Study of Bubble Size Distribution in Electrowinning of Copper and an Improvement in Acid Mist Suppression

Abstract

In the final step of the hydrometallurgical production procedures for metals like copper, zinc, and nickel, an acid mist is produced during the electrowinning process. On the anode during electrowinning, oxygen bubbles develop. Small acid-containing liquid droplets are created when these bubbles pop at the interface of the solution and the air, becoming airborne and spreading throughout the workplace. These "acid mist" droplets present a serious health risk to the workers. Additionally, it causes severe structural and equipment corrosion, which costs the sector millions of dollars annually. Little quantitative data on the production of acid mist and the factors influencing its amount was available prior to this study. Theoretical analysis of the origin of acid mist shows that, contrary to what is usually believed, the acid mist is almost entirely produced from airborne jet droplets. Jet drops are produced when a liquid jet that forms when the bubble cavity collapses disintegrate. Furthermore, despite the fact that it was widely known that the size of the electrolytically created bubbles was proportional to the amount of acid mist, no systematic measurements had been done to characterize bubble size and its correlation with material and process variables. The current study looks into the factors that determine the number of jet drops produced and bubble size. The relationship between the number of jet drops and bubble size and the mechanisms that cause the acid mist to form. For measuring the size of oxygen bubbles created on the anode during copper electrowinning, a method is developed. The bubbles are photographed in high resolution using a microscopic camera and extremely bright light source. Regardless of the operating conditions, it is discovered that bubbles are produced in a wide size distribution, with a mean diameter of cumulative 80% of the bubbles (P80) was 16 µm. The solution temperature was changed to determine its influence on bubble size. According to experimental data, the diameter of the jet drops produced during copper electrowinning can range from roughly 0.1 mm to 5 mm. Small plastic balls and beads that float are frequently employed in industry to suppress acid mist. Due to their greater buoyancy and greater coverage of the solution surface, spherical-shaped floating barriers minimize acid mist the most when compared to single-layered floating barriers. The lower density allows these to be more buoyant in the solution and more effectively intercept acid mist. Hydrophilic floating objects, on average, reduced the weight loss of bulk solution to about 83% and hydrophobic floating objects were only able to reduce the weight loss to 56% over the course of 60 minutes. The suppression of acid mist is significantly affected by the addition of hydrophilic floating coverage.