An EPR spectroscopic examination of heavy metals in humic and fulvic acid soil fractions

Electron paramagnetic spectra of humic acid and various fractions of fulvic acid from a deep peat soil were studied and related to some of the metals present. In fulvic acid, VO²⁺ occurred in complexed form. The Mn²⁺ components all had a high degree of ionicity. In the humic acid fraction Cu²⁺ was present as a copper porphyrin-type complex.     

Absorption of metals on sedimentary and peat humic acids

Humic acids isolated from marine sediments were found to be effective in absorption of various metal ions through chelation, cation exchange and surface adsorption. The quantities of metal ions complexed varied from 40 to 205 mg/g of organic matter. In the presence of equal concentrations of Co, Cu, Mn, Ni and Zn in the reaction media, humic acid and peatmoss, a rich source of humic compounds, showed preferential absorption for Cu. Copper constituted more than 50% of the metal ions complexed by organic matter. As compared with the other metal ions, its bonding strength was very firm because it could not be displaced by ferric ion or cation exchange reagents.Peatmoss, a rich source of humic acid, was found to absorb significant quantities of various metal ions. Under laboratory conditions each kg of peat absorbed about 1500 mg of various metal ions from solutions containing equal concentrations of Co, Cu, Mn, Ni and Zn. However, in the field trials with sea water, absorption of metals was limited to Zn (28.7 mg/kg), Cu (3.66 mg/kg) and Fe (2.0 mg/kg). Under-saturation of sea water for transition metals and super-saturation for alkali and alkaline earth metals appears to be a bottleneck in the effective utilization of peat as a means of recovery of metals from sea water.     

Al(III) and Fe(III) binding by humic substances in freshwaters, and implications for trace metal speciation

Published experimental data for Al(III) and Fe(III) binding by fulvic and humic acids can be explained approximately by the Humic Ion-Binding Model VI. The model is based on conventional equilibrium reactions involving protons, metal aquo ions and their first hydrolysis products, and binding sites ranging from abundant ones of low affinity, to rare ones of high affinity, common to all metals. The model can also account for laboratory competition data involving Al(III), Fe(III) and trace elements, supporting the assumption of common binding sites. Field speciation data (116 examples) for Al in acid-to-neutral waters can be accounted for, assuming that 60-70 % (depending upon competition by iron, and the chosen fulvic acid : humic acid ratio) of the dissolved organic carbon (DOC) is due to humic substances, the rest being considered inert with respect to ion binding. After adjustment of the model parameter characterizing binding affinity within acceptable limits, and with the assumption of equilibrium with a relatively soluble form of Fe(OH)₃, the model can simulate the results of studies of two freshwater samples, in which concentrations of organically complexed Fe were estimated by kinetic analysis.The model was used to examine the pH dependence of Al and Fe binding by dissolved organic matter (DOM) in freshwaters, by simulating the titration with Ca(OH)₂ of an initially acid solution, in equilibrium with solid-phase Al(OH)₃ and Fe(OH)₃. For the conditions considered, Al, which is present at higher free concentrations than Fe(III), competes significantly for the binding of Fe(III), whereas Fe(III) has little effect on Al binding. The principal form of Al simulated to be bound at low pH is Al³⁺, AlOH²⁺ being dominant at pH >6; the principal bound form of Fe(III) is FeOH²⁺ at all pH values in the range 4-9. Simulations suggest that, in freshwaters, both Al and Fe(III) compete significantly with trace metals (Cu, Zn) for binding by natural organic matter over a wide pH range (4-9). The competition effects are especially strong for a high-affinity trace metal such as Cu, present at low total concentrations (∼1 nM). As a result of these competition effects, high-affinity sites in humic matter may be less important for trace metal binding in the field than they are in laboratory systems involving humic matter that has been treated to remove associated metals.     

Organic carbon and cation associations in humic material from pond water and sediment

Organic matter was isolated from the water columns and sediments of two pond systems in the south-eastern United States. Water column material was ultrafiltered to provide three fractions, i.e. <0.45 μm, but > 50,000 daltons; <50,000 daltons, but > 5000 daltons; and <5000 daltons. Sedimentary organic matter was separated into humic acid and fulvic acid fractions based on solubility criteria and the humic acid fraction was ultrafiltered to provide the same fractions as the water column isolates. All fractions were analysed for organic carbon, Al, Ca, Cu, Fe, Mg and Mn. Infra-red spectra were also measured for the sedimentary organic fractions. Organic matter isolated from the water column of the two ponds had similar organic carbon and elemental distributions, as did the organic matter isolated from the two sediments. However, significant differences in the organic carbon and elemental distributions were observed for water column and sedimentary organic matter isolated from the same pond. These studies have relevance to diagenetic alterations of organic matter and geochemical cycles of elements within lakes.     

Partitioning of transition metals in oxidised and reduced zones of sulphide-bearing fine-grained sediments

Distribution and forms of transition metals (Ti, Zn, Ni, Co, Mn, Fe, Cu, V and Cr) were investigated in oxidised, partly oxidised and reduced zones of sulphide-bearing fine-grained sediments located in the coastal areas of western Finland. Samples for the analysis and study of vertical distribution of elements were taken from each vertical 10 cm section in pits ranging in depth between 2 and 3 metres, while bulk samples for characterisation of species and forms of metals were taken from 3 zones in each pit: the acid sulphate soil (characterised by acid and oxidising conditions), transition zone (characterised by a steep pH gradient and partly oxidising conditions) and the reduced zone (pH >6). The former samples were digested in aqua regia (3:1:2 HCl:HNO₃:H₂O), while the latter were digested in aqua regia and hot concentrated acids (HClO₄–HNO₃–HCl–HF) and were subjected to extractions with acid ammonium acetate, H₂O₂ and acid ammonium oxalate. Each leachate was analysed for metals with ICP–AES.The vertical variation in the concentrations of Ti were small at all the studied sites indicating that the sediments are homogeneous and that the total losses of other elements from the soil profiles (acid sulphate soil+transition zone) are not extensive. Field observations, extractions with ammonium oxalate, and concentration–variation patterns indicated that Fe-oxide is largely precipitated and retained also in these acid soils. There are, however, indications of redistribution of Fe within the soil profiles. The results also demonstrated that Mn, Ni, Zn, Co and Cu have been lost in considerable amounts from the acid sulphate soils. However, whereas Mn in general has been lost throughout the soil profile, part of the Zn, Ni and Co released in the acid sulphate soils have migrated downward and been reimmobilised in the transition zone immediately above the reduced zone. Also Cu has been lost from the acid sulphate soil, but generally in smaller proportions than Mn, Zn, Ni and Co. Dissolved metal sulphides seem to be major sources of the mobilised metal fractions. A main part of the V and Cr in the sediments are associated with weathering-resistant minerals. These metals are therefore, like Ti, only to a limited extent mobilised by the oxidation of the sulphide-bearing sediments.     

The coagulation,solubility and adsorption properties of Fe,Mn, Cu,Ni, Cd,Co and humic acids in a river water

River water (Water of Luce, Scotland) is used in laboratory experiments designed to investigate physical and chemical properties of Fe. Mn, Cu, Ni, Co, Cd and humic acids in riverine and estuarine systems. Using NaCl, MgCl₂ and CaCl₂ as coagulating agents, coagulation of dissolved (0.4 μm filtered) Fe, Cu, Ni, Cd and humic acids increases in a similar matter with increasing salt molarily: Ca²⁺ is the most dominant coagulating agent. Removal by coagulation with Ca²⁺ at seawater concentrations ranges from large (Fe-80%. HA-60%, Cu-40%) to small (Ni, Cd-15%) to essentially nothing (Cd, Mn-3%). Destabilization of colloids is the indicated mechanism. Solubility-pH measurements show that between a pH of 3 and 9, Fe, Cu, Ni, Mn, Co and Cd are being held in the dissolved phase by naturally occurring organic substances. Between pH of 2.2 and 1.2 a large proportion of dissolved Fe, Cu. Ni and Cd (72, 35,44 and 36% respectively) is precipitated along with the humic acids; in contrast, Mn and Co show little precipitation (3%). Adsorption-pH experiments, using unfiltered river water spiked with Cu, indicate that adsorption of Cu onto suspended particles is inhibited to a large extent by the formation of dissolved Cu-organic complexes.The experimental results demonstrate that solubilities and adsorption properties of certain trace metals in freshwaters can be opposite to those observed with artificial solutions or predicted with chemical models. Interaction with organic substances is a critical factor.     

Vanadium-fulvic acid chemistry: conformational and binding studies by electron spin probe techniques

Two fractions of soil fulvic acid (FA) were separated by gel filtration chromatography. An observed increase in volume of the heavier fraction (FA I) with increasing pH was attributed to aggregation, intramolecular negative charge repulsions and the rupture of hydrogen bonds, which control molecular conformation. Optical absorption properties and elemental analyses of both fractions were determined. The stability constants and stoichiometries of FA complexes with vanadyl, VO²⁺, at pH 5.0 and ionic strength of 0.04 M were measured by electron paramagnetic resonance (EPR) spectroscopy. EPR spectra of model VO²⁺ complexes with phthalic and salicylic acids, which are the probable functional groups present in FA, are identical to those of the VO²⁺-FA complexes. Aggregation of FA I occurs in the presence of VO²⁺ to form a complex that can be approximated as ‘(VO)₂(FA I)₆’. The average site distance between vanadyl ions in this complex is shown to be greater than 1.2 nm. EPR parameters for FA I suggest binding by carboxylate groups. These parameters are compared with those of other vanadyl complexes with fulvic and humic acids reported by others. Reduction of VO₃^? to VO²⁺ by these materials is discussed.     

Mössbauer spectroscopic studies of iron in organic material from natural sedimentary environments

⁵⁷Fe Mössbauer spectra have been obtained from samples of humic acid, fulvic acid and kerogen and from the organic material extracted from bituminous chalk with benzene-methanol. The spectra indicate that iron occurs in a trivalent form in the silicate residue of the humic acid fraction, as hydrated ferrous ions associated with the fulvic acid fraction, as pyrite in kerogen and in a form not detectable by Mössbauer spectroscopy in the benzene-methanol extract.     

New operational method of testing colloid complexation with metals in natural waters

A dialysis procedure was used to assess the distribution coefficients of ∼50 major and trace elements (TEs) between colloidal (1 kDa–0.22 μm) and truly dissolved (<1 kDa) phases in Fe- and organic-rich boreal surface waters. These measurements allowed quantification of both TE partitioning coefficients and the proportion of colloidal forms as a function of solution pH (from 3 to 8). Two groups of elements can be distinguished according to their behaviour during dialysis: (i) elements which are strongly associated with colloids and exhibit significant increases of relative proportion of colloidal forms with pH increase (Al, Ba, Cd, Co, Cr, Cu, Fe, Ga, Hf, Mn, Ni, Pb, rare earth elements (REEs), Sr, Th, U, Y, Zn, Zr and dissolved organic C) and (ii) elements that are weakly associated with colloids and whose distribution coefficients between colloidal and truly dissolved phases are not significantly affected by solution pH (As, B, Ca, Cs, Ge, K, Li, Mg, Mo, Na, Nb, Rb, Sb, Si, Sn, Ti, V). Element speciation was assessed using the Visual MINTEQ computer code with an implemented NICA-Donnan humic ion binding model and database. The model reproduces quantitatively the pH-dependence of colloidal form proportion for alkaline-earth (Ba, Ca, Mg, Sr) and most divalent metals (Co, Cd, Mn, Ni, Pb, Zn) implying that the complexation of these metals with low molecular weight organic matter (<1 kDa fraction) is negligible. In contrast, model prediction of colloidal proportion (fraction of 1 kDa–0.22 μm) of Cu²⁺ and all trivalent and tetravalent metals is much higher than that measured in the experiment. This difference may be explained by (i) the presence of strong metal-binding organic ligands in the <1 kDa fraction whose stability constants are several orders of magnitude higher than those of colloidal humic and fulvic acids and/or (ii) coprecipitation of TE with Fe(Al) oxy(hydr)oxides in the colloidal fraction, whose dissolution and aggregation controls the pH-dependent pattern of TE partitioning. Quantitative modeling of metal – organic ligand complexation and empirical distribution coefficients corroborate the existence of two colloidal pools, formerly reported in boreal surface waters: “classic” fulvic or humic acids binding divalent transition metals and alkaline-earth elements and large-size organo-ferric colloids transporting insoluble trivalent and tetravalent elements.     

Cu and Fe associated with humic acids in sediments of a tropical coastal lagoon

The amount of Cu and Fe associated with humic acids was estimated in five sediment cores from a tropical coastal lagoon (Piratininga Lagoon, Rio de Janeiro, Brazil). Core samples were analysed for humic acid contents, total Fe and Cu content. Fe and Cu associated with humic acids were also measured. Results show amounts of humic acids ranging from 0.7 to 21.7% of the dry weight of sediment (average 4.6%, standard deviation 4.4%). Concentrations of Fe and Cu ranged from 0.3 to 6.0% (average 2.2%, S.D. 1.2%) and from <1.0 to 65.0 μg g⁻¹ (average 28.6 μg g⁻¹, S.D. 16.4 μg g⁻¹), respectively. The results of strongly bound metals show that while humic acids are the main carrier for Cu, Fe does not seems to be significantly associated with this organic matter.     

Analytical problems in determining peptide nitrogen in the humic fractions of three Italian soils

Peptides were released from organic matter fractions of three Italian soils (humin, humic and fulvic acids), when the samples were hydrolyzed in Ba(ON)₂-saturated solution at 105°C for 2 hr. The peptides obtained were separated using electrophoresis and paper chromatography. The presence of polypeptides in the soil organic matter was indicated by: (1) their hydrolysis by pronase; (2) the amino acids released by 6 N HCl hydrolysis; (3) The comparison of i.r. spectra of humic fractions before and after hydrolysis with 6 N HCl.Attempts at isolating the native proteinaceous compounds using electrophoresis in polyacrylamide gel failed; additionally, our attempts to hydrolyze proteinaceous components enzymatically in unfractionated soil organic matter, as well as in its fractions, before and after methylation, with pepsin, papain and pronase, were unsuccessful. Pronase demonstrated a weak proteolytic activity only at very low substrate-enzyme ratios (20 : 1) in humic and fulvic fractions and in whole phyrophosphate extract. Deproteinated substrates treated with pronase also released free amino acids, suggesting autodigestion.In humin, humic and fulvic fractions we found a total amino acid content of 40–45%, 12–24% or 1–85, respectively. Amino acid recovery from single fractions was about 70–80% of the total content in the unfractionated soil.     

Geochemical Indication of Sinian Bedded Siliceous Rocks in the Hunan-Guizhou-Guangxi Area and Their Environmental Significance

In the Hunan-Guizhou-Guangxi area there have developed very thick bedded siliceous rocks of the late Sinian. The rocks have a fairly pure composition, with an average content of siliceous minerals exceeding 95%. They are relatively rich in Fe and Mn, and poor in Al, Ti and Mg. The Fe/Ti, (Fe+Mn)/Ti, Al/(Al+Fe+Mn) and U/Th ratios and the Al-Fe-Mn and Fe-Mn-(Ni+Co+Cu)×10 triangle diagrams all show that they are hydrothermal sedimentary siliceous rocks. In the rocks the total amount of REEs is low, the δCe shows an obvious negative anomaly and the 8Eu a weak anomaly, and LREE>HREE, all indicating that they are products of hydrothermal processes. The δ30Si and δ18O values, as well as the formation temperature of the rocks all clearly show that the silica forming the rocks comes from hot water. Besides, analyses of the depositional environment of the rocks using the MnO/TiO2 ratio and the δCe and δ30Si values yield the same conclusion that they are formed in environments from continental marginal slope     

Transport and sediment–water partitioning of trace metals in acid mine drainage: an example from the abandoned Kwangyang Au–Ag mine area, South Korea

Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO₃–HClO₄) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K _d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K _d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.     

N-15 NMR spectra of naturally abundant nitrogen in soil and aquatic natural organic matter samples of the International Humic Substances Society

The naturally abundant nitrogen in soil and aquatic NOM samples from the International Humic Substances Society has been characterized by solid state CP/MAS ¹⁵N NMR. Soil samples include humic and fulvic acids from the Elliot soil, Minnesota Waskish peat and Florida Pahokee peat, as well as the Summit Hill soil humic acid and the Leonardite humic acid. Aquatic samples include Suwannee River humic, fulvic and reverse osmosis isolates, Nordic humic and fulvic acids and Pony Lake fulvic acid. Additionally, Nordic and Suwannee River XAD-4 acids and Suwannee River hydrophobic neutral fractions were analyzed. Similar to literature reports, amide/aminoquinone nitrogens comprised the major peaks in the solid state spectra of the soil humic and fulvic acids, along with heterocyclic and amino sugar/terminal amino acid nitrogens. Spectra of aquatic samples, including the XAD-4 acids, contain resolved heterocyclic nitrogen peaks in addition to the amide nitrogens. The spectrum of the nitrogen enriched, microbially derived Pony Lake, Antarctica fulvic acid, appeared to contain resonances in the region of pyrazine, imine and/or pyridine nitrogens, which have not been observed previously in soil or aquatic humic substances by ¹⁵N NMR. Liquid state ¹⁵N NMR experiments were also recorded on the Elliot soil humic acid and Pony Lake fulvic acid, both to examine the feasibility of the techniques, and to determine whether improvements in resolution over the solid state could be realized. For both samples, polarization transfer (DEPT) and indirect detection (¹H–¹⁵N gHSQC) spectra revealed greater resolution among nitrogens directly bonded to protons. The amide/aminoquinone nitrogens could also be observed by direct detection experiments.     

Sorption of Cu and Pb to kaolinite-fulvic acid colloids: Assessment of sorbent interactions

The sorption of Cu(II) and Pb(II) to kaolinite-fulvic acid colloids was investigated by potentiometric titrations. To assess the possible interactions between kaolinite and fulvic acid during metal sorption, experimental sorption isotherms were compared with predictions based on a linear additivity model (LAM). Suspensions of 5 g L⁻¹ kaolinite and 0.03 g L⁻¹ fulvic acid in 0.01 M NaNO₃ were titrated with Cu and Pb solutions, respectively. The suspension pH was kept constant at pH 4, 6, or 8. The free ion activities of Cu²⁺ and Pb²⁺ were monitored in the titration vessel using ion selective electrodes. Total dissolved concentrations of metals (by ICP-MS) and fulvic acid (by UV-absorption) were determined in samples taken after each titration step. The amounts of metals sorbed to the solid phase, comprised of kaolinite plus surface-bound fulvic acid, were calculated by difference. Compared to pure kaolinite, addition of fulvic acid to the clay strongly increased metal sorption to the solid phase. This effect was more pronounced at pH 4 and 6 than at pH 8, because more fulvic acid was sorbed to the kaolinite surface under acidic conditions. Addition of Pb enhanced the sorption of fulvic acid onto kaolinite at pH 6 and 8, but not at pH 4. Addition of Cu had no effect on the sorption of fulvic acid onto kaolinite. In the LAM, metal sorption to the kaolinite surface was predicted by a two-site, 1-pK basic Stern model and metal sorption to the fulvic acid was calculated with the NICA-Donnan model, respectively. The LAM provided good predictions of Cu sorption to the kaolinite-fulvic acid colloids over the entire range in pH and free Cu²⁺ ion activity (10⁻¹² to 10⁻⁵). The sorption of Pb was slightly underestimated by the LAM under most conditions. A fractionation of the fulvic acid during sorption to kaolinite was observed, but this could not explain the observed deviations of the LAM predictions from the experimental Pb sorption isotherms.     

A comparison of the early diagenetic environment in intertidal sands and muds of the Manukau Harbour,New Zealand

The early diagenetic environment of intertidal sandy sediments (sands) and muddy sediments (muds) is described and compared from two cores taken from an unpolluted part of the Manukau Harbour, New Zealand. Extraction techniques characterized the form of the trace elements (Fe, Mn, S, C, Pb, Zn, Cu) at different depths in the sediment. Dissolved forms of Fe, Mn, and S were measured in interstitial water. Nonresidual metal concentrations, humic acid, FeS, and FeS₂ are an order of magnitude higher in the muds than in the sands because of dilution by unreactive sand particles. Muds contain a larger proportion of metals in the mobile fractions; exchangeable (Mn), carbonate (Mn, Fe, Zn), and easily-reducible oxide (Fe, Mn, Zn, Pb). This is due to greater surface area (for Mn adsorption); the favorable conditions for MnCO₃, FeCO₃, and FeS precipitation; and higher concentrations of easily reducible iron oxide and humic acid. Therefore, compared to the sands, muds are more important as reservoirs for toxic metals, both in terms of quantity and availability. At either site there was very little difference between the forms of Zn, Pb or Cu identified by sequential extraction as sediments changed from oxic to anoxic conditions. One reason for this is that the amounts and proportions of some of the important components that bind metals, viz., amorphous iron hydrous oxides, humic acids, and FeS₂, do not change much. Other components that do change with redox conditions, for example, manganese phases and FeS, are only minor components of the sediment. Redox conditions, then, have relatively little effect on trace-metal partitioning in the sediment matrix of these unpolluted sediments.     

New approaches to studying heavy metals in soils by X-ray absorption spectroscopy (XANES)) and extractive fractionation

A comprehensive approach to studying the nature of interaction between heavy-metal ions and the organic–mineral matrix of soils involves application of modern physical analytical techniques and chemical methods of extractive fractionation. XANES was used to obtain the first data on the near-edge fine structure of X-ray spectra for a number of heavy-metal species in ordinary chernozem. Data on the structure of soil samples saturated with Zn²⁺ and Cu²⁺ obtained by XANES (X-ray absorption near-edge structure) make it possible to elucidate the interaction mechanisms of the metals and the types of chemical bonds formed thereby. As contamination doze of with Cu and Zn is increased (from 2000 to 10 000 mg/kg soil), particularly if the metals are introduced in the form of readily solubility salts, bonding between the metals and soil components weakens. Data of extractive fractionation of metal compounds from samples saturated with Cu and Zn compounds testify that the Cu²⁺ ion is preferably retained in the organic matter of the soil, whereas the Zn²⁺ ion is bound mostly to silicates, carbonates, and Fe and Mn (hydro)oxides.     

Stability, solubility and maximum metal binding capacity in metal–humic complexes involving humic substances extracted from peat and organic compost

The aim of this work is to investigate the influence of pH and the metal:humic substances (HS) ratio on HS complexing capacity and the stability and solubility of metal–HS complexes in solution. We selected four HS with different physicochemical properties and studied their interaction with Cu(II), Zn(II) and Fe(II) at different pH and metal:HS ratios. The selected HS were a humic acid and a whole humic extract (containing the humic and fulvic acids) extracted from black peat, and a fulvic acid and a whole humic extract extracted from a compost of grape solid wastes.Our results showed that HS complexing capacity significantly varied as a function of pH, thus indicating the influence of both functional group ionisation and molecular conformation on this property. As was expected, total acidity affected the complexing capacity of the selected HS.The results related to stability and complexing capacity indicated the possible presence of two binding patterns, one at acid-neutral pH probably involving carboxylates, and another at alkaline pH probably involving carboxylates and phenolic groups. The relationship between these binding patterns and the strength of the binding process varied according to the complexed metal.Complex solubility was greatly affected by the ratio between the concentration of free ionised functional groups and the molecular weight in the HS studied.     

On the metal content and metal ion uptake of botanically specific peats and the derived humic acids

With respect to ten metals (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga) which are continguous in the Periodic Table the natural metal content and the ability to take up metal ions has been determined for three peats of defined botanical origin, each peat being sampled at three different levels. A correlation is found between the natural metal content and botanical origin. Apart from aluminium, the concentration of individual metals increased in the series Sphagnum < fen sedge < reed, the increase being statistically significant (P = 0.001) for V, Mn, Co, Ni, and Ga and for the sum of the metal ions measured.No clear correlation emerged between botanical origin and metal uptake. The metal uptake by the humic acid derived from each peat sample was also determined, and correlated with the metal uptake of the source peat itself.In all the humic acid and peat metal-uptake experiments the selectivities were very similar. V, Cr, Cu, Ga were readily taken up while Mn, Co and Zn were consistently less preferred.     

Selective sequential dissolution of organic-rich stream sediments from Talvivaara, Finland

Organic-rich stream sediments, a widely used material in geochemical prospecting in Finland, were investigated by analyzing Mn, Fe, Co, Ni, Cu and Zn after a series of selective extractions.Forty-seven organic-rich stream-sediment samples were collected in the vicinity of a sulphide mineralization in Talvivaara, eastern Finland. Loss on ignition of the samples at 500°C was 20–95%. pH of the samples, measured in the water pressed from the samples, was 3.4–6.2 with a mean of 4.2.The < 0.5 mm grain-size fraction was subjected to a sequential extraction as follows: NH₄-acetate for exchangeable cations; cold NH₂OH·HCl for dissolution of Mn oxides; H₂O₂ for destruction of organic material; hot NH₂OH·HCl for dissolution of Fe oxides; HF/HClO₄/aqua regia for dissolving the residue. Each extraction was analyzed by flame AAS for Mn, Fe, Co, Ni, Cu and Zn.Manganese and Co are mostly in exchangeable form and in the residue, while the proportion complexed by the organic components is minimal. Iron and Ni own a lot of exchangeable character although a significant proportion of these elements is complexed by the organic components. Most of Cu is in organic form. Zinc is the element most evenly distributed between extractions.