Exploring the untapped practices in bacterial-fungal mixed-based cultures for acidic treatment of metal-enriched printed circuit board waste

This study explores the extraction of metals from spent mobile phone printed circuit boards (SMPhPCBs) to address environmental and resource depletion concerns. The challenges in metal recovery from SMPhPCBs arise due to their complex composition and high metal content. While previous research has primarily focused on using bio-cyanide, bio-sulfate, and bio-ferric compounds from acidophilic bacteria, the potential of bio-oxalic acid for SMPhPCBs treatment and the alteration of their complex structure has not yet been explored. Additionally, this study suggests evaluating the untapped potential of Aspergillus niger in oxalic acid production through mixed cultures with bacteria, marking a pioneering approach. A unique culture of Bacillus megaterium and A. niger was created, inducing bio-stress by bacterial metabolites, including gluconic acid (2683 mg/l) and live/dead bacterial cells in a medium with glucose deficiency. Results demonstrated reducing sugar consumption and oxalic acid over-production in mixed cultures compared to pure cultures, ranging from 1350 to 4951 mg/l at an initial glucose concentration (IGC) of 10 g/l and 4276 to 7460 mg/l at IGC 20 g/l. This over-production is attributed to proposed fungal signaling mechanisms to bacteria. Metal extraction using organic acids and siderophores at 10 g/l pulp density, 24 h, and 60 °C yielded Mn (100 %), Pt (100 %), Pd (70.7 %), Fe (50.8 %), Co (48.3 %), Al (21.8 %), among others. The final valuable residue containing copper, gold, and silver holds potential for future recycling. The study concludes with XRD and FTIR analyses to assess the bioleaching effect on the bio-leached powder.

Evidence for Participation of 4f and 5d Orbitals in Lanthanide Metal-Ligand Bonding and That Y(III) Has Less of This Complex-Stabilizing Ability. A Thermodynamic, Spectroscopic, and DFT Study of Their Complexation by the Nitrogen Donor Ligand TPEN

The formation constants (log K₁) of lanthanide(III) (Ln) ions [except for Pm(III)] and the Y(III) cation have been measured with the ligand TPEN (N,N,N',N'-tetra-2-picolylethylenediamine). These log K₁ values show a typical variation with ionic radius, with a local maximum at Sm(III) and a local minimum at Gd(III), with an overall increase in log K₁ from La(III) to Lu(III) as the ionic radius decreases. The log K₁ for the Y(III)/TPEN complex is much lower than expected from its ionic radius, while the literature log K₁ for Am(III) is much higher. The latter effect is thought to be due to greater covalence in the M-L (metal-ligand) bond than for Ln(III) ions: the low log K₁ for Y(III) is interpreted as being due to lower covalence. The f → f transitions in the Nd(III) and Pr(III) complexes were examined for effects that might indicate the participation of f orbitals in M-L bonding. The intensity of the f → f transitions in the Nd(III)/TPEN complex was greatly increased compared to that of the Nd³⁺ aqua ion, which appeared to be due to additional sharp peaks, possibly parity forbidden transitions where parity rules were broken by covalence in the M-L bond. The Pr(III)/TPEN complex showed that all of the f → f transitions shifted to longer wavelengths by some 5 nm, with modest increases in intensity. The effects seen in the f → f transitions of Nd(III) and Pr(III) with TPEN with its six nitrogen donors were present to a much smaller extent in the EDTA and other complexes with fewer nitrogen donors. The changes in the f → f transitions of the TPEN complexes of Er(III) and Ho(III) were small, suggesting a smaller contribution of f orbitals to M-L bonding in these heavier Ln(III) ions. The intense Laporte allowed f → d transitions in Ce(III) complexes show large shifts to longer wavelengths as complexes of, for example, EDTA with increasing numbers of nitrogen donors, suggesting the participation of both f and d orbitals, or either, in M-L bonding. The nature of M-L bonding in M(III)/TPEN complexes was further investigated via density functional theory calculations.

SOLUBILITY OF Ca(II), Ni(II), Nd(III) AND Pu(IV) IN THE PRESENCE OF PROXY LIGANDS FOR THE DEGRADATION OF POLYACRYLONITRILE IN CEMENTITIOUS SYSTEMS

The solubility of Ca(OH)2(cr), β-Ni(OH)2(cr), Nd(OH)3(s) and PuO2(ncr, hyd) was investigated in cement porewater solutions containing glutarate (GTA), a-hydroxyisobutarate (HIBA) and 3-hydroxybutarate (HBA). These ligands were proposed as probable degradation...

Leaching of rare earth elements and base metals from spent NiMH batteries using gluconate and its potential bio-oxidation products

Gluconate is known to mediate metal leaching. However, during bioleaching by e.g., Gluconobacter oxydans, gluconate can be oxidized to 2-ketogluconate and 5-ketogluconate. The impact of bio-oxidation of gluconate on metal leaching has not been investigated. Therefore, the aim of this study was to investigate leaching of rare earth elements (REEs) and base metals from spent nickel-metal-hydride (NiMH) batteries using gluconate, 2-ketogluconate and 5-ketogluconate. Batch leaching assays were conducted under controlled and uncontrolled pH conditions for 14 days using 60 mM of either the individual leaching agents or their various combinations. At target pH of 6.0 ± 0.1 and 9.0 ± 0.1 and without pH control, complexolysis was the dominating leaching mechanism and higher REE leaching efficiency was obtained with gluconate, while 5-ketogluconate enabled more efficient base metal leaching. At target pH of 3.0 ± 0.1, acidolysis dominated, and the base metal and REE leaching yields with all the tested leaching agents were higher than under the other studied pH conditions. The highest base metal and REE leaching yields (%) were obtained using gluconate at target pH of 3.0 ± 0.1 being 100.0 Mn, 90.3 Fe, 89.5 Co, 58.5 Ni, 24.0 Cu, 29.3 Zn and 56.1 total REEs. The obtained results are useful in optimization of heterotrophic bioleaching.

Unexpected Deprotonation from a Chemically Inert OH Group Promoted by Metal Ions in Lanthanide-Erythritol Complexes

Single-crystal structures of five lanthanide-erythritol complexes are reported. The analysis of the chemical compositions and scrutinization of structural features in the single-crystal data of the complexes led us to find that unexpected deprotonation occurs on the OH group of erythritol of three complexes. Considering these complexes were prepared in acidic environments, where spontaneous ionization on an OH group is suppressed, we suggest metal ions play an important role in promoting the proton transfer. To find out why the chemically inert OH is activated, the single-crystal structures of 63 rare-earth complexes containing organic ligands with multiple hydroxyl groups (OLMHs) were surveyed. The formation of μ₂-bridges turns out to be directly relevant to the occurrence of deprotonation. When an OH group from an OLMH molecule participates in the formation of a μ₂-bridge, the polarization ability of the metal ions becomes strong enough to promote the deprotonation on the OH group. The above structural characteristics may be useful in the rational design of catalysts that can activate the chemically inert OH group and promote the relevant chemical conversions.

The structure and composition of solid complexes comprising of Nd(III), Ca(II) and D-gluconate isolated from solutions relevant to radioactive waste disposal

Certain complexing agents (such as D-gluconate, D-isosaccharinate, etc.) as well as actinides and lanthanides are simultaneously present in cementitious radioactive waste repositories and (in the presence of water) are capable of forming complex compounds. Such processes may immobilize radionuclides and are of importance in the thermodynamic modelling of the aqueous chemistry of waste repositories. Nd(III) is considered to be a suitable model for trivalent lanthanides and actinides, due to the similarity of their ionic radii. In the current work, solid complexes isolated from aqueous solution containing Nd(III), Ca(II) and D-gluconate (Gluc−) were investigated. In an aqueous solution containing Nd(III) and Gluc−, the formation of a precipitate was observed at pH ≥ 8. This precipitate was found to redissolve around pH ~ 11, but reprecipitated when Ca(II) ions were added to the solution. In order to gain an insight in binary and ternary aqueous systems, in the present work we report the structure of these solid complexes obtained from XRD, FT-IR, Raman, SEM-EDAX and UV-DRS measurements. The structure of these solids, where possible, was compared with those identified in solution. The compositions of these complexes are suggested to be NdGlucH−1(OH) · 2H2O and CaNdGlucH−1(OH)3 · 2H2O, respectively. In these, the chemical environment of the Nd(III) was found to be the same as that in the NdGlucH−1(OH)0(aq) solution species.