不同pH下低分子量有机酸对黄壤中铝活化的影响

用一次平衡的方法研究了不同pH下低分子量有机酸对黄壤中铝活化的影响.结果表明,低分子量有机酸体系可以通过质子和有机酸阴离子两个因素促进黄壤中铝的活化.当pH>4.3时,有机酸通过络合作用促进铝溶解的大小顺序为:柠檬酸>草酸>水杨酸>乳酸,与有机酸和铝形成络合物的稳定常数大小一致.有机酸阴离子可以通过自身的吸附增加土壤交换态铝的量,但质子作用对黄壤交换态铝的活化比有机酸阴离子的吸附起着更为重要的作用,随pH值的降低这种趋势更加明显.有机酸对交换态铝的活化作用随pH值的降低而增加.低分子量有机酸活化的铝主要分布在土壤表面的交换位上,但在柠檬酸和草酸体系中,当pH值分别大于4.40和4.55时,活化铝主要分布在土壤溶液中.     

pH和添加有机物料对3种酸性土壤中磷吸附-解吸的影响

研究了pH和添加有机物料对红壤、砖红壤和水稻土中磷吸附-解吸的影响。结果表明,砖红壤和水稻土中磷的吸附量和解吸量均随pH的升高而降低,pH对红壤中磷吸附和解吸的影响很小。土壤阳离子交换量(CEC),铁、铝氧化物含量和有机质含量是影响磷吸附的主要因素。红壤的CEC和有机质含量很低,铁、铝氧化物含量高,因而对磷的吸附量最高。砖红壤和水稻土CEC较高,土壤表面对磷的排斥作用较大,而且较高含量的有机质覆盖了土壤表面的磷吸附位,因此这2种土壤对磷的吸附量低于红壤。添加稻草并进行恒温培养可使红壤和水稻土对磷的吸附量显著减少,但对砖红壤中磷吸附的影响较小。添加稻草使土壤磷的解吸量和解吸率增加,从而增加了土壤中吸附性磷的活性。     

铝与土壤之间的表面化学反应及其后果

80年代以来，由于酸雨的发生及其对农业生产和生态环境的危害，土壤酸化问题再次成为土壤化学研究的热点．铝离子的土壤化学行为是土壤酸化的根本原因，而铝的吸附是给离子的土壤化学行为的重要方面．因此．研究铝的吸附有助于提示土壤酸化的本质，为防治土壤酸化提供有益的信息．本文综述了近30年来铝离子吸附的研究进展．其中包括吸附性铝离子的形态；铝的吸附表面；阴离子对铝吸附的影响；铝吸附的机理；铝的吸附对土壤性质的影响等．     

CrO42-对两种可变电荷土壤吸附钾的影响

用一次平衡法研究了CrO4^2-对两种可变电荷土壤吸附钾的影响，用火焰光度法测定平衡溶液中的钾，根据差减法计算土壤对钾的吸附量。结果表明，加入铬酸根能增加土壤对钾的吸附量。铬酸根对钾吸附的影响程度与土壤游离氧化铁含量和土壤对铬酸根的吸附量的大小有关。砖红壤游离氧化铁含量高于红壤，它对铬酸根的吸附量也大于红壤，因此，铬酸根对砖红壤吸附钾的影响程度大于红壤。CrO4^2-主要通过自身的吸附增加土壤的表面净负电荷，并从而增加土壤对钾的吸附量。     

砷酸根在可变电荷土壤颗粒表面的配位吸附

研究了砷在3种可变电荷土壤颗粒表面的吸附对土壤胶体Zeta电位的影响及砷酸根吸附过程中羟基的释放特征.在酸性条件下,土壤胶体吸附砷酸根后土壤表面的负电荷增加,Zeta电位下降.这说明砷酸根在土壤颗粒表面发生了专性吸附,吸附的砷酸根离子进入土壤胶体双电层的紧密层中.亚砷酸根吸附对土壤胶体Zeta电位的影响很小,说明它在土壤颗粒表面主要通过形成外圈型表面络合物而发生非专性吸附.砷酸根在土壤颗粒表面的吸附过程中有羟基释放,说明砷酸根与表面羟基发生了配位交换反应.羟基释放量随砷酸根加入量的增加和pH值的升高而增加.动力学实验结果表明,砷酸根吸附量和羟基释放量随时间具有相似的变化趋势,在开始的20min内,二者均随时间迅速增加,随后变化较小.羟基释放量与砷酸根吸附量的摩尔比也随时间的增加而增加,说明羟基释放反应滞后于砷酸根吸附反应.土壤体系中羟基释放量与砷酸根吸附量的摩尔比小于针铁矿体系,说明除铁铝氧化物外,土壤的其它固相组分也参与了对砷的吸附反应.     

土壤与酸的反应时间对土壤酸度及土壤溶液中铝离子形态分布的影响

用两种土壤研究土壤与酸的反应时间对土壤酸度及土壤溶液中铝离子形态分布的影响。结果表明,土壤溶液pH随反应时间增加而增加,安徽红壤pH的增幅大于江西红壤。在pH3.0的HNO3溶液中,土壤溶液中的总铝及Al3 均随反应时间增加而减少,而在pH3．5的HNO3溶液中,土壤溶液中总铝及Al－F络合物先随反应时间的增加而减小．然后又有所增加。     

模拟酸雨对森林红壤中铝的溶出及不同土层酸度变化的影响

为进一步探明酸沉降对森林红壤及生态环境的影响，模拟长沙地区降水酸度及离子组成，采用浸泡试验对两种森林红壤活性铝的释出及土壤理化性质的变化进行了研究。结果表明，模拟酸雨浸泡初期，土壤活性铝的释出量随浸泡次数的增加而增加，原始土壤pH值愈低，活性铝释出愈多；强酸度、高离子浓度（AR4）模拟酸雨对土壤中活性铝的溶出量远大于基础酸雨（AR3）及弱酸、低离子浓度酸雨（AR2）和对照酸雨（AR1）。模拟酸雨酸度愈大，对土壤pH值的影响愈明显，不同土层间，以A层土壤pH值下降最明显，B、C层土壤则下降较小。模拟酸雨模拟浸泡土壤25年后，土壤阳离子交换量均有不同程度下降，有机质含量高，原土壤阳离子交换量大的土壤下降幅度也大。     

Fe(Ⅲ)改性生物质炭对水相Cr(Ⅵ)的吸附试验

为考察Fe(Ⅲ)改性对生物质炭吸附水相中Cr(Ⅵ)的影响,采用吸附平衡试验结合Zeta电位、傅里叶变换红外光谱(FTIR)、X射线衍射法(XRD)等方法研究了Fe(Ⅲ)改性秸秆生物质炭对Cr(Ⅵ)的吸附作用及机制。结果表明,Fe(Ⅲ)通过与生物质炭表面官能团形成络合物及氢氧化铁表面沉淀的物理覆盖作用降低生物质炭表面负电荷,增加表面正电荷,从而促进生物质炭对Cr(Ⅵ)的吸附。Fe(Ⅲ)改性对花生秸秆炭吸附Cr(Ⅵ)的促进作用大于稻草炭,pH值为5.0时Fe(Ⅲ)改性分别使花生秸秆炭和稻草炭对Cr(Ⅵ)的最大吸附量提高79%和26%。在pH值为4.0~6.5范围内,生物质炭和改性生物质炭对Cr(Ⅵ)的吸附量均随悬液pH值升高而降低,Fe(Ⅲ)改性对生物质炭吸附Cr(Ⅵ)的促进作用也呈相似的变化趋势。改性生物质炭的表面负电荷随pH值升高而增加是Cr(Ⅵ)吸附量减小的主要原因。Cr(Ⅵ)可在改性生物质炭表面的同时发生静电吸附和专性吸附,Cr(Ⅵ)的专性吸附量也随pH值升高而减小。因此,改性秸秆生物质炭在酸性条件下对Cr(Ⅵ)有较高的吸附容量,可用于酸性废水中Cr(Ⅵ)的吸附和去除。     

2种水稻土中Cu(Ⅱ)和Pb(Ⅱ)的解吸动力学

用一次平衡法研究了2种水稻土表面吸附态Cu(Ⅱ)和Pb(Ⅱ)的解吸动力学行为及柠檬酸和酒石酸对2种重金属离子解吸的影响。结果表明,虽然2种土壤对Pb(Ⅱ)的吸附量比Cu(Ⅱ)高得多,但无论在单一重金属体系还是Cu(Ⅱ)和Pb(Ⅱ)共存体系中,Cu(Ⅱ)的解吸量均大于Pb(Ⅱ),湖州水稻土Cu(Ⅱ)的解吸量大于嘉兴水稻土,说明土壤对重金属离子的吸附亲和力越大,吸附的重金属离子越不易解吸。用E lovich方程拟合动力学数据可以获得比较满意的结果。解吸速率与时间的关系曲线表明,Cu(Ⅱ)和Pb(Ⅱ)的解吸速率随时间的增加迅速减小。Cu(Ⅱ)的解吸速率大于Pb(Ⅱ),柠檬酸和酒石酸不仅使重金属的解吸量增加,而且使Cu(Ⅱ)和Pb(Ⅱ)的解吸速率大大提高。2种有机酸对Cu(Ⅱ)解吸的促进作用大于Pb(Ⅱ),柠檬酸的促进作用大于酒石酸。     

砷酸根促进红壤吸附Cd(Ⅱ)的机制

用一次平衡实验法研究砷酸根对Cd(Ⅱ)在红壤表面吸附和解吸的影响,结果表明,加入砷酸根使土壤对Cd(Ⅱ)的吸附量和解吸量均增加,且随着砷酸根加入量的增加,土壤对Cd(Ⅱ)的吸附增量和解吸增量也均增加.当向体系中加入砷酸根后,红壤胶体的Zeta电位显著降低,说明胶体颗粒表面的净负电荷增加.这说明砷酸根主要通过自身吸附增加了土壤表面的净负电荷,从而增加了土壤对Cd(Ⅱ)的静电吸附量.研究结果还表明,在pH 3.5-6.0范围内,砷酸根均表现出对Cd(Ⅱ)吸附的显著促进作用,说明砷酸根与Cd(Ⅱ)在红壤表面的协同作用可以在比较宽的pH范围内发生.     

Effect of low molecular weight organic acids on adsorption and desorption of fluoride on variable charge soils

The effect of four low molecular weight organic acids on F⁻ adsorption by two variable charge soils was investigated using a batch method. The organic acids reduced F⁻ adsorption through competition by the acids with F⁻ for sorption sites. Oxalic and malonic acids, both of which have simpler chemical structures, were more effective than citric or malic acid. The effect of organic acids on F⁻ adsorption was more prominent at higher pH values and with larger amounts of the organic acids. The desorption study showed that the organic acids enhanced the desorption of F⁻ adsorbed by the soils. In the control and malic acid systems, desorption increased sharply with decreasing pH, while in the oxalic acid system, desorption rose slightly with decreasing pH. Desorption also increased with increasing amount of organic acid added. There are two possible mechanisms for the effect of the organic acids on F⁻ adsorption and desorption: (1)␣competition of the organic acids with F⁻ for adsorption sites and (2) dissolution of the adsorbents, especially dissolution of soil Al.     

Effects of organic acids on Cd adsorption and desorption by two anthropic soils

The objective of this experiment was to study the effects of malic, tartaric, oxalic, and citric acid on the adsorption and desorption characteristics of Cd by two typical anthropic soils (lou soil and irrigation-silted soil) in North-west China. Cadmium adsorption and desorption were studied under a range of temperatures (25°C, 30°C, 35°C, 40°C), organic acid concentrations (0.5–5.0 mmol·L^-1), and pH values (2–8). The results showed that the Cd adsorption capacity of the lou soil was significantly greater than that of the irrigation-silted soil. Generally, Cd adsorption increased as the temperature increased. In the presence of NaNO₃, the adsorption of Cd was endothermic with ΔH values of 31.365 kJ·mol^-1 for lou soil and 28.278?kJ·mol^-1 for irrigation-silted soil. The endothermic reaction indicated that H bonds were the main driving force for Cd adsorption in both soils. However, different concentrations of organic acids showed various influences on the two soils. In the presence of citric acid, chemical adsorption and van der Waals interactions were the main driving forces for Cd adsorption rather than H bonds. Although the types of organic acids and soil properties were different, the effects of the organic acids on the adsorption and desorption of Cd were similar in the two soils. The adsorption percentage of Cd generally decreased as organic acid concentrations increased. In contrast, the adsorption percentage increased as the pH of the initial solution increased. The exception was that adsorption percentage of Cd increased slightly as oxalic acid concentrations increased. In contrast, the desorption percentage of Cd increased with increasing concentrations of organic acids but decreased as the initial solution pH increased.     

Aluminum fractionation in acidic soils and river sediments in the Upper Mero basin (Galicia,NW Spain)

This study aims to determine aluminum fractions in the fine earth of acidic soils under different land uses (forest, pasture and cultivation) and in the river bed sediments of the headwater of the Mero River in order to identify and quantify Al-bearing phases to assess Al mobility and potential bioavailability (environmental availability) in the monitoring area. Sequential extraction is used to evaluate the Al partitioning into six fractions operationally defined: soluble/exchangeable/specifically adsorbed, bound to manganese oxides, associated with amorphous compounds, aluminum bound to oxidizable organic matter, associated with crystalline iron oxides, and residual fraction (aluminum within the crystal lattices of minerals). The mean concentration of total aluminum (24.01 g kg^?1) was similar for the three considered uses. The mean percentage of the aluminum fractions, both in soils and sediments, showed the following order: residual fraction ? amorphous compounds ≈ crystalline iron oxides > water-soluble/exchangeable/specifically adsorbed > bound to oxidizable organic matter ≈ Mn oxides. However, in the soils, the amorphous compounds and water-soluble/exchangeable/specifically adsorbed fraction showed considerable differences between some types of uses, the percentage of aluminum linked to amorphous compounds being higher in forest soils (16% of total Al) compared to other uses (mean about 8% of total Al). The highest values of water-soluble/exchangeable/specifically adsorbed Al were also found in forest soils (mean 8.6% of the total Al versus about 4% of pasture and cultivation), which is consistent with the lower pH and higher organic matter content in forest soils. Nevertheless, the potentially bioavailable fraction (sum of the first three fractions) is low, suggesting very low geoavailability of this element in both soils and sediments; hence, the possibility to affect the crops and water quality is minimal.     

环境中植酸的分布、形态及界面反应行为

肌-肌醇六磷酸(myo-inositol-1,2,3,4,5,6-hexakisphosphate,IHP,myo-IP6)简称植酸(Phytic acid或phytate),是大多数土壤中最为丰富的有机磷,它在环境中的界面反应影响着磷素的迁移、循环、转化、生物有效性以及环境效应.本文简要总结了环境中植酸的分布与形态,并综述了其界面反应,包括铁铝氧化物、粘土矿物、碳酸钙等对植酸的吸附解吸,多价阳离子与植酸的络合反应以及沉淀作用.土壤矿物对植酸的吸附影响其转化和生物有效性,矿物对植酸磷的吸附量一般远高于正磷酸盐.其中,弱晶质铁铝(氢)氧化物对植酸的吸附能力一般较晶形铁铝(氢)氧化物大很多.同时,分析了矿物类型、介质pH、温度、共存离子等环境条件对植酸界面反应的影响,植酸吸附对矿物表面电荷性质、颗粒大小和分散稳定性等的作用,以及植酸在金属污染土壤修复中的应用前景.最后讨论了环境中植酸的主要研究热点和方向.     

有机酸对珠江三角洲水稻土镉解吸行为的影响

用批平衡实验方法,研究了3种有机酸及其两两混合酸在一系列pH值梯度下(pH3~7)对珠江三角洲沉积型水稻土镉(Cd)解吸的影响.结果表明,只有柠檬酸及含柠檬酸的混合酸在较低酸度区(pH>5)可以显著促进Cd的解吸,这一效应与浓度成正相关,而苹果酸、草酸及二者的混合酸在所试验酸度范围均促进了Cd吸附,特别是草酸,促进作用随浓度的升高而增强.在较低pH区(pH<5),苹果酸最有利于Cd解吸,在高pH区(pH≥5),柠檬酸最有利于Cd解吸,草酸的Cd解吸能力最低.混合有机酸交互作用不显著,对Cd解吸的影响约等于各个单独酸的作用之和,但在一些酸度条件下,可存在颉颃作用.图3表2参22     

铝胁迫下马尾松幼苗有机酸分泌和根际pH值的变化

以马尾松幼苗为试验材料,选用砂培法研究铝胁迫对马尾松根际pH值、有机酸分泌以及植株中铝累积变化的影响。结果表明,高浓度铝导致根际pH值增加,当铝浓度高于300μmol.L-1时,根际pH值则趋于平稳。在测试的5种有机酸(草酸、苹果酸、柠檬酸、琥珀酸、乙酸)中,当铝浓度由0升至300μmol.L-1时,草酸和苹果酸根系分泌量随之升高,与根际pH值呈正相关关系;而当铝浓度高于300μmol.L-1时,草酸和苹果酸分泌量则趋于平稳,草酸和苹果酸的分泌影响根际pH值的变化。其次,活性铝通过根系进入植株后,由于营养作用和运输机制,出现分布差异,根部铝积累量明显高于茎和叶。当根系接触的铝浓度低于300μmol.L-1时,植株铝积累量与根际pH值,以及草酸、苹果酸分泌量呈显著正相关。