The Adsorption Behavior of Pb<Superscript>2+</Superscript> and Cd<Superscript>2+</Superscript> in the Treated Black Soils with Different Freeze-Thaw Frequencies

Batch experiments were conducted to study the effect of freeze-thaw frequency on the adsorption behavior of Pb²⁺ and Cd²⁺ and its related mechanisms. The results indicated that the adsorption capacities of Pb²⁺ and Cd²⁺ to the freeze-thaw treated soil were lower than those to the unfrozen soil, and with increasing freeze-thaw frequency, the adsorption capacities of them decreased. These were attributed to the fact that freeze-thaw cycles reduced pH value, CEC, organic matter content, and free iron oxide content of soil, and these soil properties presented negative correlations with freeze-thaw frequency. Freeze-thaw cycles reduced specific adsorption capacities of Pb²⁺ and Cd²⁺ and enhanced nonspecific adsorption ratios of Pb²⁺ and Cd²⁺ compared with the unfrozen soil. The higher freeze-thaw frequency, the higher nonspecific adsorption ratio was. However, the relationship between specific adsorption capacities of Pb²⁺ and Cd²⁺ and freeze-thaw frequency was opposite. Furthermore, the adsorption processes to the unfrozen and freeze-thaw treated soils were spontaneous, for Pb²⁺, its adsorption to soil was endothermal process, for Cd²⁺, on the contrary.     

Two-stage Batch Adsorber Design: A Time-Dependent Langmuir Model for Adsorption of Pb2+ and Cd2+ onto Modified Kaolinite Clay

The kinetics of the adsorption of Pb²⁺ and Cd²⁺ by sodium tetraborate (NTB)-modified kaolinite clay adsorbent was studied. A one-stage and two-stage optimization of equilibrium data were carried out using the Langmuir and time-dependent Langmuir models, respectively. Increasing temperature was found to increase the pseudo-second order kinetic rate constant and kinetic data for Pb²⁺ adsorption were found to fit well with the pseudo-second order kinetic model (PSOM) while that for Cd²⁺ were found to show very good fit to the modified pseudo-first order kinetic model (MPFOM). Binary solutions of Pb²⁺ and Cd²⁺ reduced the adsorption capacity of the modified adsorbent for either metal ion with increased initial sorption rate due to competition of metal ions for available adsorption sites. The use of NTB-modified kaolinite clay adsorbent reduces by approximately 72.2% and 96.3% the amount of kaolinite clay needed to adsorb Pb²⁺ and Cd²⁺ from wastewater solutions. From the two-stage batch adsorber design study, the minimum operating time to determine a specified amount of Pb²⁺ and Cd²⁺ removal was developed. The two-stage batch adsorption process predicted less than half the minimum contact time to reach equilibrium in the one-stage process for the adsorption of Pb²⁺ and Cd²⁺ by NTB-modified kaolinite clay adsorbent and requires 0.05 times the mass of the adsorbent for the single-stage batch adsorption at the same operating conditions.     

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.     

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.     

Enhanced Adsorption of Metal Ions Onto Polyethyleneimine-Impregnated Palm Shell Activated Carbon: Equilibrium Studies

In this study, palm shell activated carbon was impregnated with polyethyleneimine (PEI) and the effect of impregnation on batch adsorption of Ni²⁺, Cd²⁺or Pb²⁺ as well as the equilibrium behavior of adsorption of metal ions on PEI-impregnated AC were investigated. PEI impregnation evidently increased the single metal adsorption capacities of Ni²⁺ or Cd²⁺except for Pb²⁺, where its adsorption capacities were reduced by 16.67% and 19.55% for initial solution pH of 3 and 5 respectively. This suggested that PEI-impregnated AC could be used for selective separation of Pb²⁺ ions from other metal ions. The adsorption data of all the metal ions on both virgin and PEI-impregnated AC for both initial solution pH of 3 and 5 generally fitted the Langmuir and Redlich-Peterson isotherms considerably better than the Freundlich isotherm.     

The solid solution equilibria of lead and cadmium in polluted soils

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.     

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.     

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.     

重金属和pH值对类芦种子萌发的影响

类芦(Neyraudia reynaudiana)是一种具有极强耐干旱、贫瘠、高温等逆境的多年生禾草植物,是南方水蚀荒漠化地区、采矿采石厂及各类边坡植被自然恢复中的先锋植物。为探索在各类矿区及受重金属污染的地区采用类芦进行生态修复的可行性,通过室内发芽试验,对类芦种子在Hg2+,Cr6+,Cd2+,Pb2+,Zn2+,Cu2+等6种重金属离子胁迫及不同pH值条件下的萌发能力进行了研究。结果表明,类芦种子在pH值为5.0~9.0的范围内具有良好的萌发能力;6种重金属离子随着处理浓度的升高,对类芦种子的抑制作用逐渐加强,且出现显著抑制作用的最低浓度顺序为:Cd2+Cu2+Hg2+,Zn2+,Cr6+Pb2+;6种重金属对类芦种子活力指数出现显著影响的浓度均较显著影响发芽率、发芽势和发芽指数3个指标的浓度低,说明类芦幼苗生长比种子萌发对6种重金属更加敏感。     

Heavy Metal Uptake by Rape

Abstract

In pot experiments, the effect of single and combined pollution of soil by lead (Pb), cadmium (Cd), and zinc (Zn) and uptake of heavy metals in Brassica napus L. were investigated. There were two main factors that affected the assimilation of Pb, Cd, and Zn by rape: (i) level of soil pollution by the particular element and (ii) the combined influence of Pb, Cd, and Zn. In general, with the increase of the concentrations of Pb, Cd, and Zn in the soil, there were increases in the concentrations of those elements in the roots, stems, and seeds. The main part of the Pb and Zn amounts taken up by the roots from the soil are fixed and accumulated in the roots, and small amounts of them move through the conductive system to the seeds. Cadmium moves relatively easily from root to stem and is accumulated in higher concentrations in the top of the plant.

There is a well‐expressed synergistic interaction between Pb²⁺ and Cd²⁺, as well as of Cd²⁺ and Zn²⁺. Zinc has a highly depressing effect on the assimilation of Cd²⁺, as does Pb²⁺ on the assimilation of Zn²⁺. The combined pollution by Pb, Cd, and Zn stimulated the assimilation of these elements by the roots and foliage and eliminated the effect of Zn²⁺ on Cd²⁺ and of Pb²⁺ on Zn²⁺.     

Partial Nitritation-Anammox Granules: Short-Term Inhibitory Effects of Seven Metals on Anammox Activity

The inhibitory effect of seven different metals on the specific anammox activity of granular biomass, collected from a single stage partial nitritation/anammox reactor, was evaluated. The concentration of each metal that led to a 50% inhibition concentration (IC₅₀) was 19.3 mg Cu⁺²/L, 26.9 mg Cr⁺²/L, 45.6 mg Pb⁺²/L, 59.1 mg Zn⁺²/L, 69.2 mg Ni⁺²/L, 174.6 mg Cd⁺²/L, and 175.8 mg Mn⁺²/L. In experiments performed with granules mechanically disintegrated (flocculent-like sludge), the IC₅₀ for Cd⁺² corresponded to a concentration of 93.1 mg Cd⁺²/L. These results indicate that the granular structure might act as a physical barrier to protect anammox bacteria from toxics. Furthermore, the presence of an external layer of ammonia oxidizing bacteria seems to mitigate the inhibitory effect of the metals, as the values of IC₅₀ obtained in this study for anammox activity were higher than those previously reported for anammox granules. Additionally, the results obtained confirmed that copper is one of the most inhibitory metals for anammox activity and revealed that chromium, scarcely studied yet, has a similar potential inhibitory effect.     

可变电荷土壤和矿物Pb2+ and Cu2+吸附动力学: Ⅶ. Pb2+吸附后H+释放的动力学

The kinetics of H⁺ releasing after Pb²⁺ adsorption was studied by the potentiometric method combined with the acid-base titration curve technique. Results showed that pH of latosol, red soil and kaolinite suspensions dropped sharply, and then decreased gradually. Most of the H⁺ exchanged, more than 60%, was displaced at the first minute after Pb²⁺ was added into the suspension. More H⁺ was released at a higher concentration of Pb²⁺ added for a given sample and the amount of H⁺ released decreased in the order of red soil > latosol > kaolinite at a given concentration. The time-dependent data of H⁺ releasing of latosol, red soil and kaolinite at two concentrations could be fitted best with the second-order equation among the six equations, including second-order equation, two-constant equation, Elovich equation, parabolic diffusion equation, first-order equation and exponential equation. The H⁺/Pb²⁺ exchange stoichiometry increased with time, and a stable ratio of H⁺/Pb²⁺, being 1.73, 1.92 and 2.01 for kaolinite, latosol and red soil, respectively, was reached 25 minutes later.     

Effects of Graphene Oxide and/or Cd<Superscript>2+</Superscript> on Seed Germination,Seedling Growth,and Uptake to Cd<Superscript>2+</Superscript> in Solution Culture

With increasing graphene oxide (GO) applications in industry and biomedicine, effects of GO on microorganisms, animals, and human health have been frequently studied; however, direct and indirect effects of GO on plants are seldom concerned. In this study, effects of GO and/or Cd²⁺ on seed germination, seedling growth, and uptake to Cd²⁺ were investigated in solution culture. The results showed that GO could quickly adsorb Cd²⁺ in solution, and the higher the GO concentration was, the lower the residual Cd²⁺ concentration was in solution. Rice seed germination, seminal root length, and bud length decreased with increasing GO and Cd²⁺ concentrations respectively, while the presence of GO could alleviate the inhibitive effects of Cd²⁺ on seminal root and bud growth compared with the single Cd²⁺ treatment. In maize seedling, fresh weights of shoot and root showed similar responses to the presence of Cd²⁺ and/or GO. Compared with the single Cd²⁺ treatment, root Cd concentrations were generally increased by GO in high Cd²⁺ solution (20 mg/L), while were slightly affected by GO in low Cd²⁺ solution (5 mg/L) independent of GO concentrations except for 100 mg/L GO. Shoot Cd concentrations were decreased by low GO (100 mg/L) while were increased by high GO (>?500 mg/L) independent of Cd²⁺ concentrations in solution. Moreover, significant interactive effects of GO and Cd²⁺ on root and shoot Cd concentrations were observed. This study indicates that GO can change the effects of Cd²⁺ on seed germination, seedling growth, and uptake to Cd²⁺ in solution through its adsorption on Cd²⁺.     

Heavy Metal and Nutrient Ion Accumulation by Two Black Gram Cultivars Treated with Copper and Lead

ABSTRACT

A pot experiment was conducted to examine the uptake of nutrients (K⁺ (potassium) and Ca²⁺ (calsium)) and heavy metal (Cu²⁺ (copper) and Pb²⁺ (lead)) ions by leaves, seeds, and roots of two black gram [Vigna mungo (L.) Hepper] cultivars, ‘Mash-95018’(V₁) and ‘Mash-97’(V₂) treated with copper (Cu) and lead (Pb) at 25mg L^?1 and 50mg L^?1. This study was conducted in a greenhouse in the Botanical Garden, University of Agriculture, Faisalabad, Pakistan, during the spring of 2003. Heavy-metal treatments were applied 30 d after germination, and nutrient and heavy-metal ion uptake data were collected 10 d after treatment application. Both heavy metals in both cultivars substantially reduced nutrient ion accumulation and its translocation to seeds. Leaves had proportionately more K⁺ and Ca²⁺ than that recorded for roots and seeds after heavy-metal treatments. Nevertheless, both heavy metal (Cu²⁺ and Pb²⁺) ions ware predominantly sequestered in the roots, rather than in leaves and seeds, under their respective treatments. As the external concentrations of heavy metals increased, their uptake by the respective treated plants also increased, but nutrient ion (K⁺ and Ca²⁺) uptake was gradually reduced. This result suggests a concentration-dependent phenomenon. Overall, lead (Pb²⁺) showed more toxic effects on the uptake of essential nutrients compared with Ca²⁺, while ‘Mash-97’proved more sensitive to heavy metals than ‘Mash-95018.'     

Exploring the effect of organic matter on the interactions between mineral particles and cations with Wien effect measurements

Purpose

Understanding of the interactions between cations, mineral particles, and organic matter (OM) in soils is of paramount importance in plant nutrition and environmental science, and thus, these phenomena have been studied extensively. At present, an effective and simple tool to investigate these interactions does not exist. Based on previous studies of Wien effect in suspensions, the interactions of cations with soil mineral particles, complicated by the presence of organic matter, can be easily determined by means of Wien effect measurements, which was the objective of this study.

Materials and methods

A paddy soil originating from a yellow-brown soil, rich in organic matter, served as a test sample, from which the clay fraction of less than 2 μm in diameter was separated. Organic matter of aliquots of the clay fraction was removed by the oxidation with hot H₂O₂, and the natural and OM-free samples were saturated with various cations: Na⁺, K⁺, Ca²⁺, and Cd²⁺. The effects of OM present in the paddy soil on the interactions between the cations and the soil mineral particles were investigated by measuring the suspension Wien effect with a homemade apparatus, SHP-2.

Results and discussion

The weak electrical field electrical conductivities (EC₀) of suspensions of the natural soils saturated with various cations were higher than those of the OM-free soils. The rate of increase in electrical conductivity of suspensions of the OM-free soil, except that of suspensions saturated with Na⁺, at electrical field strengths >50～100 kV?cm^?1 was higher than those of the natural soil suspensions. The presence of OM increased the mean free binding energies of cations other than Na⁺. The increasing binding energies for K⁺ and Ca²⁺ were 0.56 and 0.57 kJ?mol^?1, respectively, which were significantly larger than the increase for Cd²⁺ as only 0.03 kJ?mol^?1. The binding energies of various cations on both natural and OM-free soils were all in the order: Na⁺?<?K⁺?<?Ca²⁺≈Cd²⁺. As opposed to its effect on the binding energies, the presence of OM reduced the mean free adsorption energies of the cations. Except for Na⁺, the adsorption energies of K⁺, Ca²⁺, and Cd²⁺ at field strengths >50 kV?cm^?1 were lower in the natural soil as compared with the OM-free soil, and the differences between the adsorption energies became larger with increasing field strengths. The presence of OM made the zeta potential of the soil particles saturated with Na⁺ and K⁺ positive, and the particles saturated with Ca²⁺ and Cd²⁺ negative.

Conclusions

Organic matter affected the interactions of cations with soil mineral particles significantly. Binding and adsorption energies, which were quantitative measures of the interactions between cations and soil particles, could be determined by Wien effect measurements in suspensions. The binding energies on natural soils were larger than those on the corresponding OM-free soils, and the adsorption energies on the natural soils were lower than those on OM-free soils.     

重金属污染对水稻田土壤硫酸盐还原菌种群数量及其活性的影响

在实验室条件下,采用重金属Cd2+、As5+、Cu2+、Pb2+和Cr3+处理黄松稻田土壤、紫色稻田土壤和红壤稻田土,28d后分析重金属污染对水稻田土壤的硫酸盐还原菌(SRB)种群数量和硫酸盐还原活性(SRA)的影响。结果表明,在每千克干土中加入200mgPb2+时,对稻田土壤的SRB种群数量和SRA有促进作用;当加入的Cd2+、As5+、Cu2+、Pb2+和Cr3+每千克干土分别超过1.0、30、500、400和200mg时,对稻田土壤SRB种群数量和SRA有明显抑制作用。随着加入量的增加,重金属对水稻田土壤的SRB种群数量和SRA的抑制作用越来越强,水稻田土壤通过自身来恢复SRB种群数量和SRA所需的时间也越长。同一种重金属元素对不同土壤的SRB种群数量和SRA抑制的污染临界值也有差异。     

Comparison of various methods for the determination of inorganic species in airborne atmospheric particulates

The performance of various filters used for determining inorganic species (heavy metals, light metals, anions and ammonium ion) in airborne particulates was comparatively assessed. Filters used in the determination of Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe³⁺, Zn²⁺, Pb²⁺, Cr³⁺, Ni²⁺, V (V), Mn²⁺ and Cd²⁺ were attacked by acid extraction (glass microfibre filters, GF/A), acid extraction and microwave oven digestion (quartz filters, QM-A), and muffle furnace calcination and microwave oven digestion (Whatman-41 cellulose filters, W-41). The behaviour of the different filters tested towards aqueous extraction for the determination of anions (Cl^?, NO ₃ ^? , SO ₄ ^? , ammonium ion and light metals (Ca²⁺, Mg²⁺, Na⁺ and K⁺) was also studied and the results obtained for the light metals were compared with those provided by acid attack. All metals except vanadium were determined by ICP-AES; cadmium, lead and vanadium were analysed for by GFAAS; anions were quantified by ion chromatography (SO ₄ ^? was also measured by ICP-AES); and ammonium ion was determined by the Indophenol Blue method.     

Competitive adsorption and desorption of oxytetracycline and cadmium with different input loadings on cinnamon soil

Purpose

The binary competitive effect could obviously influence the fate and transport behavior of oxytetracycline (OTC) and cadmium (Cd²⁺) in cinnamon soil. However, two pollutants loading into soil usually are different, perhaps because of the three reasons including occurrence of OTC before Cd²⁺, simultaneous occurrence of OTC and Cd²⁺, or occurrence of Cd²⁺ before OTC. The purpose of the study was to predict the competitive adsorption and desorption of OTC and Cd²⁺ as a function of above input loadings on cinnamon soil.

Materials and methods

Adsorption and desorption were determined using the batch equilibrium method in a single or binary system. The Freundlich equation was applied to describe the adsorption/desorption data of OTC and Cd²⁺ in order to obtain adsorption/desorption isotherms for each tested compound and the respective adsorption/desorption coefficients.

Results and discussion

The results indicated that cinnamon soil could strongly adsorb OTC with the adsorption affinity (K _f value) of more than 718 and Cd²⁺ with K _f value of more than 536 in the competitive and non-competitive system, and all adsorption and desorption isotherms of OTC and Cd²⁺ on cinnamon soil were well fitted by the Freundlich equation with r value of more than 0.99 (p?<?0.01). The coexistence of OTC and Cd²⁺ on cinnamon soil promoted significantly Cd²⁺ adsorption when Cd²⁺ firstly or simultaneously occurred on soil, but their coexistence did not affect adsorption of OTC when OTC firstly or simultaneously occurred on soil. Among the three input loadings, the pollutant with later occurring mode had lower K _f and hysteresis coefficient (HI) than the other two input loadings. According to the adsorption intensity parameter (1/n), the presence of Cd²⁺ or OTC with different input loadings could decrease the adsorption intensity of OTC or Cd²⁺ when compared with single occurrence of OTC or Cd²⁺.

Conclusions

The binary competitive effect influenced the adsorption/desorption of OTC and Cd²⁺ differently. The presence of OTC had a stronger influence on the adsorption/desorption of Cd²⁺ than the presence of Cd²⁺ on the adsorption of OTC. The later occurring pollutant on soil had stronger ecological risk than the former occurring pollutant in the binary competitive system. The physical adsorption in the single or binary system could be identified as the dominant mechanisms of OTC and Cd²⁺ adsorption.     

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.     

Saline-alkali soils of Russia

Diagnostics, methods of evaluation, and geography of saline-alkali (soda) soils are discussed. The saline-alkali soils include soils of different genetic types with the following chemical properties: the pH of the water suspensions equal to or higher than 8.5; the total alkalinity exceeding 1.4 meq/100 g of soil and the sum of water-soluble calcium and magnesium; and the presence of soluble “alkaline” salts in the soil profiles, the hydrolysis of which results in the alkaline reaction of the soils. The chemical properties of the saline-alkali soils are largely related to the presence of soda (Na₂CO₃, NaHCO₃) in the soils. According to their morphological properties, saline-alkali soils are divided into two groups: alkaline soils with an undiferentiated profile and without a morphologically pronounced solonetzic (natric) horizon, and alkaline soils with a pronounced natric horizon (solonetzes). Solonetzes, in turn, are divided into (a) alkaline solonetzes (with soda or with soda and neutral salts), (b) solonetzes salinized with neutral salts (saline soils) with increased alkalinity in the solonetzic and lower lying horizons, (c) saline solonetzes throughout the profile, and (d) leached solonetzes containing no soluble salts in the profile and almost no exchangeable sodium in the soil exchange complex (SEC) (“dead” solonetzes). The latter two groups of solonetzes cannot be ranked among the alkaline soils. The alkalinity of the saline-alkali soils under study is due to carbonate and bicarbonate ions (carbonate alkalinity), organic acid anions (organic alkalinity), and borate ions (borate alkalinity). The carbonate alkalinity is due to both soda (Na₂CO₃, NaHCO₃) and CaCO₃.