Extractant Forced-Circulation Three-Phase Extraction for the Preconcentration of Parts-per-Billion (Ppb)-Level Cadmium(II) from Natural Waters

Abstract

An extractant forced-circulation three-phase extraction (EC-TPE) device based on extraction-stripping coupling was developed for the preconcentration of Cd²⁺ in environmental samples. In this three-phase extraction (W₁/O↔O/W₂) system, Cd²⁺ in the sample solution (W₁) was fully extracted into the stripping phase (W₂) by the circular flow of an organic phase (O↔O). The extraction yield (EY) and enrichment factor (EF) reached almost 100% and 100, respectively, under the following operating conditions: 0.1 M HNO₃, 2 mL/L di(2-ethylhexyl)phosphoric acid (P204), circulation flow rate of 32 mL/min, circulation time of 45 min and stirring speed of 400 rpm. An extraction yield of more than 98.5% was still achieved after reusing the organic phase eight times. Two theoretical formulas were established for predicting the EY and EF. Thereafter, EC-TPE was applied in the preconcentration of ppb-level Cd²⁺ for flame atomic absorption spectrophotometer assay with a detection limit of 0.17 μg/L. Addition/recovery tests for Cd²⁺ were carried out with recoveries exceeding 98%, and three environmental water samples were accurately analyzed. Finally, application of the EC-TPE device was extended to a different extraction system and other metal ions: Zn²⁺, Cu²⁺, Ni²⁺, and Co²⁺. The EC-TPE device is easily established utilizing common laboratory glassware, and the enrichment operation efficiency can be conveniently improved by using more than one device simultaneously.

Keywords:

• Cd2+ preconcentration
• environmental sample treatment
• extractant forced-circulation three-phase extraction
• flame atomic absorption spectrometry (FAAS)
• heavy metal ion preconcentration

Disclosure statement

There are no conflicts of interest to declare.

Additional information

Funding

This work was supported by the Provincial Natural Science Foundation of China's Hunan Province (No. 2018JJ3206), the National Natural Science Foundation of China (No. 21706059), the Scientific Research Project of Department of Education in Hunan Province of China (No. 18B354), and the Innovation and Entrepreneurship Training Program for College Students in Hunan Province of China (No. S201910543032).