Summary
In previous studies, extracts from water‐repellent soils have been applied to wettable substrates to examine the role of organic matter in causing water repellency, but the effects of individual compounds found in water‐repellent soils have not been examined. To address this research gap, acid‐washed sand (AWS) and wettable sandy soil were coated with a range of hydrophobic organic compounds that had been identified by gas chromatography‐mass spectrometry (GC‐MS) analysis of extracts from a range of water‐repellent soils in previous published work. Saturated and unsaturated long chain acids, alkanes, amides, esters, cholesterol and β‐sitosterol were applied at various loadings to investigate the effects of chain length, molecular shape, functional group, heating, particle size and packing efficiency on soil wettability. No single compound induced repellency on AWS at loadings equivalent to the level of detection of individual compounds in water‐repellent soils by GC‐MS. The extent of water repellency induced on AWS varied considerably with compound type, suggesting that it depends more on the presence of specific compounds rather than their quantity. A combination of long chain acid and alkane was found to be the most effective at inducing water repellency. Heating at 105°C for 24 hours caused a marked increase in repellency. Particle size had no effect on degree of induced repellency across the approximately 2.5 times variation in diameter examined.
Precious metal (PM) and copper content of dynamic-RAM modules placed on the market during 1991-2008 has been analysed by AAS following comminution and acid digestion. Linear regression analysis of compositional data ordered according to sample chronology was used to identify historic temporal trends in module composition resulting from changes in manufacturing practices, and to project future trends for use in more accurate assessment of future recycling potential. DRAM was found to be 'high grade' waste with: stable levels of gold and silver over time; 80% reduction in palladium content during 1991-2008; and 0.23g/module/year increase in copper content with a 75% projected increase from 2008 by 2020. The accuracy of future recycling potential projections for WEEE using current methods based on static compositional data from current devices is questionable due to likely changes in future device composition. The impact on recycling potential projections of waste laptops, smart phones, cell phones and tablets arising in Europe in 2020 resulting from a 75% increase in copper content is considered against existing projections using static compositional data. The results highlight that failing to consider temporal variations in PM content may result in significant discrepancies between projections and future recycling potential.
Localized variations at the nanoscale in soil aggregates and in the spatial organisation of soil organic matter (SOM) are critical to understanding the factors involved in soil composition and turnover. However soil nanoscience has been hampered by the lack of suitable methods to determine soil biophysical properties at nanometre spatial resolution with minimal sample preparation. Here we introduce for the first time an Atomic Force Microscopy (AFM)-based Quantitative Nano-Mechanical mapping (QNM) approach that allows the characterisation of the role of SOM in controlling surface nano-mechanical properties of soil aggregates. SOM coverage resulted in an increased roughness and surface variability of soil, as well as in decreased stiffness and adhesive properties. The latter also correlates with nano- to macro-wettability features as determined by contact angle measurements and Water Drop Penetration Time (WDPT) testing. AFM thus represents an ideal quantitative tool to complement existing techniques within the emerging field of soil nanoscience.
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