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Nano-Scale Selective Ion Exchange used to Remove Radioactive Contamination from Water

Researchers from the University of Helsinki in Finland recently reported that they have developed a new method to remove radioactive contamination from water.  They claim their method of nano-scale selective ion exchange is faster than the conventional method and more environmentally-friendly as less radioactive solid waste is produced.

Risto Koivula, researcher at the University of Helsinki

The new method of selective ion exchange uses electrospun sodium titanate.  Electrospinning is a fibre production method which uses electric force to draw charged threads of polymer solutions or polymer melts up to fiber diameters in the order of some hundred nanometers  “The advantages of electrospun materials are due to the kinetics, i.e. reaction speed, of ion exchange,” says Risto Koivula, a scientist in the research group Ion Exchange for Nuclear Waste Treatment and for Recycling at the Department of Chemistry at the University of Helsinki.

One conventional method of removing radioactive ions from water is using granular sodium titanate as an ion exchange medium.  It is currently used to treat the 120,000 cubic meters of radioactive wastewater generated as a result of the Fukushima, Japan nuclear accident.  As radioactive wastewater is run through the ion exchanger, the radio-active ions are exchanged with the sodium in the sodium titantate.  The radioactive pollutants remain bound by the granules in the ion exchange unit.

Sodium Titanate fibres

The advantage of sodium titanate over other ion exchange media is that it is selective, which means that it is picks out only the radioactive ions from the water.  One disadvantage of ion exchange is that a water pollution problem is being transferred into a waste management problem.  When the ion exchange capacity is filled, the filtering material has to be switched out.  This leaves solid radio-active waste which must be managed.

The utilization of electrospun sodium titanate results in nano-scale spindles.  The result is an ion exchange solution that occupies less space but provides an equal treatment capability.  “Since less electrospun material is needed from the start of the process, the radio-active waste requiring a permanent repository will also fit in a smaller space,” says Koivula.

The electrospinning equipment at the University of Helsinki was developed and built in the Centre of Excellence for Atomic Layer Deposition, led by Mikko Ritala. The researchers successfully tried this quite simple method for working sodium titanate into fibre.  Koivula’s team studied the ion exchange features of fibre produced this way and found it worked like the commercially produced ones.

The utilization of this selective ion exchange method could be applied to the sites with groundwater contaminated with radioactive ions.

In Canada, the Town of Port Hope (located approximately 100 km east to Toronto) has over 1 million cubic metres of low-level radioactive waste as well as radioactive waste in treatment ponds.  The source of the radioactive contamination is the historic operation of the former radium and uranium refining activities of Eldorado Nuclear.  The wastewater treatment facility at Port Hope is a two-stage process that removes salts, heavy metals, and contaminants such as radium and arsenic.  The process involves chemical precipitation with clarification followed by reverse osmosis.

Clean-up of Radioactive Material in Port Hope Finally Underway

After decades of study and planning, the clean-up or radioactive contamination in the community of Port Hope, Ontario is finally underway.  The Town of Port Hope, located approximately 100 km (60 miles) east on Toronto on Lake Ontario, has an estimated 1.2 million cubic metres (1.5 million cubic yards) of historic low-level radioactive waste scattered at various sites throughout the town.

The contaminated soil and material will be excavated to moved to the LongTerm Waste Management Facility, which is essentially an engineered aboveground landfill where the waste will be safely contained, and the long-term monitoring and maintenance of the new waste management facility.

Other historic low-level radioactive waste – primarily soil contaminated with residue ore from the former radium and uranium refining activities of Eldorado Nuclear — and specified industrial waste from various sites in urban Port Hope will be removed and safely transported to the new facility.

The historic low-level radioactive waste and contaminated soil, located at various sites in the Municipality of
Port Hope, are a consequence of past practices involving the refining of radium and uranium by a former federal Crown Corporation, Eldorado Nuclear Limited, and its private-sector predecessors. These waste materials contain radium-226, uranium, arsenic and other contaminants resulting from the refining process.

The historic waste and surrounding environment are monitored and inspected regularly to ensure the waste does not pose a risk to health or the environment. As part of the Port Hope Area Initiative (PHAI) construction and clean-up phase, the waste will be excavated and relocated to the new Port Hope long-term waste management facility.

In an interview with CBC, Scott Parnell is the General Manager of the Port Hope Area Initiative, which is in charge of the cleanup. He says that after decades of planning, the first loads of an estimated 1.2 million cubic metres of historic low-level radioactive waste will be on the move.

Scott Parnell, general manager of the Port Hope Area Initiative, stands near the town’s harbour.

“There’s been a lot of planning a lot of studies a lot of determination into how to approach the work safely, but this will be the first time we will be removing waste from the community,” said Parnell, who has overseen similar operations in Washington state and Alaska.

The $1.28-billion cleanup operation is a recognition by the federal government that the waste is its “environmental liability.” The radioactive tailings were the byproduct of uranium and radium refining operations run by Eldorado, a former Crown corporation, between 1933 and 1988.

Parnell says that the tailings were given away for free, which helps explain how the contamination was spread through the town.

“So, basically they offered it up and it was used for fill material to level up people’s backyards, for building foundations, for those kinds of things. So, that’s how the material got spread around the community,” Parnell said.

Parnell says an estimated 800 properties may be affected, but says there’s no indication the low levels of radiation are dangerous.

“There’s little human risk associated with the waste that’s identified here in Port Hope,” he said.

The first wastes to be remediated are currently stored under tarps at three locations including the Centre Pier, the Pine Street North Extension in the Highland Drive Landfill area and at the municipal sewage treatment plant. The Centre Pier is the first site to be remediated.

Aerial image of the first locations to be remediated. (source: Canadian Nuclear Laboratories)