摘要:

SUMMARYThe formation of partially interlayered vermiculite (PIV) was studied in six Dystrochrepts derived from Tertiary sediments. Mineralogy of silt and clay fractions of gravel and fine earth separated from surface and subsurface samples were determined by X‐ray diffraction. PIV, mica, vermiculite and regularly interstratified 1:1 PIV/chlorite (PIV/Ch(l:l)) were the dominant clay minerals. The contents of these minerals were compared between the specific particle‐size fractions of gravel and fine earth for each sample and the difference was interpreted in terms of mineral transformation associated with soil formation. PIV was formed from mica and PIV/Ch(l:l) in soils with a pH(KCl) of 3.5 to 4.0 and little organic matter. Vermiculite was formed from mica in surface soils with a low pH (pH(KCl) 3.5) and abundant organic matter. PIV would form directly from mica without an intermediary phase of vermiculite and form from PIV/Ch(l:l) by partial dissolution of interlayers in chlorite lay

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01248.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYEquilibrium competitive‐adsorption coefficients derived from the application of the multi‐component Freundlich‐type Sheindorf‐Rebhun‐Sheintuch (SRS) equation appeared to have a soil‐specific, quasi‐thermodynamic basis. Using three soils, single‐solute adsorption isotherms at 288, 298, and 308 K were constructed with arsenate, phosphate, and molybdate. A Clausius‐Clapeyron‐type equation was used to estimate apparent isosteric heats of adsorption values (qiso). The adsorption of the three anions was characterized by differentqisovalues, and was generally in the order of H2PO4‐>H2AsO4‐>MoO42‐. The magnitudes of the SRS competitive coefficients derived from binary‐solute mixtures were in agreement with the distributions of the heats of adsorption of the individual anion‐soil systems. Higher competitive coefficients, indicating the preferential adsorption of solute i in a binary‐solute mixture containing solutes i and j, tended to associate with higherqisovalues for solute i relative to solute j. However, theqisovalues for the adsorption of molybdate by one soil underestimated the extent of competitive interactions

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01249.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYThe pH of samples of a soil was altered by mixing them either with acid or lime, and incubating the moistened samples at 60°C for a day. The sorption of selenate and of selenite was then measured using as background electrolytes, 0.01 M, 0.1 M and 1.0 M sodium chloride and also 0.01 M calcium chloride. The results were compared with previous studies with phosphate and fluoride.Selenite was sorbed more strongly than selenate, but not as strongly as phosphate or fluoride. Sorption of both selenite and selenate decreased with increasing pH. This decrease was more marked for selenate than for selenite; more marked in a sodium system than in a calcium one; and more marked with a dilute background electrolyte than a concentrated one. Under certain conditions, the steeper curves for the dilute electrolyte crossed the curves for the concentrated electrolyte giving points of zero salt effect. For selenite, these points of zero salt effect occurred near pH 6 and the greater the sorption the lower the pH for zero salt effect. For phosphate, the analogous value was near pH 5. For selenate, if a point of zero salt effect occurred, it was at such a high pH and such a low amount of sorption that it could not be measured. Thus, the larger the amount of sorption the lower the pH for the point of zero salt effect. This generalization applied both within and between different kinds of sorbates.The results were closely described by a model that had previously been applied to phosphate and fluoride. The model postulates that ions react with charged surfaces. The electric potentials of the reacting surfaces are affected by the identity and concentration of the background electrolyte and this produces the interactions between pH and electrolyte concentration. The model also postulates that there is a distribution of electric potentials. Anions react with surfaces which occur in the more positive tail of this distribution. The smaller the amount of the reaction the more positive the potential of the reacted surface and, therefore, the higher the pH required to decrease this potential to zero

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01250.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYSeveral levels of both selenite and selenate were incubated with separate samples of soil for periods of up to 30 d and at temperatures between 5 and 60°C. The concentrations of selenite or of selenate which caused neither desorption nor further sorption–that is, the null‐point concentrations–were then measured at 25°C. In addition, the rate of desorption was measured after incubation at 60°C for 10 d. The ability of a mechanistic model to describe the results was tested.There were large decreases in the null‐point concentrations of selenite with both increasing period and increasing temperature of incubation. These effects were modelled as due to a relatively rapid diffusive penetration and a large activation energy for diffusion. Only a small proportion of the sorbed selenite was desorbed within 3 d but, at large solution:soil ratios, desorption appeared to be still continuing. These effects were fairly well predicted by the model applied to the sorption data. For example, the continuing desorption was ascribed to the slow reversal of the diffusive penetration. For selenate, the effects of period and temperature of incubation were much smaller. These effects were modelled as due to a slower diffusive penetration and a lower activation energy. Desorption was quicker and was more nearly complete. According to the model, a large proportion remained in the adsorbed form and was more quickly removed when desorption was induced. It is argued that the behaviour of selenite is consistent with diffusion into a crystal and the large activation energy is required to enable jumps over energy barriers. On the other hand, the lower activation energy for selenate is consistent with diffusion being limited to pores or cracks.It is suggested that the residual value of selenite fertilizers would decrease because of the continuing reaction, but that this effect would be unimportant fo

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01251.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYThe reaction of copper and zinc were studied by adding the metal nitrate to a 4g:50ml suspension of calcite and water which had been equilibrated for two days, and then equilibrating for a further three days. Zinc behaved in a similar manner to cadmium in forming a surface‐solid solution of ZnχCa1‐χCO3as a result of adsorption, and the pIAP of the equilibrium solutions were close to those expected from the Thorstenson&Plummer equation. However, the continuity from adsorption to precipitation was broken by the formation of Zn5(OH)6(CO3)2which has a higher stability than ZnCO3. The CaCO3surface appears to constrain the adsorbed Zn to conform to a carbonate structure despite its lower stability than the hydroxy carbonate.The adsorption data for Cu can also be explained in terms of a surface‐solid solution of CuχCa1‐XCO3, but CuCO3is not found naturally because of much greater stability of Cu(OH)2, and so there is no independent value for the solubility of a CuCO3end‐member if a surface‐solid solution is formed. Secondary reactions are more likely to occur for Cu, especially close to the adsorption‐precipitation boundary. Continuity from adsorption to precipitation again was not found. Theory predicts that Cu is less likely to form a surface‐solid solution than Zn.Upper Chalk (calcite with 4% other minerals, mostly quartz) behaved in a similar way but with increased adsorption due to its h

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01252.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYP‐Zn interactions can affect fertilizer use and produce Zn deficiencies with certain crops. Phosphorus‐Zn sorption‐desorption reactions were studied in topsoil and subsoil samples from three Quebec soils. Soils were equilibrated with P solutions, then with Zn solutions, and finally with solutions containing no P or Zn. The first equilibration evaluated P sorption (Ps), the second evaluated Zn sorption (Zns) after P sorption (Ps), and the third evaluated Zn desorption (ZnD) as related to added P. Subsequently, Zn fractions were extracted sequentially with KNO3(Znkno3), NaOH (ZnNaOH) solutions and concentrated HN03+ H202(ZnHNO,).One mmole sorbed P resulted in increases of 0.5 to 1.0 meq (mean = 0.72) increases in cation exchange capacity (CEC). Increased Znswith added P was equivalent to 4 to 5% of the increase in CEC induced by Psin the Uplands (sand) and St. Bernard (loam) soils, and 0.4 to 0.9% in the Dalhousie (clay) soils, while one meq increase in CEC resulted in 1.5‐3.5% decrease in ZnD. There existed positive correlations between Psand extractable soil Fe materials. Phosphate sorption enhanced associations between Zns, ZnDor Zn fractions and soil organic or crystalline Fe contents, confirming that P addition increased specific sorption of Zn on Fe components. Other mechanisms including precipitation, P‐induced negative charge and ‘bridge’ effects are a

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01253.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYThe effects of lime (applied in the field) on the amounts of total and isotopically‐exchange‐able phosphate adsorbed from solutions were measured in five soils. The total amount of phosphate adsorbed without lime was in the range 200 to 1700 μg P per g of soil at 0.05 μg P cm−3of solution. Lime diminished the amount of phosphate adsorbed at all concentrations of solution in an oxisol and a dystropept; in an ultisol and another dystropept, lime tended to increase sorption at small concentrations and diminish it at large concentrations; in a dystrandept that contained spheroidal allophane and a great deal of organic matter, lime increased adsorption at all concentrations up to 1 μg P cm−3. Lime increased the proportion of added phosphate that was isotopically exchangeable in the oxisol and one dystropept, had no effect in the other dystropept, and diminished the proportion in the ultisol and dystrandept.Adsorbed phosphate was subsequently desorbed by suspending the soils in solutions without phosphate. After desorption the quantity of exchangeable phosphate in all soils was closely correlated with aluminium extracted by ammonium oxalate; buffer power was correlated in all except the dystrandept, in which it was larger per unit of aluminium than in the other soils; possibly the cause was aluminium associated with organic matter. In all soils lime diminished buffer power allowing a specific amount of exchangeable phosphate to maintain a larger concentration in solution. The beneficial effects of lime on exchangeable phosphate after desorption were consistent among soils, despite inconsistent results when the phosphate wa

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01254.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYA simple mechanistic model is developed for predicting the fate of radioactive caesium in the soil beneath grassland. A continuity equation is derived describing the diffusion, leaching and reaction of caesium in soil, with uptake by a uniformly distributed root system. The soil reaction is characterized by three phases: an instantaneous exchange, a moderately‐fast reversible reaction and a slow reversible reaction. The time‐dependent reactions and root uptake have first‐order kinetics. It is shown that caesium is unlikely to be removed from the root zone by leaching and diffusion, even under prolonged high rainfall. Therefore, since the rates of the soil reactions and root uptake are much greater than the rates of diffusion and leaching, it is not necessary to calculate the concentration profile to find the rate of uptake. The computer program for the model is just 30 lines offortran, and requires only a few seconds of micro‐computer CPU time for each year of simulation.Some predicted rates of plant uptake and distributions in the soil are given. It is seen that the fate of the caesium is markedly influenced by soil parameters dependent on soil clay content, clay mineralogy, organic matter content, cation saturation and pH, and by the rooting density. The predicted rates of uptake vary from about 0.5% to 50% per annum, which is compatible with data reported elsewhere. The predictions are intended to expose gaps in knowledge of the fate of caesium in soil: in particular, the mobility of sorbed radio‐nuclides on soil surfaces needs further study. Predictions are not given for the fate of caesium in any real situations because insufficient data are

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01255.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYSurface and subsurface samples of three tropical soils were examined with respect to their interaction with dilute solutions of sulphuric acid of pH 3. In calcareous clayey samples with a large cation exchange capacity the H+was replaced by an equivalent concentration of metal cations which remained in solution along with SO2‐4as counterion. In a coarse‐textured neutral soil with small cation exchange capacity, there was less chemical interaction and a major proportion of the H2SO4remained unchanged in the equilibrium solution. Another soil exhibited considerable ability to remove SO2‐4from solution and, therefore, the total ionic concentration was greatly reduced. Other samples showed behaviour which was intermediate to these three types.The ability to adsorb SO2‐4is one of the most important factors which determines the nature of the interaction of soil with dilute sulphuric acid. This ability was shown to be affected by the content of hydrous sesquioxides and organic matter in thes

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01256.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SUMMARYComparison was made between the chemical composition of soil solutions isolated by means of a suction method using porcelain cups and by centrifugation. The soil solutions were isolated from three depths of field plots, where the soil (Typic Haplohumod) had been subjected to various pretreatments.The cups were made of mullite and corundum as shown by X‐ray diffraction analysis. The material when powdered had a cation exchange capacity of about 10meq kg−1. Solutions with similar ionic strengths were obtained by the two methods, but the cups were found to release substantial amounts of Al and to adsorb H, Ca, K, Na and organic matter.After the cups had been placed in the soil for more than 7 months, calculations suggested that the Al activity in cup solutions was controlled by amorphous gibbsite. This amorphous material was probably produced by proton‐induced decomposition of part of the cup material. It is concluded that such cups are improper for isolation of soil solution from acid

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1989.tb01257.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY