Effect of the particle-size distribution on the adsorption of copper, lead, and zinc by Chernozemic soils of Rostov oblast

The parameters of adsorption of Cu²⁺, Pb²⁺, and Zn²⁺ cations by soils and their particle-size fractions were studied. The adsorption of metals by soils and the strength of their fixation on the surface of soil particles under both mono- and polyelement contamination decreased with the decreasing proportion of fine fractions in the soil. The adsorption capacity of the Lower Don chernozems for Cu²⁺, Pb²⁺, and Zn²⁺ depending on the particle-size distribution decreased in the following sequence: clay loamy ordinary chernozem ∼ clay loamy southern chernozem > loamy southern chernozem > loamy sandy southern chernozem. According to the parameters of the adsorption by the different particle-size fractions (C _max and k), the heavy metal cations form a sequence analogous to that obtained for the entire soils: Cu²⁺ ≥ Pb²⁺ > Zn²⁺. The parameters of the heavy metal adsorption by similar particle-size fractions separated from different soils decreased in the following order: clay loamy chernozem > loamy chernozem > loamy sandy chernozem. The analysis of the changes in the parameters of the Cu²⁺, Pb²⁺, and Zn²⁺ adsorption by soils and their particlesize fractions showed that the extensive adsorption characteristic, namely, the maximum adsorption (C _max), was a less sensitive parameter characterizing the soil than the intensive characteristic of the process—the adsorption equilibrium constant (k).     

Comparative analysis of mono- and polyelement adsorption of copper,lead, and zinc by an ordinary chernozem from nitrate and acetate solutions

Isotherms of mono- and polyelement adsorption of Cu²⁺, Pb²⁺, and Zn²⁺ by an ordinary chernozem were described by the Langmuir equation. The values of the adsorption constant k decreased in the range Cu²⁺ > Pb²⁺ ≫ Zn²⁺ for the monoelement adsorption from nitrate and acetate salt solutions, Cu²⁺ > Pb²⁺ > Zn²⁺ for the polyelement adsorption from nitrate solutions, and Pb²⁺ > Cu²⁺ ≫ Zn²⁺ for the polyelement adsorption from acetate solutions. The maximum adsorption (C _{max, ∞}) of individual cations at the polyelement contamination was always lower than at the monoelement contamination because of the mutual competition. At the same time, the values of k for the polyelement adsorption were higher than those for the monoelement adsorption because heavy metals (HMs) interact with most of the specific adsorption centers. It was shown that the ratio between the content of exchangeable cations displaced from the soil exchangeable complex (SEC) into the solution and the content of adsorbed HMs decreased with the increasing concentration of adsorbed HMs. These values could be higher (for Cu²⁺), equal, or lower than 1 (for Pb²⁺ and Zn²⁺). In the former case, this was due to the dissolution of readily soluble salts at low HM concentrations in the SEC. In the latter case, this was related to the adsorption of associated HMs and the formation of new phases localized on the surface of soil particles at high HM concentrations in the SEC.     

Adsorption features of Cu(II), Pb(II), and Zn(II) by an ordinary chernozem from nitrate,chloride, acetate,and sulfate solutions

The effect of Cl^?,SO ₄ ^2? , CH₃COO^?, and NO ₃ ^? anions on the adsorption of copper, lead, and zinc by an ordinary chernozem has been studied. The effect of the anions on the adsorption of Cu²⁺, Pb²⁺, Zn²⁺ ions is significant but uncertain. It has been shown that the attendant anions affect the shape of the adsorption isotherms, which are described by the Langmuir, Freundlich, or Henri equations. The constants of the adsorption from a nitrate solution calculated from the Langmuir equation (K _L) decrease in the following order: Cu²⁺ > Pb²⁺ >> Zn²⁺. The values of the maximum adsorption (C _max) decrease in the following order: Cu²⁺ ≥ Zn²⁺ > Pb²⁺ for acetate solutions and in the series Pb²⁺ > Zn²⁺ ≥ Cu²⁺ for nitrate solutions. The values of the Henry constants (K _H) calculated for the adsorption of the same cations from chloride solutions decrease in the same order as the values of K _L. The CH₃COO^? anion has the highest effect on the constant values. The NO ₃ ^? and Cl^? anions “switch their places” depending on the attendant cation, but their effect is always lower than that of the acetate anion. The values of C _max for copper and zinc are most affected by the CH₃COO^? anion, and the adsorption of zinc is most affected by the Cl^? and NO ₃ ^? anions. The assessment of the mobility of the adsorbed cations from the extraction with ammonium acetate (pH 4.8) has shown that the content of the desorbed metals is always lower than the content of the adsorbed cations and varies from 0.025 to 83%. According to their mobility, the adsorbed metals form the following order: Zn²⁺ > Pb²⁺ > Cu²⁺. The effect of the attendant anions on the extractability of the adsorbed cations decreases in the following order: chlorides > sulfates > acetates > nitrates.     

Cation activation of pyrophosphatases from soil microorganisms

The intracellular inorganic pyrophosphatases obtained from mixed cultures of soil microorganisms were characterised in terms of the activating cation and pH-activity profile. Microorganisms were grown in an initial culture 10 mm in tetrasodium pyrophosphate, a nutritionally non-specific aqueous medium, buffered at pH 7.0 with an organic buffer and inoculated with soil. The intracellular pyrophosphatases in a desalted, cell-free enzyme preparation were examined for activity in assays using 1 mM tetrasodium pyrophosphate and nine cations (Mg²⁺, Zn²⁺, Co²⁺, Mn²⁺, Fe²⁺, Ca²⁺, Cu²⁺, Al³⁺ and Fe³⁺) over the pH range 2–10, with appropriate buffers. Only the first 5 cations activated the enzymes. The pH-activity profiles for each cation were different and each displayed only one pH optimum. The pH optima were not greatly affected by cation concentration or kind of buffer. The specific activities at the optimum pH and cation concentration for each culture decreased in order Mg²⁺ > Zn²⁺ > Co²⁺ > Mn²⁺ > Fe²⁺. The results indicate the production of functionally similar enzymes by diverse microorganisms.     

恒电荷土壤胶体对Cu2+ 、Pb2+ 的静电吸附与专性吸附特征

供试土壤胶体对Cu2 、Pb2 的吸附强度用pH50 值表示 ,其大小次序为 :土 >黄绵土、黑垆土 >黄褐土。离子强度实验和表面络合反应机制证明恒电荷土壤胶体对Cu2 、Pb2 的吸附含有专性吸附 ,n值可作为判断专性吸附与静电吸附比例的特征值 ,低pH值时 ,以水解 -络合吸附为主 ;高pH值时 ,以水解 -络合与沉淀吸附为主。静电吸附和专性吸附的比例与pH有关 ,各土壤胶体专性吸附百分数大小为 :黄褐土 >土 >黑垆土 >黄绵土。不同土壤胶体在同一介质中对Cu2 、Pb2 的固有络合常数logKintM 值及固有络合ΔG m 负值大小次序与吸附强度大小一致。在定pH定浓条件下 ,考虑离子之间的相互作用时 ,土壤胶体对重金属离子的吸附过程可用BDM等温式描述。供试土壤胶体对Cu2 、Pb2 专性吸附ΔG m 的大小与固有络合ΔG m 接近且大小次序也一致。     

Sorption of Heavy Metals by Canola Meal

The results from this research indicate that canola meal (CM) can be used for adsorption of Zn²⁺, Cd²⁺, Cu²⁺, Pb²⁺and Ni²⁺from aqueous solutions. The order of sorption for these metals in single metal systems was as follows (molar basis): Zn²⁺> Cu²⁺> Cd²⁺> Ni²⁺> Pb²⁺. It was noted that a decrease in the concentration of CM caused a higher metal loading on the meal. Increases in the metal concentration, temperature or pH resulted in increased sorption of the metals by the meal. The systems with identical ratios of CM to Zn²⁺concentrations, regardless of their levels, resulted in the same amount of metal adsorbed per unit weight of meal. The Freundlich isotherm type model was used in this study and was found to fit the experimental equilibrium concentration data of Zn²⁺and Cd²⁺; however, the Langmuir isotherm model fit only the equilibrium data of Zn²⁺. Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) microanalyses revealed that the metal ions were sorbed mainly at the cell wall and only small amounts of ions diffused into the cytoplasm of the CM cells. The Electron Spin Resonance (ESR) tests were inconclusive regarding the direct participation of free radicals in copper sorption.     

KINETICS OF ION EXCHANGE IN SOIL ORGANIC MATTER. IV. ADSORPTION AND DESORPTION OF Pb2+, Cu2+, Cd2+, Zn2+ AND Ca2+ BY PEAT

The equilibria as well as the rates of adsorption and desorption of the ions Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ca²⁺ by soil organic matter were determined in batch experiments as a function of the amount of metal ions added to an aqueous suspension of HCl-washed peat. Simultaneous determination of the metal ions and hydrogen ions in the solution by atomic absorption spectrophotometry and pH-measurements showed that the adsorption of one divalent metal ion by peat was coupled with the release of two hydrogen ions. Since this equivalent ion-exchange process causes a corresponding increase of the electric conductivity of the solution, the rates of the adsorption and desorption processes were determined by an immersed conductivity electrode. The distribution coefficients show that the selective order for the metal adsorption by peat is Pb²⁺ > Cu²⁺ > Cd²⁺≌ Zn²⁺ > Ca²⁺ in the pH range of 3·5 to 4·5. The slope of -2, as observed in a double logarithmic plot of the distribution coefficients versus the total solution concentration confirms the equivalence of the ion-exchange process of divalent metal ions for monovalent H₃O⁺ -ions in peat. The absolute rates of adsorption, as well as the rates for the fractional attainment of the equilibrium, increase with increasing amounts of metal ions added. This behaviour is also observed for the subsequent desorption of the metal ions by H₃O⁺-ions. At a given amount of metal ions added, the absolute rates of adsorption decrease in the order Pb²⁺ > Cu²⁺ > Cd²⁺ > Zn²⁺ > Ca²⁺, while the rates for the fractional attainment of the equilibrium decrease in the order Ca²⁺ > Zn²⁺≌ Cd²⁺ > Pb²⁺ > Cu²⁺. The half times for adsorption and desorption were in the range of 5 to 15 sec.     

Chelating–Ultrafiltration Treatment of Some Heavy Metal Ions in Aqueous Solutions by Crosslinking Carboxymethyl Modified Cornstarch

Crosslinking carboxymethyl starch (CCMS) powder of degree of substitution (DS) 0.43–0.59 was prepared by the process of two steps of alkali addition synthesis. The technique of powder coupling with ultrafiltration was used to absorb Cu²⁺, Zn²⁺, Ni²⁺, Pb²⁺, and Cd²⁺ from aqueous solutions. FTIR was used to demonstrate the successfully grafting of carboxymethyl groups, and the technique of microwave plasma torch atomic emission spectrometer was applied in rapid determination of the aforementioned heavy metals ions. The results revealed that the removal sequence of heavy metal ions followed the order of Pb²⁺>Cu²⁺>Cd²⁺>Zn²⁺>Ni²⁺. By assistant of diethylene triamine penlaacetic acid, the quaternary system of Pb²⁺/Ni ²⁺/Cd²⁺/Cu²⁺ mixture solution could have the ideal separation. Besides, the influence of pH, ζ potential, DS value, and membranes molecular weight cut-off on removal of 20 mg L⁻¹ Pb²⁺ or Ni²⁺ was also investigated.     

Speciation of cadmium,copper, lead,and zinc in contaminated soils

Abstract

To investigate the activity of free cadmium (Cd²⁺), copper (Cu²⁺), lead (Pb²⁺), and zinc (Zn²⁺) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (Cd_T, Cu_T, Pb_T, and Zn_T, respectively), 0.43 MHNO₃‐extractable Cd, Cu, Pb, and Zn (Cd_N, Cu_N, Pb_N, and Zn_N, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca²⁺]. The activity of free Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L^‐1, Cu from 3.43 to 7.42 μg L^‐1, Pb from 1.23 to 5.8 μg L^‐1, and Zn from 24.5 to 34.3 μg L^‐. In saturation soil extracts, the activity of free Cd²⁺ ions constituted 42 to 82% of the dissolved fraction, for Cu²⁺the range was 0.1 to 7.8%, for Pb²⁺ 0.1 to 5.1% and for Zn²⁺2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd²⁺, Cu^2t, Pb²⁺, and Zn²⁺ ions.     

Infrared spectra of Cu2+ Pb2+ and Ca2+ complexes of soil humic substances

An infrared spectroscopic investigation of the complexes of Cu²⁺, Pb²⁺, and Ca²⁺ with humic and fulvic acids demonstrated the participation of OH and CO groups in addition to COOH in the binding of heavy-metal cations. The degree to which metal-carboxylate linkages are ionic or covalent cannot be accurately determined from the positions of antisymmetric and symmetric carboxylate stretching vibrations due to interference from covalent bonding with other groups. The apparent order of the reaction of three divalent cations with humic and fulvic acids was Cu²⁺ > Pb²⁺ > Ca²⁺.     

A Comparison of Inorganic Solid Wastes as Adsorbents of Heavy Metal Cations in Aqueous Solution and Their Capacity for Desorption and Regeneration

The adsorption capacity of seven inorganic solid wastes [air-cooled blast furnace (BF) slag, water-quenched BF slag, steel furnace slag, coal fly ash, coal bottom ash, water treatment (alum) sludge and seawater-neutralized red mud] for Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺ and Cr³⁺ was determined at two metal concentrations (10 and 100 mg?L^?1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All materials had the ability to remove metal cations from aqueous solution (fly and bottom ash were the least effective), their relative abilities were partially pH dependant and adsorption increased greatly with increasing pH. At equimolar concentrations of added metal, the magnitude of sorption at pH 6.0 followed the general order: Cr³⁺????Pb²⁺????Cu²⁺?>?Zn²⁺?=?Cd²⁺. The amounts of previously sorbed Pb and Cd desorbed in 0.01 M NaNO₃ electrolyte were very small, but those removed with 0.01 M HNO₃, and more particularly 0.10 M HNO₃, were substantial. Water treatment sludge was shown to maintain its Pb and Cd adsorption capability (pH 6.0) over eight successive cycles of adsorption/regeneration using 0.10 M HNO₃ as a regenerating agent. By contrast, for BF slag and red mud, there was a very pronounced decline in adsorption of both Pb and Cd after only one regeneration cycle. A comparison of Pb and Cd adsorption isotherms at pH 6.0 for untreated and acid-pre-treated materials confirmed that for water treatment sludge acid pre-treatment had no significant effect, but for BF slag and red mud, adsorption was greatly reduced. This was explained in terms of residual surface alkalinity being the key factor contributing to the high adsorption capability of the latter two materials, and acid pre-treatment results in neutralization of much of this alkalinity. It was concluded that acid is not a suitable regenerating agent for slags and red mud and that further research and development with water treatment sludge as a metal adsorbent are warranted.     

Removal of Copper,Lead, Methylene Green 5, and Acid Red 1 by Saccharide-Derived Spherical Biochar Prepared at Low Calcination Temperatures: Adsorption Kinetics,Isotherms, and Thermodynamics

Spherical biochar derived from saccharides (glucose, sucrose, and xylose) was prepared through two steps: pre-hydrothermal carbonization at 190 °C and calcination at low temperatures (200–325 °C). The spherical biochar was characterized by Brunauer–Emmett–Teller (BET) surface area analysis, Fourier transform infrared spectroscopy, zeta potential, scanning and transmission electron microscopies, and X-ray diffraction. The result indicated that the spherical biochar exhibited low S _BET (15–22 m²/g), but abundant superficial active oxygen-containing functional groups. The spherical biochar possessed a negatively charged surface within solution pH 2.0–11. The adsorption process of Pb²⁺, Cu²⁺, and methylene green 5 (MG5) was strongly dependent on the solution pH and reached fast equilibrium at approximately 60 min. The maximum Langmuir adsorption capacity (Q°_max) exhibited the following order: glucose-biochar > sucrose-biochar > xylose-biochar prepared at 300 °C. The selective adsorption order of glucose-biochar was Cu²⁺ (0.894 mmol/g) > Pb²⁺ (0.848 mmol/g) > MG5 (0.334 mmol/g). The electrostatic attraction played a determining role in the adsorption mechanism of pollutant cations. The adsorption of anionic dye (acid red 1) on the spherical biochar was negligible because of electrostatic repulsion. The spherical biochar can serve as a newer and promising adsorbent to remove toxic pollutant cations from water media.     

Effects of trace elements on urease activity in soils

Disposal of sewage sludges and effluents on agricultural land is becoming a widespread practice. Most sludge samples disposed on soils contain large quantities of various trace elements. Studies of 20 trace elements commonly found in sludge samples showed that they inhibit the activity of urease in soils and that their order of effectiveness as inhibitors of urease depends on the soil. When the trace elements were compared by using 5 μmiol·g^?1 soil, however, some of them showed the same order of effectiveness as urease inhibitors in the six soils studied i.e., for the monovalent and divalent ions, Ag⁺ ≥ Hg²⁺ >Cu²⁺ >Cd²⁺ >Zn²⁺ >Sn²⁺ >Mn²⁺, and generally, Fe²⁺ >Fe²⁺andCu²⁺ >Cu⁺. Other trace element ions that inhibited urease were Ni²⁺, Co²⁺, Pb²⁺, Ba²⁺, As³⁺ B³⁺, Cr³⁺, Al³⁺. V⁴⁺ Se⁴⁺ and Mo⁶⁺. Of the trace element ions studied, only As⁵⁺ and W⁶⁺ did not inhibit urease activity in soils.Studies on the distribution of urease activity showed that it is concentrated in surface soils and decreases with depth. Urease activity was proportional to organic C distribution in each soil profile and was significantly correlated with organic C in the surface soils studied.     

Formation of metal-humic acid complexes by titration and their characterization by differential thermal analysis and infrared spectroscopy

Humic acid (HA) extracted from a Eustis loamy sand (Psammentic Paleudult, Red Yellow Podzolic soil) was flocculated by titration with Al³⁺-, Fe³⁺-, Cu²⁺-, Zn²⁺-, Mn²⁺-, Ba²⁺-, Ca²⁺-, and Mn²⁺-chloride solutions, respectively, to determine possible development of metal-HA complexes, as reported by Flaig et al. (1975), and Tiurin and Kononova (1962). Titration was conducted with HA solutions with an initial pH 11.5 or 7.0. The results indicated that the cations used, except Mg²⁺, yielded insoluble complexes with HA, irrespective of initial pH. After titration, the pH of the metal-HA flocs was 6.0–7.0, which was expected in view of the presence of cation exchange and buffering capacity of HA compounds. More complex formation through electrovalent and covalent bonding by COO^? and phenolic OH groups of the HA molecule was only attained by the use of HA solutions with pH 11.5. On the other hand, less complex formation occurred by the use of HA solutions with an initial pH 7.0, through electrovalent bonding by COO^? groups. Differential thermal analysis (d.t.a.) curves of HA showed shifts in temperatures of the main decomposition peak as a result of flocculation with the different metals. Based on the type of the cations involved, the metal-humic acid flocs could be listed in the following decreasing order of thermal stability: Al³⁺ = Zn²⁺ = Mg²⁺ ≥ HA > Ca²⁺ > Ba²⁺ > Fe³⁺ > Cu²⁺ > Mn²⁺. A systematic relationship could not be found indicating that trivalent ions resulted in the formation of thermally less stable metal-humic acid flocs than divalent ions, as has been reported for HA-metal complexes. Physical mixtures of HA and metal hydroxides exhibited d.t.a. features resembling those of original (nontreated) HA, but not those of the HA-metal flocs.Infrared spectroscopy revealed increased absorption for COO^? vibrations at 1620 and 1400cm^?1 in spectrograms of metal-HA flocs compared to that of original humic acid, a phenomenon explained by many authors to be caused by bonding of the metal ions in hydrated form to the carboxyl or phenolic hydroxyl groups or both of the humic acid molecule. HA-flocs formed from solutions with an initial pH 11.5 had identical i.r. spectra compared with those formed from solutions with an initial pH 7.0.     

THE COMPLEXING OF COPPER BY HUMIFIED ORGANIC MATTER FROM LABORATORY PREPARATIONS, SOIL AND PEAT

The metal complexing properties of the colloidal and non-colloidal fractions of water extracts of peat and aerobically composted lucerne, and of chelating resin and alkali extracts of peat and soil organic matter were compared. The contributions of the non-colloidal fractions to the complexing properties of the whole extracts are considerable, and on a weight-for-weight basis are somewhat greater than that of the corresponding colloidal material. No one compound is preponderantly responsible for the complexing action. The complexing activity of the non-colloidal fractions is confined almost entirely to the acidic constituents. On the basis of the enhancement of the visible range of optical absorbance of the various preparations, Cu²⁺ is more extensively complexed than Mg²⁺, Mn²⁺, Cd²⁺, Zn²⁺, Co²⁺, Ni²⁺, and Pb²⁺.     

Activation of soil pyrophosphatase by metal ions

Inorganic pyrophosphatase activity in three soils decreased when exchangeable and soluble metals were removed by leaching with in NH₄OAc (pH 8). The effect of added metal ions at various concentrations in the leached soils showed that, at certain concentrations, Ba²⁺, Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ promoted, K⁺ and Na⁺ had no effect, and Fc²⁺ and Cu²⁺ decreased pyrophosphatase activity. At high concentrations (>50 mM). Co²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ inhibited pyrophosphatase activity in two soils. The concentration of metal ion needed for optimum activity of pyrophosphatase varied among the soils. The efficiency of the metal ions at optimum concentrations (average percentage increase for three soils in parentheses) in promoting pyrophosphatase was Ca²⁺ (47) > Mg²⁺ (42) > Ba²⁺ = Co²⁺ (29) > Ni²⁺ (27) > Zn²⁺ (20) > Mn²⁺(16). Pyrophosphatase activity in two leached soils adjusted to 50, 75, 100 or 150 mM PPi and Ca²⁺ or Mg²⁺ concentrations from 0 to 250 mM was at an optimum when the metal ion: PPi ratio was 1:1. Soil pyrophosphatase in the presence of 200 mM CaCl₂ or MgCl₂ was protected against inactivation by heat (90 C for up to 30 min).     

Adsorption of Heavy Metals on Mixed Fe-Al Oxides in the Absence or Presence of Organic Ligands

A study was carried out on the adsorption of Co²⁺, Cu²⁺, Pb²⁺, and Zn²⁺ ions on mixed Fe-Al oxides inthe absence or presence of increasing concentrations of oxalate or tartrate. Mixed Fe-Al oxides were prepared by precipitating at pH 5.5 mixtures of Fe and Al ions at initial Fe/Al molar ratios (R) of 0, 1, 2, 4, 10 and ∞ (R0, R1, R2, R4, R10 and R∞).The oxides aged 7 days at 20 °C or 30 days at 50 °C showed different chemical composition and physico-chemical and mineralogical properties. All the mixed Fe-Al oxides showed presence of poorly crystalline materials (ferrihydrite) even after prolonged aging. The heavy metals wereselectively adsorbed on the oxides. For all the precipitates aged7 days at 20 °C, the selectivity sequence wasPb²⁺> Cu²⁺ > Zn²⁺ > Co²⁺, but the pH at which 50% ofeach cation was adsorbed (pH₅₀) was different from sample tosample. It was found that usually the greater the amounts of Fe in Fe-Al gels the lower the pH₅₀ for each metal, but the adsorption of a heavy metal was not linearly related to Fe content. The pH₅₀ usually did not change significantly when the oxides were aged 30 days at 50 °C. Competitive adsorption of Cu and Zn on ferrihydrite (R∞) showed thatCu strongly prevented Zn adsorption even at an initial Zn/Cu molar ratio of 8, whereas Cu sorption was not inhibited. In thepresence of oxalate (OX) or tartrate (TR) (organic ligand/Pb molar ratio (r_L) from 0 to 7) the quantities of Pb adsorbedon the Fe-Al oxides usually increased with increasing r_L. The adsorption increase of Pb was particularly high on the oxidesricher in Fe (R4-R∞), but a significant increase was also observed on R0-R2 samples. The adsorption of Pb on the oxides hasbeen influenced not only by the presence and concentration of organic ligands but also by the sequence of addition of Pb and tartrate on the sorbents. It has been ascertained that on each oxide the greater amounts of Pb were adsorbed when tartrate wasadded before Pb and usually according to the following sequence: Tr before Pb > Pb before Tr > Pb + Tr > Pb.     

Ion exchange properties of humus acids

Ion exchange equilibriums in a complex of brown humic acids (HAs) and related fulvic acids (FAs) with cations (H⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺, Zn²⁺, Mn²⁺, Cu²⁺, Fe³⁺, and Al³⁺) have been studied, and the activity coefficients of the acid monoionic forms have been determined. The composition of the stoichiometric cell in the system of black and brown HAs and related FAs in a leached chernozem of the Ob’ region has been calculated with consideration for the earlier studies of the ion exchange properties of black HAs and related FAs. It has been shown that hydrogen, calcium, magnesium, aluminum, and iron are the major components in the exchange complex of humus acids in the leached chernozem with the other cations being of subordinate importance. In spite of some differences between the analytical and calculated compositions of the humus acids, the results of the calculations can be considered satisfactory. They indicate that calculations are feasible for such complex objects as soils, and their accuracy will improve with the expansion of the experimental studies. The physicochemical simulation of the transformation of the humus acid composition under different acid-base conditions shows that the contents of most cations decrease under alkalization, and hydroxides or carbonates become the most stable forms of these cations. Under the acidification of solutions, the binding of alkaline and alkaline-earth elements by humus acids decreases and the adsorption of iron and aluminum by humus acids increases.     

Interactions between montmorillonite and fulvic acid

The isotherms at 20°C for the adsorption of ¹⁴C-labelled fulvic acid from aqueous solutions by montmorillonite containing different exchangeable cations, have been determined. Below a concentration of 0.45 mg/ml and at near neutral pH, all samples give linear isotherms, the slope of which increases in the order Ba²⁺ < Ca²⁺ < Zn²⁺ < La³⁺ < Al³⁺ <Cu²⁺ < Fe³⁺. In the absence of interlayer expansion, the shape of the isotherms is interpreted in terms of solute entry into intercrystalline pores within a clay domain. The affinity of fulvic acid for the clay surface is related to the ionic potential or polarising power of the exchangeable cation. It is inferred that fulvic acid adsorbs by hydrogen bonding between an anionic group of the acid and a water molecule in the primary hydration shell of the saturating cation. Comparison of the data with those for the humic acid extracted from the same organic matter source, indicates that secondary interactions between adsorbed molecules or directly with the montmorillonite surface, contribute to the overall affinity. With samples saturated with Al³⁺, Fe³⁺, and Cu²⁺ ions, part of the adsorbed fulvic acid may also be attached to the clay by a complexation reaction involving the metals as such, or when they exist as polyhydroxy compounds at the mineral surface.     

ADSORPTION OF LEAD, COPPER, ZINC, COBALT, AND CADMIUM BY SOILS THAT DIFFER IN CATION-EXCHANGE MATERIALS

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.