Campbell and 2 co-authors, of the Exxon Nuclear Company, Inc., reported in early 1979 that the objectives for this study were:
1) to evaluate the territorial coastal waters of the United States of America as a uranium resource and
2) to select one or more sites for plants designed for the large scale extraction of uranium from these waters. The target production scale was to be on the order of 500-1000 metric tons (hereinafter noted as "tonnes") of uranium per year.
These objectives were the initial stages toward the further objectives of the overall study which were to select a process for the extraction and to determine the technical, economic and environmental feasibility of such an operation aimed at meeting a significant part of the Nation's energy needs in the future. A multidisciplinary group was assembled under the project management of Exxon Nuclear Company (ENC) to attain these objectives. Oregon State University (OSU) under subcontract to ENC provided scientific and technical expertise in oceanography and nuclear engineering available in its School of Oceanography and Department of Nuclear Engineering. Expertise in the Departments of Chemistry and Chemical Engineering was utilized as well.
Vitro Engineering Corporation (VEC) developed engineering flowsheets and architectural design. ENC provided overall project management and coordination and ability to transfer technology development to operating systems. Cost estimating, operating and environmental experience, as well as economic modelling were also specifically provided by Exxon Nuclear Company.
In an endeavor to assure the technical reliability of this report, a technical review committee composed of experts from the above mentioned fields who were not involved in this study was asked to review and comment on all aspects of the study three times during the course of the project. Technical Review Committee comments were taken very seriously and incorporated into the study in that much of the prior work on recovering uranium from seawater was reported by European and Japanese scientists and engineers, trips were taken to these locations to learn of the state-of-the-art. These visits were most helpful in providing a more substantial basis for the many decisions needed in arriving at sound conclusions and facility designs.
The results of the project have been recorded in two documents, each consisting of two volumes. The first document, of which this is Volume I, treats the evaluation of U. S. coastal ocean waters as a uranium resource and the selection of a suitable site for a large-scale extraction plant, noted above as the first two objectives of this study.
Volume II of this document contains the literature citations, located in this study, which are pertinent to the resource evaluation and site selection. 471 literature citations are presented there together with author, geographic and subject indices. Volume II will often be cited herein as "The Bibliography".
The companion document to this one treats, in Volume I, the selection of a chemical process suitable for large scale extraction of uranium from seawater, together with the technical, economic and environmental considerations involved in plant construction. It will often be referred to in this one as "the Feasibility Study."
Volume II of that document contains an analogous bibliography and indices. Before turning to the content of This Study, it should be noted that it was prepared in close collaboration with all the other components of the overall study, particularly with respect to site selection considerations.
Resource Evaluation
Examination of the marine and physical chemical literature revealed nothing to weaken the conception currently held by marine chemists that about 90% of the uranium in seawater occurs in the dissolved state as negatively charged uranyl-carbonate complex ions. Somewhat less than 2% occurs as negatively charged uranyl hydroxide complex ions. Other forms such as overall neutrally charged chemical forms may exist but probably in relative amounts much less than one percent.
Uranium behaves as what the oceanographer calls a conservative constituent of the oceans: It remains dissolved in the oceans on the average for periods of time which are very long compared to the circulation and mixing times of the deep waters of the oceans. This results from the annual supply and removal rates of uranium to and from the sea being very small fractions of the total amount contained therein. As a result, uranium is distributed much like sea salt in the oceans and to maximize the local resource, one should seek a location where the salinity is high. Although the concentration of uranium is quite low, about 3.3 ppb (parts per billion) in seawater of average oceanic salinity, the amount present in the total volume of the oceans is very great, some 4.5 billion tonnes. Of this, perhaps only that uranium contained in the upper 100 meters or so of the surface well-mixed layer should be considered accessible for recovery, some 160 million tonnes.
Practically speaking, the amount contained in the ocean surface layers is unlimited with respect to large scale extraction in the foreseeable future. This results from the replenishment by continental weathering and river runoff being much larger than foreseeable extraction rates.
Our study indicated that open-ocean seawater acquired for the purpose of uranium extraction would be a more favorable resource than would rivers entering the sea, the cooling water of present or planned power plants (either fossil fuel or nuclear), or the feed or effluent streams of existing plants producing other products such as magnesium, bromine, or potable and/or agricultural water from seawater. The reasons for these conclusions are:
1) In the case of rivers and streams, production on the scale of a thousand tonnes of uranium per year would require total extraction of the uranium from a major fraction of even our largest river, the Mississippi. Further, the sediment load carried by any large river would incapacitate any known process for the extraction.
2) In the case of existing power or material production plants utilizing seawater as coolant or feed, the scales are simply too small.
Our conclusion relative to marine resources is that only seawater pumped or otherwise accessed for the purpose of uranium extraction would constitute a viable resource.
Volume II
This Volume is the bibliography to Volume I and contains 471 references pertaining to the evaluation of U. S. territorial ocean waters as a potential uranium
resource and to the selection of a site for a plant designed for the large scale extraction of uranium from seawater. The work was sponsored by the U. S. Department of Energy.
Both Volume I and the present bibliography (Volume II) together with two additional documents form the final report of the project. The other two
documents deal with the selection of an industrial process for the extraction of uranium from seawater, the design of a suitable plant to carry out the process, and a study of the economic feasibility of such an endeavor. The other two documents are:
"EXTRACTION OF URANIUM FROM SEAWATER: CHEMICAL PROCESS AND PLANT DESIGN FEASIBILITY STUDY" by M. H. Campbell, J. M. Frame,
N. D. Dudey, G. R. Kiel, V. Mesec, F. W. Woodfield, S. E. Binney, M. R. Jante, R. C. Anderson, and G. T. Clark (here).
and
"SELECTED BIBLIOGRAPHY FOR THE EXTRACTION OF URANIUM FROM SEAWATER: CHEMICAL PROCESS AND PLANT DESIGN FEASIBILITY STUDY" by S. E. Binney, S. Polkinghorne, M. R. Jante, M. R. Rodman, A. C.-T. Chen, and L. I. Gordon.
These documents are Exxon Nuclear Company Report Number XN-RT-15, Volumes I and II and Oregon State University Department of Nuclear Engineering
Report Number OSU-NE-T901, Volumes I and II.
This bibliography was prepared using machine literature retrieval, bibliographic, and word processing systems at Oregon State University. The literature cited is listed by author with indices to the author's countries, geographic areas of study, and to a set of keywords to the subject matter.
Volume II is (here).
CONCLUSIONS
The possibility of recovering uranium from the sea has been considered on the basis of the existing literature. Several important conclusions are now summarized under the topics, resource evaluation and site selection.
9.1 Resource Evaluation:
a) The concentration of uranium in the oceans appears to be linearly correlated with salinity. At a salinity of 35 ppt, the uranium concentration is 3.3 PPB, which represents oceanic uranium content of 4 billion tonnes. The accessible ocean currents can supply virtually unlimited amounts of uranium for extraction. For instance, the Gulf Stream circulates over ten million tonnes of uranium annually. The cost at which the uranium is extracted from seawater might very well serve as a baseline maximum cost of uranium to be considered in the future [Ref 54, see Volume II].
b) Most of the uranium in seawater forms anionic uranyl carbonate complex ions. At 25°c and pH 8.1, approximately 98% of the uranium in seawater combines with carbonate ions to form UO2(CO3)3 and 1.7% of the uranium forms UO2(C03)34- Two species of hydroxides; UO2(OH)3 and UO2(OH)2 take up the rest of the uranium.
c) The supply of uranium to the oceans is continuous at a rate of approximately 9,000 tonnes per year by continental weathering and river runoff. The input is to the surface layers of the sea and is, therefore, accessible.
d) River waters in general have lower uranium concentrations than seawater. Some rivers do have high uranium concentrations but their volumes of flow are so much less than ocean currents that the rivers are a less favorable uranium resource. For instance, the Mississippi River discharges only 550 tonnes of uranium annually compared to the ten million tonnes circulated by the Gulf Stream.
e) Shells, sediments and other marine deposits have variable concentrations of uranium. These concentrations are usually lower than those in ores which occur on land and for this reason their materials do not seem to constitute attractive resources at present.
f) It was concluded that it is impractical to combine desalination plants with seawater uranium extraction facilities because of the limited capacity of the desalination plants. The available uranium production from the largest desalination plants under consideration today is only 1 tonne per year [Ref 242].
g) Coastal power plants circulate limited amounts of seawater for cooling purposes. Again the amounts are too small to be considered useful in the present context. Further, these plants are often located in estuaries where uranium depleted water would be trapped and more or less poorly flushed. Even assuming continuous uranium supply and 100$ recovery, the U. S. coastal power plants would have a total capacity of producing only 70 tonnes of uranium annually.
h) Certain species of marine organisms have the ability to concentrate uranium in their tissues. Considering the observed concentration factors observed so far it is at present impractical to "farm and harvest" marine organisms on the scale under consideration here.
i) Vanadium appears to be the only possible co-product although it is economically unfavorable to extract at present. This subject is discussed in the Feasibility Study.
9.2 Site Selection
a) A number of stringent conditions to be met for plant siting were discussed. The important ones are as follows: Constant, dependable uranium supply; high naturally occurring seawater salinity and temperature; low risk of fouling; favorable topography, geography, demography and geology; mild climate; low use conflicts and minimal environmental impact.
b) Floating plants and platforms were considered unfavorable in this feasibility study of uranium extraction from seawater. Therefore, potential sites for such configurations have not been treated in this report. Although this is also discussed more fully in the Feasibility Study, it may be stated here that experience with large scale operations of this type was inadequate to permit an economic feasibility estimate. However, future improvement in technology may favor these schemes.
c) Cook Inlet, Alaska was identified as the most likely plant site if a tidal system was to be used. The site was described in detail
although it was recognized that a tidal system was rated as the second choice in the Feasibility Study.
Punta Yabucoa, Puerto Rico was identified as the prime choice for a plant site for this feasibility study. The important features that
led to this choice were:
- The location is less than three kilometers from the continental shelf edge where the warm, strong and steady Antilles Current brings a constant resupply of fresh seawater to the bay and takes away the plant discharge.
- An area of more than six square kilometers of the river flood plain adjacent to the shoreline is less than three meters above mean sea level.
- An estimated 40 million gallons (150,000 cubic meters) per day of fresh water is available for process use. Storage reservoirs that
would double the supply are feasible (See Feasibility Study). - The present human population density of the area is low. Several topics requiring further research and development were revealed during the execution of this project. They were identified and discussed in the previous chapter.
Briefly, they are:
- Much better measurements of the association constants of the complex uranium chemical species which occur in seawater. No direct measurements over the range of seawater temperatures, or indeed directly in seawater itself have ever been made.
- Direct measurements of the actual uranium concentrations in the local waters of the most favorable U. S. territorial sites should be made as soon as possible. Analogous measurements must be made for any potential co-products.
- Concomitant data also required for potential sites include the oceanic chemical parameters which would affect the extraction process, either for the better or worse, e.g. dissolved oxygen levels, pH and oxidation-reduction potential of the sea water, trace metals which might interfere with the extraction and as a baseline against which to monitor contamination by the plant, inorganic and biological fouling parameters, etc.
- Biological concentration of uranium from seawater should be studied both as a potential, if low volume, source and for the possibility it offers of potentially improved inorganic extraction processes.
- Site selection information is in general much too meager for the needs of accurately evaluating the feasibility of the oceanic uranium resource.
- Detailed information on local currents, meteorological, climatic, geographic, and geologic data are required. Much undoubtedly exists which could not be accessed and collated for this limited study, and more should be done in that regard.
- The large volume of the process streams considered in this study constitute a very significant fraction of the local currents at any site considered. The effects of such process streams should be modelled hydrologically, and considered from geological, biological, and chemical viewpoints as well.
- Environmental and societal impacts will also have to be treated in great depth considering the requisite huge physical scale of the extraction plant required. Although it appears that these impacts are amenable to mitigation by current technology, certainly the scale considered here will challenge that technology.
- Much better measurements of the association constants of the complex uranium chemical species which occur in seawater. No direct measurements over the range of seawater temperatures, or indeed directly in seawater itself have ever been made.
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