Soil Zeta Potential Research Articles

Electrokinetic Forces as an Electrical Measure of Chemical Aging Potential in Granular Materials

The zeta potential of soils is an electric potential in the double-layer interface and is a physical property exhibited by any particle related to electrochemical attractive forces. On the other hand, the chemical aging phenomenon is seen as the chief mechanism of the aging of sands due to the dissolution and precipitation of minerals, resulting in the development of the cementation of particles in granular mediums. The present investigation focuses on determining whether granular materials can generate cementation due to electrokinetic forces, and if the zeta potential could be related as a measure of the potential of chemical aging. X-ray fluorescence and diffraction tests were performed to characterize four representative fractions of one kind of sand, and zeta potential studies were carried out to determine the electrical potential on the mineral surfaces of each one. Zeta potential analysis showed both dependence on the mineralogical content and the variation in the pH of the colloidal solution fluid because the increase in OH- ion concentrations increases the thickness of the diffuse double layer and the electrokinetic forces of attraction. Moreover, the zeta potential showed an increase in the thickness of the diffuse double layer, due to the electrokinetic forces, which can be associated with the development of cohesive forces with a dependence on the mineralogy of sands.

Understanding the cadmium passivation and nitrogen mineralization of aminated lignin in soil

Aminated lignin (AL) was prepared and first applied to remediation of cadmium (Cd) pollution in soil. Meanwhile, the nitrogen mineralization characteristics of AL in soil and its effect on soil physicochemical properties were elucidated by soil incubation experiment. The results showed that the Cd availability was dramatically lowered in soil by adding the AL. The DTPA-extractable Cd content of AL treatments was considerably reduced by 40.7–71.4 %. The soil pH (5.77–7.01) and absolute value of zeta potential (30.7–34.7 mV) enhanced simultaneously as the AL additions increased. The content of soil organic matter (SOM) (99.0–264.0 %) and total nitrogen (95.9–301.3 %) were gradually enhanced due to high C (63.31 %) and N (9.69 %) content in AL. Moreover, AL significantly elevated the content of mineral nitrogen (77.2–142.4 %) and available nitrogen (95.5–301.7 %). The first-order kinetic equation of soil nitrogen mineralization revealed that AL greatly enhanced nitrogen mineralization potential (84.7–143.9 %) and reduced environmental pollution by lowering the loss of soil inorganic nitrogen. AL could effectively reduce the availability of Cd through direct (self-adsorption) and indirect effects (improvement of soil pH, SOM and reduction of soil zeta potential), thereby achieving passivation of Cd in soil. In short, this work will develop a novel approach and technical support for soil heavy metal remediation, which is of great significance for improving the sustainable development of agricultural production.

Attachment of positively and negatively charged submicron polystyrene plastics on nine typical soils

Microplastics (MPs) have attracted increasing concern as emerging contaminants of global importance in recent years. Soil is considered an important sink for MPs. Due to environmental weathering, MP surfaces are often charged, but there are limited studies on the interaction of differentially charged MP with soils. This study constructed Derjaguin−Landau−Verwey−Overbeek (DLVO) potential energy profiles, investigated the interaction mechanism of polystyrene MPs (0.2 µm) with positive (MP+) and negative (MP-) charges on nine typical soils through quantitative analysis of fluorescence intensity. The attachment of MPs to different soils fitted the pseudo-second-order kinetic model well. The attachment isotherm data of MP+ fitted the linear model better, while the MP- data fitted the Langmuir model. The attachment capacity of MPs was significantly correlated with the zeta potential of soils. These results, as well as the fourier transform infrared spectroscopy (FTIR) spectra and scanning electronic microscopy (SEM) images of soils, indicated that electrostatic interactions and physical trapping were the dominant mechanisms for MP attachment to soils. These results showed a strong affinity for MPs attachment on soil and gave insights to predict the transport, fate and ecological effect of different charged MPs in soil.

Effect of sterilization on cadmium immobilization and bacterial community in alkaline soil remediated by mercapto-palygorskite.

Cadmium (Cd) pollution in alkaline soil in some areas of northern China has seriously threatened wheat production and human health. However, there are still few effective amendments for alkaline soil, and the mechanism of amendments with a good immobilization effect remains unclear. In this study, soil sterilization experiments were conducted to investigate the effects of soil microorganisms on the immobilization of a novel amendment-mercapto palygorskite (MPAL) in Cd-contaminated alkaline soils. The results showed that the mercapto on the MPAL surface was not affected by autoclaving. Compared with the control, the available Cd concentration in 0.025% MPAL treatments decreased by 18.80-29.23% after 1d of aging and stabled after 10d of aging. Importantly, the immobilization of MPAL on Cd in sterilized soil was significantly better than that in natural soil due to the changes in Cd fractions. Compared with MPAL-treated natural soil, exchangeable Cd fraction and carbonate-bound Cd fraction in MPAL-treated sterilized soil decreased by 20.79-27.09% and 20.05-26.45%, while Fe/Mn oxide-bound Cd fraction and organic matter-bound Cd fraction increased by 17.77-22.68% and 18.85-27.32%. Phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analysis found that the potential functions of the microbial community in normal and sterilized soil were different significantly. Soil sterilization increased the soil pH and decreased the arylsulfatase activity, but did not change the soil zeta potential and available sulfur. The changes in Cd fractions in MPAL-treated sterilized soil may be related to the reduction in the bacterial community and the changes in function microbial, but not to the soil properties. In addition, MPAL application had little effects on the bacterial community, soil pH value, zeta potential, available sulfur, and arylsulfatase. These results showed that the immobilization of MPAL on Cd in alkaline soil was stable and effective, and was not affected by soil sterilization and soil microorganism reduction.

Domestic wastewater infiltration process in desert sandy soil and its irrigation prospect analysis

Although domestic wastewater and its reclaimed water are alternative water resources in arid region, investigation of their negative effect must be done to prevent environmental pollution. In this paper, a short-term column experiment was conducted to simulate the infiltration process of wastewater in desert soil. Alfalfa was planted and irrigated with fresh water for control (CK), tertiary treated domestic wastewater (TTW), secondary treated domestic wastewater (STW) and raw domestic wastewater untreated (RW). The effect of wastewater application on desert soil, drainage and plant properties was evaluated. Experimental results demonstrated that the tested desert soil has no soil structure, organic matter, nor microbial community while possess high infiltration rate. The use of wastewater significantly improved plant growth, and the biomass of TTW, RW, STW were 5.5, 4.3, 2.9 times of CK. The infiltration rate of water in bare soil was high (high to low: TTW, CK, RW, STW), while plant growth reduced infiltration rate (ca. 40% with TTW and RW). Wastewater irrigation and plant growth decreased soil zeta potential, while increased formation of aggregates and bacterial abundance and diversity in soil. Top soil (0–30 cm) accumulation of nitrogen (N), phosphorus (P), organic matter and E. coli was evidenced and all could go down to deep soil and drainage with constant wastewater use. It was concluded that domestic wastewater had big potential in desert soil vegetation recovering and function restoration. Nevertheless, the N, salt, P and organic matter and E. coli in wastewater could give rise to desert soil and groundwater contamination if improper treatment was used.

Effective remediation of cadmium and zinc co-contaminated soil by electrokinetic-permeable reactive barrier with a pretreatment of complexing agent and microorganism

The combination of electrokinetic-permeable reactive barrier (EK-PRB) is considered as a promising technology for the remediation of heavy metal contaminated soils. In this study, considering the convenient operation and recycling, a new sheet PRB material of sodium alginate/polyvinyl alcohol/attapulgite was prepared and characterized using scanning electron microscopy, X-ray diffraction and fourier transform infrared spectra. Subsequently, the effect of a pretreatment of citric acid (CA) and Shewanella oneidensis (MR-1) on zinc (Zn (Ⅱ)) and cadmium (Cd (Ⅱ)) removal from soils by EK-PRB was investigated. Results showed that Zn (Ⅱ) and Cd (Ⅱ) gradually migrated from anode to cathode in electric field within 8 days’ EK-PRB remediation. The simultaneous addition of CA and MR-1 resulted into the highest electric current, the lowest pH and the more negative soil zeta potential. Correspondingly, the highest removal efficiency of Zn (Ⅱ) and Cd (Ⅱ) also occurred in CA + MR-1 group. The new sheet PRB material effectively captured Zn (Ⅱ) and Cd (Ⅱ) from soils, and the most adsorption occurred in CA + MR-1 group: 1108.36 mg/kg Zn (Ⅱ) and 53.84 mg/kg Cd (Ⅱ) nearby the cathode after 8 days’ remediation. Specifically, for both Zn (Ⅱ) and Cd (Ⅱ), the CA + MR-1 group showed the greatest reduction in exchangeable and carbonate fractions and the highest increase in Fe-Mn oxidation and residual fractions. Overall, with a pretreatment of CA and MR-1, the residual Zn (Ⅱ) and Cd (Ⅱ) in soils were greatly reduced after EK-PRB remediation, due to the migration in the electric filed and the adsorption of the new sheet PRB material.

Enhancement of electrokinetic-bioremediation by ryegrass: Sustainability of electrokinetic effect and improvement of n-hexadecane degradation

Phytoremediation-assisted electrokinetic-bioremediation is a novel technology for soil remediation. We aimed to study the effects of a plant (ryegrass) on electrokinetic-bioremediation in n-hexadecane-contaminated soil. After treatment for 40 days, the n-hexadecane degradation ratio of electrokinetic-bioremediation-ryegrass (EK-Bio-RG) was 4.86% higher than that of electrokinetic-bioremediation (EK-Bio) (p < 0.05), with a maximum constant degradation rate (107.23 ± 4.62 mg kg−1· d−1). Owing to the improved electrical conductivity, 73.28% of the initial current was maintained on the 40th day in EK-Bio-RG, which was 1.62 times that in EK-Bio. Furthermore, ryegrass reduced the soil zeta potential, which indicated the alleviation of the soil electric double layer compression and prevention of the aggregation of small soil colloids into larger ones. The fine colloidal structure was conducive to mass transfer in electrokinetic-bioremediation. An analysis of the microbial community showed that the degradation of n-hexadecane was mainly attributable to gram-positive bacteria, and a new microbial community was gradually constructed in the rhizosphere, which still metabolized n-hexadecane. The results indicated that the sustainability of the electrokinetic effect was improved combined with ryegrass, and the harmonious micro-environment in the rhizosphere was constructed which furtherly optimized the EK-Bio technology to remediate organics-polluted soil.

Impact of organic pollutants on the macro and microstructure responses of Na-bentonite

Bentonite (Bent) is a favorable buffer material for waste containment barriers, although its properties may be affected by the pore fluid chemistry. Hence, this study investigates the role of different organic pollutants including methanol, acetone, acetic acid, and citric acid on the macro and microstructure responses of Na+-Bent. The chemicals at various concentrations (0 to 80% by the volume of distilled water) were separately added to the soil samples which were then subjected to a set of tests. The results indicate that an increase in the concentration of organic permeants by decreasing the dielectric constant (ε) reduces the plasticity index, compressibility and swelling potential of soil; whereas, the permeability increases. Such changes are ascribed to a tighter packing of the clay particles, as clearly confirmed by the SEM micrographs and XRD patterns. The decrease in the absolute value of soil zeta potential also supports the development of coagulated structure in the artificially contaminated samples upon reducing the ε of solution. However, the results reveal that the sensitivity of soil properties to the variations in the ε value is pronounced at the intermediate stages of concentration (i.e. the organic fluid/water ratio<60%) when the ε is higher than 50. In addition, at relatively low concentration, the acidic permeants dramatically alter the soil fabric due to having lower pH, causing remarkable effects on the hydro-mechanical parameters as compared to the other chemicals. Overall, the organic pollutants, depending on their type and concentration, exert negative impact on the barrier performance of Na+-Bent which are not precisely comparable only with reference to the changes in the dielectric constant of pore fluid, and thereby may not be completely explained by the diffuse double layer (DDL) theory.

Zeta potential of soils with surfactants and its relevance to electrokinetic remediation

There are numerous studies on the application of electrokinetic decontamination technique to remediate heavy metal contaminated fine-grained soils. In recent studies, surfactants have been used to increase the efficiency of contaminant removal. However, there is limited data available on how physicochemical parameters such as zeta potential ( ζ) of soils changes in the presence of surfactants. Understanding the ζ potential variations of soils with surfactant addition is important because it controls the direction and magnitude of electro-osmotic permeability, which plays important role on the efficiency of electrokinetic remediation. In this study, ζ potentials of kaolinite, montmorillonite and quartz powder with Li +, Ca +2, Cu +2, Pb +2 and Al +3 in the presence of anionic, cationic and non-ionic surfactants were determined. The results indicate that anionic surfactants produce negative ζ potentials. The other surfactants produce both positive and negative ζ potentials depending on soil type and ion present in the system. The results also indicate that the ζ potential of kaolinite and quartz powder with surfactants showed similar trends; however, the absolute magnitude of the ζ potential of quartz powder is higher than that of kaolinite. The ζ potential of montmorillonite commonly shows a different trend from those of kaolinite and quartz powder. Based on the test results, it is recommended that ζ potential of soils be determined before the electrokinetic decontamination in order to maximize the efficiency of the technique.

Electrical Forces Affecting Soil and Substrate in the Detergency Process—Zeta Potential

Electrokinetic forces are of considerable importance in the mechanism of soil removal and redeposition. One electrokinetic measurement is that of the difference in potential between the immovable layer attached to the surface of a solid phase (soil or substrate) and the movable part of the diffuse layer in the body of the detergent liquid, and is termed zeta potential. Correlations have been obtained which indicate that, in a de tergent system, it is desirable that the zeta potentials of soil particles and substrate become nearly equal to reduce attractive forces tending to cause them to adhere. The effect of surfactants and electrolytes upon the zeta potential of soils and sub strates has been collated, permitting an estimate of the areas in need of further elucida tion. Cited are available correlations between zeta potential and suspension values, critical micelle concentration, and detergency values.