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. 2025 Feb 28;30(5):1110.
doi: 10.3390/molecules30051110.

Benefit of an Ultrasonic Irradiation on the Depollution by Washing of Nickel- or Zinc-Contaminated Vermiculite

Antoine Leybros  1 , Sophie Herr  1   2 , Rita Salameh  1   2 , Rachel Pflieger  2
Affiliations

Benefit of an Ultrasonic Irradiation on the Depollution by Washing of Nickel- or Zinc-Contaminated Vermiculite

Antoine Leybros et al. Molecules. .

Abstract

Pollution of soil by heavy metals has become a critical environmental issue. This study investigated an innovative approach to heavy metals removal, focusing on the desorption of nickel and zinc from vermiculite using a combination of leaching and ultrasonic (US) irradiation at 20 or 362 kHz. When 0.1 M HCl was used as a washing solution, Zn2+ desorption yields around 85% were obtained in all conditions. Under 20 kHz US, fragmentation of the particles occurred, leading to the formation of new sites where released Zn2+ could sorb, allowing improved decontamination by cation exchange. Even higher yields were obtained with the biobased citric acid. Ni2+ desorption yields were lower due to its distribution in less accessible Tessier fractions. They significantly increased under US, especially at 362 kHz. It is shown that US leads to transfer of the contaminant from less accessible fractions (in particular the residual one) to more accessible ones, and that at low frequency, new sorption sites are created by fragmentation, leading to readsorption in the exchangeable fraction. This study brought to light for the first time the potential of high-frequency US in enhancing soil washing, to a higher extent compared to low-frequency (20-50 kHz) US.

Keywords: heavy metal; nickel; sequential extraction; soil washing; ultrasound; vermiculite; zinc.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Zn and Ni kinetics of sorption at ambient temperature—[metal] = 100 mg·L−1 with [NaNO3] = 0.01 M; m/V = 1 g·L−1. (b) Zn and Ni sorption isotherms at ambient temperature—[NaNO3] = 0.01 M; m/V = 1 g·L−1. Ceq denotes the concentration reached at equilibrium.
Figure 2
Figure 2
Zn/Ni distribution in vermiculite fractions obtained using the Tessier sequential extraction protocol (for each metal, average of three different batches, the metal load of each being indicated on the y-axis).
Figure 3
Figure 3
X-ray diffractograms of vermiculite samples, of initial composition and after loading with Zn2+ (38 mg·g−1) or Ni2+ (33 mg·g−1).
Figure 4
Figure 4
Zn (a) and Ni (b) desorption kinetics from contaminated vermiculite—influence of ultrasound frequency (silent conditions, 20 and 362 kHz); m/V = 20 g/L; HCl concentration = 0.1 M.
Figure 5
Figure 5
Influence of vermiculite mass to HCl solution volume (m/V) ratio on Zn and Ni desorption from polluted vermiculite; HCl concentration = 0.1 M. (a) Zn desorption under H-silent conditions; (b) Ni desorption under H-silent conditions; (c) Zn desorption at 20 kHz; (d) Ni desorption at 20 kHz; (e) Zn desorption at 362 kHz; (f) Ni desorption at 362 kHz.
Figure 6
Figure 6
Particle size distribution of Zn/Ni polluted vermiculite before/after (a) V-silent or 362 kHz treatment; (b) H-silent or 20 kHz treatment. Properties of the used batches (B3.3, B3.4G and B3.5G) are presented in Table S1 in Supporting Information.
Figure 7
Figure 7
Evolution of Zn/Ni distribution in vermiculite fractions obtained using the Tessier sequential extraction protocol after washing with HCl 1 M during 3 h, under sonication or silent conditions: (a) Zn with m/V = 20 g/L; (b) Zn with m/V = 50 g/L, (c) Ni with m/V = 20 and 50 g/L.
Figure 7
Figure 7
Evolution of Zn/Ni distribution in vermiculite fractions obtained using the Tessier sequential extraction protocol after washing with HCl 1 M during 3 h, under sonication or silent conditions: (a) Zn with m/V = 20 g/L; (b) Zn with m/V = 50 g/L, (c) Ni with m/V = 20 and 50 g/L.
Figure 8
Figure 8
Evolution of Zn/Ni distribution in vermiculite fractions obtained using the Tessier sequential extraction protocol after washing with HCl (0.1 M) and MgCl2 (1 M). Desorption in V-silent conditions and at 362 kHz with m/V = 20 g·L−1.
Figure 9
Figure 9
Ni desorption kinetics from polluted vermiculite in silent conditions, at 362 kHz and at 20 kHz–m/V = 20 g·L−1, HCl concentration to 0.1 M and MgCl2 concentration to 0 or 1 M.
Figure 10
Figure 10
Comparison of Ni distribution in vermiculite fractions obtained using the Tessier sequential extraction protocol after washing with HCl 1 M + MgCl2 1 M or HCl 1 M alone during 3 h: (a) under 362 kHz US irradiation; (b) under 20 kHz US irradiation. m/V = 20 g/L.
Figure 11
Figure 11
Zn/Ni desorption kinetics from polluted vermiculite in 0.5 M citric acid, under silent conditions or US irradiation; m/V = 10 g·L−1: (a) Zn; (b) Ni.
Figure 12
Figure 12
Comparison of Zn/Ni distribution in vermiculite fractions obtained using the Tessier sequential extraction protocol after washing with 0.5 M citric acid during 3 h: (a) Zn; (b) Ni. m/V = 10 g/L.
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