Chemical Species of Aluminum Ions in Acid Soils

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Adsorption of Potassium and Sodium Ions by Variable Charge Soils

Adsorption of potassium and sodium ions by four typical variable charge soils of South China was studied.The results indicated that the variable charge soils saturated with H and Al showed a much higher preference for potassium ions relative to sodium ions,and this tendence could not be changed by such factors as the pH,the concentration of the cations,the dielectric constant of solvent,the accompanying anions and the iron oxide content etc.,suggesting that this difference in affinity is caused by the difference in the nature of the two cations.It was observed that a negative adsorption of sodium ions by latosol and lateritic red soil in a mixed system containing equal amount of potassium and sodium ions at low pH,which is caused by a competitive adsorption of potassium and sodium ions and repulsion of positive charge on the surfaces of soil particles for cations.The adsorption of potassium and sodium ions increased with the decreases in the dielectric constant of solvent and the iron oxide content.Sulfate affected the adsorption of potassium and sodium ions through changing the surface properties of the soils.

Interactions of Heavy Metal Ions with Paddy Soils as Inferred from Wien Effect Measurements in Dilute Suspensions

Interactions of three heavy metal ions, Cu2+, Cd2+, and Pb2+, and, for comparison, Na+ with electrodialytic clay fractions (less than 2μm in diameter) of four paddy soils as well as a yellow-brown soil as a control soil were evaluated based on measurements of the Wien effect in dilute suspensions with a clay concentration of 10 g kg-1 in four nitrate solutions of 2×10-4/z mol L-1, where z is the cation valence, and a nitric acid solution of 3×10-5 mol L-1.Field strengths ranging from 15 to 230 kV cm-1 were applied for measuring the electrical conductivities (ECs) of the suspensions. The mean free binding energies between the various cations and all of the soils determined from exchange equilibrium increased in the order: Na+ < Cd2+ < Cu2+ < Pb2+. In general, the ECs of the suspensions in the sodium nitrate solution were smaller than those of the suspensions in the heavy metal solutions because of the lower electrophoretic mobility of sodium compared to the divalent cations. In terms of relative electrical conductivity-field strength relationships, relative electrical conductivity (REC) of suspensions containing various cations at field strengths larger than about 50 kV cm-1 were in the descending order: Na+ > Cu2+ > Cd2+ > Pb2+ for all tested soils. A characteristic parameter of the REC-field strength curves,△REG200, REG at a field strength of 200 kV cm-1 minus that at the local minimum of the concave segment of the REC-field strength curves, characterized the strength of adsorption of the cations stripped off by the applied strong electrical field, and for all soils the values of△REC200 were generally in the order: Na+ < Cu2+≤Cd2+≤Pb2+.

Analysis of Macro and Micronutrients in Soils from Palestine Using Ion Exchange Membrane Technology

Ion Exchange membrane technology (IEM) is a method that allowed a single extraction process and a single subsequent measurement of different elements that are available in soil. The values of the available forms of the different macro- and micronutrients obtained by IEM extraction were compared with the values of the soluble form obtained by conventional extraction methods. In surface soil sample, the concentrations of available potassium, nitrate, phosphate, iron and boron were 37.7 mg kg–1, 17.5 mg kg–1, 3.6 mg kg–1, 171.0 μg kg–1, and 4.2 μg kg–1 respectively were greater than that of soluble forms of the same elements which were 7.0 mg kg–1, 9.2 mg kg–1, 0.4 mg kg–1, 109.0 μg kg–1, and 1.9 μg kg–1 respectively.

Diffusion of Chloride Ions in Soils:I.Influences of Soil Moisture, Bulk Density and Temperature

Diffusion coefficients of chloride ions in four soils of different texture with varying effective moisture content and varying bulk density from 1.1 to 1.6 g cm3 under three different temperatures were determined by the diffusion-cell method using 36Cl-labelled CaCl2 solution. The results showed that activation energy decreased with water content, which indicated that the threshold for diffusion was lower at a higher soil moisture rate. Therefore, the diffusion coefficient (D) of chloride ions in soil increased consistently with soil moisture. Although a near linear increase in the diffusion coefficient with increasing soil moisture or bulk density in all the soils was observed, the increase rate in different soils was not the same. The D value increased with temperature, and with temperature increased by 10℃ in the range from 5 "C to 45℃ theD valve increased by 10%～30%, averaging about 20%.

Variation of soil physical-chemical characteristics in salt-affected soil in the Qarhan Salt Lake,Qaidam Basin

Soil salinization has adverse effects on the soil physical-chemical characteristics.However,little is known about the changes in soil salt ion concentrations and other soil physical-chemical characteristics within the Qarhan Salt Lake and at different soil depths in the surrounding areas.Here,we selected five sampling sites(S1,S2,S3,S4,and S5)alongside the Qarhan Salt Lake and in the Xidatan segment of the Kunlun Mountains to investigate the relationship among soil salt ion concentrations,soil physical-chemical characteristics,and environmental variables in April 2019.The results indicated that most sites had strongly saline and very strongly saline conditions.The main salt ions present in the soil were Na^(+),K^(+),and Cl^(-).Soil nutrients and soil microbial biomass(SMB)were significantly affected by the salinity(P<0.05).Moreover,soil salt ions(Na^(+),K^(+),Ca2+,Mg^(2+),Cl^(-),CO_(3)^(2-),SO_(4)^(2-),and HCO_(3)^(-))were positively correlated with electrical conductivity(EC)and soil water content(SWC),but negatively related to altitude and soil depth.Unlike soil salt ions,soil nutrients and SMB were positively correlated with altitude,but negatively related to EC and SWC.Moreover,soil nutrients and SMB were negatively correlated with soil salt ions.In conclusion,soil nutrients and SMB were mainly influenced by salinity,and were related to altitude,soil depth,and SWC in the areas from the Qarhan Salt Lake to the Xidatan segment.These results imply that the soil quality(mainly evaluated by soil physical-chemical characteristics)is mainly influenced by soil salt ions in the areas surrounding the Qarhan Salt Lake.Our results provide an accurate prediction of how the soil salt ions,soil nutrients,and SMB respond to the changes along a salt gradient.The underlying mechanisms controlling the soil salt ion distribution,soil nutrients,and SMB in an extremely arid desert climate playa should be studied in greater detail in the future.

Free cupric ions in contaminated agricultural soils around a copper mine in eastern Nanjing City, China

To determine the environmental free metal ion activity was a recent hot issue. A method to measure low-level free cupric ion activity in soil solution extracted with 0.01 mol/L KNO3 was developed by using cupric ion-selective electrode （ISE） and calibrating with Cu-buffer solution. Three copper buffers including iminodiacetic acid （IDA）, ethylenediamine （EN）, and glycine （Gly） were compared for calibrating the Cu-ISE curves in the range of free cupric ions （pCu^2＋） 7-13. The Cu-EN buffer showed the best electrode response and thus was applied as the calibration buffer. The pCu^2＋ of 39 contaminated agricultural soils around a copper mine was measured, ranging from 5.03 to 9.20. Most Cu in the soil solutions was found to be complexed with dissolved soil organic matters, averaging 98.1%. The proportion of free Cu^2＋ ions in the soil solutions decreased with the increasing of solution pH. Soluble Cu and free Cu^2＋ ions concentrations were analyzed by multiple linear regressions to evaluate the effects of soil properties on metal levels and speciation. The results showed that soil solution pH was the most significant factor influencing pCu^2＋ （with R^2 value of 0.76）, while not important for the soluble Cu concentration.

Interaction Between Charge Characteristics and Cu^(2+) Adsorption-Desorption of Soils with Variable or Permanent Charge

Charge characteristics and Cu2+ adsorption-desorption of soils with variable charge (latosol) and per-manent charge (brown soil) and the relationship between them were studied by means of back-titration andadsorption equilibrium respectively. The amount of variable negative charge was much less in variable-chargesoil than in permanent-charge soil and increased with the pH in the system, but the opposite trend occurredin the points of zero charge (PZCs). The amount of Cu2+ ions sorbed by permanent-charge soil was morethan that by variable-charge soil and increased with the increase of Cu2+ concentration within a certainrange in the equilibrium solution. The amount of Cu2+ ions desorbed with KCl from permanent-chargesoil was more than that from variable-charge soil, but the amount of Cu2+ ions desorbed with de-ionizedwater from permanent-charge soil was extremely low whereas there was still a certain amount of desorptionfrom variable-charge soil. The increase of PZC of soils with variable or permanent charge varied with theincrement of Cu2+ ions added. When the same amount of Cu2+ ions was added, the increments of PZC andvariable negative surface charge of permanent-charge soil were different from those of variable-charge soil.

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.

Studies on Heavy Metal Pollution in Soil-Plant System:A Review

Heavy metal pollution in soil-plant system is of major environmental concern on a world scale and in China in particular with the rapid development of industry. The heavy metal pollution status in soil-plant system in China, the research progress on the bioavailability of heavy metals (affecting factors, extraction methods, free-ion activity model, adsorption model, multivariate regression model, Q-I relationship, and compound pollution), and soil remediation are reviewed in the paper. Future research and monitoring is also discussed.

Measurement of free heavy metal ion concentrations in soils using Donnan membrane technique

In natural systems heavy metals are present in very low concentrations (less than micro-molar), so precise measurement of the free metal ions is difficult. Recently, a new method has been developed called the Donnan membrane technique (DMT). Several heavy metals could be measured simultaneously using this method. Furthermore, all the metals did not interfere with each other, and the balance between the measured system and the surrounding condition could not be disturbed. Improvements were made according to the internal condition. The free heavy metal ion concentrations were measured in different systems using the improved method, and satisfied results have been obtained.

Adsorption Kinetics of Pb^(2+) and Cu^(2+) on Variable Charge Soils and Minerals:Ⅰ.Technique

A new technique for studying the adsorption kinetics of heavy metals,Pb^2+ and Cu^2+,on variable charge surfaces was established with two selective electrodes and microcomputer control system.Feasibility of the technique,including interference of other ions (mainly Fe^3+ and Al^3+),response time of electrodes,and the pH range of testing,was studied.Comparision with the most widely used miscible displacement technique,which was considered insufficient in studying 30-minute rapid reactions,at present time showed that the new technique was more advantageous in testing in situ,easy to operate,and economic.

Determination of Diffusion Coefficient and Analysis of Diffusion Factors of Cr(Ⅵ) Ion in Clay Soil

Some laboratory diffusion tests were conducted with diffusion device to determine the diffusion coefficient of Cr(Ⅵ) ion passing through Dalian red clay samples. The concentrations of Cr(Ⅵ) at different places of the samples were then measured spectrophotometrically after a standing time of 1 000 d. A one-dimensional solute transport equation was used to simulate the transport of Cr(Ⅵ) through clay samples. Back-calculation of diffusion coefficient of Cr(Ⅵ) was made with finite difference method. Parametric analysis was conducted to simulate variations in soil dry density, temperature, pH and standing time. The results show that the method used in this paper is simple and effective. The diffusion coefficient of Cr(Ⅵ) in Dalian red clay varies from 1.50×10-7 cm2/s to 2.08×10-7 cm2/s. After 1 000 d diffusion, the concentration of the source solution drops down to 1.27 mg/L from 62.5 mg/L, and the diffusion distance is only 3.5 cm. Under the assumption that diffusion coefficient is constant, the diffusion effect becomes more obvious with lower density, lower temperature, higher pH value, and much more time.

Exchange Reaction Between Selenite and Hydroxyl Ion of Variable Charge Soil Surfaces: Ⅱ. Kinetics of Hydroxyl Release

A self-made constant pH automated titration instrument was used to study the kinetics of hydroxyl release during selenite reacting with variable charge soils. The rate of hydroxyl release was very rapid at the first several minutes, then graduallyslowed down, and at last did not change any more. The experimental data was well fitted by the Langmuir kinetic equation, and with increasing selenite concentration or decreasing solution pH, the reaction lasted longer, the maximum of hydroxyl release (xm) increased, and the binding constant (k) decreased. The time of hydroxyl release with Xuwen latosol was much longer than that with Jinxian red soil.

铁离子作用下膨胀土干湿循环裂隙演化机制

为探究重金属Fe 3+作用下膨胀土干湿循环裂隙演化机制,以不同浓度Fe 2(SO 4)3溶液作用的饱和膨胀土为对象,开展干湿循环裂隙试验、扫描电镜(SEM)试验与X射线衍射(XRD)试验,研究Fe 3+作用下膨胀土干湿循环裂隙、微观结构和矿物成分的演化规律及机制。结果表明:相同干湿次数下,随Fe 3+浓度增加,土体裂隙面积率下降;随干湿次数增加,相同浓度土体裂隙面积率总体上升;Fe 3+作用下,粒间孔隙波动性微变,黏土矿物晶体结构损伤,晶层间距减小;干湿作用后,粒间孔隙剧增,土体结构破坏,晶体损伤加剧。总结出Fe 3+作用下膨胀土干湿循环裂隙演化机制为:水分子在土体内反复迁移,劣化土体结构,形成拉应力,导致裂隙产生;Fe 3+则在一定程度上缩小颗粒间距,增强抗拉强度,降低拉应力,抑制了裂隙发育。

Effects of red-yellow soil acidification on seed germination of Chinese pine

Acid treatments significantly change the physical and chemical properties of red yellow soil by lowering its pH value and leaching out aluminum(Al) ions that are harmful to the growth of plants. The structure of soil will be damaged, resulting in higher viscosity, higher water retention rate and lower air permeability of the soil. The germination rate of Chinese pine( Pinus tabulacformic Carr. ) seeds sowed in soil treated with sulphuric acid(H 2SO 4) decreased compared to that for untreated soil. The direct cause was the large amount of Al ions leached out because of low pH values(≥3.5). The added acid decreased the soil aggregation and increased the number of micro aggregates(under 250 μm in diameter). Such changes increased the soil's viscosity, which tied the pine needles to the soil after the seeds had germinated and prevented the seedlings from fully developing.

考虑地下水位影响的碱渣土地基半埋混凝土内氯离子传输试验研究

关于碱渣土地基环境下钢筋混凝土结构耐久性问题,尚未见相关研究成果,是有待研究的课题。为探究碱渣土地基混凝土内氯离子传输规律,本工作模拟真实碱渣土地基及地下水侵蚀环境,设计了三种地下水位-0.2 m、-0.5 m、-0.8 m,开展半埋于碱渣土地基的混凝土氯离子自然扩散试验,探究不同地下水位环境下混凝土地表吸附区及地下区域的氯离子分布规律。结果表明,地表吸附区由于其蒸发浓缩及毛细作用,氯离子浓度高于地下区域。氯离子浓度随地下水位的变化呈现较大差异,地表吸附区氯离子浓度随地下水位的升高呈下降趋势,地下区域地下水位的影响主要体现在试件与水位的相对位置,地下水位以下区域氯离子浓度高于地下水位以上区域。在此基础上,探究碱渣土地基半埋混凝土内氯离子传输机理,基于Fick第二定律定量研究了地下水位对表面氯离子浓度及扩散系数的影响,建立考虑地下水位影响的氯离子传输时变模型,通过与实测结果对比印证了模型的正确性,本模型可为实际工程中定量评估不同碱渣土侵蚀环境下混凝土内氯离子浓度以及服役寿命预测提供技术支持。

不同刈割时间对南北疆油莎豆根际土壤养分和盐基离子含量的影响

【目的】探究不同刈割时间对南北疆油莎豆(Cyperus esculentus)根际土壤养分和盐基离子的影响。【方法】2021年5月15日在南疆莎车县北疆阜康市种植油莎豆,分别于播种后第78、91、106和124天采集油莎豆根际土壤样品进行养分和盐基离子分析测定。【结果】采样点和刈割时间显著影响了油莎豆根际土壤的pH(P<0.05);采样点和刈割时间的交互作用显著影响了油莎豆根际土壤的pH、全氮、全磷和全钾含量(P<0.05),对油莎豆根际土壤的离子含量均没有显著影响。北疆油莎豆根际土壤的全氮、全钾、速效磷和速效钾含量显著高于南疆(P<0.05),但北疆的阳离子(钠离子、钾离子、钙离子和镁离子)含量显著低于南疆(P<0.05)。在北疆地区,油莎豆根际土壤的pH与速效钾和氯离子含量呈显著负相关关系(P<0.05),与碳酸氢根离子含量呈显著正相关关系(P<0.05)。在南疆地区,油莎豆根际土壤的pH与速效钾含量呈显著负相关关系(P<0.05),与氯离子和钠离子含量呈正相关关系。【结论】刈割改变了南北疆种植油莎豆根际土壤全钾、速效钾和速效磷含量及pH值,改变了北疆油莎豆根际土壤氯离子含量,但刈割时间和采样点(北疆)的交互作用对土壤全氮和全磷的影响最大,为实际生产中在新疆区域推广种植油莎豆提供理论依据。