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Uranium(U), element 92, is unusual in many ways [1]. Natural Uranium is a mixture of three isotopes, 234U (0.0054%), 235U (0.72%), and 238U (99.27%) [2]. Each of these isotopes is radioactive, i.e., it decays into numerous daughter elements that are also radioactive and remain in the Uranium deposit.

Uranium and its daughter elements continue to decay forming a series of new radionuclides until decay ceases at element 82, lead (Pb) [3]. Half-lives of these radionuclides vary from very long, 4.5 billion years for U, to very short, days or less for several of the daughter elements making them extremely dangerous to human health if ingested [3]. Potentially harmful radiation emitted by these radionuclides may be in the form of alpha particles (containing two protons and two neutrons with a positive charge), beta particles (either an electron or a positron), and gamma radiation (electromagnetic radiation with neither mass nor charge but the ability to travel through air and penetrate the human body.) This element mixture is brought to the surface by U mining and must be considered a potential and long lasting environmental and health threat. Tailings from U operations are extremely toxic and will remain so for many tens of thousands of years making effective remediation efforts difficult and expensive.

In the early part of the 20th century, the periodic table ended with U. Prior to 1940, only the naturally occurring actinides (those following element 89) U, thorium (Th), and protactinium (Pa) were known. Remaining actinide and post-actinide elements have been produced artificially since then with the number of known elements being 118 in 2018 [4]. Elements following U constitute 24 % of this number. Enriched U [5], containing higher amounts of the isotope 235U (ranging from 1.5 to 4.6%), is necessary to produce nuclear energy in nuclear electric generating plants. Removing the major part of the isotope 235U from natural U produces depleted U (DU), which is less radioactive and less stable than naturally occurring U and contains the above-mentioned isotopes in the ratio 99.8% 238U, 0.2-0.3% 235U, and 0.001% 234U. DU is valuable for production of armor-penetrating bullets and for many civil purposes including production of shields for protection from irradiation in hospitals and containers for the transport of radioactive materials. Highly enriched uranium, containing more than 20% 235U, is used to make explosives, such as those used in atomic weapons.

Uranium-235 is fissile meaning that neutrons emitted during fission can cause other U-235 nuclei to fission also, releasing enormous amounts of energy [6], as was evidenced in the Hiroshima and Nagasaki atomic bomb explosions that ended World War II in August 1945. This U isotope changed the face of warfare and was responsible for the first surge in demand for U as nations sought to develop atomic weapons during the period 1945-1970. The status of atomic weapons has been a major factor in international relations since World War II and continues to merit news coverage as seen in the present U.S.-North Korea and U.S.-Iran confrontations.

The fission properties of 235U provide the basis for operation of the world’s current nuclear power stations and is the major reason why U is a valuable mineral resource in 2018. Nuclear power plants produced about 12% of the world’s electricity in 2014 [7,8]. In 2016, 13 countries relied on nuclear energy to supply at least one-quarter of their total electricity. The top countries obtaining electricity from nuclear generation facilities in 2016 were (usage in billion kWh) U.S., 805, France, 384, China 210, Russia, 178, South Korea, 154, Canada, 97, Ukraine, 81, Germany, 80, United Kingdom, 65, and Sweden, 61 [7].

Asic, et al. [2] note that all phases of U processing (mining, fuel production, reactors, and re-processing) produce high amounts of nuclear waste. Depending on the application, this waste may consist of radionuclides formed upon decay of the various U isotopes, radionuclides formed by the fission process, and accompanying toxic metals such as arsenic, cadmium, and lead in the original ore. This array of metals has caused severe environmental damage and much human suffering since mining of U ore began in earnest following World War II.

One of the most unusual findings concerning our planet’s geological history is the discovery in 1972 of natural reactors in U deposits at Oklo, Gabon, Africa [9,10]. In the early history of Earth, about two billion years ago, when the oxygen supply was limited, sufficient 235U was present with 238U that natural reactors formed. These reactors, in which U was transformed into new, lighter elements as its nucleus broke in two, functioned for several million years without going critical. The abundance of new, lighter elements formed from breakup of U at the sites is evidence that the fission of U occurred during this period. During the time the reactors were active, no meltdown or explosion occurred, presumably because groundwater acted as a neutron moderator. Most of the U in this deposit was mined in the mid-twentieth century. Truly, Uranium is a most unusual element.

In this article, I focus on global production of U by the mining industry since World War II, the environmental and human health effects of this activity worldwide, how procedures for containing waste from U mining have changed in the past 70 years although they remain of concern in many non-OECD (Organization for Economic Co-operation and Development) nations, and the need for green engineering and green chemistry processes for separation and recovery of U, individual radionuclides, and individual associated toxic metals from waste and other streams. Other aspects of U chemistry will be considered in future articles.

Uranium Production Since the World War II Era and Disposal of Generated Waste

Large amounts of U were produced immediately after World War II as several nations (i.e., U.S., USSR, U.K., France) were increasing their supply of nuclear weapons. This activity is often referred to as “the nuclear arms race.” Following implementation of the Treaty on the Non-proliferation of Nuclear Weapons in 1970, mining of U for this purpose essentially ceased. The oil shortage in the mid-1970s caused increased interest in use of nuclear energy for generation of electricity. This peaceful use of nuclear energy required large quantities of U resulting in a large upsurge in mining [8]. Since the early 2000s, there has been increased interest in nuclear electric generating plants worldwide to decrease use of fossil fuels [5,6]. The need for mining U ore to meet the electrical energy demand is expected to continue into the foreseeable future.

Uranium in its natural state is a common, mildly radioactive, heavy element that exists in low concentrations in soil, rock, and water. In many places on Earth, this element is sufficiently concentrated by natural processes that it can be profitably mined. For its primary uses in atomic weapons and nuclear power plants, U-bearing ore must be mined and then milled or concentrated. Uranium has generally been mined in one of four ways, depending on the depth and ore grade of the deposit and the associated geology. These methods are surface mining, conventional underground mining, in situ recovery (ISR), and heap leach mining. Each extraction technique has broad impacts on the human and natural environment. Environmental hazards associated with U mining and recovery operations are real and widespread but were largely ignored to the detriment of the ecosystem in the early post-World War II period [1,5,11].

Ruedig and Johnson [8] and Basu, et al. [12] have described mining of U by the ISR process, which is used for approximately 45% of global U production. In this process, U is extracted via oxidative dissolution of sandstone-hosted U ore deposits by an injected lixiviant containing oxidants (e.g., dissolved oxygen, hydrogen peroxide, sulfuric acid) and complexing agents (e.g., HCO3) that oxidize insoluble U(IV) to highly soluble U(VI), uranyl carbonate. This process mobilizes U, which may potentially contaminate water resources downstream from ISR mines during and after mining ceases. Sandstone-hosted U ore deposits comprise approximately 90% of known U resources in the U.S. and about 25% worldwide. These deposits originate from reduction of U(VI) to U(IV) when U-bearing ground waters encounter reducing conditions. ISR processes are becoming more common as they enable economic recovery of low-grade ores, do not generate tailings, and have a relatively low carbon footprint, a significant improvement over U mining practices in the World War II era [12].

It is estimated [5] that cumulative production of U through 2013 totaled approximately 2.8 million tons and involved 39 countries. This total was divided as follows: Europe, 31.3%, North America, 30.6%, Africa, 16.6%, Asia, 14.4%, Australia, 6.8%, and South and Middle America, 0.2%. A shift in the order of the countries producing U has occurred in the past 70 years. Top producers in the early post-World War II period were U.S., Canada, East Germany, South Africa, and Czechoslovakia [13]. In 2013, the top five producers were Kazakhstan (38%), Canada (16%), Australia (11%), Niger (8%), and Namibia (7%) [5]. Remaining production (20%) came from 12 nations with the U.S. at 3%. Top five countries in the use of electricity derived from U-based nuclear reactors in 2013 were (tonnes U/% of world consumption): U.S. (18,350/31%), France (8,000/13.5%), PR China (4,800/8.1%), South Korea (4,500/7.6%), and Russia (3,800/6.4%) [5]. The remaining 33% of the demand came from 26 nations. The shift in production location has occurred, in part, because of the implementation of strict environmental regulations in OECD nations. Uranium is imported today by the major consumers of it. For example, the U.S. requires importation of approximately 89% of the U required to operate its nuclear electric generating plants.

Tailings from the U milling process are normally dumped as sludge into special piles. In the past, these piles were abandoned and posed (and in some instances continue to pose) serious threats to public health and safety. The structures engineered to contain the tailings have, in some cases, eroded over time and allowed radioactive waste to leak into the surrounding ecosystem, fouling nearby groundwater and surface water and exposing entire communities to dangerous levels of radioactivity. The largest such piles in the United States and Canada contain up to 30 million tons of solid material.

A recent Moab, Utah newspaper article [14a] cites a Utah Department of Health report [14b] describing current efforts to move a Uranium Mill Tailings Remedial Action (UMTRA) site from its location on the banks of the Colorado River to a location 30 miles away in the desert where the transported tailings are placed in a Department of Energy-constructed, U.S. Nuclear Regulatory Commission approved disposal cell and capped with a nine foot thick multi-layered cover composed of native soils and rocks. It is estimated that during its years of operation (1956-1984), the Moab U ore processing mill generated approximately 16 million tons (or 12 million cubic yards) of mill tailings and tailings-contaminated soil. These tailings were pumped to an unlined impoundment near the Colorado River and adjacent to the city of Moab, home of about 5,200 residents. Eventually, the tailings accumulated a pile more than 80 feet thick. The milling process removed more than 90% of the U from the ore but radium and other radioactive decay products remained in the tailings subject to scatter by wind, rain, and other means. Despite the proximity to the Colorado River and the community of Moab, removal of the tailings to a safer location did not begin until 2009. As of 2017, the project has shipped by rail about 8.7 million tons of contaminated tailings, approximately 54% of the total. The project is estimated to take until 2025 to 2032 for completion. Ecosystem exposure to these tailings could reach at least three quarters of a century before they are completely remediated and the cost of the project will be huge, perhaps multi-billions of U.S. dollars, all paid by the taxpayer.

Area residents have expressed concern about potential health effects from the U tailings [14a,14b]. Their fears may be well founded. In a cancer incidence study released in 2018 [14b], the rate of lung and bronchial cancers in Moab among men was significantly elevated for the 2010-2014 period as well as earlier periods extending back to 1980. The increased risk ranged from 2.0 to 3.3 times higher than expected when compared to rates in the rest of the state. Risks for women were also higher but specific numbers are not given. The most important risk factor for these cancers is smoking. The smoking rate in Moab is about twice that of the rest of the state (22% vs. 10.5%). However, other significant risk factors include respiratory exposure to Radium, U, and Arsenic, all of which are components of the tailings. It is likely that both smoking and exposure to U tailings are responsible for the elevated risk factors.

Winde, et al. [5] have commented on the shift in U-production to African nations as follows: The concern we have is that the lessons learned from U-mining in the US and Europe are apparently not being heeded much, if at all, in Africa. There has been too little monitoring of human exposure and environmental contamination in conjunction with African U-mining so far. The lack of more stringent controls, combined with what we do know (for example in the South African goldfields), suggests that exposure and environmental contamination is considerable and will get worse. Thus, U-mining impacts will likely continue for centuries and longer and require substantial financial and other efforts associated with remediation and compensation, as they did in the US and Europe. Current efforts of the IAEA (International Atomic Energy Agency) and other international organizations to assist developing countries with remediation of U-legacy sites are commendable but appear to be insufficient to address the problem on the required scale. It is regrettable that the lessons of the past 70 years of U-mining appear to have often not been adequately considered during the latest expansion and growth of mining in Africa. While mining has shown, for example, in South Africa, that it can be an important agent for triggering economic development, it is imperative that it be implemented responsibly using best practice. Otherwise, short-term benefits such as tax revenue and employment will soon be annihilated by the long-term legacy effects associated with environmental pollution and their associated health risks – for which again South Africa is a prime example. There is an opportunity with new mines to apply what has been learned and take a more precautionary and preventative approach. If these lessons are to be applied to Africa, it will be critical to move quickly, given the extensive mining already underway.

The concern expressed by Winde, et al. [5] is supported by the location in Africa of nearly half of the total mass of U mill tailings (2,353 million tonnes) generated through 2013. Percentage values of mill tailings accumulated by continent, as compiled by these authors, are as follows: Africa (46%), Europe (21%), North America (19%), Asia (11%), Australia (3%), and South/Middle America (0%).

Over 58,000 tonnes of U were mined in 2014 to supply fuel for the 435 nuclear reactors operating globally [8]. In the U.S., seven operational ISR mines produce 2,300 tonnes of U per year, approximately 11% of domestic U consumption. The U.S. is a large U importer, as indicated earlier. This U powers 100 reactors that generate one-fifth of the electricity needs for the U.S. [8]. Risks associated with use of ISR processes include the contamination of drinking-water aquifers with U or other radioactive and toxic metals. Mining U is an important generator of economic activity in rural parts of Wyoming and South Dakota.

Uranium is also obtained from secondary sources, such as former nuclear weapons, re-enrichment of DU, and stockpiles [15]. Intense interest has developed in obtaining U from oceans where it is present at 3 µg/L. A host of sorbent materials have been tested for this purpose in decades of effort [15]. This source may be accessed in the future, but present processes are not economically viable.

Human Health Effects of Uranium Production

Uranium is presently mined in very large quantities to supply the needs of the nuclear electric power generating industry. Prior mining activity stemming back to the World War II period have left a legacy of severe U pollution with large externality effects. It is important that individuals worldwide be aware of these dangers, especially those who (1) work and live in these environments, (2) might drink contaminated water from leaking repositories, (3) might be exposed to deadly Radon gas, and (4) pay large amounts for remediation of waste sites through their taxes, which includes most citizens.

Brugge, et al. [3] indicate that there are no known health benefits of exposure to natural U and that a growing body of evidence of effects on humans include kidney damage, developmental defects, genetic damage, and diminished bone growth. These authors suggest that growing epidemiologic evidence of various health effects in populations living near sites that released uranium into the environment is cause to be concerned that community exposures are substantial enough to cause adverse health effects. Protecting public and worker health from the toxic effects of uranium requires identifying pathways of exposure. Many such pathways are associated with abandoned mines, waste from uranium mills, wastes leaching from uranium processing plants, and consumption of drinking water contaminated with naturally occurring uranium. A particularly important aspect of uranium toxicity is that exposure to natural uranium almost always involves concurrent multiple exposures to other toxic materials. Uranium mine tailings, and to a lesser extent yellow cake (a U concentrate powder obtained from leach solutions), contains other radionuclides in the uranium decay series and toxic, non-radioactive heavy metals.” These authors go on to say that “an ongoing study of the health effects of U is needed, especially to indigenous populations living closer to the land, to routes of exposure in communities near uranium release sites, to human epidemiology for developmental defects, and to health effects at or below the established exposure standards.

Robertson, et al. [16] observe that Radon (222Rn) is a naturally occurring radioactive gas that is responsible for approximately half of the human annual background radiation exposure globally. Chronic exposure to radon and its decay products is estimated to be the second leading cause of lung cancer behind smoking, and links to other forms of neoplasms have been postulated. Ionizing radiation emitted during the radioactive decay of radon and its progeny can induce a variety of cytogenetic effects that can be biologically damaging and result in an increased risk of carcinogenesis. Suggested effects produced as a result of alpha particle exposure from radon include mutations, chromosome aberrations, generation of reactive oxygen species, modification of the cell cycle, up or down regulation of cytokines and the increased production of proteins associated with cell-cycle regulation and carcinogenesis.

Moore [17] has reported an extensive study of the “radium girls” who were exposed to Radium (Ra) while licking brushes dipped in Radium solutions prior to painting watch and clock dials. This exposure occurred in the early to mid-part of the 20th century in the U.S. Exposure to Ra by this process allowed this radionuclide to enter the body where it was deposited in bones replacing calcium. Radium emits alpha particles which cause horrific destructive effects on bony structures. These effects are documented by Moore and include disintegration of jawbones, loss of teeth, extreme pain in extremities and back, and cancer among others. As in the case of the Navajo people discussed below, the girls were not told about the hazards. Even as they suffered, they were assured by their employers that Ra was safe and that it, if anything, was beneficial to their health, as was widely believed in the early 20th century. Exposure to Ra in U waste sites is not expected to be this extreme, but ingestion through drinking water and vegetables grown in contaminated soil could have severe negative effects if the Ra enters the body.

Frisbe, et al. [18] have disputed the action of the World Health Organization (WHO) to set the drinking water guideline for U at 30 µg L-1. These authors argue that this level may not protect children, people with predispositions to hypertension or osteoporosis, people with chronic kidney disease, and anyone with a long exposure to the drinking water source. A further concern would be the level of radionuclides and toxic metals in any drinking water source containing U derived from mining waste and processing. This concern is not addressed by considering only the U concentration level.

Health Effects of Uranium mining on the Navajo Nation Population [19]

The four-corners area comprising the states of Utah, Arizona, New Mexico, and Colorado contains some of the richest deposits of U on Earth. Immediately after World War II, these deposits and others globally were accessed for the large amounts of U required to supply the needs of emerging nuclear powers for construction of their atomic weapons [5]. The four-corners area was sparsely populated in the mid-20th century, primarily by native American nations, such as the Navajo. Decades of U mining, beginning in the mid-1940s, have dotted the landscape of the Navajo Nation with piles of contaminated mine waste. The Environmental Protection Agency (EPA) has mapped over 500 abandoned U mines on the reservation, ranging from small holes dug by individual prospectors to large commercial mining operations. Individuals who worked at these mines, their families, and those who drank water, ate food grown on contaminated soil, and breathed air contaminated with gaseous products such as radon have been at risk for decades and this risk extends into the future [20].

Arnold [19] and Dawson [20] observe that, initially, as mining outfits began moving onto their land in the 1940s in the “uranium rush” the Navajo people did not know what radiation was and had no idea that it could be dangerous. There was no word in the Navajo language for “radioactivity.” Of course, at the time it is likely that few people in the U.S. knew about radioactivity other than that it had been released a few years earlier in the Hiroshima and Nagasaki atomic bomb explosions and it was dangerous. The mines offered employment at what were considered fantastic wages to a population that was living in extreme poverty. No mention was made of the poisonous mix that the workers would encounter in the mines [20]. Breathing carcinogenic radon gas, showering in radioactive water, and spreading radionuclides to family members when work clothes were washed was never recognized as being dangerous because the Navajo people were ignorant of the hazard. Children played in pools of radioactive water that had been pumped out of the mines and collected in ponds. Years later, one person remembered that the contaminated water looked and tasted perfectly clean [19]. Families used this water for cooking, drinking, and cleaning. Hogans and corrals were built with mine wastes, as were roads.

On July 16, 1979, the largest nuclear spill in U.S. history occurred when a dam broke at the United Nuclear Corporation mill containment pond at the Northeast Church Rock U mine in New Mexico. Ninety-four million gallons of mill process effluent and 1,100 tons of tailings, an acidic, radioactive sludge, poured into a large arroyo that emptied into the Puerco River [11,19]. This area was declared a Superfund site in 1983 and continues to this day to cause radiation survey instruments to register high levels of radioactive contamination. To put this spill in perspective, it occurred less than four months after the partial meltdown of the Three Mile Island nuclear reactor in Pennsylvania, released three times as much radiation, and received a tiny fraction of the news coverage. However, the Church Rock event attracted a great deal of corporate and government attention and, finally, the Navajo people learned the awful truth that the U mines and their waste product repositories were poisoning people, had done so for decades, and would continue to do so far into the future. Dawson [20] provides a case study of Navajo U workers and the health effects of occupational illnesses contracted during this period. The EPA and Navajo Nation Environmental Protection Agency have been working together for many years to remediate this Superfund site.

Winde, et al. [5] summarize the history and economic impact of U mining in the four-corners area as follows: Today, the US government frames this history as a legacy from uranium mining (and other nuclear production facilities). It is a legacy that resulted in considerable health and economic consequences and that could have been avoided. A measure of both health and economic impact is that the federal compensation program in the US for former miners and their families has awarded claims to 7,749 miners and mill workers as of March 2015. The value of these awards is USD 774 million, i.e. an average of about USD 100,000 per family. However, the economic and health impacts are larger than simply those of the miners. Almost certainly, community members who did not work in the mines also suffered adverse health outcomes, although we are just beginning to understand their cause-effect relationships, nature and extent. Environmental contamination generated by mining and milling has required extensive remediation efforts that have cost at least another USD 5 billion with efforts ongoing into the future. Most of these costs have, so far, been paid by taxpayers.

The Church Rock example reinforces the green chemistry principle that it is cheaper to prevent waste than to clean it up after it is formed. It is equally important to note that the producers of the waste and downstream customers of the U products, generally, do not pay for the cleanup operations. Rather, the negative externality effects of the spill and subsequent clean-up are borne by taxpayers. Furthermore, unique Navajo cultural beliefs and economic factors impacted whether workers and families accessed health, legal, and social services often to the detriment of the individuals involved [20]. These realities should be kept in mind by legislators and government administrators as they make and administrate laws and regulations designed to protect the public.

As early as 1879, researchers observed that U miners in Europe showed significantly elevated levels of lung cancer. Lung disease had been associated with mining of pitchblende as early as the 16th century in Europe. Uranium is a primary constituent of pitchblende, but this fact was unknown in earlier times, since this element was not discovered until 1789, and radioactivity was not discovered until 1896 by Becquerel making it impossible in the 16th century to associate lung disease with an undiscovered element that had the unsuspected and unusual property of self-disintegration to form deadly new elements. By the 1930s, scientists suspected U as the culprit in the development of this type of lung cancer. By the late 1940s and early 1950s, scientists had identified radon as the causative agent for lung cancer onset in underground miners [5]. There is little excuse for the U.S. Government and industrial companies not transmitting known information on the risks associated with U mining and processing to the Navajo people in the decades following World War II [19].

Within a decade of the start of U mining activities, Navajo miners were being diagnosed with lung cancer [18,21]. This disease was rare among the Navajo people, which was a largely nonsmoking population. Researchers in the following decades, using case-controlled studies established radiation exposure as the cause of lung cancer in these workers. Arnold [19] summarizes the studies as follows: Decades after their exposure ended, standardized mortality ratios and relative risks for lung cancer and other respiratory problems were still nearly four times higher in Navajo miners than in nonminers.

The Navajo situation provides the opportunity to study community exposure to U [19]. Ore was transported to a mill, where it was crushed and soaked in sulfuric acid to extract the U. More chemicals were added to precipitate out the U, leaving a radioactive slurry for disposal. This slurry was frequently stored in large, unlined ponds. Chris Shuey, an environmental health specialist with the Southwest Research and Information Center in Albuquerque comments [19]: Mining in the area had mostly ceased by the mid-1960s. Today, after decades of inactivity, the uranium from these ponds, waste and tailings piles, and the mines themselves is still present in highly chemically soluble forms that have been leaching into the area’s drinking water according to water testing by the EPA and the Army Corps of Engineers.

Besides radon and lung cancer, significant risks from exposure to these ores include cancers caused by radium emanations; cancer from arsenic exposure; developmental and other effects from exposure to lead; impairment of kidney function from U exposure, and inheritable genetic effects, among others. The four-corners area is only one of many regions where a legacy of early U mining exists. Saxony and Bohemia in the former East Germany were the site of U-ore production during the Cold War. A joint Soviet-German company during the period 1947-1990 produced 231,000 tons of U-ore making it the 3rd largest producer after the U.S. and Canada [5]. Remediation of the contaminated sites in these regions has taken longer than planned. Total costs for the clean-up are expected to total at least 8 billion euros. Other major sites of U pollution from the World War II era have been summarized by Winde, et al. [5].

Dewar, et al. [22] have reviewed effects resulting from generation of radioactive and other waste during U mining and processing, particularly as they apply to mining and processing of U ore in Canada. These authors express concern that health standards are set by physicists and industries, based on financial and technological convenience, rather than by those educated in and committed to public health and safety. This concern is important and points out the need for cooperative, informed involvement of citizens, public officials, and industry before U mines are opened, during their operation, and following their closure. In addition to known effects of U and its radioactive daughter products in contaminated air, water, and soil, these authors indicate that long-term problems are expected to include cancers, fertility problems and inheritable defects as background radiation increases. Examples are given of genetic effects in humans.

Asic, et al. [2] have summarized and discussed the current state of knowledge on chemical toxicity and radioactivity of depleted uranium and the effect of these properties on living systems and cell lines. This study draws attention to chromosomal aberrations, DNA damage and DNA breaks, and micronuclei formation and epigenetic changes in living systems. Depleted uranium species have been considered as a possible causative factor in these processes.

Environmental Impacts of Uranium Mining in Australia.

Heard [23] has provided an account of present U mining in Australia, compared present and past mining practices, and has contrasted present environmentally responsible U mining with present environmentally irresponsible lithium and rare earth element mining. He notes that past U mining in Australia has had significant environmental impacts on the environment. However, he provides evidence that present practices have improved to the point that they are almost unrecognizable from those in early days of U mining. Particularly, ISR processes are delivering world-leading environmental outcomes for U mining. He contrasts advances in U mining and processing in Australia with present lithium and rare earth metal mining and processing, which produce extensive waste and environmental damage. His summary provides good counsel for effective mining practices of U and other metals. The finding of this review is clear: the nature of mining practice and regulation are the key determinants of environmental outcomes. The mineral in question plays a far lesser role if any. All mining practices demand proper scrutiny, regulation and the evolution and adoption of leading practices to ensure adequate planning for environmental protection and clear forward liabilities for the management of the site through operations, progressive rehabilitation, closure, and monitoring phases. Regulators should apply scrutiny dispassionately and even-handedly. Similarly, activist organisations should seek, on the basis of evidence, to focus on the areas of most serious environmental concern to bring about lasting improvements and better outcomes, regardless of where these impacts occur in the world and regardless of the end use of the commodity being pursued.

Green Engineering and Green Chemistry Separations and Recovery

Molecular Recognition Technology (MRT) has a wide range of applications related to metal separations and recovery in various aspects of U mining and processing, radionuclide separation and recovery, and separation and recovery of toxic metals associated with U mining. These applications and the basis of MRT have been presented and discussed [24-28].

MRT separation and recovery processes are based on green engineering and green chemistry principles [26,27]. The separation process is performed in column format. The columns are loaded with SuperLig® resins consisting of a highly metal-selective ligand attached via a tether to silica gel or another substrate particle. A feed solution containing the target and impurity metals is added to the column, the target metal is selectively bound to the SuperLig® resin, and the remaining solution goes to raffinate. Following washing of the column to remove residual feed solution, the bound metal is eluted using a small quantity of eluate and recovered in concentrated form. Besides high metal selectivity, the MRT process features rapid kinetics of metal-ligand binding and release, simple elution chemistry, and ability to recover metals present in the feed solutions at extremely low levels of mg L-1 or less. High selectivity means that most separations are achieved in a single pass eliminating need for extensive processing downstream to obtain pure products. Recovery rates of metals in the feed solution are 99% or higher eliminating wastage of the target metal in tailings. No organic solvents or hazardous chemicals are used in MRT processes. These features make MRT separation and recovery processes very attractive compared to conventional separation processes from the standpoint of reduced capital and operating expenses [26, 29].

The MRT process can be used to extract and purify U from aqueous mine process streams containing significant amounts of metal impurities, such as copper and iron [24]. Use of MRT dramatically simplifies the flow sheet for U recovery from these streams because of the high selectivity for U over competing metals. Two MRT products are available for U separation, SuperLig® 171 for separation of U(VI) from acidic solutions of pH 0-1, and SuperLig® 191 for separation of uranyl ion (UO22+) from solutions of pH 6-12. Elution of U is achieved using sulfuric acid or other mineral acids.

MRT processes have removal capabilities for a wide range of metals, including those found with U and its byproducts [24-29]. These metals include base metals, such as Rhenium, Molybdenum, Copper, Zinc, Nickel, Cobalt, and Tin; and toxic metals, such as Mercury, Lead, Cadmium, and Arsenic. MRT processes have proven capabilities in the separation and recovery of a variety of elements found in decay products of U, such as Plutonium, Thorium,  Radium, and Bismuth [27,30-33], as well as elements  produced in fission of U, such as Cesium, Strontium, Technetium, Plutonium, Americium, Palladium, and Iodine [27,28,30,34]. Analytical determination of many of these metals is enhanced using MRT processes for selective separation of target metals from mixtures for analysis by inductively coupled plasma (ICP) or ultra violet spectrometry [30-34].

Conclusions

Mining and processing of U ores have left a global legacy of widespread pollution that has had and continues to have significant environmental and human health negative externality effects. These effects derive from U itself; its radioactive daughter products; accompanying toxic metals; and fission products. Many sites in the U.S. have superfund status, but remediation progress is slow and enormously expensive as exemplified by the translocation of U tailings from Moab, Utah a distance of 30 miles to Crescent Junction Utah. The burden for cleanup is placed on the taxpayer. The presence of radioactive species in waste sites compounds the problem, since radionuclides emit toxic radiation for thousands of years and have the potential to enter groundwater and aquifers. Outcomes for U mining and processing have improved markedly in recent decades in OECD nations, but are of concern in non-OECD nations, such as those in Africa where existing environmental regulations may be weak or poorly enforced. It is desirable, wherever possible, to replace low metal selectivity separation processes with green chemistry/green engineering procedures, such as MRT. Increasingly stringent environmental regulations worldwide portend a shift from conventional processes, such as solvent extraction, ion exchange, coagulation, flocculation, and sulfide precipitation to cleaner processes. The goal should be to separate and recover for reuse or proper disposal all target and impurity metals to prevent the potential environmental and health damage they can do when released to the commons.

Reed M. IZATT (Investor Intel)

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