Modeling ferricyanide adsorption on goethite: Basics and applications

Ferricyanide, [Fe^III(CN)₆]^3–, is an anthropogenic and potentially toxic contaminant in soil. Its adsorption on goethite has been previously studied, but not evaluated with a surface complexation model (SCM) considering the effects of pH and ionic strength. Therefore, we carried out batch experiments with ferricyanide and goethite suspensions with different ferricyanide concentrations (0.075 mM and 0.15 mM), ionic strengths (0.01 and 0.1 M), and pH (ranging from 4 to 7.4). Adsorption data were then interpreted with the 1‐pK Stern and the charge distribution model assuming monodentate inner‐sphere ferricyanide surface complexes on goethite (lg K = 10.6), which are known from infrared spectroscopy. Furthermore, we applied the SCM to ferricyanide adsorption in previous studies on ferricyanide adsorption in the presence of sulfate and on the solubility of Fe‐cyanide complexes in a suspension of a loess loam. The SCM correctly reflected ferricyanide adsorption in the batch experiments as well as the effects of pH and ionic strength. The SCM also described ferricyanide adsorption in the presence of sulfate, because the ferricyanide adsorption measured and that modeled were significantly correlated (R² = 0.80). Furthermore, we applied the SCM to a study on the solubility of Fe‐cyanide complexes in soil under varying redox conditions so that ferricyanide adsorption on goethite and precipitation of Fe‐cyanide complexes were considered. The actual ferricyanide concentrations were rather reflected when applying the SCM compared to those modeled in an approach in which exclusively precipitation was taken into account. We conclude that ferricyanide adsorption on goethite should be included into geochemical modeling approaches on the mobility of Fe‐cyanide complexes in subsoils.     

Irreversibility of sulfate sorption on goethite and hematite

Sulfate ion adsorption and desorption experiments carried out on synthetic goethite and hematite and natural hematite show adsorption to be a highly irreversible reaction. All oxides showed an increase in sulfate ion adsorption with decrease in pH. Only a small fraction of sorbed sulfate was desorbable after 48 hr, and only at a pH of 3. Extreme irreversibility of sulfate sorption on these common soil minerals suggests that adsorbed sulfate is more immobile in watersheds than previously considered and that recovery models which inherently assume reversibility may need to be modified.     

A Regional Perspective on Present and Future Soil Chemistry at 16 Swedish Forest Sites

Assessing the timescales of recovery, by the use of dynamic models, will be used as input to the policy process to abate acidification. In this study the multilayer dynamic soil chemistry model SAFE was applied to 16 forest sites in Sweden, covering a sulfur deposition gradient of 1.2–11 kg S/ha/yr. Soil samples were collected at all sites and the pH and sulfate concentration dependent isotherm, used for modeling sulfate adsorption in SAFE, was parameterized for every site. A new way of implementing the nutrient uptake distribution in SAFE was developed, which allows the uptake distribution between layers in the rooting zone to vary with time, depending on the availability of base cations in the individual layers. Model output was compared to measurements of base cation concentration, total inorganic Al, pH and Bc/Al both site-by-site and cumulatively for all sites, and the usefulness of these comparisons is discussed from a policy viewpoint. Future projections of recovery show that the overall recovery, expressed as minimum Bc/Al ratio > 1 in the rooting zone, is slow. Assuming full implementation of the UNECE LRTAP Gothenburg Protocol and no further emission reductions thereafter, 44% of the modeled sites still have a Bc/Al ratio below 1 in 2100 in some soil layer within the rooting zone.     

熟污泥改性黄土对镉的吸附解吸特征

使用序批实验方法,研究熟污泥改性黄土对镉(Cd)的吸附解吸特征。结果表明:Cd初始添加浓度大于20 mg/L,供试改性黄土对Cd的吸附等温线发生显著变化;Freundlich型吸附等温式是描述供试改性黄土对Cd吸附过程的最佳模型。各土样对Cd的解吸量与吸附量的关系可以用幂函数很好地描述。随着土样中熟污泥含量的增加,Cd的吸附固定作用增强。有机质成分是影响供试土样Cd固定能力最大的因素。     

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

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

Zinc Adsorption by Mineral Soils of Finland

Abstract

Zinc adsorption by 10 (pH 4.0–6.5) cultivated mineral soils from Finland was studied in batch experiments. Additions of Zn ranged up to 600 mg kg^?1 of soil and the corresponding equilibrium concentrations were 0.1–13 mg 1^?1. In each soil, Zn adsorption conformed to the Freundlich isotherm. Despite a relatively low initial Zn adsorption by the acidic soils, each of the soils proved to have a high potential to adsorb Zn, but the capacity was highly pH dependent. In addition to the conventional Freundlich adsorption isotherms, calculated separately for each soil, extended Freundlich-type isotherms that also incorporate soil pH and other soil characteristics were used to describe Zn adsorption of several soils simultaneously in one equation. The pH-dependent Freundlich adsorption isotherm proved to serve as a practical tool to assess Zn adsorption by soils varying in pH and other characteristics.     

汞在泥炭上的吸附特征研究

采用批次法研究了汞在三江平原泥炭、吉林双阳泥炭上等温吸附特征及介质pH值、背景离子浓度的影响。实验结果表明:两种泥炭吸附等温线均同时符合Langmuir和Freundlich等温吸附方程,而与Langmuir方程的拟合效果更好; 在溶液汞浓度相同时,温度升高,泥炭对汞的吸附量降低;在相同的条件下,三江平原泥炭对汞的吸附量大于吉林双阳泥炭对汞的吸附量;两种泥炭对汞的吸附量受pH值的影响明显且都在pH 6.0左右具有最大的吸附量;在酸性条件下,吸附介质的pH值升高利于泥炭对汞的吸附;介质的离子浓度升高,可以使两种泥炭对汞的吸附量迅速降低。     

The adsorption of copper by soil samples from scotland at low equilibrium solution concentrations

At low solution concentrations of copper in the presence of 0.05 M CaCl₂, adsorption isotherms for copper on soil samples were essentially linear. Although no direct correlations were found between isotherm gradients and individual soil properties, the gradients were of the same order of magnitude as predictions based on gradients obtained for some specific soil components. The soil components which appear to be most important in copper adsorption and which were used to obtain the predictions were organic matter and iron and manganese oxides. The amounts of adsorbed copper remaining isotopically exchangeable or extractable with EDTA in the short term increased with the amount of copper adsorbed but the proportions of adsorbed copper estimated by each of these techniques remained constant. Concentrations of copper in solution increased (adsorption decreased) at pH values below 4.5 and above 6.5.     

2,4-D 对铜在乌栅土胶体和红壤胶体上吸附的影响

应用批平衡法研究了农药2,4-D对Cu在乌栅土胶体和红壤胶体上吸附的影响。结果表明,Cu在两种土壤胶体上的吸附等温线均符合Langmuir方程,Cu在乌栅土胶体上的吸附量较其在红壤胶体上的吸附量要高;在pH3.0～6.7范围内,两种土壤胶体对Cu的吸附量均随溶液pH的升高而升高。2,4-D增加了Cu在土壤胶体上的吸附,2,4-D的浓度越高,Cu的吸附量越大,这主要是由于2,4-D的存在显著增加了平衡液的pH,从而增加了土壤胶体表面所带负电荷量。     

砂壤中铜的吸附行为及其影响因素研究

研究了果园附近砂壤中Cu的吸附行为，并探讨了pH值及土壤有机质对吸附的影响。结果表明，供试土壤对Cu的吸附行为可用Freundlieh方程拟合，电性吸附态Cu较易解吸；而专性吸附态Cu较难解吸。动力学实验表明，最初4h内的吸附量占总吸附量的60％以上，8h后达到平衡；而解吸在最初30min内占了近80％，2h后可达平衡。低pH值时，H^＋和Cu发生竞争吸附，可明显抑制土壤对Cu的吸附；随pH值的升高，抑制作用减弱，其logKd与pH呈线性正相关；在中性和偏碱性范围，pH值对土壤吸附Cu的影响不大。原土去除有机质后对Cu的分配系数降低了10倍。     

水稻秸秆生物质炭对土壤磷吸附影响的研究

本文以水稻秸秆为原料,分析了不同热解温度下生物炭的性质,并利用批处理实验,分析了生物炭添加量和热解温度对土壤磷吸附特性的影响。结果表明：随着热解温度的升高,生物炭的碳化程度、比表面积和磷含量增加。生物炭添加显著减少了土壤对磷的吸附量,而且随着生物炭热解温度的增加,土壤对磷的吸附量显著增加。Langmuir方程和Freundlich方程都能够较好地拟合生物炭对土壤磷的等温吸附。准一级动力学方程和准二级动力学方程可较好地描述生物炭对土壤磷吸附动力学的行为。通过以上研究结果可知,水稻秸秆生物炭可以减少土壤对磷的吸附并增加土壤有效磷的含量,因此在土壤改良方面具有一定的应用潜力。     

Selective Adsorption of Silver Ions from Highly Acidic Aqueous Solutions by Polymers Containing Multiple Sulfur Groups

A polymer (PDMTD) containing multiple sulfur groups is prepared and used for selective adsorption of silver ion from aqueous solution. The batch adsorption experiments are conducted to research the effects of the different parameters on adsorption of silver ion, including pH, adsorption time, and initial Ag(I) concentration. The maximum uptake of Ag(I) is 127.89 mg/g at pH?=?1. The adsorption equilibrium data are fitted with different isotherm and kinetics models. The results show that the adsorption process of Ag(I) follows a pseudo-second-order kinetic model and Langmuir isotherm mode. Chelation interaction between Ag(I) and sulfur and nitrogen atom is the main adsorption mechanism. PDMTD shows the good selectivity from the coexisting ions and can be reused at least five times. The polymers containing multiple sulfur groups have wide application prospect to selectively capture silver ions from highly acidic aqueous solutions.     

某极度酸化的酸性硫酸盐土壤中可溶性和交换性酸的特征

An extremely acidified acid sulfate soil(ASS) was investigated to characterise its soluble and exchangeable acidity,The results showed that soluble acidity of a sample dtermined by titration with a KOH soulution was much significantly greater than that indicated by pH measured using a pH meter,paricularly for the extremely acidic soil samples,This is because the total soluble acidity of the extremely acidic soil samples was mainly composed of various soluble Al and Fe species,possibly in forms of Al sulfate complexes(e.g.,AlSO4^ ) and feerous Fe(Fe^2 )_,It is therefore suggested not to use pH alone as an indicator of soluble acidity in ASS,particularly for extremely acidic ASS,It is also likely that AlSO4^ actively participated in cation exchange reactions.It appears that the possible involvement of this Al sulfate cation in the cation adsorption has significant effect on increasing the amount of acidity being adsorbed by the soils.     

Removal of Zn2+ from Aqueous Solution using Castor Seed Hull

The effects of various experimental parameters on adsorption of Zn²⁺ metal ion from its aqueous solution by castor seed hull and also by activated carbon have been investigated using batch adsorption experiments. It has been found that the amount of zinc adsorbed per unit mass of the hull increases with the initial metal ion concentration, contact time, solution pH and with the amount of the adsorbent. Kinetic experiments clearly indicate that adsorption of zinc on both castor hull and activated carbon is a three-step process??a rapid adsorption of the metal ion, a transition phase, and an almost flat plateau. This has also been confirmed by the intraparticle diffusion model. It has also been found that the zinc adsorption process followed pseudo-second order kinetics. The kinetic parameters including rate constants have been determined at different initial metal ion concentration, pH, amount, and type of adsorbent, respectively. The Langmuir and Freundlich adsorption isotherm models have been used to interpret the equilibrium adsorption data. The Langmuir model yields better correlation coefficients. The monolayer adsorption capacities (q _m ) of castor hull and activated carbon have been compared with those for others reported in the literature. The value of separation factor (R _L ) derived from the Langmuir model gives an indication of favorable adsorption. Finally, from comparative studies, it has been found that castor hull is a potentially attractive adsorbent as compared to commercial activated carbon for the removal of zinc from aqueus effluents.     

不同磷浓度处理暗棕壤对Zn2+吸附解吸行为的研究

通过等温吸附试验,研究不同磷含量处理暗棕壤对Zn2+的吸附解吸行为,结果表明:(1)随平衡液中Zn2+浓度的增加,3种处理暗棕壤对Zn2+的吸附作用均表现为:低浓度下(0～100 mg/L),吸附量增加迅速,随着浓度升高(100～150 mg/L),吸附量变缓并渐趋平衡,含磷量高的土壤吸附Zn2+的量较高。(2)Freundlich、Langmuir和Temkin方程均能很好描述Zn2+在3种不同磷含量暗棕壤上的吸附等温线,拟合效果依次为Freundlich>Langmuir>Temkin。经参数计算,较高磷含量有利于提高暗棕壤的最大吸附量和土壤对Zn2+的缓冲容量,而磷含量不同对Zn2+在暗棕壤上的吸附力没有太大影响。(3)3种不同磷含量处理暗棕壤吸附量与解吸量关系图形状相似,呈高度线性相关,均表现为暗棕壤对Zn2+的解吸量随吸附量的增加而增加,磷含量较高土壤有利于Zn2+的固定且不易解吸。     

Contribution of soil components to adsorption of Pepper Mild Mottle Virus by Japanese soils

The Pepper Mild Mottle Virus (PMMoV) is a soil-borne virus that causes the mosaic disease to Capsicum ssp. This virus disease had been controlled by soil fumigation using methyl bromide, but the method was banned in 2005. Therefore, a new management and control technology that replaces methyl bromide is required. In the present study, the adsorption of PMMoV by soils that is considered to be one of the most important factors of the virus inactivation was examined. We used eight soil samples with different types of clay compositions and humus contents for the PMMoV adsorption experiments at three different pH levels (pH 4, 5 and 7). Large amounts of PMMoV particles were adsorbed by the soil samples with a low humus content at the low pH. This was attributed to the increase in the positive charges of the soil samples. On the other hand, low virus adsorptions were observed at the pH levels in the soils with a high organic matter content. There were close negative correlations (P < 0.05) between the PMMoV adsorption by the soils and the humus content of the soil samples. We considered that the inhibitory effect of humus against the virus adsorption is rather important in most soils in Japan.     

Studies on Selective Uptake Behavior of Hg(II) and Pb(II) by Functionalized Poly(Ethylene Terephthalate) Fiber with 4-Vinyl Pyridine/2-Hydroxyethylmethacrylate

The adsorption behavior of 4-vinyl pyridine and 2-hydroxyethylmethacrylate grafted poly(ethylene terephthalate) fiber toward the Hg(II) and Pb(II) ions in aqueous solutions was studied by a batch equilibration technique. The influence of the treatment time was considered as well as the pH of the solution, the initial metal ions concentration, the graft yield, and the temperature. Such parameters as the adsorption kinetics, the adsorption isotherm, and the desorption time were further studied. Maximum adsorption occurred at pH 3 and pH 6 for Hg(II) and Pb(II), respectively. The adsorption kinetics followed the mechanism of the pseudo-second-order equation for heavy metal ions. The adsorption data is a good fit with Freundlich isotherm. Desorption studies indicated that the maximum percent recovery of Hg(II) and Pb(II) was 93.4% and 76.3%, respectively with 1 M HNO₃.     

Effect of pH,Temperature, and the Role of Ionic Strength on the Adsorption of Mercury(II) by Typical Chinese Soils

A series of batch experiments were conducted to assess the effects of pH, temperature, and ionic strength on mercury adsorption by black and red soils. The results showed that the mercury adsorption increased when the temperature increased from 5 to 15 °C for red soil, whereas for black soil, the amount of adsorption was greater at 25 °C than at other temperatures. At the same temperature, the adsorption capacity of the black soil was greater than that of the red soil. The adsorption capacity of mercury by soils was not influenced by initial pH, sodium nitrate (NaNO₃),or sulfate ion (SO₄ ^2–). However, the change of chloride ion (Cl^?) concentrations had a great effect on mercury adsorption. When the concentration was increased from 10^?3to 10^?1mol L^?1, the adsorption capacity of mercury on both soils (especially for the red soil) decreased sharply.     

甲硫嘧磺隆在土壤中的吸附和解吸特性研究

Methiopyrsulfuron is a new low-rate sulfonylurea herbicide for weed control in wheat; however, there is a lack of published information on its behavior in soils. In this study, methiopyrsulfuron adsorption and desorption were measured in seven soils sampled from Heilongjiang, Shandong, Jiangxi, Sichuan, Anhui, and Chongqing provinces of China using a batch equilibrium method. The Freundlich equation was used to described its adsorption and desorption. Adsorption isotherms were nonlinear with the values of Kf-ads, the Freundlich empirical constant indicative of the adsorption capacity, ranging from 0.75 to 2.46, suggesting that little of this herbicide was adsorbed by any of the seven soils. Soil pH and organic matter content (OM) were the main factors influencing adsorption; adsorption was negatively correlated with pH and positively correlated with OM. Methiopyrsulfuron desorption was hysteretic on the soils with high OM content and low pH.     

Adsorption of Cadmium and Zinc onto Micaceous Minerals: Effect of Siderophore Desferrioxamine B

The mobility, bioavailability, and environmental fate of heavy metals in soil are controlled by their adsorption onto soil minerals and solid organic matter. The adsorption is strongly affected by the presence of various low-molecular-weight organic acids. In this study, effect of hydroxamate siderophore desferrioxamine B (DFOB) on cadmium (Cd) and zinc (Zn) adsorption onto two micaceous clay minerals, muscovite and phlogopite, was evaluated in batch experiments. Results showed that the presence of DFOB diminished the adsorption of Cd and Zn onto both minerals, particularly under neutral to alkaline pH conditions. For instance, at pH 8.2, the presence of DFOB caused a decrease in the adsorption of Zn onto phlogopite by nearly 50%. The equilibrium adsorption of Cd and Zn was satisfactorily described using Freundlich isotherm. The adsorption isotherms showed that the affinity of Cd and Zn onto the minerals decreased in the presence of DFOB. For example, at pH 8.0, the presence of siderophore caused a decrease in the Freundlich adsorption isotherm coefficient K_F for Zn adsorption onto muscovite and phlogopite from 4.60 to 0.07 L g^-1 and from 3.56 to 0.36 L g^-1, respectively. These findings confirm the potential influence of siderophore on the fate of Cd and Zn in arid soils containing substantial contributions of micaceous silicate minerals.