Influence of pH and organic substance on the adsorption of As(V) on geologic materials

The adsorption of As(V) on alumina, hematite, kaolin and quartz has been measured as a function of pH (2 to 10), and As concentrations (10^?4 to 10 ^?8 M; in the alumina and kaolin systems only). The effects of sulfate (0 to 80 mg L^?1) and fulvic acid (0 to 25 mg L^?1) were studied. The charge of the solid surface and the As speciation in solution (determined by pH) were the most important chemical parameters affecting the sorption behavior. At pH below PZC of the solid, there was a qualitative correlation between the adsorption and the anion exchange capacity of the solid. For hematite at low pH (below 5) there was a reduction of the adsorption possibly related to the formation of positively charged species. The presence of sulfate or fulvic acid reduced the adsorption.     

The Adsorption of Fluoride Ion from Aqueous Solution by Activated Alumina

The adsorption of fluoride ion in aqueous solution by using alumina was studied in this research. The experimental resultsindicated that the removal efficiency was influenced significantly by solution pH and the optimum operating pH wasfound to be in the range of 5 to 7. For neutral and acidic solutions, the adsorption capacities of fluoride by alumina wasinterfered by the presence of sulfate. The Langmuir and Freundlich isotherms can well describe the equilibrium behaviorsof the adsorption processes. The experimentally determined lowvalues of activation energy indicate nonspecific adsorption isthe predominant mechanism. The surface reaction-limiting batchkinetic model can adequately describe the removal behaviors offluoride ion by alumina adsorption in the batch system.     

The Importance of Including the pH Dependence of Sulfate Adsorption in a Dynamic Soil Chemistry Model

Sulfate adsorption is an important process when modeling the dynamics of recovery from acidification. In the dynamic soil chemistry model SAFE sulfate adsorption is modeled by a pH and sulfate concentration dependent isotherm. This isotherm has been parameterized by fitting it to data from batch experiments on soil samples using multiple linear regression. The soil samples were from the B-horizon from three sites, two from the Lake Gårdsjön area in south-west Sweden and one from southern Poland. The pH dependency of sulfate adsorption is important. The batch experiments show that the adsorbed amount, at a specific sulfate concentration, increases considerably with decreasing pH. This implies that the adsorbed pool of anthropogenic sulfate in soils may remain fairly high during the recovery phase. Although a decrease of sulfate concentration is commonly seen, the modeled pH increase is often slow, and thus delays in the modeled desorption of anthropogenic sulfate can be expected.     

Adsorption of Potassium and Calcium Ions by Variable Charge Soils

Interactions of potassium and calcium ions with four typical variable charge soils in South China were examined by measuring pK-0.5pCa value with a potassium ion-selective electrode and a calcium ion-selective electrode,and pK value with a potassium ion-selective electrode.The results showed that adsorption of potassium and calcium ions increased with soil suspension pH,and the tendency of the pK-0.5pCa value changing with pH differed with respect to pH range and potassium to calcium ratio.Adsorption of equal amount of calcium and potassium ions led to release of an identical number of protons,suggesting similar adsorption characteristics of these two ions when adsorbed by variable charge soils.Compared with red soil,latosol and lateritic red soil had higher adsorption selectivities for calcium ion.The red soil had a greater affinity for potassium ion than that for calcium ion at low concentration,which seems to result from its possession of 2:1 type minerals,such as vermiculite and mica with a high affinity for potassium ion.The results indicated that adsorption of potassium and calcium ions by the variable charge soils was chiefly caused by the electrostatic attraction between the cations and the soil surfaces.Moreover,it was found that sulfate could affect the adsorption by changing soil surface properties and by forming ion-pair.     

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.     

电解质阴离子和pH对可变电荷土壤硫酸盐吸附的影响

The effects of three electrolyte anions, ionic strength and pH on the adsorption of sulfate by two variable charge soils, with different surface charge properties were studied. Under the conditions of the same pH and ionic strength the effect of electrolyte anions on the adsorption of sulfate was in the order of Cl^- > NO₃^- > ClO₄^-, indicating the difference of the nature among these three anions. For Ferralsol in the same concentration of chloride and perchloride solutions, the two sulfate adsorption-pH curves could intersect at certain pH value. When pH was higher than the intersecting point, more sulfate was adsorbed in the perchloride solution, while when it was lower than the intersecting point, more sulfate was adsorbed in the chloride solution. In different concentrations of electrolyte solution, the curves of the amount of oxy-acid anion adsorbed, which changed with pH, could intersect at a certain pH, which is termed point of zero salt effect (PZSE) on adsorption. The nature of electrolyte anions influenced obviously the appearance of PZSE for sulfate adsorption. For ferralsol the curves of adsorption converged to about pH 7 in NaCl solution seemed to intersect in NaNO₃ solution and to have a typical PZSE for sulfate adsorption in NaClO₄ solution. For Acrisol the three curves of adsorption were nearly parallel in NaCl and NaNO₃ solutions and converged to pH 6.5 in NaClO₄ solution.     

Reactions of nucleic acid bases with inorganic soil constituents

The adsorption at pH's 4, 6 and 8 of adenine, guanine, cytosine, thymine and uracil on clays (montmorillonite, illite and kaolinite), Fe- and Al-oxides (goethite, hematite and gibbsite), a soil, and on a laboratory-prepared fulvic acid-montmorillonite complex was investigated. Portions of the clays and soil were saturated with H⁺, Fe³⁺ and Ca²⁺.Quantitatively, the extent of adsorption of nucleic acid bases by the clays was proportional to their exchange capacities, but the nature of the dominant cation had only minor effects. By contrast, the adsorption was strongly affected by pH, tending to decrease with increase in pH. Adsorption on goethite and gibbsite was lower than that on clays, while adsorption of nucleic acid bases on soils was slightly lower than that on oxides. The fulvic acid-montmorillonite complex adsorbed substantial, although smaller amounts of purines and pyrimidines, than did montmorillonite alone. The main adsorption mechanism at pH 4 appeared to be cation exchange whereas at pH 8 complex formation between the nucleic acid bases and cations on inorganic surfaces seemed to occur.The results of this and earlier work show that both inorganic and organic soil constituents adsorb nucleic acid bases. Which adsorption reaction predominates will depend on the clay and organic matter content and on the pH.     

Comparison of phosphate adsorption on clay minerals for soilless root media

Abstract

The greenhouse industry aims to decrease phosphate discharge to help reduce eutrophication of surface waters, to reduce fertilizer consumption, and to maintain a more constant level of plant‐available phosphate. Iron and aluminum oxides and some aluminosilicate minerals are efficient sorbents for phosphate. The phosphate adsorption characteristics of synthetic hematite (α‐Fe₂O₃), goethite (α‐FeOOH), and allophane (Si₃Al₄O₁₂ nH₂O), and a commercial alumina (A1₂O₃) were evaluated to determine their potential for reducing phosphate leaching from soilless root media. The pH dependence of phosphate adsorption and maximum adsorption capacities were determined by reacting each mineral with various levels of phosphate between pH 4.0 and 9.0 in a 10 mM potassium chloride (KCl) background solution. Adsorbed phosphate was determined by loss from solution. Adsorption envelopes (adsorbed phosphate versus pH) showed a decrease in phosphate adsorption with increasing pH, particularly for alumina and allophane, and at greater added phosphate concentrations. The maximum adsorption capacities per unit mass of the minerals at pH 5.4 decreased in the order allophane > alumina ? goethite > hematite. When expressed on a surface area basis, the order of maximum adsorption capacity remains the same except that alumina exceeded that of goethite. The allophane, goethite, and alumina sorbed enough phosphate that 3 to 9 g of these minerals would retain the amount of phosphate required for a high nutrient element requiring plant such as chrysanthemum.     

柠檬酸对三种人工合成氧化铁磷吸附特性的影响

试验采用了3种人工合成的氧化铁为材料,研究了氧化铁对磷的吸附以及柠檬酸对氧化铁磷吸附特性的影响。结果表明:3种人工合成的氧化铁对磷的吸附特性及柠檬酸对氧化铁吸附磷的影响都可用Langumir方程来描述,都达到了极显著水平。从磷的最大吸附量(Sm)、吸附反应常数(K)和最大缓冲容量(MBC)来看,未加入柠檬酸时,水铁矿对磷的吸附在容量和强度方面均为最高;而在加入柠檬酸时,3种人工合成的氧化铁对磷的吸附能力的顺序并无差别,水铁矿和针铁矿的磷Sm和MBC要比赤铁矿大很多。     

Sulfate mobility in an outwash soil in Western Washington

The effect of acidic precipitation on cation leaching in a second-growth Douglas-fir ecosystem at the Thompson Research Center is reviewed. Sulfate mobility and soil pH buffering power were tested by applications of heavy doses of H₂SO₄ to the study plot. Sulfate at high concentrations proved to be immobilized, presumably by adsorption to soil sesquioxide surfaces. Soil sulfate adsorption was determined at varying sulfate concentrations, and two mechanisms of adsorption are implied by the shapes of the isotherms.     

Sulfate and Calcium Movement in an Allophanic Soil—The Relevance of Ion‐Pair Adsorption in the Soil–Plant System

Cooperative adsorption involving anions and cations, termed ion‐pair adsorption (IPA), is reported to increase the retention of some ions in certain soils. Sulfate and calcium can exhibit such interaction, and this affects their movement through the soil. Ion‐pair adsorption is shown here in miscible displacement experiments with a variable‐charge soil. The relevance of IPA under more realistic conditions is further investigated in a pot experiment. Rapeseed (Brassica napus) was grown at two different irrigation regimes and with two sulfur fertilizer sources. Calcium sulfate (CaSO₄·2H₂O) was used to induce IPA in contrast to potassium sulfate (K₂SO₄). The results suggest that IPA reduces sulfate and calcium leaching only in the short term. Continued irrigation dissipates the differences between the two fertilizer sources. Final soil ion concentrations and the plant uptake could not be related to IPA, evidencing the short‐term relevance of IPA. The influence of IPA on the bioavailability of calcium and sulfate to plants still demands further study.     

三种铁氧化物的磷吸附解吸特性以及与磷吸附饱和度的关系

采用三种人工合成铁氧化物(针铁矿、赤铁矿和水铁矿)比较了结晶态和无定形铁氧化物对磷的吸附—解吸特性以及与磷吸附饱和度的关系。结果表明,三种铁氧化物的磷吸附特性均可用Langumir方程来描述,相关系数均大于0.9,达到极显著水平。从磷最大吸附量(Qm)、吸附反应常数(K)和最大缓冲容量(MBC)三项吸附参数综合考虑,水铁矿(无定形)对磷的吸附无论在容量还是强度方面均比结晶态铁氧化物针铁矿和赤铁矿大得多。水铁矿吸附的磷比针铁矿和赤铁矿所吸附的磷更难解吸;水铁矿的大量活性表面并没有表现出增加磷释放的作用。磷吸附饱和度有望作为评价土壤或铁氧化物磷吸附—解吸的强度和容量因子的一个综合指标。     

硫酸根离子添加顺序对可变电荷土壤吸附铜离子的影响

研究了SO2-4添加顺序对三种可变电荷土壤(昆明铁质砖红壤、徐闻砖红壤和江西红壤)吸附Cu2+的影响,作为对照,也研究了其对恒电荷土壤(黄棕壤、棕壤)以及两种不同矿物(高岭石与针铁矿)吸附铜离子的影响。实验结果表明,在同等条件下,SO2-4添加顺序对两类表面性质不同的土壤吸附Cu2+有着不同的影响。对于恒电荷土壤,SO2-4添加顺序对土壤吸附Cu2+几乎没有影响。同等pH条件下,对可变电荷表面而言,加入CuSO4者具有最高的Cu2+吸附率;对昆明砖红壤、徐闻砖红壤以及针铁矿和高岭石而言,先加入Cu2+者相对先加入SO2-4者Cu2+吸附率更高;对江西红壤而言,上述这个次序则刚好相反。SO2-4浓度和有机质去除对同等pH条件下铜离子吸附率高低的排序并无实质性影响。     

Phosphate-induced aggregation kinetics of hematite and goethite nanoparticles

Purpose

The purpose of the present study is to examine the effect of phosphate on the aggregation kinetics of hematite and goethite nanoparticles.

Materials and methods

The dynamic light scattering method was used to study the aggregation kinetics of hematite and goethite nanoparticles.

Results and discussion

Specific adsorption of phosphates could promote aggregation through charge neutralization at low P concentrations, stabilize the nanoparticle suspensions at medium P concentrations, and induce aggregation through charge screening by accompanying cations at high P concentrations. Two critical coagulation concentration (CCC) values were obtained in each system. In NaH₂PO₄, the goethite CCC at low phosphate concentrations was smaller than hematite and vice versa at high phosphate concentrations. Stronger phosphate adsorption by goethite rapidly changed the zeta potential from positive to negative at low phosphate concentrations, and the zeta potential became more negative at high phosphate concentrations. The clusters of hematite nanoparticles induced by phosphate adsorption had an open and looser structure. Solution pH and the phosphate adsorption mechanisms in NaH₂PO₄, KH₂PO₄, and Na₃PO₄ solutions affected zeta potential values and controlled the stability of hematite suspensions during aggregation. High pH and preference for non-protonated inner-sphere complexes in Na₃PO₄ solution decreased the zeta potential of positively charged hematite and promoted aggregation. Activation energies followed the order NaH₂PO₄ > KH₂PO₄ > Na₃PO₄ at low P concentrations. K⁺ was more effective than Na⁺ in promoting hematite aggregation due to the non-classical polarization of cations.

Conclusions

Phosphate can enhance or inhibit the aggregation of hematite and goethite nanoparticles in suspensions by changing surface charge due to specific adsorption onto the particles. The phosphate-induced aggregation of the nanoparticles mainly depended on the initial concentration of phosphate.

     

秸秆碳和硫酸铝对富营养化水体中氮磷的吸收去除效应及其影响因素

为解决中国水体富营养化问题,将秸秆碳与硫酸铝作为一种有效吸附水体中总氮、总磷的吸附剂,通过室内模拟试验,采用平衡吸附法,考察了秸秆碳和硫酸铝投加量、pH值、振荡时间、温度、扰动、秸秆碳粒径等不同环境因素条件下对吸附效果的影响。结果表明:在秸秆碳和硫酸铝投加量为0.2 mg/L、振荡时间为120 min的条件下,吸附效果最好,去除率可达80%以上。通过对各因素与秸秆碳、硫酸铝对总氮和总磷的吸附效果分析得知,加入适量的秸秆碳和硫酸铝,可以降低水体中总氮、总磷的含量,吸附效果对温度、振荡时间、pH值变化敏感,这也为解决水体富营养化问题提供了基础依据。     

铁氧化物-胡敏酸复合物对磷的吸附吸附

本试验通过设置不同磷酸根浓度、 pH和不同电解质及电解质强度梯度,研究磷酸根在针铁矿-胡敏酸（HA）复合物和赤铁矿-胡敏酸（HA）复合物表面的吸附特性。X射线衍射（XRD）、 扫描电镜（SEM）和红外光谱（FTIR）图谱显示: 铁氧化物包覆胡敏酸后其内部结构特性保持不变; 氧化铁与胡敏酸通过氢键形成粒径大、 表面光滑的铁氧化物-HA复合微粒,且复合物比表面减小; 形成的氧化铁-胡敏酸复合物对磷的吸附能力增强,且针铁矿复合物的吸附能力大于赤铁矿复合物,均为多层吸附过程; pH增高抑制铁氧化物复合物对磷的吸附,同时电解质浓度增加促进复合体对磷的吸附,且反应后体系pH随之降低。     

恒电荷土壤及可变电荷土壤与离子间相互作用的研究Ⅲ Cu2+和Zn2+的吸附特征

研究了3种典型可变电荷土壤和4种典型恒电荷土壤在不同pH和不同浓度下单纯及共存体系中Cu2 和Zn2 的吸附及其影响因素。结果表明,两类土壤对Cu2 或Zn2 的吸附量均随平衡浓度增加而增大,符合Langmuir吸附等温式;当Cu2 、Zn2 浓度一定时,pH升高使Cu2 、Zn2 吸附量增大,但当pH >5时,Cu2 、Zn2 吸附量随pH变化甚微,出现一个接近最大吸附量的“平台”。当添加Cu2 、Zn2 浓度相同,但二种离子的总浓度不同时,平衡液的Cu2 /Zn2 浓度比均小于1,说明两类土壤对Cu2 的吸附选择性大于Zn2 ,且这种趋势不因pH和离子浓度而改变。当Cu2 、Zn2 共存时,使可变电荷土壤的Zn2 吸附量减小约70 % ,是恒电荷土壤降低量的约1.5倍;可变电荷土壤吸附一个Cu2 或Zn2 时所释放H 的平均数,明显大于恒电荷土壤者,说明可变电荷土壤对Cu2 及Zn2 的吸附中专性吸附的比例较恒电荷土壤大     

赤铁矿改性生物炭回收水中磷及其作为磷肥的效果

利用生物炭材料的吸附作用回收污水中的磷，作为磷肥应用到土壤进行农业生产是一种简单有效、成本低廉的措施，成为解决环境污染和磷资源紧缺问题的一种潜在方案。该研究采用单因素结合响应面方法优化赤铁矿（H）改性核桃壳生物炭（BC）的制备工艺。通过模型拟合分析了改性生物炭（H-BC）对水中磷（P）的吸附特性，并测试表征探讨其吸附机理。最后，将饱和吸附磷后的改性生物炭（H-BC-P）应用到土壤，采用盆栽试验分析其作为磷肥的效果和潜力。结果表明：核桃壳/赤铁矿质量比为1:1，在850 ℃下热解45 min制得的改性生物炭对磷的去除率达到98.42%，饱和吸附量为15.59 mg/g。H-BC吸附P的过程更符合准二级动力学模型和Freundlich模型，表明该过程是多分子层吸附，化学吸附是限制吸附速率的主要步骤。酸性条件有利于H-BC对P的吸附，从成本角度考虑，H-BC的最佳用量为2.5 g/L。H-BC-P可以改良酸性土壤pH，增加土壤全磷和Olsen-P含量。黄棕壤和红壤中生菜的生物量均有明显增加。研究表明赤铁矿改性生物炭是一种环境友好的磷吸附剂，且吸附磷后的残渣可以作为磷肥应用到土壤。     

Zn Adsorption by Variable Charge Soils in Relation to pH

Zn adsorption by pure oxides or in the presence of a high concentration of inner electrolyte has been extensively studied.But,in studies on Zn adsorption in the complicated soil system,especially in variable charge soils,profound knowledge about the absorption mechanism still lacks.In this paper,taking Zn ion adsorption by two typical variable charge soils as the object of the study,author discusses the relation between Zn adsorption and pH and possible adsorption mechanisms.The results showed that in the low pH range where the amount of Zn adsorbed did not exceed 50% of Zn added,the specific adsorption was the diminant mechanism.The species of Zn specifically adsorbed was free Zn^2 ion.In the middle and high pH ranges,the mechanisms of specific and electrostatic adsorptions co-existed,accounting for about 70% and 30%,respectively.Noteworthily,in the high pH range,the hydroxyl Zn ion (ZnOH^ ) from Zn^2 hydrolysis probably was a preferable species for specific absorption.     

硫酸盐对锌和镉在可变电荷土壤上吸附的影响

SO4^2- and Zn^2 or Cd^2 were added to three variable charge soils in different sequences.In one sequence sulfate was added first ,and in the other,Zn^2 or Cd^2 first.The addition of sulfate to the system invariably caused an increase in adsorption of the heavy metal added,with the effect more remarkable whn the soil reacted with the sulfate prior to the metal.the shift in pH50 for both Zn and Cd adsorption was aslo comparatively larger in the first sequence of reactions .It was suggested that the increase in negative charge density and the resultant negative potential of the soil were the primary cause of the pronounced effect of sulfate on adsorption of Zn or Cd,and the formaiton of the ternary surface complex-S-SO4-M might also play a role in the effect.