The chlor-alkali industry historically relied on mercury-cell technology for the production of chlorine and caustic soda, with liquid mercury serving as the cathode in electrolysis. This process, while effective, led to significant mercury contamination of equipment, buildings, and surrounding soils. The Minamata Convention on Mercury, a global treaty adopted in 2013, mandates the phase-out of mercury-based processes and the environmentally sound management of mercury wastes. In Europe, the transition away from mercury-cell technology is largely complete, and the majority of mercury recovered from decommissioned facilities has already been stabilized and stored in accordance with best practice, ensuring compliance with both EU legislation and international commitments to reduce mercury pollution.
However, mercury is notoriously difficult to detect in certain forms, such as when it is present in embedded residues, hidden pockets and under coatings which makes comprehensive decontamination essential before steel is reused. Effective removal and verification not only protect health and the environment but also ensure that recycled metals remain compliant with regional or local standards.
Complex Polymer, Ebonite and GPR wastes.
The use of protective coatings to protect steel parts from corrosion, such as glass reinforced plastic, ebonite and other polymers create complex waste streams. During decontamination and demolision these materials are often removed along with complex corrosion products, caustic residues and mercury. When this is mixed with decontamination chemicals and water a complex blend is formed which is often outwith the acceptance criterea of treatment plants.
Another key issue is the recycling or disposal of mercury impacted steel. Residual mercury can adhere to or permeate steel surfaces, posing risks if the material is recycled or sent to landfill without proper decontamination.
Hg Ops can work with clients to find ways of sorting and stabilising such wastes either on site or at treatment facilities. By doing so we bring the waste into the agreed acceptance criteria and allow for environmentally sound disposal.
Steel from chlor alkali can hold hidden surprises
Mercury and mercury compounds can be found in steel everywhere in chlor alkali plants. Years of contact with mercury vapour in the air means that even steel which has not been in direct contact with liquid mercury or mercury containing fluids can be impacted. XRF analysis can quickly highlight the presence of mercury however it can also give false negative readings where mercury is hidden under the surface. This can pose dangers to workers cutting and grinding steel as the small amounts of mercury heat up and form toxic clouds of vapour around the workers. Exposure can be fast and difficult to detect without proper monitoring.
Mercury has also been observed finding its wasy behind welds, between sandwiched steel plating and even in "worm holes" caused by Galvanic Corrosion. A steel componant can be fully decontaminated on the outer surface but hold a pocket with liquid mercury inside. In the picture below, mercury has made its way through pinhole openings corroded through welds and filled a void created by galvanic corrosion. An understanding of the potential of this mechanism allows the decontamiantion team to identify and check for such cases and avoid costly cross contamination which can occur when liquid mercury appears at recycling sites or landfills.
Steel smelting posses other issues. As we search for low carbon steel sources, it makes sense that decontaminated steel should be recycled. However the impact of residual or hidden mercury in steel should be taken into account at the smelter. EU regulations strictly limit the presence of mercury in recycled steel, recognising the potential for trace contamination to be released during recycling or smelting. If you imagine trace mercury in the surfaces of a tonne of scrap steel on its way to an electric arc furnace. That small amount of mercury will be released in a single cloud as the steel is quickly heated past the boiling point of mercury and up to 1,600 °C. It is the responsibility of the waste generator to ensure compliance with the steel smelters acceptance criterea and avoid costly rejections.
How can Hg Ops support you during decommissioning of chlor-alkali plants?
- Audit sites to identify and quantify waste and contamination
- Run tests and create procedures to sort and manage wastes to ensure compliance with treatment facilities
- Assess steel process equipment to find and plan for potentially hidden pockets of mercury
- Find and assess environmentally sound disposal routes for liquid mercury and mercury waste
- Ensure ADR and IMDG compliant mercury waste transport by managing the process or auditing your subcontractors
- Apply for the necessary Basel Convention Permits where international waste transfer is necessary
- Conduct tests to ensure decontamination of materials is complete before disposal or recycling
- Advise on decontamination methods and audit processes
- Audit and recycling waste outlets to ensure compliance and mercury safety
- Advise and audit subcontractors and develop protocols on safe handling of mercury and mercury waste
- Provide best in class training on mercury as a waste, contaminant and toxin
- Training of staff who will be in contact with mercury or mercury contamiantion to ensure safety from exposure