Effect of Low Molecular Weight Organic Anions on the Adsorption of NO3− by Variable Charge Soils

Low molecular weight organic acids exist widely in soils and have been implicated in many soil processes. The results in the present paper showed that the presence of organic anions led to a decrease in the adsorption of NO₃⁻. The effect of citrate was much larger than that of oxalate and malate. Among different soils, the effect for Hyper-Rhodic Ferralsol and Rhodic Ferralsol was larger than that for Haplic Acrisol, which was related to the content of iron oxides in these soils. The effect of organic anions decreased with the increases in pH value and the amount of organic anions added. The organic anions depressed the adsorption of NO₃⁻ through two mechanisms, the competition of the organic anions for adsorption sites with NO₃⁻ and the change of soil surface charge caused by the specific adsorption of organic anions.     

邻苯二甲酸和水杨酸在可变电荷土壤中的吸附行为

研究了2种低分子量有机酸邻苯二甲酸和水杨酸在2种代表性可变电荷土壤红壤和砖红壤中的吸附行为。结果表明,可变电荷土壤对有机酸的吸附容量较大,对邻苯二甲酸的吸附亲和力大于对水杨酸的亲和力,在砖红壤中2种有机酸的吸附量大于在红壤中的,这与土壤的游离铁、铝氧化物的含量一致。土壤氧化铁在有机酸吸附中起着重要作用,粘土矿物如高岭石对有机酸的吸附量很小。有机酸的吸附涉及专性吸附和静电吸附2种机制,并以前者为主。当pH小于4.5时,pH的改变对有机酸的吸附影响不大;当pH大于4.5时,有机酸的吸附量随pH的增加而减小。     

Adsorption of phthalic acid and salicylic acid by two variable charge soils as influenced by sulphate and phosphate

Low‐molecular‐weight (LMW) organic acids exist widely in soils, especially in the rhizosphere, and the adsorption of these acids may affect their reactions in soils. The adsorption behaviour of phthalic acid and salicylic acid by two variable charge soils (a Rhodic Ferralsol and a Haplic Acrisol) was investigated. Both soils exhibited great adsorption capacity for these organic acids, with a greater affinity for phthalic acid. The Rhodic Ferralsol adsorbed more organic acids of both kinds than the Haplic Acrisol, which was consistent with the content of iron and aluminum oxides in the two soils. The iron oxides in these soils played a significant role in adsorption of the organic acids, whilst the soil aluminosilicate minerals, such as kaolinite, showed a small adsorption capacity. The presence of phosphate and sulphate caused a decrease in the adsorption of both organic acids because of their competition with them for sorption sites. The phosphate showed a bigger inhibition on the adsorption than sulphate as a result of a greater amount of phosphate adsorbed by the soils. The adsorption of both organic acids was affected by pH only slightly at pH < 4.5. However, the adsorption decreased with the increase in pH at pH > 4.5. A similar trend was observed for the phosphate system, but the opposite was seen for the sulphate system. This suggests that the inhibition of sulphate on the adsorption of the organic acids decreased with the increase in pH, because the adsorption of sulphate decreased strongly with increasing pH.     

可变电荷土壤中铜离子的解吸

研究了我国四种可变电荷土壤红壤、赤红壤、砖红壤和铁质砖红壤以及二种恒电荷土壤黄棕壤和黑土中吸附性铜离子的解吸特征。研究结果表明 ,可变电荷土壤吸附的一部分铜离子可以被去离子水解吸 ,而且在pH～解吸率曲线上在一定pH值时出现解吸率最大值。在最大值时不同土壤中铜离子解吸率的大小与土壤中氧化铁的含量有关。氧化铁的含量越高 ,在最大值时铜离子的解吸率越大。当用中性电解质解吸可变电荷土壤吸附的铜离子时 ,电解质的浓度越大 ,解吸率越低。与此相反 ,恒电荷土壤吸附的铜离子不能被去离子水解吸 ,只能被中性电解质解吸 ,且电解质的浓度越高 ,解吸率越大。这表明 ,可变电荷土壤中吸附性铜离子的解吸规律 ,完全不同于恒电荷土壤中者。本文初步讨论了其原因     

阴离子对可变电荷土壤吸附铜离子的影响机理

根据NO-3、Cl-和SO24-对可变电荷土壤和恒电荷土壤吸附Cu2+的影响的比较,探讨了阴离子对可变电荷土壤吸附Cu2+的影响机理。结果表明,当3种阴离子的浓度相同时,在SO24-体系中铁质砖红壤对Cu2+的吸附率较在NO3-和Cl-体系中大得多,而在浓度相同的3种阴离子体系中,黄棕壤对Cu2+的吸附率相差不大。在离子强度相近的NaCl体系中,砖红壤对Cu2+的吸附率相近。在3种阴离子体系中,随着pH升高,砖红壤对Cu2+的吸附率均增大;但在NO-3体系和Cl-体系中Cu2+的吸附率相近;而在SO24-体系中Cu2+的吸附率最大。随着Na2SO4浓度的增大,铁质砖红壤和砖红壤对Cu2+的吸附率减小。但在0.005 mol L-1和0.05 mol L-1Na2SO4体系中,Cu2+的吸附率大于在不含Na2SO4的体系中者。而在0.5 mol L-1Na2SO4体系中,Cu2+吸附率小于在不含Na2SO4体系中者。在3种浓度的Na2SO4体系中,黄棕壤对Cu2+的吸附率均小于在不含Na2SO4体系中者。总之,阴离子可通过离子强度、专性吸附和形成离子对影响土壤对Cu2+的吸附。在可变电荷土壤中,阴离子对Cu2+吸附的影响机理较在恒电荷土壤中复杂得多。     

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。     

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.     

不同NaNO_3浓度下可变电荷土壤铜离子解吸率的分配及影响因素

研究了江西红壤和昆明铁质砖红壤在去离子水中和在0.1molL-1NaNO3溶液中吸附铜离子后,依次在包括去离子水在内,浓度由低到高的NaNO3溶液中解吸时,铜离子解吸率在不同吸附pH段的分配规律。结果表明,随着吸附pH的升高,可在去离子水中解吸的铜离子解吸率变化规律与在NaNO3溶液中者完全不同。在所研究的吸附pH范围内,大致以吸附pH3.7~4.0为界,低于此值时,吸附性铜离子基本以在去离子水中解吸为主,反之则基本为交换性解吸。土壤中氧化铁含量和吸附时溶液的NaNO3浓度越高,则能被交换解吸的铜离子所占总解吸率的比例越低。其原因与不同pH段各种铜离子吸附态在不同吸附条件下的比例分配以及解吸对体系pH的影响有关。     

The effect of pH on zinc adsorption by a lateritic soil in the presence of citrate and oxalate

A change in the pH of the rhizosphere may alter the effect that organic ligands have on the concentration of Zn in the soil solution. To assess this effect, Zn adsorption by a lateritic soil was measured in the presence of 0, 1 and 3 mM of citrate and oxalate at nine values of pH ranging from pH 2 to 8. The concentrations of Zn and the ligands remaining in the solution were determined after 17 h shaking with the soil at soil:liquid ratio of 1:5. Subsequently, Zn speciation was calculated. The effectiveness of an organic ligand (L) in changing Zn adsorption was influenced by the sign of the charge of the Zn-L complex, the point of zero salt effect (PZSE) of the soil, the pH of the soil solution and the quantity of the complex formed. When the pH was above the PZSE of the soil, citrate decreased Zn adsorption by up to 38% whereas it increased Zn adsorption by as much as 51 % when the pH was below the PZSE. Oxalate had a similar but smaller effect than citrate under the conditions of the experiment. Zn adsorption was correlated with the concentration of zinc citrate in both pH regions (r2>0.98) and with oxalate above pH 2.7. The increase in Zn adsorption at low pH could have been caused by the adsorption of negatively charged Zn-L complexes.     

有机酸对铝氧化物吸附磷的影响

以存在不同配位阴离子 (硫酸根、磷酸根、草酸根、柠檬酸根 )时合成的铝氧化物为对象 ,用平衡吸附法研究了草酸、柠檬酸等的浓度和 pH对铝氧化物吸附磷的影响 ,并讨论有机酸影响磷吸附的机制。结果表明 :六种合成铝氧化物的最大吸磷量 (Xm)介于 0.189～ 0.838mmol/g ,以Al(OH)x的吸磷量最高 ,铝 柠檬酸复合物 (Al-CA)的吸磷量最低 ;有机酸浓度升高时 ,铝氧化物的吸磷量降低 ,且柠檬酸的影响程度高于草酸 ;先加 pH为 2的草酸或酒石酸 ,Al(OH)x对磷的次级吸附量最低 ,而有机酸pH为 3时 ,Al(OH)x对磷的次级吸附量达最高 ,有机酸溶液 pH由 4增至 9,铝氧化物吸磷量变化不大或逐渐降低。有机酸与磷混合加入同单加磷相比 ,pH 3时差异较小 ,pH 4～ 6时差异最显著 ,pH 7～ 8时又减小 ;有机酸降低铝氧化物吸磷量的机理包括酸性溶解和络合竞争两方面 ,在 pH 2时以前者为主 ,pH 3～ 9时以后者为主 ,且铝氧化物表面的吸附点位对供试配位阴离子都是亲合的     

Effects of Organic Anions on Phosphate Adsorption and Desorption from Variable—Charge Clay Minerals and Soil

Effects of citrate and tartrate on phosphate adsorption and desorption from kaolinite,goethite,amorphous Al-oxide and Ultisol were studied.P adsorption was significantly decreased as the concentration of the organic anions increased from 10^-5 to 10^-1 M.At 0.1 M and pH 7.0,tartrate decreased P adsorption by 27.6%-50.6% and citrate by 37.9-80.4%,depending on the kinds of adsorbent.Little Al and/or Fe were detected in the equilibrium solutions,even at the highest concentration of the organic anions.Effects of the organic anions on phosphate adsorption follow essentially the competitive adsorption mechanism.The selectivity coefficients for competitive adsorption can be used to compare the effectiveness of different organic anions in reducing P adsorption under given gonditions. Phosphate desorption was increased by 3 to 100 times in the presence of 0.001 M citrate or tartrate compared to that in 0.02 M KCl solution alone.However,for all the soil and clay minerals studied the amount of P desorbed by citrate or tartrate was generally lower than or close to that of isotopically exchangeable P.The effect of organic anions on phosphate desorption arises primarily from ligand exchange.     

外源低分子量有机酸对碳酸钙预处理的酸性土壤中活性铝钙镁影响的研究

通过在所研究的第四纪红黏土发育的红壤中混入CaCO3,研究在pH缓冲体系中外加低分子量有机酸对土壤中Al、Ca和Mg的影响。结果表明:无论加CaCO3与否,在pH 4.5的条件下外源草酸、柠檬酸、苹果酸的加入均使土壤可溶性Al显著提高,交换性Al显著下降和交换性Ca显著升高;加入CaCO3的情况下,3种有机酸处理的交换性Mg均显著提高。3种有机酸促进Al溶解能力的大小顺序为:柠檬酸>草酸>苹果酸,这一结果与有机酸和Al形成络合物的稳定常数大小一致。另一方面,3种有机酸处理下,CaCO3预处理均引起可溶性Al的显著升高和交换性Al的下降。双因素方差分析表明,有机酸通过络合作用或沉淀作用对可溶性和交换性Al、Ca和Mg均具有绝对的影响优势,CaCO3仅对可溶性和交换性Al、交换性Ca有显著影响,由于实验中pH缓冲体系的控制,这种影响主要通过Al与Ca、Mg的竞争交换作用实现。总体来说,外源低分子量有机酸的加入使土壤活性Al显著升高,活性Ca、Mg略有升高,有机酸在酸性土壤中的作用需从有机酸溶解阳离子的角度进一步评价。     

Fractionation of extractable aluminum in acid soils: A review and a proposed procedure

Abstract

Different forms of soil aluminum (Al) are involved in the retention of anions and cations, phytotoxicity of Al in acid soils, CEC reduction and soil physical properties such as aggregate stability and water infiltration. Therefore it is desirable to quantify the different forms of Al in soil especially acidic soils. A rationale was developed from a literature survey to identify the following fractions of Al: (a) exchangeable quantified by 1M KC1 extraction; (b) organic bound quantified by 0.1M CuCl₂ + 0.5M KCl extraction; (c) sorhed Al extractable with 1M NE₄OAc at pH 4.0; (d) amorphous Al oxide and hydroxide and amorphous aluminosilicates (if present) extractable with 0.2M ammonium oxalate at pH 3.0; and (e) interlayered Al extractable with 0. 33M sodium citrate at pH 7.3. Pools (a), (b), and (c) are extracted sequentially. Amorphous Al oxide and hydroxide (pool d) is calculated from ammonium oxalate extractable Al minus (a + b + c). Interlayered Al is calculated from sodium citrate extractable Al minus ammonium oxalate extractable Al. The latter two extractions are done on separate subsamples of soils. From preliminary studies and data for 13 soil samples it is suggested that this fractionation of soil Al is more meaningful than that obtained by the KCl ‐> K₄P₂O₇ ‐> ammonium oxalate > citrate‐bicarbonate‐dithionite extraction sequence.     

Lime potential of variable charge soils

The lime potentials of several electrodialysed variable charge soils of Australia and China were directly measured with two ion-selective electrodes when titrated with Ca(OH)₂. The lime potential (pH – 0.5 pCa) was higher for the Ferralsol than that for the Acrisol or the Luvisol. The presence of organic matter led to a lower pH – 0.5 pCa value. The pH – 0.5 pCa curve was closely related to the pH curve for a given soil, but was more distinct than the latter. Lime potential ranges of 1.5–3.0, 3.0–5.0 and 5.0–7.0 corresponded to pH ranges of about 4.0–5.2, 5.2–7.0 and 7.0–8.2 respectively.     

Effects of phthalic and salicylic acids on Cu(II) adsorption by variable charge soils

In the present study, the effect of two substituted benzoic acids on Cu(II) adsorption onto two variable charge soils was investigated, with the emphasis on the adsorption and desorption equilibrium of Cu(II). Results showed that the presence of organic acids induced an increase in Cu(II) adsorption onto the two soils. The extent of the effect was related to the initial concentrations of Cu(II) and organic acid, the system pH, and the nature of the soils. The effect of organic acids was greater for Oxisol than for Ultisol. Phthalic acid affected Cu(II) adsorption to a greater extent than salicylic acid did. The effect of organic acids varied with pH. The adsorption of Cu(II) induced by organic acids increased with increasing pH and reached a maximum value at approximately pH 4.5, and then decreased. It can be assumed that the main reason for the enhanced adsorption of Cu(II) is an increase in the negative surface charge caused by the specific adsorption of organic anions on soils because the desorption of Cu(II) adsorbed in organic acid systems was greater than that for the control. The desorption of Cu(II) absorbed in both control and organic acid systems also increased with increasing pH; it reached a maximum value at pH ∼5.25 for control and salicylic acid systems and at pH ∼5.1 for a phthalic acid system, then decreased. This interesting phenomenon was caused by the characteristics of the surface charge of variable charge soils.     

Effects of H2SO4 and HNO3 on Soil Acidification and Aluminum Speciation in Variable and Constant Charge Soils

The difference in effect on acidification and species of aluminum speciation between HNO₃ and H₂SO₄for two contrasting types of soils in surface charge was investigated. The results show that the effect of H₂SO₄ on acidification of variable charge soils (Ferric Acrisol and Haplic Acrisol) of subtropical regions wasweaker than that of HNO₃, due to the specific adsorption of SO₄ ^2- and the accompanied release of OH^-. For two constant charge soils, Haplic Luvisol andEutric Cambisol, the difference in effect between the two acids is small. The concentrations of total inorganic monomeric aluminum, Al³⁺, Al-F complexes and Al-SO₄complexes in the extract from variable charge soils are alsolower in H₂SO₄ systems than those in HNO₃ systems, whereas the reverse is true for constant charge soils, except the concentration of Al³⁺. For variable charge soils, Al-F complexes are the major species of inorganic monomeric aluminum at high pH butAl³⁺ might contribute to a largepart at low pH, while for constant charge soils Al-F complexes contribute almost exclusively to the inorganic monomeric aluminum. The presence of a large amount of SO₄ ^2- in the extract from the constant charge soilsleads to a higher proportion of Al-SO₄ complexes in totalinorganic monomeric aluminum than that from variable charge soil, although the numerical value of proportion is small.     

铝(氢)氧化物对有机酸和磷酸根的竞争吸附研究

研究了磷 /草酸浓度比 (Cp/Cox)、草酸 (OX)与磷 (P)加入顺序、多种有机酸共存等条件下铝 (氢 )氧化物 (Al(OH)x)对有机酸和磷的吸附量变化。结果表明 :磷浓度一定时 ,随Cp/Cox减小 ,Al(OH)x吸附磷量降低 ,吸附OX量增高 ,吸附阴离子总量一般随浓度升高而增加 ;Cp/Cox相同时 ,5种加入方式吸P顺序为P/OX P -OX OX +P OX -P OX/P ;Cp/Cox不同时 ,Al (OH)x吸附配位体的总量也相应变化 ;几种有机酸共存时 ,Al(OH)x对体系中的各种阴离子均有吸附 ,且相互影响和制约 ,总吸附量取决于离子种类和浓度 ,3种有机酸影响P吸附量的顺序为柠檬酸 (CA) 草酸 (OX) 酒石酸 (Tar) ;Al (OH)x加磷后随平衡时间延长 ,先吸附的OX和CA对吸附P量的影响逐渐减弱 ,它们的相对亲合力越来越成为主导因素。     

有机酸根与铝氧化物表面吸附磷的解吸

研究了有机酸根离子与合成铝氧化物表面吸附磷解吸的相互关系。结果表明:（1）有有机酸时比无有机酸时吸附的磷具有更高的解吸率,无草酸且加磷pH为4时,0.01molL-1KCI对磷的解吸率最低,草酸与磷共存且pH为6时磷的解吸率最高;（2）高浓度有机酸可解吸低浓度有机酸难解吸的磷,草酸难解吸的磷可为等浓度的柠檬酸极解吸;（3）不同浓度草酸和柠檬酸对铝-草酸复合物吸附磷的解吸率比对Al（OH)x的低,而对铝-柠檬酸复合物吸附磷的解吸率则比对Al（OH）x的高;（4）柠檬酸对铝-磷复合物中磷的解吸量随柠檬酸浓度升高而增大。这些结果证明,有机酸对铝氧化物吸附磷的解吸机理包括配位交换和溶解,有机酸可促进磷的解吸,提高磷的有效性。     

Adsorption/Desorption of Organic Anions in Brazilian Oxisols

Abstract

Organic anions affect solute mobility in soils. This study evaluated citrate and oxalate adsorption (0 to 4 mmol L^?1, soil–solution 1∶100, pH 5.5, ionic strength 30 mmol L^?1 as NaCl, 72‐h reaction) and desorption (pH 5.5, 30‐mmol L^?1 NaCl, 72 h) on A‐ and B‐horizon samples of two Brazilian Oxisols. Langmuir and Freundlich isotherms were used to assess adsorption maximum, distribution coefficients (Kf, Ku), and buffer index. Adsorption maximums (mol kg^?1) for red Latossol‐A, red Latosol‐B, red‐yellow Latosol‐A, and red‐yellow Latosol‐B horizons follow: citrate 0.0318, 0.0272, 0.0289, 0.0392; oxalate 0.0641, 0.0329, 0.0538, 0.0380. Kf (mol^1?1/n kg^?1 L^1/n) follows: citrate 0.3550, 0.3781, 0.4211, 0.2024; oxalate 1.0916, 0.0637, 1.8228, 0.0922. Buffer index (mol kg^?1)(mol kg^?1)^?1 follows: citrate 0.0841, 0.0756, 0.0738, 0.0264; oxalate 0.3787, 0.0862, 0.3233, 0.1082. Both anions showed great affinity for variable‐charge soils. The distribution curves for Ku showed higher adsorption energy in B‐ than in A‐horizons.     

连续解吸中离子强度对可变电荷土壤和高岭石体系pH的影响

研究了两种可变电荷土壤中在去离子水中和0.1 mol L-1 Na NO3溶液中吸附铜离子和钙离子后依次被浓度从低到高的Na NO3溶液连续解吸时,离子强度变化对每次解吸前后体系p H变化(Δp H)的影响,为了进一步了解其相关机理,作为对照,也研究了各种条件下,离子强度变化对高岭石Δp H的影响。结果表明,无论是否有吸附性二价阳离子的存在,或者吸附性阳离子属性(专性吸附型离子或电性吸附型离子)如何,当样品依次被去离子水、0.01 mol L-1 Na NO3、0.1 mol L-1 Na NO3以及1 mol L-1 Na NO3解吸时,在去离子水中和Na NO3溶液中的解吸过程对Δp H的影响截然不同。总体而言,如果解吸时体系离子强度趋于降低,Δp H将为正值,反之则为负值,且Δp H变幅开始增大时的起始点所对应的p H吸附基本相同,该起始点应该与高岭石ZPC(电荷零点)紧密相关。对上述结果的分析表明,解吸过程中,引起上述Δp H变化规律的根本原因之一是连续解吸过程中的离子强度变化导致的可变电荷表面的表面电位变化。