EFFECTS OF IONIC STRENGTH ON CHEMISORPTION AND POTENTIAL-DETERMINING SORPTION OF PHOSPHATE BY SOILS

Amounts of inorganic phosphate (P) sorbed by two unfertilized soils, during times less than required to reach equilibrium, were affected by the ionic strength and cation species of the matrix solution. For non-equilibrium conditions the amounts of P sorbed increased with increasing ionic strength and were greater with Ca²⁺ than Na⁺. For higher P additions, resulting in equilibrium solution P concentrations greater than 30 to 40μrnole 1^?1, the effects of the matrix solution on P sorption were maintained at equilibrium, whereas at lower P additions the dependence of sorption on matrix solution composition was eliminated at equilibrium. Equilibrium sorption isotherms for each soil and matrix solution were described by three Langmuir equations, which corresponded to distinct concentration ranges or regions (I, II, and III) on the overall isotherm. The free energies of sorption (ΔG) for each region, were essentially independent of the soil matrix solution. The sorption maxima for regions I and II of the isotherm for a particular soil were also virtually independent of the matrix solution used. The sorption maximum for region III, however, was markedly dependent on the matrix solution, implying a potential-determining (p.d.) sorption mechanism.     

电解质种类和浓度影响磷酸根解吸的机理研究

本文研究了吸附性阳离子、电解质浓度和组成影响几种矿物和土壤吸附态磷的解吸的机理。结果表明,吸附性阳离子影响磷酸根解吸与离子桥有关。桥接静电场愈强,被束缚磷的释放就愈困难。电解质阳离子对磷酸根解吸的影响则取决于其对表面负电荷的屏蔽效应。阳离子电价高,屏蔽作用大,磷解吸就少。电解质浓度影响吸附态磷的解吸主要与表面电位的变化有关。当pH>PZC值时,提高电解质浓度降低表面负电位,从而减少磷的吸附;当pH<PZC时,提高电解质浓度则降低表面正电位,促进磷的解吸。磷酸根解吸盐效应零点(P_PZSE)值一般都介于土壤或矿物样品吸附磷酸根前后测得的两个PZC值之间。不同浓度电解质溶液中磷解吸量之差与吸附层电位变化量(△ψ_x)呈正相关。     

EFFECTS OF IONIC STRENGTH AND NATURE OF THE CATION ON DESORPTION OF PHOSPHATE FROM SOIL

The effects of cations on desorption of phosphate previously added to soil were studied by mixing phosphated soil with solutions of chloride salts at a range of solutionitoil ratios and for periods which ranged from 1 to 96 h. Phosphate desorbed was then related to the experimental variables by a pair of simultaneous equations. In calcium chloride, the rate of desorption of phosphate was inversely proportional to the calcium concentration. Desorption was faster in 0.01 M magnesium chloride than in 0:01 M calcium chloride, and faster in 0.03 M sodium chloride than in either magnesium or calcium chloride. Addition of a further supply of the cation on an exchange resin increased the rate for both sodium and magnesium but decreased it for calcium. A range of monovalent cations formed a sequence from fastest to slowest of: Li⁺ > Na⁺ > NH₄^?> K ⁺, Rb ⁺ > Cs ⁺. The identity and concentration of the cations had a large effect on the concentration of phosphate when the solution: soil ratio was small. There were also large effects in the amount of phosphate desorbed when the solution: soil ratio was large and the concentration of phosphate approached zero. This suggested that the escaping tendency of the phosphate was decreased when the cations which balanced the negative charge on the adsorbed phosphate were close to the surface.     

EFFECTS OF SOLUTION: SOIL RATIO ON PHOSPHATE SORPTION BY SOILS

Isotherms for the sorption of inorganic phosphate (P) by three contrasting soils during 40 h showed a dependence on solution: soil ratio. Above a final solution P concentration of 0.5 μg ml^?1, more P was sorbed at a solution: soil ratio of 5:1 than at 40:1 for a given level of P in solution. With time up to 146 h, the effect of solution: soil ratio on P sorption was kinetically controlled. Equilibrium solution P concentrations, estimated by extrapolation of the linear relationships between solution P concentration and the reciprocal of time to I/t= o (i.e. t=∞)appeared to be coincident for each solution:soil ratio at high and the low levels of added P. Consequently, sorption isotherms at equilibrium would be coincident, irrespective of the solution soil ratio used. The kinetic control of solution: soil ratio on P sorption is interpreted in terms of the number of P sorbing sites and initial solution P concentration on the rate of P sorption by soils.     

TIME-DEPENDENT SORPTION OF PHOSPHATE BY SOILS AND HYDROUS FERRIC OXIDES

The sorption of inorganic phosphate (P) by soils and hydrous ferric oxides was studied at times up to 192h. An initially rapid decrease in solution P concentration was followed by a much slower decrease between 48 and 192h with soils, Fe gel. and natural goethite, whereas synthetic goethite gave a well-defined equilibrium condition after only 48h. Resolution of the sorption isotherms showed that the increase in P sorption with time involved an appreciable shift of P from a more-physically sorbed form to a chemisorbed form. This was supported by chemical fractionation which showed that NaOH-extractable P was fairly constant with increasing sorption time, whereas the additional sorbed P was extracted by citrate-dithionite-bicarbonate from soils, and by HC1 from Fe gel and natural goethite. These sorbents contained short-range (amorphous) material, whereas synthetic goethite, from which all sorbed P was NaOH –extractable. did not. It is proposed that the time-dependent sorption of P and the associated shift of P to chemisorbed forms, involves the diffusion of P into “structurally porous”, short-range order material.     

MECHANISMS OF PHOSPHATE SORPTION BY SOILS AND HYDROUS FERRIC OXIDE GEL

Data for the sorption of added inorganic phosphate (P) by contrasting soils and iron oxide gel were resolved by a method of successive approximation of the Langmuir sorption constants. Three distinct Langmuir equations described the overall isotherm irrespective of the experimental conditions used. Free energies of sorption (ΔG) for a particular region were similar for each soil and for iron oxide gel under all experimental conditions. In contrast, the sorption maximum for each region was influenced by the sorbent and experimental conditions. Because of the pronounced similarities in their P sorption characteristics iron oxide gel was used as a model surface for P sorption by soils. Three mechanisms for P sorption by iron oxide gel and by soils are proposed: (i) chemisorption at protonated surface sites, (ii) chemisorption by replacement of surface hydroxyls, and (iii) a more-physical sorption of P as a potential-determining ion.     

EFFECTS OF CATION EXCHANGE MATERIAL ON ZINC ADSORPTION BY SOILS

The adsorption of Zn by soils which are different in their major cation-exchange materials was measured at equilibrium Zn concentrations up to 10^?2 M in 10^?2 to 10^?3 M CaCl₂. The results are interpreted on K^Zn_Ca[Zn]_soil plots, where K^Zn_Ca is the selectivity coefficient defined by the equation All natural samples except those containing halloysite exhibited no or very small specific Zn adsorption. All Ca-saturated samples exhibited specific Zn adsorption dependent on cation-exchange materials. The cation-exchange sites with high selectivities for Zn (K^Zn_Ca > 10) constitute more than 40 per cent of the total exchange sites in soils containing allophane, imogolite, and halloysite, whereas those with moderate to low selectivities for Zn (K^Za_Ca < 10) predominate in montmorillonitic, vermiculitic, and humic soils. Differences in the contribution of the respective cation-exchange materials to specific Zn adsorption are discussed relating to differences in the origin of their negative charge.     

稻作制、有机肥和地下水位对红壤性水稻土磷的吸持作用的影响

从１９８２～１９９４年,对稻作制,有机肥和地下水位三因素多水平的定位试验土壤,进行磷的恒温吸附试验,研究不同稻作制和地下不位以及施用有机肥对红壤性水稻土对磷的吸持作用的影响,结果表明,各处理土壤磷的恒温吸附曲线形状都很相似,均属于高亲和力的“Ｌ”型曲线,所有吸附资料与三个已知吸附模型的拟合程度的均达极显著水平,其中以一元Ｌａｎｇｍｕｉｒ模型优于Ｆｒｅｕｎｄｌｉｃｈ和Ｔｅｍｋｉｎ两个模型,三种稻作制     

pH对土壤吸持磷酸根的影响及其原因

本文选择了浙江、江苏15个性质变化范围较大的土壤样品,研究在两种支持电解质、不同pH条件下对磷酸根的吸持反应。结果表明,加碱提高强酸性土壤的pH值,导致交换性铝的水解和羟基铝聚合物的生成,增加对磷的吸持。磷酸根同酸性土壤的反应,可促进交换性铝的水解,释放出H⁺,降低体系的pH。在CaCl₂介质中,当pH>6时,可能有磷酸钙类盐形成,使溶液中磷浓度显著降低。有机质对土壤吸持磷有重要影响。在低pH下有机质通过与Al³⁺形成络合物,阻碍溶液中A1³⁺的水解,并与磷酸根竞争羟基铝化合物表面的反应点位,从而降低酸性土壤对磷酸根的吸附量。     

上海土壤磷的吸附特性及缓冲性能的研究

本文以上海土壤为对象,研究选定了土壤磷等温吸附试验条件为:水土比10,平衡时间6天,控温25℃,磷加入量为100,200,400,600μgP/g土,溶液基质为0.01M CaCl₂。磷缓冲能力试验条件为:平衡时间2天,磷加入量为20,40,100,200μgP/g土。根据Freundlich, Tempkin和Langmuir方程计算的土壤吸附指标与土壤类型及土壤性质有密切关系,是土壤磷素肥力的重要指标。反映土壤缓冲能力的“磷肥指标”与土壤有机质、粘粒、活性铝及pH值相关较好。上海几种主要土壤中以青紫泥的最大吸附量(X_m),0.2ppm P吸附量和“磷肥指标”为最高,其次为青黄土,沟干泥和黄泥头,最小为夹沙泥。应用磷吸附指标与“磷肥指标”来预测土壤需磷量,初步试验是可行的,但实际应用还需进一步试验研究。     

离子强度和pH对可变电荷土壤与铜离子相互作用的影响

研究了离子强度和pH对可变电荷土壤表面电荷与铜离子吸附的影响。作为对照 ,也研究了它们对恒电荷土壤黄棕壤的有关性质的影响。结果表明 ,随pH升高 ,土壤的表面负电荷增加 ,正电荷减少。对于可变电荷土壤 ,可出现电荷零点 (pH0 )。随pH升高 ,土壤对Cu2 的吸附量增大。随着离子强度增大 ,恒电荷土壤对Cu2 的吸附百分率明显降低 ,可变电荷土壤对Cu2 离子的吸附百分率也降低 ,但降低的幅度比恒电荷土壤者小得多。土壤中氧化铁的含量越高 ,降低的幅度越小。对于含 2 1 %左右游离氧化铁的铁质砖红壤 ,即使支持电解质NaNO3的浓度高达 1molL- 1,对Cu2 的吸附仍然几乎没有影响。从离子强度和pH与土壤表面电荷和铜离子吸附的关系 ,可以推测在土壤对铜离子的吸附中 ,既存在电性吸附 ,又存在专性吸附。在可变电荷土壤对铜离子的吸附中 ,专性吸附较为重要     

SOME NEW EQUATIONS TO DESCRIBE PHOSPHATE SORPTION BY SOILS

Phosphate sorption was studied on surface and subsurface soils sampled from the old field experiments at Askov, Denmark. Two empirical three-parameter equations, an extended Freundlich and an extended Langmuir equation are proposed and compared with the Langmuir, the Freundlich, the ‘double’ Langmuir, the Gunary, and the Fitter-Sutton equations. In the proposed equations the affinity parameter of the Langmuir equation and the exponent of the Freundlich equation are replaced by the term Bc ^?D the value of which decreases with increasing phosphate concentration, c. On average the Freundlich equation thus modified yielded the closest fit to the sorption data. This was followed by the Fitter-Sutton, the modified Langmuir, the ‘double’ Langmuir, the Gunary, the Freundlich, and finally the Langmuir equation. Out of the three equations that yielded the closest fit to the sorption data the correlation between the parameters within the equations, furthermore, was least for the proposed extended Freundlich equation. Therefore, this equation may be generally suitable for describing phosphate sorption by soils.     

土壤中黑碳对农药敌草隆的吸附-解吸迟滞行为研究

采用批处理振荡法和连续稀释法分别测定了敌草隆在人工添加黑碳土壤和自然形成的不同有机质和黑碳含量的土壤中的吸附一解吸行为。吸附结果表明，人工添加黑碳的土壤对敌草隆的吸附强度和吸附容量以及吸附等温线的非线性均随土壤黑碳添加浓度的增加而逐步增大；自然土壤的吸附容量和吸附强度随土壤总有机质含量增加而增加，但吸附等温线的非线性则与土壤中黑碳对有机质的相对含量有关，黑碳比例越高，等温线非线性越大。解吸实验结果表明，无论是人工添加黑碳的土壤还是自然土壤，对敌草隆的解吸迟滞作用均随土壤黑碳含量增高而愈明显。     

A PHOSPHATE SORPTION INDEX FOR SOILS

Phosphate sorption isotherms covering a wide concentration range (10^?6 to 5 × 10^?3m phosphate) were determined for 42 soil samples at 20 °C by a standardized technique. The slope of a plot of the sorption, x, against the logarithm of the equilibrium solution phosphate concentration, log c, measured at c= 10^?4M, proved a suitable reference index to characterize the phosphate sorbing properties of the soils. Several single-point methods were tested by statistical correlation against this reference index. Of these, the sorption, x, from one addition of 150 mg P/100 g soil gave r= 0.951, but r= 0.974 when the equilibrium concentration was also taken into account in the quotient x/log c. This quotient is therefore suggested as a simple yet adequate way of indicating a fundamental soil property, its phosphate sorption isotherm.     

SPECIFIC ADSORPTION OF SILICATE AND PHOSPHATE BY SOILS

The adsorption of silicate and phosphate from pure and mixed solutions by four soils known to fix phosphate strongly has been measured. The adsorption at constant pH for each acid from its pure solution follows the Langmuir isotherm. The maximum adsorption of silicate by three of the soils from the pure solution occurs at pH 9.2, and the maximum adsorption curve for phosphate by two of the soils from its pure solution has a break in its slope at pH 6.4 and 11.6. These pHs are all just below the pK values for the dissociation of hydrogen ions from the undissociated silicic acid or the acid phosphate anions. The presence of silicate in a mixed solution, which is sufficiently concentrated in both silicate and phosphate to give maximum adsorption of either if in pure solution, does not affect the amount of phosphate adsorbed until the pH is over 6.5–7.0. At this pH the maximum adsorption curve for silicate crosses that for phosphate. The presence of phosphate in the mixed solution always depresses the adsorption of silicate. The maximum amount of silicate-plus-phosphate adsorbed from this mixed solution is either a little less than or equal to the amount of silicate adsorbed from the pure silicate solution if the pH is above 7. When silicate displaces phosphate, or phosphate displaces silicate, more moles of the displacing acid are adsorbed than moles of the displaced acid released. These results for soils are similar to those of Hingston et al. for the adsorption of silicate and phosphate by goethite.     

淹水条件下施加石灰和有机质对酸性土壤性质和磷吸附的影响

每公斤土加入2克碳酸钙和(或)三叶草的5个老成土和1个氧化土,在淹水培育45天后风干,结果发现:(1)淹水土壤风干,其pH比淹水时低,但仍比未淹水的高;(2)淹水降低了土壤中0.5MCuCl₂提取的铝量,石灰和三叶草处理使3个轻质土中的铝量进一步降低,但3个粘质土则呈现相反的趋势;(3)改良剂使3个轻质土吸附的磷减少,而使3个粘质土吸附的磷增加。前者增加的原因是因为通过还原作用和氧化作用形成了较多的活性表面,而后者的减少则可能是粘粒表面所形成的水化氧化物胶膜堵塞了原有的吸附位,从而使吸附位减少(4)改良剂对磷解吸的影响,是降低了3个轻质土的磷解吸,而增加了3个粘质土的磷解吸;(5)经淹水风干处理土壤的磷吸附量与草酸盐提取的铁、铝、锰及CuCl₂溶液提取的铝有很高的相关性,表明控制淹水土壤磷吸持的土壤组分,不仅包括无定形铁,而且也包括羟基铝聚合物。     

SORPTION OF INORGANIC PHOSPHATE BY IRON- AND ALUMINIUM- CONTAINING COMPONENTS

The amounts of inorganic P sorbed by a range of Fe- and Al- containing components varied appreciably and decreased in the order allophane > fresh Al gel > Fe gel pseudoboehmite > aged Al gel > dried Fe gel > Fe-coated kaolinite > haematite > goethite > akaganeite > gibbsite = ground kaolinite > dispersed kaolinite. Al gel sorbed 30 to 70 times more P than gibbsite, and Fe gel sorbed approximately 10 times more P than its crystalline analogues (haematite, goethite. and akaganeite). Despite large differences in the extent of P sorption, the form of the isotherm was essentially the same for each sorbent. The ability of freshly-prepared Al gel suspensions to sorb P decreased with ageing, a property not shown by Fe gel. Drying of Fe gel at 80°C, however, caused an approximately 4-fold decrease in P sorption. Precipitation of Fe gel (2% Fe) on the surface of kaolinite increased P sorption by a factor of 10. The occurrence of Fe gel as a coating apparently presents more sorption sites to solution per unit weight of Fe gel than Fe gel alone. A linear relationship (r= 0.98) was obtained between the amount OH^? sorbed per unit increase in pH value (‘hydroxyl buffering’) and the overall P sorption maximum for each sorbent. Hydroxyl buffering provided a better index of P sorption potential than specific surface area. Except for the crystalline Fe sorbents, isotherms obtained by plotting fractional sorption saturation against final solution P concentration for the sorbents were essentially coincident with those for several contrasting soils. For crystalline Fe components a lower relative amount of weaker sorption, as opposed to chemisorption, of the overall sorption maximum was obtained. Differences in the extent of P sorption. however, appear to be primarily related to the number of functional M-OH groups presented at the solid-solution interface.     

多种有机酸共存对可变电荷土壤吸附磷的影响

研究了２种或３种有机酸在不同浓度组合时对可变电荷土壤吸附磷酸根离子的影响,结果表明:（１）有机酸的种类、各自的浓度及总浓度对土壤吸附磷有显著影响;（２）土壤组成及表面性质不同时,有机酸与磷的竞争效果也不大相同;（３）多种有机酸混存对土壤吸附磷量的影响不等于各单一有机酸贡献的简单加和。因此,根际环境中有机酸、磷在土壤表面的相互作用还有许多待探讨的问题。     

土壤磷酸盐吸持作用的研究

18个供试土样,在较宽的磷浓度范围内(0—100μmP/g土),它们的吸磷特征与Langmuir,Freundlich和Temkin方程式都有很好的相关性(r值大多在0.97以上),尤以Langmuir方程式最佳。各供试土样吸磷能力差异很大,其最大M从大约300μg P/g土(黑垆土)到1500/μg P/g土(砖红壤),火山灰土则高达5000μg P/g土。当加入100μm P/g土时,上述各土壤吸磷量分别占加入磷量的10%,47%和95%左右。土壤粘粒含量以及无定形和结晶态游离氧化铁铝含量均各与M显著相关。土粒的比面可作为单一的指标,它能较妥切而综合地反映土壤的吸磷能力。有机质对土壤吸磷能力的影响是复杂的,它可以增加或减少M值。耕作施肥特别是红壤旱改水多年后,显著地降低了原土壤的M和K值。砂潮新成土上不同施肥处理小区的吸磷等温线表明,土壤中新增加的粗有机物质对磷的吸持作用多发生在磷浓度较高的范围内,它是以吸附量高而吸附结合能低为特征的。