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What is electrowinning ?
Electrowinning is the electrochemical recovery of metals from their dissolved state. It involves the application of electrical current between two electrodes immersed in a metal bearing solution (known as electrolyte). Under the correct conditions the dissolved metal will plate on to the negative electrode (cathode).
Why does the EMEW® cell out perform conventional electrowinning technology? |
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The high performance of the EMEW® cell technology is achieved through a hydraulic mechanism which achieves higher rates of metal ion transport to a cathode than in a conventional electrowinning reactor. The essential difference is that the EMEW® cell is constructed from a pair of concentric tubular, rather than planar, electrodes. The ends of the assembly are fitted with plastic end caps, thus forming a closed chamber through which target solution can be pumped at high rate. The resulting high flow and efficient mixing result in 'forced' and continual supply of metal ions to the surface of the cathode. |
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Which metals can EMEW® recover? |
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The EMEW® cell can recover gold, silver, platinum, cadmium, cobalt, copper, nickel, tin, zinc, lead, manganese, and a variety of other metals. |
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What is the cathode area of the EMEW® cell? |
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The 150mm plating cell has a cathode area of 0.5 M˛. The 200mm powder cell has a cathode area of 1.0 M˛. |
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What is the production rate of an EMEW® cell? |
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This will vary depending on the metal being recovered and the solution characteristics, however in a typical sulphate solution, a single plating cell can produce up to 12 kg per day. A powder cell produce around 25 kg per day.
What is the difference between the plating cell and the powder cell?
The plating cell produces a coherent solid metal cathode that "plates" to the starter sheet inside the cell. It has a cathode area of 0.5 m2 and is typically used for concentrations above 1 g/l
The powder cell produces a powder deposit, which is harvested using a flushing process. It has a cathode area of 1.0 m2 and is typically used for concentrations below 1 g/l.
Can the powder cell be used to recover metals at a higher concentration?
Yes, through the use of a continuous grade circuit. |
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Can the EMEW® cell recover silver from a solution that contains high levels of copper? |
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Yes. The EMEW® cell can selectively electrowin a specific metal in the presence of others, the order in which metals are removed from solution is determined by their position on the metal activities series. |
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To what level can the EMEW® cell recover metals? |
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Again this does depend somewhat on the solution chemistry and the target metals. However in the case of gold the EMEW® cell has achieved a discharge level of 0.01 ppm and 0.1 ppm for copper. |
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Does the EMEW cell have any moving or rotating parts?
No, the pump is the only moving part of the plant.
What is the flow rate through each cell?
Approximately 6000 liters per hour in the plating cell and 2000 litres per hour in the powder cell
At what weight will the cathode require harvesting?
Approximately 25 kg.
How long does it take to harvest a single cell/cathode?
About 1 to 2 minutes for plating cells. Powder cells are harvested automatically.
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Does the EMEW cell release acid mist into the environment?
During conventional electrowinning of metals (e.g. zinc, copper), oxygen bubbles are produced at the anodes. When these bubbles reach the surface they burst, liberating an aerosol of sulfuric acid called acid mist, which can affect the health of operators, the environment and plant infrastructure, The EMEW technology captures ALL gases that can be generated and makes them available for collection and safe disposal or reuse. This feature of EMEW provides significant improvements to the working environment.
What is the anode made of? |
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For low pH solutions the anode (DSA®) is made from a titanium tube that is coated with iridium oxide. For high pH solutions the anode is typically constructed of stainless steel. |
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What is the life of the Anode? |
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Electrometals use the world leading Dimensionally Stable Anode (DSA®) from the De Nora Group. In most cases the anode life is 4 to 6 years, at which point the anode may require recoating. |
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What happens to the gases that are produced as part of the normal electrowinning process? |
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The EMEW® cell is a totally enclosed unit. All gases are captured in the top of each cell and can be vented as appropriate. |
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Does the EMEW® cell alter the laws of electrochemistry? |
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No, all the laws still apply |
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How much cathode area is there in a commercial EMEW® plant? |
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Depending on the application this can vary from only a few square centimeters to over 1000 M˛.
Are there any commercial EMEW systems installed?
Yes, we have commericial facilities in Asia, Africa, North America, South America and Europe.
Is electrowinning a new process?
No, electrowinning has been a commercial process for almost 100 years.
How uniform in thickness is the copper cathode?
Very uniform as the current distribution is very even
How does the copper cathode quality differ to that of conventional EW?
It will be higher purity as the EMEW process is less prone to contaminants |
