100 higher compared to RLE with hydrometallurgical treatment of leaching residues 136 Energy use of ISF is more than 25 times higher compared to RLE per tonne of zinc pro duced The RLE process is much more electrointensive with 4 17 MWh electricity needed to produce one tonne of zinc 137 With regard to secondary production over 40 of the zinc used annually originates from recycled metal 138 Much of this comes from zinccoated steel e g zinc used in used in roof i n g a n d a u t o m o t i v e T h i s i s placed in the EAF being used to recycle steel Zinc is relatively volatile and leaves the furnace with other gases It is collected on cooling as zinc dust EAF dust T oday this dust is highly contaminated with iron Therefore this dust is frst processed in W aelz kilns to separate it from iron Iron come out as a slag for construction and roads while zinc comes out as an o xide This zinc o xide is further refned by zinc smelters in the process described above 139 Figure 28 C O 2 eq emissions from Zinc production Mt C O 2 eq in the EU and Norway Source Inter national Zinc Assocation Between 1990 and 2015 the GHGs from zinc production in the EU28 and Norway fell 38 Major reductions in direct emissions 62 came about due to the shift from the cok e intensive pyrometallurgical ISF process towards the more energy efcient electrolytic RLE process In 1990 there were 22 zinc refneries in the countries of the EU27 plus Norway producing zinc metal using three technologies 136 Ecofys et al 2009b 137 Brook Hunt a W ood Mack enzie company 138 Secondary production includes recycling in zinc smelters and in the brass industry the zinc compound industry and remelting 139 CIES ND plants operate a direct leach process on a part of the fow which allows to bypass the roasting step Zinc sulphide ore roasting usually tak es place in a fuidised bed furnace at around 1000 C with air being blown in through a perforated bottom The most important reaction is the conversion of zinc sulfde to zinc o xide 134 The o xidized zinc is dissolved in acid and other metals are separated as byproduct from this zinc fow Pure zinc metal is f nally recovered by electrolysis where zinc is deposited at the cathodes The zinc deposit on the cathodes is stripped of molten and cast into ingots The metal is at least 99 95 pure It is possible to mak e very high purity zinc 99 995 pure by adjusting electrolysis condi tions such as temperature and current density Metal of this purity is required for diecasting alloys containing aluminium magnesium and copper 135 A pyrometallurgical process after the RLE route can recover the lost zinc lead silver indium germanium from the residues It is waste material and needs energy and reducing agent to mak e pure slag and metal fume for metals recovery In the ISF process zinc concentrate is agglomerated by sintering and then directly lead into the Imperial Smelting Furnace together with cok e Cok e acts as energy source and reducing agent In the RLE as well as in the ISF process secondary raw materials such as zinc o xide or EAF dusts can be added Byproducts of these processes include sulphuric acid lead precious metals cadmium copper indium germanium nick el and cobalt Figure 27 left Direct emissions of Zinc production source Ecofys 2009b r ight energy use per tonne of zinc Source Brook Hunt a W ood Mack enzie Company The fgures above illustrate important diferences between both the CO 2 intensity direct emissions and energy use of RLE and ISF technologies Direct emissions of ISF are a factor 134 CIES ND 135 Ibidem Specic emissions k g CO t zinc Electricity GJt Zn Other energy GJt Zn 4325 52 20 43 ISF RLE RLEhyrdo ISF RLE ISF 15 5 48 4 Indirect Emissions Mt CO eq Direct Emissions Mt CO eq 2015 2005 1990 3 7 3 158 5501 2343 2664 4202 2493 3394 3 122 1080 0 910 2484 38 MET ALS IN A CLIMA TE NEUTRAL EUROPE A 2050 BL UEPRINT 46