from the Six-foot-seven-foot-eight-foot-bunch! dept.
Heavy metals contaminate ground and surface waters from a variety of sources such as industrial effluent or fertilizers or pesticide applications. Cadmium and lead are the most common and toxic metals found in aqueous environments. They are persistent, they migrate, they accumulate in biological tissues, and they are carcinogenic. Removing these metals effectively and cheaply has been a big environmental challenge. There are a number of approaches to remove them including reverse osmosis, ion-exchange, chemical precipitation, coagulation, electrochemical treatment, and physical adsorption. Of these, adsorption is seen as very promising due to it being cost-effective, widely available, and easy to implement. There are a wide variety of adsorbent materials from the mundane (activated carbon, diatomaceous earth, polymers, etc.) to the exotic (carbon nanotubes and graphene oxide), but biochar has shown to be very efficient and cost-effective.
Biochar is generated from incomplete combustion of organic material at low temperatures under oxygen-starved conditions. It can be made using any organic material, such as forest and crop residues, algae, etc., and it results in a material with unique physiochemical properties such as producing a very porous material with abundant functional groups that bind to the metals. A group of researchers investigated the effectiveness of biochar made from banana waste, particularly the stem and leaves. They chose bananas because it is the fourth-most grown crop in the world. After a harvest, the stems and leaves are discarded in the field. Since the bananas only make up about 12% of the plant mass, this means a significant amount of biowaste is generated. They found that they could recycle the banana waste residues effectively for preparing adsorbents for treatment of heavy metals in contaminated water, and they hope that this would promote agricultural waste recycling as well as providing material for treating contaminated water.
Absorption at Wikipedia.
Xiyang Liu, Gaoxiang Li, Chengyu Chen, et al. Banana stem and leaf biochar as an effective adsorbent for cadmium and lead in aqueous solution [open], Scientific Reports (DOI: 10.1038/s41598-022-05652-7)
Monsanto's RoundUp, a widely used pesticide, uses the active ingredient Glyphosate and it may be up for another serious beating. Medical specialists and scientists in Sri Lanka has found that when glyphosate comes in contact with heavy metals like cadmium, arsenic, manganese and cobalt which exist naturally in the soil or fertilizer, it becomes highly toxic and has a high likelihood of causing fatal kidney disease for anyone that comes into contact with it. And because the substance binds to metals it will not show up in current tests. The report (and another one) is published in International Journal of Environmental Research and Public Health and has resulted in that the Sri Lanka president to ban glyphosate immediately.
Exposure to glyphosate causes a drop in amino acid tryptophan levels, which interrupts the necessary active signalling of the neurotransmitter serotonin, which is associated with weight gain, depression, Parkinson's and Alzheimer's disease. The report show that industry and regulators knew as long ago as the 1980's and 1990's that glyphosate causes malformation, but that information was not made public. Glyphosate is also a teratogenic.
Monsanto has been in the news quite recently.
Many are going to ask, "What's so weird about this one corner?" and I'm here to answer.
The end of Irving Avenue, where it meets Moffat Street, in Ridgewood, Queens, is the most radioactive spot in the entire state of New York, and would be the northeast's if not for NJ's McGuire Air Force Base in Burlington County (called "the most contaminated base" in 2007 by the United States Environmental Protection Agency).
In 1918, chemical engineer Alcan Hirsch, and his brother, mining chief Marx Hirsch, opened a chemical plant where today sits most of the businesses on Irving Ave's north side. In 1920, they christen it Hirsch Laboratories, and later added the mining company Molybdenum Corporation (aka Molycorp). The Hirsch brothers sold the lab in 1923 to Harry Wolff and Max Alport, who renamed it Wolff-Alport Chemical Company, but continued their mining operations, and supplied W-A Chemical with the rare-earth metals needed to produce a huge list of products.
The plant processed Monazite sand, which, when treated with Sulfuric Acid, separates into the rare-earth Sodium Sulfate, but also the radioactive waste known as Thorium Pyrophosphate.
It wasn't till the United States' nuclear weapons program in 1942, known as the Manhattan Project, that Thorium became useful. Until 1947, when the Atomic Energy Commission began to purchase the fertile heavy element from Wolff-Alport, and for the full 20-years prior, the Thorium waste was simply dumped into the area's sewers.
"Thorium waste dumped into the area's sewers." Amazing.
Metal-organic frameworks (MOFs) are a special class of sponge-like materials with nano-sized pores. The nanopores lead to record-breaking internal surface areas, up to 7800 m2 in a single gram. This feature makes MOFs extremely versatile materials with multiple uses, such as separating petrochemicals and gases, mimicking DNA, hydrogen production and removing heavy metals, fluoride anions, and even gold from water—to name a few.
One of the key features is pore size. MOFs and other porous materials are classified based on the diameter of their pores: MOFs with pores up to 2 nanometers in diameter are called "microporous," and anything above that is called "mesoporous." Most MOFs today are microporous, so they are not useful in applications that require them to capture large molecules or catalyze reactions between them—basically, the molecules don't fit the pores.
So more recently, mesoporous MOFs have come into play, because they show a lot of promise in large-molecule applications. Still, they aren't problem-free: When the major focus in the field is finding innovative ways to maximize MOF surface areas and pore sizes, addressing the collapsing problem is top priority.
[...] After adding the polymer to the MOFs, their high surface areas and crystallinity were maintained even after heating the MOFs at 150°C—temperatures that would previously be unreachable due to pore collapse. This new stability provides access to many more open metal coordination sites, which also increases the reactivity of the MOFs.
The new system is the latest in a series of applications based on initial findings six years ago by members of the same research team, initially developed for desalination of seawater or brackish water, and later adapted for removing radioactive compounds from the cooling water of nuclear power plants. The new version is the first such method that might be applicable for treating household water supplies, as well as industrial uses.
[...] The biggest challenge in trying to remove lead is that it is generally present in such tiny concentrations, vastly exceeded by other elements or compounds. For example, sodium is typically present in drinking water at a concentration of tens of parts per million, whereas lead can be highly toxic at just a few parts per billion. Most existing processes, such as reverse osmosis or distillation, remove everything at once, Alkhadra explains. This not only takes much more energy than would be needed for a selective removal, but it's counterproductive since small amounts of elements such as sodium and magnesium are actually essential for healthy drinking water.
The new approach uses a process called shock electrodialysis, in which an electric field is used to produce a shockwave inside an electrically charged porous material carrying the contaminated water. The shock wave propagates from one side to the other as the voltage increases, leaving behind a zone where the metal ions are depleted, and separating the feed stream into a brine and a fresh stream. The process results in a 95 percent reduction of lead from the outgoing fresh stream.
[...] The process still has its limitations, as it has only been demonstrated at small laboratory scale and at quite slow flow rates. Scaling up the process to make it practical for in-home use will require further research, and larger-scale industrial uses will take even longer.
Huanhuan Tian, Mohammad A. Alkhadra, Kameron M. Conforti, et al. Continuous and Selective Removal of Lead from Drinking Water by Shock Electrodialysis, ACS ES&T Water (DOI: 10.1021/acsestwater.1c00234)