The invention discloses a method for extracting high-value
alkali metal from
salt lake brine or
seawater through membrane extraction-back extraction. The method is implemented through
continuous operation and comprises the following steps of: fixing an
ion exchange blend membrane in a membrane component, allowing an organic solution containing an extracting agent to contact
salt lake brine or
seawater which contains
alkali metal ions by a first
ion exchange membrane, and allowing
alkali metal ions to pass through the
ion exchange membrane and be combined with the organic solution containing the extracting agent to obtain
metal complex; then transmitting an organic solution of the
metal complex to a second
ion exchange membrane and allowing the organic solution of the
metal complex to contact a back extraction solution by the second
ion exchange membrane, and allowing the metal ions to pass through the
ion exchange membrane to enter the back extraction solution; during membrane extraction-back extraction, and circulating feed liquid, the back extraction solution and the organic solution containing the extracting agent on one side of the first ion exchange membrane, on one side of the second ion exchange membrane and between the first and second
ion exchange membranes; and performing back extraction until a certain concentration of the back extraction solution is reached, and separating
lithium,
rubidium or
caesium precipitates to obtain the final product. The invention provides a high-efficiency, low-cost and feasible
route for industrial production of alkali
metal salts.