Titanium anodes coated with mixed metal oxides, often called MMO or DSA anodes, are used in chlor-alkali and chlorate plants, electroplating, copper foil production, electrowinning, water treatment and cathodic protection. When an anode reaches the end of its service life it is usually replaced or sent for recoating. The spent anode still holds value in two places: the precious metal left in its coating and the titanium underneath.
What is inside a spent MMO anode
The base of the anode is a titanium substrate, usually commercially pure titanium in the form of expanded mesh, plate, tube, rod or wire. On top of it sits a thin oxide coating that does the electrochemical work.
- Ruthenium-based coatings are common where the anode produces chlorine, for example in chlor-alkali, chlorate and electrochlorination cells.
- Iridium-tantalum coatings are common where the anode produces oxygen, for example in copper foil, electrowinning and many plating lines.
- Platinum-plated anodes are a separate group with a different coating structure, and they are valued in a different way.
What changes the value of a lot
No two lots of spent anodes are the same. These are the points a buyer looks at first:
- Coating type. Iridium, ruthenium and platinum have very different market prices, so identifying the coating is the first step.
- Remaining coating. Coating wears away during service. An anode removed early holds more metal than one run until it failed.
- Attachments. Copper conductor bars, titanium-clad copper, bolts, plastic and rubber parts add weight that is not anode. Removing them, or telling the buyer about them, avoids surprises.
- Condition. Heavy scale, salt deposits and other contamination make sampling and processing harder.
- Quantity and sorting. A lot sorted by coating type and application is easier to assess than a mixed pile.
How the coating content is checked
A handheld XRF analyser can identify the coating elements on site and show whether pieces in a lot are similar. For a firm figure on precious metal content, representative samples are analysed in a laboratory. For mixed or unknown lots, it is common to agree on sampling before the material moves.
Preparing your anodes before asking for a price
- Take a photo of the whole lot and close-ups of the coated surface.
- Note the process the anodes came from, such as chlor-alkali, plating or copper foil.
- Keep any labels, drawings or original specifications.
- Estimate the total weight and the share of copper or other attachments.
- Keep different anode types apart where you can.
With this information a buyer can give a first assessment from photos and decide whether a sample or an on-site inspection is the next step.