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1.
Soil chemical properties are affected significantly by surface charge characteristics of the soil. Interaction between oppositely charged particles in variable‐charge soils plays an important role in variation of soil electrochemical properties. In this study, the effects of Al oxides on surface charge and acidity properties of kaolinite and an Alfisol during electrodialysis were investigated. The results indicated that Al oxides, when mixed into kaolinite or the Alfisol, decreased the effective cation exchange capacity (ECEC) and exchangeable acidity and inhibited the decrease in pH. Gibbsite had less effect than γ‐Al2O3 and amorphous Al(OH)3 in reducing the ECEC and acidity of kaolinite and the Alfisol; γ‐Al2O3 and amorphous Al(OH)3 displayed comparable effects. However, this effect is inconsistent with the order of the surface positive charge per unit mass that the Al oxides carried. Their effect on the ECEC of kaolinite and Alfisol varied irreversibly with ionic strength of the bathing solutions. X‐ray diffraction spectra indicated that amorphous Al(OH)3 and γ‐Al2O3 were more effective than gibbsite in decreasing peak intensity of electro‐dialyzed kaolinite when mixed with these Al oxides at the same rate. The results demonstrated that Al oxides could decrease the effective negative charge and inhibit acidification of kaolinite and an Alfisol through diffuse‐double‐layer overlapping between oppositely charged particles and coating of Al oxides on these materials. Both mechanisms intensified with increasing rate of added Al oxides, which can therefore act as anti‐acidification agents in variable‐charge soils.  相似文献   

2.
The controls of soluble Al concentration were examined in three situations of acid sulfate conditions:1) experimental acid sulfate conditions by addition of varying amounts of Al(OH)3(gibbsite) into a sequence of H2SO4 solutions;2)experimental acid sulfate conditions by addition of the same sequence of H2SO4 solutions into two non-cid sulfacte soil samples with known amounts of acid oxalate extractable Al; and 3) actual acid sulfate soil conditions.The experiment using gibbsite as an Al-bearing mineral showed that increase in the concentration of H2SO4 solution increased the soluble Al concentration,accompanied by a decrease i the solution pH, Increasing amount of gibbsite added to the H2SO4 solutions also increased soluble Al concentration,but resulted in an increase in solution pH.Within the H2SO4 concentration range of 0.0005-0.5mol L^-1 and the Al(OH)3 range of 0.01-0.5g(in 25 mL of H2SO4 solutions),the input of H2SO4 had the major control on soluble Al Concentration and pH .The availability of Al(OH)3，however,was responsible for the spread fo the various sample points,with a tendency that the samples containing more gibbsite had a higher soluble Al concentration than those containing less gibbsite at equivalent pH levels.The experimental results from treatment of soil samples with H2SO4 solutions and the analytical results of acid sulfate soils also showed the similar trend.  相似文献   

3.
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   

4.
Apparent cation–exchange equilibria and solubility of aluminium were analysed in two acidic forest soils: a Cambisol and a Cambic Podzol. Soil solution was obtained by a centrifuge drainage method from fresh soil samples and with suction lysimeters. The total positive charge of the measured cations as well as the concentrations of the cations were generally much larger in the centrifugates than in the lysimeter solutions, which implies that total charge of soil solution is larger in small pores than in large pores. Hydrogen ion in particular was concentrated in some of the centrifugates, the ratio centrifugate:lysimeter solution being over 10. The total positive charge of the measured cationsdecreased with increasing depth with both methods. Theapparent cation–exchange coefficients K H-Ca, K Al-Ca, and K K-Ca had different values in the methods, and the variation in the cation exchange coefficients was larger in the lysimeter method than in the centrifuging method. The coefficient K Mg-Ca had similar values in both methods. The results imply that mobile solution could not have cation–exchange equilibria with bulk exchangeable cations in the soils, although solution in small pores seemed to have equilibria. Solubility of Al did not follow the solubility of an Al(OH)3 phase in the centrifugates, and the centrifugates with a H+ activity larger than 60 μmol were undersaturated with respect to the gibbsite. Solubility of Al was between gibbsite and amorphousAl(OH)3 in the lysimeter solutions. Differencesbetween the centrifugates and the lysimeter solutionsin the ion concentrations and in the apparent chemicalequilibria were similar for both soils studied.  相似文献   

5.
Clay–Al hydroxide polymer systems (CAlHO) can bind heavy metals effectively. Their adsorption behaviour depends on the type of metal. We studied the dependence of Al‐loading and pH on the adsorption of Pb to Na‐saturated montmorillonite–Al hydroxide polymer systems. The available binding sites on the Al hydroxide polymers (AlHO) had a strong affinity for Pb ions, whereas a minor amount of Pb was bound to the clay surface. The pH had a pronounced effect on the Pb binding to the AlHO. At pH 6.0, AlHO effectively adsorbed Pb. The amount of Pb adsorbed to the AlHO, expressed per mole Al, increased with increasing amount of AlHO fixed. Lead bound to the AlHO could easily be removed by exchange and is therefore reversibly bound to the AlHO. Probably, Pb is outer‐sphere bound to the AlHO and an electrostatic bonding mechanism is involved. At pH 5.0 there was almost no adsorption of Pb to the AlHO, and the adsorption of Pb to the clay surface was limited because Al3+ ions competed with Pb2+ for exchangeable sites. At pH 6.6 and relatively large Pb concentrations, separate precipitates of Pb(OH)2 and Al(OH)3 were formed. Results from experiments in pure clay systems suggest that the Pb(OH)2 precipitate was present as positively charged Pb polymers.  相似文献   

6.
Abstract

Solubility and kinetic data indicated that concentrations of aluminum (Al) extracted with 1 M KCl are determined by the solubility of a precipitated A1(OH)3 phase in soils dominated by variable charge minerals. Kinetic studies examining the release of Al on non‐treated and KCl treated residues indicated the precipitation of an acid‐labile Al phase during the extraction procedure. The log ion activity products estimated for the KCl extracts ranged between 8.1–8.6 for the reaction Al(OH)3 + 3H+ < = > Al3++ 3H2O, which was similar to the solubility product of several Al(OH)3phases. The mechanism proposed for Al precipitation indicated that Al released by exchange with added K+ hydrolyzed and released H+ that was readily adsorbed on surfaces of variable charge minerals. The increased ionic strength of the extracting solution further increased the amount of H+adsorbed to the variable charge surface and reduced the H+ concentration in the aqueous phase. Consumption of H+ induced further hydrolysis of Al, resulting in supersaturation of the extracting solution and formation of polynuclear hydroxy Al species. It was concluded that the 1 M KCl extraction does not quantitatively extract salt exchangeable Al from variable‐charge soils.  相似文献   

7.
We experimentally determined the adsorption characteristics of natural, freshly precipitated Al(OH)3 for SO4 and PO4. The fresh Al precipitate occurred in stream sediment of Jachymov Stream (Czech Republic). The Al-rich sediment strongly adsorbed added PO4 prior to acidification experiment; this sorbed PO4 was released only after substantial dissolution of the sediment, at pH?<?3.67. Sorption of P by Al(OH)3 appears to be an important control on dissolved PO4 concentration in surface waters, unless there is a large excess of PO4. Acidification of the sediment-solution system caused protonation of the sediment surface, thereby increasing the adsorption capacity for SO4. Maximum SO4 adsorption occurred at pH 4.2, below which dissolution of the sediment offset the increasing anion adsorption capacity, and formation of AISO4 + inhibited the increasing SO4 adsorption capacity. This research demonstrates that there are important pH thresholds for anion adsorption in freshwaters below which dissolution of the Al(OH)3 substrate reduces total capacity for anion adsorption. In freshwaters, with sufficient concentrations of suspended Al(OH)3, or in Al(OH)3-rich sediment, PO4 mobility will be severely restricted. Suspended Al(OH)3 in acidified surface waters cannot strongly influence SO4 concentrations because of the considerably higher total SO4 concentrations compared to the available surface area.  相似文献   

8.
Conductimetric titrations, with NaOH, of solutions containing Al ion detect two OH-ions of Al in the acid range, with OH/Al ratios of ions such as Al(OH)2+ and A16(OH)3+15; in the alkaline range aluminate Al(OH)?14 is formed. Similar titrations of an Al-kaolin, prepared by acid washing, give results that can be adequately interpreted in terms of these three ions, i.e. by the reaction with alkali of Al3+ ions balancing the permanent isomorphous replacement charge. If there are reactions with alkali at the edge-faces of the kaolin, e.g. the neutralization of residual positive edge-charge, these edge-charges must be small in comparison with the permanent charge. Bonding by the complex ion Al6(OH)3+15, formed on the surfaces of clay particles, explains why the viscosity of Al clays is greatest at the five-sixths stage of neutralization, because the formation of the hydroxide Al(OH)3 is theoretically equivalent to the measurement of the permanent charge.  相似文献   

9.
Potassium (K) and nitrogen (N) are essential nutrients for plants. Adsorption and desorption in soils affect K+ and NH + 4 availabilities to plants and can be affected by the interaction between the electrical double layers on oppositely charged particles because the interaction can decrease the surface charge density of the particles by neutralization of positive and negative charges. We studied the effect of iron (Fe)/aluminum (Al) hydroxides on desorption of K+ and NH + 4 from soils and kaolinite and proposed desorption mechanisms based on the overlapping of diffuse layers between negatively charged soils and mineral particles and the positively charged Fe/Al hydroxide particles. Our results indicated that the overlapping of diffuse layers of electrical double layers between positively charged Fe/Al hydroxides, as amorphous Al(OH) 3 or Fe(OH) 3 , and negatively charged surfaces from an Ultisol, an Alfisol, and a kaolinite standard caused the effective negative surface charge density on the soils and kaolinite to become less negative. Thus the adsorption affinity of these negatively charged surfaces for K+ and NH + 4 declined as a result of the incorporation of the Fe/Al hydroxides. Consequently, the release of exchangeable K+ and NH +4 from the surfaces of the soils and kaolinite increased with the amount of the Fe/Al hydroxides added. The greater the positive charge on the surfaces of Fe/Al hydroxides, the stronger was the interactive effect between the hydroxides and soils or kaolinite, and thus the more release of K+ and NH + 4 . A decrease in pH led to increased positive surface charge on the Fe/Al hydroxides and enhanced interactive effects between the hydroxides and soils/kaolinite. As a result, more K+ and NH + 4 were desorbed from the soils and kaolinite. This study suggests that the interaction between oppositely charged particles of variable charge soils can enhance the mobility of K+ and NH + 4 in the soils and thus increase their leaching loss.  相似文献   

10.
Monomeric silica solutions were mixed with solutions containing AlCl3, or Al(OH)2-55Cl0-45 to give a SiO2/Al2O3, ratio varying from 8 to 8.0 and were kept at pH 6–0, 7.0, or 8.0 over a period of about I year. All precipitates which formed from solutions with SiO2/Al2O3 ratios of 1–0 or higher were X-ray amorphous. The SiO2/Al2O2, ratio of the precipitate varied in the range from 1.0 to 3.0. It increased with the Si concentration and the SiO2/Al2O3 ratio of the parent solution and with reaction time. The pH did not affect the SiO2/Al2O3 ratio of the precipitate but did affect its dispersion and flocculation. Al3+ and Al(OH)2.55+0.45 reacted differently with silica and yielded different reaction products. These differences were interpreted in terms of the stability of hydroxy-Al polymer units in the reaction. The amount of NaOH per Al atom which was required to reach and maintain the same pH, increased with the increasing SiO2/A12O ratio of the precipitate, but the value was generally lower than that predicted from ‘one in four’ substitution of Si by Al in four-fold co-ordination. A ‘neutralization’ of the positive charge on the hydroxy-Al cations by silica was pointed out also to be a cause of the extra acidity. Implications of these observations on synthetic amorphous aluminosilicates to the genesis, structure, and properties of their natural counterparts were discussed.  相似文献   

11.
Using a soil from a newly reclaimed area where high dispersibility of fine particles had led to poor physical properties in the field, changes in dispersibility and charge characteristics after artificial precipitation of Al hydroxides onto the soil were investigated. Al hydroxides were precipitated by neutralization with NaOH of an acidic A1C13 solution in which the soil samples were placed.

When the titration rates were changed, no significant differences in dispersibility were observed in the resultant soils. In the systems with the addition of 2 g kg-1 or less of A1(OH)3, dispersion ratios of clays were almost identical with those of blank samples although the specific surface areas were reduced. In the systems with 5 g kg-1 or more of A1(OH)3, considerable effects of Al hydroxides on reduction of clay dispersibility were recognized (e.g. 10 g kg-1 addition yielded less than one-third of the original ratio of the clay dispersion). A slightly larger decrease in dispersion was observed by the addition of 15 g kg-1 or more. As the amount of added Al increased, the amount of negative charges of the soil decreased while that of positive charges increased. The charge characteristics of the system with the addition of 20 g kg-1 of A1(OH)3 were closer to those of the adjacent forest soil which was characterized by a very low dispersibility. It was inferred that added Al hydroxides polymerized to form Al polycation species that were not readily exchangeable, neutralizing negative charges of clays, and acting as interparticle bonding between the clays. On the other hand, forest soils were considered to have acquired a physical stability against the dispersion of fine particles as free Al oxides had been accumulated in the process of natural weathering. It was concluded that charge characteristics primarily determined the dispersion and flocculation behavior of soils and that Al hydroxides were important modifiers of charge characteristics of soils.  相似文献   

12.
Although the increased mobilization of aluminum from soils to surface waters is widely recognized as one of the most important ecological effects of acidic deposition, lumped-parameter mathematical models of acidification response typically overestimate the change in Al concentration under changing deposition by a considerable margin. The assumption of equilibrium with gibbsite (Al(OH)3) in the MAGIC model and other models of acid-base chemistry is shown to be inconsistent with measured values for a large variety of lake and stream databases. A modified algorithm for predicting Al concentration, based on empirical relationships evident in field data, provided superior estimates of changes in Al concentration in three long-term monitoring data sets and under experimental conditions at two experimental watershed manipulation sites.  相似文献   

13.
Sorption and desorption characteristics of four organic phosphates (OPs) with different molecular sizes and structures (glycerophosphate, GP; glucose‐6‐phosphate, G6P; adenosine triphosphate, ATP; myo‐inositol hexakisphosphate, IHP) and inorganic phosphate (Pi) on three aluminium (Al) (oxyhydr)oxides (amorphous Al(OH)3, boehmite and α‐Al2O3) were investigated. The maximum sorption amounts of OPs and Pi increased with decreasing crystallinity of the minerals on a per mass basis: α‐Al2O3 < boehmite < amorphous Al(OH)3. With an exception of IHP sorption on amorphous Al(OH)3, the maximum surface area‐based sorption densities increased with decreasing molecular weight (MW) of OPs and Pi: IHP < ATP < G6P < GP < Pi. Despite having the largest MW, IHP had greater sorption amounts on amorphous Al(OH)3 than the other OPs because of the transformation of surface complexes to surface precipitates. Sorption kinetics of OPs was first a rapid sorption followed by a long and slow sorption process. Of the three Al (oxyhydr)oxides, amorphous Al(OH)3 had the greatest first rapid sorption density and initial sorption rate of OPs within 5 minutes, both factors decreasing with increasing MW of OPs. The initial desorption percentages of OPs by KCl generally increased with decreasing MW of OPs, whereas the maximum desorption percentages of OPs by citrate were four to five times those achieved with KCl. Overall, strong specific sorption of OPs occurs on the surface of Al (oxyhydr)oxides, and molecular structure and size of OPs, as well as crystallinity and crystal structure of the minerals, are the key factors affecting the interfacial reactions and environmental behaviour of OPs.  相似文献   

14.
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   

15.
Reaction of Ca-Montmorillonite and Ca-Vermiculite with CO2 The treatment of Ca-montmorillonite and Ca-vermiculite with carbonic acid (Pco2 = 2 atm) has shown the following results: In the pH range of ± 3.9–6.0 Ca is exchanged by H directly only on pH dependent (variable) charge sites (Cav), whereas, Ca on permanent charge sites (Cap) is exchanged only by lattice cations mainly Al released by proton attack. Therefore, with regard to proton uptake from carbonic acid the two Ca-clays behave as extremely weak acids. The exchange of Cav proceeds rapidly that of Cap much more slowly, the first one is essentially reversible the latter at least not within a short period of time. The proportion of Cav is found from a graphical extrapolation of the Ca saturation-pH-function (fig. 3). Al released during the initial stage of the reaction is non exchangeable, prevents the expandable minerals partly from collapsing on K tratement (verm. much more than mont.) and has an OH/Al ratio of about 2. On treating the same clay sample several times or at low suspension concentrations exchangeable Al with OH/Al = O occurs. Exchangeable hydrogen was never detected. Vermiculite is less resistent against carbonic acid than montmorillonite. The results were discussed in respect to the mechanism of release of lattice constituents and in respect to Al release under the influence of CO2-concentrations of soils.  相似文献   

16.
A. Violante  P. Violante 《Geoderma》1978,21(2):147-159
In synthetic chlorite-like complexes, amounts of amorphous and/or crystalline hydrous aluminum oxide were determined through use of H-bentonite that converts into Albentonite by reaction with Al-gel or gibbsite. In Al(OH)x-complexes with less than 1,000 mequiv. of Al per 100 g of clay, hydrous aluminum oxide gel remains held on clay surfaces without crystallizing for a long time. The neutralization reaction between a one-symmetry-concentration of H-bentonite and chlorite-like complexes at 10°C is initially very fast and seems to affect exclusively the hydrous oxide in suspension or adsorbed on the external surfaces and edges of clay particles. After a few hours, the interlayer Al-gel begins to be neutralized and the reaction rate decreases according to first-order kinetics. In complexes of equal ages, more time is required to neutralize the hydrous oxide precipitated in the presence of clay than added to the clay, because of a different interlayering.The kinetics of reactions between complexes characterized by amorphous and crystalline aluminum hydroxide (more than 1,000 mequiv. aluminum per 100 g of clay) and H-bentonites were studied. H-bentonite reacts with gibbsite much more slowly than it does with amorphous forms, always according to first order kinetics.  相似文献   

17.
A computer simulation was done to illustrate how the equilibrium solubility and speciation of Al in well-aerated soil solutions may be affected by pH (from 2.0 to 10.0), organic acids (citric, oxalic, phthalic, and salicylic acid), metal ions (K, Mg, Ca, Al, Fe), inorganic ligands (F, OH, SO4, PO4, CO3, and SiO3), and type of Al-containing solid [kaolinite, gibbsite, or amorphous Al(OH)3] thought to be present. The simulation indicated that the type of Al-oxide/hydroxide considered has a substantial influence on the inorganic and organic equilibrium composition of the soil solution, and on the occurrence (or non-occurrence) of other Al-minerals such as KA13(SO4)2(OH)6 (alunite) and Al(SO4)(OH)-5H2O (jurbanite).  相似文献   

18.
The hydrous oxides of Mn, Fe, and Al avidly sorbed Sb from μM Sb(OH), solutions, with uptake levelling off as initial Sb concentration increased. Capacity values decreased along the sequence MnOOH > Al(OH)3 > FeOOH. The amount sorbed by each substrate decreased gradually at pH values > 6. Addition of 0.4M CH3COONa to the aqueous phase (to minimise retention of weakly bound Sb) had little effect on MnOOH uptake capacity (～160 mmol, kg?1 at pH < 7) but retention dropped rapidly at higher pH. With the other two substrates (pH 6–7) the calculated capacity values for specific Sb sorption were ～ 45 mmol kg?1 FeOOH and ～ 33 mmol kg? Al(OH)3; about a third of the total capacity values. On these substrates specific Sb sorption tended to peak in the pH 7 to 8 region. The pH response pattern was modified using Sb tartrate sorbate solutions. Factors influencing Sb sorption included substrate surface charge, chemical form of Sb and surface interactions. Formation of a sparingly soluble metal coating was indicated by the uptake plateaus observed when increasing amounts of solid were added to Sb solutions containing acetate.  相似文献   

19.

Purpose

The purpose of this study was to elucidate the mechanisms for pectin-enhanced adsorption of heavy metal cations on variable charge minerals.

Materials and methods

Batch experiments were conducted to investigate the adsorption of pectin and copper(II) by amorphous Fe/Al hydroxides. The morphology, mineralogy, and functional groups of pectin–Fe/Al hydroxides were examined using X-ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy analysis.

Results and discussion

The amount of pectin adsorbed by amorphous Al(OH)3 was much greater than that by amorphous Fe(OH)3 at pH values between 3.5 and 6.5 due to the higher positive charge density on Al(OH)3 and greater electrostatic attraction between the hydroxide and pectin compared with Fe(OH)3. The addition of pectin decreased the positive surface charge on amorphous Fe and Al hydroxides. The presence of pectin enhanced the adsorption of Cu(II) by the Fe and Al hydroxides. The increase in Cu(II) adsorption on amorphous Fe hydroxide was more obvious at low pH values than at higher pH values, while an opposite changing trend was observed for amorphous Al hydroxide. At pH 3.9, 4.3, and 4.9, pectin increased Cu(II) adsorption by Fe hydroxide from 24.4, 76.6, and 177.0 mmol/kg to 61.6, 98.8, and 192.0 mmol/kg, i.e., Cu(II) adsorption was increased by 37.2, 22.2, and 15.0 mmol/kg, respectively. At pH 4.3 and 4.9, pectin increased Cu(II) adsorption by Al hydroxide from 3.7 and 27.0 mmol/kg to 17.3 and 69.4 mmol/kg, i.e., Cu(II) adsorption was increased by 13.6 and 42.4 mmol/kg, respectively. The greater adsorption of pectin by Al hydroxide was mainly responsible for the larger enhancement of pectin on Cu(II) adsorption on Al hydroxide at higher pH values compared with Fe hydroxide.

Conclusions

The adsorption of pectin on Fe and Al hydroxides decreased the positive charge on the hydroxides and thus enhanced the adsorption of Cu(II) by the hydroxides.
  相似文献   

20.
Suspensions of Al(OH)3 gel, gibbsite or alumina were loaded with varying amounts of Cu, Cd, Zn, or Pb ions by varying the system pH. A complex relationship between metal uptake and equilibrium pH was noted (due to substrate buffering) but total loss of metal ion from solution was observed at pH > 6.5. The pre-loaded particles were back-extracted with fifteen different chemical solutions and the percentage of sorbed ion retrieved generally varied along the sequence NaCl, CaCl2 < MgCl2, NH4NO3 < CH3OOONH4, Na citrate, Na4P2O7, EDTA, DTPA ≈ CH3OOOH, H2C2O4, HCI, HN03. The recovery value varied with initial surface loading and an observed minimum around 1 gruel M2+ per 20 mg solid is considered to reflect changes in metal species nature (e.g., bonded M2+, MOH+, precipitated M(OH)2) and substrate surface charge. In the ‘minima’ region less than 10% of metal ion was displaced by many reagents. With different loadings up to 40% was displaceable by salts (i.e., weakly sorbed) while acids or complex formers at times released over 90 % of the pre-sorbed metal species. It was concluded that the degree of metal ion interaction varied with the initial system pH, with retention being due to a combination of weak adsorption, occlusion in gels, chemi-sorption and precipitation of M(OH)2.  相似文献   

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