首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The buffering of protons and hydroxyl ions in acid soils was studied by the addition of small amounts of HCl, H2SO4, and NaOH in consecutive batch experiments using surface soils and subsoils from two Cambisols and one Podzol. A chemical equilibrium model was used to study the main buffer processes. The model included inorganic complexation and multiple cation exchange, and also the solubility of jurbanite and Al(OH)3 for the subsoils. Buffering of protons was predicted quite well by the model for the surface soil of the Spodi-Dystric and Spodic Cambisols, suggesting that multiple cation exchange was the main buffer process. For the Podzol surface soil, however, the model overestimated proton buffering by cation exchange considerably. Hydroxyl buffering in acid surface soils could be described well by the model for the Podzol soil only. For the Cambisols, hydroxyl buffer reactions included not only cation exchange, but also solubilization of large amounts of organic matter and presumably deprotonation of dissolved organic carbon (DOC). Modelling proton and hydroxyl buffering in subsoils suggested that equilibrium with AJ(OH)3 was not maintained for the Podzol and spodic Cambisol. Sulphate sorption had to be considered to describe titration experiments in all three soils. The assumption of jurbanite being in equilibrium with soil extracts was useful only for the Spodi-Dystric Cambisol.  相似文献   

2.
The results of physico-chemical investigations of an Ultisol subsoil under a 2-year old fallow in eastern Amazonia are presented. Subsoil chemistry was studied using 4 different approaches: i) concentrations of H, Na, K, Ca, Mg, Mn, Al, and Fe in seepage water were measured under field conditions, ii) the equilibrium soil chemistry was studied in sequential batch experiments where the soil was treated with different solutions, iii) results of batch experiments were simulated with a chemical equilibrium model, and iv) the seepage data were calculated using selectivity coefficients obtained by modelling the batch experiments. The model included multiple cation exchange, precipitation/dissolution of Al(OH)3 and inorganic complexation. Cation selectivity coefficients were pKx/Casel: X = Na: 0.3, K: 0.8, Mg: ?0.1, and Al: 0.4. The amount of cations sorbed ranged from ?0.2 to 2.0 (K), ?0.7 to 2.3 (Mg), ?1.6 to 1.8 (Ca), ?4.8 to 3.6 (Al) and 0.0 to 8.5 (Na) mmolc kg?1. The model predictions were good with values lying within 0.3 pH units (for the pH range 3.7 to 7.2), and 3% of CEC for individual cations. The most important proton buffer reaction seemed to be the dissolution of gibbsite and a large release of Al into the soil solution. When selectivity coefficients obtained by the modelling procedure were used to predict the field data for cation concentrations in the seepage water, they decreased in the following order: Na > K > Ca > Mg > Al. These calculated values were similar to the measured order: Na > Ca > K ≈ Mg > Al. Thus the options for managing these soils should be carefully chosen to avoid soil acidification which may result from inappropriate use of fertilizer during the cropping period.  相似文献   

3.
Four soils were treated with HNO3, CaCO3 and K2SO4 to enable observation of the response of the soil solution composition and the solution A1 ion activity (Al3+) to the treatments and to time. The clay fraction of three of the soils was dominated by illite, kaolinite and quartz. The fourth was minated by kaolinite and iron oxides. The initial pH in 0.01 M CaCl2 varied between 4.0 and 5.0 and the organic carbon content from 0.7 to 1.1%. The soil solutions from soils dominated by kaolinite, illite and quartz were generally supersaturated with respect to quartz and well ordered kaolinite, and unsaturated with respect to illite. The soil solutions from the soil dominated by kaolin and iron oxide were generally unsaturated with respect to quartz but still saturated with respect to ell crystallized kaolin. Within mineral groups such as Al2SiO5 compounds, A12Si2O5(OH)4 (kaolinite group), and Al(OH)3 (A1 oxide) minerals, the more soluble forms became less supersaturated or unsaturated with time for many treatments. Lime treatment usually increased the ion activity product of AI(OH)3 in all soils, and of minerals with the composition, Al2SiO5, in the illite/kaolinite soils. Acid treatment reduced the apparent solubility of Al(OH)3, and the A1 silicates in the Al2SiO5, and Al2, Si2, O5,(OH)4, mineral groups on all soils. These results are interpreted to indicate that lime treatment led to the formation of trace quantities of more soluble A1 minerals that subsequently controlled (Al3+), whereas acid treatment dissolved trace quantities of such minerals leaving less soluble minerals to control (Al3+). The results suggest that, in mineral soils such as these, (Al3+) is under the control of inorganic dissolution and precipitation processes. These processes conform to expectations given the free energy of various inorganic aluminium compounds. Furthermore the sequence of dissolution and formation processes appears to be governed by the Gay-Lussac—Ostwald step rule.  相似文献   

4.
Predictions of changes in soil solution chemistry and exchangeable cations which occur on ash deposition after slash burning are complex and may be facilitated by the use of chemical models. Multi-ion sorption in the topsoil of an Amazonian Acrisol was studied by sequentially adding small amounts of electrolytes to soil and mixtures of soil and ash in batch experiments. A chemical equilibrium model that included inorganic complexation, multiple cation exchange and sparingly soluble salts (aluminium hydroxide and magnesian calcites) was used to interpret the results. The model predicted well the pH and sorption values in all experiments in which there was no addition of ash. The model suggested that cation exchange was the main process determining concentrations of soil solutions in all cases where neutral salt solutions were added, and that proton buffering was achieved by the dissolution of Al(OH)3 which was followed by Al3+ adsorption. Calculation of ion activity products in solutions from various batch experiments in soil + ash mixtures suggested that magnesian calcites of differing solubility may be in equilibrium with the activities of Mg2+ and Ca2+ in solution. An incongruent dissolution of Mg resulted in less soluble magnesian calcites in the ash. The model estimated satisfactorily the pH and the sorption of ions for all experiments with differing ash additions to the soil. Most of the Ca and significant amounts of Mg added in the ash are expected to remain for a long time in the soil and may determine the Ca and Mg status of the soil solution, primarily controlled by principles of solubility products.  相似文献   

5.
This paper presents aluminium (Al)-solubility data for two acid forest soils (Inceptisol and Spodosol), obtained in connection with lysimeter measurements (tension-cup and zero-tension lysimeters) and batch equilibrium experiments. The solubility of Al obtained in the batch experiments was used as a reference to test whether Al3+in soil solutions collected by the lysimeters was in equilibrium with secondary forms of solid-phase Al (Al(OH)3or organically bound Al). The relation between pH and Al3+activity found for the zero-tension lysimeter solutions collected from the Inceptisol agreed well with that obtained in the batch experiment. This suggests that Al3+in the lysimeter solutions were in, or close to, equilibrium with the solid phase, whether this was organically bound Al (A horizon) or an Al(OH)3phase (B horizon). For the tension-cup lysimeters, solutions obtained from the Inceptisol B and Spodosol Bs1 horizons were generally close to equilibrium with respect to secondary solid-phase Al (apparently Al(OH)3; average ion activity product was 109.3and 108.8, respectively), whereas the Inceptisol A and Spodosol Bh solutions were not. The Al solubility in Inceptisol A and Spodosol Bh horizons was consistently higher than that obtained in the batch equilibrium experiment, indicating that the sampled solution partly originated from the underlying horizons. Thus, tension-cup lysimeters should be used with care in soils (or in parts of soil profiles) having steep solute concentration gradients because the soil volume from which the sample is drawn with this lysimeter type seems to be poorly defined.  相似文献   

6.
四种常规方法提取伊利石有效钾的机制比较   总被引：1，自引：0，他引：1  
采用化学分析、X射线衍射、中红外光声光谱以及原子力显微镜的方法,比较了0.2 mol L~(-1)四苯硼钠法、1 mol L~(-1)沸硝酸法、2 mol L~(-1)冷硝酸法和2 mol L~(-1)热盐酸法浸提伊利石中有效钾的机制。结果表明,四苯硼钠法浸提时,伊利石中钾素释放量达到全钾量的59.5%,且基本均通过层间交换反应予以释放,结构离子铁、铝和硅释放量极低;采用三种酸溶液浸提时,其钾素释放量仅占全钾量的1.53%~2.46%,通过层间交换反应释放的钾量占释放量的比例为88.4%~94.0%。四苯硼钠浸提时伊利石层间距扩大,产生次生过渡矿物,并形成富硅表层,但在伊利石表面无溶蚀特征;三种酸溶液浸提时伊利石结构无改变,但其结晶度降低,且表面有明显的溶蚀特征。因此,土壤矿物层间钾是作物可利用有效钾的主要来源,三种酸溶液浸提方法一方面低估了有效钾容量,另一方面提取了一部分不能为植物所利用的结构态钾,不适宜于用来评价伊利石及土壤有效钾库容量。  相似文献   

7.
The acid- and base-buffering properties of 84 non-calcareous surface soil samples were studied by batch titration with HCI or KOH at a constant ionic strength of I = 0.1. The soil samples were classified according to their pH of zero point of titration (ZPT). Differential buffer values, dB(H) or dB(OH) (H+ or OH? as meq kg?1 needed to reduce or increase the soil pH sequentially by 0.5 units, respectively), were introduced to describe the course of titration curve and the intensity of buffer action. In all soils, the first acid-buffer value, dB(H)0→0.5, varied from 8 to 78 meq kg?1 and the second one, dB(H)0.5→1, from 10 to 138 meq kg?1. The corresponding base-buffer values, dB(OH)0→0.5 and dB(OH)0.5→1, ranged from 10 to 48 and from 14 to 44 meq kg?1, respectively. The most acid soils were most strongly buffered against acid, and the soils with the highest initial pH against base. The results reveal the acid-buffering by exchange reactions to be very important. In the soils with ZPT≦5.4, the first acid-buffer value was dependent on the content of organic matter and oxalate-soluble Al, whereas in the more acid soils the role of clay became significant. Thus, it was concluded that at higher pHs the foremost inactivation of H+ is attributable to soil components of pH-dependent charges, and the significance of constituents of permanent charges to increase with proceeding acidification. In strongly acid soils (ZPT≦4.8) the very effective buffering seemed to be primarily due to the dissolution of Al-hydroxides and, thus, to exert detrimental effects on the edaphic environment. The general rank of soil factors explaining the variation in the base-buffer values was in accord with the neutralization sequence, i.e. the strongest acid in the soil being neutralized first. In the strongly acid soils (ZPT≦4.8) the base-buffer values seemed to depend on the clay as well as KCl- and NH4OAc-extractable Al, whereas in the soils with higher initial pH mostly on organic C.  相似文献   

8.
Paper mill residuals may beneficially be used to improve the fertility of tropical acid soils. The effects of paper pulp on soil pH, exchangeable Al and soil solution composition of three acid tropical soils were compared with the effects of equivalent rates of lime in two batch experiments. Paper pulp was more effective than lime in increasing soil pH. However, both amendments were equally effective in decreasing exchangeable Al. Paper pulp and lime similarly influenced the composition of the soil solution by increasing soil solution pH, dissolved organic carbon, inorganic carbon, NO3, SO4, Ca and Mg. The supply of nitrate by the soil, however, was reduced in paper pulp treatments compared to lime treatments. Nitrate had a major role in controlling nutrient concentrations in the soil solution. Reduced NO3 concentrations in paper pulp treated soils compared to limed soils could therefore result in lower nutrient availability and limited losses by leaching.  相似文献   

9.
The acid–base buffering of gleyic gray-humus soils developed in brook floodplains and undisturbed southern-taiga landscapes has been characterized by the continuous potentiometric titration of soil water suspensions. During the interaction with an acid, the major amount of protons (>80%) is consumed for the displacement of exchangeable bases and the dissolution of Ca oxalates. In the O and AY horizons, Mn compounds make the major contribution (2–15%) to the acid buffering. The buffer reactions with the participation of Al compounds make up from 0.5 to 1–2% of the total buffering capacity, and the protonation of the surface OH groups of kaolinite consumes 2–3% of the total buffering capacity. The deprotonation of OH groups on the surface of Fe hydroxides (9–43%), the deprotonation of OH groups on the surface of illite crystals (3–19%), and the dissolution of unidentified aluminosilicates (9–14%) are the most significant buffer reactions whose contributions have been quantified during the interaction with a base. The contribution of the deprotonation of OH groups on the surface of kaolinite particles is lower (1–5%) because of the small specific surface area of this mineral, and that of the dissolution of Fe compounds is insignificant. In the AY horizon, the acid and base buffering of soil in the rhizosphere is higher than beyond the rhizosphere because of the higher contents of organic matter and nonsilicate Fe and Al compounds.  相似文献   

10.
Soil minerals are known to influence the biological stability of soil organic matter (SOM). Our study aimed to relate properties of the mineral matrix to its ability to protect organic C against decomposition in acid soils. We used the amount of hydroxyl ions released after exposure to NaF solution to establish a reactivity gradient spanning 12 subsoil horizons collected from 10 different locations. The subsoil horizons represent six soil orders and diverse geological parent materials. Phyllosilicates were characterized by X-ray diffraction and pedogenic oxides by selective dissolution procedures. The organic carbon (C) remaining after chemical removal of an oxidizable fraction of SOM with NaOCl solution was taken to represent a stable organic carbon pool. Stable organic carbon was confirmed as older than bulk organic carbon by a smaller radiocarbon (14C) content after oxidation in all 12 soils. The amount of stable organic C did not depend on clay content or the content of dithionite–citrate-extractable Fe. The combination of oxalate-extractable Fe and Al explained the greatest amount of variation in stable organic C (R2 = 0.78). Our results suggest that in acid soils, organic matter is preferentially protected by interaction with poorly crystalline minerals represented by the oxalate-soluble Fe and Al fraction. This evidence suggests that ligand exchange between mineral surface hydroxyl groups and negatively charged organic functional groups is a quantitatively important mechanism in the stabilization of SOM in acid soils. The results imply a finite stabilization capacity of soil minerals for organic matter, limited by the area density of reactive surface sites.  相似文献   

11.
The processes controlling the retention and release of aluminium in acid forest soils are still subject to controversy, and therefore a universal hypothesis as to what mechanisms are operating has not been firmly established. By studying the Bs horizons of Swedish and Swiss podzolized soils, and by analysing data in the literature, we have found that aluminium hydroxide, and in some cases also poorly ordered imogolite, may control Al solubility in moderately acid (pH > 4.2–4.3) Bs horizons. The strongest evidence in support of the presence of a quickly reacting Al(OH)3 pool came from the temperature dependence of Al solubility in a Bs horizon, which was consistent with the reaction enthalpy of an Al(OH)3 phase such as gibbsite, and from the observation that the ion activity product for Al(OH)3 was the same regardless of whether equilibrium was reached from over‐ or undersaturation. The pool of Al(OH)3 is commonly small and may be completely dissolved after large additions of acid. This may be explained by the continuing redissolution of reactive Al(OH)3 to form less soluble imogolite‐type phases. By using the same methods it was found that soil suspensions did not reach equilibrium with poorly ordered imogolite even after 17 days. Thus, imogolite probably does not control Al solubility in the short term in many soils despite the common occurrence of this mineral. This is due to the relatively slow kinetics of imogolite formation and dissolution, especially at low temperatures and at small solution H4SiO4 concentrations.  相似文献   

12.
The forests of the German Solling area are heavily impacted by acidic deposition. Analysis of soil solutions derived from suction lysimeters in the field reveal strong vertical gradients of Al-activity in the soil solution and increasing activity with soil depth. Temporal pattern of Al- activity in soil solutions under field conditions cannot easily be predicted by equilibrium models using Al(OH)3 dissolution. Percolating disturbed soil samples under laboratory conditions with artificial acid soil solutions undersaturated to Al(OH)3 solids resulted in high rates of Al release in the 30–40 cm layer and revealed Al(OH)3 as a possible Al-activity controlling solid. The laboratory findings are not in coincidence with field observations. This discrepancy with respect to the regulation of Al activity in the 30–40 cm layer is attributed to the effect of soil structure and the interaction of macropores and micropores under field conditions. Al activity of the soil solution in the 0–10 cm layer seems to be regulated by exchange reactions with organic substances.  相似文献   

13.
Aqueous Aluminum Species in Acidic Forest Soils - Influence of Water Pathways and Solubility Equilibria In the seepage of three typical Black Forest soils (Haplic Podzol, Dystric Cambisol, Dystric Planosol) the fractions ‘Labile-Monomeric Al’, ‘Stabile-Monomeric Al’ and ‘Acid-soluble Al’ were analyzed. Activities of aqueous Al species and saturation indices (SI) with respect to various Al-bearing minerals were calculated from ‘Labile-Monomeric Al’, using the computer program WATEQF. Al-mobilization/immobilization processes were evaluated by means of AI/CI molar ratios. With 1.5 mg/L in average, the Altotal concentrations are relatively low in all studied soils. In the O-horizon leachates, 70 to 80% of aqueous Al occur as ‘Stabile-Monomeric’ and ‘Acid-soluble’ forms mainly consisting of organo-complexes. This portion decreases in the mineral soil to 35% in the podzol and the planosol as well as to 10% in the Cambisol. Simultaneously, Al3+ increases to 40% (planosol), 50 (podzol), and 70% (cambisol). In all horizons, 5 to 15% of Altotal are covered by Al-fluoride-complexes, whereas Al-sulfate-complexes are insignificant. With 5 to 10% monomeric Al-OH-ions play a role only in the subsoil. Aluminum is strongly mobilized in the upper mineral horizons of all studied soils. In the planosol and the cambisol, Al is immobilized in the subsoil. In the subsoil of the podzol, in contrast, Al reveals further mobilization due to a distinct internal production of HNO3 and H2SO4 as a consequence of mineralization of organic matter. In the podzol, rapid percolation in macropores is crucial for Al dynamics, whereas in the planosol the temporal variation of the perched water table. Leachates from all O-horizons and upper mineral horizons as well as from the planosol subsoil are undersaturated with respect to the solubility of all mineral phases considered. With SI > O imogolite appears to be a permanently stable mineral in the subsoils of both podzol and cambisol. There is evidence for the Al(OH)3 interlayer of Al-chlorites controlling Al dynamics in the subsoil of the podzol. Al(OH)SO4 type minerals are not likely to regulate aqueous Al activities in any of the studied soils.  相似文献   

14.
The importance of amorphous Al-compounds regarding Al-release rates in carbonate-free, sandy soils In a preceding investigation the kinetics of proton consumption and the release of elements in carbonate-free, sandy forest soil horizons was analyzed by pH-stat-titrations. The soil matrix should reveal losses of Al and DOC equivalent to the amounts mobilized, and several extraction procedures (wet combustion: Corg; Pyrophosphateextraction: Alp, Corg-p; Oxalate-extraction: Alo) were applied in order to distinguish between different pools. In eight of the ten horizons investigated the dissolution of Al resulted in equivalent decreases of organically bound Al (Alp), four of them also exhibited reductions of Corg-p?levels equal to the release of DOC. For the other two horizons, Al mobilization could be attributed to the dissolution of organic and inorganic amorphous Al-compounds, each fraction contributing about half of the total. Like the release of Al and DOC, the losses of Alp, Alo and inorganically bound Al (Alo?Alp) could be well described as 1st order reactions, the constants of dissolution [h?1] of Alp (0.027), Alo (0.023) and Corg-p (0.026) being in accordance with those of Al-(0.027) and DOC- (0.024) release, respectively. For the dissolution of inorganic Al-compounds the reaction constants (0.066 and 0.052) were calculated to be nearly double.  相似文献   

15.
WANG Jing-Hua 《土壤圈》1995,5(3):193-202
The sensitivity of a large number of variable charge soils to acid rain was evaluated through examining pH-H2SO4 input curves. Two derivative parameters, the consumption of hydrogen ions by the soil and the acidtolerant limit as defined as the quantity of sulfuric acid required to bring the soil to pH 3.5 in a 0.001mol L-1 Ca(NO3)2 solution, were used. The sensitivity of variable charge soils was higher than that of constant charge soils, due to the predominance of kaolinite in clay mineralogical composition. Among these soils the sensitivity was generally of the order lateritic red soil > red soil > latosol. For a given type of soil within the same region the sensitivity was affected by parent material, due to differences in clay minerals and texture. The sensitivity of surface soil may be lower or higher than that of subsoil, depending on whether organic matter or texture plays the dominant role in determining the buffering capacity. Paddy soils consumed more acid within lower range of acid input when compared with upland soils, due to the presence of more exchangeable bases, but consumed less acid within higher acid input range, caused by the decrease in clay content.  相似文献   

16.
Exchange reactions between 0.0in AlCl3 solutions of different pH and Ca-saturated montmorillonite, vermiculite, illite, and soils from the Park Grass Experiment at Rothamsted and the Deerpark Experiment, Wexford, Ireland, showed that Al3+ and Al(OH)2+ were adsorbed from solutions of pH > 4.0 and Al3+ and H+ from solutions of pH < 3.0. When Al was adsorbed, the cation exchange capacity of Ca-saturated soils and clays increased. Conventional Ca: Al exchange isotherms showed that Al3+ was strongly preferred to Ca2+ on all soils and clays. The equilibrium constant for Ca: Al exchange, K, was identical for soils before and after oxidizing their organic matter and did not vary, for any exchanger, with Al-saturation or the initial pH of the AlCl3 solution. This proved the validity of the procedure used for calculating exchangeable Al3+. K values for Ca:Al exchange favoured Al3+ in the order: vermiculite > Park Grass soil > Deerpark soil > illite > montmorillonite. The influence of surface-charge densities of the clay minerals on this order is discussed and a method proposed and tested for calculating the K value of a soil from its mineralogical composition.  相似文献   

17.
The contribution of different proton sources to pedogenetic soil acidification was evaluated for three Japanese forest soils, i.e. ando soil, podzolic soil and brown forest soil in relation to the respective soil forming processes. Soil acidification rate and net proton generation were quantified based on the theory of proton budget for the respective soil horizon compartments (mainly the O, A and B horizons) by measuring fluxes of solutes entering and leaving the soil horizon compartment and vegetation uptake. Protons were produced by the dissociation of organic acids and nitrification in the O horizon and then consumed by adsorption and decomposition of organic acids and nitrate uptake by vegetation in deeper soil horizons at all plots. Excess uptake of cation over anion by vegetation was highest among proton sources in the whole soil compartment at all plots. Pedogenetic soil acidification was considered to include cation leaching from surface soil horizons due to proton generation by the dissociation of organic acids and nitrification and subsequent cation excess accumulation in wood in the growth stage of forests. In ando soil, andosolization resulted from the low contribution of net proton generation by the dissociation of organic acids as well as a lower soil acidification rate and complete acid neutralization. Dissolved organic carbon (DOC) fluxes in ando soil were lower than those in podzolic soil and brown forest soil due to high adsorption capacity of amorphous materials. In podzolic soil, podzolization resulted from intensive acidification in the O horizon, which derived from net proton generation by the dissociation of organic acids and nitrification as well as cation excess uptake by vegetation due to concentrated fine root biomass in the O horizon, and subsequent high proton efflux to subsoil. The high fluxes of DOC and Al leached from surface soil horizons were considered to contribute to eluviation of Al from surface soil and illuviation in subsoil in podzolic soil. In brown forest soil, brunification resulted from a lower DOC flux from the O horizon due to high decomposition and adsorption by oxides, where podzolization was weakened by high acid neutralization. Thus, the three representative processes involved in the pedogenesis of Japanese forest soils were well characterized by quantification of the respective proton-generating and consuming processes in each soil horizon.  相似文献   

18.
The clay mineralogy of two red-black soil toposequences on basic igneous rocks in Kenya has been investigated. Besides some illite and amorphous material kaolinites predominate in the slope soils (ultisols) whereas smectites are the main clay minerals in the soils of the depressions (vertisols). The kaolinites are poorly crystalline and have high surface area. According to chemical analysis, IR spectroscopy, and D.T.A. the smectites appear to be a ferriferous member of the montmorillonite-beidellite series having approximately 0·5 Fe3+ in octahedral and 0·2 Al per O10(OH)2 in the tetrahedral position. The profile and slope distribution of kaolinites and smectites led to the conclusion that the smectites are the first weathering product and, depending on hydrological conditions governing the soil solution composition (Si, Mg, pH), either persist (depression) or are decomposed (slope) and followed by kaolinites.  相似文献   

19.
The analysis of model experiments on the dissolution of clay minerals showed that, beginning from a certain moment, this process reaches a steady state and proceeds at a constant rate. The minimum dissolution rate was observed in a neutral environment, where this value varied in the range from n × 10?14-n × 10?12 mol/(m2 s). Under acidic and alkaline conditions, this value increased to n × 10?12 or n × 10?10 mol/(m2s) for most clay minerals. The first stage of the dissolution mechanism involved the formation of protonated (in an acidic environment) and deprotonated (in an alkaline environment) complexes, which destabilized and polarized metal-oxygen (or metal-hydroxyl) bonds in the crystal lattice. At the second stage, the rupture of Si-O and Al-O bonds and the release of these components into the solution occurred at a specific concentration of these complexes, and this stage largely controlled the dissolution rate of the mineral. The presence of organic ligands forming mononuclear polydentate complexes on the surface of the mineral particles at the same solution pH increased the dissolution rate of the minerals by several times and sometimes by an order of magnitude proportionally to the concentration of these complexes on the surface of the particles. It was found that the dissolution rates of kaolinite, illite, and smectite in the podzolic horizon of loamy podzolic soil calculated from the losses of clay minerals in the soil profile with consideration for the soil age exceeded the corresponding values obtained in model laboratory experiments at the same pH values by several orders of magnitude. The revealed differences could be related to the long-term functioning of biota in native soils and the existing uncertainties in the assessment of the active surface of mineral particles.  相似文献   

20.
低分子量有机酸对促进可变电荷土壤中铝溶解的影响   总被引：7，自引：2，他引：7  
Low-molecular-weight （LMW） organic acids exist widely in soils and play an important role in soil processes such as mineral weathering, nutrient mobilization and A1 detoxification. In this research, a batch experiment was conducted to examine the effects of LMW organic acids on dissolution of aluminum in two variably charged soils, an Ultisol and an Oxisol. The results showed that the LMW organic acids enhanced the dissolution of A1 in the two investigated soils in the following order： citric 〉 oxalic 〉 malonic 〉 malic 〉 tartaric 〉 salicylic 〉 lactic 〉 maleic. This was generally in agreement with the magnitude of the stability constants for the Al-organic complexes. The effects of LMW organic acids on Al dissolution were greater in the Ultisol than in the Oxisol as compared to their controls. Also, the accelerating effects of citric and oxalic acids on dissolution of A1 increased with an increase in pH, while the effects of lactic and salicylic acids decreased. Additionally, when the organic acid concentration was less than 0.2 mmol L-I, the dissolution of A1 changed Iittle with increase in acid concentration. However, when the organic acid concentration was greater than 0.2 mmol L^-1,the dissolution of A1 increased with increase in acid concentration. In addition to the acid first dissociation constant and stability constant of Al-organic complexes, the promoting effects of LMW organic acids on dissolution of A1 were also related to their sorption-desorption equilibrium in the soils.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号