Parameterization and regionalization of Cd sorption characteristics of sandy soils. II. Regionalization: Freundlich k estimates by pedotransfer functions

The aim was to describe Cd sorption in spatially variable sandy soils of the ‘Fuhrberger Feld’ catchment area as a prerequisite for prognosis of Cd transport in soil and of the threat of groundwater pollution. Thus, the possibility is evaluated to derive a generalized Freundlich equation based on multiple regressions relating the retention parameters k and M (from isotherm data of part 1 of this study) to basic soil properties (pedotransfer functions). For the parameter M (exponent), the correlation ‘measured vs estimated’ was weak (r² < 0.5) whereas k was well predictable by pedotransfer functions. The best regression was obtained if organic carbon (OC). clay content and H⁺ activity were combined as independent variables (r² up to 0.96). The obtained k values were much higher than those from comparable literature models, probably due to lower ionic strength and different composition of our background solutions used for the isotherms. As a critical evaluation, the estimates for k were used to derive solute Cd concentrations (C_est) which then were compared to measured data (range 0.1–3 μg L^?1). The best but still unsatisfactory r² was 0.77, obtained if G_est was compared to Cd in 0.01 M_c Ca(NO₃)₂ equilibria (Cd₀). Cd in fresh soil solution (Cd_z) showed no significant correlation with C_est, except for one relationship where OC had been excluded from the preceding multiple regression of k. Generally, the role of the variable OC remained unclear. Direct multiple regressions of measured solute Cd vs soil properties (bypassing k, no sorbed fraction) yielded much closer correlations, with r² = 0.9 for Cd₀ vs OC, H⁺ activity, clay (log data, OC decreases C) and r² = 0.7 for Cd₂ vs OC, H⁺ activity, clay (log data, OC enhances C).     

Organic matter effects on phosphorus sorption in sandy soils

Phosphorus (P) sorption processes in soils contribute to important problems in agriculture: a deficiency of this plant nutrient and eutrophication in aquatic systems. Soil organic matter (SOM) plays a major role in sorption processes, but its influence on P sorption remains unclear and needs to be elucidated to improve the ability to effectively manage soil P. The aim of this research was to investigate the influence of SOM on P sorption. The study was conducted in sandy soil profiles and in topsoils before and after removal of SOM with H₂O₂. The results were interpreted with the Langmuir and Freundlich isotherms. Our results indicated that SOM affected P sorption in sandy soils, but that P sorption also depended on specific soil properties (e.g. values of the degree of P saturation (DPS), P sorption capacity (PSC) and pH) often related to land use. Removal of SOM decreased PSC in most of the topsoils tested; other soil properties became important in controlling P sorption. An increase in P desorption observed after SOM removal indicated that SOM was potentially that soil constituent which increased P binding and limited P leaching from these sandy soils.     

初始浓度对六氯苯在土壤中的吸附-解吸的影响及解吸

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L^-1) by using 0.01 mol L^-1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r²) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.     

Improved cadmium sorption isotherms by the determination of initial contents using the radioisotope 109Cd

Cadmium (Cd) sorption isotherms were estimated by two different analytical approaches to assess the influence of initial Cd concentrations of soil matrix on the sorption of added Cd. For the laboratory experiments a heterogeneous set of samples was collected to include a wide range of different initial Cd concentrations. Comparison of both analytical methods (conventional analysis, radioanalysis) resulted in a strong conformity of Cd contents in solution at equilibrium. The calculated Cd concentrations in the soil solid phase differ according to the analytical approach for considering the initial contents. The determination of the initial contents by the proposed radioanalytical method with ¹⁰⁹Cd resulted in long linear Freundlich‐isotherms, even in the low concentration range. Thus, radioanalysis seems to be the most suitable method to recognise the initial contents of Cd in soil. EDTA extractable Cd represent the initial concentrations, which are averaged over solid and liquid phase. However, depending on the sorption characteristics of the soil these rates vary. In the investigated set of soil samples 52.3 to 99.3% of Cd must be added to the solid phase.     

Freundlich和Temkin等温线模型热力学参数的计算

Derivation of the Freundlich and Temkin isotherm models from the kinetic adsorption/desorption equations was carried out to calculate their thermodynamic equilibrium constants.The calculation formulase of three thermodynamic parameters,the standard molar Gibbs free energy change,the standard molar enthalpy change and the standard molar entropy change,of isothermal adsorption processes for Freundlich and Temkin isotherm models were deduced according to the relationship between the thermodynamic equilibrium constants and the temperature.     

土壤组分对广东省酸性水稻土磷吸附参数的影响

Soil components affecting phosphate sorption parameters were studied using acid paddy soils derived from basalt, granite, sand-shale and the Pearl River Delta sediments, respectively, in Guangdong Province.For each soil, seven 2.50 g subsamples were equilibrated with 50 mL 0.02 mol L-1 (pH=7.0) of KCl containing 0, 5, 10, 15, 25, 50 and 100 ng P kg-1, respectively, in order to derive P sorption parameters (P sorption maximum, P sorption intensity factor and maximum buffer capacity) by Langmuir isotherm equation. It was shown that the main soil components influencing phosphate sorption maximum (Xm) included soil clay, pH,amorphous iron oxide (Feo) and amorphous aluminum oxide (Alo), with their effects in the order of Alo ＞Feo ＞ pH ＞ clay. Among these components, pH had a negative effect, and the others had a positive effect.Organic matter (OM) was the only soil component influencing P sorption intensity factor (K). The main components influencing maximum phosphate buffer capacity (MBC) consisted of soil clay, OM, pH, Feo and Alo, with their effects in the order of Alo ＞ OM ＞ pH ＞ Feo ＞ clay. Path analysis indicated that among the components with positive effects on maximum phosphate buffer capacity (MBC), the effect was in the order of Alo ＞ Feo ＞ Clay, while among the components with negative effects, OM ＞ pH. OM played an important role in mobilizing phosphate in acid paddy soils mainly through decreasing the sorption intensity of phosphate by soil particles.     

Parameterization of Freundlich adsorption isotherms for heavy metals in soils from an area with intensive livestock production

Adsorption coefficients are valuable tools used to estimate the environmental relevance of heavy metal contamination. However, their determination with batch experiments is laborious. Thus, attempts have been made to deduce these coefficients from soil parameters. However, the application of the resulting parameterized equations to different sets of samples has often yielded poor results. Hence, the objectives of the present study were (1) to deduce basic soil properties governing the coefficients of Freundlich adsorption isotherms for Cd, Cu, Ni, Pb, and Zn, and (2) to derive parameterized isotherms and examine their accuracy. For this purpose, 30 topsoil and nine subsoil samples were investigated which represented one Podzol‐Cambisol‐Gleysol soilscape in an area with intensive livestock production in Lower Saxony, Germany. Total background concentrations (aqua regia digestion) of heavy metals in topsoils ranged from 0.290 (Cd) to 19.2 mg kg^—1 (Zn) and exhibited elevated mobilizable proportions (NH₄EDTA pH 4.6 extract) of 17 (Ni) — 66 % (Zn) from the total concentration. Background concentrations were higher in topsoils than in subsoils by factors of 1.7 (Ni) — 28 (Zn). These differences were assigned to the special situation of heavy metal input mostly originating from animal excrements. The isotherms obtained by batch experiments showed larger coefficients K_F for partition among soil solid phase and soil solution in topsoils than in subsoils by a factor of 3.5. The coefficients of the isotherms were significantly correlated with routinely determined soil properties such as cation exchange capacity and pH (R = 0.36—0.89). Parameterized isotherms were calculated for each metal by inserting the relevant parameters in multiple linear regression equations. Among these parameters were the soil pH, cation exchange capacity, total metal concentration, and the concentrations of organic carbon, clay, fine silt, and various pedogenic oxides. The K_F values, separately calculated for topsoils and subsoils, agreed well with those determined by batch experiments (R = 0.63—0.97). Therefore, parameterized isotherms are valuable tools for the prediction of heavy metal partition in soils from one soilscape and for a risk assessment in the investigated, densely stocked area and similar areas.     

The Langmuir parameters of orthophosphate and pyrophosphate sorption for ammoniated tropical soils

Abstract

The Langmuir parameters of orthophosphate (OP) and pyrophosphate (PP) sorption for the ammoniated tropical soils were determined. Positive linear relationships between OP and PP sorption maxima and amounts of anhydrous NH₃ added were noticed. Indexes of bonding energy of OP and PP increased exponentially as ammoniation level of the soils increased from 33 to 100% of ammonia retention capacity.     

Specific sorption of trace amounts of cadmium by soils

Abstract

Sorption of trace quantities of Cd in four soils of different chemical and mineralogical properties, was studied. Initial Cd concentrations were between 15 to 150 μg. 1^?1. The sorption isotherms were linear and had a positive intercept in three of the soils, indicating a constant partition‐high affinity sorption isotherm (Giles et. al⁶). The data also followed the Freundlich sorption isotherm, and the Freundlich K parameter was taken as a measure of the relative affinity of the different soils for the Cd metal sorbed. Cadmium sorbed was extracted by IN‐NH₄C1 followed by 0.1N HC1, and the fraction remaining in the soils was considered specifically sorbed Cd. This fraction also followed a linear sorption isotherm, and was around 30% for the four soils studied. The sorption order for the amount of specifically sorbed Cd showed that the Boomer soil (kaolinite‐iron oxides) had the lowest affinity for specific sorption of this metal. This was taken as evidence that kaolinite and iron oxides have a lower capacity for retaining cadmium through specific sorption mechanism(s) than the materials present on the other soils (2:1 layer silicates and humic substances). The existence of specific mecha‐nism(s) responsible by the sorption of trace quantities of Cd in soil solutions has important implications on soil‐plant relationships, Cd mobility in soil profiles and control of Cd activity in soil solutions.     

N mineralization parameters of sandy arable soils

The objective of this study was to experimentally investigate net N mineralization in sandy arable soils and to derive adequate N mineralization parameters for simulation purposes. Long‐term incubations at 35 °C were done for at least 200 days with 147 sandy arable soils from Northwest Germany. To cumulative net N mineralization curves the simultaneous two‐pool first‐order kinetic equation was fitted in order to differentiate between N mineralization from an easily decomposable, fresh organic matter pool (N_fast) and from a slowly decomposable pool (N_slow) of more humified OM. North German loess soils served as a reference, since available model parameters were mainly derived from those soils. Although curve patterns in sandy soils often somewhat deviated from typical double‐exponential patterns, the mineralization equation generally could be fitted. Two pools were clearly revealed, but a transfer of the standard parameters was found to be not appropriate — except maybe for the pool size of the fast decomposable N pool. The mean k_fast at 35 °C (0.1263 d^—1) is about 46% higher than the known ’︁standard’ loess value, indicating better conditions for decomposition of fresh residues at this temperature. The mean k_slow at 35 °C (0.0023 d^—1), which is 60% lower than reported earlier from loess soils, and much lower mineralization rates of the slowly decomposable N pool give reason to the presence of generally more resistant organic material in these sandy soils. The relation between N_slow and total N was found to be not close enough to derive the pool size of slowly decomposable N just from total N as done for loess soils. Reducing the variability is necessary, promising approaches exist. The eight reference loess soils revealed — on an average — the known N mineralization parameters.     

改性油菜秸秆生物质炭吸附/解吸Cd2+特征

该研究选用蒸汽爆破油菜秸秆,对其进行羟基磷灰石和KMnO4浸渍处理,再用壳聚糖和NaOH溶液改性所获得的生物质炭改性,以比较表面特性变化和吸附/解吸Cd~(2+)的特征。结果表明,改性处理可有效地在生物质炭表面负载相应官能团,如羟基磷灰石处理使生物质炭表面磷酸盐增多,比表面积提高至225.68 m2/g;而壳聚糖、KMnO4和NaOH处理,则引入了-NH2和-OH、-COOH等酸性含氧官能团。尽管改性生物质炭表面电荷减少,但Cd~(2+)吸附容量却提高了13%～315%,其吸附行为可用Langmuir等温吸附式拟合,并符合Pseudosecondorder吸附动力学方程。改性后,生物质炭对Cd~(2+)的吸附主要为专性吸附,其初始吸附速率提高了65%～379%,而解吸率降低了17%～91%,表明对Cd~(2+)的吸附更快且更加稳定,具有良好的应用潜力。     

Characterization of clay and fine silt fractions of forest soils by standardized K/Ca sorption isotherms

For better comparison of selectivity characteristics of clay and fine silt fractions sorption isotherms standardized on the cation exchange capacity (CEC) are useful. Due to the effect of the CEC on the sorption isotherms, it is necessary to characterize the exchanging substance with regard to different ion selectivities with standardized potassium/calcium‐(K/Ca) sorption isotherms. This procedure helps to complete the knowledge about the mineralogical composition, which is obtained by X‐ray powder diffractometry. A Haplic Luvisol from boulder marl shows distinct differences in its K selectivity both between different particle size fractions and different horizons. This is partly due to the presence of smectites and vermiculites which are differently distributed within the particle size fractions. The increase of K selectivity with increasing particle diameter in the calcareous C horizon can be attributed to the marginal expansion of mica/illite by Ca²⁺ ions. The K selectivity of individual particle size fractions in different horizons of a Gleyic Cambisol from glacial sand shows major similarities. If pedogenic chlorite is formed, no changes in selectivity characteristics can be observed.     

Adsorption and desorption of arsenate in Louisiana rice soils

Adsorption and desorption of arsenic (As) in the soil are dominant parameters that affect the mobility and bioavailability of arsenic. Batch arsenate adsorption and desorption experiments were conducted using soils collected from three Louisiana, USA, aquaculture ponds representing different crayfish farming and rice cultural practices. Arsenate adsorption behavior in the soils was investigated using Freundlich and Langmuir sorption equations. Results demonstrated that the Langmuir isotherm model was the best fit based on statistical correlation with soil properties governing adsorption, for the entire range of arsenate concentrations for all soils. Adsorption of As(V) was governed by soil physicochemical properties especially Fe and Al oxides, clay and organic matter. Desorption of As(V) was initially fast, but with increasing incubation times desorption occurred progressively slower. Chemical fractionation of arsenic in the soils showed that the most mobile fraction represented 4.74–5.18% of the total arsenic. A part of this mobile fraction could potentially be taken up by rice and enter the food chain, but would require additional research to quantify.     

几种铵盐对土壤吸附Cd2+和Zn2+的影响

采用平衡吸附法,研究了不同铵盐对潮褐土、红壤吸附Cd2+、Zn2+的影响。结果表明,土壤对Cd2+、Zn2+的吸附量随平衡溶液中Cd2+、Zn2+浓度的增加而增加;潮褐土和红壤对Cd2+、Zn2+的最大吸附量为:Zn2+ Cd2+,且潮褐土红壤;随NH4HCO3浓度的增加,两种土壤对Cd2+、Zn2+的吸附率显著提高,NH4Cl、NH4NO3和(NH4)2SO4抑制红壤对Cd2+、Zn2+的吸附及潮褐土对Cd2+的吸附,对潮褐土Zn2+的吸附率影响不显著;铵盐浓度相同时,红壤对Cd2+吸附率为:NH4HCO3NH4ClNH4NO3≈ (NH4)2SO4,红壤对Zn2+吸附率为:NH4HCO3NH4Cl NH4NO3(NH4)2SO4。     

Phosphorus sorption isotherm characteristics and availability parameters of Appalachian acidic soils

Abstract

Phosphate (P) sorption isotherms have been widely used to characterize the P status and to establish fertilizer requirements of soils. Recently, mechanistic models have successfully described the nutrient uptake by plants under changing soil and plant parameters. Phosphorus sorption characteristics of eleven representative soils of the Appalachian Region of the United States were evaluated, and experimental P adsorption data were fitted to Temkin, Freundlich, and Langmuir equations to determine the relative importance of the soil parameters in P retention and supply to plant roots. The Barber and Cushman model was used to predict the effect of P fertilization on P uptake by plant. The soils of Appalachia differ considerably with respect to the retention of added P. All three isotherm equations gave good fit with the experimental data and were reliable to describe the P quantity/ intensity relationships of these soils. The following sequence of P adsorption capacity in various soils was established: Tate (BA)? Hayesville (Bt) > Westmoreland (Bt2) ～ Upshur (Btl) ～ Gilpin (A) > Lily (A) ～ Dandridge (E) ～ Watauga (Ap) > Ashe (A) ～ Berks (A) ～ Dekalb (A). In spite of the great differences among soil properties related to surface area and degree of weathering of these soils, the content of free iron (Fe) oxides was the only soil property that correlated with the constants of the isotherm equations. Amounts of P required to give 0.20 μg P/mL varied with soils and were closely related to the constants of the isotherm equations. Soil P parameters from the P adsorption isotherms were used to determine a measure of Cli, b, and De instead of those used conventionally in the Barber and Cushman (1981) model to predict P uptake by corn. Predicted P uptake by corn varied with soils, even at the same P concentration in equilibrium solution (0.20 μg P/mL) or when an equal amount (90 μg P/mL) of P was added to all soils. Predictions of P uptake, however, were not correlated with the amount of P required to give 0.20 μg P/mL in 0.01M CaCl₂ solution or with the constants of the isotherm equations used. Diffusion coefficient and equilibrium P concentration in solution, and two intensity factors, were more important than buffer power in predicting P supplied to roots. These findings may help to explain the lack of significant correlations between the constants of the P isotherm equations and P uptake.     

Relationship between Gu(II) sorption and active H+ sorption sites of soils

Sorption characteristics of Cu(PI) were investigated using six soils coPBected in Korea (JUF9 SUM, and HHM) and in Japan (HNG, TWD, and ISM). The Cu(IH) sorption amount increased with increasing initial Cu(II) concentration. The maximnm sorption amount of @u(PI) increased in the order of KHM< ISK< JUM < JUF < TWD < KNG, and was related to the pH and BZSE of soils. The H⁺ release curves due to Cu(II) sorption apparently were characterized by a two or three step pattern. The amount of H⁺ released due do Cu(II) sorption increased with the increase in the Cu(II) sorption amount. The amount of protons released per Cu(II) sorbed onto soils with a larger Gu(II) sorption amount tended to be smaller compared with soils with a smaller Cu(HHQ sorption amount. The W⁺ sorption amount of the original soils and those with Cu(II) sorption at the PZSE, which was referred to as σ_P (Sakurai et al. 1988: Soil Sci. Plant Nutr., 34, 171–182; 1996: Jpn. J. Soil Sci. Plant Nutr., 67, 32–39), was determined by the STPT method proposed by Sakurai et al. (4988: Soil Sci. Plant Nutp., 34, 171–182). The active H⁺ sorption sites of soils were used for Cu(II) sorption and their amount decreased after Cu(II) sorption because they were covered with Cu(II). Soils with a larger amount of active H⁺ sorption sites exhibited a higher aEamity to Cu(II) khan those with a smaller amount of active H⁺ sorption sites. The Cu(II) sorption created a positive charge in soils, causing the decrease in the amount of active H⁺ sorption sites.     

Effect of liming on hexazinone sorption and desorption behavior in various soils

Liming is a practice commonly used to modify soil acidity, neutralize aluminum, and increase calcium and magnesium in the soil. Liming can change herbicide retention processes and consequently weed control and potential environmental contamination. The effects of liming on the sorption and desorption of hexazinone in different soils were evaluated. Samples from seven Brazilian soils were collected and separated into two subsamples, with and without limestone incubation. Hexazinone was quantified using ultra high-performance liquid chromatography. The sorption and desorption coefficients were determined in soils using Freundlich isotherms. Increasing the pH did not alter the sorption kinetics of hexazinone in the same soil class. The shortest sorption time of hexazinone occurred in soils with higher organic matter (OM) and clay content. Liming reduced the sorption and increased the desorption of hexazinone in the soils, which was caused by the increase in pH and reduction of OM content. Although the application of limestone increased desorption, the rate at which this process occurred was less than the sorption rate of hexazinone in most cases. In alkaline soils, the recommended dose of hexazinone for pre-emergence application should be low to avoid leaching and reduce the contamination of groundwater resources.     

Kinetics of sorption of orthophosphate and pyrophosphate by ammoniated tropical soils

Abstract

A laboratory experiment was conducted to study kinetics of sorption of orthophosphate (OP) and pyrophosphate (PP) from dilute solutions by three ammoniated tropical soils. Milligrams of P sorbed by soil (?P) and shaking time (t) showed a linear relationship: ?P = a + b √t. The data suggested two diffusion — controlled processes during P sorption. In general, due to ammoniation, initial sorption rate of OP (in linear region I) increased while that of PP decreased. PP was sorbed more than OP. Sorption rate of OP and PP in linear region II showed a tendency to decrease with increasing ammoniation levels.     

Adsorption isotherms of copper and zinc in clay minerals of calcareous soils and their effects on X-ray diffraction

Reactions of elements with the water mineral interface are important and affect their bioavailability and transportation within soil. Effects of metal sorption on X-ray-diffraction (XRD-photographs) of clay minerals have been not studied. Therefore, sorption experiments were done on clay fractions of two calcareous soils using 12 concentrations of 0–2000 mg L^?1 Zn(NO₃)₂ and Cu(NO₃)₂. Langmuir and Freundlich isotherms’ coefficients were determined. After sorption, XRD-diffraction were prepared and compared with those of initial samples. Langmuir (R² = 0.996–0.999 and SE = 0.001–0.002) and Freundlich equation were the best-model for Zn and Cu-sorption, respectively. Sorption energy was higher for Zn than Cu, whereas the maximum concentration of sorbed-Cu was higher than that of Zn. Distribution coefficient (K_d) of Cu were more (threefold) than that of Zn. The K_d values representing the slope of Freundlich isotherms decreased according to linear regression equations (R² = 0.72–0.91) as the equilibrium concentrations of metals increased. No significant differences were observed among XRD-photographs of applied concentrations (some negligible differences were found in position/sharpness of peaks). Dry-XRD-method resulted in omission of intensity peaks at 2θ which may interfere in recognition of clays that show a maximum intensity >1.4 nm in the mentioned 2θ. Zinc can become more leachable especially in Shekarbani-soil-series, whereas, Cu highly adsorb on clay minerals and can show less tendency to transportation.