A selective extraction process for recovering vanadium (IV) over chromium was proposed with use of a mixed extractant consisting of di(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP). The influence of various factors, which included the initial aqueous pH value, the concentration of leach solution and D2EHPA, phase ratio (O/A), extraction equilibrium time and extraction temperature in the extraction process on the separation of V and Cr was investigated. Under the condition of the optimum extraction, vanadium extraction was above 94.0%. Meanwhile, under the optimum stripping conditions, the vanadium stripping was above 93.0% utilizing 1.5 mol/L sulfuric acid as the effective stripping reagent. The regeneration and reusability of the loaded organic phases after stripping were discussed. In addition, continuous three-stage extraction and stripping strategy indicated that the aggregate loss of vanadium was 0.885% and that the purity of vanadium was more than 99.9%. Under the condition of the optimum precipitation, when the pH value of the stripping solution was adjusted to 7.0 with ammonia water, the precipitation efficiency reached 99.93%. The calcination conditions (above 680 °C in air) were finally determined by TG-DTA and TG-MS experiments, and the V2O5 obtained by calcination was characterized by XRD. Additionally, a method for detecting impurity elements in vanadium matrix without interference was established. The recovery technology has practical significance in enlarging production scale, reducing specific energy consumption and cost, and realizing automatic control in vanadium leaching process.
An extraction system consisting of di-2-ethylhexyl phosphoric acid (D2EHPA), tributyl phosphate (TBP), and kerosene was developed for selective recovery of aluminium ions from the leaching solution of cathode materials of spent ternary lithium-ion batteries. The proposed system could significantly separate nickel, cobalt, manganese, and lithium ions from aluminium ions in the leachate. A four-stage cross-flow extraction process using D2EHPA-TBP-kerosene with 40% saponification degree could recover 99.48% of Al 3+ at pH of 1.68 and O/A phase ratio of 1:1. After one-stage washing and five-stage stripping processes, a stripping solution containing nearly pure Al 3+ could be obtained. Then, the Al 2 (SO 4 ) 3 ‧ 17H 2 O product was recovered from the stripping solution by the cooling crystallization method with a yield of 92.63% and a purity of 99.32%. The extraction system showed very stable extraction ability during ten consecutive extraction–washing–stripping cycles. Finally, a cation exchange mechanism was explored by using Fourier transform infrared spectroscopy (FT-IR) characterization.
The solvent extraction and separation process of Sc(III) and Fe(III) from a strongly acidic and highly concentrated ferric solution using mixtures of di(2-ethylhexyl) phosphate (D2EHPA) and tri-n-butyl phosphate (TBP) in sulfonated kerosene was studied. The effects of various parameters, including D2EHPA concentration, dosage of TBP, and phase ratio, were investigated for the extraction process. The results indicated that the extraction rate of Sc(III) was 99.72% with 1.09% Fe(III) co-extracted after two stages of counter-current extraction under optimal conditions. Moreover, saturation capacity and slope analysis were used to determine the reaction mechanism. Sc(III) is extracted in the form of HSc(SO 4 ) 2 ·4HL. Further separation of Sc(III) and Fe(III) was realized in a scrubbing and stripping process. First, 98.67% of the co-extracted iron in the loaded organic phase was scrubbed with a dilute HCl solution by a three-stage counter-current scrubbing. Then, 85.00% of Sc(III) can be stripped efficiently with a 2-mol/L NaOH solution saturated in 1-mol/L NaCl by three-stage cross-current stripping.
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