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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: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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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, Jackson Nkoh Nkoh, Jiuyu Li, Jun Jiang, 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: Yuanchun Yu, Haoye Tang, Wei Qian, Ruhai Wang, Jun Jiang, 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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enhancing phosphorus availability in two Variable Charge Soils by the amendments of crop straw biochars
Arabian Journal of Geosciences, 2020Co-Authors: Muhammad Kamran, Jackson Nkoh Nkoh, Jun JiangAbstract:More recent works implied that biochar enhanced P availability in Variable Charge Soils. However, the involved mechanisms have not been clearly defined. In the present study, we evaluated the effects of peanut and rice straw biochars on improving P availability (Olsen-P) in an Oxisol and an Ultisol. Incubation experiments, with different amendments including peanut straw biochar (PC), rice straw biochar (RC), acid-washed peanut straw biochar (APC), acid-washed rice straw biochar (ARC), and Ca(OH)2, were performed. After 56-day incubation without and with 50 mg P kg–1 loading, Olsen-P, pH, electrical conductivity (EC), and exchangeable acidity in the amended Soils were analyzed. Results showed that PC greatly increased soil pH, EC, cation exchange capacity (CEC), and Olsen-P and decreased exchangeable acidity in biochar-amended Soils followed by RC when compared with the control and other treatments. However, APC, ARC, and Ca(OH)2 application did not increase P availability greatly. The results manifested that an adequate amount of functional groups together with high alkalinity in PC and RC was responsible for the increase in Olsen-P in both Soils. Thus, application of biochar with higher functional groups and alkali mutually inhibited P adsorption and increased its availability in Variable Charge Soils. The increase in soil pH enhanced the dissociation of acidic functional groups on the biochars and thus increased the ability of these anionic functional groups to compete for adsorption sites on the Soils with phosphate and decreased phosphate adsorption by the Soils, which was the main mechanism for the increase in Olsen-P content in the Soils induced by the biochars.
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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: Jackson Nkoh Nkoh, Jun Jiang, Jing Yan, Muhammad KamranAbstract:Abstract 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
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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, Jackson Nkoh Nkoh, Jiuyu Li, Jun Jiang, 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: Yuanchun Yu, Haoye Tang, Wei Qian, Ruhai Wang, Jun Jiang, 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).
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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The mechanism of chromate sorption by three Variable Charge Soils.
Chemosphere, 2008Co-Authors: Jun Jiang, Yong Wang, Anzhen ZhaoAbstract: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 zeta 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 zeta 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 arsenate on adsorption of cd ii by two Variable Charge Soils
Chemosphere, 2007Co-Authors: Jing Liang, Anzhen Zhao, Yong Wang, Xin Jiang, Wenfeng TanAbstract:The effect of arsenate on Cd(II) adsorption in two Variable Charge Soils and the desorption of Cd(II) pre-adsorbed in the presence of arsenate were studied. The batch type experiments showed, the presence of arsenate led to increase in Cd(II) adsorption and the desorption of pre-adsorbed Cd(II). Further it was observed that the extent of adsorption and desorption of Cd(II) was greatly influenced by the initial concentrations of arsenate and Cd(II), the solution pH, and the nature of the Soils. In general the increase in arsenate concentration and pH favored the uptake of Cd(II). Moreover, the arsenate concentration influenced more in Hyper-Rhodic Ferralsol than Rhodic Ferralsol at least for the Cd(II) adsorption/desorption. This may be due to the content of Fe/Al oxides in these Soils. The larger the content of Fe/Al oxides, the more the adsorption of arsenate by the soil, hence greater the uptake of Cd(II). It can be assumed that the enhanced Cd(II) adsorption was mainly due to the increase in net negative surface Charge of the soil induced by the adsorption of arsenate, because the presence of arsenate led to the decrease in zeta potential of these soil suspensions. The increase of electrostatically adsorbed Cd(II) was responsible for the increase in the desorption of Cd(II) pre-adsorbed in the presence of arsenate.
Jackson Nkoh Nkoh - One of the best experts on this subject based on the ideXlab platform.
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enhancing phosphorus availability in two Variable Charge Soils by the amendments of crop straw biochars
Arabian Journal of Geosciences, 2020Co-Authors: Muhammad Kamran, Jackson Nkoh Nkoh, Jun JiangAbstract:More recent works implied that biochar enhanced P availability in Variable Charge Soils. However, the involved mechanisms have not been clearly defined. In the present study, we evaluated the effects of peanut and rice straw biochars on improving P availability (Olsen-P) in an Oxisol and an Ultisol. Incubation experiments, with different amendments including peanut straw biochar (PC), rice straw biochar (RC), acid-washed peanut straw biochar (APC), acid-washed rice straw biochar (ARC), and Ca(OH)2, were performed. After 56-day incubation without and with 50 mg P kg–1 loading, Olsen-P, pH, electrical conductivity (EC), and exchangeable acidity in the amended Soils were analyzed. Results showed that PC greatly increased soil pH, EC, cation exchange capacity (CEC), and Olsen-P and decreased exchangeable acidity in biochar-amended Soils followed by RC when compared with the control and other treatments. However, APC, ARC, and Ca(OH)2 application did not increase P availability greatly. The results manifested that an adequate amount of functional groups together with high alkalinity in PC and RC was responsible for the increase in Olsen-P in both Soils. Thus, application of biochar with higher functional groups and alkali mutually inhibited P adsorption and increased its availability in Variable Charge Soils. The increase in soil pH enhanced the dissociation of acidic functional groups on the biochars and thus increased the ability of these anionic functional groups to compete for adsorption sites on the Soils with phosphate and decreased phosphate adsorption by the Soils, which was the main mechanism for the increase in Olsen-P content in the Soils induced by the biochars.
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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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mechanism of cu ii and cd ii immobilization by extracellular polymeric substances escherichia coli on Variable Charge Soils
Environmental Pollution, 2019Co-Authors: Jackson Nkoh Nkoh, Jun Jiang, Jing Yan, Muhammad KamranAbstract:Abstract 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
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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, Jackson Nkoh Nkoh, Jiuyu Li, Jun Jiang, 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.
Ruhai Wang - One of the best experts on this subject based on the ideXlab platform.
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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: Yuanchun Yu, Haoye Tang, Wei Qian, Ruhai Wang, Jun Jiang, 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 of cd ii by two Variable Charge Soils in the presence of pectin
Environmental Science and Pollution Research, 2016Co-Authors: Ren-kou Xu, Minhua Zhao, Wei Qian, Ruhai Wang, Yuanchun YuAbstract:Batch experiments were conducted to investigate cadmium(II) (Cd(II)) adsorption by two Variable-Charge Soils (an Oxisol and an Ultisol) as influenced by the presence of pectin. When pectin dosage was less than 30 g kg−1, the increase in Cd(II) adsorption with the increasing dose of pectin was greater than that when the pectin dosage was >30 g kg−1. Although both Langmuir and Freundlich equations fitted the adsorption isotherms of Cd(II) and electrostatic adsorption data of Cd(II) by the two Soils well, the Langmuir equation showed a better fit. The increase in the maximum total adsorption of Cd(II) induced by pectin was almost equal in both the Soils, whereas the increase in the maximum electrostatic adsorption of Cd(II) was greater in the Oxisol than in the Ultisol because the former contained greater amounts of free Fe/Al oxides than the latter, which, in turn, led to a greater increase in the negative Charge on the Oxisol. Therefore, the presence of pectin induced the increase in Cd(II) adsorption by the Variable-Charge Soils mainly through the electrostatic mechanism. Pectin increased the adsorption of Cd(II) by the Variable-Charge Soils and thus decreased the activity and mobility of Cd(II) in these Soils.
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effect of pectin on adsorption of cu ii by two Variable Charge Soils from southern china
Environmental Science and Pollution Research, 2015Co-Authors: Wei Qian, Yuanchun Yu, Ruhai Wang, Ren-kou XuAbstract:The influence of pectin on Cu(II) adsorption by two Variable-Charge Soils (an Oxisol and an Ultisol) was investigated. Pectin increased the adsorption, and the extent of adsorption increased linearly with the dose of pectin, being greater in the Oxisol than that in the Ultisol because the adsorption of pectin by the Oxisol was greater. Both Langmuir and Freundlich equations fitted the adsorption isotherms of Cu(II) for both Soils well. The fitting parameters of both equations indicated that pectin increased not only the adsorption capacity of the Soils for Cu(II) but also the adsorption strength of Cu(II). The effect of pectin decreased with rising pH in the pH range 3.5–6.0, although the extent of electrostatic adsorption of Cu(II) by both Soils was markedly greater over the pH range. Fourier-transformed infrared spectroscopy analysis and zeta potential measurement of soil colloids indicated that adsorption of pectin by the Soils made the negative Charge on both Soils more negative, which was responsible for the increase in the electrostatic adsorption of Cu(II) induced by the addition of pectin. In conclusion, pectin-enhanced adsorption of Cu(II) especially at low pH would be beneficial to the Soils as it would decrease the activity and mobility of Cu(II) in acidic Variable-Charge Soils.
