (HBI) is used when the product is to be transported. Briquetting increases density and chemical stabiUty. The predominant direct reduction processes (MIDREX and HyL III) are based on natural gas as a fuel and reductant source. They are economically attractive in regions where natural gas is cheap and abundant, especially if iron ore is available nearby (see Iron BY DIRECT reduction). ... 

As can be seen in Figure 8, the proportion of world pig iron produced in the United States has decreased dramatically since 1950. Also notable is the widening gap between pig iron and steel production, indicating the increasing use of recycled iron or scrap (see Recycling, ferrous metals) and alternative iron sources such as DRI and HBI. The increased demand for scrap is reflected in scrap iron prices (Fig. 9), which in turn have spurred growth in direct reduction processes. 

The carbon content of DRI depends primarily on the direct reduction process used and the way the process is operated. Carbon content can be adjusted within limits by operating changes within the DR process. Most steelmakers prefer slightly more carbon than is required to balance the remaining FeO in the DRI. DRI from gas-based processes typically contains 1 to 2.5% carbon, mostly in the form of cementite [12169-32-3] Fe C. DRI containing approximately 6 to 7% carbon in the form of cementite is called iron carbide. DRI from coal-based, rotary-kiln processes contains very low (ca 0.5%) levels of carbon. 

The gangue content of DRI is typically comprised of oxides such as Si02, AI2O2, CaO, MgO, Ti02, K2O, Na20, MnO, etc, and is dictated by the chemistry of the iron ore used. The phosphoms in DRI is normally in the form of P2 5- Sulfur content in the DRI depends on the sulfur level in the ore and reductant, and the amount of sulfur released or absorbed by the DRI during the reduction process. 

DR Processes Under Development. The 1990s have seen continuous evolution of direct reduction technology. Short-term development work is focusing on direct reduction processes that can use lower cost iron oxide fines as a feed material. Use of fines can represent a 20 30/1 (20%) savings in DRI production cost compared to use of pehets or lump ore. Some examples of these processes include FASTMET, Iron Carbide, CIRCOFER, and an improved version of the EIOR process. 

Pldgeon Process. The Pidgeon (46—49) process (Fig. 6) was the first commercial thermal reduction process usiag siUcoa, and was developed ia the 1940s. This process is used by Timminco (Haley, Oatario, Canada) and Ube Industries (Japan). The overall reaction for this process is... 

Reduction. Heterogeneous catalytic reduction processes provide effective routes for the production of maleic anhydride derivatives such as succinic anhydride [108-30-5] (26), succinates, y-butyrolactone [96-48-0] (27), tetrahydrofuran [109-99-9] (29), and 1,4-butanediol [110-63-4] (28). The technology for production of 1,4-butanediol from maleic anhydride has been reviewed (92,93). 

In the past, all grades of refined ferromanganese were made by various modifications of multistep silicon reduction processes. Depending on the carbon content desired in the product, a manganese ore and lime mixture was allowed to react with the silicon in silicomanganese or low carbon silicomanganese in an open, electric-arc furnace. The equilibrium reaction is... 

Reduction processes are characterized either by the reducing agent selected or by the physical state of the metallic product. The separation of reaction products determines the choice and design of the furnace. Reduction processes are classified according to the physical state of the reduced metal. 

Reduction to Liquid Metal. Reduction to Hquid metal is the most common metal reduction process. It is preferred for metals of moderate melting point and low vapor pressure. Because most metallic compounds are fairly insoluble in molten metals, the separation of the Hquified metal from a sohd residue or from another Hquid phase of different density is usually complete and relatively simple. Because the product is in condensed form, the throughput per unit volume of reactor is high, and the number and si2e of the units is rninimi2ed. The common furnaces for production of Hquid metals are the blast furnace, the reverberatory furnace, the converter, the flash smelting furnace, and the electric-arc furnace (see Furnaces, electric). 

Refining Processes. AH the reduction processes yield an impure metal containing some of the minor elements present in the concentrate, eg, cadmium in 2inc, or some elements introduced during the smelting process, eg, carbon in pig iron. These impurities must be removed from the cmde metal in order to meet specifications for use. Refining operations may be classified according to the kind of phases involved in the process, ie, separation of a vapor from a Hquid or soHd, separation of a soHd from a Hquid, or transfer between two Hquid phases. In addition, they may be characterized by whether or not they involve oxidation—reduction reactions. 

Mine Safety AppHances Company, USA (MSA) developed a reduction process usiag sodium and KCl to produce potassium metal ia the 1950s (4) ... 

Aluminum can be produced by metaHothermic, carbothermic, or electrolytic reduction processes. The earliest commercial process for producing aluminum (1855—1893) was sodiothermic reduction of aluminum haUdes. Once the HaH-HAroult process became commercial, however, sodiothermic reduction was not competitive. 

A fourth ahoy separation technique is fractional crystallization. If shica is co-reduced with alumina, nearly pure shicon and an aluminum shicon eutectic can be obtained by fractional crystallization. Tin can be removed to low levels in aluminum by fractional crystallization and a carbothermic reduction process using tin to ahoy the aluminum produced, fohowed by fractional crystallization and sodium treatment to obtain pure aluminum, has been developed (25). This method looked very promising in the laboratory, but has not been tested on an industrial scale. 

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