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1.
2.
Mohsen Jalali Ziba Hourseresht 《Communications in Soil Science and Plant Analysis》2017,48(9):1089-1104
In the present study, a laboratory experiment was designed to compare the 0.01 M calcium chloride (CaCl2) and diethylenetriaminepentaacetic acid (DTPA) extraction methods for their ability to predict cadmium (Cd), copper (Cu), iron (Fe), Manganese (Mn), nickel (Ni), and zinc (Zn) availability and mobility in five calcareous soils. The soils were spiked with different amounts of metals (0, 50, 100, 200, and 400 mg kg?1) both in binary (Cu and Zn; Ni and Cd; Fe and Mn) and in multi-systems (Cd, Cu, Fe, Mn, Ni, and Zn) and incubated for 1 months at field capacity. In metal-spiked soils, both extraction methods showed a linear relationship of extractable to total metals for all soils. The fraction of total metals extracted by DTPA was much higher than the fraction extracted by CaCl2, which was attributed to the formation of soluble metal-complexes in the complexing extracts calculated by the Visual Minteq program. DTPA extraction method showed higher selectivity for Cu over other metals both in binary and in multi-systems. Different order of metals extractability was found in binary and multi-systems for both extraction methods. Solid/solution distribution coefficient (Kd) was calculated by the ratio of the solid phase to soil solution concentration of metals extracted by CaCl2 or DTPA extraction methods. Both in binary and in multi-systems, the average Kd (l kg?1) of metals by soils were in the order of Mn (5398) > Fe (4413) > Zn (3376) > Cu (2520) > Ni (969) > Cd (350) in the CaCl2-extractable metals and Fe (35) ≥ Ni (34) > Zn (18) > Mn (11.2) > Cu (6.3) > Cd (4) in the DTPA-extractable metals. Results showed that among the six studied metals, Cd had the lowest Kd, implying a relative higher mobility in these calcareous soils. The Visual Minteq indicated that in the CaCl2-extraction method and in both binary and multi-systems the dominant species for Cu, Mn, Ni, and Zn were Cu2+, Mn2+, Ni2+ and Zn2+, respectively, while for Cd and Fe, the dominant species were CdCl+ and Fe(OH)2+, respectively. 相似文献
3.
Magnetic resonance imaging methods to reveal the real-time distribution of nickel in porous media 总被引:1,自引:0,他引:1
A. B. Moradi S. E. Oswald J. A. Massner K. P. Pruessmann B. H. Robinson & R. Schulin 《European Journal of Soil Science》2008,59(3):476-485
Direct and non‐destructive measurement of the sorption, diffusion and mobility of ions and molecules in porous media has applications in industry and environmental science. We used magnetic resonance imaging (MRI) to visualize the dynamic distribution of paramagnetic nickel (Ni+2) ions in porous media. Various MRI sequences were tested to image Ni2+ at small concentrations. Noisy gradient echo images had poor contrast between samples containing various Ni2+ concentrations. Turbo spin echo and spoiled gradient echo images showed a linear relation between Ni2+ concentrations and signal intensity over a wide range of concentrations. Spoiled gradient echo images resolved Ni2+ concentrations (down to 30 mg litre?1) better than turbo spin echo images. However, for smaller concentrations, uncertainty in intensity values increased. A T1 measurement, obtained using an inversion recovery sequence, showed a linear correlation between T1 and Ni2+ concentration down to 1.5 mg litre?1. In a glass bead medium with an ion exchange resin as an Ni sink, the real‐time development of the Ni2+ depletion zone around the resin, as Ni was sorbed into the resin, was imaged by T1 mapping. A spatial resolution of 0.58 mm and a temporal resolution of less than a minute were achieved. The two‐dimensional Ni2+ gradient that was determined from MRI agreed well with geochemical modelling results. The results of this study showed that MRI, in particular T1 mapping, can quantify microscale behaviour of paramagnetic species in porous media. However, ferromagnetic components that naturally occur in most soils can easily disturb the MRI signal. 相似文献
4.
Cindy Silva Moreira José Carlos Casagrande Luís Reynaldo Ferracciú Alleoni Otávio Antônio de Camargo Ronaldo Severiano Berton 《Journal of Soils and Sediments》2008,8(6):442-451
Background, aim, and scope The retention of potentially toxic metals in highly weathered soils can follow different pathways that variably affect their
mobility and availability in the soil–water–plant system. This study aimed to evaluate the effects of pH, nature of electrolyte,
and ionic strength of the solution on nickel (Ni) adsorption by two acric Oxisols and a less weathered Alfisol.
Materials and methods The effect of pH on Ni adsorption was evaluated in surface and subsurface samples from a clayey textured Anionic ‘Rhodic’
Acrudox (RA), a sandy-clayey textured Anionic ‘Xantic’ Acrudox (XA), and a heavy clayey textured Rhodic Kandiudalf (RK). All
soil samples were equilibrated with the same concentration of Ni solution (5.0 mg L−1) and two electrolyte solutions (CaCl2 or NaCl) with different ionic strengths (IS) (1.0, 0.1 and 0.01 mol L−1). The pH of each sample set varied from 3 to 10 in order to obtain sorption envelopes.
Results and discussion Ni adsorption increased as the pH increased, reaching its maximum of nearly pH 6. The adsorption was highest in Alfisol, followed
by RA and XA. Competition between Ni2+ and Ca2+ was higher than that between Ni2+ and Na+ in all soil samples, as shown by the higher percentage of Ni adsorption at pH 5. At pH values below the intersection point
of the three ionic strength curves (zero point of salt effect), Ni adsorption was generally higher in the more concentrated
solution (highest IS), probably due to the neutralization of positive charges of soil colloids by Cl− ions and consequent adsorption of Ni2+. Above this point, Ni adsorption was higher in the more diluted solution (lowest ionic strength), due to the higher negative
potential at the colloid surfaces and the lower ionic competition for exchange sites in soil colloids.
Conclusions The effect of ionic strength was lower in the Oxisols than in the Alfisol. The main mechanism that controlled Ni adsorption
in the soils was the ionic exchange, since the adsorption of ionic species varied according to the variation of pH values.
The ionic competition revealed the importance of electrolyte composition and ionic strength on Ni adsorption in soils from
the humid tropics.
Recommendations and perspectives The presence of NaCl or CaCl2 in different ionic strengths affects the availability of heavy metals in contaminated soils. Therefore, the study of heavy
metal dynamics in highly weathered soils must consider this behavior, especially in soils with large amounts of acric components. 相似文献
5.
ABSTRACT Dissolution of phosphate rocks (PR) in soils requires an adequate supply of acid (H+) and the removal of the dissolved products [calcium (Ca2 +) and dihydrogen phosphate (H2PO4 ?)]. Plant roots may excrete H+ or OH? in quantities that are stoichiometrically equal to excess cation or anion uptake in order to maintain internal electroneutrality. Extrusion of H+ or OH? may affect rhizosphere pH and PR dissolution. Differences in rhizosphere acidity and solubilization of three PRs were compared with triple superphosphate between a grass (Brachiaria decumbens) and a legume (Stylosanthes guianensis) forage species at two pH levels (4.9 and 5.8) in a phosphorus (P)-deficient Ultisol with low Ca content. The experiment was performed in a growth chamber with pots designed to isolate rhizosphere and non-rhizosphere soil. Assessment of P solubility with chemical extractants led to ranking the PRs investigated as either low (Monte Fresco) or high solubility (Riecito and North Carolina). Solubilization of the PRs was influenced by both forage species and mineral composition of the PR. The low solubility PR had a higher content of calcite than the high solubility PRs, which led to increased soil pH values (> 7.0) and exchangeable Ca, and relatively little change in bicarbonate-extractable soil P. Rhizosphere soil pH decreased under Stylosanthes but increased under Brachiaria. The greater ability of Stylosanthes to acidify rhizosphere soil and solubilize PR relative to Brachiaria is attributed to differences between species in net ion uptake. Stylosanthes had an excess cation uptake, defined by a large Ca uptake and its dependence on N2 fixation, which induced a significant H+ extrusion from roots to maintain cell electroneutrality. Brachiaria had an excess of anion uptake, with nitrate (NO3 ?) comprising 92% of total anion uptake. Nitrate and sulfate (SO4 2 ?) reduction in Brachiaria root cells may have generated a significant amount of cytoplasmic hydroxide (OH?), which could have increased cytoplasmic pH and induced synthesis of organic acids and OH? extrusion from roots. 相似文献
6.
《Soil Science and Plant Nutrition》2013,59(3):362-368
Abstract The aluminum solubility of acidified soils both from furrows and under tree canopies of a tea garden was studied using equilibrium experiments in 0.01 mol L?1 CaCl2 solution systems. The soils were originally classified as allophanic Andosols. The furrow soils were more severely acidified because of the heavy application of nitrogen fertilizer, especially in the upper soil horizons (pH[H2O] of 3.6–3.8 in the A1 and 2A2 horizons). These acidified soils were characterized by the dissolution of allophanic materials (allophane, imogolite and allophane-like materials) and by an increase in Al–humus complexes. Ion activity product (IAP) values of the strongly acidified soil horizons were largely undersaturated with respect to imogolite (allophanic clay) or gibbsite. Plots of p(Al3+) as a function of pH strongly indicated that Al solubility of the soils was largely controlled by Al–humus complexes, especially in the A1 horizon. In the canopy soils, which were more weakly acidified (pH[H2O] 4.9–5.0), Al solubility was close to that of gibbsite and allophanic materials, indicating that the solubility is partly controlled by these minerals. 相似文献
7.
ADSORPTION OF LEAD, COPPER, ZINC, COBALT, AND CADMIUM BY SOILS THAT DIFFER IN CATION-EXCHANGE MATERIALS 总被引:4,自引:0,他引:4
The adsorption of Zn2+, Pb2+, Cu2+, Co2+, and Cd2+ (M2+) by soils was measured at concentrations ranging from 10-7 to 10-2 M in 10-3 to 10-2 M CaCI2. Exchange between Ca2+ and M2+, and solubility products [M2+][OH?]2 indicate that M2+ is not precipitated as hydroxide but is adsorbed on cation-exchange sites. The proportion of selective adsorption sites with specified values of the selectivity coefficient calculated using Ca as reference ion, increased in the order montmorillonite < humus, kaolinite, < allophane. imogolite < halloysite, iron oxides. Raising the soil pH by Ca-saturation increased both the amount and affinity of adsorption. Selectivity of adsorption increased in the order Mg, Ca < Cd, Co < Zn < Cu, Pb, and the selectivity coefficient varied from < 1 to > 10 000. The formation of the coordination complexes of heavy metal with deprotonoted OH and COOH groups as ligands is suggested as a possible mechanism of selective adsorption. 相似文献
8.
《Soil Science and Plant Nutrition》2013,59(2):115-124
Abstract Aluminum (Al)–humus complexes are abundant in the A horizons of non-allophanic Andosols and contribute to the unique properties of volcanic ash soils, such as high reactivity with phosphate ions and a low bulk density. Natural non-allophanic Andosols commonly show Al toxicity to plant roots. There have been very few studies examining the contribution of Al–humus complexes to the Al toxicity of plant roots, although the complexes are the probable source of the toxic Al. We extracted humic substances from the A horizon of a non-allophanic Andosol using NaOH solution and reacted the humic substances and partially neutralized the AlCl3 solution at three pH conditions (pH 4.0, 4.5 and 5.5) to prepare pure Al–humic substance complexes. The Al solubility study (equilibrium study in 10?2 mol L?1 CaCl2) and the Al release study (a stirred-flow method using 10?3 mol L?1 acetate buffer solution adjusted to pH 3.5) indicated that all the synthetic complexes easily and rapidly release monomeric Al into the liquid phase with slight changes in pH and ion strength, although the Al contents and their extent of polymerization are considerably different among the complexes. A plant growth test was conducted using a medium containing the Al–humic substance complexes and perlite mixture. Root growth in burdock (Arctium lappa) and barley (Hordeum vulgare L.) was reduced equally by all three complex media, and the roots showed the typical injury symptoms of Al toxicity. These results indicate that in soils dominated by Al–humus complexes the Al released from the Al–humus complexes, as well as the exchangeable Al adsorbed by soil minerals, is definitely toxic to plant roots. 相似文献
9.
New experiments have been conducted to determine the speciation of dissolved mercury (Hg) over wide pH (1–12) and sulfide concentration ranges (0.5–30 mM) and in the presence of elemental sulfur (S0) or Hg0, conditions that encompass those of near-bottom and pore waters of sediments. Samples containing synthetic red mercuric sulfide (HgS, cinnabar), buffer solution, aliquots of bisulfide (HS?1) solution, and, in special cases, S0 or Hg0 were prepared anaerobically and allowed to equilibrate for several months. Filtered samples were analyzed for pH, total sulfide (ΣS2?), and total mercury [Hg]tot. Plots of [Hg]tot values vs. pH at varying ΣS2? verified the formation of three previously known mercury-sulfide complexes (HgS2Hn n?2) and revealed that a new Hg2SOH+ complex is important at low pH and low ΣS2?. Our constants for ionic strength (I) 0.7 and 250 C are as follows: K1=10?5.76(+0.71, ?1.02) for HgScinn+H2S ? HgS2H2 0; K2=10?4.82(+0.72, ?1.10) for HgScinn+HS? ? HgS2H?; K3=10?13.41(+0.76, ?0.93) for HgScinn+HS? ? HgS2 2?+H+; K4=10?8.36(+0.71, ?0.93) for 2HgScinn+H++H2O ? Hg2SOH++H2S. With decreasing pH, below 1, Hg solubility decreased sharply, indicating the formation of a new solid phase, inferred to be corderoite (Hg3S2Cl2). From our solubility data, we calculated the free energy of formation (ΔGf o) of Hg3S2Cl2 to be ?396 (+3, ?11) kJ/mol. In experiments where excess S0(s) was present, a new mercury-polysulfide dimer was identified; its formation constant is K5=10?1.99(+0.69, ?1.27) for 2HgScinn+2HS? + nS0 ? Hg3S4 IISn oH2 2?. Data from experiments where Hg0(aq) was added confirmed the reversibility of HgS dissolution. An application of our mercury-sulfide speciation model to a natural anoxic basin, Saanich Inlet, British Columbia, is discussed. 相似文献
10.
Fei Zang Shengli Wang Zhongren Nan Jianmin Ma Yu Wang Yazhou Chen Qian Zhang Yepu Li 《Journal of Soils and Sediments》2017,17(10):2524-2536
Purpose
The objectives of this study were to explore the influences of pH on the release of Cu, Zn, Cd, Pb, Ni, and Cr in sediments derived from the upstream, middle, and downstream reaches of Dongdagou stream in Gansu Province, Northwest China, and to examine the fractionation changes of heavy metals in the sediments after reaching their release equilibrium under different pH conditions.Materials and methods
Sediment samples were obtained using a stainless steel grab sampler to collect the uppermost 10 cm of sediment from the channel bed. The pH-dependent release experiment was conducted in the solid-to-liquid ratio of 1:20 at different pH values (2, 4, 6, 8, 10, and 12) at room temperature. The total Cu, Zn, Cd, Pb, Ni, and Cr concentrations in the sediments were digested using an acid digestion mixture (HNO3 + HF + HClO4) in an open system. Metal fractionation of selected sediments was obtained using the Tessier sequential extraction procedure. Heavy metal concentrations in the samples were determined using atomic absorption spectrophotometry.Results and discussion
The mean concentrations of heavy metals in sediments decreased in the following order: Zn (1676.67 mg kg?1) > Pb (528.65 mg kg?1) > Cu (391.34 mg kg?1) > Cr (53.48 mg kg?1) > Ni (34.27 mg kg?1) > Cd (11.53 mg kg?1). Overall, the solubility of Cu, Zn, Cd, Pb, and Ni decreased with increasing pH, and they were strongly released at pH 2. Moreover, the solubility of Cr increased with increasing pH, and its release was highest at pH 12. After reaching the release equilibrium of heavy metals under different pH conditions, the percentages of organic Cu, Zn, Cd, and Fe-Mn oxyhydroxide Pb decreased, compared to their initial fractions. The residual fractions of Ni and Cr were dominant, regardless of pH.Conclusions
The average concentrations of Cu, Zn, Cd, and Pb in sediments were highly elevated compared with the soil background values in Gansu Province, China. The results of this pH-dependent release experiment showed that the release behaviors of Cu, Zn, Pb, and Cr followed an asymmetric V-shaped pattern, whereas Cd and Ni followed an irregular L-shaped pattern. The changes in the release of heavy metals in sediments were related to their redistribution between chemical fractionations.11.
Interaction between dilute (mg L?1) NaF solutions and clay suspensions (0.08 % w/v) has been examined as a function of pH (range 3 to 8), clay type (Na+- or Ca2+-kaolinite, illite, montmorillonite) and NaF concentration. No F loss from solution was detected at pH > 6.5, while enhanced uptake was found on decreasing the pH, especially in the 4 to 3 region. Removal of F from 1 to 6 × 10?4 M NaF was only slightly dependent on weight of solid, but did increase with [F?]. It is proposed that F losses are due to the formation of sparingly soluble Al species (e.g. cryolite, Na fluoro silicate), occasionally augmented with CaF2 formation (Ca2+-clays). The Al is released by proton attack on the lattice, following conversion of the suspended solids into the unstable H+-form, either through acid addition (pH < 5) or through hydrolysis of the Na+-form material. The latter process was most pronounced with the illite and montmorillonite samples. The amount of F fixed by montmorillonite was roughly double that held by the other two clays, and had a maximum value (pH 3) of ~ 4 mg g?1, using 11 mg L?1 NaF solutions. Soluble fluoro-complexes, similar in quantity to the retained F, were detected, in many of the studies. It was concluded that contact of the clay components of soils or sediments with mg L?1 levels of F in adjacent aqueous phases would result in only a minor proportion being retained. 相似文献
12.
《Communications in Soil Science and Plant Analysis》2012,43(16):1913-1933
Rice is the staple food crop for about 50% of the world's population. It is grown mainly under two ecosystems, known as upland and lowland. Lowland rice contributes about 76% of the global rice production. The anaerobic soil environment created by flood irrigation of lowland rice brings several chemical changes in the rice rhizosphere that may influence growth and development and consequently yield. The main changes that occur in flooded or waterlogged rice soils are decreases in oxidation–reduction or redox potential and increases in iron (Fe2+) and manganese (Mn2+) concentrations because of the reductions of Fe3+ to Fe2+ and Mn4+ to Mn2+. The pH of acidic soils increased and alkaline soils decreased because of flooding. Other results are the reduction of nitrate (NO3 ?) and nitrogen dioxide (NO2 ?) to dinitrogen (N2) and nitrous oxide (N2O); reduction of sulfate (SO4 2?) to sulfide (S2?); reduction of carbon dioxide (CO2) to methane (CH4); improvement in the concentration and availability of phosphorus (P), calcium (Ca), magnesium (Mg), Fe, Mn, molybdenum (Mo), and silicon (Si); and decrease in concentration and availability of zinc (Zn), copper (Cu), and sulfur (S). Uptake of nitrogen (N) may increase if properly managed or applied in the reduced soil layer. The chemical changes occur because of physical reactions between the soil and water and also because of biological activities of anaerobic microorganisms. The magnitude of these chemical changes is determined by soil type, soil organic-matter content, soil fertility, cultivars, and microbial activities. The exclusion of oxygen (O2) from the flooded soils is accompanied by an increase of other gases (CO2, CH4, and H2), produced largely through processes of microbial respiration. The knowledge of the chemistry of lowland rice soils is important for fertility management and maximizing rice yield. This review discusses physical, biological, and chemical changes in flooded or lowland rice soils. 相似文献
13.
Groundwater samples were collected from shallow aquifers underneath an industrial complex in the Eastern Province of Saudi Arabia. Arsenic (As) concentrations in the groundwater samples varied between 10?8.6 and 10?6.8 M (0.18 and 11.14 µg L?1), with an average of 10?7.5 M (2.19 μ L?1). The analysis of variance for the analytical data showed that sampling locations had significantly affected As concentrations in the groundwater samples. Analytical and thermodynamic calculations showed that H2ASO4 ? was the most predominant As species in acidic groundwater samples, and HAsO4 2? was the most abundant species in alkaline groundwater samples. Concentrations of H3AsO4° and AsO4 3? were too low to be important in this study. Reduced As chemical forms were also expected to be very low. All the groundwater samples were undersaturated with respect to the thermodynamic solubility isotherms of Ca3(AsO4)2(c), Fe3(AsO4)2(c), and Mn3(AsO4)2(c) minerals. Lack of reliable thermodynamic data for these arsenates could be responsible for differences between the theoretical and measured concentrations of As in the shallow groundwater samples. The general trend in the distribution of HAsO4 2? activities in the groundwater samples was parallel to that of the Ca3(AsO4)2 solubility isotherm but different from those of Fe3(AsO4)2(c), and Mn3(AsO4)2(c). These data suggest that As concentrations in the groundwater samples were probably controlled by the precipitation and dissolution of Ca3(AsO4)2 type mineral. A three step hypothesis for As interactions in groundwater/soil system is proposed that combines both solid phase formation and adsorption of As onto the solid colloidal surfaces. This hypothesis is expected to better represent As behavior in groundwater/soil environment. 相似文献
14.
15.
Two acidic soils (initial pH, 4.6) with contrasting soil organic C (SOC) contents (11.5 and 40 g C kg?1) were incubated with 13C-labelled lime (Ca13CO3) at four different rates (nil, target pH 5, 5.8 and 6.5) and three application depths (0–10, 20–30 and 0–30 cm). We hypothesised that liming would stimulate SOC mineralisation by removing pH constraints on soil microbes and that the increase in mineralisation in limed soil would be greatest in the high-C soil and lowest when the lime was applied in the subsoil. While greater SOC mineralisation was observed during the first 3 days, likely due to lime-induced increases in SOC solubility, this effect was transient. In contrast, SOC mineralisation was lower in limed than in non-limed soils over the 87-day study, although only significant in the Tenosol (70 μg C g?1 soil, 9.15%). We propose that the decrease in SOC mineralisation following liming in the low-C soil was due to increased microbial C-use efficiency, as soil microbial communities used less energy maintaining intracellular pH or community composition changed. A greater reduction in SOC mineralisation in the Tenosol for low rates of lime (0.3 and 0.5 g column?1) or when the high lime rate (0.8 g column?1) was mixed through the entire soil column without changes in microbial biomass C (MBC) could indicate a more pronounced stabilising effect of Ca2+ in the Tenosol than the Chromosol with higher clay content and pH buffer capacity. Our study suggests that liming to ameliorate soil acidity constraints on crop productivity may also help to reduce soil C mineralisation in some soils. 相似文献
16.
Y. N. Zhu X. H. Zhang Q. L. Xie D. Q. Wang G. W. Cheng 《Water, air, and soil pollution》2006,169(1-4):221-238
The solubility and stability of calcium arsenates at 25 °C was determined by both precipitation and dissolution experiments. Ca3(AsO4)2? 3H2O(c), Ca3(AsO4)2? 21/4H2O(c), Ca5(AsO4)3(OH)(c) and Ca4(OH)2(AsO4)2? 4H2O(c) were identified in our experiment over a wide range of pH and for Ca/As molar ratios between 1.25 and 4.0. The solids precipitated at pH = 3 ~ 7 and Ca/As = 1.5 were phase-pure and well-crystallized Ca3(AsO4)2? xH2O(c) and had relatively larger grain size than those formed at pH > 7. Based on the analytical results and using the computer program PHREEQC, the solubility products for Ca3(AsO4)2? 3H2O(c), Ca3(AsO4)2? 21/4H2O(c), Ca5(AsO4)3(OH)(c) and Ca4(OH)2(AsO4)2? 4H2O(c) were calculated as K sp of 10? 21.14(10? 20.01 ~ 10? 22.02), 10? 21.40(10? 20.08 ~ 10? 21.98), 10? 40.12(10? 37.53 ~ 10? 42.72) and 10? 27.49(10? 26.10 ~ 10? 28.91), respectively. Correspondingly, the free energies of forming (Δ G f o ) of these calcium arsenates were calculated to be ?3787.87 kJ/mol, ?3611.50 kJ/mol, ?5096.47 kJ/mol and ?4928.86 kJ/mol. 相似文献
17.
A method for the measurement of Pb and Cd in equilibrium soil solutions involving soil equilibration with a dilute Ca electrolyte, centrifugation and filtration to <0.2 μm was evaluated. The procedure was subsequently used for the analysis of 100 Pb- and 30 Cd-contaminated soils. Solutions were analysed for Pb- and Cd using graphite-furnace AAS and the concentrations of Pb2+ and Cd2+ were estimated using standard speciation calculations. The concentrations of Pb and Cd found in the soil solutions were in the range 3.5–3600 μg dmp ?3 and 2.7–1278 μg dm ?3 respectively; both ranges represented less than 0.1% of the total metal concentration in the soils. Depending on solution pH, Pb +2 accounted for between 42–78% of Pb in solution while about 65% of Cd in solution was present as Cd+2. The concentrations of Pb2+ and Cd2+ in solution suggested that the soil solutions were undersaturated with respect to the solid phases PbC03 and CdC03 but supersaturated with respect to Pb5(P04)3Cl and, for some samples, Cd3(P04)2 respectively. However, for both metals, a good empirical relationship was obtained between the total metal concentration in soil (mol kg?1), free metal concentration in solution (mol dm?3) and solution pH. The relationships took the general form of a pH-dependent Freundlich adsorption equation: For both lead and cadmium relationships, the values ofn and K1 were close to unity, so that the distribution coefficient could be estimated from pH and a single metal-dependent constant, K2. The algorithms appeared to be valid over a metal concentration range of four logarithmic units and pH range of 3.5–7.5. 相似文献
18.
G. Brümmer 《Geoderma》1974,12(3):207-222
Results of laboratory experiments with soil material saturated with sea water indicate that, as predicted by thermodynamics, manganese (III, IV)-oxides are first reduced to Mn2+-ions (beginning at about +450 mV at pH 6.1.; E7 ≈ +400 mV), next amorphous iron (III)-oxides are reduced to Fe2+-ions (beginning at about +220 mV at pH 6.0; E7 ≈ +160 mV), and finally sulphates are reduced to sulphides (beginning at about +10 mV at pH 6.0; E7 ≈ -50 mV). Direct quantitative relations between redox potentials, pH-values and Mn2+- (or Fe2+-) contents of water-saturated soils and sediments and calculated redox reactions of known manganese and iron systems could not be established.The influence of organic redox systems produced by microbial fermentation processes on the measured potentials and on the reduction of manganese and iron oxides is discussed.A reduction of the oxides by microbially formed sulphides, which themselves are oxidized by this process, seems also to be possible. Therefore, sulphides do not occur as stable sulphur phase in higher amounts before all available Fe-oxides are reduced to Fe2+-ions. Then formation of iron monosulphides takes place by precipitation of Fe2+- ions by sulphides (H2S, HS). In a sulphide-stabilized environment redox reactions of sulphur — especially the reaction H2Saq = S0 + 2 H+ + 2 e? — may determined the measured potentials.The results show that the dynamics and morphology of hydromorphic soils and sediments are strongly dependent on microbial processes. 相似文献
19.
M. Simonsson 《European Journal of Soil Science》2000,51(4):655-666
Complexation with organic matter controls the activity of dissolved Al3+ in many soils. The buffering intensity of these soils is largely dependent on the H+/Al3+ exchange ratio, i.e. the number of protons consumed by the solid phase when one Al3+ is released. Here, the H+/Al3+ exchange ratio was determined from batch titrations using solutions of fulvic acid (FA) as a model for soil organic matter. Aluminium was added, from 1.04 to 6.29 mmol Al per g FA, which is within the range of humus‐bound Al found in the upper B horizon of podzolized soils. Furthermore, pH was varied with NaOH to give values between 3.5 and 5.0. The H+/Al3+ exchange ratio ranged between 1.49 and 2.23 with a mean of 1.94. It correlated positively with pH and the total concentration of Al present. Theoretically, this can be explained with a partial hydrolysis of bound Al. The slope of logAl (log10 of Al3+ activity) against pH generally underestimated the actual exchange ratio, which can partly be attributed to the systems being diluted (100 mg FA l?1). However, where 4 mmol Al or more had been added per g FA, the logAl slope gradually approached ?3 between pH 4.5 and 5.0. This might be the result of a shift from Al3+ activity control by humus complexation to control by Al(OH)3(s). 相似文献
20.
Solubility of a proto-imogolite sol in oxalate solutions 总被引:1,自引:0,他引:1
The amounts of aluminium liberated from a proto-imogolite (P-I) sol by 1–3 mM oxalate at pH 4·8–7·1 are found to be in excellent agreement with those calculated on the basis of the solubility product of the P-I sol, and the stability constants for aluminium oxalate complexes established earlier. Calculated solubility curves are presented for proto-imogolite sols in the presence of 10?3, 10?4 and 10?5 M total oxalate over the pH range 4–8, and also for the case where oxalate concentrations are controlled by solid calcium oxalate in the presence of 0·05, 0·5 and 5 mM calcium ion. We conclude that the presence of a proto-imogolite allophane in podzol B horizons of pH 5·0 requires oxalate concentrations less than 10?5 M. For fertile agricultural soils with typical calcium concentrations (approximately 5 mM) in the soil solution, aluminium oxalate concentrations would be limited by calcium oxalate solubility to less than 10?6 M in the presence of proto-imogolite allophane at pH values exceeding 5·5. In leached podzolic soils calcium concentrations are generally less than 0·05 mM, and would not limit the formation of aluminium oxalate complexes. 相似文献