The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Ren-kou Xu - One of the best experts on this subject based on the ideXlab platform.
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the mechanism for inhibiting acidification of Variable Charge soils by adhered pseudomonas fluorescens
Environmental Pollution, 2020Co-Authors: Ren-kou Xu, Jackson Nkoh Nkoh, Zhi-neng HongAbstract:Abstract Acidification in Variable Charge soils is on the rise due to increased acid deposition and use of nitrogenous fertilizers. The associated low pH and cation exchange capacity make the soils prone to depleted base cations and increased levels of Al3+. Consequently, Al toxicity to plants and soil infertility decrease crop yield. This study was designed to investigate the effect of Pseudomonas fluorescens on the acidification of two Ultisols. The simulated acidification experiment demonstrated that the pH of bacteria-treated soil was higher than that of control under similar conditions, suggesting that the adhered bacteria inhibited soil acidification. This observation was attributed to the association of organic anions (RCOO− or RO−) on bacteria with H+ to form neutral molecules (RCOOH or ROH) and reducing the activity of H+ in solution. The bacteria also inhibited the increase in soil soluble Al and exchangeable Al during soil acidification. The adhesion of bacteria on the soils increased soil effective cation exchange capacity (ECEC) and exchangeable base cations at each pH compared to control. The release of exchangeable base cations from bacteria-treated soil, and the decrease in soil ECEC and exchangeable base cations with decreasing pH confirmed that protonation of organic anions on adhered bacteria was mainly responsible for the inhibition of soil acidification. The change of zeta potential of the bacteria with pH and the ART-FTIR analysis at various pH provided more evidence for this mechanism. Therefore, the bacteria in Variable Charge soils played an important role in retarding soil acidification.
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The role of extracellular polymeric substances in bacterial adhesion onto Variable Charge soils
Archives of Agronomy and Soil Science, 2019Co-Authors: Nkoh Jackson Nkoh, Zhi-neng Hong, Ren-kou XuAbstract:ABSTRACTWe investigated the role of extracellular polymeric substances (EPS) in the adhesion of Pseudomonas fluorescens, Bacillus subtilis, and Escherichia coli on four Variable Charge soils. Catio...
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the role of extracellular polymeric substances in bacterial adhesion onto Variable Charge soils
Archives of Agronomy and Soil Science, 2019Co-Authors: Nkoh Jackson Nkoh, Zhi-neng Hong, Ren-kou XuAbstract:We investigated the role of extracellular polymeric substances (EPS) in the adhesion of Pseudomonas fluorescens, Bacillus subtilis, and Escherichia coli on four Variable Charge soils. Cation exchan...
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mechanism of cu ii and cd ii immobilization by extracellular polymeric substances escherichia coli on Variable Charge soils
Environmental Pollution, 2019Co-Authors: Ren-kou Xu, Jun Jiang, Jiuyu Li, Jackson Nkoh Nkoh, Muhammad Aqeel KamranAbstract:: Extracellular polymeric substances (EPS) found in soils can reduce the mobility of heavy metals through the use of both electrostatic and non-electrostatic mechanisms. Their effects vary from one soil type to another. The influence of EPS from Escherichia coli on the adsorption behaviors of Cu(II) and Cd(II) by two bulk Variable Charge soils, Oxisol and Ultisol, was studied at constant and varied pH, and the results were compared to a constant Charge Alfisol. The maximum adsorption capacities of the soils were significantly (P < 0.05) enhanced in the presence of EPS, with Cu(II) adsorption being greater. Interaction of EPS with soils made the soil surface Charge more negative by neutralizing positive Charges and shifting the zeta potentials in a negative direction: from -18.6 to -26.4 mV for Alfisol, +5.1 to -22.2 mV for Oxisol, and +0.3 to -28.0 mV for Ultisol at pH 5.0. The adsorption data fitted both the Freundlich and Langmuir isotherms well. Preadsorbed Cd(II) was more easily desorbed by KNO3 than preadsorbed Cu(II) from both the control and EPS treated soils. The adsorption of both metals was governed by electrostatic and non-electrostatic mechanisms, although more Cu(II) was adsorbed through the non-electrostatic mechanism. The information obtained in this study will improve our understanding of the mechanisms involved in reducing heavy metals mobility in Variable Charge soils and hence, their bioavailability.
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effect of tea polyphenols on copper adsorption and manganese release in two Variable Charge soils
Journal of Geochemical Exploration, 2018Co-Authors: Jun Jiang, Ruhai Wang, Wei Qian, Yuanchun Yu, Haoye Tang, Ren-kou XuAbstract:Abstract Batch experiments were conducted to investigate the effects of tea polyphenols (TPs) on Cu(II) adsorption and Mn2+ released in two Variable-Charge soils (an Oxisol and an Ultisol). The results confirmed that TPs enhanced Cu(II) adsorption onto and the release of Mn2+ from the two soils. The adsorption of TPs decreased the positive Charge of soils or made negatively Charged soil more negative. TPs can enhance Cu(II) adsorption by the two soils through an electrostatic mechanism, but its effects mainly occur through a non-electrostatic mechanism; namely, formation of soil-tea polyphenols-Cu2+ ternary complexes on soil surfaces. Tea polyphenols increased not only the maximum adsorption capacity of the two soils for Cu(II), but also the binding strength of Cu(II) on the soils. The presence of TPs increased the release of Mn2+ from the two soils through reductive dissolution of soil Mn oxides by TPs, and this was more evident in the Oxisol due to greater amount of easily reducible manganese in the soil. The amount of Mn2+ released from the soils increased with decreasing pH, and this was more evident in the presence of TPs. Cu2+ and Mn2+ competed with each other for adsorption sites on the soils, which increased the release of Mn2+ from the soils and decreased the adsorption of Cu(II). Overall, TPs enhanced Cu(II) adsorption by Variable Charge soils and could therefore increase the immobilization of Cu(II) in the soils. However, TPs increased the amount of Mn2+ released from Variable-Charge soils and thus the activity of manganese in the soils.
Jun Jiang - One of the best experts on this subject based on the ideXlab platform.
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mechanism of cu ii and cd ii immobilization by extracellular polymeric substances escherichia coli on Variable Charge soils
Environmental Pollution, 2019Co-Authors: Ren-kou Xu, Jun Jiang, Jiuyu Li, Jackson Nkoh Nkoh, Muhammad Aqeel KamranAbstract:: Extracellular polymeric substances (EPS) found in soils can reduce the mobility of heavy metals through the use of both electrostatic and non-electrostatic mechanisms. Their effects vary from one soil type to another. The influence of EPS from Escherichia coli on the adsorption behaviors of Cu(II) and Cd(II) by two bulk Variable Charge soils, Oxisol and Ultisol, was studied at constant and varied pH, and the results were compared to a constant Charge Alfisol. The maximum adsorption capacities of the soils were significantly (P < 0.05) enhanced in the presence of EPS, with Cu(II) adsorption being greater. Interaction of EPS with soils made the soil surface Charge more negative by neutralizing positive Charges and shifting the zeta potentials in a negative direction: from -18.6 to -26.4 mV for Alfisol, +5.1 to -22.2 mV for Oxisol, and +0.3 to -28.0 mV for Ultisol at pH 5.0. The adsorption data fitted both the Freundlich and Langmuir isotherms well. Preadsorbed Cd(II) was more easily desorbed by KNO3 than preadsorbed Cu(II) from both the control and EPS treated soils. The adsorption of both metals was governed by electrostatic and non-electrostatic mechanisms, although more Cu(II) was adsorbed through the non-electrostatic mechanism. The information obtained in this study will improve our understanding of the mechanisms involved in reducing heavy metals mobility in Variable Charge soils and hence, their bioavailability.
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effect of tea polyphenols on copper adsorption and manganese release in two Variable Charge soils
Journal of Geochemical Exploration, 2018Co-Authors: Jun Jiang, Ruhai Wang, Wei Qian, Yuanchun Yu, Haoye Tang, Ren-kou XuAbstract:Abstract Batch experiments were conducted to investigate the effects of tea polyphenols (TPs) on Cu(II) adsorption and Mn2+ released in two Variable-Charge soils (an Oxisol and an Ultisol). The results confirmed that TPs enhanced Cu(II) adsorption onto and the release of Mn2+ from the two soils. The adsorption of TPs decreased the positive Charge of soils or made negatively Charged soil more negative. TPs can enhance Cu(II) adsorption by the two soils through an electrostatic mechanism, but its effects mainly occur through a non-electrostatic mechanism; namely, formation of soil-tea polyphenols-Cu2+ ternary complexes on soil surfaces. Tea polyphenols increased not only the maximum adsorption capacity of the two soils for Cu(II), but also the binding strength of Cu(II) on the soils. The presence of TPs increased the release of Mn2+ from the two soils through reductive dissolution of soil Mn oxides by TPs, and this was more evident in the Oxisol due to greater amount of easily reducible manganese in the soil. The amount of Mn2+ released from the soils increased with decreasing pH, and this was more evident in the presence of TPs. Cu2+ and Mn2+ competed with each other for adsorption sites on the soils, which increased the release of Mn2+ from the soils and decreased the adsorption of Cu(II). Overall, TPs enhanced Cu(II) adsorption by Variable Charge soils and could therefore increase the immobilization of Cu(II) in the soils. However, TPs increased the amount of Mn2+ released from Variable-Charge soils and thus the activity of manganese in the soils.
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adsorption properties of subtropical and tropical Variable Charge soils implications from climate change and biochar amendment
Advances in Agronomy, 2016Co-Authors: Ren-kou Xu, Nik Qafoku, Eric Van Ranst, Jiuyu Li, Jun JiangAbstract:Abstract This review paper attempts to summarize the progress made in research efforts conducted over the past years to study the surface chemical properties of the tropical and subtropical soils, usually called Variable Charge soils, and the way they response to different management. The paper is composed of an introductory section that provides a brief discussion on the surface chemical properties of these soils, and five other review sections. The focus of the following sections is on the evolution of surface chemical properties during the development of the Variable Charge properties (second section), interactions between oppositely Charged particles and the resulting effects on the soil properties and especially on soil acidity (third section), the surface effects of low molecular weight organic acids sorbed to mineral surfaces and the chemical behavior of aluminum (fourth section), and the crop-straw-derived biochar-induced changes of the surface chemical properties of these soils (fifth section). A discussion on the effect of climate change Variables on the properties of the Variable Charge soils is included at the end of this review paper (sixth section).
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mobilization of phosphate in Variable Charge soils amended with biochars derived from crop straws
Soil & Tillage Research, 2015Co-Authors: Ren-kou Xu, Jun Jiang, Min Yuan, David L BishAbstract:Abstract The content of available phosphorus in Variable-Charge soils is often low due to the strong adsorption of phosphate by the soils. The application of crop straw-derived biochars can change surface chemical properties of Variable-Charge soils, and thus, should affect phosphate adsorption and phosphorus availability in the soils. However, little information is available on the effect of biochars on the mobility and bioavailability of phosphate in Variable-Charge soils. The objectives of this study were to investigate the effect of crop straw-derived biochars incorporated on phosphate adsorption by Variable-Charge soils, and then gain insight into the mechanisms for the effect of biochars on phosphate adsorption. Results showed that crop straw-derived biochars are characterized by large specific surface area, highly negative Charged surface, ample of anionic functional groups, and moderate concentrations of divalent Ca 2+ and Mg 2+ . The incorporation of the biochars increased soil CEC (cation-exchange capacity), thus, increased the repulsion of soil surfaces to phosphate, and subsequently decreased the phosphate adsorption by the soils. The ample anionic functional groups on added biochars competed for the adsorption sites on the Variable-Charge soils with phosphate, and thus, inhibited phosphate adsorption by the soils. The Ca 2+ and Mg 2+ from the biochars formed precipitates with phosphate in the soils and have the potential to increase apparent phosphate adsorption. Rice straw biochar with the higher CEC and the lowest contents of Ca 2+ and Mg 2+ showed the greatest inhibition on the phosphate adsorption, and thus, could likely be the best choice as amendment to mobilize phosphate in the Variable-Charge soils. The phosphate adsorption by both control soil and biochars-amended soils decreased with rising pH. Incorporation of the biochars increased the pH of the amended soils, thereby, further mobilizing phosphate in the soils.
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adsorption of pb ii on Variable Charge soils amended with rice straw derived biochar
Chemosphere, 2012Co-Authors: Tianyu Jiang, Ren-kou Xu, Jun Jiang, Zhuo LiAbstract:Two Ultisols and one Oxisol from tropical regions of southern China were incubated with rice straw biochar to investigate the effect of biochar on their surface Charge and Pb(II) adsorption using batch methods. The incorporation of biochar induced a remarkable increase in soil cation exchange capacity after 30 d of incubation. The incorporation of biochar significantly increased the adsorption of Pb(II) by these Variable Charge soils; the enhancement of adsorption of Pb(II) by these soils increased with the addition level of biochar. Adsorption of Pb(II) involved both electrostatic and non-electrostatic mechanisms; however, biochar mainly increased Pb(II) adsorption through the non-electrostatic mechanism via the formation of surface complexes between Pb
Anzhen Zhao - One of the best experts on this subject based on the ideXlab platform.
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effect of biochars on adsorption of cu ii pb ii and cd ii by three Variable Charge soils from southern china
Environmental Science and Pollution Research, 2013Co-Authors: Ren-kou Xu, Anzhen ZhaoAbstract:The purpose of this study is to compare the relative contribution of different mechanisms to the enhanced adsorption of Cu(II), Pb(II) and Cd(II) by Variable Charge soils due to incorporation of biochars derived from crop straws. The biochars were prepared from the straws of canola and peanut using an oxygen-limited pyrolysis method at 350 °C. The effect of biochars on adsorption and desorption of Cu(II), Pb(II) and Cd(II) by and from three Variable Charge soils from southern China was investigated with batch experiments. Based on the desorption of pre-adsorbed heavy metals, the electrostatic and non-electrostatic adsorptions were separated. EDTA was used to replace the heavy metals complexed with biochars and to evaluate the complexing ability of the biochars with the metals. The incorporation of biochars increased the adsorption of Cu(II), Pb(II) and Cd(II) by the soil; peanut straw char induced a greater increase in the adsorption of the three metals. The increased percentage of Cd(II) adsorption induced by biochars was much greater than that for the adsorption of Cu(II) and Pb(II). Cu(II) adsorption on three Variable Charge soils was enhanced by the two biochars mainly through a non-electrostatic mechanism, while both electrostatic and non-electrostatic mechanisms contributed to the enhanced adsorption of Pb(II) and Cd(II) due to the biochars. Peanut straw char had a greater specific adsorption capacity than canola straw char and thus induced more non-electrostatic adsorption of Cu(II), Pb(II) and Cd(II) by the soils than did the canola straw char. The complexing ability of the biochars with Cu(II) and Pb(II) was much stronger than that with Cd(II) and thus induced more specific adsorption of Cu(II) and Pb(II) by the soils than that of Cd(II). Biochars increased heavy metal adsorption by the Variable Charge soils through electrostatic and non-electrostatic mechanisms, and the relative contribution of the two mechanisms varied with metals and biochars.
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the mechanism of chromate sorption by three Variable Charge soils
Chemosphere, 2008Co-Authors: Jun Jiang, Ren-kou Xu, Yong Wang, Anzhen ZhaoAbstract:Abstract Adsorption of chromate and desorption of the pre-adsorbed chromate were studied using three representative Variable Charge soils from the south of China. The mechanisms of the adsorption were discussed based on the hydroxyl release and the change of ζ potential during the chromate adsorption. The adsorption and desorption of chromate followed the same order: the Hyper-Rhodic Ferralsol > the Rhodic Ferralsol > the Haplic Acrisol. The adsorption and the desorption both increased with elevation of the equilibrium chromate concentration and decreased with increasing of the soil solution pH. The percentage of the specific adsorption of chromate was 54.0–59.4%, 54.3–60.3%, and 43.9–46.2% for the Hyper-Rhodic Ferralsol, the Rhodic Ferralsol, and the Haplic Acrisol, respectively; the percentage of the electrostatic adsorption was 40.0–46.6%, 39.7–45.8%, and 50.8–56.5% for the three soils, respectively. These findings suggest that both the specific adsorption and the electrostatic adsorption contributed to the chromate adsorption by the Variable Charge soils. The hydroxyl release during the chromate adsorption shared the same trend with the adsorption envelopes, and decreased with increasing of pH. This is attributed to the exchange of chromate with the hydroxyl on the soil particle surfaces and the formation of a chemical bond between chromate and the surface. Our results indicate that the adsorption of chromate resulted in a shift of ζ potential-pH curves of the soil colloids to negative values, which suggests that the adsorption increased the negative surface Charge and decreased the surface potential of the soil colloids.
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Effect of arsenate on adsorption of Zn(II) by three Variable Charge soils
Soil Research, 2007Co-Authors: Jing Liang, Ren-kou Xu, Diwakar Tiwari, Anzhen ZhaoAbstract:The effect of arsenate on adsorption of Zn(II) in 3 Variable Charge soils (Hyper-Rhodic Ferralsol, Rhodic Ferralsol, and Haplic Acrisol) and the desorption of pre-adsorbed Zn(II) in the presence of arsenate were investigated in this study. Results showed that the presence of arsenate led to an increase in both the adsorption and desorption of Zn(II) in these Variable Charge soils. It was also suggested that the enhanced Zn(II) adsorption by arsenate was mainly due to the increase in negative surface Charge of the soils induced by the specific adsorption of arsenate, and the increase in electrostatically adsorbed Zn(II) was responsible for the increase in the desorption of Zn(II). The effect of arsenate on Zn(II) adsorption primarily depends on the initial concentration of arsenate and Zn(II), the system pH, and the nature of soils. The enhanced adsorption of Zn(II) increased with the increase in the initial concentration of arsenate and the amount of arsenate adsorbed by the soils. The presence of arsenate decreased the zeta potential of soil suspensions and soil IEP and thus shifted the adsorption edge of Zn(II) to a lower pH region. The effect of arsenate on Zn(II) adsorption in these 3 soils followed the order Hyper-Rhodic Ferralsol > Rhodic Ferralsol > Haplic Acrisol, which was consistent to the contents of iron oxides in these soils and the amount of arsenate adsorbed by the soils.
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Effect of Low Molecular Weight Organic Anions on Adsorption of Potassium by Variable Charge Soils
Communications in Soil Science and Plant Analysis, 2005Co-Authors: Ren-kou Xu, Anzhen Zhao, Guoliang JiAbstract:Abstract Low‐molecular‐weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four LMW organic acids on the adsorption of potassium (K) by two Variable Charge soils was investigated. The results showed that the presence of organic anions led to an increase in K adsorption. The ability of organic anions to induce K adsorption followed the order: citrate>malate>malonate≈oxalate>acetate. The adsorption of K induced by organic anions increased with the increases in pH and the concentration of the anions. Both Langmuir and Freundlish equations can be used to describe the adsorption of K by Variable Charge soils in the presence of organic anions. Adsorption of ions is a direct consequence of carrying of surface Charge for soils. Recent works have shown that the presence of organic anions led to an increase in negative surface Charge and a decrease in positive surface Charge of Variable Charge soils. The results indicate...
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effect of low molecular weight organic anions on surface Charge of Variable Charge soils
Journal of Colloid and Interface Science, 2003Co-Authors: Ren-kou Xu, Anzhen Zhao, Guoliang JiAbstract:Abstract Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four low-molecular-weight organic acids on the surface Charge of three Variable Charge soils was investigated. The results showed that the presence of organic anions led to an increase in negative Charge and a decrease in positive Charge. Positive Charges decreased to a larger extent than negative Charges. The effect of different anions on surface Charge followed the order citrate > malate > oxalate > acetate. For hyper-rhodic ferrasol and rhodic ferrasol, the change of positive Charge decreased with the increase in pH, while that of negative Charge increased with the increase in pH. Among different soils the extent of change in surface Charge was related to their iron oxides content. When free iron oxides were removed from the soil, the effect of organic anions on surface Charge decreased sharply. These findings may be of practical significance for Variable Charge soils low in nutrient-retaining capacity by increasing the retaining capacity for cations such as potassium and calcium considerably but decreasing that for anions such as nitrate remarkably.
Ole K. Borggaard - One of the best experts on this subject based on the ideXlab platform.
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sorption of glyphosate and phosphate by Variable Charge tropical soils from tanzania
Geoderma, 2007Co-Authors: Anne Louise Gimsing, C. Szilas, Ole K. BorggaardAbstract:Abstract Sorption of glyphosate and phosphate by four contrasting soils from Tanzania, an Andisol (Sasanda), two Oxisols (Lubonde, Mlingano) and an Ultisol (Nkundi), with Variable-Charge clay minerals was studied by batch sorption experiments, during which glyphosate and phosphate were added separately as well as together (competitive sorption). Agreement was found between glyphosate and phosphate sorption and between sorbed glyphosate/phosphate and contents of aluminium and iron extractable by oxalate and dithionite-citrate-bicarbonate (oxides and allophane/imogolite). The Langmuir sorption maxima of glyphosate ranged from 15.5 mmol kg− 1 (Nkundi) to 126 mmol kg− 1 (Sasanda), while that of phosphate varied from 5.8 mmol kg− 1 (Nkundi) to 78.5 mmol kg− 1 (Sasanda). Nearly double the amount of glyphosate than phosphate was sorbed, indicating dominance of monodentate glyphosate-soil surface complexes, while the prevailing phosphate-soil complexes seem to be bidentate. Therefore, phosphate appears more strongly bonded than glyphosate, which agrees with much higher affinities calculated by the Langmuir equation for phosphate than glyphosate. In the competitive experiments, the order of glyphosate and phosphate addition affected the final sorption but in a complex way. Despite stronger bonding of phosphate than glyphosate, phosphate could only displace small amounts of pre-sorbed glyphosate. In this case, the amounts of sorbed glyphosate and phosphate were nearly additive. In contrast, pre-sorbed phosphate suppressed glyphosate sorption, in particular on the volcanic soil (Sasanda), maybe because sorbed phosphate increases the negative Charge on the soil surface, making it more repellent to the negatively Charged glyphosate molecules. Accordingly, additive as well as competitive sorption can dominate the reaction of Variable-Charge soils with glyphosate and phosphate.
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Sorption of glyphosate and phosphate by Variable-Charge tropical soils from Tanzania
Geoderma, 2007Co-Authors: Anne Louise Gimsing, C. Szilas, Ole K. BorggaardAbstract:Sorption of glyphosate and phosphate by four contrasting soils from Tanzania, an Andisol (Sasanda), two Oxisols (Lubonde, Mlingano) and an Ultisol (Nkundi), with Variable-Charge clay minerals was studied by batch sorption experiments, during which glyphosate and phosphate were added separately as well as together (competitive sorption). Agreement was found between glyphosate and phosphate sorption and between sorbed glyphosate/phosphate and contents of aluminium and iron extractable by oxalate and dithionite-citrate-bicarbonate (oxides and allophane/imogolite). The Langmuir sorption maxima of glyphosate ranged from 15.5 mmol kg- 1 (Nkundi) to 126 mmol kg- 1 (Sasanda), while that of phosphate varied from 5.8 mmol kg- 1 (Nkundi) to 78.5 mmol kg- 1 (Sasanda). Nearly double the amount of glyphosate than phosphate was sorbed, indicating dominance of monodentate glyphosate-soil surface complexes, while the prevailing phosphate-soil complexes seem to be bidentate. Therefore, phosphate appears more strongly bonded than glyphosate, which agrees with much higher affinities calculated by the Langmuir equation for phosphate than glyphosate. In the competitive experiments, the order of glyphosate and phosphate addition affected the final sorption but in a complex way. Despite stronger bonding of phosphate than glyphosate, phosphate could only displace small amounts of pre-sorbed glyphosate. In this case, the amounts of sorbed glyphosate and phosphate were nearly additive. In contrast, pre-sorbed phosphate suppressed glyphosate sorption, in particular on the volcanic soil (Sasanda), maybe because sorbed phosphate increases the negative Charge on the soil surface, making it more repellent to the negatively Charged glyphosate molecules. Accordingly, additive as well as competitive sorption can dominate the reaction of Variable-Charge soils with glyphosate and phosphate. © 2006 Elsevier B.V. All rights reserved.
Guoliang Ji - One of the best experts on this subject based on the ideXlab platform.
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Effects of phthalic and salicylic acids on Cu(II) adsorption by Variable Charge soils
Biology and Fertility of Soils, 2006Co-Authors: Ren-kou Xu, Shuangcheng Xiao, Guoliang JiAbstract:In the present study, the effect of two substituted benzoic acids on Cu(II) adsorption onto two Variable Charge soils was investigated, with the emphasis on the adsorption and desorption equilibrium of Cu(II). Results showed that the presence of organic acids induced an increase in Cu(II) adsorption onto the two soils. The extent of the effect was related to the initial concentrations of Cu(II) and organic acid, the system pH, and the nature of the soils. The effect of organic acids was greater for Oxisol than for Ultisol. Phthalic acid affected Cu(II) adsorption to a greater extent than salicylic acid did. The effect of organic acids varied with pH. The adsorption of Cu(II) induced by organic acids increased with increasing pH and reached a maximum value at approximately pH 4.5, and then decreased. It can be assumed that the main reason for the enhanced adsorption of Cu(II) is an increase in the negative surface Charge caused by the specific adsorption of organic anions on soils because the desorption of Cu(II) adsorbed in organic acid systems was greater than that for the control. The desorption of Cu(II) absorbed in both control and organic acid systems also increased with increasing pH; it reached a maximum value at pH ∼5.25 for control and salicylic acid systems and at pH ∼5.1 for a phthalic acid system, then decreased. This interesting phenomenon was caused by the characteristics of the surface Charge of Variable Charge soils.
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Effect of Low Molecular Weight Organic Anions on Adsorption of Potassium by Variable Charge Soils
Communications in Soil Science and Plant Analysis, 2005Co-Authors: Ren-kou Xu, Anzhen Zhao, Guoliang JiAbstract:Abstract Low‐molecular‐weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four LMW organic acids on the adsorption of potassium (K) by two Variable Charge soils was investigated. The results showed that the presence of organic anions led to an increase in K adsorption. The ability of organic anions to induce K adsorption followed the order: citrate>malate>malonate≈oxalate>acetate. The adsorption of K induced by organic anions increased with the increases in pH and the concentration of the anions. Both Langmuir and Freundlish equations can be used to describe the adsorption of K by Variable Charge soils in the presence of organic anions. Adsorption of ions is a direct consequence of carrying of surface Charge for soils. Recent works have shown that the presence of organic anions led to an increase in negative surface Charge and a decrease in positive surface Charge of Variable Charge soils. The results indicate...
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effect of low molecular weight organic anions on electrokinetic properties of Variable Charge soils
Journal of Colloid and Interface Science, 2004Co-Authors: Ren-kou Xu, Chengbao Li, Guoliang JiAbstract:Abstract It is known that some inorganic anions can be adsorbed by Variable-Charge soils specifically, resulting in the lowering of the ζ potential of the clay particle. Reasoning similarly, organic anions should also have such an effect. In this article, the effect of the anions of five low-molecular-weight (LMW) organic acids existing widely in soils on the ζ potentials of two Variable-Charge soils was examined. The results showed that the presence of organic anions led to a decrease in ζ potential. The effect of different anions on ζ potential followed the order oxalate>citrate>malate>maleate>acetate. The effect increased with the increase in anion concentration and decreased with the increase in pH. The extent of the effect on different soils was apparently related to their iron oxide content. The presence of organic anions also led to a decrease in the isoelectric point (IEP) of the soil. The IEPs of two soils in organic anion systems followed the order acetate>maleate>malate>citrate. No IEP was detected for the oxalate system.
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effect of low molecular weight organic anions on surface Charge of Variable Charge soils
Journal of Colloid and Interface Science, 2003Co-Authors: Ren-kou Xu, Anzhen Zhao, Guoliang JiAbstract:Abstract Low-molecular-weight (LMW) organic acids exist widely in soils and have been implicated in many soil processes. In the present paper, the effect of the anions of four low-molecular-weight organic acids on the surface Charge of three Variable Charge soils was investigated. The results showed that the presence of organic anions led to an increase in negative Charge and a decrease in positive Charge. Positive Charges decreased to a larger extent than negative Charges. The effect of different anions on surface Charge followed the order citrate > malate > oxalate > acetate. For hyper-rhodic ferrasol and rhodic ferrasol, the change of positive Charge decreased with the increase in pH, while that of negative Charge increased with the increase in pH. Among different soils the extent of change in surface Charge was related to their iron oxides content. When free iron oxides were removed from the soil, the effect of organic anions on surface Charge decreased sharply. These findings may be of practical significance for Variable Charge soils low in nutrient-retaining capacity by increasing the retaining capacity for cations such as potassium and calcium considerably but decreasing that for anions such as nitrate remarkably.
