Strontium recovery from seawater

Clinoptilolite has been demonstrated to be the most appropriate sorbent for strontium recovery from seawater, as well as ftom other natural waters and brines [248-250]. This most common zeolite is characterized by the composition (Na, IO4 CaAl6Si3o072 24 H2O. The main advantages of applying clinoptilolite for recovery of strontium from seawater is attributed to the ease with which it is regeneratable by ammonium salts... 

Figure 13 Concentrations of alkali earth metals at different stages of the cascade process in the course of strontium recovery from seawater (see text).

Selective separation of strontium from calcium at significant SrCl2 concentration levels up to 2 g/L was obtained with KB-4 carboxylic add exchanger employed in a Higgins-type contactor [246]. The pilot unit for strontium recovery from seawater in the closed (and practically waste-free) processing scheme was constructed in the Okhotsk Sea region (Sakhalin power station). The data obtained with the new pilot plant have shown that several components will be recovered simultaneously from seawater. The unit is estimated to produce more than 150 kg of SrCOj, more than 5000 kg of KNOj, and about 2 kg of RbNOj [15]. However, recovery of strontium is still uneconomical. Its cost is expected to become comparable to that of strontium produced from traditional, land-based sources. 

According to the latest estimates of Skinner [18], elements potentially recoverable from seawater are sodium, potassium, magnesium, calcium, strontium, chlorine, bromine, boron, and phosphorus because of their practically unlimited presence in the ocean. After improving respective technologies, recovery of the following elements is expected to become profitable as well lithium, rubidium, uranium, vanadium, and molybdenum. Additional profit can be gained since desalinated water will probably be obtained as a by-product. This could be important for countries with a very limited number of freshwater sources (e.g., Israel, Saudi Arabia). 

The number of publications involved with the recovery of rubidium from seawater is very limited. Most of the work in this field is by Russian scientists, who have proposed several schemes for the combined recovery of rubidium, strontium, and potassium with natural zeolites [15, 19, 250-253, 257]. A number of inorganic sorbents with high selectivity toward rubidium were also synthesized for the recovery of rubidium from natural hydromineral sources, including seawater. Ferrocyanides of the transition-metal ions were shown to exhibit the best properties for this purpose [258, 259]. Mordenite (another natural zeolite) has recently been proposed for selective recovery of rubidium from natural hydromineral sources as well [260]. A review of the properties of inorganic sorbents applicable for the recovery of rubidium from hydromineral sources has been published [261]. Studies of rubidium recovery fix>m seawater [15, 19, 250-253] have shown that the final processing of rubidium concentrates, especially the selective separation of Rb -K mixtures remains the major problem. A report was recently published showing that this problem can be successfully solved by countercurrent ion exchange on phenolic resins [262]. 

Smalley P.C., Raiheim A., Dickson J. A.D. and Emery D. (1988) 87Sr/86Sr in waters from the Lincolnshire Limestone aquifer, England, and the potential of natural strontium isotopes as a tracer for a secondary recovery seawater injection process in oilfields. Applied Geochem. 3, 591-600. 

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