Ion Transport and Permeability in an Allophanic Andisol at Low pH

Allophanic Andisols have a significant pH-dependent charge. The positive charge increases and the negative charge decreases as pH decreases; therefore, anion movement becomes slower and cation movement becomes faster as pH decreases in the soil. At low pH, soil dispersion occurs easily due to electric repulsive force. The permeability of the soil then decreases because of structural changes that occur when dilute HCl or HNO3 is percolated in the soil. However, soil permeability does not decrease when dilute H2SO4 is percolated in the soil. This is because SO4 2- strongly adsorbs on the soil surface at low pH and the soil remains flocculated

Upward Infiltration into Porous Media as Affected by Wettability and Anionic Surfactants

Abstract: The influence of surfactants on water infiltration in soil is not fully understood. The objective of this study was to propose a model for evaluating effects of an anionic surfactant on upward infiltration under saturated conditions in porous materials with highly contrasting wettability. The simplified equation for upward infiltration based on Darcy's law is equivalent to the widely used Washburn equation. We experimentally determined upward infiltration of sodium dodecyl sulfate (SDS) solution (0–700 mol m−3) into 60-cm-long, 2-cm-diameter columns filled with air-dry materials (glass beads, sand, leaf mold, peat moss, or polyethylene particles). In hydrophilic glass beads and sand, the infiltration rate decreased as the SDS concentration increased due to a decrease in solution surface tension (from 72 to 38 mN m−1). The proposed model could describe the infiltration in all materials and at all concentrations when fitting to the initial parts of the curve of infiltration front vs. time. Contact angles were obtained by fitting the model to the measured height of the infiltration front in the saturated range as a function of time. In columns filled with hydrophobic materials, the infiltration rate increased with SDS concentration, corresponding with a decrease in contact angles from >125 to 69° for polyethylene particles and from 102 to 43° for peat moss. In leaf mold, the infiltration rate decreased as the SDS concentration increased, probably due to swelling. The proposed equation was found useful for calculating saturated hydraulic conductivity and contact angles but limited in the case of swelling porous material.Abbreviations: SDS, sodium dodecyl sulfate; CMC, critical micelle concentration

Adsorption of anionic surfactant (sodium dodecyl sulfate) on silica

The adsorption of an anionic surfactant sodium dodecyl sulfate (SDS) on a negatively charged silica was studied to provide a better understanding of surfactant adsorption phenomena in an electrostatic repulsion environment between surfactant and soil. The adsorption experiment was conducted under different electrolyte concentration and pH. Results indicated that adsorption happened with hydrophobic interaction, although electrostatic repulsion was generated between SDS and silica surface. The adsorption amount decreased with decreasing electrolyte concentration and increasing pH due to the increase of electrostatic repulsion. The influence of electric potential near the silica surface on the adsorption was confirmed with the modified Langmuir adsorption equation, 1-pK basic Stern model and zeta potential. Because silica is ubiquitous in soils and the water environment, the adsorption characteristics of an anionic surfactant is important when we consider the fate of an anionic surfactant in the environment. The result is also useful when considering the fate of agricultural chemicals which contain negative charge and hydrophobic sites

Sulfate adsorption on a volcanic ash soil (allophanic Andisol) under low pH conditions

The mechanisms of SO4 adsorption on clays have been investigated by many researchers. However, few researches have focused on the fraction of SO4 that is adsorbed in the diffuse layer to the total adsorbed SO4. We investigated SO4 adsorption in detail on an allophanic Andisol (volcanic ash soil.), especially the fraction of SO4 adsorbed in the diffuse layer to the total adsorbed SO4, conducting experiments under conditions of low pH (pH 3.3 and 4.3) and low ion concentrations (1.0 and 0.1 molc m^[-3]) to avoid a strong negative surface charge of the soil particles. SO4 and NO3 adsorption under their competitive conditions were measured by a batch method using mixtures of HNO3 and H2SO4. Exchangeable SO4 and NO3 were extracted with 1000 molc m^[-3] KCI. Strongly adsorbed SO4 was extracted with 10 molc m^[-3] NaOH after the extraction with 1000 molc m^[-3] KCI. The exchangeable SO4 made up to 72 to 77% of the total adsorbed SO4. These results suggested that both inner-sphere and outer-sphere complexes co-exist in the allophanic Andisol at low pH. SO4 was strongly selective over NO3 under these conditions. We compared adsorbed amounts calculated by the Gouy-Chapman model with the measured values at solution conditions of pH 3.3 and 1.0 molc m^[-3]. The model overestimated NO3 adsorption and underestimated SO4 adsorption. The difference is due to the fact that SO4 adsorption in the Stern layer is neglected. Next, we calculated SO4 adsorbed in the diffuse layer using the Stern-Gouy-Chapman model under the assumption that all the measured NO3 adsorbed was in the diffuse layer. Our results indicated that the SO4 in the diffuse layer made up only less than 6% of the total adsorbed SO4. Most of the adsorbed SO4 is likely to be found in direct contact with the soil surface

Effect of adsorption site potential on adsorption of sodium dodecylbenzenesulfonate in highly humic volcanic ash soil

Sodium dodecylbenzenesulfonate (DBS) is a very useful and widely used anionic surfactant. This surfactant sometimes creates environmental problems when it is released into the water environment. However, the factors influencing the adsorption of DBS in soil have not been studied well. In this study, the influence of the potential at the adsorption site on the adsorption of DBS in a soil was first elucidated using a theoretical adsorption equation. The soil was a highly humic soil with a negative charge. The amount of DBS adsorbed was measured with a batch method for different electrolyte concentrations of sodium chloride (NaCl) at pH 4.5 and 6.5. The adsorption site potential of the soil was obtained with the modified Langmuir adsorption equation. The adsorption of DBS decreased as the electrolyte concentration decreased and as the pH increased because the repulsive electric potential between DBS and the soil increased. These results were confirmed by the obtained adsorption site potential and the measured electrophoretic mobility. The difference between the adsorption of DBS with a linear and with a branched carbon chain was also detected, and this difference was related to the free energy of micellization. Because DBS adsorption is strongly affected by electrolyte concentration and pH, these two factors must be carefully considered to predict the fate of DBS in soil and water environments

Precise estimation of dodecylbenzenesulfonate in aqueous solution containing dissolved organic matter extracted from soil using UV-spectrometry

Precise estimation of sodium dodecylbenzenesulfonate (DBS) is essential for understanding its adsorption in soils, transport, toxicity, fate, and its application in the remediation of contaminated soil and groundwater. DBS can be easily identified by its conjugated double bond systems of benzene rings under the ultraviolet (UV) spectrum of a spectrophotometer. However, benzene group components of dissolved organic matter (DOM) also absorb light in the UV spectrum, and this effect is responsible for the excess quantities of DBS that are falsely measured by spectrophotometers. This study was conducted to propose a method for accurately measuring the DBS concentration of a solution containing DOM. To elucidate the influence of DOM during the UV-spectroscopic measurement of DBS in an aqueous solution, 222.5 nm UV and 400 nm UV-vis spectra were measured. The DOM was extracted from a highly humic non-allophanic volcanic ash (Andosol) soil by using 1 mmol NaCl/L and 100 mmol NaCl/L solutions as the extractants. The absorbances at both 222.5 and 400 nm increased in proportion to the increase in the DOM concentration. The relationship between the absorbances at the two different wavelengths could be expressed as a linear relationship. On the other hand, the absorbance at 400 nm did not increase with the increase in the DBS concentration, whereas the absorbance at 222.5 nm increased with the increase in the DOM concentration. Therefore, we inferred that the influence of DOM on the absorbance value of the DBS-DOM complex solution at 222.5 nm could be eliminated by using the linear relationship between the two different absorbances of the DBS-free DOM solution. This method makes it possible to easily measure the DBS concentration of a solution from soil water, streams or industrial effluents containing DOM, without using reagents. Highlights Dodecylbenzenesulfonate in a solution is overestimated in the presence of dissolved organic matter. Dodecylbenzenesulfonate becomes precisely detectable using 222.5 and 400 nm spectrophotometry. Our proposed method is simple, rapid, efficient, and requires no special reagent or recurring cost. This method can be used for precise DBS estimation in soil water, streams, or industrial effluents

土壌中の溶質移動に及ぼす粗孔隙と荷電の影響に関する研究

京都大学0048新制・論文博士博士(農学)乙第8018号論農博第1795号新制||農||639(附属図書館)学位論文||H4||N2517(農学部図書室)UT51-92-U254(主査)教授 丸山 利輔, 教授 久馬 一剛, 教授 高橋 強学位規則第4条第2項該当Doctor of Agricultural ScienceKyoto UniversityDFA

Influence of high pH state of dodecylbenzenesulfonate and dissolved organic matter complex solution on the ultraviolet spectrometry of dodecylbenzenesulfonate

Dodecylbenzenesulfonate (DBS) is an anionic surfactant that is the most commonly used ingredient in modern cleaning agents. Globally, billions of liters of untreated DBS are released daily into natural water bodies, which may lead to fatal consequences in micro and macro living entities, and destroy the natural ecosystem. Therefore, a simple, precise, rapid, and inexpensive method for measuring DBS is crucial for developing countries. The conventional ultraviolet (UV) spectrophotometric method cannot accurately estimate the DBS concentration in a solution containing a considerable quantity of dissolved organic matter (DOM). Recently, a new spectrometric method was developed using the 222.5 nm UV and 400 nm UV-visible (UV-vis) spectra to precisely estimate DBS concentration in the DBS-DOM complex solution. However, this newly developed method is yet to be validated under higher pH conditions. The accuracy of DBS measurements from the DBS-DOM complex solution under lower pH (5.5 and 6.5) and higher pH (12.5) conditions was compared in this study using the previously developed method. With the higher pH, the influence of the electrolyte increased the absorbance under the 222.5 nm UV spectrum. However, such influence decreased with the increase in DBS and DOM concentration. The UV-vis absorbance at 400 nm decreased under higher pH values when the DOM concentration increased, owing to the conformational change in DOM. Despite the contrasting trends of the absorbances in the two spectra, the studied method was proven to be equally applicable and efficient, even under higher pH conditions

Influence of organic matter on the adsorption of sodium dodecylbenzene sulfonate on volcanic ash soil

Sodium dodecylbenzene sulfonate (DBS), an anionic surfactant, is used as an important content of detergent. Its discharge without treatment causes environmental problem and its adsorptive behavior in soils is not fully understood. In this study, the adsorption behavior of DBS of linear carbon chain on volcanic ash soil was investigated before and after removing most of the organic matter from the soil. The soil used in the experiment is highly humic non- allophanic Andisol soil. Non-allophanic Andisol and DBS have negative charge, which helped to observe the negative-negative soil-surfactant interaction. The adsorption isotherm amount was measured at the electrolyte concentration of 100 mmol L-1 NaCl in order to get the smooth adsorption isotherm and to shorten the diffuse double layer. The adsorption amounts were increased by increasing the concentration of DBS in both soils. The soil having organic matter showed the more adsorption compared to the soil after removing most of the organic matter at different pH conditions. It was also observed that adsorption amount was higher at lower pH. These results indicate that organic matter has increased the adsorption of DBS on volcanic ash soil at all pH condition

Adsorption of Sodium Dodecylbenzene Sulfonate on Highly Humic Non-allophanic Andisol at High-Electrolyte Concentration

To clarify the adsorption characteristics of surfactants, it is important to understand the surfactant behavior in the soil and water environments.However,there are few adsorption studies for highly humic soil. In this study, the adsorption characteristics of dodecylbenzene sulfonates in a highly humic soil were investigated. A non‒allophanic Andisol was used since this soil contains a large amount of humic substances and is only negatively charged. Thus, electrically, only repulsive force is generated between the soil and the surfactant. The adsorption amount was measured using the batch method at an electrolyte concentration of 100 mmol L－1 NaCl in order to shield the electric fi eld near the soil particle surface and emphasize hydrophobic reactions. The adsorption isotherm was examined using the Langmuir‒Freundlich‒Hill equation. The adsorbed amount increased sharply with increasing concentrations in the low‒concentration range. The sharp increase indicated cooperative adsorption caused by hydrophobic interaction among the carbon chains of adsorbing surfactants. The adsorption amount became higher at a lower pH because electrostatic repulsion between the soil and the surfactant decreased. The adsorption of dodecylbenzene sulfonate with a linear carbon chain was larger than that with a branched chain due to the diff erence of the carbon chain structure