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1.
砷是农田土壤重金属污染的主要元素之一,在砷污染农田土壤的修复过程中往往忽视纳米颗粒能够使结合态的砷重新释放,导致有效态砷浓度升高,探究土壤中黏土矿物对氧化石墨烯(Graphene Oxide,GO)和五价砷(As(V))在多孔介质中迁移行为的影响,对进一步完善农田土壤砷修复理论以及提高农作物产量、保护人体健康具有重要意义。该研究利用蒙脱石和高岭石改性石英砂,通过砂柱迁移试验系统地研究了GO、As(V)和GO-As(V)在填加0%、10%、30%和50%的蒙脱石和高岭石改性石英砂柱中的迁移行为。研究结果表明,随着高岭石和蒙脱石改性石英砂填加比例的增加,GO和As(V)的迁移能力均呈降低趋势,且GO和As(V)在不同条件下的迁移曲线均存在显著差异(P0.05);GO在50%高岭石和蒙脱石改性石英砂柱中的回收率相对于石英砂柱分别下降了14%和17%,As(V)分别下降了15%和12%;在共迁移试验中,GO和As(V)在石英砂柱中回收率分别上升至99%和100%。分析表明,As(V)在蒙脱石改性石英砂柱中的迁移能力大于高岭石改性石英砂,而GO与之相反;当GO和与As(V)共迁移时,二者在介质中的迁移能力均大于其单独迁移。本研究表明GO、As(V)释放到土壤后,能够加速As(V)的迁移,造成土壤砷污染的扩大化。  相似文献   

2.
Increasing the phosphorus (P) saturation of sandy soils may cause an increase in the rate of transport of dissolved P to groundwater. We hypothesize that by increasing sorption of P, soil colloids such as iron (Fe) oxides are also mobilized, because the adsorption of P causes the surface charge to become more negative, which increases the repulsive forces between the colloids and the sand grains, and between the colloids in suspension. Goethite particles adsorbed to fine quartz sand and precipitated goethite coatings on coarse quartz sand were used as model systems to test this hypothesis. Soil samples from a Cambisol Bw horizon and a Gleysol Bg horizon were also investigated. We conducted a series of batch experiments with increasing concentrations of ortho‐P and inositol hexaphosphate (IHP). The adsorption of P and the dispersion of colloids were determined by measuring P, Fe, aluminium and carbon concentrations in supernatants before and after ultracentrifugation. Dispersed colloids were characterized according to their optical density, zeta potential and particle size. The addition of P caused mobilization of goethite and soil colloids when a critical P saturation, corresponding to a zeta potential of about ?20 mV, was exceeded. To induce colloid mobilization in soils, one to two orders of magnitude larger equilibrium concentrations of dissolved P were necessary, compared with those required for the model systems. The adsorption of IHP reduced the zeta potential of colloids more effectively than the adsorption of ortho‐P per mol P. Environmentally significant concentrations of colloidal P (> 0.1 mg P litre?1) were released from soil samples at equilibrium concentrations of dissolved P < 0.1 mg P litre?1. We conclude that the sorption and accumulation of P in sandy subsoils that might occur as a result of excessive fertilization might induce the mobilization of colloids and colloidal P.  相似文献   

3.

Purpose

This study was conducted in order to examine the effect of colloidal particles on electrochemical properties of charged larger size materials.

Materials and methods

A self-made streaming potential apparatus was used to measure the zeta potentials of Fe/Al oxide-coated quartz. The effects of colloidal particles of kaolinite and montmorillonite on the electrochemical properties of Fe/Al oxide-coated quartz were investigated through comparing the difference in zeta potential of the coated quartz in electrolyte and clay suspension.

Results and discussion

The change of zeta potentials of the coated quartz, when clay suspensions flowed through, increased with the increasing concentrations of kaolinite and montmorillonite and degree of coating with Fe/Al oxides, and decreased with increased ionic strength of the suspensions. Electrostatic attraction between clay colloids and the coated quartz was the key factor influencing the interaction between the oppositely charged particles. The deposition of colloidal particles of kaolinite and montmorillonite on coated quartz and the overlapping of the diffuse layers of electrical double layers between the oppositely charged particles were responsible for the change in zeta potential of Fe/Al oxide-coated quartz. The relative contribution of the deposition of clay particles to the change in zeta potential was greater than that of the overlapping of diffuse layers.

Conclusions

When clay suspensions flowed through the saturated sand of Fe/Al oxide-coated quartz, both overlapping of diffuse layers between charged sand and clay particles and deposition of clay particles contributed to change of zeta potential of the coated quartz.
  相似文献   

4.

Purpose

Colloid migration in subsurface environments has attracted considerable attention in recent years because of its suspected role in facilitating transport of strongly adsorbed contaminants to groundwater. The influence of bulk solution pH or ionic strength on model colloid (i.e., latex microsphere, amorphous silica colloids) transport is well established, while little attention has been paid to water-dispersible soil colloids. In this study, saturated packed columns were conducted to explore the mechanism of transport and fate of water-dispersible soil colloids and facilitating transport of Cu during transients in solution chemistry.

Materials and methods

Water-dispersible soil colloids were fractionated from a Cu-contaminated soil sample. Transport of soil colloidal suspensions was conducted with varying pH and ionic strengths, and then, re-entrainment of those retained colloids after completion the transport experiments was conducted by changing pore water solution transient ionic strength and pH conditions. Meanwhile, transport and fate of the Cu strongly adsorbed on the soil colloids were determined under different ionic strength conditions.

Results and discussion

The transport behavior of soil colloids in porous media was found to depend on the pH and ionic strengths of bulk solution. An increase in solution ionic strength and decrease in solution pH resulted in greater deposition which was revealed by the collision efficiency (??). It increased from 0.15 to 1.0 when solution composition changed from 0 to 50?mM NaNO3 and decreased dramatically from 1.0 to 0.035 as the solution pH converted from 2.97 to 8.94. The results were in agreement with Derjaguin?CLandau?CVerwey?COverbeek theory. Upon stepwise reduction in ionic strength of eluting fluid or enhancement in its pH, a sharp release of colloids retained in the column occurred in each step. Meanwhile, the value of FRE NaOH that reveals the effect of NaOH solution at pH?11 on the mobilization of retained colloids deposited in the primary minimum increased from 38.6% to 64.6% when the ionic strength of bulk solution changed from 0 to 50?mM NaNO3 and decreased from 86.7% to 35.8% as the solution pH from 2.97 to 8.94. In addition, the transport and fate of the Cu strongly adsorbed on soil colloids were highly consistent with the results of soil colloids.

Conclusions

The colloid collision efficiency (??) decreased as the pH of bulk solution increased and increased as the ionic strength of bulk solution increased in saturated columns packed with pure quartz sand, and NaOH solution at pH?11 poses a predominant role on mobilization of the retained colloids deposited in the primary minimum. Meanwhile, the strongly adsorbed Cu on soil colloids almost cannot be detached from its carrier under the competition of coexisted cations in the bulk solution and cotransport with its carrier under different ionic strengths.  相似文献   

5.
Sorption of antibiotics to clay minerals is a key process controlling their transport and fate in environment. In this study, the effects of pH, ionic strength, and Cu(II) on ofloxacin (OFL) sorption to kaolinite were investigated by batch sorption experiments. The results of sorption edge experiments suggested that OFL sorption to kaolinite was pH and ionic strength dependent. Cation exchange was a major contributor to the sorption of OFL+ to kaolinite. The decreased OFL sorption with increasing ionic strength indicated the formation of outer-sphere complexation. When solution pH was lower than 7.0, Cu-OFL complexes facilitated OFL sorption through electrostatic attraction or formation of kaolinite-Cu-OFL and kaolinite-OFL-Cu ternary surface complexes. However, existence of free Cu(II) cation in solution competed for sorption sites, and thus suppressed OFL sorption. When solution pH was higher than 7.0, Cu(II) existed as Cu(OH)2, and the Cu-OFL complexes in aqueous phase and solid phase (precipitation) enhanced OFL removal efficiency from solution. The results imply that Cu(II) effects should be taken into account in the evaluation of OFL mobility in environment.  相似文献   

6.
孔隙空间对聚苯乙烯胶体滞留与释放的影响   总被引:1,自引:0,他引:1  
为加深孔隙空间对胶体运移影响的认识,在不同pH与离子强度下,研究了胶体在经酸洗或水洗后的玻璃珠或石英砂中的迁移行为。结果表明:粒径相同的玻璃珠与石英砂(0.45~0.60mm)相比,形状一致的玻璃珠形成的孔隙空间(孔隙率0.38)小于石英砂(0.45)。酸洗与水洗后的玻璃珠表面成分变化不大(0~0.6%),经酸洗的介质后能提供更多有利吸附位点。在高pH(10)环境下,石英砂经酸洗或水洗后,胶体滞留量增大(72.1%和69.2%)。提高溶液pH到10后出现的胶体吸附增加,是颗粒接触点、非流动区或低流速区和涡流区滞留等孔隙空间滞留机制引起的,用DLVO理论无法解释。在离子强度为0.001mol/L或0.05mol/L环境下,酸洗石英砂中胶体滞留量比酸洗玻璃珠的分别高16.3%和28.0%,表明介质孔隙空间增大可加强颗粒接触点、非流动区或低流速区和涡流区滞留,然而优先流能够削弱孔隙空间滞留机制对胶体的滞留。此外,超纯水解吸时仅使少量胶体(3.9%)从玻璃珠与石英砂介质的孔隙涡流区中解吸出来,表明涡流区对胶体的保留不是胶体滞留在介质中的主要机制。  相似文献   

7.
胶体颗粒对不同粒径饱和多孔介质渗透性的影响   总被引:1,自引:0,他引:1  
探讨胶体颗粒在多孔介质中迁移所发生的物理、化学及生物作用过程,在许多学科中具有重要的科学意义。采用室内石英砂柱实验,开展了定水头条件下不同浓度和粒径的胶体颗粒在饱和多孔介质中的运移行为研究。共使用了3种胶体粒径、3种浓度的胶体溶液和3种粒径范围的石英砂。实验表明:多孔介质的相对渗透系数K/K0(K为各时刻计算所得的渗透系数,K0为初始渗透系数)减小程度与颗粒浓度成正比;胶体颗粒越大,越易在表层沉积,而小颗粒易向下部迁移,但总体来看粒径效应没有浓度效应明显;当胶体颗粒在不同粒径的饱和多孔介质中迁移时,粒径大的多孔介质各段K/K0均有明显降低,而粒径小的只在表层变化明显。不同条件下总体相对渗透系数与时间之间呈二次方相关关系,但当多孔介质粒径较小时,相关性不显著。介质渗流流速及砂柱不同位置胶体颗粒浓度变化与介质渗透性变化相对应。用扫描电镜(Scanning Electron Microscope,SEM)进行定性表征,进一步说明胶体颗粒会堵塞多孔介质孔隙影响其渗透性。实验中发现当输入浓度C0小于0.5 g·L–1且dp/Dp>0.018(dp为胶体颗粒粒径,Dp为石英砂算数平均粒径)时,会出现多孔介质局部K/K0增大的现象。  相似文献   

8.

Potentiometric and ion-selective electrode titrations together with batch sorption/desorption experiments, were performed to explain the aqueous and surface complexation reactions between kaolinite, Pb, Cd and three organic acids. Variables included pH, ionic strength, metal concentration, kaolinite concentration and time. The organic acids used were p-hydroxybenzoic acid, o-toluic acid, and 2,4-dinitrophenol. Titrations were used to derive previously unavailable aqueous conditional stability constants for the organometallic complexes. Batch results showed that aqueous lead-organic complexation reduced sorption of Pb by kaolinite. Cadmium behavior was similar, except for 2,4-dinitrophenol, where Cd sorption was increased. Metal sorption increased with increasing pH and decreasing ionic strength. Distribution ratios (K d 's) decreased with increasing solid/solution ratio. The subsurface transport of lead and cadmium may be enhanced via complex interactions with organic wastes or their degradation products and sorbent mineral surfaces.

  相似文献   

9.
采用室内砂柱模拟试验方法研究了红壤和黑土两种土壤胶体对草萘胺在砂质土柱中迁移的影响。结果表明,整个淋滤过程中红壤和黑土胶体的回收率比较高,分别达到66.76%和74.75%;胶体促进了草萘胺在砂质土柱中的迁移,与对照相比(无胶体),加入红壤和黑土胶体后草萘胺的回收率分别提高了9.82%和10.63%。但是吸附在胶体上迁移的草萘胺数量比较少,只占到迁移总量的1.15%(红壤)和1.68%(黑土),物理非平衡机制可能在迁移过程中起支配作用。  相似文献   

10.
ABSTRACT

Veterinary antibiotics can enter the environment especially agricultural soils via animal manure application in which Sulfadiazine (SDZ) is considered as one of the most used antibiotic. After soil application, it may be transported into subsurface water. The sorption behavior of SDZ is not only influenced by the soil type but also by soil organic matters as well. Hence, an experiment was executed aimed to study sorption/desorption processes of SDZ under experimental conditions in three various soils treated by different bio fertilizers including rice husk compost (RHC), rice husk biochar (RHB) and Micrococcus yunnanensis (My) bacterium. Sorption/desorption data of soils with and without bio-fertilizers were well fitted with Freundlich model (R2 = 0.97). Results showed that bio-amended soils had higher values of kd sorption ranged from 1.16 to 52.4 without and with bio-fertilizers application respectively, proposing low sorption of SDZ with substantial risk of leaching without bio-fertilizers application. Also for the desorption cycle values of Kd increased from 1.03 to 39.1 without and with bio-fertilizers application, respectively. Furthermore, there was a hysteresis effect using organic matter. As a result of bio-fertilizers application, a significant value of SDZ was strongly adsorbed on the soil particles which was not desorb through desorption process.  相似文献   

11.
Fluoride (F) sorption by acidified montmorillonite, montmorillonite and kaolinite has been investigated as a function of period of agitation, pH, initial fluoride concentration and clay amount. In case of montmorillonite and kaolinite, F sorption is insignificant at pH > 7, while it is maximum at pH 4. Enhanced F sorption by acidified montmorillonite is noted at pH < 10, maximum being at pH 6. Significant concentration of Al3+,Fe3+ and silica are released from acidified montmorillonite lattice (pH ≈ 2; 1:10 w/v), which decreased considerably owing to the formation of hydroxy (Al and Fe) silicates on subsequent base addition. Soluble fluoro-complexes at pH ≈ 2 and chemical interaction of F with hydroxy (Al and Fe) silicates at pH > 4, are potent sink for F in case of acidified montmorillonite. Soluble fluoro-complexes are also detected in case of montmorillonite and kaolinite at pH ≈ 4. Saturation indices (SIs) for acidified montmorillonite, over the studied pH range (2–10) has also been computed.  相似文献   

12.
唐嘉  朱曦  刘秀婷  张烨坤  田锐  李航 《土壤学报》2020,57(2):381-391
土壤胶体是土壤具备肥力与生态功能的物质基础,土壤胶体凝聚与分散影响着土壤中一系列微观过程和宏观现象。采用动态光散射技术比较研究三种碱金属阳离子(Li+、Na+、K+)引发不同类型黏土矿物(2︰1型蒙脱石和1︰1型高岭石)胶体凝聚中的Hofmeister效应。研究发现,Li+、Na+、K+作用下蒙脱石、高岭石胶体的凝聚速率、临界聚沉浓度及活化能都存在明显差异,表现出强烈的Hofmeister效应。当电解质浓度为20 mmol·L–1时,K+引发蒙脱石胶体凝聚的速率为66.61 nm·min–1,远高于Na+、Li+引发蒙脱石胶体凝聚速率(5.93、4.41 nm·min–1);而与之对应的临界聚沉浓度则呈现K+(蒙脱石21.8 mmol·L–1、高岭石34.6 mmol·L–1)低于Na+(蒙脱石57.6 mmol·L–1、高岭石85.8 mmol·L–1)低于Li+(蒙脱石81.8 mmol·L–1、高岭石113.9 mmol·L–1)规律,胶体凝聚中活化能可合理解释此现象。电解质浓度为25 mmol·L–1时,Li+、Na+、K+引发蒙脱石、高岭石胶体凝聚的活化能分别为1.97 kT、1.43 kT、0 kT和2.94 kT、1.71 kT、0.49 kT,说明蒙脱石、高岭石胶体凝聚过程中Hofmeister效应序列均为Li+相似文献   

13.
Sorption of chlorpyrifos to selected minerals and the effect of humic acid   总被引:3,自引:0,他引:3  
Sorption of chlorpyrifos (CPF) from 2.85 microM (1 mg/L) aqueous solutions in 0.01 M NaCl to montmorillonite, kaolinite, and gibbsite was investigated at 25 degrees C. Uptake of CPF by kaolinite and gibbsite was generally <10%, with pH having at most a small effect. Sorption to montmorillonite was significantly greater, with approximately 50% of the initial CPF being removed from solution below pH 5. Above pH 5 the sorption decreased to about 30%. About 70% of CPF was sorbed to kaolinite and gibbsite after 30 min, whereas on montmorillonite only 50% sorbed in an initial rapid uptake (approximately 30 min) followed by slower sorption, with a maximum achieved by 24 h. Although CPF desorbed completely from kaolinite in methanol, only about two-thirds was desorbed from montmorillonite. CPF has only a weak affinity for the surfaces of kaolinite and gibbsite. In the case of montmorillonite, sorption is significantly stronger and may involve a combination of sorption to external surfaces and diffusion into microporous regions. At pH >6 increased negative surface charge results in a lower affinity of CPF for the external surface. In the presence of 50 mg/L humic acid (HA) the amount of CPF sorbed on gibbsite and kaolinite was 3-4 times greater than that in the binary systems. The HA forms an organic coating on the mineral surface, providing a more hydrophobic environment, leading to enhanced CPF uptake. The HA coating on montmorillonite may reduce access of CPF to microporous regions, with CPF tending to accumulate within the HA coating.  相似文献   

14.
Colloids can play an important role in the leaching of lead (Pb) in soils, and liming to increase pH may produce conditions conducive to colloid release. We studied the effect of pH and the role of counterion valency on the mobilization of Pb in two topsoil horizons of a former shooting range. In batch experiments, the release of both dissolved and colloidal Pb was studied at a pH range between 3 and 7. The pH was adjusted with solutions of nitric acid (pH 3) and KOH and Ca(OH)2 (pH 4–7) and the chemical composition, size and charge of the mobilized colloids were determined. In the presence of the monovalent K+‐ion concentrations of colloidal and dissolved Pb increased markedly with increasing pH. Colloids were stabilized not only by electrostatic but also by steric repulsion. Organic colloids seem to dominate at low pH of the KOH‐treatment; at pH > 4 mineral particles were also dispersed. Even though the presence of the Ca2+ ion reduced the concentrations of colloidal Pb more than did the K+ ion, our results of the Ca(OH)2 treatment show that the relevance of both colloidal and dissolved Pb increases at a pH of about 5.8. Risk assessment on limed sites should therefore take into account both dissolved and colloidal Pb in judging the likelihood of Pb leaching.  相似文献   

15.
The formation features of nanoadsorption polyelectrolyte (PE) layers with the formation of a mineral-organic matrix on the surface of clay minerals and soils (kaolinite, montmorillonite, quartz sand, gray forest soil, and chernozemic soil) have been elucidated by direct adsorption measurements. It has been found that the experimental values for the limit adsorption of polyacrylamide (PAM) and polyacrylic acid (PAA) on all the minerals are significantly higher than the calculated values for the formation of a monolayer. This indicates adsorption on the surface of not only separate macromolecules but also secondary PE structures as packets or fibrils determining the cluster-matrix structure of the modified surface. The study of the electro-surface properties (electrophoretic mobility, electrokinetic potential, pH, and electroconductivity) of mineral and soil particles adsorption-modified with PEs has confirmed the differences in the adsorption mechanisms (from physical sorption to chemisorption) with the formation of surface compounds depending on the different polar groups of PEs and the mineral type.  相似文献   

16.
The effect of Rhodopseudomonas pallustris bacterium on the sorption of 16 isotopes of lanthanides by quartz and goethite at different pHs values was studied. pH of sorption solution and affinity of elements to surface seems to be most important parameters in the interactions between metal ions and surfaces of biological and mineral sorbents. At acidic (pH°4) and neutral (pH°7) conditions these interactions was affected by electrostatic forces; at alkaline conditions (pH°9) the mechanism of lanthanides precipitation was dominant. Microorganisms sufficiently affected on lanthanides sorption by quartz at acidic and neutral conditions, but largest one was at pH°7. They increased sorption of all elements by goethite at pH°4. There was negligible effect of bacteria on the sorption of lanthanides at pH°7 and 9 by goethite that demonstrates greater affinity of the elements to goethite surface. Microorganisms increased concentration of lanthanides in the nonexchangeable states on the surfaces of quartz at pH°7 and 9, and on the surface of goethite at pH°7 in comparison to the minerals alone. It may be attributed to formation of low-soluble complexes of lanthanides with organic substances, produced by bacterium.  相似文献   

17.
The pedogenic horizons of nine profile pits dug across three toposequences were studied to determine the soil mineralogical characteristics and its implications on sustainable management of the fertility of some tropical Alfisols in Nigeria. Results showed that the epipedon which were predominantly ochric had textures that ranged from sand to sandy loam, while the subsurface (B/Bt) horizons had sandy clay loam to sandy clay texture and were gravelly (31.79–83.04%). The soil reaction ranged from strongly acid to neutral (pH 5.10 to 7.05). Calcium and magnesium dominated the exchange sites and accounted for about 75% of the exchangeable bases. Illite/mica and kaolinite were the dominant minerals in the clay fractions, while quartz, mica, and feldspars dominated the fine sand and silt fractions of the soils. While the presence of illite and mica could be important for potassium nutrition in these soils, kaolinite and oxides of iron could also cause phosphorus fixation.  相似文献   

18.
Abstract

Manganese (Mn) in soils occurs mainly as hydrous oxides in the form of nodules, concretions or coatings on the surface of soil particles playing an important role in the retention of nutrients or heavy metals. Boron (B) is one of these elements found to be fixed by Mn‐oxides in a relatively available form. This research was conducted to study B sorption by Mn‐oxides prepared in the laboratory in relation to soil pH. Two Mn‐oxides were prepared as coatings on the surface of quartz sand, pyrolusite and birnessite. Boron sorption experiments carried out with uncoated sand (US), pyrolusite‐coated sand (PS), and birnessite‐coating sand (BS) showed that B sorption was increased in PS and BS in comparison to US. Total B sorption was greater on BS than PS and BS sorbed more unrecoverable B by dilute hydrochloric acid method. In US and PS, B sorption was linearly increased with pH. In BS, maximum B sorption occurred at pH 8.5. The operating mechanisms seems to be H bonds between boric acid and OH groups in pyrolusite and lingand exchange between borate and surface hydroxyls in birnessite.  相似文献   

19.
Adsorption and desorption of salmon sperm DNA on four different colloidal fractions from Brown Soil and clay minerals were studied. The adsorption isotherms of DNA on the examined soil colloids and minerals conformed to the Langmuir equation. The amount of DNA adsorbed followed the order: montmorillonite?fine inorganic clay>fine organic clay>kaolinite>coarse inorganic clay>coarse organic clay. A marked decrease in the adsorption of DNA on organic clays and montmorillonite was observed with the increase of pH from 2.0 to 5.0. Negligible DNA was adsorbed by organic clays above pH 5.0. As for inorganic clays and kaolinite, a slow decrease in DNA adsorption was found with increasing pH from 2.0 to 9.0. The results implied that electrostatic interactions played a more important role in DNA adsorption on organic clays and montmorillonite. Magnesium ion was more efficient than sodium ion in promoting DNA adsorption on soil colloids and minerals. DNA molecules on soil colloids and minerals were desorbed by sequential washing with 10 mM Tris, 100 mM NaCl and 100 mM phosphate at pH 7.0. A percentage of 53.7-64.4% of adsorbed DNA on organic clays and montmorillonite was released, while only 10.7-15.2% of DNA on inorganic clays and kaolinite was desorbed by Tris and NaCl. The percent desorption of DNA from inorganic clays, organic clays, montmorillonite and kaolinite by phosphate was 39.7-42.2, 23.6-28.8, 29.7 and 11.4%, respectively. Data from this work indicated that fine clays dominate the amount of DNA adsorption and coarse clays play a more important role in the binding affinity of DNA in soil. Organic matter may not favor DNA adsorption in permanent-charge soil. The information obtained is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil.  相似文献   

20.

Purpose

Colloid-facilitated transport of metals is widely observed while manure is used for the improvement of contaminated soil. Details on the mechanism of colloid-associated metal transport are still lacking. This work investigated the nature of water-dispersible colloids (WDC) from different organic manures, differentiated the significance of clay and organic colloids in the metal transport, and finally provided direct and quantitative evidence for the importance of WDC in the colloid-facilitated transport of metals.

Materials and methods

Column experiments were conducted to assess the overall significance of WDC from effective microbial inoculated manure (EM) and leaf mulch (LM) for metal transport in alkali-contaminated soil. The properties of organic colloids such as hydrophilicity, aromaticity, and functional characteristics were analyzed by DAX-8 resin column, specific UV absorbance, and Fourier-transform infrared spectroscopy, respectively. Colloid identification and metal species determination were conducted using a combination of X-ray absorption near-edge structure, X-ray fluorescence spectroscopy, and transmission electron microscopy coupled with energy-dispersive X-ray analysis.

Results and discussion

Approximately 100 % of Pb, 69 % of Zn, and 38 % of Cu in the colloidal particles came from soil clay in the presence of EM colloids, while more than 80 % of Pb, Zn, and Cu in the LM colloids. Combined with the quantities of colloidal metals, it revealed that clay release was inhibited in the former and enhanced in the latter. The quantities of Cu and Zn associated with the EM colloids were much higher than that with the LM colloids. The contrary result was observed for Pb. LM colloids increased the quantities of organically associated Pb significantly.

Conclusions

Clay-associated metal transfer was influenced by the nature of WDC. Microbial manure colloids inhibited the clay-associated transfer of metals in the soils probably due to the presence of polysaccharide and microbially derived extracellular proteins. Leaf mulch colloids, with more hydrophobicity and aromaticity, enhanced the clay-facilitated transfer of metals in the soils.
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