Disclosed are applications of a carboxylic compound serving as an extracting agent and a metal ion extraction method. The carboxylic compound is provided with the structure as represented by formula I. The extracting agent as represented by formula I is characterized by a secondary atom at position α of the carboxyl group, in distinction from a primary carbon carboxylic acid at position α and a tertiary carbon carboxylic acid at position α, the presence of a secondary carbon carboxylic acid provides a proper steric hindrance, provides improved selectivity with respect to ions, and provides a high separation coefficient, low stripping acidity, and high load rate when used for the extraction and separation of metal ions; moreover, the carboxylic compound of formula I has great stability and low aqueous solubility, allows an extraction process to be stable, reduces environmental pollution, reduces costs, and provides significant application prospects.

In a method for recovering an active metal of a lithium secondary battery, a sulfuric acid solution is added to a lithium metal composite oxide so as to prepare a sulfated active material solution. A transition metal is extracted from the sulfated active material solution. A lithium precursor is recovered by adding a lithium extracting agent to the solution remaining after the transition metal has been extracted from the sulfated active material solution. In the method, the amount of impurities is reduced, and sulfuric acid and the neutralizing agent can be recycled so that a high-yield lithium precursor recovery is enabled.

A method for recovering NiSO.sub.4.6H.sub.2O crystals from a nickel rich organic phase is provided. The method includes contacting a nickel rich organic phase with an aqueous strip solution of sufficient H.sub.2SO.sub.4 concentration to extract nickel from the organic phase and of sufficient Ni.sup.2+ concentration to precipitate NiSO.sub.4.6H.sub.2O crystals and form a nickel lean organic phase. Also provided are methods for recovering NiSO.sub.4.6H.sub.2O crystals that include preceding processing steps, including low temperature pressure oxidation (LTPOX) autoclaving of a nickel sulphide concentrate to afford a pregnant leach solution (PLS).

A method for extracting rare earth elements from aqueous solution, comprising: (i) acidifying an aqueous solution containing said rare earth elements with an inorganic acid to result in an acidified aqueous solution containing said rare earth elements and containing the inorganic acid in a concentration of 1-12 M, wherein said rare earth elements are selected from lanthanides, actinides, or combination thereof, and (ii) contacting the acidified aqueous solution with an aqueous-insoluble hydrophobic solution comprising a rare earth extractant compound dissolved in an aqueous-insoluble hydrophobic solvent to result in extraction of one or more of the rare earth elements into the aqueous-insoluble hydrophobic solution by binding of the rare earth extractant compound to the one or more rare earth elements, wherein the rare earth extractant compound has the following structure:

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provided that at least one of the conditions (a)-(d) applies.

A method for recycling nickel, cobalt and manganese from a feed liquid containing nickel, cobalt and manganese, the method comprising: (1) subjecting the feed liquid to a first extraction to obtain an aqueous phase 1 and an organic phase 1; (2) subjecting the aqueous phase 1 to a second extraction to obtain an organic phase 2 and an aqueous phase 2 having a pH value of 5-7.5; and (3) successively subjecting the organic phase 2 to washing and reverse extraction to obtain a solution containing nickel, cobalt and manganese, wherein an extractant A used in the second extraction comprises a carboxylic acid extractant.

A method for recycling nickel, cobalt and manganese from a feed liquid containing nickel, cobalt and manganese, the method comprising: (1) subjecting the feed liquid to a first extraction to obtain an aqueous phase 1 and an organic phase 1; (2) subjecting the aqueous phase 1 to a second extraction to obtain an organic phase 2 and an aqueous phase 2 having a pH value of 5-7.5; and (3) successively subjecting the organic phase 2 to washing and reverse extraction to obtain a solution containing nickel, cobalt and manganese, wherein an extractant A used in the second extraction comprises a carboxylic acid extractant.

The present application provides a method for separating nickel from lithium, comprising: (1) performing a saponification reaction on an extraction reagent and an alkaline compound to obtain a saponified extraction agent, wherein the extraction reagent comprises a specific carboxylic acid compound; (2) performing extraction and layering on a nickel-lithium feed liquid by using the saponified extraction agent obtained at step (1), so as to obtain a loaded organic phase and a raffinate water phase; and (3) using a back extraction agent to perform back extraction on the loaded organic phase obtained at step (2), so as to obtain a metal ion enrichment solution and a regenerated organic phase.

The present application provides a method for separating nickel from lithium, comprising: (1) performing a saponification reaction on an extraction reagent and an alkaline compound to obtain a saponified extraction agent, wherein the extraction reagent comprises a specific carboxylic acid compound; (2) performing extraction and layering on a nickel-lithium feed liquid by using the saponified extraction agent obtained at step (1), so as to obtain a loaded organic phase and a raffinate water phase; and (3) using a back extraction agent to perform back extraction on the loaded organic phase obtained at step (2), so as to obtain a metal ion enrichment solution and a regenerated organic phase.

The present application provides an N,N-dihydrocarbonyl amino carboxylic acid, preparation method therefor and use thereof. The N,N-dihydrocarbonyl amino carboxylic acid can be used as an extractant for enriching rare earth elements from raw materials containing low-concentration rare earth elements, separating and purifying yttrium element from a mixed rare earth raw material, and separating elements such as aluminum, iron, radioactive thorium, radioactive uranium and actinide from a mixed rare earth raw material, etc. The compound can be synthesized in a simple and cost-efficient way. As an extractant, it has good chemical stability and has good resistance against strong acid and strong alkali without decomposition.

The present application provides an N,N-dihydrocarbonyl amino carboxylic acid, preparation method therefor and use thereof. The N,N-dihydrocarbonyl amino carboxylic acid can be used as an extractant for enriching rare earth elements from raw materials containing low-concentration rare earth elements, separating and purifying yttrium element from a mixed rare earth raw material, and separating elements such as aluminum, iron, radioactive thorium, radioactive uranium and actinide from a mixed rare earth raw material, etc. The compound can be synthesized in a simple and cost-efficient way. As an extractant, it has good chemical stability and has good resistance against strong acid and strong alkali without decomposition.