The influence of aminopolycarboxylates on the sorption of copper (II) cations by (Hydro)oxides of iron,Aluminum, and manganese

The influence of some complexing agents of (poly)aminopolycarboxylic acids (diethylenetriaminopentaacetic acid (DTPA), ethylenediaminotetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and iminodiacetic acid (IDA)) on the sorption of Cu²⁺ by crystal and amorphous (hydr)oxides of Fe(III), Al(III), and Mn(IV) that are widespread mineral components of soils was studied. The obtained results are considered in terms of complex-formation in the solution and on the sorbent’s surface. The effect of the complexing agents on the metal sorption (mobilization/immobilization) is determined by (1) the stability, structure, and sorption capability of compexonates formed in the solution; (2) the acidity, and (3) the nature of the sorbent. The desorption effect on Cu²⁺ cations was found to change in the following sequence of complexing agents: EDTA > DTPA ? NTA > IDA. The high-dentate complexing agents (EDTA, DTPA) had the greatest impact on ?u²⁺ cations bound with crystalline (hydr)oxides of Fe, Al, and Mn. The low denticity of the complexing agents (IDA, NTA) and binding of ?u²⁺ with amorphous sorbents leads to the weakening of desorption. The decrease in acidity promoted the mobilization of the metal under the influence of complexing agents; the increase in acidity caused its immobilization. The growth in the mobility of heavy metals bound with soil (hydr)oxides of Fe, Al, and Mn due to the complexing agents entering the surface and ground water is considered a factor of ecological risk.     

Effect of Low Molecular Weight Organic Anions on Adsorption of Aluminum by Variable Charge Soils

To examine the effect of organic anions on adsorption of Al by variable charge soils at different pH values, the adsorption by three soils in the presence of three low-molecular-weight aliphatic carboxylic acids was investigated. The results showed that the effect depended on pH, the type of organic anions and their concentration. The presence of citrate and oxalate led to an increase in the adsorption of Al at low pH and low concentration of organic anions, with citrate showing a stronger effect than oxalate. For example, the maximum increments of Al adsorption in the presence of citrate were 131.9, 104.8 and 32.9% in the Hyper-Rhodic Ferralsol, the Rhodic Ferralsol and the Ferric Acrisol, respectively, whereas in the presence of oxalate it was 36.1% in the Rhodic Ferralsol. At high pH or high concentration of organic anions, they showed an inhibiting effect on the adsorption of Al. For example, citrate caused the increase in Al adsorption by 164.0, 131.0 and 61.0% at pH3.85 and the decrease in Al adsorption by 15.2, 19.5 and 45.6% at pH 4.8 for the Hyper-Rhodic Ferralsol, the Rhodic Ferralsol and the Ferric Acrisol, respectively. In the citrate and oxalate systems, the adsorption of Al increased with the increase in the concentration of organic anions, reaching a maximum values at about 0.4 mmol L^?1, and then decreased. When the concentration of organic anions was higher than about 1.0 mmol L^?1, both citrate and oxalate inhibited the adsorption of Al. The ability of organic anions in increasing the adsorption at low pH and decreasing the adsorption at high pH followed the same order: citrate > oxalate > acetate. The increase of Al adsorption at low pH is caused by the increase in soil negative surface charge as a result of the adsorption of organic anions by variable charge soils, while the decrease of Al adsorption at high pH and high concentration of organic anions is related to the competition of organic ligands for aluminum ions with soil surface. After the removal of free iron oxides from the soil, Al adsorption decreased in the presence of citrate, the anion species most strongly adsorbed by variable charge soils and complexed with aluminum ions. For example, for the Rhodic Ferralsol and the Ferric Acrisol, the removal of free iron oxides caused a decrease in the adsorption of Al in the presence of citrate at pH4.4 by 26.2 and 21.9%, respectively.     

A Study on Al(III) and Fe(II) Ions Sorption by Cattle Manure Vermicompost

Cattle manure vermicompost has been used for the adsorption of Al(III) and Fe(II) from both synthetic solution and kaolin industry wastewater. The optimum conditions for Al(III) and Fe(II) adsorption at pH?2 (natural pH of the wastewater) were particle size of ≤250?µm, 1 g/10 mL adsorbent dose, contact time of 4 h, and temperature of 25°C. Langmuir and Freundlich adsorption isotherms fitted reasonably well in the experimental data, and their constants were evaluated, with R ² values from 0.90 to 0.98. In synthetic solution, the maximum adsorption capacity of the vermicompost for Al(III) was 8.35 mg g^?1 and for Fe(II) was 16.98 mg g^?1 at 25°C when the vermicompost dose was 1 g 10 mL^?1, and the initial adjusted pH was 2. The batch adsorption studies of Al(III) and Fe(II) on vermicompost using kaolin wastewater have shown that the maximum adsorption capacities were 1.10 and 4.30 mg g^?1, respectively, at pH?2. The thermodynamic parameter, the Gibbs free energy, was calculated for each system, and the negative values obtained confirm that the adsorption processes were spontaneous.     

Aluminum and iron(III) species in the soil solution including organic complexes with citrate and humic substances

The solubility of Al and Fe in soil is of relevance for their toxicity and availability, respectively, to plant roots. Humic substances as the main part of stable soil organic matter and citrate which is often excreted by P deficient plants are strong complexants of Al and Fe(III). Therefore, equations were developed to calculate the Al and Fe(III) species distribution in the soil solution in the presence of humic substances and citrate as organic ligands. Calculations in the pH range 4.0–7.0 showed that at higher pH humic-Al complexes were the most important species whereas AlOH-citrate^? dominated between pH 4.0 and 5.4. Free monomeric Al and AlSO₄⁺ were of minor relevance. Iron(III) species calculations showed that humic-Fe complexes were the main species in the pH range 4.0–7.0. But if mugineic acid, a Fe complexing phytosiderophore released into the rhizosphere by graminaceous plant species, was present in the soil solution (10^?6 M), Fe-mugineic acid complexes accounted for most of the Fe in solution. Fe-citrate^? was relevant at lower pH but contributed little to Fe(III) species at pH > 6.0. The results demonstrate the strong importance of the considered organic ligands for Fe and Al in the soil solution.     

THE MECHANISM OF PHOSPHATE ADSORPTION BY KAOLINITE, GIBBSITE, AND PSEUDOBOEHMITE

The adsorption isotherms (20°C) of phosphate on two potassium kaolinites and two aluminium oxides have been determined at pH values from 3 to 10 and at concentrations ranging from 10^?4 to 10^?2M. The reversibility of the adsorption with respect to pH and concentration has also been examined. The isotherms result from at least three types of adsorption site (regions I, II, and III) of widely different reactivities. The number of adsorption sites increases to a limit with decrease in pH for regions I and II. The behaviour of region III is more complex. The different adsorbents behave in essentially the same manner and differ only in the number of adsorption sites. It is tentatively suggested that regions I and II are located on an edge –Al(OH)₂ of the adsorbents, while region III results from penetration into some amorphous region of the crystal surface.     

Factors affecting the soil sorption of iodine

Iodine-129 is an important radionuclide released from nuclear facilities because of its long radioactive half-life and its environmental mobility. Its retention in surface soils has been linked to pH, organic matter, and Fe and Al oxides. Its inorganic solution chemistry indicates I will most likely exist as an anion. Three investigations were carried out to provide information on the role of the inorganic and organic chemistry during sorption of I by soil. Anion competition using Cl^? showed that anion exchange plays a role in I sorption in both mineral and organic soils. The presence of Cl decreased the loss of I^? from solution by 30 and 50% for an organic and a carbonated sandy soil respectively. The I remaining in solution was associated primarily with dissolved organic carbon (DOC). The loss rate from solution appears to depend on two reactions of I with the soil solids (both mineral and organic) creating both a release to and a loss from solution, and the reaction of I with the DOC (from very low to high molecular weight). Composition analyses of the pore water and the geochemical modelling indicate that I sorption affects the double-charged anion species in solution the most, particularly SO₄ ^?. Iodide introduced to natural bog groundwater at three concentrations (10^?3, 10^?1 and 10 meq L^?1) remained as I^? and was not lost from solution quickly, indicating that the association of I with DOC is slow and does not depend on the DOC or I concentration. If sorption of I to soil solids or DOC is not sensitive to concentration, then stable I studies, which by necessity must be carried out at high environmental concentrations, can be linearly extrapolated to radioactive I at much lower molar concentrations.     

Factors Affecting the Formation,Nature, and Properties of Iron Precipitation Products at the Soil–Root Interface

Abstract

A number of iron oxides (hematite, goethite, lepidocrocite, maghemite, and magnetite) or short‐range ordered precipitates (ferrihydrite) may be found in soil environments, but in the rhizosphere the presence of organic ligands released by plants (exudates) or microorganisms promote the formation of ferrihydrite. Iron ions are liberated into soil solution by acidic weathering of minerals and then precipitated either locally or after translocation in soil environments. Humic and fulvic acids as well as organic substances produced by plants and microorganisms are involved in the weathering of primary minerals. Organic compounds play a very important role in the hydrolytic reactions of iron and on the formation, nature, surface properties, reactivity, and transformation of Fe oxides. Organic substances present in the rhizosphere interact with Fe promoting the formation of ferrihydrite and organo‐mineral complexes. The solubility of Fe precipitation products is usually low. However, the formation of soluble complexes of Fe(II) or Fe(III) with organic ligands, usually present in the rhizosphere increases the solubility of Fe‐oxides. Mobilization of Fe from Fe oxides by siderophores is of great importance in natural systems. They can form stable Fe(III) complexes (pK up to 32) and thus mobilize Fe from Fe(III) compounds. These higher Fe concentrations are important for the supply of Fe to plant roots which excrete organic acids at the soil–root interface. Iron oxides adsorb a wide variety of organic and inorganic anions and cations, which include natural organics, nutrients, and xenobiotics. There is competition between anions and cations for the surfaces of Fe‐oxides. Root exudates suppress phosphate or sulfate adsorption on Fe‐oxides. This is a mechanism by which plant roots mobilize adsorbed phosphate and improve their phosphate supply. Anions adsorption on iron oxides modify their dispersion/flocculation behavior and thus their mobility in the soil system. That can increase or decrease the possibility of contact between Fe‐oxides and organics or organisms able to dissolve them.     

The specific adsorption of organic and inorganic phosphates by variable‐charge oxides

We measured the reaction of inorganic phosphate and of four organic phosphates with three aluminium hydroxides or oxides. We compared the fit of the Langmuir equation with that of an equation designed to allow for the feedback effect of adsorption on the electric potential. We also fitted a four‐plane model to describe the effects of pH on adsorption and ζ potential. For inorganic phosphate, the Langmuir equation described adsorption curves poorly, indicating that there was a large feedback effect of adsorption on the electric potential of the adsorption plane. For the organic phosphates, the deviations from the Langmuir equation were not as marked, indicating that there was little feedback effect. Nevertheless, there was a large effect on the ζ potential of the phosphated aluminium (hydr)oxides. We suggest that when a large organic phosphate molecule is adsorbed, the charge conveyed to the surface is repelled electrostatically to the outside of the new surface. There is therefore a large effect on the ζ potential and a small effect on the potential of the adsorption plane. This suggestion was supported by the fit of the four‐plane model, for which, with increasing molecular weight, the mean position of the charge conveyed to the surface by adsorption was moved further from the plane carrying the potential determining ions (H⁺ and OH^?).     

Effects of dissolved organic matter on the mobility of copper in a contaminated sandy soil

Changes in land use can result in increased soil organic matter content, and decreases in Ca and pH which will affect the mobility of Cu in soil. We studied how the mobility and coagulation of dissolved organic matter and pH affected the mobility of Cu in contaminated sandy soil by batch and column experiments in the laboratory. The soil, with pH ranging from 3.8 to 5.7, had been polluted with Cu in the range 0.13–1.9 mmol kg^?1 more than a decade ago. Calcium and Cu bound by dissolved organic matter (purified humic acid) was determined in the pH range 4–8; Cu²⁺ concentration ranged from 10^?4 to 10^?12M and Ca²⁺ concentration from 10^?3 to 10^?6M. Binding of Cu by dissolved organic matter as affected by Ca and pH could be predicted well with the non-ideal competitive adsorption (NICA) model. Coagulation of dissolved organic matter was affected by the amount of trivalent (Al³⁺) and divalent (Ca²⁺ and Cu²⁺) cations in solution. There was little effect of pH on coagulation between pH 4 and 6. The concentration of the divalent cations, Ca²⁺ and Cu²⁺, at which coagulation of dissolved organic matter appeared could be explained by differences in the binding of Ca and Cu by dissolved organic matter. Binding of Cu by dissolved organic matter as well as by solid organic matter, both affected by Ca and pH, could be described well with the NICA model. We investigated the coagulation and mobility of dissolved organic matter in column experiments and found that they enhanced Cu mobility. Three processes, Cu desorption by soil, dissolved organic matter coagulation and Cu complexation by dissolved organic matter, act simultaneously in the soil columns. All three with counteracting effects on Cu mobility are influenced by Ca and pH and could be adequately represented by the multicomponent NICA model.     

Adsorption of mercury compounds by tropical soils II. Effect of soil: Solution ratio,ionic strength,pH, and organic matter

Mercury adsorbed from HgCl₂ and 2-methoxy-ethylmercury chloride (Aretan) solutions by three contrasting soils showed a dependence on soil: solution ratio and initial Hg concentration in soil solution. Changing the soil solution ratio from 1: 10 to 1 : 100 but keeping the initial concentration constant resulted in an increase in Hg adsorption from both Hg compounds. A similar change in soil: solution ratio accompanied by a decrease in initial concentration, on the other hand, resulted in decrease in Hg adsorption. Upon manipulating of the pH of the surface soils, adsorption of HgCl₂ at 100 mg Hg L^?1 concentration increased from about 701 :o over 95 mg Hg kg^?1 when pH was raised from 5.0 to 8.0. Precipitation of Hg may also have contributed to this trend. Aretan adsorption by these soils, on the other hand, changed little with change in pH. Removal of organic matter from soil resulted in large reductions of Hg adsorbed, as much as 95 % from the HgCl₂ solutions, but only up to 31 % from Aretan solutions. This suggests that organic matter in soil played a mayor role in the adsorption of inorganic Hg whereas the soils' mineral fractions were involved more in the adsorption of the organic Hg compound.     

Comparison of the influence of tannic acid and selected low-molecular-weight organic acids on precipitation products of aluminum

The crystallization and surface properties of hydrolytic reaction products of Al precipitated in the presence of 1.0 · 10^?6M and 1.0 · 10^?4M tannic acid from systems at the initial Al concentrations of 1.1 · 10^?4M and 1.1 · 10^?3M and OH/Al molar ratios of 2.0 or 3.0 were examined.X-ray diffraction analyses show that the structural distortion within the hydrolytic precipitation products of Al increases with the molar ratio of tannic acid to Al. The non-crystalline to poorly ordered hydrolytic precipitation products of Al, including pseudoboehmite, are formed in the presence of tannic acid and are shown by transmission electron micrographs to be fine, shapeless and hollow colloids which are deformed and aggregated. In contrast to low molecular weight organic acids (p-hydroxybenzoic, aspartic, malic, and citric acids), the influence of tannic acid on the surface reactivities of the precipitation products of Al cannot be solely explained on the basis of its chemical affinity towards Al. In addition to complexation, the physical adsorption of the tannic acid initially present at 1.0 · 10^?6M apparently promotes structural distortion in the precipitation products and thereby increases the specific surface and the formation of active sites for surface charge development and for phosphate and Ca retention to an extent even greater than that observed with the more strongly complexing malic acid. On the other hand, when the concentration of tannic acid is increased to 1.0 · 10^?4M, the physical adsorption of the tannic acid, while enhancing Ca retention through its ability to ionize and provide negative charges, hampers phosphate retention by masking some of the active sites.     

Sodium hypochlorite oxidation reduces soil organic matter concentrations without affecting inorganic soil constituents

Oxidative treatment can isolate a stable organic matter pool in soils for process studies of organic matter stabilization. Wet oxidation methods using hydrogen peroxide are widely used for that purpose, but are said to modify poorly crystalline soil constituents. We investigated the effect of a modified NaOCl oxidation (pH 8) on the mineral composition of 12 subsoils (4.9–38.2 g organic C kg^?1) containing varying amounts of poorly crystalline mineral phases, i.e. 1.1–20.5 g oxalate‐extractable Fe kg^?1, and of different phyllosilicate mineralogy. Post‐oxidative changes in mineral composition were estimated by (i) the determination of elements released into the NaOCl solution, (ii) the difference in dithionite‐ and oxalate‐extractable Si, Al and Fe, and (iii) the specific surface areas (SSAs) of the soils. The NaOCl procedure reduced the organic C concentrations by 12–72%. The amounts of elements released into the NaOCl extracts were small (≤ 0.14 g kg^?1 for Si, ≤ 0.13 g kg^?1 for Al, and ≤ 0.03 g kg^?1 for Fe). The SSA data and the amounts of dithionite‐ and oxalate‐extractable elements suggest that the NaOCl oxidation at pH 8 does not attack pedogenic oxides and hydroxides and only slightly dissolves Al from the poorly crystalline minerals. Therefore, we recommend NaOCl oxidation at pH 8 for the purpose of isolating a stable organic matter pool in soils for process studies of organic matter stabilization.     

STUDIES ON SOIL COPPER

Adsorption isotherms were determined for the specific adsorption of copper by soils and soil constituents. Adsorption was found to conform to the Langmuir equation. The Langmuir constants, a (adsorption maximum) and b (bonding term), were calculated. Soils were found to have specific adsorption maxima at pH 5.5 of between 340 and 5780 μg g^?1, and a multiple regression analysis revealed that organic matter and free manganese oxides were the dominant constituents contributing towards specific adsorption. Adsorption maxima for soil constituents followed the order manganese oxides > organic matter > iron oxides > clay minerals, which supported the findings for whole soils. The cation exchange capacities (non-specific adsorption) of the test soils were found to be far greater than the specific adsorption maxima. However, evidence suggests that, for the relatively small amounts of copper normally present in soils, specific adsorption is the more important process in controlling the concentration of copper in the soil solution.     

有机酸对高岭石, 针铁矿和水铝英石吸附镉的影响

Effects of organic acids （oxalic, acetic, and citric） on adsorption characteristics of Cadmium （Cd） on soil clay minerals （kaolinite, goethite, and bayerite） were studied under different concentrations and different pH values. Although the types of organic acids and minerals were different, the effects of the organic acids on the adsorption of Cd on the minerals were similar, i.e., the amount of adsorbed Cd with an initial solution pH of 5.0 and initial Cd concentration of 35 mg L^-1 increased with increasing concentration of the organic acid in solution at lower concentrations, and decreased at higher concentrations. The percentage of Cd adsorbed on the minerals in the presence of the organic acids increased considerably with increasing pH of the solution. Meanwhile, different Cd adsorption in the presence of the organic acids, due to different properties on both organic acids and clay minerals, on kaolinite, goethite, or bayerite for different pHs or organic acid concentrations was found.     

Effects of acidification and natural organic materials on the mobility of arsenic in the environment

Effects of acidification on adsorption and potential mobility of various As forms have been studied in batch-type distribution experiments. The adsorption of As on alumina decreased in the order As(V) > MMAA = DMAA > As(III) at pH below 6 and As(V) > As(III) > MMAA = DMAA at pH above 6. The adsorption reached a maximum around pH 5 for As(V), pH 7 for As(III) and pH 4 for MMAA and DMAA. The presence of a fulvic acid at concentration levels of 10 mg L^?1 or higher generally reduced the As adsorption in the pH range 5 to 7. In light of both laboratory and field observations environmental acidification would increase the leaching of As from soils or sediments to surface and groundwaters under reducing conditions, but could also reduce the mobility due to enhanced adsorption under oxidizing conditions.

     

铝同晶替代对铁(氢)氧化物表面活性的影响研究进展

铝同晶替代现象在铁(氢)氧化物中普遍存在，可改变铁(氢)氧化物的结构、表面特性和反应活性，影响土壤中元素的行为、形态和归趋。运用文献计量法分析了铝同晶替代铁(氢)氧化物的国内外研究现状，分别综述了铝同晶替代对铁(氢)氧化物晶体结构、表面电荷和界面过程的影响，从静电作用、比表面积、位点组成与密度、Fe/Al位点亲和性以及空位缺陷等方面阐明了铝同晶替代对铁(氢)氧化物表面活性和吸附行为的影响机制。在此基础上，提出了未来研究应着眼于构建铝替代量–结构–反应活性定量关系、深入探究铝同晶替代铁(氢)氧化物不同晶面上的界面机制，以及将研究对象与体系过渡到实际土壤等。     

低分子量有机酸对可变电荷土壤铝活化动力学的影响

从动力学角度研究了几种低分子量有机酸对2种酸性土壤中铝的活化和活化铝在土壤固/液相之间分配的影响。结果表明:对于络合能力弱的醋酸和乳酸,主要通过质子作用活化铝,且活化作用明显小于盐酸。而络合能力较强的苹果酸、草酸和柠檬酸,主要通过络合作用促进铝的释放,且这种作用随有机酸根阴离子络合能力的增强而增加。在氧化铁含量较高的砖红壤中,苹果酸、草酸和柠檬酸通过专性吸附增加土壤表面负电荷,从而增加土壤交换态铝;但在氧化铁含量较低的红壤中,草酸和柠檬酸主要通过形成可溶性铝络合物降低交换态铝。活化铝在土壤固/液相间的分配主要决定于溶液中有机阴离子与土壤固相表面对铝离子的竞争。醋酸和乳酸活化的铝主要以交换态铝存在;而草酸和柠檬酸活化的铝主要以有机酸-铝络合物存在于溶液中,特别是在氧化铁低的红壤中,这将促进铝在土壤-水体中的迁移。     

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 associations between humic acids and iron or aluminium on the flocculation and aggregation of kaolin and quartz

The aggregative effect of organic matter on soil particles is conditioned by its composition and concentration and the degree to which it is associated with metal ions and oxides in the soil. We treated suspensions of kaolin or quartz substrates at pH 5 with metal (Fe or Al; c. 3 to 23 mg g^?1 of substrate) or humic acid (HA; 7 to 53 mg g^?1 of substrate) or both. In the absence of added Fe or Al, the proportion of HA retained by the substrate decreased from 98.5 to 50.8% for kaolinitic samples, and from 35.8 to 23.4 for quartz-based samples, as the HA dose increased. In the presence of Fe or Al, the proportion of HA removed from solution increased and was always >91%. Untreated kaolin flocculated between pH 2.0 and 4.5. This flocculation interval narrowed as the dose of HA increased, widened as the dose of HA-A1 increased, but was barely affected by HA-Fe. Similarly, the aggregative effect of HA-Fe associations on kaolin was smaller than that of HA-A1 associations, which induced formation of aggregates >100 μm that were essentially absent in the untreated substrate. There was a similar but less marked difference between the aggregative effects of HA-Fe and HA-A1 on quartz.     

低分子量有机酸对高岭石中铝释放的影响

选择了几种土壤中可能存在的低分子量脂肪羧酸 ,研究了它们对高岭石中铝释放的影响。结果表明 ,有机酸可以通过络合作用促进高岭石中铝的释放。几种有机酸对体系中可溶性铝影响的大小顺序为 :草酸 >柠檬酸 >丙二酸 >苹果酸 >乳酸。草酸、柠檬酸和乳酸对可溶性铝释放的促进作用随体系pH的升高而减小 ,其中草酸体系中可溶性铝随pH的变化幅度最大。在苹果酸体系中 ,可溶性铝随pH的升高而稍有增加。体系中的可溶性铝随有机酸浓度的增加而增加 ,而交换性铝随柠檬酸浓度的增加而减少 ,先随苹果酸浓度增加而增加 ,然后又逐渐减少。与对照相比 ,柠檬酸和草酸使交换性铝的量减小 ,苹果酸和乳酸在低pH下使交换性铝明显增加 ,而苹果酸在较高pH下使交换性铝减少。有机酸影响释放出的铝在固液相间的分配比 ,苹果酸在低pH下使体系中释放出的大部分铝以交换性形态存在 ,而在较高pH下 ,大部分铝以可溶形态存在。在草酸体系中 ,释放出铝的大部分都以可溶形态存在。不同有机酸的不同表现与体系中铝的溶解平衡、铝的吸附 -解吸平衡、有机酸的吸附 -解吸平衡、有机酸的离解平衡和铝与有机酸的络合 -离解平衡有关。