CHAPTER 14 Capture and Fixation of Sulfur About 85% of the world’s primary copper originates in sulfide minerals Sulfur is, therefore, evolved by most copper extraction processes The most common form of evolved sulfur is SO2 gas from smelting and converting SO2 is harmful to fauna and flora It must be prevented from reaching the environment Regulations for ground level SO2 concentrations around copper smelters are presented in Table 14.1 Other regulations such as maximum total SO2 emission (tonnes per year), percent SO1 capture and SO2-in-gas concentration at point-of-emission also apply in certain locations In the past, SO2 from smelting and converting was vented directly to the atmosphere This practice is now prohibited in most of the world so most smelters capture a large fraction of their SOz It is almost always made into sulfuric acid, occasionally liquid SO2 or gypsum Copper smelters typically produce 2.5 - 4.0 tonnes of sulfuric acid per tonne of product copper depending on the S K Uratio of their feed materials This chapter describes: (a) offgases from smelting and converting (b) manufacture of sulfuric acid from smelter gases (c) future developments in sulfur capture 14.1 Offgases From Smelting and Converting Processes Table 14.2 characterizes the offgases from smelting and converting processes SOz strengths in smelting furnace gases vary from about 70 volume% in Inco flash furnace gases to volume% in reverberatory furnace gases The SO2 strengths in converter gases vary from about 40% in flash converter gases to to 12 volume% in Peirce-Smith converter gases 217 18 Extractive Metallurgy of Copper Table 14.1 Standards for maximum SO2 concentration at ground level outside the perimeters of copper smelters Maximum SOz + SO, concentration Country Time period (parts per million) U.S.A (EPA, 2001) Yearly mean daily mean 3-hour mean 0.03 0.14 0.5 I-hour mean 0.02 I O recommendation 0.25 0.5 hour average Ontario, Canada (st Eloi et ai., 1989) 0.3 (regulation) Yearly mean daily mean The offgases from most smelting and converting hrnaces are treated for SO2 removal in sulfuric acid plants The exception is offgas from reverberatory furnaces It is too dilute in SO2 for economic sulfuric acid manufacture This is the main reason reverberatory furnaces continue to be shut down The offgases from electric slag cleaning furnaces, anode furnaces and gas collection hoods around the smelter are dilute in SOz,