Reductants gaseous

The description given apphes to DR processes that are based on the use of gaseous reductants ia shaft furnaces, batch retorts, and fluidized beds. In the processes that use sohd reductants, eg, coal (qv), the reduction is accomphshed to a minor extent first by volatiles and reduciag gases that are released as the coal is heated and then by CO that is formed by gasification of fixed carbon contained ia the coal char with CO2. Reductioa by sohd carboa and coal volatiles ia kilns is insignificant. 

Metafile arsenic can be obtained by the direct smelting of the minerals arsenopyrite or loeUingite. The arsenic vapor is sublimed when these minerals are heated to about 650—700°C in the absence of air. The metal can also be prepared commercially by the reduction of arsenic trioxide with charcoal. The oxide and charcoal are mixed and placed into a horizontal steel retort jacketed with fire-brick which is then gas-fired. The reduced arsenic vapor is collected in a water-cooled condenser (5). In a process used by Bofiden Aktiebolag (6), the steel retort, heated to 700—800°C in an electric furnace, is equipped with a demountable air-cooled condenser. The off-gases are cleaned in a sembber system. The yield of metallic arsenic from the reduction of arsenic trioxide with carbon and carbon monoxide has been studied (7) and a process has been patented describing the gaseous reduction of arsenic trioxide to metal (8). 

Carbon (coke) consumption, as a fuel and as a producer of the gaseous reductant, carbon monoxide, takes place in the blast furnace. An alternative source of such carbon, along with... 

B. Meddings and V. N. Mackiw, Gaseous Reduction of Metals from Aqueous Solutions, in Unit Processes in Hydrometallurgy, p. 354, Gordon and Breach, New York, 1964. 

D. J. I. Evans, Production of Metals by Gaseous Reduction from Solution Processes and Chemistry in Advances in Extractive Metallurgy p. 831, IMM, London, 1968. 

Extraction of a selected metal by applying solvent extraction, ion exchange, electrolysis, or gaseous reduction. 

The thermal stability of NOx adsorbed species and their reactivity in the presence of gaseous reductant molecules was addressed by thermal decomposition in He (TPD) or by heating in flowing H2/He mixtures [temperature-programmed surface reaction (TPSR)], respectively. In these cases, after NOx adsorption and He purge at the adsorption temperature (300 100oC), the samples were cooled to RT under flowing He. Then the samples were heated at 15°C/min up to 500-600°C in He (TPD) or in He + H2 (2000 ppm) (H2-TPSR). 

Meddings and Mackiw (58) Thermodynamic feasibility and equilibria in gaseous reduction of dissolved metal species. 

Other references in Table in discuss applications in precipitation of metal.compounds, gaseous reduction of metals from solution, equilibrium of copper in solvent extraction, electrolyte purification and solid-liquid equilibria in concentrated salt solutions. The papers by Cognet and Renon (25) and Vega and Funk (59) stand out as recent studies in which rational approaches have been used for estimating ionic activity coefficients. In general, however, few of the studies are based on the more recent developments in ionic activity coefficients. 

T0882 Westinghouse Hanford Company, In Sim Gaseous Reduction System T0886 Westinghouse Savannah River Company/EnviroMetal Technologies, Inc. 

T0882 Westinghouse Hanford Company, In Situ Gaseous Reduction System T0887 Westinghouse Savannah River Corporation, Transportable Vitrification System T0892 WRS Infrastructure Environmental, Inc., Soil Washing Process... 

The possibility that reducing gases such as sulfur dioxide, carbon monoxide or hydrogen can be used under pressure to effect the final precipitation of metals from their solutions is an obvious and, in some instances, an attractive alternative to electrowinning or cementation.411 Of the commercial plants built to produce metals in powder form by gaseous reduction of the metals from... 

The gas other than oxygen which has been most extensively studied as a reactant with solids is, of course, hydrogen and the first and longest section of this chapter is therefore devoted to gaseous reduction. The theory of this topic, especially in relation to iron oxides [1, 2], well exemplifies much of the general theory of solid state kinetics as reviewed by one of us [3] in an earlier volume of this series. For the present purpose, therefore, we have reworked the necessary discussion of kinetic equations into the specific topic of Sect. 2. 

A voluminous literature exists on the kinetics of gaseous reduction of solids in connection with industrial applications. In particular, that of iron oxides has been comprehensively reviewed by Manning and Philbrook [1] As these authors evaluate the situation Although the science of iron ore reduction is nearly a hundred years old, it is still best characterized by uncertainty, by inconsistent experimental data and by conflicting theories . This evaluation seems to us quite adequate (except, perhaps, that a case could be made for replacing a hundred years by three thousand years ), and the statement is applicable to reductions of other solids. 

Gaseous reductants Hydrogen sulfide was formerly a popular reductant for Fe(IIl) because of its selectivity. The removal of the excess requires lengthy boiling. 

Figure 1. Gibbs free energy per molecule of O2 versus temperature for reduction of transition metal oxides with gaseous reductants. (From Alan Cottrell, An Introduction to Metallurgy, 2nd ed., Edward Arnold Publishers, London, 1975, Fig. 7.1, with permission.)...

The AAC process consists of the following steps 17 Gaseous Reduction... 

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