acid mist reduction techniques in copper electrowinning

Introduction

Electrowinning is the final stage of extracting copper, zinc, nickel and many other non-ferrous metals from their ore. As part of the electrowinning process, large volumes of oxygen gas in the form of micro-bubbles are generated at the lead anodes (Al Shakarji et al., 2010). The burst of these bubbles at the free surface of the solution ejects fine acid-containing droplets into the air of which some become airborne and disperse throughout the workplace. This acidic mist not only poses a serious health hazard to the workers but also accelerates the corrosions of the cathodes, anodes, hanger bars and other equipment of the tankhouse. In our previous publications, we quantified the effects of various process parameters (such as solution temperature and acidity) on the size of the generated bubbles and on the amount of generated acid mist (Al Shakarji et al., 2011a, Al Shakarji et al., 2011b).

In many of the electrowinning tankhouses, plastic balls or beads are employed to reduce the formation of acid mist in the tankhouse. About 63% of the electrowinning plants worldwide use plastic balls, 23% use beads, and 36% use a chemical suppressant (such as FC-1100, Dowfax and Quillaja) to reduce acid mist (Robinson and Clayton, 2010). These plastic objects float on the surface of the electrolyte providing a barrier that prevents the acidic droplets, caused by the burst of oxygen bubbles, from becoming airborne.

These floating objects are good mist suppressors only in thick layers (Mella et al., 2006). Using thick layers of plastic balls or beads, however, often results in thin upper cathode deposit making it difficult to strip the produced copper from the cathode. Another disadvantage of using balls and beads is difficult housekeeping. The floating barriers are small, 2–20mm in diameter, and easily slip into the pipes and pumps blocking the flow of electrolyte and damaging the equipment (Mella et al., 2006). Moreover, it is very hard to maintain a thick layer of these floating objects covering the entire 

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