Browsing by Author "Hinz, C."
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Dikinya, O.; Hinz, C.; Aylmore, G. (Elsevier http://www.linkinghub.elsevier.com/retrieve/pii/S0016706108001365, NaN, 2008)[more][less]
Abstract: The dynamics of the process of self-filtration in soil columns have been evaluated for two soils with different structural cohesion (Balkuling agricultural soil and a mining residue) by carrying out experiments focusing on microscopic particle behaviour during filtration. Soil column experiments were set up to simultaneously measure changes in hydraulic gradients (ΔH/ΔL) along the columns and outflow particle sizes and concentrations during pressure leaching with solutions of 100, 10 and 1 mmol/L NaCl and deionised water. The lowest ionic strength has resulted in more reduced hydraulic conductivity and relatively more release of colloids associated with hydrodynamic shear and dispersion. Steady increases in hydraulic gradient (ΔH/ΔL) and corresponding decreases in relative saturated hydraulic conductivity (K/Ko) with time were observed for both soils and follow similar trends at all column depths. The most severe increases in ΔH/ΔL and decreases in K/Ko always occurred near the inlet to the columns and the decline gradually decreased along the column. The decrease in K/Ko and increase in ΔH/ΔL were clearly influenced by the size as well as the concentration of migrating particles in the porous medium. The finer mobile particles in the mining residue were clearly more readily self-filtered at the lower concentration than the larger Balkuling soil particles producing more rapid increases in ΔH/ΔL and decreases in K/Ko. This was attributable to more effective self-filtration and more pore clogging probably due to increased development of the diffuse double layer, swelling and dispersion within the soil matrix at these concentrations. URI: http://hdl.handle.net/10311/488 Files in this item: 1
Dikinya_Geoderma_2008.pdf (1.429Mb) -
Dikinya, O.; Hinz, C.; Aylmore, L.G. (Csiro, http://www.publish.csiro.au/nid/84.htm, NaN, 2007)[more][less]
Abstract: The paper examines the effects of electrolyte concentration and sodium adsorption ration (SAR) on the relative saturated hydraulic conductivity (RHC) and the ionic behaviour of calcium (Ca) and sodium (Na) ions in the Na-Ca echange complex. Batch binary exchange and saturated column transport experiments were carried out to quantify these effects using agricultural Balkuling soil and mining residue. Generally, RHC has been found to decrease with time, with increasing SAR and with decreasing electrolyte concentration. The more rapid decrease in RHC in the mining residue, particularly at the lowest concentration (1 mmol/L), was consistent at all SAR values. The decreases in RHC were likely to be caused by partial blocking of pores by dispersed clay particles, as evidenced by the appearance of suspended clay particles in the effluent during leaching. Significant differences in RHC were abserved in the passage of fronts of decreasing electrolyte concentration for CaCl2 and SAR 15 solutions through the soil columns. These differences were attributable to structural alterations (slaking) of the media and the nature of the particles released and mobilised within the porous structure at a given point in the column. Measurements at the critical threshold concentration and turbidity increase in SAR to 15 is initially accompained by erractic RHC, presumably due to the break up of soilaggregates under the increased swelling forces. The less coherent mining residue soil was substantially more vulnerable to blockage of pores than the Balkuling soil in which clay particles are likely to be more readily mobilised, and hence available to re-deposit and occlude the matrix pores. URI: http://hdl.handle.net/10311/312 Files in this item: 1
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Dikinya, O.; Lehmann, P.; Hinz, C.; Aylmore, G. (Wiley http://www.interscience.doi.wiley.com/10.1002/hyp.6299, NaN, 2008)[more][less]
Abstract: A pore-scale model based on measured particle size distributions has been used to quantify the changes in pore space geometry of packed soil columns resulting from a dilution in electrolyte concentration from 500 to 1 mmol l 1 NaCl during leaching. This was applied to examine the effects of particle release and re-deposition on pore structure and hydraulic properties. Two different soils, an agricultural soil and a mining residue, were investigated with respect to the change in hydraulic properties. The mining residue was much more affected by this process with the water saturated hydraulic conductivity decreasing to 0Ð4% of the initial value and the air-entry value changing from 20 to 50 cm. For agricultural soil, there was little detectable shift in the water retention curve but the saturated hydraulic conductivity decreased to 8Ð5% of the initial value. This was attributed to localized pore clogging (similar to a surface seal) affecting hydraulic conductivity, but not the microscopically measured pore-size distribution or water retention. We modelled the soil structure at the pore scale to explain the different responses of the two soils to the experimental conditions. The size of the pores was determined as a function of deposited clay particles. The modal pore size of the agricultural soil as indicated by the constant water retention curve was 45 μm and was not affected by the leaching process. In the case of the mining residue, the mode changed from 75 to 45 μm. This reduction of pore size corresponds to an increase of capillary forces that is related to the measured shift of the water retention curve. URI: http://hdl.handle.net/10311/490 Files in this item: 1
Dikinya_HP_2008.pdf (1.769Mb)
Now showing items 1-3 of 3