University of Rhode Island researchers have studied the chemical compound ferrate and developed methods of making it more effective in treating water sources for contaminants.
Ferrate is a molecule made of iron and oxygen, according to chemistry professor and researcher Dugan Hayes. Ferrate acts as a powerful oxidizing agent because of its unique chemical structure of FeO4.
This chemical formula indicates that ferrate consists of one iron atom (Fe) and four oxygen atoms (O).
The iron molecule in ferrate has a charge of positive six, which indicates that the iron has lost six electrons, Hayes explained.
Rust, a common form of iron, has a charge of positive three, indicating a loss of three electrons. Having lost six electrons, scientists would expect ferrate to be a highly unstable molecule, according to Hayes, but when mixed with potassium salt, is stable.
However, when dissolved in water, ferrate becomes unstable and forms hydroxyl radicals, which can oxidize contaminants in a water sample.
According to Hayes, oxidation is the process of losing electrons because ferrate has lost many of its electrons and is unstable in water, it will begin to pull electrons off of other molecules. This changes the molecular structure of the contaminants, and eliminates them from the water source.
Ferrate is effective in oxidizing many of the potential contaminants found in water.
“It’s really effective against anything that is an organic compound, or is composed of organic compounds,” Hayes said. “The main limitation is that it can’t help with heavy metals because you can’t oxidize away a metal.”
When ferrate is done treating the water source, it will turn into rust, which is non-toxic, and settle to the bottom of the water sample where it can then be filtered out.
Hayes and his team study the synergistic effects of U.V. light on ferrate’s ability to oxidize contaminants from water sources.
According to Hayes, iron that has a charge of positive four and five is more powerful oxidant than iron with a positive six charge. In order to make ferrate have a charge of positive four or five, electrons must be donated to the iron atom. This is often done with a chemical reducing agent.
Hayes and his team use U.V. light to complete this process.
“What happens when this compound absorbs U.V. light is that one of the electrons on oxygen goes onto the iron in a process called ligand metal charge transfer,” Hayes said. “This, in essence, does the same thing as adding a chemical reducing agent does.”
Cali Antolini, a former graduate student at URI, was instrumental in the process of designing and implementing experiments with Hayes to find out more about how U.V. light affects ferrate. Since this topic has not been heavily researched, many experiments left the team with more questions to answer than they originally thought. Antolini took countless measurements and designed new experiments to gain further knowledge. Antolini defended her dissertation and graduated with her PhD last spring. She is now pursuing a postdoctoral degree at Stanford.
According to Hayes, the team found that after four nanoseconds, 85% of the iron atoms stimulated by U.V. light will go back to their original state of having a positive six charge. 15% will stay the same, and the iron will have a charge of positive four or five.
If the remainder of the molecules keeps getting stimulated from the U.V. light, eventually all of the iron will have a lower charge and the sample will be very effective in oxidizing contaminants.
Hayes uses ultra short laser pulses of 100 femtoseconds, or a trillionth of a second long which take pictures of the reactions to see them taking place.
“By taking all of these snapshots and piercing everything together, we can watch the electrons move in the molecule,” Hayes said.
Associate Professor of Civil and Environmental Engineering Joseph Goodwill collaborated with Hayes on this study.
Goodwill and his team study how to implement ferrate as a treatment of water sources.
Currently, there is no full scale usage of ferrate in a water treatment system.
“My hope is that we can provide more data and information about possible use cases and possible optimization, and in that way make it more accessible at the full scale,” Goodwill said.
According to Goodwill, chlorine is the most common chemical additive in water treatment.
“When chlorine was first developed to disinfect and treat water, it was an amazing public health breakthrough,” Goodwill said.
However, there are some downsides to chlorine treatment such as the potential chemical byproducts created after chlorine is added to water. Goodwill believes that ferrate can be a better alternative, especially for rural or small communities in the United States, and globally.
“The reason I feel compelled to do that is because in order to treat very challenging or contaminated sources of water requires really advanced, complicated, and sometimes expensive technology,” Goodwill said. “Ferrate, in my view, can do many of the things that more complicated and expensive approaches can do, but does so in an elegantly simple way.”
According to Goodwill, this is possible because the addition of ferrate to water treatment would not require dramatic change to the preexisting water treatment systems. This makes the use of ferrate very accessible.
“It has been an absolute joy working with Dugan and his team, and it’s been rewarding to engage with them on a fundamental chemistry question and then apply it in a way that solves an environmental problem,” Goodwill said.
URI researchers have been some of the first to study ferrate and its applications in water treatment. With more research, ferrate could soon become the new best treatment of water contaminants.