Reaction kinetics of the adsorption and desorption of nickel, zinc and cadmium by goethite. I. Adsorption and diffusion of metals

The reactions of Ni, Zn and Cd with goethite were studied over a range of initial metal concentrations (10⁻⁶ to 10⁻⁴M), pH values (4 to 8), reaction times (2h to 42d) and temperatures (5 to 35°C). The adsorption of metals increased with pH, reaction time and temperature. Adsorption of Ni increased relative to Zn and Cd with increasing time and temperature. The initially rapid adsorption of metals within a few hours was followed by a much slower reaction linearly related to time^1/2, interpreted as diffusion–controlled penetration of goethite. The pH–dependent relative diffusion rates (Ni > Zn > Cd) were influenced by both affinity for goethite surfaces and by ionic radius. Diffusion coefficients of the three metals ranged from about 10⁻¹⁹to 10⁻²⁰cm²s⁻¹. The corresponding activation energies of diffusion were also calculated (Ni 35, Cd 55, Zn 90 kJ mol⁻¹). Our view about the reactions of heavy metals with goethite involves (i) adsorption of metals on external surfaces, (ii) solid–state diffusion of metals from external to internal binding sites, and (iii) metal binding and fixation at positions inside the goethite particles. The general parameters of these processes are related to the hydrolytic properties (p K values) and the ionic radii of the metals. The results show that goethite may be an efficient sink for trace metals.     

The reactions of cadmium with calcium carbonate surfaces

The reaction of cadmium with calcite was studied with 10⁻⁶–10⁻²M Cd²⁺ using 4g CaCO₃ and 50 ml solution. The calcite-water suspension was equilibrated for 2 d before adding Cd(NO₃)₂. The CaCO₃ surface has a high affinity for Cd and at < 1 μmol g⁻¹ a linear adsorption isotherm (C-type) describes the reaction, whereas precipitation of CdCO₃ on calcite predominates at higher Cd additions. In the latter case pH decreased and solutions were undersaturated with respect to CaCO₃ indicating that CdCO₃ prevented the CaCO₃ surface from reacting with the acidity generated from CdCO₃ precipitation. The data for low Cd additions suggests that an ideal surface solid solution is formed between CdCO₃ and CaCO₃ and the Thorstenson and Plummer equation expressing the pIAP values of surface solid solutions is valid. Equilibrium was attained for low Cd additions in several minutes, whereas precipitation was a slow process; at the changeover point distinction between the two processes is difficult. The reacting surface area calculated from the maximum adsorption of Cd is 0.5-1.0 times that measured by the BET method.
The Cd-reacting surface areas of four natural calcareous minerals were much less than those found by the BET method which includes the surfaces of other minerals present. The Thorstenson and Plummer equation may be a useful way to relate solution composition and carbonate-adsorbed Cd in contaminated soils.     

The effect of soil texture and soil drainage on emissions of nitric oxide and nitrous oxide

Abstract. Agricultural soils are important sources of the tropospheric ozone precursor NO and the greenhouse gas N₂O. Emissions are controlled primarily by parameters that vary the soil mineral N supply, temperature and soil aeration. In this field experiment, the importance of soil physical properties on emissions of NO and N₂O are identified. Fluxes were measured from 13 soils which belonged to 11 different soil series, ranging from poorly drained silty clay loams to freely drained sandy loams. All soils were under the same soil management regime and crop type (winter barley) and in the same maritime climate zone. Despite this, emissions of NO and N₂O ranged over two orders of magnitude on all three measurement occasions, in spring before and after fertilizer application, and in autumn after harvest. NO emissions ranged from 0.3 to 215 μg NO-N m^–2 h^–1, with maximum emissions always from the most sandy, freely drained soil. Nitrous oxide emissions ranged from 0 to 193 μg N₂O-N m^–2 h^–1. Seasonal shifts in soil aeration caused maximum N₂O emissions to switch from freely drained sandy soils in spring to imperfectly drained soils with high clay contents in autumn. Although effects of soil type on emissions were not consistent, N₂O emission was best related to a combination of bulk density and clay content and the NO/N₂O ratio decreased logarithmically with increasing water filled pore space.     

Caesium and strontium diffusion through sodium montmorillonite at elevated temperature

Counter ionic migration rates of dilute Cs⁺ and Sr²⁺ against sodium in a Na-montmorillonite gel are measured using a radially perfused diffusion cell. Enhanced or surface diffusion for caesium is observed both at ambient and elevated temperature. To quantify these surface diffusivities the ion-exchange properties of the diffusing species are required. Thus, exchange isotherms for caesium against sodium on montmorillonite at 22 and 90°C are given for 10⁻¹, 10⁻², and 10⁻³M background NaCl concentrations. Caesium counterion surface diffusivities at 22 and 90°C are 2.2*10⁻⁶ and 8.0 * 10⁻⁶ cm² s⁻¹, respectively. These values are found to be essentially independent of background ionic strength over the range 10⁻³ to 10⁻¹ m NaCl. Experimental evidence of enhanced transport through Na-montmorillonite for the divalent cation Sr²⁺ is also confirmed with a surface diffusivity of 2 * 10⁻⁶ cm² s⁻¹ at 22°C and in 10⁻¹ m NaCl.     

Respiration of nitrous oxide in suboxic soil

Reduction of nitrous oxide (N₂O) is an autonomous respiratory pathway. Nitrous oxide is an alternative electron acceptor to O₂ when intensive biological activity and reduced diffusivity result in an O₂ deficit. Hypoxic or anoxic micro sites may form even in well-aerated soils, and provide a sink for N₂O diffusing through the gas-filled pore space. We reproduced similar in vitro conditions in suboxic (0.15% O₂) flow-through incubation experiments with samples from a Stagnosol and from a Histosol. Apparent half-saturation constants ( k _m) for N₂O reduction were similar for both soils and were, on average, 3.8 μmol mol⁻¹ at 5°C, 5.1 μmol mol⁻¹ at 10°C, and 6.9 μmol mol⁻¹ at 20°C. Respiration of N₂O was estimated to contribute a maximum proportion of 1.7% to total respiration in the Stagnosol (pH 7.0) and 0.9% in the Histosol (pH 2.9).     

Boron Deficiency in Mango (Mangifera indica L.): A Cause Delineation Study in Acidic Soils of Maharashtra, India

Boron deficiency is a major production constraint of Mango cv Alphonso in western coast, Maharashtra, India. The soils are sandy-loam, light, acidic in reaction and receive high annual precipitation of above 2,500 mm. The leaf and soil B status was low with an average of 23 and 0.25 mg kg⁻¹ respectively. About 60% of the orchards were found to be deficient in B. The B adsorption study using Langmuir adsorption isotherm revealed that the adsorption capacity of B by these soils was low with an average adsorption maxima (b) of 16.62 μg g⁻¹ and bonding energy constant ( K ) of 0.09 mL μg⁻¹ making soil B susceptible to leaching. The Mango leaf N status was in excess range, which aggravated B deficiency through growth dilution. A significant negative correlation was observed between leaf B and leaf N (statistically significant at 1% level (p=0.01)). The free Al status of the soils was found to be fairly high, and its detrimental effect on root growth was observed which led to inefficient absorption of limited soil B by roots. The climatic conditions of Konkan like high humidity, high temperature and long sunshine hours also favored widespread incidence of B deficiency, low yield and poor quality. The response of Mango cv Alphonso to the B application was found to be more in foliar than in soil application.     

Release of potassium from some benchmark soils of India

Release of potassium from 15 surface samples of benchmark Alluvial, Red and Black soils of India to 0.01 M solutions of BaCl₂, CaCl₂, NH₄Cl and NaCl was studied in soils either untreated or pretreated with 5 × 10⁻³ M KCl. In the untreated soils, the efficacy of the extractants declined in the sequence: BaCl₂ > NH₄Cl > CaCl₂ > NaCl. Cumulative K-release was greatest from Black soils, followed by Red and Alluvial soils. From soils pretreated with 5 * 10⁻³ M KCl, more K was released than retained, and more 'native' K was released than that from untreated soils. Increase in the release of 'native' K decreased in the sequence: Red > Alluvial > Black soils. The amounts of surface and internal K, desorption rate constants and parabolic diffusion constants were calculated from K release to the various electrolytes.     

Phytoextraction of Cd and Zn with Thlaspi caerulescens in field trials

Abstract. Phytoextraction is the remediation of heavy metal contaminated soils using plants that take up metals. Hyperaccumulating plants such as Thlaspi caerulescens are often studied for their possible use for decontamination of Cd and Zn rich soils, but few field trials have been reported, although they are necessary to validate the results of hydroponic and pot studies. This article reports field data for T . caerulescens grown on a calcareous and an acidic soil, both contaminated 20 years ago by either atmospheric depositions or septic-tank wastes. Accelerated cropping using transplants grown three times in eight months was compared to Thlaspi sown twice during the same period. Both were followed by one crop of sown Thlaspi . High Cd and Zn concentrations in the plant shoots compensated for the low biomass production. Annual metal exports with transplanted Thlaspi were 130 g Cd ha⁻¹ and 3.7 kg Zn ha⁻¹ on the calcareous soil and 540 g Cd ha⁻¹ and 20 kg Zn ha⁻¹ on the acidic soil. We concluded that within the framework of the Swiss legislation, remediation of Cd-contaminated soils could be achieved within less than 10 years with one crop of Thlaspi per year, but differences in soil properties could affect the rate of phytoextraction significantly. Total Zn content in both soils was too high to be remediated by T . caerulescens in a realistic time span. Thlaspi did not decrease the NaNO₃-extractable fraction of Cd or Zn in either of the soils.     

The status of atmospheric concentrations of ammonia in an intensive dairy farming area in central Japan

(pp. 41–46)
Silicon availability in 36 commercial nursery bed soils was evaluated by four methods the phosphate buffer (pH 6.2, 40 mmol L⁻¹), incubation, supernatant and acetate buffer (pH 4.0, 1 mol L⁻¹) Methods. The influence of silicon availability in the nursery bed soils on the silicon uptake of rice Oryza sativa L. cv. Hitomebore seedlings and the effect of silicon fertilizer application were examined in a glass house in 2002.
The results revealed that the best correlation between silicon content in rice seedlings and available silicon in soils was obtained with the phosphate buffer-solution method ( r  = 0.86). More precise evaluation of available silicon was achieved by grouping soils based on these phosphate absorption coefficients (PAC). The correlation coefficients between silicon content in rice seedlings and available silicon in soils were 0.92 and 0.72 for volcanic soils (PAC > 1500) and non volcanic soils (PAC < 1500), respectively.
We concluded that the phosphate buffer method is the most easily adjusted method for estimation of silicon availability in nursery bed soils, and silicon fertilizers should be applied when silicon availability in non-volcanic nursery bed soils goes below 200 mg kg⁻¹, whereas the level is less than 350 mg kg⁻¹ in volcanic soils.     

Soil S availability in upland pastures of NE Scotland: relationship of extractable soil S and soil respiration to soil and site characteristics

Abstract. The mean extractable sulphur (S) concentration in 315 upland topsoil samples collected in 1988/89 from beneath pasture in NE Scotland was 13 μg S g⁻¹ (range 2–77 μg S g⁻¹). More than two thirds of the samples had S concentrations less than that acceptable for productive soils. Continued decreases in atmospheric S inputs may have increased this proportion subsequently. The analysis of herbage S also indicated that two-thirds of the samples were below 0.2% S. A 'respirometric index', namely CO₂ produced during cellulose decomposition without added S as a percentage of that produced with added S, was significantly less than 100% in a quarter of the soils. Results of three different extraction procedures suggested that sulphate in the soils was present mainly as free plus adsorbed rather than precipitated forms. Soil extraction identified a significant non-sulphate S fraction, presumably organic S. The variability in extractable S stemmed from a combination of geographical, depositional and local site and soil factors. Extractable S was significantly correlated with soil organic matter content and inversely with soil pH and together these factors explained 37% of the variability. While significant differences in mean concentrations between geographical area, soil association and drainage status were evident, no trends could be observed between the major soil subgroups or with altitude.     

Phytoextraction of Cd and Zn with Salix viminalis in field trials

Abstract. Use of high biomass crops such as the willow Salix viminalis to extract metals for soil remediation has been proposed as an alternative to the low biomass-producing hyperaccumulating plants. High yields compensate for the moderate heavy-metal concentrations in the shoots of such species. We report the first long-term trials using Salix viminalis to extract heavy metals from two contaminated soils, one calcareous (5 years) and one acidic (2 years). Total metals extracted by the plants were 170 g Cd ha⁻¹ and 13.4 kg Zn ha⁻¹ from the calcareous soil after 5 years, and 47 g Cd ha⁻¹ and 14.5 kg Zn ha⁻¹ from the acidic soil after 2 years; in the first year outputs were negligible. After 2 years, Salix had performed better on the acidic soil because of larger biomass production and higher metal concentrations in shoots. Addition of elemental sulphur to the soil did not yield any additional benefit in the long term, but application of an Fe chelate improved the biomass production. Cd and Zn concentrations were significantly higher in leaves than stems, highlighting the necessity to collect leaves as well as shoots. On both soils, concentration in shoots decreased with time, indicating a decrease in extraction efficiency.     

Long-term effects of lantana residue additions on water retention and transmission properties of a medium-textured soil under rice–wheat cropping in northwest India

Abstract. Hydraulic properties of soils after rice cropping are generally unfavourable for wheat cultivation. Poor drainage, delayed planting and oxygen stress in the root zone may adversely affect the wheat crop after lowland rice cultivation. We studied long-term effects of lantana ( Lantana spp. L.) residue additions at 10, 20 and 30 t ha⁻¹ yr⁻¹ (fresh biomass) on physical properties of a silty clay loam soil under rice–wheat cropping in northwest India. At the end of ten cropping cycles, soil water retention, infiltration rate, saturated hydraulic conductivity and drying rate of soil increased significantly with lantana additions. The available water capacity (AWC), on volume basis, declined at rice harvest (from 22.0 to 18.8–20.9%), but increased at wheat harvest (from 12.9 to 13.4–15.0%) after lantana treatment. The volumes of water transmission (>50 μm) and storage pores (0.5–50 μm) were greater, while the volume of residual pores (<0.5 μm) was smaller in lantana-treated plots than in controls at both rice and wheat harvest. Infiltration rate in the lantana-treated soil was 1.6–7.9 times that of the control (61 mm d⁻¹) at rice harvest, and 2–4.1 times that of the control (1879 mm d⁻¹) at wheat harvest. Thus lantana addition improved soil hydraulic properties to the benefit of the wheat crop in a rice–wheat cropping sequence.     

The effects of lime on adsorption and desorption of phosphate in five Colombian soils

The effects of lime (applied in the field) on the amounts of total and isotopically-exchange-able phosphate adsorbed from solutions were measured in five soils. The total amount of phosphate adsorbed without lime was in the range 200 to 1700 μg P per g of soil at 0.05 μg P cm⁻³ of solution. Lime diminished the amount of phosphate adsorbed at all concentrations of solution in an oxisol and a dystropept; in an ultisol and another dystropept, lime tended to increase sorption at small concentrations and diminish it at large concentrations; in a dystrandept that contained spheroidal allophane and a great deal of organic matter, lime increased adsorption at all concentrations up to 1 μg P cm⁻³. Lime increased the proportion of added phosphate that was isotopically exchangeable in the oxisol and one dystropept, had no effect in the other dystropept, and diminished the proportion in the ultisol and dystrandept.
Adsorbed phosphate was subsequently desorbed by suspending the soils in solutions without phosphate. After desorption the quantity of exchangeable phosphate in all soils was closely correlated with aluminium extracted by ammonium oxalate; buffer power was correlated in all except the dystrandept, in which it was larger per unit of aluminium than in the other soils; possibly the cause was aluminium associated with organic matter. In all soils lime diminished buffer power allowing a specific amount of exchangeable phosphate to maintain a larger concentration in solution. The beneficial effects of lime on exchangeable phosphate after desorption were consistent among soils, despite inconsistent results when the phosphate was adsorbed.     

Aluminium speciation and pH of an acid soil in the presence of fluoride

The aim was to determine whether the addition of F to an acid soil reduces the concentration of free Al³⁺ and other forms that have been shown to be toxic to plants. The ability of two different extracts to reflect Al speciation in the soil solution was also investigated. Addition of F (0-5.2μmolg⁻¹) to an acid soil (pH 4.15, soil solution) increased the pH and total concentrations of Al and F in the soil solution whereas Al³⁺ remained constant or decreased. Soil solution pH, total soluble Al and Al extracted by 0.01 m CaCl₂ are not good predictors of the likelihood of aluminium toxicity in soils containing soluble fluoride.     

Observations on the spatial and temporal variation in the phosphorus status of lakes in the British Isles

Abstract. An examination of total phosphorus (TP) concentrations from 902 lakes in England, Scotland and Northern Ireland (NI), suggest that only Scottish lakes have a high percentage (73%) of oligotrophic waters (TP<10 μg PI^-1). The TP status of upland lakes in NI was greater than Scottish lakes particularly if lake catchments were afforested. Although lowland lakes in NI drain a predominately non-urbanized landscape, 38% of lakes below 100 m had TP concentrations > 100 μg PI^-1 and only 29% <35 μg PI^-1. English lakes tended to have higher TP concentrations (70% > 101 μg PI^-1) which may reflect P inputs from sewage treatment works (STWs) although lakes draining agricultural catchments frequently produced high TP concentrations. Between 1985 and 1995, annual point source TP inputs to Loch Leven, Scotland, declined by 8 tonnes P or 40% of the 1985 TP loadings to the Loch. As point source inputs were proportionally richer in dissolved molybdate reactive phosphorus (MRP) than diffuse inputs, the MRP loading was reduced by 46%. From 1974 to 1995, TP concentrations in Lough Neagh (NI) increased despite reduced TP inputs from STWs. Partitioning of annual TP loadings from two major inflowing rivers to Lough Neagh, showed river MRP loadings from non-point sources had been increasing at annual rates of 1.9 and 2.3 kg P km^-2. The remaining non-MRP river loadings had not been influenced by lower TP loads from STWs and showed no tendency to increase with time. Insufficient data is available from other lake systems in the British Isles to judge whether the increase in non-point source MRP loadings observed in the Lough Neagh catchment has been repeated elsewhere.     

Fate of nitrogen in cattle slurry following surface application or injection to grassland

Two field experiments commencing in winter (December) and spring (April) were conducted to determine the fate of nitrogen (N) in cattle slurry following application to grassland. In each experiment three methods of application were used: surface application, and injection ± the nitrification inhibitor, nitrapyrin. Slurry was applied at 80t ha⁻¹, (≡248 kg total N ha⁻¹ in the winter experiment, and 262 kg N ha⁻¹ in the spring experiment). From slurry applied to the surface, total losses of N through NH₃ volatilization, measured using a system of wind tunnels, were 77 and 53 kg N ha⁻¹ respectively for the winter and spring experiments. Injection reduced the total NH₃ volatilization loss to ∼2 kg N ha ⁻¹. Following surface application, loss by denitrification, measured using an adaptation of the acetylene-inhibition technique, was 30 and 5 kg N ha⁻¹ for the two experiments. Larger denitrification losses were observed for the injected treatments; in the winter experiment the loss from the injected slurry without nitrapyrin was 53 kgN ha ⁻¹, and with nitrapyrin 23 kgN ha⁻¹. Total denitrification losses for the corresponding injected treatments in the spring experiment were 18 and 14 kg N ha ⁻¹. Apparent recoveries of N in grass herbage in both experiments broadly reflected the differences between treatments in total gaseous loss.     

The influence of parent material and livestock intensification on plant-available phosphorus values by the Olsen method in Northern Ireland

Abstract. Leaching of phosphorus (P) from agricultural land is the major cause of eutrophication of surface waters in Northern Ireland. However, soil testing using the Olsen method has shown that while soil P in some catchment areas of the Province is low, surface waters within these catchments are, nonetheless, every bit as eutrophic as other local catchments where soil P is high. Soil P measurements on over 6000 samples from Northern Ireland soils (A horizon only) have indicated that Olsen-P values of improved grassland on most parent materials are linearly related to animal intensification. Exceptions are soils derived from peat, marl and basalt. For each of the latter soils, the measured Olsen-P was shown to be around 10 mg L^–1 lower than expected for farms with similar intensification on other parent materials. In particular, the mean Olsen-P values of samples from basaltic soils under grass with total Fe above 62 g kg^–1 and total Mg above 16 g kg^–1 were significantly lower than those from basaltic soils with low total Fe (<37 g kg^–1) and total Mg (<8 g kg^–1). As a result of the depressed Olsen-P value, excessive quantities of P may be applied to these soils to maintain a recommended soil P index thereby enhancing the potential for nutrient enrichment of adjacent surface waters. In such cases, coworkers have shown that acid ammonium oxalate may be a better extractant than bicarbonate as an indicator of plant-available P.     

Iron oxides in lateritic soils from Western Australia

Lateritic soils developed from dolerite contained larger amounts of goethite and haematite than those developed from granite. The goethite/(goethite + haematite) ratio in granitic soils ranged from 0.55 to 1 and from 0.29 to 0.83 in doleritic soils. Maghemite ranged in abundance from 0 to 10% and it only occurred in duricrust. Mole % Al substitution ranged from 16 to 33% in goethite and from 2.5 to 10% in haematite and was similar for both granitic and doleritic soils. Al substitution in maghemite was <5%. A significant, positive correlation (P<0.01) occurred between Al substitution in goethite and the amount of gibbsite in the soil. The dehydroxylation temperature of goethite ranged from 292 to 334°C and was positively correlated with the mole % Al substitution. Goethite crystals varied in size from 16 to 26 nm and haematite crystals from 18 to 59 nm. Goethite and haematite crystals occurred as aggregates of subrounded platy crystals.
Iron oxides obtained by NaOH treatment contained much of the minor element contents of the soils; mean concentrations (μg g⁻¹) were: Zn 19.9, Cu 31, Mn 68, Ni 140, Co 32, Cr 394 and V 696. These minor elements were most abundant in iron oxides derived from dolerite, but were not preferentially associated with goethite or haematite.     

Fixation of radiocaesium traces in a weathering sequence mica → vermiculite → hydroxy interlayered vermiculite

Radiocaesium fixation in soils is reported to occur on frayed edge sites of micaceous minerals. The weathering of mica in acid soils may therefore influence the Cs⁺ fixation process and thereby the mobility of the radiopollutant. We produced a laboratory weathering model biotite → trioctahedral vermiculite → oxidized vermiculite → hydroxy interlayered vermiculite (HIV) and quantified the Cs⁺ fixation of each mineral both in a fixed K⁺–Ca²⁺ background and in acid conditions. The transformation process was achieved through K depletion by Na-tetraphenylboron, oxidation with Br₂ and Al-intercalation using NaOH and AlCl₃. In a constant K⁺–Ca²⁺ background, vermiculite fixed 92–95% of the initial ¹³⁷Cs⁺ contamination while biotite and HIV fixed only 18–33%. In acid conditions, the interlayer occupancy by either potassium (biotite) or hydroxy-Al groups (HIV) strongly limited Cs⁺ fixation to 1–4% of the initial ¹³⁷Cs⁺ contamination. Cs⁺ fixation occurred on vermiculitic sites associated with micaceous wedge zones. Though both oxidized and trioctahedral vermiculites fixed similar Cs⁺ amounts in a constant K⁺–Ca²⁺ background (92–95%), the oxidized vermiculite retained much more radiocaesium in acid conditions (78–84% against 54–59%), because of its dioctahedral character.     

Interaction forces between soil particles: shear moduli of the < 2 μm size fraction

The shear moduli of the < 2 μm size fraction of three soils have been measured for samples of 10–35% w/w solid. Samples were thixotropic, the shear modulus increasing with time. This increase can be described by simple models and visualized in terms of the formation of links between particles. For a given soil the shear modulus increases with ionic form in the order Ca²⁺∼Mg²⁺ + + < Li⁺ and varies in a complex manner with electrolyte concentration.