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Electrolysis / Electrowinning
Low current density electrolysis
Description
- Plate the contaminate metals on a ‘dummy’ electrode to remove them from the bath
- Recover expensive metals (nickel, cadmium, gold, silver)
- Water can be reused or disposed of
- Used by a variety of plating and finishing processes
- Typically used for concetnrated solutions: process tanks, drag-out rinses, ion exchange regenerant
- Can NOT be performed in-line
- Batch: performed in process tank, when the tank is not operational
- Continuous: performed in a side-tank, and return the solution to the process tank (preferably via a filter)
Advantages
- Metals are removed from solution
- Plated metal may be reusable, recyclable, or sellable
- Reduces water use and wastewater generation
Limitations
- Does not work on chromium
Implementation Process
- Determine cost effectiveness
- Initial expense --> cost of unit, installation
- Operation expenses --> energy, labor, maintenance, anode, cathode
- Savings --> metal recovery, reduced treatment costs
- Purchase and install an electrowinning unit
- Typical Operating Conditions:
- Target contaminates: copper, zinc, lead and iron
- Cathodes: made of corrugated steel sheets
- Anode to cathode spacing: 4 inches
- Current density: dependant on metals being removed, usually between 2-8 amps/ft2
- Time: 2-5 amp-hr/gal
- Agitatation increases the speed of removal
- Train and monitor employees – give incentives for superior performance
High current density electrolysis
Description
- Oxidize the contaminate metal
- Typical uses:
- Oxidize trivalent chromium to hexavalent chromium in chromic acid baths (eg: chromium plating, chromic acid anodizing)
- Gas-off chloride as chlorine
Implementation Process
- Determine cost effectiveness
- Initial expense --> cost of unit, installation
- Operation expenses --> energy, labor, maintenance, anode, cathode
- Savings --> metal recovery, reduced treatment costs
- Purchase and install an electrowinning unit
- Typical Operating Conditions:
- Anode to cathode ratio: between 10:1 and 30:1
- Current density: 100 to 300 amps/ft2
- Anodes: made of lead or lead alloy
- Train and monitor employees – give incentives for superior performance
Resources
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