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.

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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.

Summary The potential of biochar to ameliorate soil water repellency has not been widely studied. Previous studies have focused on the potential for biochar to induce or exacerbate existing water repellency rather than alleviate it. This study investigates the effect of adding wettable biochar to water‐repellent soil by comparing the water drop penetration times (WDPTs) of a control and biochar‐amended soil. The potential of wettable biochar to act as a physical amendment to water‐repellent soil was evaluated by mixing coarsely‐ground biochar (CGB, particle size range 250–2000 µm) or finely‐ground biochar (FGB, particle size range < 250 µm) with one strongly and one severely naturally water‐repellent soil in various quantities, and then measuring the WDPT for each mixture. When biochar particles did not fall within the size range of existing soil particles, an initial increase in both mean WDPT (WDPTM) and variation in WDPT was observed with small additions of biochar. These effects possibly result from increased surface roughness and inhibition of infiltration by the suspension of drops above the average soil–air interface at a few hydrophobic points. Both CGB and FGB reduced soil water repellency, FGB more effectively than CGB. The addition of 10% w/w FGB reduced soil WDPT by 50%, and 25% FGB eliminated repellency. Direct absorption of water by biochar and an increase in soil surface area in contact with water are the predominant physical mechanisms involved. This exploratory study suggests biochar has the potential to amend water‐repellent soil.

Charcoals have long been used to adsorb organics from water and other substrates; we hypothesise that biochar may act in a similar way when mixed with soil, removing hydrophobic organic compounds from the soil surfaces. To test this hypothesis, we developed quantitative methods for addition of two hydrophobic organic compounds (octadecane and octadecanoic acid, commonly found in naturally hydrophobic soils) to, and their subsequent extraction from, acid washed sand (as a model for sandy soil). We then measured the quantity of the organic compounds which remained on the sand after: deposition; subsequent addition of 0, 1, 5, 10, 25 or 40% wettable biochar; and storage for 1, 10, and 30 days in solutions of pH 3, 6 or 9. We found that there were small reductions in hydrophobic compound coverage of sand with 1 and 5% biochar additions, but that 10% biochar reduced coverage by 50%, and ≥ 25% biochar reduced coverage by 100%. The significance of these results in understanding the potential of wettable biochar to remove hydrophobic compounds from sandy soils, and thus act as an ameliorant of soil water repellency, is discussed.

Phosphogypsum (PG), a byproduct of the phosphate fertilizer industry, was produced and stockpiled at the Agrium Fort Saskatchewan facility from 1965 to 1991. Upon decommissioning, the outer slopes of the PG stacks were reclaimed by applying 15 cm of topsoil and planting a non-native seed mix. Physical, chemical, and hydrologic evaluations of the cover system confirmed that plants were successfully growing in various soil capping depths and were often rooting more than 200 mm into the PG. Percolation past the substrate into PG during a typical storm event was low (< 10 mm), and runoff from the stacks was negligible. Runoff quality met most guidelines, but some parameters, including fluoride, were up to 18 times higher than provincial or federal guidelines for soil and water quality. However, the cover system, when applied appropriately, does meet basic reclamation objectives. The exceedances are found in areas where the cover system has been compromised by erosion or mixing or in areas where the cover system has not been fully applied, such as roads or the inner basin. In areas where the cover system has been applied successfully, basic reclamation requirements are met.