End-of-life electrical and electronic equipment is the potential secondary resource for economically-viable precious metals (PMs), e.g., gold (Au), palladium (Pd), or platinum (Pt). The hydrometallurgical processes produce acidic leachates during the recovery of PMs from waste sources, while the selective recovery of Au, Pd, or Pt from such a matrix is challenging either due to the chemical similarities of elements or complexities in the sources and matrices. A total of nine solid-phase extraction (SPE) systems, all claimed to designed for separation of PMs from complex matrices, was evaluated at varying solution pH (≤ 2 to 10) based on the selectivity towards Au, Pd, or Pt. The observation was used to develop a technique for selective Au, Pd, or Pt separation from acidic waste solutions using a macrocycle-equipped SPE. The feed solution flow-rates, eluent-type or compositions has been optimized to achieve maximum separation efficiency of the target analytes. The relative affinity of the macrocycles in solid-phase toward the ions (Pd > Au > Pt) is the core phenomenon of the proposed technique, and the host-guest type interaction is expected to be more stable than the resinbased separation processes. Furthermore, application of the macrocycle-equipped SPE system is advantageous regarding economics as it minimizes the impact of coexisting ions in the matrix and provides unaltered separation performance for several loading-elution cycles.
Abstract. The westerly wind travelling at high altitudes over eastern Asia transports
aerosols from the Asian deserts and urban areas to downwind areas such as
Japan. These long-range-transported aerosols include not only mineral
particles but also microbial particles (bioaerosols), that impact the
ice-cloud formation processes as ice nuclei. However, the detailed relations
of airborne bacterial dynamics to ice nucleation in high-elevation aerosols
have not been investigated. Here, we used the aerosol particles captured in
the snow cover at altitudes of 2450 m on Mt Tateyama to investigate
sequential changes in the ice-nucleation activities and bacterial communities
in aerosols and elucidate the relationships between the two processes. After
stratification of the snow layers formed on the walls of a snow pit on
Mt Tateyama, snow samples, including aerosol particles, were collected from
70 layers at the lower (winter accumulation) and upper (spring accumulation)
parts of the snow wall. The aerosols recorded in the lower parts mainly came
from Siberia (Russia), northern Asia and the Sea of Japan, whereas those in
the upper parts showed an increase in Asian dust particles originating from
the desert regions and industrial coasts of Asia. The snow samples exhibited
high levels of ice nucleation corresponding to the increase in Asian dust
particles. Amplicon sequencing analysis using 16S rRNA genes revealed that
the bacterial communities in the snow samples predominately included plant
associated and marine bacteria (phyla Proteobacteria)
during winter, whereas during spring, when dust events arrived frequently,
the majority were terrestrial bacteria of phyla
Actinobacteria and Firmicutes.
The relative abundances of Firmicutes (Bacilli) showed a significant positive
relationship with the ice nucleation in snow samples. Presumably, Asian dust
events change the airborne bacterial communities over Mt Tateyama and carry
terrestrial bacterial populations, which possibly induce ice-nucleation
activities, thereby indirectly impacting climate change.
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