Chloridation

Chloridation

 

(in Russian, khloridovozgonka), one of the chlorination processes in nonferrous metallurgy, used to remove the metal chlorides formed during roasting in the gas phase and to separate them from the unchlorinated material.

Chloridation, which is based on the high volatility of the chlorides of many metals, is carried out in tube, shaft, electric, or fluidized-bed furnaces at temperatures that ensure high vapor pressures of the sublimating chlorides and the rapid volatilization of the chlorides. Chlorinating agents include chlorine, hydrogen chloride, calcium chloride, and rock salt. The gases formed in the furnace exit through dust catchers, which collect the dust from the chloride vapors. They are then cooled to condense the metal chlorides, which are either recovered in electrostatic precipitators or in condensers (the dry method) or in scrubbers (the wet method). The free hydrogen chloride is absorbed by lime milk or a solution of calcium chloride and then returned to the head of the process.

Chloridation has a number of advantages. It makes possible a high recovery of metals, owing to the great chemical activity of chlorine, and the almost complete separation of nonferrous metals from iron in one operation. It affords the possibility of selectively sublimating a particular metal chloride by altering the composition of the gas phase. It also makes possible the achievement of a high degree of concentration, resulting in the recovery from low-grade ores of very rich chlorides, from which commerical metals are then obtained. One disadvantage is the necessity of maintaining a high partial pressure, which is achieved with the large excess of chlorine already present in the production cycle.

Chloridation is used in industry in the production of titanium, beryllium, zirconium, and other rare metals. To obtain titanium, chlorine is blown through pellets of titanium slags and coke at 700°–800°C in electric shaft furnaces or in chlorinators during chlorination of melts. The reducing atmosphere ensures virtually complete chlorination of the oxides of titanium and a number of other metals. The easily volatilized TiCl4 and SiCl4 are condensed in the form of a liquid, while AlCl3, FeCl3, and VOCl3 are obtained as solids; the slightly volatile chlorides of calcium, manganese, and magnesium together with the unchlorinated oxides remain in the solid residue.

Chloridation is also beginning to be used for the recovery of heavy nonferrous and precious metals. Thus, pyrite cinders are pelletized with calcium chloride and subjected to chloridation at 1100° to 1200°C in an oxidizing atmosphere. In this case, more than 94 percent of the copper, zinc, lead, gold, and silver are volatilized and recovered, while the oxides of iron, silicon, calcium, and other elements are not chlorinated; the roasted pellets are then supplied to ferrous metallurgy. Processes are being developed for the selective recovery of copper, tin, bismuth, lead, gold, and silver from complex sulfide ores, as well as for the recovery of nickel, cobalt, and manganese from oxidized nickel ores. Chloridation also looks promising for the processing of various industrial products.

REFERENCE

Korshunov, B. G., and S. L. Stefaniuk. Vvedenie v khlornuiu metallurgiiu redkikh elementov. Moscow, 1970.

I. D. REZNIK

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