Acid Mist Suppression in Copper Electrowinning

Acid Mist Suppression in Copper Electrowinning

In the electrowinning of copper process, immersing metal cathodes and inert conductive anodes are employed in an aqueous solution of copper sulphate containing free sulphuric acid (CuSO4-H2SO4-H2O electrolyte). An electrical potential is applied between the anodes and cathodes, and pure metallic copper is generated from the electrolyte onto the cathodes. Copper is electrodeposited on the cathodes for about one week, after which harvesting is done while water dissociates into hydrogen ions and oxygen at the anode.
 
In the copper electrowinning process, sulphuric acid is used to leach the copper out to form a weak solution of copper sulphate which is then electrowon to recover the copper metal. The solution for electrowinning normally contains copper sulphate and sulphuric acid. A lead anode and stainless steel cathode are immersed in an electrolyte bath containing the copper sulphate/sulphuric acid solution. An electrical current passes from the anode to the cathode, giving rise to an electrochemical reaction whereby metallic copper is deposited onto the cathode. Simultaneously, oxygen is released at the anode surface. The oxygen form bubbles that detach from the anode and rise through the electrolyte. At the free surface of the electrolyte, the bubbles burst and give rise to acid mist which is a fine spray of acid droplets suspended in the air space above the electrolyte bath. Acid mist poses a significant health hazard to operators.

Several techniques have been used in the past to control acid mist concentration in electrowinning tank houses; they include surfactants, mechanical methods, hooding, forced coalescence, and improved ventilation.Hooding of the cells is the most efficient method of controlling acid mist above electrowinning cells as it completely isolates the system from the environment. However, this approach may not be practical in cells where it is necessary to remove electrodes for frequent harvesting as well as being a very costly and inconvenient solution to the acid mist problem. In forced coalescence, larger bubbles are formed to reduce aerosol emissions.

Ventilation acts by displacing the mist before it gets into the breathing zone of the workers. This system is used as a secondary control measure, by diluting the aerosols instead of preventing them. Ventilation is used as a secondary system or in combination with an effective acid mist suppression system.