After one adsorption and elution, the uranium concentration increased from 3.3 μgU/L (note: U/L is the unit/L) in seawater to 9mgU/L (note: U/L is the unit/L) in the eluent, an increase of nearly 3,000 times. However, the uranium concentration at this time is still very low and needs further enrichment. The anion exchange resin can be used for secondary adsorption, and then the uranium on the ion exchange resin can be leached by neutral salt solution. The uranium concentration in the second leaching solution is about 3.5gU/L (note: U/L is the unit/L). Uranium can be precipitated from this leaching solution by conventional methods to prepare uranium salt products. 1, adsorption method, using adsorbents such as hydrated titanium oxide, basic zinc carbonate, galena and ion exchange resin to adsorb trace uranium in seawater;
2. Biological enrichment method, which uses specially cultivated algae to enrich trace uranium in seawater. According to experiments, some algae have great uranium enrichment ability, and their uranium content even exceeds that of low-grade uranium deposits.
3. Bubble separation method: A certain amount of uranium trapping agent, such as iron hydroxide, is added to seawater, and then aerated and bubbled to separate uranium from seawater. It should have the properties of large adsorption capacity, fast adsorption speed, good selectivity, good chemical stability, good mechanical strength, easy elution and regeneration, no pollution to the ocean and low price.
Firstly, inorganic adsorbents, such as hydrated titanium oxide, are mainly studied. In order to obtain hydrated titanium oxide with certain mechanical strength, a titanium-carbon composite agent combining titanium gel-polyacrylamide gel adsorbent and polyvinyl alcohol was developed. Later, it was found that the mechanical strength of hydrated titanium oxide series adsorbents was not ideal, so it turned to the main research of organic adsorbents. The results show that in the industrial production of synthetic fibers, the adsorption capacity, adsorption selectivity and mechanical strength of polyacrylamide oxime, a direct derivative of polyacrylonitrile, are better than those of hydrated titanium oxide. The adsorption device should be able to contact with a large amount of seawater, and it is energy-saving and cheap. According to their respective coastal conditions, countries all over the world have studied the ways of using natural ocean current, tidal current, wave energy and pump drive to make the adsorption device contact with a large amount of seawater. The experiment in Japan is to transport seawater to the adsorption column by mechanical pump, and the exhausted seawater is discharged into the sea and taken away by ocean currents. Because this method needs to transport a lot of seawater, it consumes a lot of energy. Because there is no warm ocean current along the coast, Germany mainly studies and develops floating adsorption devices that move in seawater, such as devices attached to ships, in order to achieve the effect similar to ocean current driving. Sweden has studied a kind of storage tank, which uses waves to make the water level in the tank higher than the sea level, and then uses the water level difference to make seawater pass through the adsorption bed. China, the United States and the former Soviet Union are also conducting similar engineering research.