Chapter 12 - Capture and Fixation of Sulfur

Abstract

This chapter highlights that most copper is extracted from sulfide minerals so that sulfur, in some form, is a byproduct of most copper extraction processes. The usual byproduct is sulfuric acid, made from the SO2 produced during smelting and converting. Conventional sulfuric acid production entails: Cleaning and drying the furnace gases; catalytically oxidizing their SO2 to SO3 (with O2 in the gas itself or in added air) and; absorbing the resulting SO3 into a 98.5% H2SO4–H2O sulfuric acid solution. The process is autothermal when the input gases contain about 4 or more vol.-% SO2. The double absorption acid plants being installed in the 2000s recover >99.7% of the input SO2. SO2 recovery can be increased even further by scrubbing the acid plant tail gas with basic solutions or by adding more catalyst beds with Cs-promoted catalyst. Some modern smelting processes produce extra-strong SO2 gases, 13+% SO2. These strong gases tend to overheat during SO2 oxidation, causing catalyst degradation and inefficient SO2 conversion. This problem is leading to the development of catalysts, which have low ignition temperatures and high degradation temperatures. Installation of pre-converters or the recently introduced LUREC process are also used to handle high SO2 strength feed gas. Two other alternatives are also under development: quasi-isotherme-katalyse and wet gas sulfuric acid-double condensation.