Variable Charge Components Research Articles

Termite bioturbation effects on electro-chemical properties of Ferralsols in the Upper Katanga (D.R. Congo)

Although the significant impact of mound-building termites on physical, chemical and biochemical soil properties over large areas of the (sub-) tropics has often been discussed, little is known about the influence of termites on electro-chemical properties of Ferralsols. In this study, we compared the curves describing the total cation exchange capacity (CEC T), the base cation exchange capacity (CEC B), and the anion exchange capacity (AEC) across a range of pH values ( charge fingerprint) and point of zero charge (pH 0) of Macrotermes falciger biogenic structures with soils not affected visually by termites (control soils). The results show that termite activities lowered considerably the pH 0 values, the actual AEC, the actual preferential adsorption of Al on the exchange complex (CEC T–CEC B) and the AEC variability (dAEC/dpH); and increased considerably the soil pH, the cation exchange capacities (CEC B and CEC T), the permanent negative charge ( σ p) and the CEC's variability (dCEC B/dpH and dCEC T/dpH). The lowering of pH 0 values (1.6-fold) was attributed to the bonding of negatively charged organic matter with protonated oxide sites and largely to the enrichment in permanent negative charge (about 2-fold), suggesting the termites' ability to change soil mineralogical properties. The mean pH 0–pH 0.002 values indicate the evolution of negative (− 2.0 to − 3.6 units) and positive (+ 0.6 units) charges on the variable charge components of mound and control soils, respectively. The study demonstrates that Macrotermes biogenic structures have a mixed charge system with higher permanent and variable charges than the surrounding Ferralsols.

Cadmium Sorption–Desorption by Soils in the Absence and Presence of Phosphate

Batch experiments were carried out to determine the effect of phosphate anion (P) on the sorption–desorption of cadmium (Cd). The soils selected for the study were two kaolinitic Alfisols and two Andisols, which differ in their variable charge components. At the natural soil pH, Cd sorption in the absence of P was related to the net negative surface charge of the soils. Sorption of P increased the negative charge of the soils but the increase per unit amount of P added decreased with increasing P sorption. Both pH and soil characteristics influence the effect of P on Cd reactions. In the Alfisols, P and Cd were sorbed in similar amounts and the effect of increasing P rates on Cd sorption–desorption reactions was negligible. In the allophanic Andisols, whose capacity to bind P exceeds several times their capacity to retain Cd, the sorption of Cd was clearly enhanced with increasing P rates. In these soils, two distinct effects of P addition on Cd retention were observed. The first one arose from variations in the soil-suspension pH and the concomitant changes in soil surface charge. The second effect was directly related to the amount of sorbed P. Most of the Cd sorbed in the four soils was strongly bonded. In the Andisols, increasing P sorption on the surfaces restricted Cd desorption.

Immobilization and phytoavailability of cadmium in variable charge soils. III. Effect of biosolid compost addition

The effect of pH-increases due to Ca(OH)2 and KOH addition on the adsorption of cadmium (Cd) was examined in two soils which varied in their variable-charge components. The effect of Ca(OH)2 on immobilization and phytoavailability of Cd from one of the soils, treated with various levels of Cd (0–10 mg Cd kg−1 soil), was further evaluated using mustard (Brassica juncea L.) plants. Cadmium immobilization in soil was evaluated by a chemical fractionation scheme. The addition of Ca(OH)2 and KOH increased the soil pH, thereby increasing the adsorption of Cd, the effect being more pronounced in the soil dominated by variable charge components. There was a greater increase in Cd2+ adsorption in the KOH-treated than the Ca(OH)2-treated soil, which is attributed to the greater competition of Ca2+ for adsorption. Increasing addition of Cd enhanced Cd concentration in plants, resulting in decreased plant growth (i.e., phytotoxicity). Although addition of Ca(OH)2 effectively reduced Cd phytotoxicity, Cd uptake increased at the highest level, probably due to decreased Cd2+ adsorption resulting from increased Ca2+ competition. There was a significant inverse relationship between dry matter yield and Cd concentration in soil solution. Addition of Ca(OH)2 decreased the concentration of the soluble + exchangeable Cd fraction but increased the concentration of inorganic-bound Cd fractions in soil. Since there was no direct evidence for CdCO3 or Cd(OH)2 precipitation in the variable charge soil used for the plant growth experiment, alleviation of phytotoxicity can be attributed primarily to immobilization of Cd by enhanced pH-induced increases in negative charge.

The effects of anion sorption on sorption and leaching of cadmium

The effect of chloride, sulfate, nitrate, and phosphate anions on the sorption and leaching of cadmium was examined in 2 soils (Manawatu silt loam and Egmont clay loam) which differ in their variable charge components. There was a larger sorption of cadmium in the presence of phosphate than in the presence of sulfate, nitrate, and chloride, and the difference was more pronounced in the Egmont soil. In soils, specific sorption of phosphate increases the negative charge. The increase in negative charge per unit amount of phosphate sorbed decreased with increasing phosphate sorption. The sorption of cadmium increased in response to phosphate sorption. The phosphate-induced cadmium sorption resulted from the increase in negative charge due to phosphate sorption. Column studies indicated that cadmium was less susceptible to leaching in the presence of phosphate than in the presence of nitrate.

Charge characteristics in relation to free iron and organic matter of soils from Bambouto Mountains, Western Cameroon

We have examined the charge characteristics, with special emphasis on the role of free Fe and organic matter, of humid tropical soils from Bambouto Mountains, Western Cameroon. The soils, which are formed from tuff, basalt and trachyte, are dominated by kaolinite and sesquioxides. The amounts of Fe oxides in them increase somewhat with depth. Open 2:1 phyllosilicates are present in trace amounts. The point of zero charge of the variable charge components, pH0, is around 4 in the topsoil (0–20 cm) and around 6 at 100–150 cm depth. In the subsoils, pH0 exceeds soil pH presumably because of large quantities of Fe oxides. Deferration increases both soil pH and pH0, but diminishes the anion exchange capacity. Oxides and oxyhydrates of Fe have positive surface charge, so their removal from the soils would result in overall loss of positive charge. Increases in soil pH would bring about an increase in the cation exchange capacity of the soils. Hence, management practices that reduce soil acidity should reduce loss of essential basic cations via leaching.

Surface charge characteristics of kaolinitic tropical soils

Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs + adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1–10 mmol L −1 and pH value 2–6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density.

Surface charge characteristics of kaolinitic tropical soils

Surface charge properties of four representative kaolinitic soils from the humid tropics (Brazil) were investigated by a methodology involving independent measurements of net total permanent and variable charge components. Permanent structural charge was determined by Cs+ adsorption, whereas variable charge was quantified by simultaneous proton titration and background electrolyte (LiCl) adsorption measurements. Data were obtained for homoionic soils suspended in LiCl solutions of ionic strength 1–10 mmol L−1 and pH value 2–6. Corrections were made in the titration data for proton consumption resulting from dissolution and aqueous-phase complexation reactions. Conjunctive use of proton titration and electrolyte adsorption data yielded independent assessments of proton surface charge densities and points of zero charge. The surface charge data were tested successfully for consistency with the law of surface charge balance. Three of the soils exhibited similar surface charge behavior, with no pronounced effect of differences in either organic C or Fe and aluminum oxide content. One soil containing significant manganese oxides showed points of zero charge well below those of the other three soils. The point of zero net charge (p.z.n.c) for the soils was ≤4, lower than values reported for specimen kaolinite. The point of zero net proton charge (p.z.n.p.c.) increased with decreasing ionic strength. In all cases, the presence of small quantities of structural charge in 2:1 clay minerals had a significant effect on surface charge properties; e.g., for all soils, p.z.n.c. < p.z.n.p.c. These characteristics of surface charge were shown to be consistent with the behavior of a mixture of kaolinite, organic matter, and a small quantity of 2:1 clay minerals. In conformity with the law of surface charge balance, ionic strength effects were found to be removed by plotting net adsorbed ion charge against net proton surface charge density.

Reactions with Variable-Charge Soils

A1 The ionic species present in soil solutions.- Dissociation constants.- Values for dissociation constants.- The behaviour of some typical anions.- The behaviour of some cations.- A2 Variable charge oxides as soil constituents and as models of soil constituents.- The oxides present in soils.- Synthetic oxides as models of soil oxides.- The reaction of cations with oxides.- The reaction of anions with oxides.- Changes in charge resulting from adsorption.- Summary.- A3 Describing and explaining the adsorption behaviour of oxides.- The differences between describing and explaining.- The single-plane model.- The three-plane model.- The four-plane model.- Summary.- A4 The rate of reaction with oxides.- The rate of the adsorption reaction.- The rate of the second reaction.- Description of date using the model for rate of reaction.- Consequences of the model of the rate of reaction.- Summary.- A5 The four-plane model and how it works.- Varying the charge parameters.- Varying the parameters that describe adsorption.- Varying the dissociation characteristics.- Varying the background electrolyte.- Varying the amount of adsorption.- Summary.- A6 Fixed charge and variable charge components in soil.- The definition of surface charge.- The effects of adsorbed ions.- Separating permanent and fixed charge.- Is it important to distinguish permanent and variable charge?.- A7 The reaction of anions and cations with soil.- The effects of concentration on sorption.- Effects of time on sorption.- Describing the rate of the reaction.- The effect of level of application.- Effects of temperature.- Repeated additions of a nutrient and desorption.- Effects of pH and of electrolyte concentration 71 Summary.- A8 Modelling the reaction of anions and cations with soil.- The three assumptions of the model.- The formal equations of the model.- Modelling the characteristics of sorption.- The individual effects of the parameters of the model.- Summary.- B1 Speciation in solution.- Contains BASIC programs MOLLY and ZNOHP to calculate ion species.- B2 Solving simultaneous equations - the four-plane model.- Contains BASIC program BOWDEN which solves the simultaneous equations of the model.- B3 Deriving equations to describe adsorption and rate of adsorption.- Presents algebra to show the solutions of rate equations in some practical cases.- B4 Modifications to the four-plane model.- Contains BASIC program ZNCL2 and RATEOX which apply the four-plane model to metal adsorption and to the rate of the reaction.- B5 Fitting models to data.- Considers the problems of finding the best value of parameters and presents BASIC program FITPINIT which fits data to the four-plane model.- B6 Applying models to soil.- Presents BASIC programs THETA and DIFPLUS which simulate the behaviour of soil and FITTHETA and FITRATE which fit date to models.- B7 Describing reaction of ions with soil.- Considers the problems which arise where sorption is calculated from the change in solution concentration. Program PREDX solves simultaneous equations to predict sorption. FITFUNC fits various functions to the observed variable.

Changes in zero point of charge (ZPC), phosphate retention, and specific surface area of some variable charge soils after several chemical treatments

Abstract Zero point of charge (ZPC), phosphate retention percentage, phosphate absorption coefficient, and specific surface area of variable charge soils subjected to several chemical treatments were determined for the evaluation of the intrinsic properties which would not appear in the untreated state. Three extraction reagents, 1 M KC1, acid-oxalate, and dithionite-citrate-bicarbonate, were used for the treatment of samples from two volcanic ash soils from Japan and two strongly weathered soils from Thailand, and the amounts of Al, Fe, and Si in the extracts were determined. All of these values were closely related with each other, reflecting the characteristics of variable charge components. In particular, the values of ZPC, phosphate absorption coefficient, and specific surface area were considered to be useful parameters to analyze amorphous oxides or hydroxides qualitatively; their high contents resulted in higher values of ZPC, phosphate absorption coefficient, and specific surface area. In addition, in soil samples with a low ZPC, it was pointed out that Al dissolution due to strong acidification of the time of the determination of ZPC, and subsequent development of permanent negative charges of crystalline layer silicates may result in ZPC values lower than those operating under field conditions.

Use of serpentinite in the defluoridation of fluoride‐rich drinking water

A newly developed, HCl treated method is described for the enhancement of fluoride uptake by serpentinite in an aqueous medium. Fluoride adsorption and desorption reactions in treated serpentinite were investigated, over the range of fluoride concentrations (1–10 mg/1). The zero point charge of the variable charge components (pH0), and total surface charge (σp) of serpentinite were also investigated. At equal concentrations of total fluoride in solution, fluoride retention was greatest at pH = 5.2 and decreased both at low and high pH. Thermodynamic properties for fluoride adsorption at 25°C and 50°C were investigated. The isosteric heat of adsorption (?H) was calculated for treated surfaces and heterogeneity of this surfaces was examined. Finally, Differential Thermal Analysis (DTA) and X‐ray Diffraction (XRD) patterns were observed for raw, treated and fluoride‐contacted surfaces. According to DTA and XRD patterns, structural changes were observed with HCl treatment.

Fixed charge and variable charge components in soil

Fixed charge and variable charge components in soil

The responsiveness of heavy vehicle registrations to interstate tax differentials

Although the literature is rich on the subject of tax competition between states and regions, little analysis has been published on the responsiveness of interstate highway users to variations in vehicle registration fees and other motor vehicle taxes. While intrastate motor vehicle owners can avoid road user taxes only through tax evasion, firms engaged in interstate commerce have wide discretion in determining where to register their vehicles. Vehicle mobility and high enforcement costs, combined with the institution of registration reciprocity, give interstate motor carriers this discretion. Under registration reciprocity, a vehicle properly registered in one state can legally travel in any other state without having to pay additional registration fees. For an 80,000 pound vehicle, these annual fees presently range f rom $35 to $2200. Thus, a priori, one might expect some responsiveness to these fee differentials. Heavy vehicle registrations in a given state are responsive to differences in registration fees, sales tax rates, property taxes, and membersh ip in p ropor t i ona l regis trat ion compacts. It is the purpose of this note to report how responsive are heavy vehicle registrations in a given state to differentials in the model the carrier selects from its states of operation that state for vehicle registration which would minimize the fixed-charge component of yearly operation. Although there are no variable charge components associated with this optimal choice, the cost differential realized from a judicious selection of vehicle domicile can be affected further by interstate differences in vehicle ad-valorem taxes (most notably the property tax) and differences in motor vehicle sales tax rates and bases. One can, therefore, determine that the annual number of heavy vehicle registrations in a state is a function of the derived demand for transport services in that state and the total registration cost differential (inclusive of registration fees, ad-valorem taxes, and sales taxes) between that state and any other contiguous states connected by a motor carrier route that is common to both states. To estimate this relation, the authors use the regression equation:

Influence of organic matter and phosphate content on the point of zero charge of variable charge components in oxidic soils

The point of zero charge of the variable charge components (pH,) of oxidic soils formed on basaltic parent material in humid tropical Queensland has been measured on samples from virgin rainforest and cultivated fertilized fields. The average amount of free iron in these soils is about 10%. Soils with low organic matter content and low extractable phosphorus have high pH, values. Regression analysis showed pH, to be reduced by about one pH unit for each 1% increase in organic carbon or for each 100 �g/g increase in extractable phosphorus. Implications with respect to cation and anion exchange capacities are briefly discussed.

Ammonium‐calcium exchange equilibria in soils and weathered pumices that differ in cationexchange materials

SUMMARYThe retention of NH4+ and Ca2+ on soil and weathered pumice samples containing constant and/or variable charge components was measured in different NH4CI‐CaCl2 solutions. The NH4+/Ca2+ selectivity of each sample was evaluated using a quotient of the partition of NH4+ on the exchange sites and in the solution relative to that of Ca2+. It increased with decreasing pH and increasing NH4Cl‐CaCl2 concentration for a given equivalent fraction of NH4+ in the solution. These effects were quantitatively explained in terms of the changes of NH4+ and Ca2+ concentrations in the solution and in the diffuse double‐layer of the ion‐exchange material as predicted by the law of mass action and the electric double layer theory. The NH4+/Ca2+ selectivity of different exchange materials showed a similar variation among their exchange sites and increased in the order humus, allophane and imogolite (Si/Al ratio 0.5) &lt; allophane (Si/Al ratio 1.0), montmorillonite &lt; vermiculite, illite &lt; halloysite. The origin of negative charge, the steric features around the exchange sites and clay‐humus interaction are suggested as being important in determining the NH4+/Ca2+ selectivity.

Using variable charge characteristics to understand the exchangeable cation status of oxic soils

The model of Uehara and Gillman was used to estimate the amounts of permanent surface charge, and variable surface charge at soil pH, in two soils from the high rainfall region of coastal Queensland. For each soil series, samples from virgin rain-forest were compared with soil collected from nearby sugarcane fields. One soil contained relatively large amounts of permanent negative charge (up to 3 m.e. per 100g), and hence was moderately supplied with exchangeable cations, while the other soil was dominated by variable charge components and at soil pH contained sufficient positive charge to reduce exchangeable cations to near zero values, despite the presence of about 1 m.e. per 100 g of permanent negative charge. In the latter the position of soil pH with respect to the point of zero charge is of utmost importance for the development of cation exchange capacity. The effect of adsorbed sulfate on positive charge measurement, and valency of the ion used for negative charge measurement, are briefly discussed.