Ion imprinted polymers for metal separations from seawater, selecting uranium over vanadium.
There is growing consternation among scientists about the depletion of critical elements of the periodic table, many of which are integral to the so called "renewable energy" industry, which despite unjustified worldwide popularity is not sustainable, not safe, and not effective at doing anything at all about the most serious environmental issue ever to come before humanity, climate change.
This periodic table from the Royal Chemical Society (UK) shows the elements of concern:
The importance of elemental sustainability and critical element recovery
Note that among the actinides, uranium is included. Why Neptunium is even mentioned is something of a mystery to me. It's a synthetic element. Despite the minor criticisms and objections I may have, these papers point to an important issue before humanity, we in this generation are depleting the chemical elements that also should belong to all future generations.
There are many such periodic tables available in the scientific literature and while they all focus on important issues in sustainability, they all rely on certain assumptions and can and do vary considerably. Most rely on assumptions about the technology of element recovery, assuming that the practices of the 20th and 21st century are the only technologies that can be applied to resources.
Most of us who have been concerned with environmental sustainability will be familiar with the "peak oil" arguments that were fashionable a few years back; regrettably and at great cost to the future of humanity what were once "unconventional sources" of oil and gas, for example horizontal fracturing ("fracking" ) and oil sands were developed at great cost to and with great contempt for all future generations. Peak oil has, regrettably, not come to pass, at least not yet
Critics of the nuclear industry, which I personally regard as the only safe, sustainable, and economically feasible source of energy available to the greater bulk of humanity, the only source of energy that can eliminate human poverty without destroying the environment, often speak of "peak uranium."
I have calculated elsewhere that humanity could in fact double the energy available to the average citizen of the world - which can be expressed as a continuous average watt-year - by converting just roughly 13,000 tons of uranium to plutonium and fissioning it. Current Energy Demand; Ethical Energy Demand; Depleted Uranium and the Centuries to Come The current figure for the average continuous power per year for the average citizen of the world is 2500W, roughly 1/4 the demand of the average American. By contrast, billions of tons of carbon dioxide are dumped with no restriction into the planetary atmosphere each year, and the rate of such dumping is increasing, not decreasing, as a result of the pixilated faith in so called "renewable energy" which has not worked, is not working and will not work, despite the squandering of trillions of dollars on it in the last decade alone.
But what about peak uranium?
Actually the supply of uranium is infinite in the sense that humanity would never under any circumstances ever be able to succeed in consuming all of it that is available. This is because there are over 5 billion tons of it naturally in the earth's oceans, and any effort to remove it would be defeated by the recharge from crustal and mantle sources. (I elaborated on this at some length elsewhere: Sustaining the Wind: Is Uranium Exhaustible?
Many thousands of papers, maybe tens of thousands of papers have been published on the recovery of uranium from seawater over the last 50 or 60 years, and they are becoming more and more sophisticated and interesting. This approach is economically viable because of the extremely high energy to mass ratio of plutonium synthesized from uranium in comparison to all other forms of energy. Slightly less than 100 grams of plutonium could supply the entire lifetime needs of an individual who lived to be a hundred years old while consuming on an average continuous basis 5000 watts of power.
In my general reading in one of my favorite journals, Industrial Engineering Chemistry Research I came across an interesting one, referring to an issue in "chemical imprinting," this one: Surface Ion-Imprinted Polypropylene Nonwoven Fabric for Potential Uranium Seawater Extraction with High Selectivity over Vanadium. (Lixia Zhang†, Sen Yang†, Jun Qian†, and Daoben Hua, Ind. Eng. Chem. Res., 2017, 56 (7), pp 1860–1867)
Whenever seawater is processed to cover uranium, the element vanadium is also recovered, thus reducing the efficiency of uranium recovery. These scientists have utilized a technique that I really love, again, chemical imprinting, in which a polymer (or other extracting agent) is formed in the presence of the element (or molecule) that it is designed to separate. These scientists formed polymers in the presence of uranium so that little (nanoscale) pockets would form it that precisely fit uranium.
Some text from the paper describes this approach:
A surface ion-imprinting technique has been successfully used to remove uranium with high selectivity from aqueous solution.31?35 For instance, Preetha et al.31reported uranyl ion imprinted polymer particles for uranium removal from nuclear power reactor effluents, and Qian et al.33prepared a magnetic surface ion-imprinted microsphere through locating polymerization for selective and rapid uranium separation from aqueous solution of pH 5.0. However, there are few reports on surface ion-imprinted materials for uranium extraction from seawater until now...
In this paper, a polypropylene is functionalized by a glycidyl (epoxide) ester of methyl methacrylate using ? radiation, and further elaborated with the actual uranium recognition species, a quartenary imidazole copolymer (from a vinyl imidizaole monomer) with vinyl benzyl chloride - similar to those found in ionic liquids - with the imprinted and supporting polymers linked via a thiocarbonate functionalized intermediate.
The resulting polymer can be eluted (for uranium) with EDTA, and the reported recovery of uranium was 133.3 mg/g of the woven polymer, quite good for these kinds of polymers. The polymer showed high selectivity not only for vanadium, but also copper, zinc, iron and cobalt.
Esoteric, I know, but interesting.
= new reply since forum marked as read
