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Sensing of Toxic Metals Using Innovative Sorption-Based Technique
Published in Arup K. Sengupta, Ion Exchange and Solvent Extraction, 2017
Chatterjee Prasun K., SenGupta Arup K.
The different heavy metals such as zinc, copper, nickel, and lead that are the subjects of interest in the present study, because of the configurations of their electron shells, they all are strong Lewis acids, that is, good electron pair acceptors. Lewis acids are defined as elemental species with a reactive vacant orbital (e.g., vacant 3d orbital for Cu, Zn) or an available lowest unoccupied molecular orbital. In other words, any elemental species with a net positive charge behaves as a Lewis acid because it acts as an electron pair acceptor. The electron clouds of these atoms are more readily deformed by the electric field of other species (e.g., ligands). They have many valence electrons, higher polarizability, and may be visualized as “soft sphere” ions. In general, metals with higher polarizability are found to have increased strength covalent bonding.4,11,34 Thus, all these metals exhibit strong coordination interactions (i.e., coordinate covalent bonding) as central atoms with a variety of ligands or electrondonating species (Lewis base) containing O, N, and S. All these metal cations have coordination number (C.N.) 4 or more (e.g., Zn2+ C.N. 4 and Cu2+ C.N. 6). Such metal–ligand interactions are commonly designated as a Lewis acid–base interaction or formation of an inner sphere complex through electron pair sharing. Hard cations such as Na+, K+, and Ca2+ are spherically symmetric, not easily deformed, poor electron pair acceptors, and interact weakly with these ligands, forming only outer sphere complexes (electrostatic interactions).4,11,35
Bioremediation potential and primary mechanism of Sporosarcina pasteurii for cadmium (Cd) and lead (Pb) in contaminated tailings
Published in Chemistry and Ecology, 2023
In addition, an increase of Fe-Mn oxides-bound Cd/Pb appeared in tailings as bacterial concentration (OD600) increased, indicating immobilisation of HMs through a series of biochemical reactions. Firstly, OH- released by bacteria eliminated H+ in Fe-Mn minerals, exposing metal cation binding sites to promote minerals’ adsorption or ion exchange ability. Secondly, abundant HMs in the Fe-Mn oxide and calcite phase was observed, which was speculated to result from the sorption of HMs on the surface of minerals and incorporating them into the crystal structures of minerals [35, 36]. Finally, the formation of an inner-sphere complex via the complexation reaction [37, 38] allowed HMs to associate with oxides, and improve the stabilisation of heavy metal ions. Therefore, the decrease of exchangeable HMs and the increase of carbonate-bound HMs took priority to reduce the availability of Cd and Pb in S. pasteurii-treated tailings, followed by a rise of Fe-Mn oxides-bound HMs.
Co-precipitation synthesis of non-cytotoxic and magnetic cobalt ferrite nanoparticles for purging heavy metal from the aqueous medium: Pb(II) adsorption isotherms and kinetics study
Published in Chemistry and Ecology, 2022
Monika Mahmud, Md. Sahadat Hossain, Mashrafi Bin Mobarak, Sazia Sultana, Suriya Sharmin, Samina Ahmed
In sharp contrast, after Pb(II) adsorption asymmetric stretch for the (υas[-COO - ]) group shifted to 1524 cm−1 from 1553 cm−1 and symmetric stretch for the (υs[−COO−]) group shifted to 1406 cm−1 from 1421 cm−1, which indicates that the -COO– group of oleic acid was involved in the adsorption process. Moreover, After the adsorption peak at the tetrahedral region, 553 cm−1 is shifted to 561 cm−1, and the Fe–Co alloy system at 1063 cm−1 is shifted to 1041 cm−1, which indicates the strong attractions with Pb(II) ions. Consequently, shifting of the peak position suggests electrostatic attraction and the inner-sphere complex formation with the metal ions. In Figure 3(b), the SEM image after adsorption visualises the adsorbed lead species.
Removal of Cadmium(II) by hydrated manganese dioxide: behaviour and mechanism at different pH
Published in Environmental Technology, 2022
Yao Wang, Wanzhen Xie, Fencun Xie
To explore the regeneration stability, six cycles of adsorption–desorption were carried out. We took 5 mL HMO to adsorb 100 mL wastewater containing 50 and 100 mg·L−1 Cd(II) and desorbed in 0.5 mol·L−1 HCl solution for 2 h, then washed with pure distilled water until the conductivity touched 0.02 μs·cm−1 for the next recycle. The result was shown in Figure 17. With the increase of the recycle times, both adsorption capacity and removal rate decreased. For waste water containing 50 mg·L−1 Cd(II), the removal rate could maintain 80.04% after four cycles, and the adsorption capacity decreased slightly. While for waste water containing 100 mg·L−1 Cd(II), the removal rate drops linearly and it could only keep 63.19% after four cycles. It was obvious that the removal rate and adsorption capacity of Cd (II) both decreased with the increase in recycle times, especially after four times, the removal rate deeply decreased to 63.04% for 50 mg·L−1 Cd(II) wastewater and to 35.01% for 100 mg·L−1 Cd(II) wastewater after six cycles. There are two potential reasons outline follow. It was obvious that the loss of HMO at the adsorption–desorption cycle process contributed to the decrease of removal efficiency. For the other reason might own to adsorption sites being occupied by stable inner-sphere complex. Therefore, we believed that the HMO adsorbing Cd(II) could be regenerated several times with a high efficiency by adding HCl.