Einfluss eisenhaltiger Klärschlämme auf Kenngrößen der P‐Verfügbarkeit in Ackerböden

Influence of iron content in sewage sludges on parameters of phosphate availability in arable soils The use of iron salts for the P elimination in sewage plants is widely used. But it is not clear whether the P availability in arable soils is negatively influenced by iron compounds or not. The aim of the investigations was, therefore, to study the influence of two sewage sludges with a high and a low Fe content respectively on P sorption and phosphate concentration (P_i) in the soil solution after application of CaHPO₄ or sewage sludge to 5 loamy and 4 sandy soils (pot experiments and 1 silty loam (field experiment)). Soils were analyzed 1, 6, and 13 months after P application. Sludge Gö contained 12 kg P and 65 kg Fe (t DM)^—1 (P : Fe = 1 : 5.4) and sludge Sh 25 kg P and 39 kg Fe (t DM)^—1 (P : Fe = 1 : 1.5). The basic P application was 60 kg P ha^—1 (= 30 mg P (kg soil)^—1 in the pot experiment, as sludge or as CaHPO₄). P uptake by maize was determined in a separate pot experiment with a loamy soil and the same P application rate. The P sorption capacity remained similar in all soils after application of sludge Sh (P : Fe = 1:1.5) compared with soils without sludge, however, after application of sludge Gö the P sorption increased by 16% (0—59%). After application of sludge Sh the mean P_i concentration increased in loamy soils by 34% and in sandy soils by 15%. On the other hand the P_i concentration decreased after applying sludge Gö by 13% and 36% as compared to the controls of the respective soils. In the field experiment the P_i concentration of plots with a high P level (50 mg lactate soluble P (kg soil)^—1) was also significantly decreased after application of 10 t sludge Gö (126 kg P ha^—1) in comparison with triple phosphate. One month after the application of increasing amounts of sludge Gö (5, 10, 15 t DM ha^—1) both the concentration of oxalate‐soluble Fe in the soil and the P sorption were increased. The elevated relationship between these two parameters was highly significant (r² = 0.6 — 0.97). Plant uptake of P was less after application of sludge Gö than after application of sludge Sh and much less than P uptake from CaHPO₄. Sewage sludges with a P : Fe ratio of 1 : 5 should not be recommended for agricultural use, as the P availability is significantly reduced. Iron salts should not be used for conditioning of sludges.     

Land Application of Aluminum Water Treatment Residual: Aluminum Phytoavailability and Forage Yield

Negative impacts of land‐applied aluminum (Al)–rich water treatment residuals (WTRs), which have been suggested to improve soil phosphorus (P) sorption, could include excessive immobilization of plant‐available P and Al phytotoxicity. We studied the impacts of an Al‐rich WTRs on agronomic returns and plant Al concentrations in glasshouse and field studies. The glasshouse study was a 4 × 2 × 3 factorial experiment with one control in a randomized complete block design and three replicates. Four sources of P were each applied at two agronomic rate [44 kg P ha^?1, P‐based rate; and 179 kg plant‐available nitrogen (PAN) ha^?1, N‐based rate] to topsoil (0–15 cm) of a sandy, siliceous, hyperthermic Arenic Alaquods. Three WTR rates (0, 10, and 25 g kg^?1 oven‐dry‐weight basis) were further applied, whereas the control received neither P source nor WTRs. Bahiagrass (Paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were continuously grown in succession for 18 months. Applied WTRs increased soil Al but not plant Al concentrations (22–80 mg Al kg^?1), which fell within the normal concentration range for pasture plants. In the glasshouse, when WTRs were incorporated with the soil, bahiagrass dry matter (DM) accumulation was reduced, but ryegrass DM was not affected even at 25 g kg^?1 WTR. A 2‐year field study, with same treatments but two rates of WTRs (0 and 10 g kg^?1 WTR) surface applied to established bahiagrass on the same soil type (Spodosols) showed neither reduced yields nor increased plant Al phytoavailability in the WTR treatments. The studies show no increase in plant Al is associated with Al‐WTRs applied to reduce excess soil‐soluble P and P losses but plant DM accumulation may be reduced.     

Effect of Manure Types and Period of Incubation on Phosphorus-Sorption Indices of a Weathered Tropical Soil

Application of animal manures with inorganic phosphate (PO₄) fertilizer is proposed as one of the management options to improve availability and solubility of applied phosphate in weathered soil. We studied the effects of poultry, cattle, and goat manures at different incubation periods (0 to 120 days) on phosphorus (P) sorption indices of a weathered sandy clay loam soil. The soil P adsorption isotherms conformed to the H curve. Generally, the soil P-sorption efficiency decreased as the number of days of incubation increased irrespective of manure amendments. Manure application reduced the P-sorption efficiency of the soil; the lowest P-sorption efficiency was observed after 30 days of incubation. The data conformed to adsorption models in the order Temkin > Freundlich > Langmuir. Cattle, goat, and poultry manures reduced the adsorption constants in all models. Standard phosphate requirement and P-buffering capacity were also reduced with the application of the manures.     

Sorption and desorption of triadimefon by soils and model soil colloids

Sorption-desorption of the azole fungicide triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2, 4-triazol-1-yl)-2-butanone] on eight soils and a series of single, binary, and ternary model soil colloids was determined using the batch equilibration technique. Regression analysis between Freundlich sorption coefficients (K(f)) and soil properties suggested that both clay and organic C (OC) were important in triadimefon sorption by soils, with increasing importance of clay for soils with high clay and relatively low OC contents. Triadimefon sorption coefficients on soil were not significantly affected by the concentration of electrolyte or the presence of soluble soil material in solution, but they were highly dependent on the soil:solution ratio due to the nonlinearity of triadimefon sorption on soil. Freundlich sorption isotherms slopes were very similar for all soils (0.75 +/- 0.02). Desorption did not greatly depend on the concentration at which it was determined and showed higher hysteresis for more sorptive soils. Results of triadimefon sorption on model sorbents supported that both humic acid and montmorillonite-type clay constituents contribute to triadimefon retention by soil colloids.     

Sorption and Desorption of Fluoride in Soil Polluted from The Aluminium Smelter at Årdal in Western Norway

Fluoride (F) accumulation and transport in soil columns near the aluminium smelter at Årdal in Western Norway are studied together with fluoride sorption capacity, and the effect of pH and ionic strength on F solubility in soil. Unpolluted soil columns of 50 cm height placed at different distances from the smelter (1–0 km) accumulated from 0.27 g F m-² to 1.5 g F m-² during a 5 months period. Fluoride accumulation was high in the upper 0–10 cm of the soil columns where 50–90% of the accumulated F was found. Laboratory sorption experiments showed that the sorption of added F in the Ah-horizons increased with increased distance from the smelter at Årdal, in accordance with decreasing previous pollution from the smelter. The B-horizons sorbed considerably more F than the Ah-horizons, due to higher content of Al-oxides/hydroxides. Maximum sorption of F occurred at pH 4.8–5.5. Fluoride solubility increased with increased ionic strength. Continued deposition of F may increase the availability to plants and soil organisms. Leaching of F from soil to groundwater or surface water will be strongly dependent on the presence and thickness of a B-horizon, and probably also on underlying horizons.     

磷对土壤As(V)固定与活化的影响

P和As的化学性质相近,在土壤中存在竞争吸附的关系,因而土壤中P浓度增加可能会影响As的固定和活化。本文通过等温吸附和浸提实验,模拟施P对黄棕壤中As固定和活化的影响。实验结果表明,提高溶液P浓度能够减少土壤对As的吸持能力,并增加As从土壤中的解吸量。在P浓度较低的情况下,这种影响尤其显著,As的解吸量与P浓度成极显著的线性相关关系。因此,不能忽视施用P肥对土壤As活化和迁移的影响。持续增加溶液的P浓度时,这种影响的程度逐渐减弱,可能与土壤中存在不同类型的吸附位有关。     

Modelling cations in three acid soils with differing acid input in Germany

Prediction of concentration changes of cations in soil solutions is complex, and chemical models are necessary for the purpose. The objective of this study was to determine whether the reactions considered in a coupled equilibrium model were appropriate to predict cation concentrations when the initial equilibrium was disturbed by adding small amounts of electrolytes. Multi-ion sorption in three acid soils (two Cambisols and a Podzol) was studied by sequentially adding small amounts of electrolytes to samples of the soils in batch experiments. A chemical equilibrium model that included inorganic complexation and multiple cation exchange was used to interpret the results. For the subsoils, the solubility of jurbanite was also included in the model. Model results for the two Cambisol surface soils agreed well or satisfactorily with the measured pH and sorption values of Na, K, Mg, Ca, Mn, Al and Fe, with a few exceptions. Linear correlation coefficients were generally between 0.97 and 1, and the regressin coefficients for cations (modelled against measured) lay between 0.6 and 1.3. For the subsoils sorption of sulphate was described satisfactorily for the spodic dystric Cambisol and to some extent for the spodic Cambisol. Correlation coefficients for subsoils lay between 0.63 and 1, and the regression coefficients (modelled against measured) were between 0.9 and 1.6 for the Cambisols. The model did not predict pH and sorption data in surface and subsurface soils with very small amounts of exchange capacities, pointing to the significance of cation buffering resulting from exchange sites. This study showed the usefulness and limitations of equilibrium models to predict the composition of the soil solution.     

天然土壤对BDE-47的吸附特征

研究了BDE-47在3种不同有机质含量的天然土壤上的吸附行为,包括吸附过程动力学和热力学等温线。结果表明,双室一级动力学模式较单室一级动力学模式更适于描述BDE-47在天然土壤上的吸附过程动力学特征,尤其是在吸附初始阶段（0-49h）。快吸附在自吸附初始到表观吸附平衡的整体吸附过程中占据优势地位,而慢吸附的贡献率则逐渐增加并在97h后达到相对稳定。快吸附达到其吸附容量的时间远快于慢吸附。在吸附开始阶段的3~5h,BDE-47吸附总量的增加主要决定于快吸附,但在后续的吸附阶段,慢吸附的影响逐渐成为主导。因BDE-47水相溶解度很低,在较窄的平衡浓度范围内,线性分配模式和非线性Freundlich模式对BDE-47的吸附等温线都能提供很好的拟合结果。在Freundlich模型结果中,具有较低（0.72%）和较高（7.90%）TOC分数的土样的非线性指数n都明显低于1.0（分别为0.75±0.03和0.74±0.02）,表明2种土样在相应的BDE-47平衡浓度范围内表现出一定的非线性吸附特征;而另一TOC分数居中（2.86%）的土样则表现出显著的线性行为,其非线性指数n明显接近1.0（1.03±0.03）。     

Sorption of humic acid on Fe oxides,bacteria, and Fe oxide-bacteria composites

Purpose

Sorption of humic substances on other soil components plays an important role in controlling their function and fate in soil. Sorption of humic substances by individual soil components has been studied extensively. However, few studies reported the sorption characteristic of humic substances on composites of soil components. This study aimed to investigate the sorption characteristics of humic acid on Fe oxide-bacteria composites and improve the understanding on the interaction among humic substance Fe oxide bacteria in soil.

Materials and methods

Humic acid was purchased from Sigma-Aldrich and was purified. Hematite and ferrihydrite were synthesized in the lab. Bacillus subtilis and Pseudomonas putida were cultivated in Luria-Broth medium and harvested at stationary growth phase. Batch sorption experiments were carried out at pH 5.0. Various amounts of humic acid were mixed with 20 mg of Fe oxide, bacteria, or Fe oxide-bacteria composite (oxide to bacteria of 1:1) in 10 mL of KCl (0.02 mol L^?1) to construct sorption isotherms. The effects of phosphate concentration and addition order among humic acid, Fe oxide, bacteria on the sorption of humic acid were also studied. The sorption of humic acid was calculated by the difference between the amount of humic acid added initially and that remained in the supernatant.

Results and discussion

The maximum sorption of humic acid on hematite, ferrihydrite, B. subtilis and P. putida was 73.2, 153.5, 69.1, and 56.7 mg C g^?1, respectively. The maximum sorption of humic acid on examined Fe oxide-bacteria composite was 28.2–57.2 % less than the predicted values, implying that the sorption of humic acid was reduced by the interaction between Fe oxides and bacteria. The presence of phosphate exerted negligible influence on the sorption of humic acid on bacteria while it inhibited the sorption of humic acid on Fe oxides. On Fe oxide-bacteria composites, inhibiting influences followed by promoting or weak inhibiting effects of phosphate with increasing concentration on the sorption of humic acid were found.

Conclusions

The interaction between Fe oxides and bacteria reduced the sorption of humic acid; moreover, the reduction was greater by the interaction of bacteria with ferrihydrite than that with hematite. Phosphate exerted negligible and inhibiting influence on the sorption of humic acid by bacteria and Fe oxides, respectively. On Fe oxide-bacteria composites, humic acid sorption was initially inhibited and then promoted or weakly inhibited by phosphate with increasing concentration.     

Sorption of organic acids in acid soils and its implications in the rhizosphere

Organic acids have been implicated in many soil-forming and rhizosphere processes, but their fate in soil is poorly understood. We examined the sorption of four simple short-chain organic acids (citric, oxalic, malic and acetic) in five acid soils and on synthetic iron hydroxide (ferrihydrite). The results for both soils and ferrihydrite indicated that the sorption depended on concentration in the following order of strength: phosphate >> oxalate > citrate > malate >> acetate. The sorption reactions in soil were shown to be little influenced by pH, whereas for ferrihydrite, sorption of all ligands increased strongly with decreasing pH. The sorption of organic anions onto ferrihydrite was influenced to a lesser extent by the presence of metal cations in solution. From the results we calculated that when organic acids enter solution they rapidly become sorbed onto the soil's exchange complex (> 80% within 10 min), and we believe that this sorption will greatly diminish their effectiveness to mobilize nutrients from the rhizosphere.     

有机酸对几种土壤胶体吸附解吸镉离子的影响

用平衡法研究了有机酸对土壤胶体吸附 解吸Cd2 的影响。结果表明 ,黄棕壤、红壤、砖红壤胶体Cd2 最大吸附容量 (Qm)分别为 4 3 7、16 8、1 5 8mmolkg-1。在加入Cd2 浓度相同的条件下 ,土壤胶体Cd2 吸附量随有机酸浓度的升高呈峰形曲线变化。当有机酸与Cd2 共存时 (竞争吸附 ) ,低浓度的草酸 (小于0 5～ 2mmolL-1)或柠檬酸 (小于 0 0 2 5～ 0 2mmolL-1)提高Cd2 吸附量 ,高浓度的草酸或柠檬酸能降低Cd2 吸附量。吸附有机酸后的土壤胶体 (次级吸附 )对Cd2 次级吸附量的影响与竞争吸附一致 ,但两者的Cd2 吸附量变化幅度不一样。这是由于两种吸附体系液相中有机酸残留浓度不同所致。土壤胶体吸附态Cd2 的解吸结果表明 ,草酸浓度不仅影响Cd2 的总解吸量、总解吸率 ,还影响土壤胶体表面KNO3 解吸态与DTPA解吸态Cd2 的分配比例     

Modelling the effects of ageing on Cd,Zn, Ni and Cu solubility in soils using an assemblage model

Ageing reactions can reduce trace metal solubility and can explain natural attenuation of contaminated soils. We modelled ageing reactions in soil with an assemblage model that considers slow reactions in Fe‐oxyhydroxides and reversible sorption on organic matter and clay minerals. Metal adsorption kinetics on Fe‐oxyhydroxides was obtained from data with synthetic oxyhydroxides. Metal solubility and isotopic exchangeability data were obtained from 28 soils amended with Ni, Zn, Cu and Cd metal salts and monitored for 850 days. The assemblage model was constructed in WHAM 6.0 and used soil properties and dissolved organic matter as input data. The model was first validated to predict dissolved metal concentrations, based on the concentration of isotopic exchangeable metals. The model overestimated metal solubility without parameter adjustment by mean factors of 4–7, and successful fits were obtained by increasing the specific surface area of Fe‐oxyhydroxides from measured values of synthetic systems to a value of 600 m² g^?1 recommended by other authors. The effect of ageing on the isotopic exchangeable metal fraction was subsequently modelled starting from the predicted fraction of metals present on Fe‐oxyhydroxides immediately after soil spiking. The observed isotopic exchangeable metal fractions of Ni, Zn and Cd agreed reasonably well with predicted values. The model predicts that ageing reactions are more pronounced at higher pH because metal sorption is increasingly directed to oxyhydroxide surfaces with increasing soil pH. Modelling fixation of Cu requires more information on fixation of that metal in organic matter.     

Cadmium soil sorption at low concentrations: I. Effect of time,cadmium load,pH, and calcium

Sorption of Cd at low concentrations onto two Danish soils (loamy sand, sandy loam) was examined in terms of kinetics and governing factors. From an environmental point of view soil sorption of Cd is a fast process: More than 95% of the sorption takes place within 10 min, equilibrium is reached in 1 hr, and exposures up to 67 wk did not reveal any long term changes in Cd sorption capacities. The soils have very high affinity for Cd at pH = 6.00 (10^?3 M CaCl₂) exhibiting distribution coefficients in the order of 200 to 250 (soil Cd concentration/solute Cd concentration). However, the sorption isotherms describing the distribution of Cd between soil and solute are slightly curvelinear. In the pH-interval 4 to 7.7, the sorption capacity of the soil approximately increases 3 times for a pH increase of one unit. Increasing the Ca concentration from 10^?3 to 10^?2 M reduces the sorption capacity of the sandy loam to one third.     

Pesticide adsorptivity of aged particulate matter arising from crop residue burns

Particulates (ashes) arising from the burning of crop residues are potentially effective adsorbents for pesticides in agricultural soils. To determine the long-term adsorptive sustainability of ashes, a wheat (Triticum aestivum L.) ash was aged under environmentally relevant conditions (in CaCl(2) solution at room temperature and pH 7) in soil extract for 1 month and in a soil (1% ash) for a period of up to 12 months. The aged ash and ash-amended soil were used to sorb diuron from water. The diuron sorption was also measured in the presence of atrazine as a competing pesticide. There was no observed microbial impact on the stability of the wheat ash in soil. All isotherms with the ash were nonlinear type-I curves, suggestive of the surface adsorption. On a unit mass basis, the ash in soil extract was 600-10000 times more effective than the soil in sorbing diuron. Adsorption of dissolved soil organic matter (DOM) during aging on the ash surfaces reduced the diuron adsorption by 50-60%. Surface competition from the atrazine adsorption also reduced the ash adsorption of diuron by 10-30%. A total of 55-67% reduction in diuron sorption by the ash-amended soil was observed. Due to its high initial adsorptivity, the ash fraction of the aged ash-amended soil contributed >50% to the total diuron sorption. Thus, the wheat ash aged in the soil remained highly effective in adsorbing diuron. As crop residues are frequently burned in the field, pesticides in agricultural soils may be highly immobilized due to the presence of ashes.     

伊朗西部地区碱性土壤中共离子对Zn吸附的影响

Zinc(Zn) is essential to plant growth and relatively mobile in soils.This study was conducted to assess the effect of common ions(Ca 2+,K +,Na +,NH + 4,Cl,NO 3,and H 2 PO 4) on sorption of Zn in surface samples of ten calcareous soils from western Iran using 10 mmol L 1 KCl,KNO 3,KH 2 PO 4,Ca(NO 3) 2,NaNO 3,and NH 4 NO 3 solutions as background electrolytes.The results indicated that both NH + 4,K +,and Ca 2+ equally decreased Zn sorption as compared to Na +.Zinc sorption was decreased by H 2 PO 4 as compared to NO 3 and Cl.The Langmuir and Freundlich equations fitted closely to the sorption data of all ions.The Langmuir maximum,bonding energy constant,and Freundlich distribution coefficient for Zn sorption differed among the various ionic background electrolytes.Langmuir sorption parameters showed that the presence of H 2 PO 4 decreased the maximum Zn adsorbed,but increased the bonding energy.Although K + and NH + 4 equally influenced maximum Zn adsorbed,they differed in their effect on the distribution coefficient of Zn in soils.Values of saturation index calculated using Visual MINTEQ indicated that at the low Zn concentration,Zn solubility was controlled by sorption reactions and at the high Zn concentration,it was mainly controlled by sorption and mineral precipitation reactions,such as precipitation of Zn 3(PO 4) 2.4H 2 O,Zn 5(OH) 6(CO 3) 2,and ZnCO 3.For most ionic background electrolytes,soil pH,CaCO 3,and cation exchange capacity(CEC) were significantly correlated with sorption parameters.     

玉米秸秆水溶性物质对白浆土吸附锌离子的影响

应用平衡吸附法,研究外源玉米秸秆水溶性物质(WSS)对白浆土吸附Zn2+的影响,影响因素主要包括温度(298 K和318 K)、WSS浓度和接触时间(1～1 440 min)。结果表明:(1)不同温度条件影响下,白浆土对Zn2+的吸附热力学曲线主要包括起始的快速升高、中间的吸附平台和继续升高直至平衡3个阶段,经历电性吸附向配位吸附转变,最终促使二者共存。Langmuir方程能较好描述白浆土对Zn2+的吸附特征,升高温度有利于提高白浆土对Zn2+的最大缓冲容量,另外,白浆土对Zn2+的吸附是非自发、吸热且混乱度增加的过程。(2)玉米秸秆WSS的加入可有效抑制白浆土对Zn2+的吸附固定,减少两者的亲和力,降低白浆土对Zn2+的吸附强度,增大Zn2+在土壤溶液中的移动,有利于提高其植物有效性。(3)随玉米秸秆WSS浓度的增大,白浆土对Zn2+的吸附强度逐渐降低,可采用线性方程较好描述。(4)白浆土对Zn2+的动力学吸附主要包括短期快速吸附和长期慢速吸附两个阶段,第一阶段两个处理的吸附率分别达79.51%和96.80%。玉米秸秆WSS的加入可有效提高短期快速吸附阶段白浆土对Zn2+的吸附率,但同时WSS的加入却减少了白浆土对Zn2+的吸附固定。Elovich和双常数方程描述白浆土对Zn2+的吸附有较为明显的优势,WSS的添加扰乱了白浆土对Zn2+的动力学吸附过程。     

Modelling changes in cations in the topsoil of an Amazonian Acrisol in response to additions of wood ash

Predictions of changes in soil solution chemistry and exchangeable cations which occur on ash deposition after slash burning are complex and may be facilitated by the use of chemical models. Multi-ion sorption in the topsoil of an Amazonian Acrisol was studied by sequentially adding small amounts of electrolytes to soil and mixtures of soil and ash in batch experiments. A chemical equilibrium model that included inorganic complexation, multiple cation exchange and sparingly soluble salts (aluminium hydroxide and magnesian calcites) was used to interpret the results. The model predicted well the pH and sorption values in all experiments in which there was no addition of ash. The model suggested that cation exchange was the main process determining concentrations of soil solutions in all cases where neutral salt solutions were added, and that proton buffering was achieved by the dissolution of Al(OH)₃ which was followed by Al³⁺ adsorption. Calculation of ion activity products in solutions from various batch experiments in soil + ash mixtures suggested that magnesian calcites of differing solubility may be in equilibrium with the activities of Mg²⁺ and Ca²⁺ in solution. An incongruent dissolution of Mg resulted in less soluble magnesian calcites in the ash. The model estimated satisfactorily the pH and the sorption of ions for all experiments with differing ash additions to the soil. Most of the Ca and significant amounts of Mg added in the ash are expected to remain for a long time in the soil and may determine the Ca and Mg status of the soil solution, primarily controlled by principles of solubility products.     

The effects of pH and chloride concentration on mercury sorption. II. By a soil

The pH of a soil was altered by incubation with either acid or lime, and the sorption of mercury was measured in the absence of chloride and at three chloride concentrations. In the absence of chloride there were only small effects of pH on sorption between pH 4 and 6; sorption decreased at higher pH. Addition of chloride decreased sorption at low pH but had little effect on sorption at high pH. Consequently, in the presence of chloride, sorption increased with increasing pH between pH 4 and 6 and then decreased. Many of the mercury sorption curves were sigmoid. This was explained by assuming that a small amount of complexing material was present in the solution after mixing with the soil. Calculation of the mercury species present in solution was made difficult by uncertainties about the postulated complexing material. Nevertheless, between pH 4 and pH 5.8, it was possible to explain the effects of pH and of chloride concentration on sorption as entirely due to changes in the HgOH⁺ concentration.     

Competitive sorption of cadmium and lead in acid soils of Central Spain

The bioavailability and ultimate fate of heavy metals in the environment are controlled by chemical sorption. To assess competitive sorption of Pb and Cd, batch equilibrium experiments (generating sorption isotherms) and kinetics sorption studies were performed using single and binary metal solutions in surface samples of four soils from central Spain. For comparisons between soils, as well as, single and binary metal solutions, soil chemical processes were characterized using the Langmuir equation, ionic strength, and an empirical power function for kinetic sorption. In addition, soil pH and clay mineralogy were used to explain observed sorption processes. Sorption isotherms were well described by the Langmuir equation and the sorption kinetics were well described by an empirical power function within the reaction times in this study. Soils with higher pH and clay content (characterized by having smectite) had the greatest sorption capacity as estimated by the maximum sorption parameter (Q) of the Langmuir equation. All soils exhibited greater sorption capacity for Pb than Cd and the presence of both metals reduced the tendency for either to be sorbed although Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter (k) was always greater for Pb than for Cd. However, these k values tended to increase as a result of the simultaneous presence of both metals that may indicate competition for sorption sites promoting the retention of both metals on more specific sorption sites. The kinetic experiments showed that Pb sorption is initially faster than Cd sorption from both single and binary solutions although the simultaneous presence of both metals affected the sorption of Cd at short times while only a minor effect was observed on Pb. The estimated exponents of the kinetic function were in all cases smaller for Pb than for Cd, likely due to diffusion processes into micropores or interlayer space of the clay minerals which occurs more readily for Cd than Pb. Finally, the overall sorption processes of Pb and Cd in the smectitic soil with the highest sorption capacity of the studied soils are slower than in the rest of the soils with a clay mineralogy dominated by kaolinite and illite, exhibiting these soils similar sorption rates. These results demonstrate a significant interaction between Pb and Cd sorption when both metals are present that depends on important soil properties such as the clay mineralogy.     

Cation treatment and drying‐temperature effects on nonylphenol and phenanthrene sorption to a sandy soil

The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na⁺, Ca²⁺, or Al³⁺ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na⁺ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca²⁺ and Al³⁺ decreased it. The ¹H‐NMR relaxometry analyses showed that Al³⁺ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca²⁺ or Na⁺. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.