摘要:

SUMMARYThe aim was to determine whether the addition of F to an acid soil reduces the concentration of free Al3+and other forms that have been shown to be toxic to plants. The ability of two different extracts to reflect Al speciation in the soil solution was also investigated. Addition of F (0‐5.2μmolg−1) to an acid soil (pH 4.15, soil solution) increased the pH and total concentrations of Al and F in the soil solution whereas Al3+remained constant or decreased. Soil solution pH, total soluble Al and Al extracted by 0.01mCaCl2are not good predictors of the likelihood of aluminium toxicity in soils containing soluble fluo

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01188.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYEquations are given for calculating the initial distribution when a solute is (a) applied at the surface (b) placed below the surface and (c) mixed uniformly in a given depth of top soil. These equations are plugged into a predictive model developed by the authors (Rachhpal‐Singh&Nye, 1986a) to compare the concentration profiles of ammoniacal‐nitrogen and soil pH, and ammonia volatilization losses under the three methods of urea application. Placement of urea gave smaller ammonia losses than uniform mixing in the same depth of soil, which in turn gave smaller losses than surface application. Half‐time for ammonia volatilization was about 6 days irrespective of the method and depth of urea application. Concentration profiles of ammoniacal‐nitrogen and soil pH were more affected by variation in the depth of placement than by depth of mixing. The experimental ammonia volatilization losses and the concentration profiles of ammoniacal‐nitrogen and soil pH agreed very well with those predicted by

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01189.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYBatch adsorption experiments were conducted with a mixture of solutes at low equilibrium concentrations of Cd (0.7‐12.6 μg1−1), Co (18‐118μg1−1, Ni (22‐330 μg 1−1), and Zn (40‐1480 μg1−1) in 38 different soils. Statistical correlations indicated that metal sorption onto the soils was influenced by the presence of clays and hydrous oxides of Fe and Mn. Based on calculated distribution coefficients for these metals, Co will generally exhibit the highest mobility in soils, but the mobility of Zn will increase faster with decreasing pH. Two types of empirical relationships are developed from these data to estimate values for the distri

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01190.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe reaction of cadmium with calcite was studied with 10−6–10−2M Cd2+using 4g CaCO3and 50 ml solution. The calcite‐water suspension was equilibrated for 2 d before adding Cd(NO3)2. The CaCO3surface has a high affinity for Cd and at<1 μmol g−1a linear adsorption isotherm (C‐type) describes the reaction, whereas precipitation of CdCO3on calcite predominates at higher Cd additions. In the latter case pH decreased and solutions were undersaturated with respect to CaCO3indicating that CdCO3prevented the CaCO3surface from reacting with the acidity generated from CdCO3precipitation. The data for low Cd additions suggests that an ideal surface solid solution is formed between CdCO3and CaCO3and the Thorstenson and Plummer equation expressing the pIAP values of surface solid solutions is valid. Equilibrium was attained for low Cd additions in several minutes, whereas precipitation was a slow process; at the changeover point distinction between the two processes is difficult. The reacting surface area calculated from the maximum adsorption of Cd is 0.5‐1.0 times that measured by the BET method.The Cd‐reacting surface areas of four natural calcareous minerals were much less than those found by the BET method which includes the surfaces of other minerals present. The Thorstenson and Plummer equation may be a useful way to relate solution composition and carbonate‐adsorbed Cd in

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01191.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe reactions of Ni, Zn and Cd with goethite were studied over a range of initial metal concentrations (10−6to 10−4M), pH values (4 to 8), reaction times (2h to 42d) and temperatures (5 to 35°C). The adsorption of metals increased with pH, reaction time and temperature. Adsorption of Ni increased relative to Zn and Cd with increasing time and temperature. The initially rapid adsorption of metals within a few hours was followed by a much slower reaction linearly related to time1/2, interpreted as diffusion–controlled penetration of goethite. The pH–dependent relative diffusion rates (Ni>Zn>Cd) were influenced by both affinity for goethite surfaces and by ionic radius. Diffusion coefficients of the three metals ranged from about 10−19to 10−20cm2s−1. The corresponding activation energies of diffusion were also calculated (Ni 35, Cd 55, Zn 90 kJ mol−1). Our view about the reactions of heavy metals with goethite involves (i) adsorption of metals on external surfaces, (ii) solid–state diffusion of metals from external to internal binding sites, and (iii) metal binding and fixation at positions inside the goethite particles. The general parameters of these processes are related to the hydrolytic properties (pKvalues) and the ionic radii of the metals. The results show that goethite may be an efficient sin

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01192.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYCounter ionic migration rates of dilute Cs+and Sr2+against sodium in a Na‐montmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion‐exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for 10−1, 10−2, and 10−3M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2*10−6and 8.0 * 10−6cm2s−1, respectively. These values are found to be essentially independent of background ionic strength over the range 10−3to 10−1mNaCl. Experimental evidence of enhanced transport through Na‐montmorillonite for the divalent cation Sr2+is also confirmed with a surface diffusivity of 2 * 10−6cm2s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01193.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe bulk density of slices cut from resin impregnated soil blocks was obtained by immersion in paraffin. Total porosity was then calculated using measured density of soil solids and the density of the resin. Macroporosity (>350 μm) was obtained by image analysis and microporosity was derived as the difference between total porosity and macroporosity. On four separate sampling occasions throughout the year, there was a good agreement between values of microporosity obtained in this way and volumetric water contents measured at the time of sampling

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01194.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYAggregates of a fine textured (61% clay, 33% silt) soil with a high coefficient of linear expansion (20%) were exposed to successive wet/dry cycles in their natural state and after mechanical reworking. In both cases aggregate size decreased; the reworked sample initially consisted of larger aggregates, but their size fell more rapidly, and after four cycles both the reworked and natural aggregates had a similar size distribution. A model was developed which successfully predicts the proportion of aggregates in each size grade at thenth cycle from that present at the outset. The rate of decrease in aggregates size declined with aggregate size and on both reworked and natural samples the dispersion ratio was low (≤5%

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01195.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe crystallinity of soil kaolinites as a function of clay particle‐size and soil age was investigated in soil chronosequences of the Shingle House Creek and Hawkesbury River alluvial terraces in south‐eastern Australia. The youngest soils (late Holocene) in each sequence are texturally uniform Entisols containing kaolinite and illite. The oldest soils (Pleistocene to late Tertiary) are Ustalfs with strong textural differentiation and are predominantly kaolinitic. With increasing age, textural B horizons are increasingly enriched in kaolinite and in particles of fine clay (<0.2 μm) size. In two sub‐fractions of the fine clay (0.2‐0.06 μm;<0.03 μm), no corresponding changes were observed in the crystallinity of kaolinites (as measured by the index,Ck) with age. However, values ofCkwere significantly higher in the coarse clay (2‐0.2 μm) than for both fine clay fractions in all except the Ultic Paleustalf of the oldest, possibly late Tertiary, terrace of the Hawkesbury River sequence. In this soil,Ckvalues are low in all three clay‐size fractions.In these sequences, the effects of both clay particle‐size and soil age were identified in the crystallinity of kaolinites. Disorder as a result of pedogenesis, however, was associated only with the most prolonged weathering and the strongest soil textura

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01196.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

SUMMARYThe effect of boiling 5 M NaOH on the nature of poorly crystalline iron oxides in some iron pans from Scottish soils has been investigated by IR and Mössbauer spectroscopy in conjunction with XRD. In samples that contained goethite and other crystalline oxides there was substantial production of goethite from the less well‐defined phases as a result of the alkali treatment. Neither kaolinite nor humic acid, when added to the samples, was effective in preventing this transformation, although some inhibition was observed. There was, however, no goethite production with a pan that had no crystalline iron oxides, although this could be stimulated by the addition of small amounts of either goethite or haematite. The practice of using the boiling alkali method routinely for the concentration of crystalline iron oxides in soils should, therefore, be considered carefully, since any co‐existing crystalline and non‐crystalline phases are likely to lead to the transformation of the latter to go

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1988.tb01197.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY