Influence of soil composition on adsorption of glyphosate and phosphate by contrasting Danish surface soils

The herbicide glyphosate and inorganic phosphate are strongly adsorbed by inorganic soil components, especially aluminium and iron oxides, where they seem to compete for the same adsorption sites. Consequently, heavy phosphate application may exhaust soil's capacity to bind glyphosate, which may lead to pollution of drain‐ and groundwater. Adsorption of phosphate and glyphosate to five contrasting Danish surface soils was investigated by batch adsorption experiments. The different soils adsorbed different amounts of glyphosate and phosphate, and there was some competition between glyphosate and phosphate for adsorption sites, but the adsorption of glyphosate and phosphate seemed to be both competitive and additive. The competition was, however, less pronounced than found for goethite and gibbsite in an earlier study. The soil's pH seemed to be the only important factor in determining the amount of glyphosate and phosphate that could be adsorbed by the soils; consequently, glyphosate and phosphate adsorption by the soils was well predicted by pH, though predictions were somewhat improved by incorporation of oxalate‐extractable iron. Other soil factors such as organic carbon, the clay content and the mineralogy of the clay fraction had no effect on glyphosate and phosphate adsorption. The effect of pH on the adsorption of glyphosate and phosphate in one of the soils was further investigated by batch experiments with pH adjusted to 6, 7 and 8. These experiments showed that pH strongly influenced the adsorption of glyphosate. A decrease in pH resulted in increasing glyphosate adsorption, while pH had only a small effect on phosphate adsorption.     

Reactions of nucleic acid bases with inorganic soil constituents

The adsorption at pH's 4, 6 and 8 of adenine, guanine, cytosine, thymine and uracil on clays (montmorillonite, illite and kaolinite), Fe- and Al-oxides (goethite, hematite and gibbsite), a soil, and on a laboratory-prepared fulvic acid-montmorillonite complex was investigated. Portions of the clays and soil were saturated with H⁺, Fe³⁺ and Ca²⁺.Quantitatively, the extent of adsorption of nucleic acid bases by the clays was proportional to their exchange capacities, but the nature of the dominant cation had only minor effects. By contrast, the adsorption was strongly affected by pH, tending to decrease with increase in pH. Adsorption on goethite and gibbsite was lower than that on clays, while adsorption of nucleic acid bases on soils was slightly lower than that on oxides. The fulvic acid-montmorillonite complex adsorbed substantial, although smaller amounts of purines and pyrimidines, than did montmorillonite alone. The main adsorption mechanism at pH 4 appeared to be cation exchange whereas at pH 8 complex formation between the nucleic acid bases and cations on inorganic surfaces seemed to occur.The results of this and earlier work show that both inorganic and organic soil constituents adsorb nucleic acid bases. Which adsorption reaction predominates will depend on the clay and organic matter content and on the pH.     

Competitive adsorption between phosphate and carboxylic acids: quantitative effects and molecular mechanisms

The competitive adsorption at the water‐goethite interface between phosphate and a carboxylic acid, either oxalate, citrate, 1,2,3,4‐butanetetracarboxylic acid (BTCA), mellitate or Suwannee River Standard Fulvic Acid 1S101F (FA), was investigated over a wide pH range (3–9) by means of batch experiments and attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. The quantitative results from the competitive adsorption measurements show that the efficiency of the organic acids in competing with phosphate was in the order oxalate < citrate < BTCA ≅ FA < mellitate. Oxalate showed no detectable effect, whereas the effect in the mellitate system was strong, and the aggregative results indicate that an increasing number of carboxylic groups favours competitive ability towards phosphate. The infrared spectroscopic results show conclusively that competition for goethite surface sites between carboxylic acids and phosphate is not a ligand‐exchange reaction between inner‐sphere surface complexes. Instead, ligands capable of multiple H‐bonding interactions are required to out‐compete and desorb surface complexes of phosphate. The fact that partially protonated organic acids are the most efficient emphasizes the importance of both H‐accepting carboxylate groups and H‐donating carboxylic acid groups for the competitive effect.     

铁氧化物-胡敏酸复合物对磷的吸附吸附

本试验通过设置不同磷酸根浓度、 pH和不同电解质及电解质强度梯度,研究磷酸根在针铁矿-胡敏酸（HA）复合物和赤铁矿-胡敏酸（HA）复合物表面的吸附特性。X射线衍射（XRD）、 扫描电镜（SEM）和红外光谱（FTIR）图谱显示: 铁氧化物包覆胡敏酸后其内部结构特性保持不变; 氧化铁与胡敏酸通过氢键形成粒径大、 表面光滑的铁氧化物-HA复合微粒,且复合物比表面减小; 形成的氧化铁-胡敏酸复合物对磷的吸附能力增强,且针铁矿复合物的吸附能力大于赤铁矿复合物,均为多层吸附过程; pH增高抑制铁氧化物复合物对磷的吸附,同时电解质浓度增加促进复合体对磷的吸附,且反应后体系pH随之降低。     

磷的吸附和表面电荷特征及其与华南地区某些土壤矿物的关系

The phosphate adsorption and surface charge characteristics of the tropical and subtropical soils derived from different parent materials in China were determined, and their relations to soil mineralogy were analysed. The results showed that all soil phosphate adsorption curves were well fitted by Freundlich equation and Langmuir equation. The maximum buffering capacity of P ranged from 66 to 9 880 mg kg^-1, with an increasing order of purple soil, skeletal soil, red soil, lateritic red soil, yellow soil and latosol; and the highest value was 149 times the lowest value, which indicated great differences among these soils in phosphate adsorption and supplying characteristics. The pH₀ (zero point of charge) values obtained by salt titration-potential titration varied from 3.03 to 5.49, and the highest value was found in the latosol derived from basalt whereas the lowest value was found in the purple soil. The correlation analysis indicated that the main minerals responsible for phosphate adsorption in the soils were gibbsite, amorphous iron oxide and kaolinite; and the pH₀ was mainly controlled by kaolinite, gibbsite and oxides.     

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.     

Phosphate adsorption on uncoated and humic acid-coated iron oxides

Purpose

The phosphate adsorption on natural adsorbents is of particular importance in regulating the transport and bioavailability of phosphates in environmental system. In soils, oxides are often associated with organic matter and form mineral-organic complexes. The aim of the present paper was to investigate the mechanisms of phosphate adsorption on these complexes.

Materials and methods

Phosphate adsorption on uncoated and humic acid (HA)-coated iron oxide complexes was investigated at different ionic strengths and pH by isotherm experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.

Results and discussion

Results showed that HA-coated iron oxide complexes caused a decrease in the specific surface area (SSA) and the isoelectric point (IEP) of oxides. Phosphate adsorption on iron oxides was insensitive to changes of ionic strength, while it increased on the complexes with increasing ionic strength. The presence of HA decreased the maximum adsorption and the affinity of phosphate on the complexes. The zeta potential of phosphate-bound iron oxides linearly reduced with the increment of phosphate surface coverage, while the zeta potential of complexes with adsorbed phosphate kept at the same level. ATR-FTIR analysis suggested the formation of phosphate-metal complexation. The presence of HA promotes the formation of the monodentate phosphate complexes at pH 4.5 and significantly influenced phosphate species at pH 8.5.

Conclusions

The amount of phosphate adsorbed was reduced, and the phosphate speciation was also influenced when phosphate was adsorbed on HA-coated iron oxide complexes compared with phosphate adsorption on pure goethite and hematite.

     

Presence of bacteria reduced phosphate adsorption on goethite

Despite extensive studies, the information obtained from pure iron and aluminum (hydr)oxides cannot fully explain phosphate fixation in natural soils because of the ubiquitous interactions between (hydr)oxides and bacteria in soil. The effect of bacteria (Bacillus subtilis subsp. and Pseudomonas fluorescens) on phosphate adsorption on goethite (α‐FeOOH) was systematically examined under varying reaction times, phosphate concentrations, pH, ionic strength and bacteria dosage. Batch experiments in all cases showed significantly less adsorption on bacteria–goethite complexes than on pure goethite, demonstrating an inhibitory effect of bacteria. The inhibition of phosphate adsorption increased with bacterial loading, and showed a significant, non‐linear correlation with the decrease in the goethite positive charge induced by the bacteria. Moreover, in both the desorption experiment and in situ, the attenuated total reflectance Fourier‐transform infrared (ATR‐FTIR) spectra suggested a competition of bacteria surface groups (phosphate and carboxyl) with solution phosphate for hydroxyl on goethite. Therefore, the negative influences of bacteria on phosphate adsorption on goethite were probably caused by the surface charge modification and the competitive adsorption induced by the bacteria. Under most conditions, the effects of B. subtilis subsp. were conspicuous, while only slight influences were found for P. fluorescens. This difference between the two bacteria species was explained by differences in their surface charge, group content and chemical interaction with goethite. These findings uncover an important role of bacteria in phosphate phyto‐availability and mobility in natural environments.     

磷酸盐在水铁矿及水铁矿-胡敏酸复合体表面的吸附

The adsorption of phosphate onto ferrihydrite (FH) and two FH-humic acid (HA) complexes, obtained by co-precipitating FH with low (FH-HA1) and relatively high amounts of humic acid (FH-HA2), was studied through kinetics and isotherm experiments to determine the differences in phosphate adsorption between FH-HA complexes and FH and to reveal the mechanism of phosphate adsorption onto two soil compositions. The isoelectric point (IEP) and the specific surface area (SSA) of the mineral decreased as the particle porosity of the mineral increased, which corresponded to an increase in the amount of organic carbon. The adsorption capacity of phosphate was higher on FH than on FH-HA1 and FH-HA2 at the scale of micromoles per kilogram. The initial adsorption rate and adsorption affinity of phosphate decreased with an increase in the amount of HA in the mineral. The sensitivity of phosphate adsorption to the change in the pH was greater for FH than for FH-HA complexes. Ionic strength did not affect the adsorption of phosphate onto FH and FH-HA1 at a lower pH, and the increase in the ionic strength promoted phosphate adsorption at a higher pH. However, for the FH-HA2 complex, the increase in the ionic strength inhibited the adsorption of phosphate onto FH-HA2 at a lower pH and increased the adsorption at a higher pH.     

Adsorption of phthalic acid and salicylic acid by two variable charge soils as influenced by sulphate and phosphate

Low‐molecular‐weight (LMW) organic acids exist widely in soils, especially in the rhizosphere, and the adsorption of these acids may affect their reactions in soils. The adsorption behaviour of phthalic acid and salicylic acid by two variable charge soils (a Rhodic Ferralsol and a Haplic Acrisol) was investigated. Both soils exhibited great adsorption capacity for these organic acids, with a greater affinity for phthalic acid. The Rhodic Ferralsol adsorbed more organic acids of both kinds than the Haplic Acrisol, which was consistent with the content of iron and aluminum oxides in the two soils. The iron oxides in these soils played a significant role in adsorption of the organic acids, whilst the soil aluminosilicate minerals, such as kaolinite, showed a small adsorption capacity. The presence of phosphate and sulphate caused a decrease in the adsorption of both organic acids because of their competition with them for sorption sites. The phosphate showed a bigger inhibition on the adsorption than sulphate as a result of a greater amount of phosphate adsorbed by the soils. The adsorption of both organic acids was affected by pH only slightly at pH < 4.5. However, the adsorption decreased with the increase in pH at pH > 4.5. A similar trend was observed for the phosphate system, but the opposite was seen for the sulphate system. This suggests that the inhibition of sulphate on the adsorption of the organic acids decreased with the increase in pH, because the adsorption of sulphate decreased strongly with increasing pH.     

施用有机物料对土壤镉形态的影响

采用室内培养试验,研究作物新鲜秸秆和腐熟猪粪对模拟镉（Cd）污染的土壤中Cd形态转化的动态影响。结果表明,各处理土壤交换态Cd含量随培养时间均逐渐降低。碳酸盐结合态和铁锰氧化物结合态Cd含量先增加后降低, 而有机质结合态和残渣态Cd含量则逐渐增加。添加秸秆可增加土壤交换态Cd含量,但随时间延长,增幅逐渐降低, 猪粪则可降低土壤交换态Cd含量。添加有机物后土壤交换态Cd含量的变化主要是由有机质结合态或残渣态Cd含量的变化而引起。秸秆和猪粪对土壤Cd形态的转化与土壤胡敏酸（HA）和富里酸（FA）的变化有关。秸秆对能活化土壤Cd的FA增加幅度大于对能钝化土壤Cd的HA增加幅度,降低HA/FA比,但降幅随时间逐渐减少; 猪粪在整个培养阶段对HA增加幅度均大于FA的增加幅度,增加HA/FA比。秸秆和猪粪均可降低潮土pH而提高红壤pH,但只有猪粪可通过提高红壤pH降低Cd向交换态转化。添加秸秆和猪粪后,Cd由低活性态向交换态转化与HA/FA呈显著负相关。     

Adsorption of glycerophosphate on goethite (α‐FeOOH): A macroscopic and infrared spectroscopic study

Adsorption, desorption, and precipitation reactions at environmental interfaces govern the bioavailability, mobility, and fate of organic phosphates in terrestrial and aquatic environments. Glycerophosphate (GP) is a common environmental organic phosphate, however, surface adsorption reactions of GP on soil minerals have not been well understood. The adsorption characteristics of GP on goethite were studied using batch adsorption experiments, zeta (ζ) potential measurements, and in situ attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR). GP exhibited fast initial adsorption kinetics on goethite, followed by a slow adsorption. The maximum adsorption densities of GP on goethite were 2.00, 1.95, and 1.44 μmol m^?2 at pH 3, 5, and 7, respectively. Batch experiments showed decreased adsorption of GP with increasing pH from 3 to 10. Zeta potential measurements showed a remarkable decrease in the goethite isoelectric point upon GP adsorption (from 9.2 to 5.5), suggesting the formation of inner‐sphere surface complexes. In addition, the ATR‐FTIR spectra of GP sorbed on goethite were different from those of free GP at various pH values. These results suggested that GP was bound to goethite through the phosphate group by forming inner‐sphere surface complexes.     

Study of Interaction Between Glyphosate and Goethite Using Several Methodologies: an Environmental Perspective

Glyphosate (N-(phosphonomethyl) glycine) is one of the most widely used herbicides in the world. Experiments using distilled water or CaCl₂ extractor resulted in as much as 60% of glyphosate being desorbed from goethite. When Mehlich 1 extractor was used, desorption could reach up to 73%. At pHs 2.0, 4.0, 6.0, and 8.0, an increase in salt content decreased the adsorption of glyphosate onto goethite. This indicates that most of the glyphosate is bound weakly to goethite through an outer-sphere complex. Thus, in soils with a high goethite content, glyphosate will contaminate groundwaters or rivers easily. FT-IR spectra showed that glyphosate interacts with goethite through the phosphate group and, at high pH, the amine group could be involved. Evidences of the interaction of the amine group of glyphosate with goethite were also obtained from the EPR spectra that showed, at high pH, a distortion in the octahedral symmetry of iron. In addition to the adsorption decrease with an increase in pH, a decrease of desorption at high pH occurs. This probably occurs because, at high pH, glyphosate interacts with goethite as a monodentate complex and through the amine group. The adsorption results fit best to a Freundlich isotherm model. This is in good agreement with the desorption results, indicating the presence of at least two adsorption sites—one for outer-sphere complexes and the other of inner-sphere complexes. The experimental results fit well with both pseudo-second-order and diffusion-limited models. The experimental results also fit well with a diffusion-limited model; however, the C value was different from zero. Therefore, the adsorption process was not controlled by diffusion only. Adsorption of glyphosate onto goethite is a complex process that could involve intra-particle diffusion. After adsorption of glyphosate onto goethite, a large decrease of pH_pzc was observed. The surface area and pore volume of goethite did not change with the adsorption of glyphosate.     

铁铝氧化物–层状硅酸盐矿物互作对Cr (Ⅵ)和As (Ⅴ)吸附的影响

以高岭石、蒙脱土、针铁矿和三水铝石四种单一典型土壤矿物以及针铁矿-蒙脱石和三水铝石-蒙脱石（质量比为1:1）两种代表性土壤矿物复合体为吸附材料，采用吸附平衡实验、能谱分析（(EDS）、红外光谱、扫描电镜、酸碱滴定和zeta电位测定等方法，研究了铁铝氧化物与层状硅酸盐矿物之间的相互作用对Cr(Ⅵ)和As(Ⅴ)吸附的影响及其机制。吸附平衡实验和EDS实验结果表明，两种复合体对Cr(Ⅵ)和As(Ⅴ)的吸附容量均小于其两种组成矿物单一体系吸附量的平均值，即铁铝氧化物与蒙脱石的互作降低了这些氧化物对Cr(Ⅵ)和As(Ⅴ)的吸附能力。表面性质表征结果表明，与蒙脱石复合后，针铁矿与三水铝石表面的正电荷均被完全中和，电荷符号发生反转。与理论值相比，三水铝石-蒙脱石复合体的表面位点总浓度无明显变化，比表面积减小。针铁矿-蒙脱石复合体的比表面积与理论值无明显差异，但矿物表面位点浓度减小，表面羟基红外吸收峰强度减弱。氧化物与层状硅酸盐矿物互作改变了矿物表面性质，这可能是导致氧化物对Cr(Ⅵ)和As(Ⅴ)的吸附能力降低的主要原因。当评估污染元素在土壤中有效性时应当考虑土壤固相组分间的互作对离子吸附的影响。     

ADSORPTION ON HYDROUS OXIDES. III. FULVIC ACID AND HUMIC ACID ON GOETHITE, GIBBSITE AND IMOGOLITE

Adsorption isotherms were obtained for fulvic and humic acids on synthetic gibbsite and goethite and on a natural imogolite. The results were interpreted with the help of spectra of the adsorption complexes, and measurements of hydroxyl displaced. The mechanism of adsorption involved ligand exchange with the surface hydroxyl groups and hydrogen bonding. The hydroxyl groups displaced included singly coordinated species on the (100) face of goethite and on the edge faces of gibbsite. The doubly coordinated hydroxyl groups on the (001) face of gibbsite were not replaced, and this face adsorbed only un-ionized fulvic acid probably by a hydrogen bonding mechanism. Imogolite adsorbed most fulvic acid because of its high porosity. Only isolated places on its surface reacted with fulvic acid to form carboxylate groups.     

Adsorption Kinetics of Pb2+ and Cu2+ on Variable Charge Soils and Minerals: Ⅲ. Adsorption Kinetics of Pb2+ Within 30 Minutes

The adsorption kinetics of Pb2+ on different soils and minerals with variable charges was studied by the two ion-selective electrode technique at different pH and concentrations. The results showed that more than 95% of adsorption on all the samples occurred during the first 5 minutes. All adsorption time-dependent data could fit the surface second-order equation very well. The values of Xm were goethite > kaolinite, and latosol > red soil at the same initial reaction concentration. The values of k were kaolinite > > goethite, and latosol > red soil at the same reaction pH and initial concentration.     

Beta-thujaplicin: new quantitative CZE method and adsorption to goethite

Beta-thujaplicin (beta-TH) is a toxic tropolone derivative present in the heartwood of western red cedar (Thuja plicata) and is used as a preservative and antimicrobial additive in a number of commercial goods. beta-TH released from western red cedar timber used outdoor and from other products containing beta-TH may transfer to soil and leach to groundwater and surface waters. The objective of this study was to quantify the adsorption of beta-TH to goethite as a typical model for geosorbents. Adsorption was studied using pH-adjusted goethite suspensions with solid:solution ratios of 1:500, 0.01 M NaNO(3) electrolyte, and 20 degrees C. beta-TH was determined using a new capillary zone electrophoresis (CZE) method providing a detection limit of 0.21 microM. Near-sorption equilibrium was attained within 48 h. beta-TH showed maximum adsorption at low pH (3.8) and a 70% drop in adsorption from pH 6.2 to 8.8. The Langmuir type adsorption isotherm at pH 5.5 approached a maximum adsorption of 220 micromol/g (= 6.2 micromol/m(2)), which is more than twice the amount of phosphate adsorbed under similar conditions. The affinity of beta-TH for goethite is low as compared with organic ligands such as citrate, oxalate, and 2,4-dihydroxybenzoate. The adsorption data and FTIR analyses indicate that beta-TH is most likely adsorbed as monodentate mononuclear surface complexes at the surface of goethite. Hydrophobic adsorption is thought to contribute to the adsorption, in particular at low pH. The strong adsorption of beta-TH to goethite suggests low mobility in most soil environments, the risk of contamination increasing in soils with high pH (calcareous material), low contents of iron and aluminum oxides, phyllosilicates, and organic matter.     

Comparison of phosphate adsorption on clay minerals for soilless root media

Abstract

The greenhouse industry aims to decrease phosphate discharge to help reduce eutrophication of surface waters, to reduce fertilizer consumption, and to maintain a more constant level of plant‐available phosphate. Iron and aluminum oxides and some aluminosilicate minerals are efficient sorbents for phosphate. The phosphate adsorption characteristics of synthetic hematite (α‐Fe₂O₃), goethite (α‐FeOOH), and allophane (Si₃Al₄O₁₂ nH₂O), and a commercial alumina (A1₂O₃) were evaluated to determine their potential for reducing phosphate leaching from soilless root media. The pH dependence of phosphate adsorption and maximum adsorption capacities were determined by reacting each mineral with various levels of phosphate between pH 4.0 and 9.0 in a 10 mM potassium chloride (KCl) background solution. Adsorbed phosphate was determined by loss from solution. Adsorption envelopes (adsorbed phosphate versus pH) showed a decrease in phosphate adsorption with increasing pH, particularly for alumina and allophane, and at greater added phosphate concentrations. The maximum adsorption capacities per unit mass of the minerals at pH 5.4 decreased in the order allophane > alumina ? goethite > hematite. When expressed on a surface area basis, the order of maximum adsorption capacity remains the same except that alumina exceeded that of goethite. The allophane, goethite, and alumina sorbed enough phosphate that 3 to 9 g of these minerals would retain the amount of phosphate required for a high nutrient element requiring plant such as chrysanthemum.     

ADSORPTION ON HYDROUS OXIDES I. OXALATE AND BENZOATE ON GOETHITE

The adsorption of oxalic acid on synthetic goethite (α-FeOOH) was studied using adsorption isotherms. Infrared spectra were obtained for goethite-oxalate complexes at several points on the isotherms. On a goethite preparation with a phosphate sorption capacity of 200|μmolg^?1 the amounts of oxalate strongly adsorbed varied from near zero at pH 8 to about l00μmolg^?1 at pH 4 and below. At pH 3.4, the first l00μmolg^?1 of oxalic acid added was strongly adsorbed as a binuclear complex (FeOOC–COOFe), replacing two singly-coordinated OH groups by ligand exchange. At higher concentrations a further 200 μrnol g^?1 of oxalic acid formed a monodentate complex (FeOOC–COOH) so that more oxalate could be accommodated. Benzoic acid was weakly adsorbed on goethite with one benzoate oxygen replacing one singly-coordinated OH. The other oxygen of the COO group fitted into the goethite surface so that the benzene ring was at a high angle to the (100) face.