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elting of zinc sulfide concentrates by forced melt circulation offers substantial energy savings in comparison with the roast leach electrowin (RLE) process. In 2002, Japanese research[1] indicated that ‘‘new smelting technology using the Warner Process would be more efficient and preferable over the traditional methods of zinc extraction.’’ Since then, concerns about energy consumption and global climate change have increased dramatically. Accordingly, this article is focused on slashing even further the electrical energy input. The modified technology is natural gas based. For pure zinc sulfide, the projected energy savings are about 73 pct, provided gaseous zinc is condensed efficiently. High zinc recovery from gases containing zinc vapor is only possible if fog formation is avoided. An inherent problem with both condensers and cooler absorbers is the formation of fog in the bulk gas phase, which can drastically reduce recovery efficiency. Fog may be formed when vapors are cooled to the point at which the operating partial pressure of the condensing vapor is greater than the saturated vapor pressure at the bulk gas temperature. The so-called ‘‘operating line’’ (locus of the partial pressure of the vapor species vs the bulk gas temperature) is not a straight line, but rather it is curved with a slope at any given point along it, given by Gardner[2] as   2=3   dpv P
pv Pr pv
pc ¼ fðaÞ ½1 Sc dTv pBM Tv
Tc where f(a) is a factor to allow for the sensible heat of the diffusing vapor:

N.A. WARNER, Emeritus Professor, is with the University of Birmingham, Birmingham, United Kingdom. Contact e-mail: warnerna@ btopenworld.com Manuscript submitted October 24, 2008. Article published online February 5, 2009. METALLURGICAL AND MATERIALS TRANSACTIONS B

  1
e
a fðaÞ ¼ a

½2

 2=3   Pr Mv Cpv P
pc a¼ Sc MCp P
pv

½3

According to Hanna,[3] Eq. [1] must be solved by numerical integration in order to determine whether the cooling path of the vapor/gas mixture crosses the saturation curve at any point and, hence, establish if there is a possibility of fog formation. More recently, Turner Jones[4] has studied zinc vapor condensation in further detail. Again, these studies indicate that recovery of bulk zinc (solid or liquid) is very prone to fog formation unless conditions are controlled so that fog formation is minimized. This aspect is crucial to the success or failure of direct zinc smelting. Superficially, oxidized zinc fume or blue powder is most definitely not an acceptable product. Vacuum dezincing of liquid copper matte dispersed in a continuous phase of molten copper is believed to be the key to low energy direct zinc smelting. Massive circulation of dispersed melt between a vacuum vessel and a sump immediately beneath is undertaken independently of the very much smaller circulation rate of matte using a gas lift pumping system in an external melt circulation loop. The essence of the overall approach was introduced in the author’s plenary address at ‘‘Zinc Processing ‘08’’ on zinc metal production from bulk