Ore preheating

Figure 54 shows diagramatically the two-phase magnetizing roaster for low-grade iron ores—dilute-phase ore preheating in an upper section of i.d. 1,050 mm, and dense-phase reduction with producer gas in a lower section of i.d. 825 mm. The roasting consisted of a mild reduction with producer gas... 

SL/RN Process. In the SL/RN process (Fig. 4), sized iron ore, coal, and dolomite are fed to the rotary kiln wherein the coal is gasified and the iron ore is reduced. The endothermic heat of reduction and the sensible energy that is required to heat the reactants is provided by combustion of volatiles and carbon monoxide leaving the bed with air introduced into the free space above the bed. The temperature profile in the kiln is controlled by radial air ports in the preheat zone and axial air ports in the reduction zone. Part of the coal is injected through the centerline of the kiln at the discharge end. The hot reduced iron and char is discharged into an indirect rotary dmm cooler. The cooled product is screened and magnetically separated to remove char and ash. 

FIOR Process. In the FIOR process, shown in Figure 5, sized iron ore fines (0.04—12 mm) are dried in a gas-fired rotary dryer. A skip hoist dehvers the dry fines to lock hoppers for pressurizing. The fines pass through four fluidized-bed reactors in series. Reactor 1 preheats the ore to 760°C in a nonreducing atmosphere. Reactors 2, 3, and 4 reduce the ore at 690—780°C. At higher (ca 810°C) temperatures there is a tendency for the beds to defluidize as a result of sticking or hogging of the reduced material. 

In Western Mining s flash smelting proeess, reaetion air is preheated to 480°C (920°F) and enriehed until the oxygen eontent is 24%. The reaetion eharge and eombustion air are mixed, and heat for smelting eomes from the eombustion of fuel oil (some of it present in the flux) and sulfur in the eoneentrate. The proeess yields matte, a refined ore with 44% niekel eontent. 

Zincite). ZnO, mw 81.38, white or yellowish-white amorph odorless powd with a bitter taste, mp 1975° (subl and decomps), d 5.47—5.606 g/cc. V si sol in w. sol in mineral acids, dil acet acid and NH4OH. Coml prepn is from Zn or ores such as Franklinite or Zinc Blende by vapzn in a CO atm with subsequent oxidation of the vapors with preheated air. Lab. prepn is by converting anhya zinc oxalate to ZnO by heating at... 

To guard against incomplete reduction of ore fines which would be elutriated prematurely during preheating, the midsection combustion was adjusted to produce a mildly reducing flame containing approximately 4%... 

SPIREX A DR process for making iron powder or hot briquetted iron from iron ore fines. Three stages are used. The first is a circulating fluidized bed preheater whose turbulent conditions reduce the particle size of the ore. The second and third stages achieve the reduction in fluidized beds, fed by reducing gases from a MIDREX reformer. Developed by Midrex Direct Reduction Corporation and Kobe Steel. A demonstration plant was scheduled to be built at the Kobe Steel plant in Venezuela in 1997. 

Zinc oxide is obtained as an intermediate in recovering zinc from minerals (See Zinc, Recovery). The oxide is prepared by vaporizing zinc metal and oxidation of the zinc vapors with preheated air (French process). The oxide can be produced by other processes. Another method involves roasting franklinite and other ores with coal and then oxidizing the product in air. 

A 250-ton-per-day plant in Tongguanshan roasts a highly refractory copper ore of low grade. In a mixture of preheated ore and small amounts of anthracite and common salt, copper is volatilized as chloride and transported to the coke surface, where it deposits in the metallic state. 

The selective leaching of the nickel and cobalt from the gangue material is carried out in Pachuca-type leaching vessels with 98% sulfuric acid at temperatures between 450 and 500°F and with equivalent pressures between 400 and 600 psi. A typical leach liquor contains 6 gm/liter Ni, 0.6 gm/liter Co, 0.6 gm/liter Fe, 2.3 gm/liter Al, and 67 gm/liter SO4. Each batch is leached for about 90 min to extract 95% of the metal values. Preheating and heating of the ore slurry is by direct steam absorption in the reaction vessel. The barren residue is separated from the leach liquor by countercurrent decantation to a density of 55-60% solids. The solids are washed with very little dilution and about 99.5% of the soluble value are recovered. 

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