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1.
Using a soil from a newly reclaimed area where high dispersibility of fine particles had led to poor physical properties in the field, changes in dispersibility and charge characteristics after artificial precipitation of Al hydroxides onto the soil were investigated. Al hydroxides were precipitated by neutralization with NaOH of an acidic A1C13 solution in which the soil samples were placed.

When the titration rates were changed, no significant differences in dispersibility were observed in the resultant soils. In the systems with the addition of 2 g kg-1 or less of A1(OH)3, dispersion ratios of clays were almost identical with those of blank samples although the specific surface areas were reduced. In the systems with 5 g kg-1 or more of A1(OH)3, considerable effects of Al hydroxides on reduction of clay dispersibility were recognized (e.g. 10 g kg-1 addition yielded less than one-third of the original ratio of the clay dispersion). A slightly larger decrease in dispersion was observed by the addition of 15 g kg-1 or more. As the amount of added Al increased, the amount of negative charges of the soil decreased while that of positive charges increased. The charge characteristics of the system with the addition of 20 g kg-1 of A1(OH)3 were closer to those of the adjacent forest soil which was characterized by a very low dispersibility. It was inferred that added Al hydroxides polymerized to form Al polycation species that were not readily exchangeable, neutralizing negative charges of clays, and acting as interparticle bonding between the clays. On the other hand, forest soils were considered to have acquired a physical stability against the dispersion of fine particles as free Al oxides had been accumulated in the process of natural weathering. It was concluded that charge characteristics primarily determined the dispersion and flocculation behavior of soils and that Al hydroxides were important modifiers of charge characteristics of soils.  相似文献   

2.
Changes in dispersibility and charge characteristics of two soils with different colloidal properties were investigated after various extracting treatments of free oxides. The soil samples were taken from the upland field in a reclaimed area (highly dispersive) and from the B horizon of an adjacent forest area (physically stable), both of which derived from the same parent material. Special attention was paid to selective extraction of Al and Fe oxides. After the extraction of free oxides by conventional methods such as DCB or oxalate treatment, dispersibility of the soils which always became too high made it difficult to relate the amounts of removed oxides with the changes in dispersibility. Thus, extractions by milder treatments were designed in order to remove varying amounts of free oxides using several organic salt solutions. Among the treatments, citrate and oxalate extracted more Al oxides, followed by tartrate. Dithionite, acetate, and NaCl extracted only trace amounts of Al oxides. This order seemed to be controlled by the stability constants of organo-Al complexes. The changes in dispersibility of the residual soil were related to the amount of extracted Al, especially for the forest soil, but not to Fe or Si. After these treatments, the amount of positive charges of the soil decreased while that of negative charges increased. For instance, the amount of total charges of the forest soil after DCB treatment was 1.5 times larger than that of the non-treated soil at the dispersion pH, which was mainly attributed to the removal of Al oxides. Although the amount of removed Al oxides was relatively small, the changes in dispersibility of the residual forest soil were drastic, indicating that free oxides (mainly Al) removed by milder treatments were the most external, active fractions. This interpretation suggests the practical importance of the release of amorphous sesquioxides in the natural weathering process in preventing the dispersion of potentially dispersive soils.  相似文献   

3.
对 3种可变电荷土壤和 4种恒电荷土壤在不同 pH、不同浓度、不同相伴阴阳离子下混合体系中Cl-和NO3-的吸附进行了测定。结果表明 ,在Cl-和NO3- 共存体系中 ,Cl-比例增大使可变电荷土壤Na+吸附量及OH-释放量增加 ,而对恒电荷土壤影响不大。Cl-和NO3-吸附量随平衡Cl-和NO3-浓度增加而增大 ,随pH升高而减少。但恒电荷土壤在上述各种条件下对Cl-和NO3-吸附均相同 ,而可变电荷土壤对Cl-吸附量大于NO3-的吸附量 ;NO3-、Cl-的选择系数为 0.51～0.78,Cl-和NO3-的相对吸附量分别为56.9%和 43.1%。在不同相伴阳离子下 ,可变电荷土壤平衡溶液Cl-/NO3-比值均小于 1,且为Na+K+Ca2+Mg2+Fe3+;而恒电荷土壤Cl-/NO3-比值为 1左右 ,且不受阳离子类型的影响。由此认为 ,Cl-和NO3-在两类土壤中均以电性吸附为主 ,恒电荷土壤对Cl-和NO3-的亲合力及吸附机理相同 ;而可变电荷土壤对Cl-的亲合力 NO3- ,Cl-存在着专性吸附  相似文献   

4.
Mercury adsorbed from HgCl2 and 2-methoxy-ethylmercury chloride (Aretan) solutions by three contrasting soils showed a dependence on soil: solution ratio and initial Hg concentration in soil solution. Changing the soil solution ratio from 1: 10 to 1 : 100 but keeping the initial concentration constant resulted in an increase in Hg adsorption from both Hg compounds. A similar change in soil: solution ratio accompanied by a decrease in initial concentration, on the other hand, resulted in decrease in Hg adsorption. Upon manipulating of the pH of the surface soils, adsorption of HgCl2 at 100 mg Hg L?1 concentration increased from about 701 :o over 95 mg Hg kg?1 when pH was raised from 5.0 to 8.0. Precipitation of Hg may also have contributed to this trend. Aretan adsorption by these soils, on the other hand, changed little with change in pH. Removal of organic matter from soil resulted in large reductions of Hg adsorbed, as much as 95 % from the HgCl2 solutions, but only up to 31 % from Aretan solutions. This suggests that organic matter in soil played a mayor role in the adsorption of inorganic Hg whereas the soils' mineral fractions were involved more in the adsorption of the organic Hg compound.  相似文献   

5.
This paper describes the conditions for dispersion and flocculation of clays, and the impact of this process on soils of contrasting textures cropped with rice. Clay seems to be translocated down the profiles and along a topographic sequence. The clays are mixed kaolinite–smectite. The cation exchange capacity of these clays exceeds 20 cmolc kg?1. Both the proportion of smectite and clay content increase with increasing depth and from the top to the lower part of the sequence. The pH ranges from 5 to 8. The aluminium oxide content is small. The soil solutions collected during the rainy season were analysed for Fe2+ and major cations. We calculated the sodium adsorption ratios (SAR) taking into account Fe2+ and compared them with the critical coagulation concentration (CCC) found in a previous study. The Fe2+ contributed to a decrease in the SAR of cropped soils. The comparison between SAR, total electrolyte concentrations and CCC values showed that the dispersible clays are likely (i) to disperse in the abandoned and non‐saline fields, (ii) to flocculate in the saline and uncropped soils as a result of the large salt content and in the cropped soils because of either large salt or Fe2+ content, and (iii) to disperse in the flood water and at the surfaces of abandoned fields under rain. No evidence for ferrolysis was found. The observed contrasting textures and clay mineralogy can be explained by clay translocation controlled by salinity and rice farming.  相似文献   

6.
A cell consisting of a chloride-selective electrode and a nitrate-selective electrode was directly put in the soil suspension to determine the concentration ratio NO3?/Cl? for studying the adsorption of these two ions by three soil samples from variable charge soils. It was found that such factors as the iron oxide content of the soil, the pH of the suspension, the concentration of the respective anion, the kind of accompanying cations, and the dielectric constant of solvent etc. can all affect the amounts and the ratio of the two anions adsorbed. The adsorption was chiefly caused by coulombic force, but another mechanism, presumably a covalent force between the anion and the metal atom on the surface of soil particles, may also be involved, at least for chloride ions.  相似文献   

7.
Inceptisols and Vertisols are two dominant soil orders that support major agricultural production in India. These soils often exist in semi-arid and arid regions. Low precipitation and high evaporation demand leads to salt accumulation in these areas. The problem of salt accumulation is further compounded by the presence of saline/alkaline groundwaters. We evaluated the effect of modified Ca/Mg waters on ionic composition, dispersion, and clay flocculation of sodic Inceptisols, saline-sodic Inceptisols, and normal Vertisols from different parts of India. A completely randomized factorial design with three replications of individual soils were sequentially leached with five pore volumes of deionized, saline water of 60 and 120 me L?1 total electrolyte concentration (TEC) at a fixed SAR of 5.0 mmol1/2 L?1/2 and Ca:Mg ratio of 2:1, 1:1 and 1:2. Application of saline waters decreased pH and increased EC of the soil leachates after leaching five pore volumes of three Ca/Mg ratios of 60 and 120 me L?1 solutions in sodic Inceptisols and normal Vertisols. In saline-sodic Inceptisols, application of saline waters decreased both pH and electrical conductivity (EC) of the soil leachates. Preferential Ca2+ holding in soil was only noticed in sodic Inceptisols when leaching process was performed with independent saline waters, but Mg2+ has a tendency to hold in soil upon application of independent saline waters for all soils except sodic Inceptisols. Periodic application of deionized water could increase soil dispersion and decreased flocculation of clay particles. Mg2+ ion had less flocculating vis-à-vis high-dispersion effect on soil clays than the Ca2+ ion.  相似文献   

8.
A pH-glass and calcium-selective electrode pair was used for the measurement of lime potential of soils. The lime potential was higher when measured in CaCl2 solutions of high concentration and with high solution to soil ratio for soils with considerable positive charge. Water or 10?3 M CaCl2 solution and a solution to soil ratio of 1:1 is suggested. Some examples of the application of the proposed method in soil research are given.  相似文献   

9.
Two Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp?3 Ca(NO3)2, and various concentrations of NaNO3 (0.01–1.5 mol dm?3) as background solutions at a range of pH values (3–8). In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable-charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable-charge components, there was a characteristic pH below which increasing ionic strength of NaNO3 increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH>PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non-specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.  相似文献   

10.
The release of hydroxyl ions from two variable charge soils associaed with the adsorption of chloride in NaClO4 solutions was examined.The complete release required about 10 minutes The release decreased with the increase in the NaClO4 concentration at first and eventually was little affected by the latter.The adsorption of Cl^-1 was almost linearly related with the quantity of NaCl added to the system,while the OH^- release-NaCl curve varied with the soil type and the concentration of NaClO4.The logarithm of the quantity of released OH^- was linearly related with the pH ,The ratio of release OH^- to adsorbed Cl^- was larger in dilute NaClO4 solutions than in concentrated solutions and decreased with increasing NaCl.  相似文献   

11.
磷酸盐吸附对可变电荷土壤正负电荷的影响   总被引：9，自引：1，他引：9       下载免费PDF全文
赵安珍  张效年 《土壤学报》1997,34(2):123-129
本文研究了华南地区不同类型的可变电荷土壤，并对磷酸盐的吸附量和吸附磷后土壤的正、负电荷的变化，以及ｐＨ和游离氧化铁对这种变化的影响进行了研究。结果表明，土壤吸磷量与土壤游离氧化铁含量成良好的正相关。土壤吸磷后正电荷减少，负电荷增加，土壤电荷量与吸磷量之间呈抛物线状相关。吸附１摩尔磷酸盐对土壤净负电荷的贡献在０．３－１．０摩尔之间。土壤中的游离氧化铁使吸附的磷对土壤负电荷的贡献减少。  相似文献   

12.
R. MOREAU  J. P&#;TARD 《土壤圈》2004,14(4):409-423
Highly weathered soils are distributed in the humid and wet-dry tropics, as well as in the humid subtropics. As a result of strong weathering, these soils are characterized by low activity clays, which develop variable surface charge and related specific properties. Surface reactions regarding base exchange and soil acidification, heavy metal sorption and mobility, and phosphorus sorption and availability of the tropical highly weathered soils are reviewed in this paper. Factors controlling surface reactivity towards cations and anions, including ion exchange and specific adsorption processes, are discussed with consideration on practical implications for rational management of these soils. Organic matter content and pH value are major basic factors that should be controlled through appropriate agricultural practices, in order to optimise favorable effects of colloid surface properties on soil fertility and environmental quality.  相似文献   

13.
The adsorption of the insecticidal Cry1Ab protein of Bacillus thuringiensis (Bt) on Na-montmorillonite (M-Na) and soil clay fractions was studied. The aim of this study was not to find the adsorption capacity of the soils from the experimental field site, where Bt corn (MON810) was cultivated, but rather to characterize the adsorption behavior of the Cry1Ab protein at concentrations typically found at experimental field sites. In kinetic experiments, the Cry1Ab protein adsorbed rapidly (<60 min) on M-Na. As the concentration of M-Na was varied and the added Cry1Ab protein concentration was kept constant (20 and 45 ng ml−1), the adsorption per unit weight of Cry1Ab protein decreased with increasing concentrations of M-Na. Adsorption of Cry1Ab protein on M-Na decreased as the pH value of the suspension increased. All adsorption isotherms could be described mathematically by a linear regression with the parameter k, the distribution coefficient, being the slope of the regression line. Although their mineralogical composition was nearly identical, the soil clay fractions showed different k values. The different k values were correlated with the physical and chemical properties of the soil clay fractions, such as the organic carbon content, the specific external surface area, and the electrokinetic charge of the external surfaces of the clays, as well as with the external surface charge density. An increase in the amount of soil organic matter, as well as an increase in the electrokinetic external surface charge of the soil clays, decreased the distribution coefficient k. An increase of the specific external surface areas of the soil clays resulted in a higher distribution coefficient k.Less than 10% of adsorbed Cry1Ab protein was reversibly adsorbed on the soil clays and, thus, desorbed. The desorption efficiency of distilled water was higher than that of a solution of CaCl2 (2.25 mmol) and of dissolved organic carbon (50 mg C l−1).  相似文献   

14.
不同土地利用方式土壤对铜、镉离子的吸附解吸特征   总被引：1，自引：0，他引：1  
采用一次平衡法对Cu2+、Cd2+在城市及城郊农田、林地、草地3种土地利用方式土壤中的吸附解吸过程进行比较研究, 结果表明: Cu2+、Cd2+在3种土地利用方式土壤中的吸附量均随平衡液浓度的增加而增大, Cu2+、Cd2+在农田土壤上的吸附量均高于林地和草地土壤。分别用Langmuir和Freunlich两种等温吸附方程对吸附过程进行拟合, 3种土壤对Cu2+的吸附过程运用Langmuir方程拟合效果好, 而对Cd2+的吸附过程运用Freunlich方程拟合效果更好。Cu2+在3种土壤的解吸量大小顺序为农田>林地>草地, Cd2+在3种土壤的解吸量大小顺序为农田>草地>林地。两种离子在3种土壤中的动态吸附是个快速反应的过程, 随时间延长, 吸附反应趋于平衡。运用双常数函数方程和Elovich方程能较好地拟合重金属在土壤上的吸附动力学过程。Cu2+、Cd2+的吸附与土壤黏粒含量、有机质含量、CEC和pH均有关。  相似文献   

15.
Abstract

Although there is generally no physical problem with salt‐affected soils when irrigated with saline and sodic waters, physical deterioration of the soils often results when leached with good quality (low salt and low sodium) irrigation water or by rain. Two major mechanisms of swelling and dispersion of clay particles have been proposed to be responsible for reduction in hydraulic conductivity (HC). The type and amount of clay minerals are major factors influencing the swelling and dispersion properties of soil in the presence of saline‐sodic solutions. The study was initiated to improve the understanding of swelling and dispersion processes in response to saline‐sodic conditions, particularly the role of the type and amount of clay minerals of the tested soils and the concentration of the leaching solutions. The study was conducted in a series of two leaching experiments. In the first experimental soil samples were leached with solutions of different combinations of 100 meq (NaCl+CaCl2)L‐1 and sodium adsorption ratio (SARs) 5, 10, 15, and 20. In the second, 8 samples of them selected to be leached with solutions of the same SARs of 5, 10, 15, and 20, but the higher concentration of 1000 meq (NaCl+CaCl2)L‐1. The changes in the HCs were determined through the concept of “the Sensitivity Index‐SI values”;. In general, solutions with lower concentrations and higher SAR resulted in greater reductions in the soil HC (i.e, SI value), and the SI values and SAR level showed a negative linear relationship. With respect to the regression equations between the SI values and the swelling/dispersion processes, and the relatively coarse texture as well as the mineralogical composition of the tested soils which shows the dominant clay minerals in almost all tested soils is non‐expanding dispersive quartz, illite and chlorite, it may be concluded that the slaking of the soil structure is responsible for blockage of the conducting pores and reduction in the HCs of the tested soils.  相似文献   

16.
Adsorption of Potassium and Calcium Ions by Variable Charge Soils   总被引：1，自引：1，他引：1  
Interactions of potassium and calcium ions with four typical variable charge soils in South China were examined by measuring pK-0.5pCa value with a potassium ion-selective electrode and a calcium ion-selective electrode,and pK value with a potassium ion-selective electrode.The results showed that adsorption of potassium and calcium ions increased with soil suspension pH,and the tendency of the pK-0.5pCa value changing with pH differed with respect to pH range and potassium to calcium ratio.Adsorption of equal amount of calcium and potassium ions led to release of an identical number of protons,suggesting similar adsorption characteristics of these two ions when adsorbed by variable charge soils.Compared with red soil,latosol and lateritic red soil had higher adsorption selectivities for calcium ion.The red soil had a greater affinity for potassium ion than that for calcium ion at low concentration,which seems to result from its possession of 2:1 type minerals,such as vermiculite and mica with a high affinity for potassium ion.The results indicated that adsorption of potassium and calcium ions by the variable charge soils was chiefly caused by the electrostatic attraction between the cations and the soil surfaces.Moreover,it was found that sulfate could affect the adsorption by changing soil surface properties and by forming ion-pair.  相似文献   

17.
亚热带土壤不同矿物组分中铬的吸附   总被引：1，自引：0，他引：1  
Safe application of chromium (Cr)-containing organic industrial wastes to soil requires considering the ability of the soil to adsorb Cr.In this study,the maximum Cr adsorption capacity was assessed for the bulk samples and their clay and iron-free clay fractions of four subtropical soils differing in mineralogy.To this end,the samples were supplied with Cr(Ⅲ) nitrate solutions at pH 4.5 or 5.5.The results of Cr(Ⅲ) adsorption fitted to a Freundlich equation and the adsorption capacity was positively correlated with soil organic matter and iron oxide contents.The clay fractions adsorbed more Cr per unit mass than the bulk soils and the iron-free clay fractions.The Cr(Ⅲ) adsorption capacity increased with increasing soil pH due to more charges on adsorbing surfaces.Our results suggest that the soils rich in organic matter and iron oxides and having a pH above 4.5 are suitable for application of Cr(Ⅲ)-loaded industrial wastes.  相似文献   

18.
The cause of the decrease in the Fe2+ concentration of the soil solution in the later period of soil waterlogging was investigated. After 7-d incubation of the soil solutions separated from previously waterlogged soils (PWdS), a greyish precipitate (PPT) was observed in the soil solutions. The color of the PPT became reddish brown after separation from the solutions and freeze-drying. The PPT observed in 14-d-PWdS contained 352.6 g Fe kg-1, 62.5 g C kg-1, 22.6 g P kg-1, 11.3 g Si kg-1, 9.9 g N kg-1, 0.7 g Al kg-1 and a trace amount of Mn. However, Ca, Mg, K, and Na could not be detected. It was concluded that the separated PPT was dominated by amorphous ferric hydroxide based on the chemical analysis, broad IR absorption band at 585 cm-1 and exothermic peak at 301°C. The data of chemical analysis and the characteristic IR bands of the PPT suggested that organic substances and presumably aluminosilicate anion were adsorbed onto the freshly-formed ferric hydroxide. The dominant phase of the greyish PPT in the reductive soil solution was considered to be ferrous PPT and was assumed to consist mainly of carbonate and/or hydroxide, and concomitantly of phosphate. The formation of the ferrous PPT in the soil solution in the later period of soil waterlogging was considered to (i) cause the decrease of concentration of Fe2+ ion and of other divalent cations such as Ca2+ due to the re-adsorption of Ca2+ on soil clays through the cation exchange reaction with Fe2+ ion, and consequently (ii) enhance the dispersion of the soil colloidal suspension.  相似文献   

19.
《Geoderma》1994,63(1):43-52
The sorption of selenite by two allophanic soils containing high amounts of variable charge materials was studied. Selenite sorption exhibited a maximum near pH 4 and decreased, although not proportionally, with increasing pH. Only negligible amounts of selenite were sorbed above pH 7.In the two soils, the addition of selenite caused a release of sulphate (SO2−4), silicate (Si) and hydroxyl ion (OH−) and an increase in cation (Na+) adsorption. No measurable amount of phosphate (P) was released. Increase in negative charge as measured by Na+ adsorption accounted for 48 and 18% of selenite sorbed (soils 1 and 2, respectively), the rest being accounted for by release of anions. The results presented here are consistent with the widely held view that selenite and phosphate are sorbed onto variable charge surfaces by a similar mechanism (ligand exchange).  相似文献   

20.
POTASSIUM-ALUMINIUM EXCHANGE IN ACID SOILS I. KINETICS   总被引：1，自引：0，他引：1  
A kinetic method is described and investigated for determining exchangeable Al in acid soils using M NH4Cl solutions the pH and leaching rate of which was critical for obtaining accurate and reproducible values. Molar concentrations of ammonium acetate displaced at least part of the Al chelated to functional groups in the soil organic matter. The adsorption kinetics of K and Al from 10?3 M chloride solutions on the NH4-saturated forms at the original soil pH of these, under leaching conditions similar to the ‘extraction’ method, showed that, when the atom ratio K/A1 > 1 in the equilibrating solution, initially more K was adsorbed than at equilibrium, although Al did not ‘over-equilibrate’ when K/A1 < 1. At least 24 h were required for attaining equilibrium in K :A1 equilibria work with soils and clays. The kinetics of desorption (extraction method) and adsorption of K and Al obeyed the first-order and parabolic rate respectively. This is attributed to the large difference in anion concentrations in the two methods.  相似文献   

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