Modern chlor-alkali plants rely on dimensionally stable anodes, commonly known as DSA anodes, to produce chlorine, caustic soda, and hydrogen from sodium chloride brine. These anodes are typically manufactured from commercially pure titanium mesh, expanded metal, or louvered plate that has been coated with a thin mixed metal oxide, or MMO, catalyst layer.
The coating is the anode's critical functional component. It enables efficient chlorine evolution under highly corrosive operating conditions, including hot brine, an acidic anolyte, chlorine gas generation, and high electrical current densities. A typical chlor-alkali anode coating may contain ruthenium dioxide, titanium dioxide, iridium dioxide, tin oxide, zirconium oxide, or related metal oxides selected for conductivity, catalytic activity, durability, and adhesion to the titanium substrate. Ruthenium dioxide is particularly important because it is highly active for the chlorine-evolution reaction. In practice, it helps the anode generate chlorine efficiently while reducing the electrical energy required to operate the cell. Titanium dioxide and other valve-metal oxides provide stability and structure, while certain formulations may include iridium to improve durability and performance in demanding service environments. Although the precious-metal coating is very thin, the total coated surface area in an industrial electrolyzer stack can be extensive. A single bank may contain dozens or hundreds of individual titanium anode elements, each with several square meters of active surface. Across an entire bank, even a relatively light catalyst loading can represent a meaningful quantity of ruthenium-bearing material.
Commercial chlor-alkali membrane cells are arranged in large electrolyzer stacks. Depending on the technology platform and plant capacity, a stack may include roughly 100 to 170 individual cell elements. These elements are compressed in a filter-press configuration between structural end frames and connected through electrical bus systems. A representative industrial bank may contain approximately 150 anode elements. Individual elements often have active projected areas of roughly 2.7 to 3.3 square meters. This means a complete bank can contain several hundred square meters of ruthenium-coated titanium surface.
Fresh chlor-alkali MMO coatings commonly contain ruthenium loadings of about 10 to 15 grams per square meter of projected active area. However, actual loading varies by manufacturer, cell technology, operating current density, target lifetime, and coating chemistry. Some anodes are primarily ruthenium-titanium oxide systems, while others use ruthenium, iridium, and titanium oxides in proprietary ratios. As a result, a typical full-size chlor-alkali anode bank may contain a substantial original inventory of ruthenium when installed. Even after years of operation, retired banks can retain a meaningful amount of ruthenium and, where applicable, iridium in the remaining MMO coating.
A common misconception in the scrap and recycling market is that a spent chlor-alkali anode has no remaining precious-metal value because it has reached the end of its operating life. Often, that is not technically accurate. Operators usually remove chlor-alkali anodes from service because cell voltage rises to a level that makes continued operation inefficient. In chlorine manufacturing, electricity is a major operating expense. As anode performance changes, even a modest increase in cell voltage can significantly affect plant power consumption. As a result, operators frequently schedule replacement or refurbishment before an anode fails.
The principal cause of anode retirement is frequently something other than complete loss of the catalyst coating. Instead, it is often related to passivation at the titanium-to-coating interface. MMO coatings have a porous, micro-cracked structure formed during their thermal manufacturing process. Over time, brine and acidic electrolyte can migrate through small coating imperfections and reach the titanium substrate underneath. Under strong anodic conditions, exposed titanium forms titanium dioxide. While titanium dioxide is chemically stable, it is electrically resistive. As this barrier layer develops, it interferes with current transfer from the titanium base metal to the outer catalytic coating. The cell voltage rises, electrical efficiency falls, and the anode becomes unsuitable for continued industrial service.
This process can occur while a significant portion of the original ruthenium-containing coating remains attached to the titanium surface. In other words, an anode may be operationally "spent" in the cellroom while still retaining recoverable catalyst material. Industry experience and electrochemical analysis commonly support the view that decommissioned chlor-alkali anodes can retain a substantial fraction of their original ruthenium loading. The exact amount depends on operating conditions, coating design, service duration, current density, brine quality, maintenance history, and whether the anode has been recoated previously. Nevertheless, retired anodes should not automatically be assumed to be ordinary titanium scrap.
Ruthenium-based MMO coatings are valued primarily for their catalytic performance in chlorine evolution. They are engineered to deliver low overpotential, high conductivity, chemical resistance, and long-term stability in aggressive brine electrolysis environments.
In chlor-alkali production, these coatings are used on titanium anodes in membrane cells and, in some cases, diaphragm-cell or specialty electrolysis systems. They support continuous chlorine generation while minimizing energy consumption and maintaining stable electrical performance over multi-year operating cycles. Beyond conventional chlor-alkali production, ruthenium-containing MMO anodes also support electrochlorination, sodium chlorate production, hypochlorite generation, brine treatment, industrial water disinfection, marine antifouling systems, and certain electrochemical oxidation processes. The exact coating chemistry changes depending on whether the intended reaction is chlorine evolution, oxygen evolution, chlorate formation, or another electrochemical process. The titanium substrate is equally important. Titanium is lightweight, corrosion-resistant, structurally strong, and well suited to aggressive chloride environments when paired with the right conductive coating. This combination of titanium support metal and precious-metal oxide catalyst creates a durable electrode system that can operate for years in demanding industrial conditions. When the coating's active life ends, the titanium substrate may still be suitable for controlled stripping, recoating, reuse, or recycling. Specialized recovery channels can also handle the remaining precious-metal coating, rather than losing it in conventional scrap processing.
Chlor-alkali anodes can look like ordinary titanium mesh or fabricated titanium components. Still, several features may indicate that the material is MMO-coated and may contain ruthenium or other platinum-group metals. The most common form is expanded titanium mesh, although anodes may also be fabricated as perforated plates, louvered sheets, wire mesh, or more complex electrode assemblies. The surface may appear dark gray, black, blue-gray, or matte metallic, depending on the coating formulation, age, cleaning history, and wear. After years of service, coatings may be visibly cracked, mottled, faded, or partially discolored.
Anode documentation can provide the most reliable initial information. Useful records include the original equipment manufacturer, anode serial numbers, installation date, cell technology, recoating history, active surface area, and coating description. Terms such as DSA, MMO, RuO₂/TiO₂, Ru/Ir/Ti, chlorine anode, membrane-cell anode, or electrochlorination anode may indicate the presence of recoverable precious-metal oxide coatings. Surface screening methods may also help with preliminary identification. Portable X-ray fluorescence equipment can show some metals on surfaces that are easy to reach, but it may not be able to give a complete picture of the total coating inventory. Representative sampling and controlled assay procedures are generally more appropriate where accurate metal-content determination is required.
Decommissioned chlor-alkali anodes are not simply obsolete titanium components. They are specialized industrial materials that may contain titanium substrate metal, residual ruthenium-bearing coating, and potentially iridium-bearing catalyst layers. Their recovery potential depends on the original coating formulation, active area, operating history, condition of the titanium base, and the amount of catalyst remaining after service. Specialized buyers, refiners, and electrode-recovery companies actively evaluate spent MMO-coated titanium anodes for precious-metal recovery, titanium reclamation, and recoating opportunities. Material a conventional scrap yard may overlook can interest companies equipped to assess and process ruthenium- and iridium-bearing coatings.
For plant operators, maintenance contractors, demolition companies, and industrial scrap suppliers, the first practical step is to identify the anode type and preserve equipment records. Rather than assuming the material is standard titanium scrap, owners should consider having the lot reviewed for MMO coating content, precious-metal indicators, and potential recovery or reuse options. We are actively buying spent chlor-alkali anodes, MMO-coated titanium mesh, DSA electrodes, ruthenium-coated titanium components, and iridium-bearing industrial anode materials. Lots may be evaluated based on anode type, dimensions, condition, coating history, photographs, serial numbers, and available operating documentation.
