Technically, it is possible to separate uranium from seawater. This design paper seeks to propose a process intensified way to separate uranium from seawater using amidoxime containing polymer due to the high affinity of the uranyl-carbonate complex towards the polyamidoxime resin. The process justification was based on the economic criteria: production cost, physicochemical criteria: concentration and reactivity, technical criteria: extracting methods from a complex aqueous system.
The separation process firstly is the adsorption of uranyl ions using ionic exchange resin in the form of a chelating polymer adsorbent. A buoyant platform with adsorbent polymer made of polyethylene fibres that comes into contact directly with seawater powered by a wind turbine which is mounted on top of the platform, continuously takes the adsorbent from the seawater after campaign time through an elution and regeneration process and then returns it to the seawater for reuse. After the adsorbent has been loaded with uranyl ions, additional downstream processes are explored to recover the uranium including cleansing of the adsorption polymer to remove organic materials, desorption: elution of the adsorbed uranium ions from the adsorption polymer with a suitable solution, purification of the eluent: removal of other desorbed compounds, concentrating the solution, solvent extraction of uranium from the solution with a mixture of an organic solvent and a specific complexing agent and finally conversion into yellow cake or uranium oxide U_3 0_8. Next, factors that go into the Uranium separation cost and financial justifications have been included. In the future, we recommend researchers to make use of organically sourced, biodegradable substrates such as chitin which could be a good source of green chemistry alternative to conventional plastic polymers that represents a potential source of an uneasy degradable solid pollutant.
Table of Contents
ABSTRACT
INTRODUCTION
Overview
Aim and Objectives
LITERATURE REVIEW
Uranium Ion Bonding Mechanism
Alternative Methods of Separation
Separation Method
Constraints
ANALYSIS SECTION
Process Selection and Description
Process Selection Justification
Equipment Design and Specification
Wind Turbine and Buoyant Platform
Amidoxime polymer synthesis
Elution and Regeneration Flow Chart
Elution and Regeneration Overview
Heat and Mass Requirement
Plant Availability and Location
Environmental Impact
Pipework and Pumping Systems
Health and Safety
Safety Protection Devices
Control Strategies and Systems
Capital Cost Estimations and Financial Justification
RECOMMENDATION
CONCLUSION
REFERENCES
Disclaimer
The ideas and design of this project should not be used without first assessing and consulting a professional because it based on theoretical information gathered from literature sources. Our thoughts and ideas could change from time to time as we learn and acquire more knowledge in this field. It should be noted that the conclusions of these design project are highly hypothetical sequence of processes and are based on unproven extrapolations and untried technology.
ABSTRACT
Technically, it is possible to separate uranium from seawater. This design paper seeks to propose a process intensified way to separate uranium from seawater using amidoxime containing polymer due to the high affinity of the uranyl-carbonate complex towards the polyamidoxime resin. The process justification was based on the economic criteria: production cost, physicochemical criteria: concentration and reactivity, technical criteria: extracting methods from a complex aqueous system. The separation process firstly is the adsorption of uranyl ions using ionic exchange resin in the form of a chelating polymer adsorbent. A buoyant platform with adsorbent polymer made of polyethylene fibres that comes into contact directly with sea water powered by a wind turbine which is mounted on top of the platform, continuously takes the adsorbent from the seawater after campaign time through an elution and regeneration process and then returns it to the seawater for reuse. After the adsorbent has been loaded with uranyl ions, additional downstream processes is explored to recover the uranium including cleansing of the adsorption polymer to remove organic materials, desorption: elution of the adsorbed uranium ions from the adsorption polymer with a suitable solution, purification of the eluent: removal of other desorbed compounds, concentrating the solution, solvent extraction of uranium from the solution with a mixture of an organic solvent and a specific complexing agent and finally conversion into yellow cake or uranium oxide U308. Next, factors that goes into the Uranium separation cost and financial justifications have been included. In future, we recommend researchers to make use of organically sourced, biodegradable substrates such as chitin which could be a good source of green chemistry alternative to conventional plastic polymers that represents a potential source of an uneasy degradable solid pollutant.
Keywords: Uranium extraction Uranyl ion; Seawater; Adsorption polymer; Adsorption kinetics; Separation; Reusability; Wind turbine; buoyant platform; Chelating ligand.
List of Tables
Table 1 Health and Safety
Table 2 Safety Protection Devices
Table 3 Control Strategies and System
List of Figures
Figure 1: An image of how the amidoxime ligands binds with the Uranyl cation to form a chelate complex. Adapted from “How Amidoximate Binds the Uranyl Cation”by Vukovic, S.; Watson, L. A; Kang, S. O.; Custelcean, R.; Hay, B. P. Inorganic Chemistry (2012), 51, page 3855-3859
Figure 2: An image of the structure of UO2CO334 — complex when it is bonded and how it exists in the seawater. Adapted from “Structure of,UO2CO334 —complex” by H. Sodaye et al (2009), page 9-32
Figure 3: An image of a three-dimensional view of continuous uranium separation system with adsorbent belt looped around the turbine mast proposed by Picard et al. (2014) Adapted from “Extraction of Uranium from Seawater: Design and Testing of a Symbiotic System” Nuclear Technology, 188(2), 2014 by M. Picard, C. Baelden, Y. Wu, L. Chang, and A H. Slocum
Figure 4: A image of the Process flow chart of the separation process of uranium from seawater using amidoxime adsorbents designed for the purpose of this work
Figure 5: An image of the front view and side view equipment design of wind turbine and buoyant platform designed for the purpose of this work
Figure 6: An image of how a trunk polymer is synthesised to form an amidoxime polymer used as an ion exchanger resin for the separation of uranium. Adapted from “Current Status of Uranium Collection from Seawater” presented at Lawrence Berkeley National Laboratory, by Tamada, M et al., (2010)
Figure 7: An image of the flow chart of elution and regeneration process using KHCO3 and NaOH treatment for the process. This flow chart was designed for the purpose of this work
Figure 8: An image of a graph for the estimation of $555/kg of uranium separation cost using estimated figures for the purpose of this work
Figure 9: An image of a graph for the estimation of equipment cost using estimated figures for the purpose of this work
Figure 10: An image of a graph for the chemical cost of adsorbent synthesis using estimated figures for the purpose of this work
Figure 11: An image of a graph for the breakeven and payback period analysis using estimated figures for the purpose of this work
INTRODUCTION
Overview
Dissolved uranium content in seawater is estimated to be 4.5 billion metric tons. It is approximately 3.3 ppb, and its concentration varies in direct proportion to changes in salinity. Since seawater is slightly basic under normal coastal conditions (pH 8.0±0.4) uranium exists primarily as t/O2(CO3) (Tamada, 2009). Currently, 61000 metric tonnes of uranium are needed annually to meet global energy demand (Tamada, 2009). Since it represents an essentially unlimited supply, this sustainable source if convincingly shown to be recoverable at a suitable cost, environmentally friendly and energy efficient way, can establish a huge alternative to conventional methods for example, one (1) gram of uranium- 235 can theoretically produce through nuclear fission, as much energy as burning 1.5 million grams of coal (Einsley, 2001).
Aim and Objectives
To propose a process intensified design project for separation of uranium from seawater.
To make recommendations for further design improvement for future research works.
LITERATURE REVIEW
Uranium Ion Bonding Mechanism
The dominant form of the uranyl ion in seawater is the tricarbonate complex,^O2(CO3) which associates with Ca[2]+, a major cation in seawater, to form a Ca2U02(C03) (aq) 3 ternary complex, the dominant uranyl species in seawater. The uranyl ion binds to the two adjacent amidoxime ligands on the adsorbent material to form a chelate complex.
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Figure 1
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Figure 2
Figure 1: An image of how the amidoxime ligands binds with the Uranyl cation to form a chelate complex. Adapted from “How Amidoximate Binds the Uranyl Cation”by Vukovic, S.; Watson, L. A; Kang, S. O.; Custelcean, R.; Hay, B. P. Inorganic Chemistry (2012), 51, page 3855-3859.
Figure 2: An image of the structure of UO2(CO3)2 complex when it is bonded and how it exists in the seawater. Adapted from “Structure of,UO2(CO3)| complex” by H. Sodaye et al (2009), page 9-32.
Alternative Methods of Separation
Several methods for separation of uranium on large scale have been explored including solvent extraction, ion exchange, foam separation, co-precipitation, biological separation and adsorption (Sodaye et al, 2007). Adsorption method using amidoxime containing polymer drew attention due to the high affinity of the uranyl-carbonate complex towards the polyamidoxime resin.
Separation Method
Selective adsorption of (U02)[2]+via chelating polymer adsorbent by Kim et al (2013) has proven to be a promising field and interest to most researchers due to cost, adsorption capacity and environmental footprints (Zhang et al 2013; Seko et al 2003 and Anivudhan et al 2011). Membrane filtration, coagulation and precipitation were found to have issues as high operating cost, durability and toxicity (Kanno et al 1984; Van Reis et al 2007).
Constraints
The extremely low concentration of uranium and the relatively high concentrations of other number of dissolved chemical species in seawater have important consequences on the adsorption kinetics that would be able to separate uranium from seawater. For example, some ions particularly vanadium and iron are relatively adsorbed in large whilst amounts of calcium and magnesium are adsorbed in small amounts. This may necessitate a complicated elution process (Sodaye et al, 2007).
ANALYSIS SECTION
Process Selection and Description
Selective adsorption via chelating polymer will be used in the extraction of uranium from seawater. A platform with buoyant braid adsorbent made of polyethylene fibres on a polypropylene trunk that has direct contact with sea water powered by a floating wind turbine which continuously takes the adsorbent from the sea after campaign time through an elution and regeneration process and then returns it to the sea for reuse. The elution, regeneration and purification plant are housed on the upper platform out of the seawater.
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Figure 3: An image of a three-dimensional view of continuous uranium separation system with adsorbent belt looped around the turbine mast proposed by Picard et al. (2014). Adapted from “Extraction of Uranium from Seawater: Design and Testing of a Symbiotic System” Nuclear Technology, 188(2), 2014 by M. Picard, C. Baelden, Y. Wu, L. Chang, and A. H. Slocum.
Figure 4: A image of the Process flow chart of the separation process of uranium from seawater using amidoxime adsorbents designed for the purpose of this work.
Process Selection Justification
The uranium separation process consists of three basic steps: adsorbent synthesis, adsorbent deployment, and elution and purification of uranium. The adsorbent material is reusable, though not indefinitely, and it undergoes an autonomous process which consist of multiple deployment, elution and purification cycles. Also, to forgo the cost of active pumping it was important to make use of ocean current to flow past the adsorbent system. Hence, eliminating the offshore mooring and labour cost; reduces size of area of land required; increasing the energy output; high/maximum recovery of uranium; reduction in capital and operating cost.
Equipment Design and Specification
Individual equipment design that is required for the design project consist of a wind turbine and buoyant platform, an adsorbent synthesis design, and elution and regeneration tanks.
Wind Turbine and Buoyant Platform
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Figure 5
Figure 5: An image of the front view and side view equipment design of wind turbine and buoyant platform designed for the purpose of this work.
Amidoxime polymer synthesis
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Figure 6
Figure 6: An image of how a trunk polymer is synthesised to form an amidoxime polymer used as an ion exchanger resin for the separation of uranium. Adapted from “Current Status of Uranium Collection from Seawater” presented at Lawrence Berkeley National Laboratory, by Tamada, M et al., (2010).
Elution and Regeneration Flow Chart
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Figure 7: An image of the flow chart of elution and regeneration process using KHCO3 and
NaOH treatment for the process. This flow chart was designed for the purpose of this work.
Elution and Regeneration Overview
Because uranium is strongly bonded to amidoxime groups in the adsorbent, its removal from the adsorbent material without causing damaging effects on adsorbent performance is a challenging problem, for example using hydrochloric acid causes a significant reduction to the adsorbent’s loading capacity for repeated usage. The elution of uranium in the elution process is to use potassium bicarbonate with addition of sodium bicarbonate to prevent hydrolysis. Moreover, after the acid elution, the adsorbent requires a NaOH reconditioning process, which involves heating the adsorbent in 2.5% NaOH solution at 80°C to regenerate the active functional groups for reuse. The NaOH is vital for the removal of seawater organic matter that are adsorbed on the chelating polymer.
Heat and Mass Requirement
Based on the general conservation law: Output= Input + Generation - Consumption - Accumulation. For steady state, accumulation for mass and energy balances will be zero (0). For mass balance, there will be no generation and consumption. Hence, the final equation reduces to : Output =Input+ Generation -Consumption. Active pumping would require high energy since it uses high power hence it would also be an energy input. Energy costs for plant operation and maintenance offshore consumes large amounts of electricity. A very energy-intensive process is the regeneration process of the eluant by steam stripping because it is energy consuming.
Plant Availability and Location
A suitable plant location will depend on these factors, seawater currents, seawater surface winds, seawater surface temperature, wind profile exponent, turbulence intensity. The plant capacity is set at 2000 tonnes per year and will operate 24 hour per day without any downtimes.
Environmental Impact
With the current uranium adsorbent materials, Uranium and vanadium are the predominant metal adsorbed. This could be a potential concern since some marine inhabitants utilize vanadium, but there is little evidence that organisms require vanadium or uranium as an essential element. The utilization of uranium seems to be a subsidiary need for the marine organism and not essential for life. In contrast to uranium, vanadium, appears to have a much larger function in biological systems.
Pipework and Pumping Systems
Pipework: In specifying the pipework for the process design, the parameters considered are material of construction, optimum diameter, schedule number, nominal size, internal diameters and pipe wall thickness. The preferred schedule number is 80 constructed from 304 stainless steel.
Pumps: In specifying the pumping systems for the process design, the parameters considered are material of construction, pump type, power of pump, type of fluid transported and pump head. The preferred pump is a Centrifugal pump that is constructed from a stainless steel.
Health and Safety
Table 1 Health and Safety
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Safety Protection Devices
Table 2 Safety Protection Devices
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Control Strategies and Systems
Table 3 Control Strategies and System
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Capital Cost Estimations and Financial Justification
The adsorption synthesis, adsorbent capacity, recycle efficiency of the adsorbent, chemicals usage, deployment mechanism, plant operation and equipment cost have the direct relevance to the cost of the uranium separation from seawater.
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Figure 8
Figure 8:An image of a graph for the estimation of $555/kg of uranium separation cost using estimated figures for the purpose of this work.
Figure 9: An image of a graph for the estimation of equipment cost using estimated figures for the purpose of this work.
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Figure 10
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Figure 11
Figure 10: An image of a graph for the chemical cost of adsorbent synthesis using estimated figures for the purpose of this work.
Figure 11: An image of a graph for the breakeven and payback period analysis using estimated figures for the purpose of this work.
RECOMMENDATION
It is recommended that adsorbent synthesis should be made of organically sourced, biodegradable substrates such as chitin which could be a good source of green chemistry alternative to conventional plastic polymers that represents a potential source of an uneasy degradable solid pollutant.
CONCLUSION
Although there are several ways for uranium separation, the offshore wind turbine( to produce energy that would be required) on a buoyant platform that continuously takes the adsorbent designed to have a high affinity of the uranyl-carbonate complex from the seawater after campaign time through an elution and regeneration process( housed on the platform above the seawater) and then returns the adsorbent back to the seawater for the seawater current to flow past the system( to forgo the high energy demand for active pumping) for reuse for some number of cycles before degrading( to save cost implication of adsorbent production) has proved to be the most process intensified method for separation of uranium from seawater. The cost analysis and payback period on investment has been financially justified.
REFERENCES
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- Sylvester Gyasi (Author), 2023, The Separation of Uranium from Seawater using Amidoxime containing Polymer, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/1354766
