Commercial vessels and offshore energy facilities rely on seawater electrochlorination systems to prevent biological fouling, protect cooling-water systems, maintain firewater and process-water reliability, and comply with ballast-water treatment regulations. These systems generate sodium hypochlorite directly from seawater, allowing operators to avoid storing large volumes of hazardous biocide chemicals onboard. However, when an electrolytic cell reaches end of life, operators often remove it during drydock, overhaul, turnaround, or decommissioning and classify it as ordinary titanium scrap. This can be a costly mistake. Many spent electrochlorination cells contain residual ruthenium and iridium in their catalytic coatings, even when they are no longer electrically serviceable. The valuable metals aren't found in large, visible pieces. They are contained in a thin mixed-metal oxide coating on the titanium anode surface. Because the coating is only microns thick, it's easy to overlook its value. Yet the ruthenium and iridium contained in a multi-cell bank may be worth substantially more than the titanium substrate itself.
The anode is the critical component in a marine electrochlorination cell. Most anodes use a Grade 1 or Grade 2 titanium substrate in expanded mesh, plate, tube, or fabricated frame assemblies. Titanium is highly corrosion resistant, but it cannot operate uncoated as a seawater anode. When titanium is anodically polarized in chloride-containing seawater, it rapidly forms a titanium dioxide (TiO₂) film. This oxide layer is electrically insulating and prevents current from flowing efficiently. To use titanium as an anode, manufacturers apply a mixed-metal oxide coating, commonly known as an MMO or dimensionally stable anode coating.
These coatings generally contain ruthenium oxide and iridium oxide. Ruthenium is highly effective for chlorine evolution, while iridium helps improve stability and coating life. Many systems also include titanium dioxide, tin dioxide, tantalum pentoxide, or similar stabilizing oxides. These supporting materials improve structural durability, reduce coating cracking, and slow catalyst erosion. Typical commercial marine anodes contain roughly 8 to 25 grams of total precious metal per square meter of active surface area. Ruthenium commonly makes up 65% to 75% of the noble-metal component, while iridium accounts for approximately 25% to 35%.
The word "spent" can be misleading in electrochlorination service. Most marine anodes are not removed because every gram of ruthenium and iridium has been consumed. Operators remove them because the cell voltage rises beyond the acceptable operating limit. Marine electrochlorination systems operate under constant-current conditions. As anodes degrade, resistance increases, and the rectifier must supply more voltage to maintain the required current. A voltage increase of approximately 10% to 15% above the normal operating baseline can trigger alarms or force a shutdown to prevent excess power consumption and damage to the electrical equipment.
Titanium substrate passivation, rather than total loss of the catalyst layer, often causes this electrical failure. MMO coatings have a micro-fissured, porous surface structure. Over time, seawater can penetrate coating defects and contact the titanium substrate. The exposed titanium then oxidizes underneath the coating, creating a dielectric TiO₂ barrier at the interface.
Once this insulating layer forms, the catalytic coating above it may remain physically present but become electrically disconnected from the titanium base. The anode loses performance even though substantial quantities of ruthenium and iridium may remain attached to the surface. In many marine and offshore applications, a spent anode can retain approximately 30% to 50% of its original precious-metal loading. The actual amount depends on current density, service duration, coating chemistry, scale formation, mechanical wear, and why the cell was removed from service. A visual inspection alone cannot determine how much PGM remains.
Generic scrap yards usually buy spent anodes based on titanium weight. From their viewpoint, the MMO coating is an unwanted impurity that complicates titanium recycling. For commercially pure titanium and high-performance titanium alloys, titanium remelting processes need clean, controlled feedstock. Ruthenium, iridium, tantalum, refractory oxides, and oxygen-rich residues can affect melt chemistry and may contribute to metallurgical defects. As a result, many titanium recyclers discount coated anodes, pay only basic titanium scrap rates, or reject heavily coated material altogether.
This approach overlooks that the PGM coating, though very thin, can represent most of an anode bank's monetary value. A 200-kilogram commercial ballast-water treatment anode bank may sell for only a few hundred dollars as titanium scrap. However, if it contains residual ruthenium and iridium, a specialized precious-metal refiner may value the same bank much higher. For example, a 25-square-meter shipboard cell bank originally coated with 12 grams of PGM per square meter could contain approximately 200 grams of ruthenium and 100 grams of iridium when new. If about 45% remains after service, the bank could still hold roughly 90 grams of ruthenium and 45 grams of iridium. The final recoverable value depends on assay results, refining yield, processing charges, and market prices, but it can far exceed the titanium-only value.
The value opportunity is even greater in offshore operations. Fixed production platforms, tension-leg platforms, semi-submersible rigs, FPSOs, and drilling units use seawater continuously for cooling, water injection, crude processing, deluge systems, and utility networks. Large offshore electrochlorination skids may contain 50 to 120 square meters of active anode surface. These installations often use robust plate banks, tubular electrodes, heavy busbars, and large titanium frames. During a major platform turnaround, life-extension project, or decommissioning campaign, operators may remove several complete cell banks at the same time. Because replacement intervals can range from six to ten years, operators may not always consider the accumulated material as a recoverable asset. However, a large offshore lot can contain several hundred grams of ruthenium and iridium. Proper evaluation before disposal can therefore meaningfully affect project economics.
Specialized refiners recover the valuable metals through chemical stripping and hydrometallurgical processing. Instead of melting the coated titanium directly, the refiner separates the MMO layer from the substrate. Ruthenium and iridium are then converted into metal-bearing solutions and purified through processes such as ion exchange, solvent extraction, precipitation, and final refining.
This approach recovers the precious metals separately while preserving the titanium substrate for cleaner recycling. Once the coating is removed, the remaining titanium can be returned to the secondary metal market with fewer contamination concerns. The commercial value of a lot should be based on confirmed content, not assumptions. OEM specifications and active surface-area estimates are useful starting points, but representative sampling and chemical assay should support the final settlement. X-ray fluorescence can provide preliminary screening, while laboratory analysis provides the most reliable basis for determining recoverable ruthenium and iridium.
Prepare spent electrochlorination cells carefully before transport. The metal components are generally stable when clean and dry, but assemblies removed from service may contain trapped hypochlorite, chlorinated brine, chlorate salts, mineral scale, chlorine gas, or hydrogen. Neutralize residual oxidants with an appropriate reducing solution, such as sodium bisulfite, sodium metabisulfite, or sodium thiosulfate. Then flush the system thoroughly with fresh water to remove salts and chemical residues. After flushing, fully drain and dry the assemblies before packing for transport. This preparation helps prevent chlorine off-gassing, corrosive leakage, and shipping complications. Thoroughly cleaned and dried spent cells intended for legitimate metals recovery may be handled through applicable scrap-metal and precious-metal-recycling pathways. However, exact requirements depend on local, national, maritime, and international regulations.
Marine and offshore electrochlorination cells are often replaced because they have reached the end of their electrical life, not because their precious-metal catalyst has disappeared. The difference is important. A cell that can no longer produce chlorine efficiently may still contain enough ruthenium and iridium to justify specialized evaluation and refining. Shipyards, offshore operators, salvage contractors, and vessel owners should review spent MMO mesh, titanium plates, tubular anodes, or complete cell banks for recoating potential and PGM recovery value before selling them as ordinary scrap. Recoating may be appropriate where the titanium substrate remains structurally sound. Where the substrate is warped, pitted, cracked, or unsuitable for reuse, precious-metal refining offers an alternative recovery route. The ruthenium in a marine electrochlorination cell is easy to miss because it is distributed across a thin oxide coating. But the value is real. By recognizing that passivated anodes aren't necessarily depleted, operators can avoid losing high-value platinum-group metals in low-value titanium scrap streams and turn an overlooked decommissioning liability into working capital.
