Circular bioeconomy and environmental benignness through microbial recycling of e-waste: A case study on copper and gold restoration.

This study has attempted to ascertain the linkages between circular bio-economy (CirBioeco) and recycling of electronic (e-)waste by applying microbial activities instead of the smelter and chemical technologies. To build the research hypothesis, the advances on biotechnology-driven recycling processes for metals extraction from e-waste has been analyzed briefly. Thereafter, based on the potential of microbial techniques and research hypothesis, the structural model has been tested for a significance level of 99%, which is supported by the corresponding standardization co-efficient values. A prediction model applied to determine the recycling impact on CirBioeco indicates to re-circulate 51,833 tons of copper and 58 tons of gold by 2030 for the production of virgin metals/raw-materials, while recycling rate of the accumulated e-waste remains to be 20%. This restoration volume of copper and gold through the microbial activities corresponds to mitigate 174 million kg CO2 emissions and 24 million m3 water consumption if compared with the primary production activities. The study potentially opens a new window for environmentally-friendly biotechnological recycling of e-waste under the umbrella concept of CirBioeco.

Total recycling of all the components from spent auto-catalyst by NaOH roasting-assisted hydrometallurgical route.

Total recycling of all valuable metals such as PGMs, Ce, Al and Mg from the spent automobile catalysts has been explored. The alkali roasting was performed under NaOH, 0.5-3.0 g; temperature, 300-800 °C; and time, 10-60 min. The phase transformation from cordierite to the soluble products (NaAlO2, Na2MgSiO4) was influenced by the temperature, following the diffusion-controlled model (Ea(roasting), 6.4 kJ/mol). XRD analysis of the roasted mass revealed that the refractory phases of cordierite and γ-alumina could be eliminated at ≥600 °C at sample-to-NaOH mass ratio, 1:1. The leaching of the roasted mass followed an intermediate-controlled mechanism for aluminum leaching with (Ea(Al-leaching) value of 20.3 kJ/mol), while it was diffusion-controlled for magnesium leaching (Ea(Mg-leaching), 8.9 kJ/mol). At the optimum leaching condition (1.0 M H2SO4, 90 °C, 60 min, yielding >95% aluminum and magnesium), a significant amount of PGMs was also leached. Thereafter, the cementation process was investigated with Al0-powder that could precipitate >99% PGMs within 15 min at 90 °C. The yielded concentrate of PGMs and CeO2 was subsequently leached in 6.0 M HCl with 2.0 M NaClO3 that dissolved >97% PGMs, leaving the residue as the CeO2 concentrate. Individual metals can be recovered by following established separation and purification techniques.

Hydrometallurgical recycling of surface-coated metals from automobile-discarded ABS plastic waste.

The ammoniacal leaching of surface-coated metals from automobile-discarded ABS plastics followed by their recovery through solvent extraction has been investigated. The leaching of ABS (typically containing 4.1% Cu, 1.3% Ni, and 0.03% Cr) could efficiently dissolve the ammine complexes of Cu and Ni, leaving Cr unleached as fine particles. The optimization studies for achieving the maximum efficiency revealed that the leaching of metal ions in different ammoniacal solutions follows the order CO32- > Cl- > SO42-. The leaching carried out in a carbonate medium by maintaining the total NH3 concentration 5.0 M at a NH4OH/(NH4)2CO3 ratio of 4:1, pulp density of 200 g/L, agitation speed of 400 rpm, temperature of 20 °C, and time of 120 min yielded the optimum efficiency of >99% Cu and Ni (i.e., 8.14 g/L and 2.57 g/L, respectively, in the leach liquor). Subsequently, the solvent extraction of metals from ammoniacal leach liquor as a function of extractant (LIX 84-I) concentration and organic-to-aqueous (O:A) phase ratio was examined. Based on the extraction data, a three-stage counter-current extraction at O:A = 1:1 was validated using 0.8 M LIX 84-I, yielding the quantitative extraction of both metals into the organic phase. Thereafter, the stripping of metals in acid solutions indicated that 0.5 M H2SO4 could quantitatively strip Ni from the loaded organic phase; however, ∼27% Cu was also co-stripped. The rest of Cu from the Ni-depleted organic phase was separately stripped with 1.0 M H2SO4 that can be directly sent to the electrowinning process. On the other hand, the co-stripped metals from the acidic solution can be easily separated, again using LIX 84-I as the extractant, by adopting the pH-swing method. Finally, a process has been proposed for the hydrometallurgical recovery of surface-coated metals from waste ABS plastics; that does not affect the physicochemical characteristics of the polymer substances for their reuse.

Synthesis of 1-Amino-3-[2-(1,7-dicarba-closo-dodecaboran(12)-1-yl)ethyl]cyclobutanecarboxylic Acid: A Potential BNCT Agent.

The synthesis of an unnatural amino acid, 1-amino-3-[2-(1,7-dicarba-closo-dodecaboran(12)-1-yl)ethyl]cyclobutanecarboxylic acid, was achieved. This new potential BNCT agent was prepared via the monoalkylation of m-carborane with 4-bromobutene to produce 4-m-carboranyl-1-butene, which was then subjected to a 2 + 2 cycloaddition using dichloroketene. The resultant boronated cyclobutanone was reductively dechlorinated prior to the formation of the corresponding hydantoin, which was hydrolized to the title compound in excellent yield.

Synthesis, radioiodination, and biodistribution of some nido- and closo-monocarbon carborane derivatives.

Iodination and radioiodination reactions of several anionic nido- and closo-monocarbon carboranes were conducted. Iodinations occurred more rapidly with nido-carboranes than with closo-carboranes. The most rapid iodination and radioiodination reactions occurred with unsubstituted carboranes. C-amino and C-ammonium derivatives did not iodinate under the conditions studied. Both nido- and closo-carboranes with C-NH-acetyl and C-NH-succinyl substituents iodinated, but the nido-carboranes iodinated under milder reaction conditions. Biodistributions of nido-1-succinylamido-[(131)I]carborane and closo-1-succinylamido-[(125)I]carborane were similar in mice, but blood clearance of the nido- compound was slower.