Long-term effects of bone char and lignocellulosic biochar-based soil amendments on phosphorus adsorption–desorption and crop yield in low-input acidic soils

Although the addition of biochar has been shown to reduce the phosphorus (P) adsorption capacity of soil, quantitative evidence of this has mainly been provided by incubation experiments and it is therefore essential to conduct long-term field trials to draw general conclusions. It is largely unknown whether bone char has a greater effect than lignocellulosic biochar on P adsorption–desorption processes and crop yield. The aim of this study was to determine the long-term (8 years) effect of bone char and biochar on P adsorption–desorption and crop yield in low-input acidic soils. The results showed that bone char decreased the maximum P adsorption capacity (Q_m) by 10% and increased the desorption capacity (D_s) by 150% compared with the control (i.e. without a soil amendment). The desorption ratio was highest for the bone char treatment (10.3%) and three times more than the control. Plant-available P was seven times greater under bone char than the control. There was no variation in adsorption–desorption characteristics, desorption ratio and plant-P available content between bone char and lignocellulosic biochar treatments. The average yield increment following the application of bone char and biochar was 1.7 and 1.4 Mg ha⁻¹ for maize and 1.8 and 1.9 Mg ha⁻¹ for soya bean, respectively. Despite the low application rate (4 t ha⁻¹ year⁻¹), these findings demonstrated that the long-term application of bone char and biochar-based amendments enhanced P availability in low-input cropping systems, mainly by altering the P adsorption and desorption capacity of soils.     

Quantifying effects of primary parameters on adsorption–desorption of atrazine in soils

Purpose

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of atrazine in soils. Equilibrium batch experiments were carried out to investigate the adsorption–desorption characteristics of atrazine. The objectives of this study were to (1) determine and quantify the main soil parameters governing atrazine adsorption and desorption phenomena; (2) find the correlativity between the identified soil parameters; and (3) investigate the universal desorption hysteresis traits.

Materials and methods

Fifteen soils with contrasting physico-chemical characteristics were collected from 11 provinces in eastern China. The equilibrium time was 24 h both for adsorption and desorption experiments. Atrazine was detected by Waters 2695/UV HPLC.

Results and discussion

Adsorption isotherms of atrazine could be well described by the Freundlich equation (r?≥?0.994, p?<?0.01). The total organic carbon (TOC) was the first independent variable that described 53.0 % of the total variability of K _f, followed by the pH (9.9 %), and the clay (4.0 %) and silt (1.2 %) contents, separately; while the primary soil properties that affect desorption parameters included the TOC, pH, free Fe₂O₃ (Fe_d) and the sand content, with the biggest contribution achieved by the TOC (ranged from 48.5–78.1 %). The results showed that when the content ratio of clay to TOC (RCO) was less than 40, the atrazine adsorption was largely influenced by the organic matrix, while when the RCO was greater than 40, they were vital affected by the clay content.

Conclusions

Adsorption–desorption isotherms of atrazine in soils were nonlinear. The content of TOC, clay, and iron oxides, as well as the pH value were the key soil parameters affecting the adsorption–desorption of atrazine in soil, among which the RCO especially exhibited relevance. Additionally, the desorption hysteresis existed for atrazine retention in all 15 tested soils, and the hysteretic effect enhanced with the increasing time for desorption. This would be ascribed to the heterogeneity physical–chemical properties of these soils.     

Effects of Long-Term Fertilization on the Form of Inorganic Phosphorus and the Characteristic of Adsorption and Desorption in Black Soil

Changes of inorganic phosphorus forms and the characteristics of phosphorus adsorption and desorption were studied under a long-term fertilization experiment in black soil. Results showed that the forms of inorganic phosphorus ranged as O–P < Ca₂–P < Ca₈–P < Al–P < Ca₁₀–P < Fe–P. Therefore, Fe–P was the main inorganic phosphorus form in this study. The capacity of phosphorus adsorption with phosphate treatments was higher than with no-phosphorus treatments. The optimal fitted equation was the Langmuir equation. Phosphorus desorption was related to the binding energy. Positive correlation between phosphorus adsorption and desorption without phosphorus addition was found; however, negative correlations among the phosphate treatments had been observed.     

Cobalt,copper, and manganese adsorption by aluminium and iron oxides and humic acid

Abstract

Adsorption of cobalt (Co), copper (Cu), and manganese (Mn) by synthetic aluminium oxide, ferrihydrite, goethite, extracted humic acid, and a sandy soil sample were determined as a function of metals concentration (0–1.2 mM) and pH (3.8–8.2). For each pH and adsorbent, the Langmuir adsorption maximum (adsorption capacity) was calculated. The position of the adsorption curves for Co, Cu, and Mn as a function of pH has been shown to be related to the first hydrolysis constant of the cations in solution (pK₁). The sequence of preference of the three metals to the studied adsorbents decreased in order Cu >> Co > Mn. The results obtained from this study showed that the Co, Cu, and Mn adsorption characteristics of soils are probably controlled to large extent by their organic matter and oxides contents.     

Adsorption and desorption of organotin compounds in organic and mineral soils

Organotin compounds (OTC) are deposited from the atmosphere into terrestrial ecosystems and can accumulate in soils. We studied the adsorption and desorption of methyltin and butyltin compounds in organic and mineral soils in batch experiments. The adsorption and desorption isotherms for all species and soils were linear over the concentration range of 10–100 ng Sn ml^?1. The strength of OTC adsorption correlated well with the carbon content and cation exchange capacity of the soil and was in the order mono‐ > di‐ > tri‐substituted OTCs and butyltin > methyltin compounds. The OTC adsorption coefficients were much larger in organic soils (K_d > 10⁴) than in mineral soils. The adsorption and desorption showed a pronounced hysteresis. Trimethyltin adsorption was partly reversible in all soils (desorption 2–12% of the adsorbed amounts). Dimethyltin, tributyltin and dibutyltin exhibited reversible adsorption only in mineral soils (desorption 4–33% of the adsorbed amounts). Mono‐substituted OTCs adsorbed almost irreversibly in all soils (desorption < 1% of adsorbed amounts). Trimethyltin was more mobile and more bioavailable in soils than other OTCs. It might therefore be leached from soils and accumulate in aquatic ecosystems. The other OTCs are scarcely mobile and are strongly retained in soils.     

Effect of flow rate on the adsorption and desorption of glyphosate,simazine and atrazine in columns of sandy soils

Adsorption and desorption of the herbicides glyphosate [N-phosphonomethyl-aminoaceticacid], simazine [6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine] and atrazine [6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine] were studied in four sandy soils from Western Australia. Distribution coefficients (K_ds) were calculated from breakthrough curves (BTCs) resulting from leaching step changes in concentrations through small saturated columns of soil at flow rates ranging from 0.3 to 30 m day^–1. A comparison was made with K_ds obtained after batch equilibrating solutions of the herbicides with the same soils. The K_ds of herbicides in soils decreased with increasing flow rate and most strongly for glyphosate in soils rich in clay content. Resulting increases in mobility of about 40–50% were estimated for simazine and atrazine and > 50% for glyphosate at flow rates of 3 m day^–1. Adsorption and desorption rates were estimated by fitting numerically simulated BTCs to experimental BTCs. Best fits were obtained with a time-dependent Freundlich adsorption equation. The resulting coefficient for time dependency in the equation suggests that the rates of adsorption and desorption are controlled mainly by diffusion in an adsorbing layer on or in soil particles.     

Does Particle Size of Clinoptilolite Zeolite Have a Role in Textural Properties? Insight through Differential Pore-Volume Distribution of Barret,Joyner, and Halenda Model

Analysis of differential pore-volume distribution (PVD) patterns of commercial clinoptilolite fractions [(<125 µ (Z8; fine), 125–250 µ (Z9; medium), and >250 µ (Z10; coarse)] has been conducted experimentally using an analyzer to measure the nitrogen (N₂) adsorption isotherms. The differential PVDs of the clinoptilolite fractions were calculated from the hysteresis loop according to the adsorption and desorption curves of the Barret, Joyner, and Halenda (BJH) model. The adsorption and desorption cycles of BJH produced heterogeneous as well as dissimilar differential PVD patterns with assorted peaks. While the adsorption curve has prolonged up to 300 nm, the desorption cycle was confined up to 190-nm pore diameter only. In the adsorption cycle, all the clinoptilolite fractions displayed U-shaped curves and had a differential pore volume in the range of 3 × 10^–3 to 8 × 10^–3 cm³/g A° in the micropore region with a sole peak at 1.75 nm for the fine fraction (Z8). In contrast, the curves were linear in the mesoporous region for all the fractions, with the fine fraction (Z8) having the greatest differential pore volume, whereas the other two fractions were almost parallel to each other. The desorption cycle has revealed an inverted V-shape curve with no definite patterns for the microporous region. Although the adsorption cycle could ascertain the micropore region, the desorption cycle was unable to do so. It was apparent from the differential PVD of the BJH model that fraction size has a major role in determining the textural properties of clinoptilolite fractions.     

Influence of nitrate and chloride on the adsorption and transport of sulphate in soils

The adsorption and desorption of SO₄ was investigated as a function of KCI and KNO₃ concentration using soils with contrasting surface-charge properties. In the net negatively-charged soils, additions of C1 or NO₃ of up to about 0.05–0.10 M increased the adsorption of SO₄ but at higher concentrations adsorption decreased. In contrast, adsorption by the net positively-charged soils decreased with concentration increase over the entire range (0 to 1 M) investigated. The effects of CI and NO₃ on the adsorption of SO₄ were practically identical. The different pattern of SO₄ adsorption in the two groups of soils in response to addition of KCI or KNO₃ can at least partly be explained in terms of the effect of electrolyte on soil pH. The depression in pH of net negatively-charged soils induced by an indifferent electrolyte favours adsorption of SO₄; but, because pH changes in the opposite direction in positively-charged soils, SO₄ adsorption decreases in these soils. The distribution of a pulse of 35S-labelled SO₄ in soil columns after leaching with KCI solutions, ranging in concentration from 0 (H₂O) to 0.10 M, clearly reflected the manner in which electrolyte concentration affected the adsorption of SO₄. The distribution of ³⁵S was reasonably well simulated using the general transport equation combined with the Freundlich equation to describe the adsorption/desorption of SO₄. In contrast to other inorganic anions (H₂PO₄ and OH) applied in agricultural practice, C1 and NO₃ may have beneficial effects on the S economy of many soils by decreasing leaching losses of SO₄.     

稻谷水分吸附与解吸等温线拟合模型的选择及其参数优化

评价5种最常用的数学模型对中国不同类型的稻谷(籼稻、粳稻、糯稻)吸附与解吸等温线数据的拟合效果,以确定最佳拟合模型及其参数。测定中国不同类型稻谷的吸附与解吸等温线数据,用非线性回归进行统计分析并评价数学模型的拟合效果。结果表明,美国农业工程学会(ASAE)推荐的修正Chung-Pfost模型及其参数并不能与中国稻谷的吸附与解吸等温线数据很好地拟合。Strohman-Yoerger模型最适于拟合籼稻、粳稻的吸附与解吸等温线及糯稻的吸附等温线。而修正Oswin模型最适合拟合糯稻的解吸等温线。Strohman-Yoerger模型拟合籼稻、粳稻吸附等温线的参数C₁、C₂、C₃、C₄分别为1.44871、0.20898、7.32345、0.18647;拟合解吸等温线的参数C₁、C₂、C₃、C₄分别为2.25071、0.24167、8.32543、0.19035;拟合珍糯吸附等温线的参数为1.55680,0.19179,6.19676,0.17155。修正Oswin模型拟合珍糯的解吸等温线的参数为13.63642,-0.05638,3.60042。本研究为中国的稻谷贮藏与加工提供了基础性数据。     

Phosphorus buffering capacity of substrate clays and its significance for plant cultivation

Peat is commonly used as the main component of horticultural substrates, but it has a very low buffering capacity for the anionic macronutrient phosphorus (P), which can be increased by the addition of clays. The aim of this study was to characterize the P adsorption capacity of different substrate clays and to evaluate its significance for plant P uptake. Substrate clays were characterized with a single‐point batch experiment and adsorption and desorption isotherms. The data were fitted to the Langmuir equation for a calculation of the maximum adsorption capacity. Additionally, the contents of oxalate extractable Fe and Al (ΣFe_ox + Al_ox) were determined. The influence of a varying P adsorption capacity of the clays on the P availability to plants in the respective peat–clay substrates and pure peat was investigated in a growth experiment with Impatiens walleriana fertigated with 0, 17, and 35 mg P L^?1 solution, respectively. The observed and calculated (Langmuir) P adsorption capacity of the clays could be well‐characterized by both the batch experiment and the adsorption isotherms and was highly correlated with the ΣFe_ox+Al_ox. A higher P adsorption capacity of the clay amendment in mixed substrates resulted in a lower P concentration in the substrate solution, while the CAT extractable P concentration (P_CAT) was the same. Plant growth and shoot P concentrations were enhanced in the substrates, showing a higher P adsorption capacity, since plants were able to take up the whole amount of P_CAT, and also part of the non‐CAT extractable P. However, the release rate was too low to ensure optimal plant growth, which was in accordance with the result of the desorption experiment. The absolute extent of P release was increased with the increasing P adsorption capacity of the clays and higher degree of P saturation (DPS).     

Relationship between Freundlich isotherm Coefficients,log K F and 1 / n for atrazine desorption from soils in Japan

Desorption experiments were conducted on 21 soils at 3 atrazine concentrations. The Freundlich isotherm was used to estimate atrazine desorption. For the relationship between Freundlich isotherm coefficients, log K _F and 1 / n, 1 / n was also represented by a linear regression of log K _F as in the case of atrazine adsorption. All the linear regression lines of desorption exhibited larger slopes and intercepts than those of adsorption. When the atrazine concentration was high, the slope and intercept values were smaller than those for the desorption regression lines. The results showed that the larger the capacity of a soil to adsorb atrazine, the lesser the amount of atrazine desorbed. For the cultivated soils except for Andisols, the percentages of atrazine taken from solutions using the sequential exchange method after the first adsorption experiments, were the same as those desorbed from soils in relation to the initial amount adsorbed. Thus, reversible adsorption occurred in the soils due to weak physical adsorption.     

ADSORPTION, DESORPTION AND SOLUBILITY RELATIONSHIPS OF LEAD AND CADMIUM IN SOME ALKALINE SOILS

In some alkaline soils of Punjab (India) the adsorption, desorption and solubility relationships of lead and cadmium were investigated and the results analysed by the Langmuir equation. Both the metals are retained in soils by adsorption on mineral interfaces and interaction with organic matter and calcium carbonate. At high concentrations, these probably precipitate as hydroxides. Sequential desorption of Pb and Cd with 1 MKCI and 0.05 MCu(CH₃COO)₂ provided a measure of their exchangeable and chelated form.     

Evaluation of Differential Pore-Volume Distribution (DPVD) Patterns of Porous Clinoptilolite Fractions

Analysis of differential pore-volume distribution (DPVD) patterns of a commercial Clinoptilolite has been conducted experimentally using an analyzer by measuring the N₂ adsorption isotherm. The commercial material was fractionated by sieving through sequential sieves: <125 µ (Z8; fine), 125–250 µ (Z9; medium), and >250 µ (Z10; coarse). The DPVD of the fractions were calculated from the hysteresis loop according to the adsorption and desorption curves of Dollimore-Heal (DH) model. The adsorption cycle had produced dissimilar differential pore volume distribution patterns. For the 10-nm pore width, fine and medium fractions had a maximum pore volume up to 0.0016 cm³/g nm, while the coarse fraction had a little greater value up to 0.002 cm³/g nm. Moreover, the medium fraction had too many hills and valleys in the DPVD. However, the desorption cycle–based DH analysis did not show any marked variation in the DPVD pattern.     

Boron adsorption and desorption in some acid soils of West Bengal,India

Laboratory and greenhouse experiments were conducted to determine the influence of soil properties on adsorption and desorption of boron (B) as well as to estimate the degree of reversibility of adsorption reactions. The utility of Freundlich and Langmuir equations for characterizing the plant availability of applied B in soils was established using soybean [Glycine max (L.) Merr.] as a test crop. The adsorption-desorption study revealed that Fe₂O₃ and clay were primarily responsible for retaining added B in all the 25 different soils under investigation. Organic carbon, pH and cation exchange capacity (CEC) positively influenced the adsorption of B while free Fe₂O₃, organic carbon and clay retarded release of B from these soils. The degree of irreversibility (hysteresis) of B adsorption/desorption increased with increase in organic carbon and CEC of these soils. Freundlich isotherm proved more effective in describing B adsorption in soils as compared to Langmuir equation. The split Langmuir isotherm demonstrated that any of the adsorption maxima, calculated from lower, upper or entire isotherm, could be of practical use. Contrary, bonding energy coefficient, calculated either at lower or higher equilibrium concentration failed to show any practical benefit. Regression models as a function of B application rate and adsorption equation parameters to predict B uptake from applied B, demonstrated the utility of Langmuir and Freundlich equation parameters.     

黄土性土壤在连续液流条件下吸附、解吸磷酸根的动力学研究

采用连续液流法研究了黄土性土壤吸附,解吸磷酸根的动力学性质。结果表明：（１）供试土壤对磷酸根的吸附,解吸扫速率可分为快,中,慢三种反应类型;（２）描述吸附,解吸反应的最优模型均为Ｅｌｏｖｉｃｈ方程,最差模型分别为一级反应方程及双常数方程,拟合差的模型对反应速率变化“敏感”,可用于反应类型划分和机理研究;（３）粘粒含量及代换量对吸附速率有著影响,游离铁对吸附速率,ＣａＣＯ３对较低温度下的吸附及较高温     

Adsorption of phosphate and organic matter on metal (hydr)oxides in arable and forest soil: a mechanistic modelling study

Phosphate (PO₄) and organic matter (OM) compete for adsorption to metal (hydr)oxides. Our objective was to quantify the effect of OM on PO₄ solubility in forest and arable soil by desorption experiments and surface complexation (SC) modelling. We sampled different types of soil along an age gradient (≈50–2500 years) and from different depths (0–80 cm). The soil types are calcareous and cover a range of soil organic carbon (SOC) contents (5.6–43.5 g kg^?1), PO₄ contents (0.2–5.9 mmol kg^?1) and water‐soluble PO₄ concentrations (0.03–13.4 µm ). Assuming that PO₄ concentrations are controlled by desorption, PO₄ concentrations were expected to correlate with the PO₄ loading on metal‐(hydr)oxide surfaces. However, we show that the PO₄ loading alone is a poor predictor of PO₄ solubility because its solubility increases with increasing SOC content. These data were explained by SC modelling, which shows a decrease in the apparent adsorption affinity of PO₄ with increasing OM loading on to the metal (hydr)oxides. As a consequence, if the competition with OM is disregarded in SC modelling, it results in underestimation of the PO₄ concentration by several orders of magnitude. For forest soil, predicted OM loadings increase slightly with increasing soil age. For arable soil, however, OM loadings were much smaller, which we explain by the replacement of PO₄ with OM. Overall, adsorption interactions strongly affect PO₄ solubility and levels of OM and PO₄ stabilization in soil.     

Adsorption and desorption dynamics of citric acid anions in soil

The functional role of organic acid anions in soil has been intensively investigated, with special focus on (i) microbial respiration and soil carbon dynamics, (ii) nutrient solubilization or (iii) metal detoxification and reduction of plant metal uptake. Little is known about the interaction dynamics of organic acid anions with the soil matrix and the potential impact of adsorption and desorption processes on the functional significance of these effects. The aim of this study was to characterize experimentally the adsorption and desorption dynamics of organic acid anions in five agricultural soils differing in iron and aluminium oxide contents and using citrate as a model carboxylate. Results showed that both adsorption and desorption processes were fast in all soils, reaching a steady state within approximately 1 hour. However, for a given total soil citrate concentration (c_t) the steady state was critically dependent on the starting conditions of the experiment, whether most of the citrate was initially present in solution (c_l) or held on the solid phase (c_s). Specifically, desorption‐led processes resulted in significantly smaller steady‐state solution concentrations than adsorption‐led processes, indicating that hysteresis occurred. As it is not possible to distinguish between different adsorption and desorption pools in soil experimentally, a new dynamic hysteresis model that relies only on measured soil solution concentrations was developed. The model satisfactorily explained experimental data and was able to predict dynamic adsorption and desorption behaviour. To demonstrate its use, we applied the model to two relevant situations involving exudation and microbial degradation. The study highlighted the complex nature of citrate adsorption and desorption dynamics in soil. We conclude that existing models need to incorporate both temporal and hysteresis components to describe realistically the role and fate of organic acids in soil processes.     

土壤对镉的吸附与解吸——Ⅰ.土壤组份对镉的吸附和解吸的影响

采用选择溶解法研究了有机质、游离铁、无定型硅、铝等土壤组份对青黑土、黄棕壤、红壤和砖红壤胶体吸附和解吸Cd的影响。结果表明,去除有机质后胶体吸附Cd减少,这可能是由于交换吸附的减少所致;游离铁的去除使得黄棕壤、红壤和砖红壤的吸附量显著减少,显示了在这些土壤中游离氧化铁专性吸附的重要性;随着无定形铝含量的上升,吸附量下降,这是因为铝离子占据了高能量的吸附位。经不同处理后的土壤胶体,其Cd的解吸顺序(解吸%)大致为:去无定型硅、铝者>去游离铁者>去有机质者>原胶体,但在不同土壤和不同pH条件下该顺序略有差别。研究结果为控制和改造土壤Cd污染提供了理论依据。     

Effects of sediment components and TiO2 nanoparticles on perfluorooctane sulfonate adsorption properties

Purpose

Here, the roles of sediment components in perfluorooctane sulfonate (PFOS) adsorption onto aquatic sediments and relevant adsorption mechanisms were investigated in terms of adsorption isotherms and influences of TiO₂ nanoparticles (NPs) contamination.

Materials and methods

Due to the complexity of the sediments, instead of randomly selecting different component sediments, the selective dissolution method was used to better explore the effects of sediment compositions, such as sediment organic matter (SOM) and ferric oxides (dithionite–citrate–bicarbonate [DCB] Fe), and TiO₂ NPs pollution on PFOS adsorption. Mathematical equations (Freundlich, Langmuir, and Temkin) were used to describe the adsorption behavior of PFOS on different sediments and adsorption mechanisms of multiple pollutant interactions. Moreover, the characterization methods of zeta potential, nitrogen (N₂) adsorption–desorption, and scanning electron microscopy (SEM) analysis, as well as Fourier transform infrared (FT-IR) spectroscopy, explained effects of the sediment components and TiO₂ NPs on PFOS adsorption properties in view of physicochemical theories.

Results and discussion

The adsorption isotherms of PFOS on six tested sediments were all nonlinear (Freundlich model, R² = 0.992~1.000). The Freundlich sorption affinities (K_F) of PFOS on S (original sediments), S1 (sediment organic matter (SOM)-removed S), and S2 (ferric oxides (DCB Fe)-removed S1) were 0.232, 0.179, and 0.120, respectively. Both SOM and DCB Fe influenced the physicochemical properties of the sediments, e.g., zeta potential, specific surface area, and permanent negative charge. The addition of TiO₂ NPs increased the K_F of PFOS for S, S1, and S2 by approximately 9.9%, 14.5%, and 26.7%, respectively, by increasing the zeta potential and specific surface area (S_BET, S_ext, and S_micro) and by changing the water and oil properties of the three sediments. However, the addition of TiO₂ NPs decreased the linearity of the sorption isotherm (1/n). FT-IR spectroscopy showed that hydrophobicity, ion exchange, surface complexation, and hydrogen bonding interactions (non-fingerprint region) could all play a role in PFOS sorption onto tested sediments. However, the hypothesis of hydrogen bonding to promote PFOS adsorption on sediment layer silicates (fingerprint region) should be studied further.

Conclusions

The content of both SOM and DCB Fe affected the physicochemical properties of sediment. Both SOM and DCB Fe showed a positive relationship with sorption of PFOS on sediment. The addition of TiO₂ NPs increased PFOS sorption by altering the sediment surface properties. Hydrophobic interactions certainly impelled and ligand and ion exchange and hydrogen bonding (non-fingerprint region) could promote PFOS sorption on the sediments.

     

Competitive adsorption and desorption of oxytetracycline and cadmium with different input loadings on cinnamon soil

Purpose

The binary competitive effect could obviously influence the fate and transport behavior of oxytetracycline (OTC) and cadmium (Cd²⁺) in cinnamon soil. However, two pollutants loading into soil usually are different, perhaps because of the three reasons including occurrence of OTC before Cd²⁺, simultaneous occurrence of OTC and Cd²⁺, or occurrence of Cd²⁺ before OTC. The purpose of the study was to predict the competitive adsorption and desorption of OTC and Cd²⁺ as a function of above input loadings on cinnamon soil.

Materials and methods

Adsorption and desorption were determined using the batch equilibrium method in a single or binary system. The Freundlich equation was applied to describe the adsorption/desorption data of OTC and Cd²⁺ in order to obtain adsorption/desorption isotherms for each tested compound and the respective adsorption/desorption coefficients.

Results and discussion

The results indicated that cinnamon soil could strongly adsorb OTC with the adsorption affinity (K _f value) of more than 718 and Cd²⁺ with K _f value of more than 536 in the competitive and non-competitive system, and all adsorption and desorption isotherms of OTC and Cd²⁺ on cinnamon soil were well fitted by the Freundlich equation with r value of more than 0.99 (p?<?0.01). The coexistence of OTC and Cd²⁺ on cinnamon soil promoted significantly Cd²⁺ adsorption when Cd²⁺ firstly or simultaneously occurred on soil, but their coexistence did not affect adsorption of OTC when OTC firstly or simultaneously occurred on soil. Among the three input loadings, the pollutant with later occurring mode had lower K _f and hysteresis coefficient (HI) than the other two input loadings. According to the adsorption intensity parameter (1/n), the presence of Cd²⁺ or OTC with different input loadings could decrease the adsorption intensity of OTC or Cd²⁺ when compared with single occurrence of OTC or Cd²⁺.

Conclusions

The binary competitive effect influenced the adsorption/desorption of OTC and Cd²⁺ differently. The presence of OTC had a stronger influence on the adsorption/desorption of Cd²⁺ than the presence of Cd²⁺ on the adsorption of OTC. The later occurring pollutant on soil had stronger ecological risk than the former occurring pollutant in the binary competitive system. The physical adsorption in the single or binary system could be identified as the dominant mechanisms of OTC and Cd²⁺ adsorption.