Macias and Rodriguez de San Miguel 2023 - PIM separation of Pb(II), Cd(II), and Zn(II) from seawater

Macias and Rodriguez de San Miguel optimized polymer inclusion membranes (PIMs) for selective transport of Cd(II), Pb(II), and Zn(II) in saline media and seawater matrices. This is primary remediation and separation-method evidence, not seawater occurrence evidence: synthetic and collected seawater matrices were spiked with defined metal-ion concentrations, and the measured endpoints are transport fractions, separation factors, membrane stability, and preconcentration behavior.

Key numbers

Matrices and feed concentrations

The study used synthetic seawater at 35% salinity, commercial deep seawater collected from the Gulf of California, and surface seawater from Tecolutla beach, Veracruz, Mexico. The Gulf of California and Tecolutla waters were used within 5 days as feed matrices after refrigeration. The Tecolutla water had pH 8.1 and conductivity 51.65 mS/cm at 23.7 C; the commercial seawater had pH 8.2.

For the three-metal selectivity design, feed phases contained Zn(II), Pb(II), and Cd(II) at combinations of 5e-5 or 1e-4 mol/dm3:

These are spiked feed concentrations for method testing, not native seawater occurrence measurements.

Membrane optimization

For Cd(II), Table 3 reports 24 hour pertraction results for a Box-Behnken design. Membrane 8, with coded composition -1.0 CTA, 0.0 NPOE, and 1.0 Aliquat 336, left Cd(II) not detectable in the feed phase and put 0.98 of the species fraction in the stripping phase. Membrane 12 also performed strongly, with feed fraction 0.014 and stripping fraction 0.96, but the authors selected membrane 8 because the mathematical optimum was fragile and difficult to manipulate.

For Pb(II), the selected PIM used 0.05 g CTA, 0.0453 g TEHP, and 0.0503 g D2EHPA. TEHP was chosen over NPOE and TBEP because it maintained better Pb(II) transport as NaCl increased.

Seawater separation performance

The three-compartment setup placed feed solution in the center and two stripping phases on either side: 0.1 mol/dm3 HCl + 0.1 mol/dm3 NaCl for S1 and 0.1 mol/dm3 HNO3 for S2. One PIM used Aliquat 336 for Cd(II) transport and the other used D2EHPA for Pb(II) transport.

The authors report that lowering the initial concentrations of the three ions increased recovery and transport efficiency because membrane active-site saturation was reduced. In the best-separation compositions B and C, the system allowed S(Cd) and S(Pb) of about 1000 and 10 < S(Zn) < 1000, depending on seawater matrix and experimental conditions. Some experiments reached separation factors as high as 10,000.

The conclusion gives two typical 48 hour Tecolutla-seawater examples:

The authors also report excellent transport efficiencies above 99.9% and successful operation over three 48 hour cycles, with feed renewal after each cycle allowing simultaneous preconcentration of target metal ions. Zn(II) accumulated in the Aliquat 336 membrane over cycles, reducing S1 selectivity by the third cycle; Pb(II) transport efficiency gradually declined, but no other metal was detected in S2, so Pb selectivity was retained.

Methods (brief)

PIMs were prepared by casting and solvent evaporation from cellulose triacetate, plasticizer, and carrier/extractant mixtures. Two-compartment cells were used for individual Cd(II) and Pb(II) optimization, and a three-compartment cell was used for simultaneous Cd(II), Pb(II), and Zn(II) separations. The exposed membrane area was 4.9 cm2 and each compartment held 100 cm3. Experiments were performed in duplicate with average RSD within 5%.

Metal cations were prepared from 1000 mg/L standards. Synthetic seawater followed standard salinity recipes; collected seawater matrices were spiked for feed-phase experiments. Metal determinations were performed by differential pulse voltammetry using a portable potentiostat. PIM chemical stability was checked by FTIR and reflection infrared mapping microscopy.

Implications

Certification: Do not use this source in food, seafood, seawater, bottled-water, or ingredient occurrence pools. The seawater matrices were spiked method-test feeds; the paper does not report native Pb, Cd, or Zn concentrations in Gulf of California or Tecolutla seawater.

App: Context for marine-remediation and preconcentration methods. The study supports the feasibility of paired PIM systems for selectively moving Cd(II) and Pb(II) into different stripping phases while delaying or separately handling Zn(II).

Courses: Useful for teaching the distinction between occurrence data and separation-performance data, plus how matrix chemistry, salinity, pH, and active-site saturation affect metal transport.

Wiki pages this source may touch

• remediation-evidence
• lead
• cadmium
• zinc
• index

Verification notes

This page was built from the full PDF, including the abstract, seawater-matrix description, transport-cell methods, Table 2 selectivity design, Table 3 Cd(II) membrane optimization, Pb(II) plasticizer selection, NaCl and pH effects, separation-factor discussion for commercial Gulf of California and Tecolutla seawater matrices, stability/preconcentration discussion, FTIR stability tables, and the conclusion. Brand names for commercial seawater and analytical materials are intentionally omitted under the brand firewall. Products and ingredients are intentionally empty because no food, ingredient, drinking-water field sample, or consumer-product matrix was sampled.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.