Mineralogical characteristics and transformations during long-term operation of a zerovalent iron reactive barrier

Design and operation of Fe0 permeable reactive barriers (PRBs) can be improved by understanding the long-term mineralogical transformations that occur within PRBs. Changes in mineral precipitates, cementation, and corrosion of Fe0 filings within an in situ pilot-scale PRB were examined after the first 30 months of operation and compared with results of a previous study of the PRB conducted 15 months earlier using X-ray diffraction and scanning electron microscopy employing energy dispersive X-ray and backscatter electron analyses. Iron (oxy)hydroxides, aragonite, and maghemite and/or magnetite occurred throughout the cores collected 30 mo after installation. Goethite, lepidocrocite, mackinawite, aragonite, calcite, and siderite were associated with oxidized and cemented areas, while green rusts were detected in more reduced zones. Basic differences from our last detailed investigation include (i) mackinawite crystallized from amorphous FeS, (ii) aragonite transformed into calcite, (iii) akaganeite transformed to goethite and lepidocrocite, (iv) iron (oxy)hydroxides and calcium and iron carbonate minerals increased, (v) cementation was greater in the more recent study, and (vi) oxidation, corrosion, and disintegration of Fe0 filings were greater, especially in cemented areas, in the more recent study. If the degree of corrosion and cementation that was observed from 15 to 30 mo after installation continues, certain portions of the PRB (i.e., up-gradient entrance of the ground water to the Fe0 section of the PRB) may last less than five more years, thus reducing the effectiveness of the PRB to mitigate contaminants.     

Metolachlor dechlorination by zerovalent iron during unsaturated transport

Permeable zerovalent iron (Fe0) barriers have become an established technology for remediating contaminated ground water. This same technology may be applicable for treating pesticides amenable to dehalogenation as they move downward in the vadose zone. By conducting miscible displacement experiments in the laboratory with metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide; a chloroacetanilide herbicide] under unsaturated flow, we provide proof-of-concept for such an approach. Transport experiments were conducted in repacked, unsaturated soil columns attached to vacuum chambers and run under constant matrix potential (-30 kPa) and Darcy flux (approximately 2 cm d(-1)). Treatments included soil columns equipped with and without a permeable reactive barrier (PRB) consisting of a Fe0-sand (50:50) mixture supplemented with Al2(SO4)3. A continuous pulse of 14C-labeled metolachlor (1.45 mM) and tritiated water (3H2O) was applied to top of the columns for 10 d. Results indicated complete (100%) metolachlor destruction, with the dehalogenated product observed as the primary degradate in the leachate. Similar results were obtained with a 25:75 Fe0-sand barrier but metolachlor destruction was not as efficient when unannealed iron was used or Al2(SO4)3 was omitted from the barrier. A second set of transport experiments used metolachlor-contaminated soil in lieu of a 14C-metolachlor pulse. Under these conditions, the iron barrier decreased metolachlor concentration in the leachate by approximately 50%. These results provide initial evidence that permeable iron barriers can effectively reduce metolachlor leaching under unsaturated flow.     

Enhancing metolachlor destruction rates with aluminum and iron salts during zerovalent iron treatment

Pesticide-contaminated soil may require remediation to mitigate ground and surface water contamination. We determined the effectiveness of zerovalent iron (Fe(0)) to dechlorinate metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methyl ethyl) acetamide] in the presence of aluminum and iron salts. By treating aqueous solutions of metolachlor with Fe(0), we found destruction kinetics were greatly enhanced when Al, Fe(II), or Fe(II) salts were added, with the following order of destruction kinetics observed: Al2(SO4)3 > AlCl3 > Fe2(SO4)3 > FeCl3. A common observation was the formation of green rusts, mixed Fe(II)-Fe(III) hydroxides with interlayer anions that impart a greenish-blue color. Central to the mechanism responsible for enhanced metolachlor loss may be the role these salts play in facilitating Fe(II) release. By tracking Al and Fe(II) in a Fe(0) + Al2(SO4)3 treatment of metolachlor, we observed that Al was readily sorbed by the corroding iron with a corresponding release of Fe(II). The manufacturing process used to produce the Fe(0) also profoundly affected destruction rates. Metolachlor destruction rates with salt-amended Fe(0) were greater with annealed iron (indirectly heated under a reducing atmosphere) than unannealed iron. Moreover, the optimum pH for metolachlor dechlorination in water and soil differed between iron sources (pH 3 for unannealed, pH 5 for annealed). Our results indicate that metolachlor destruction by Fe(0) treatment may be enhanced by adding Fe or Al salts and creating pH and redox conditions favoring the formation of green rusts.     

Inorganic pigments made from the recycling of coal mine drainage treatment sludge

Continuous industrial development increases energy consumption and, consequently, the consumption of fossil fuels. Coal mineral has been used in Brazil as a solid fuel for thermoelectric generators for several years. However, coal exploitation affects the environment intensely, mainly because Brazilian coal contains excess ash and pyrite (iron disulfide). According to the local coal industry syndicate, the average annual coal run per mine is 6 million ton/year; 3.5 million ton/year are rejected and disposed of in landfills. Besides pyrite, Brazilian coal contains Mn, Fe, Cu, Pb, Zn, Ge, Se, and Co. Additionally, the water used for coal beneficiation causes pyrite oxidation, forming an acid mine drainage (AMD). This drainage solubilizes the metals, transporting them into the environment, making treatment a requirement. This work deals with the use of sedimented residue from treated coal mine drainage sludge to obtain inorganic pigments that could be used in the ceramic industry. The residue was dried, ground and calcined ( approximately 1250 degrees C). The calcined pigment was then micronized (D(50) approximately 2mum). Chemical (XRF), thermal (DTA/TG), particle size (laser), and mineralogical (XRD) analyses were carried out on the residue. After calcination and micronization, mineralogical analyses (XRD) were used to determine the pigment structure at 1250 degrees C. Finally, the pigments were mixed with transparent glaze and fired in a laboratory roller kiln (1130 degrees C, 5min). The results were promising, showing that brown colors can be obtained with pigments made by residues.     

Reduction of copper(II) by iron(II)

Laboratory and field investigations have clearly demonstrated the important role of reduced iron (Fe(II)) in reductive transformations of first-row transition metal species. However, interactions of Fe(II) and copper (Cu) are not clearly understood. This study examined the reduction of Cu(II) by Fe(II) in stirred-batch experiments at pH 5.2 and 5.5 as influenced by chloride (Cl-) concentration (0.002-0.1 M), initial metal concentration (0.1-9.1 mM), and reaction time (1-60 min) under anoxic conditions. Reduction of Cu(II) to Cu(I) by dissolved Fe(II) was rapid under all experimental conditions and the stability of the products explains the driving force for the redox reaction. Under conditions of low [Cl-] and high initial metal concentration, >40% of total Cu and Fe were removed from solution after 1 min, which accompanied formation of a brownish-red precipitate. X-ray diffraction (XRD) patterns of the precipitates revealed the presence of cuprite (Cu2O), a Cu(I) mineral, based on d-spacings located at 0.248, 0.215, 0.151, and 0.129 nm. Fourier transform infrared (FTIR) spectroscopy corroborated XRD data for the presence of Cu2O, with features located at 518, 625, and 698 cm(-1). Increasing [Cl-] stabilized the dissolved Cu(I) product against Cu2O precipitation and resulted in more Fe precipitated from solution (relative to Cu) that appears to be present as poorly crystalline lepidocrocite (gamma-FeOOH). This process may be important in anoxic soil environments, where dissolved Fe(II) levels can accumulate.     

Sorption and degradation of alachlor and metolachlor in ground water using green sands

Reactive barriers are used for in situ treatment of contaminated ground water. Waste green sand, a by-product of gray-iron foundries that contains iron particles and organic carbon, was evaluated in this study as a low-cost reactive material for treating ground water contaminated with the herbicides alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide] and metolachlor [2-chloro-6'-ethyl-N-(2-methoxy-1-methylethyl)-o-acetoluidide]. Batch and column tests were conducted with 11 green sands to determine transport parameters and reaction rate constants for the herbicides. Similar Fe-normalized rate constants (K(SA)) were obtained from the batch and column tests. The K(SA) values obtained for green sand iron were also found to be comparable with or slightly higher than K(SA) values for Peerless iron, a common reactive medium used in reactive barriers. Partition coefficients ranging between 3.6 and 50.2 L/kg were obtained for alachlor and between 1.0 and 54.8 L/kg for metolachlor, indicating that the organic carbon and clay in green sands can significantly retard the movement of the herbicides. Partition coefficients obtained from the batch and column tests were similar (+/-25%), but the batch tests typically yielded higher partition coefficients for green sands exhibiting greater sorption. Calculations made using transport parameters from the column tests indicate that a 1-m-thick reactive barrier will result in a 10-fold reduction in concentration of alachlor and metolachlor for seepage velocities less than 0.1 m/d provided the green sand contains at least 2% iron. This level of reduction generally is sufficient to reduce alachlor and metolachlor concentrations below maximum contaminant levels in the United States.     

Combined application of QEM-SEM and hard X-ray microscopy to determine mineralogical associations and chemical speciation of trace metals

We describe the application of quantitative evaluation of mineralogy by scanning electron microscopy in combination with techniques commonly available at hard X-ray microprobes to define the mineralogical environment of a bauxite residue core segment with the more specific aim of determining the speciation of trace metals (e.g., Ti, V, Cr, and Mn) within the mineral matrix. Successful trace metal speciation in heterogeneous matrices, such as those encountered in soils or mineral residues, relies on a combination of techniques including spectroscopy, microscopy, diffraction, and wet chemical and physical experiments. Of substantial interest is the ability to define the mineralogy of a sample to infer redox behavior, pH buffering, and mineral-water interfaces that are likely to interact with trace metals through adsorption, coprecipitation, dissolution, or electron transfer reactions. Quantitative evaluation of mineralogy by scanning electron microscopy coupled with micro-focused X-ray diffraction, micro-X-ray fluorescence, and micro-X-ray absorption near edge structure (mXANES) spectroscopy provided detailed insights into the composition of mineral assemblages and their effect on trace metal speciation during this investigation. In the sample investigated, titanium occurs as poorly ordered ilmenite, as rutile, and is substituted in iron oxides. Manganese's spatial correlation to Ti is closely linked to ilmenite, where it appears to substitute for Fe and Ti in the ilmenite structure based on its mXANES signature. Vanadium is associated with ilmenite and goethite but always assumes the +4 oxidation state, whereas chromium is predominantly in the +3 oxidation state and solely associated with iron oxides (goethite and hematite) and appears to substitute for Fe in the goethite structure.     

Carbonate mineralization of volcanic province basalts

Flood basalts are receiving increasing attention as possible host formations for geologic sequestration of anthropogenic CO₂, with studies underway in the United States, India, Iceland, and Canada. Basalts from the United States, India, and South Africa were reacted with aqueous dissolved CO₂ and aqueous dissolved CO₂–H₂S mixtures under supercritical CO₂ (scCO₂) conditions to study the geochemical reactions resulting from injection of CO₂ in such formations. Despite the basalt samples having similar bulk chemical composition, mineralogy and dissolution kinetics, long-term static experiments show significant differences in rates of mineralization as well as compositions and morphologies of precipitates that form when the basalts are reacted with CO₂ and CO₂–H₂S mixtures in water. For example, basalt from the Newark Basin in the United States was by far the most reactive of any basalt tested to date. Reacted grains from the Newark Basin basalt appeared severely weathered and contained extensive carbonate precipitates with significant Fe content. In comparison, the post-reacted samples associated with the Columbia River basalts from the United States contained calcite grains with classic “dogtooth spar” morphology and trace cation substitution (Mg and Mn). Carbonation of the other basalts produced precipitates with compositions that varied chemically throughout the entire testing period. The Karoo basalt from South Africa appeared the least reactive, with very limited mineralization occurring during the testing with CO₂-saturated water. Compositional differences in the precipitates suggest changes in fluid chemistry unique to the dissolution behavior of each basalt sample reacted with CO₂-saturated water. No convincing correlations were identified between basalt reactivity and differences in bulk composition, mineralogy, glassy mesostasis quantity or composition. Moreover, the relative reactivity of different basalt samples was unexpectedly different in the experiments conducted with aqueous dissolved CO₂–H₂S mixtures versus those with CO₂ only. For example, the Karoo basalt was highly reactive in the presence of aqueous dissolved CO₂–H₂S, as evident by nodules of carbonate coating the basalt grains after 181 days of testing. However, the most reactive basalt in CO₂–H₂O, Newark Basin, formed only iron sulfide coatings in tests with a CO₂–H₂S mixture, which inhibited carbonate mineralization.     

Field-scale remediation of a metolachlor-contaminated spill site using zerovalent iron

Pesticide spills are common occurrences at agricultural cooperatives and farmsteads. When inadvertent spills occur, chemicals normally beneficial can become point sources of ground and surface water contamination. We report results from a field trial where approximately 765 m3 of soil from a metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] spill site was treated with zerovalent iron (Fe0). Preliminary laboratory experiments confirmed metolachlor dechlorination by Fe0 in aqueous solution and that this process could be accelerated by adding appropriate proportions of Al2(SO4)3 or acetic acid (CH3COOH). The field project was initiated by moving the stockpiled, contaminated soil into windrows using common earth-moving equipment. The soil was then mixed with water (0.35-0.40 kg H2O kg(-1)) and various combinations of 5% Fe0 (w/w),2% Al2(SO4)3 (w/w), and 0.5% acetic acid (v/w). Windrows were covered with clear plastic and incubated without additional mixing for 90 d. Approximately every 14 d, the plastic sheeting was removed for soil sampling and the surface of the windrows rewetted. Metolachlor concentrations were significantly reduced and varied among treatments. The addition of Fe0 alone decreased metolachlor concentration from 1789 to 504 mg kg(-1) within 90 d, whereas adding Fe0 with Al2(SO4)3 and CH3COOH decreased the concentration from 1402 to 13 mg kg(-1). These results provide evidence that zerovalent iron can be used for on-site, field-scale treatment of pesticide-contaminated soil.     

Occurrence and rates of terminal electron-accepting processes and recharge processes in petroleum hydrocarbon-contaminated subsurface

The occurrence and rates of terminal electron acceptor processes, and recharge processes in the unsaturated zone of a boreal site contaminated with petroleum hydrocarbons in the range C(10) to C(40) were examined. Soil microcosms were used to determine the rates of denitrification, iron (Fe) reduction, sulfate (SO(4)) reduction, and methanogenesis in two vertical soil profiles contaminated with oil, and in a noncontaminated reference sample. Furthermore, the abundances of the 16S rRNA genes belonging to Geobacteracaea in the samples were determined by real-time quantitative polymerase chain reaction (PCR). Analyses of ground water chemistry and soil gas composition were also performed together with continuous in situ monitoring of soil water and ground water chemistry. Several lines of evidence were obtained to demonstrate that both Fe reduction and methanogenesis played significant roles in the vertical profiles: Fe reduction rates up to 3.7 nmol h(-1) g(-1) were recorded and they correlated with the abundances of the Geobacteracaea 16S rRNA genes (range: 2.3 x 10(5) to 4.9 x 10(7) copies g(-1)). In the ground water, ferrous iron (Fe(2+)) concentration up to 55 mg L(-1) was measured. Methane production rates up to 2.5 nmol h(-1) g(-1) were obtained together with methane content up to 15% (vol/vol) in the soil gas. The continuous monitoring of soil water and ground water chemistry, microcosm experiments, and soil gas monitoring together demonstrated that the high microbial activity in the unsaturated zone resulted in rapid removal of oxygen from the infiltrating recharge thus leaving the anaerobic microbial processes dominant below 1.5 m depth both in the unsaturated and the saturated zones of the subsurface.     

RELATION OF PHYSICAL AND MINERALOGICAL PROPERTIES TO STREAMBANK STABILITY1

ABSTRACT. Alluvial streambank materials from nine unstable and six stable reaches showed little variation in physical and mineralogical properties. The bulk density of all the samples was so similar that they could be considered from the same population. Particle size distributions showed that the clay fractions were slightly, but significantly, higher for the stable reaches. The mineralogy of all samples was also quite similar. The sand-sized grains of the stable areas were less rounded than those of the unstable areas. This somewhat angular shape of the grains may have produced an interlocking between grains that added stability to the bank material. Also, clay coatings on the sand-sized grains from the stable areas may have caused cementation between grains that also strengthened the material.     

Pilot-scale treatment of RDX-contaminated soil with zerovalent iron

Soils in Technical Area 16 at Los Alamos National Laboratory (LANL) are severely contaminated from past explosives testing and research. Our objective was to conduct laboratory and pilot-scale experiments to determine if zerovalent iron (Fe(0)) could effectively transform RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in two LANL soils that differed in physicochemical properties (Soils A and B). Laboratory tests indicated that Soil A was highly alkaline and needed to be acidified [with H2SO4, Al2(SO4)3, or CH3COOH] before Fe(0) could transform RDX. Pilot-scale experiments were performed by mixing Fe(0) and contaminated soil (70 kg), and acidifying amendments with a high-speed mixer that was a one-sixth replica of a field-scale unit. Soils were kept unsaturated (soil water content = 0.30-0.34 kg kg(-1)) and sampled with time (0-120 d). While adding CH3COOH improved the effectiveness of Fe(0) to remove RDX in Soil A (98% destruction), CH3COOH had a negative effect in Soil B. We believe that this difference is a result of high concentrations of organic matter and Ba. Adding CH3COOH to Soil B lowered pH and facilitated Ba release from BaSO4 or BaCO3, which decreased Fe(0) performance by promoting flocculation of humic material on the iron. Despite problems encountered with CH3COOH, pilot-scale treatment of Soil B (12 100 mg RDX kg(-1)) with Fe(0) or Fe(0) + Al2(SO4)3 showed high RDX destruction (96-98%). This indicates that RDX-contaminated soil can be remediated at the field scale with Fe(0) and soil-specific problems (i.e., alkalinity, high organic matter or Ba) can be overcome by adjustments to the Fe(0) treatment.     

Physicochemical and mineralogical characterization of soil-saprolite cores from a field research site, Tennessee

Site characterization is an essential initial step in determining the feasibility of remedial alternatives at hazardous waste sites. Physicochemical and mineralogical characterization of U-contaminated soils in deeply weathered saprolite at Area 2 of the DOE Field Research Center (FRC) site, Oak Ridge, TN, was accomplished to examine the feasibility of bioremediation. Concentrations of U in soil-saprolite (up to 291 mg kg(-1) in oxalate-extractable U(o)) were closely related to low pH (ca. 4-5), high effective cation exchange capacity without Ca (64.7-83.2 cmol(c) kg(-1)), amorphous Mn content (up to 9910 mg kg(-1)), and the decreased presence of relative clay mineral contents in the bulk samples (i.e., illite 2.5-12 wt. %, average 32 wt. %). The pH of the fill material ranged from 7.0 to 10.5, whereas the pH of the saprolite ranged from 4.5 to 8. Uranium concentration was highest (about 300 mg kg(-1)) at around 6 m below land surface near the saprolite-fill interface. The pH of ground water at Area 2 tended to be between 6 and 7 with U concentrations of about 0.9 to 1.7 mg L(-1). These site specific characteristics of Area 2, which has lower U and nitrate contamination levels and more neutral ground water pH compared with FRC Areas 1 and 3 (ca. 5.5 and <4, respectively), indicate that with appropriate addition of electron donors and nutrients bioremediation of U by metal reducing microorganisms may be possible.     

PREDICTIVE CAPABILITIES OF BATCH-EXTRACT EXPERIMENTS USING WATER FROM A COAL MINE1

ABSTRACT: The ability of batch-extraction experiments to predict postmining ground water quality was evaluated. As a basis for evaluation, mineralogical and water quality data were used to identify the geochemical reactions that controlled the major-ion chemistry in batch-extraction experiments. The experiments used water and spoil material collected from a surface-coal mine in the Powder River basin of northeast Wyoming. The batch-extraction experiments consisted of a 2:1 solid:liquid ratio of ground water and spoil material (by weight). The chemical composition of the resulting batch-extracts was determined after a contact time of 24 hours. Thermodynamically-favorable reactions included calcite precipitation, gypsum dissolution, and formation of kaolinite as a result of orthoclase feldspar hydrolysis. Three reaction models were consistent with the therinodynanuc and mineralogic data. In general, the extracts had smaller major-ion concentrations than did the water samples collected from the spoil aquifer. Correction ratios were calculated from these experiments and could be used in combination with additional batch-extractions at existing or future lease areas to predict the quality of the ground water after mining.     

Effects of oxide coating and selected cations on nitrate reduction by iron metal

Under anoxic conditions, zerovalent iron (Fe(0)) reduces nitrate to ammonium and magnetite (Fe3O4) is produced at near-neutral pH. Nitrate removal was most rapid at low pH (2-4); however, the formation of a black oxide film at pH 5 to 8 temporarily halted or slowed the reaction unless the system was augmented with Fe(2+), Cu(2+), or Al(3+). Bathing the corroding Fe(0) in a Fe(2+) solution greatly enhanced nitrate reduction at near-neutral pH and coincided with the formation of a black precipitate. X-ray diffractometry and scanning electron microscopy confirmed that both the black precipitate and black oxide coating on the iron surface were magnetite. In this system, ferrous iron was determined to be a partial contributor to nitrate removal, but nitrate reduction was not observed in the absence of Fe(0). Nitrate removal was also enhanced by augmenting the Fe(0)-H2O system with Fe(3+), Cu(2+), or Al(3+) but not Ca(2+), Mg(2+), or Zn(2+). Our research indicates that a magnetite coating is not a hindrance to nitrate reduction by Fe(0), provided sufficient aqueous Fe(2+) is present in the system.     

Heavy metals removal and hydraulic performance in zero-valent iron/pumice permeable reactive barriers

Long-term behaviour is a major issue related to the use of zero-valent iron (ZVI) in permeable reactive barriers for groundwater remediation; in fact, in several published cases the hydraulic conductivity and removal efficiency were progressively reduced during operation, potentially compromising the functionality of the barrier. To solve this problem, the use of granular mixtures of ZVI and natural pumice has recently been proposed. This paper reports the results of column tests using aqueous nickel and copper solutions of various concentrations. Three configurations of reactive material (ZVI only, granular mixture of ZVI and pumice, and pumice and ZVI in series) are discussed. The results clearly demonstrate that iron-pumice granular mixtures perform well both in terms of contaminant removal and in maintaining the long-term hydraulic conductivity. Comparison with previous reports concerning copper removal by ZVI/sand mixtures reveals higher performance in the case of ZVI/pumice.     

Nitrate reduction in the presence of wüstite

Recent strategies to reduce elevated nitrate concentrations employ metallic Fe0 as a reductant. Secondary products of Fe0 corrosion include magnetite (Fe3O4), green rust [Fe6(OH)12SO4], and wüstite [FeO(s)]. To our knowledge, no studies have been reported on the reactivity of NO3- with FeO(s). This project was initiated to evaluate the reactivity of FeO(s) with NO3- under abiotic conditions. Stirred batch reactions were performed in an anaerobic chamber over a range of pH values (5.45, 6.45, and 7.45), initial FeO(s) concentrations (1, 5, and 10 g L(-1)), initial NO3- concentrations (1, 10, and 15 mM), and temperatures (3, 21, 31, and 41 degrees C) for kinetic and thermodynamic determinations. Suspensions were periodically removed and filtered to measure dissolved nitrogen and iron species. Solid phases were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Nitrate reduction by FeO was rapid and characterized by nearly stoichiometric conversion of NO3- to NH4+. Transient NO2- formation also occurred. The XRD and SEM results indicated the formation of Fe3O4 as a reaction product of the heterogeneous redox reaction. Kinetics of NO3- reduction suggested a rate equation of the type: -d[NO3-]/dt = k[FeO]0.57[H]0.22[NO3-]1.12 where k = 3.46 x 10(-3) +/- 0.38 x 10(-3) M(-1) s(-1), at 25 degrees C. Arrhenius and Eyring plots indicate that the reaction is surface chemical-controlled and proceeds by an associative mechanism involving a step where both NO3- and FeO(s) bind together in an intermediate complex.     

Ferron逐时络合比色法研究聚硅硫酸铁中铁的形态

通过实验制备了一种新型无机高分子絮凝剂聚硅硫酸铁（PFSS），用Ferron逐时络合比色法测定了PFSS中铁的形态，考察了熟化时间、Fe3+／SiO2摩尔比对铁的形态分布及转化规律的影响。不同Fe3+／SiO2摩尔比的PFSS中Fe（a）的量最多、占50％以上，Fe（c）在35％～50％之间，Fe（b）在0～5％之间。研究表明：铁的形态分布及其转化规律与溶液的高酸度及聚硅酸的存在有关。     

Iron and Zinc status in soils, water and staple food cultivars in Itakpe, Kogi State of Nigeria

The levels of iron (Fe) and zinc (Zn) were quantitatively determined in soil and water samples as well as in staple food cultivars in Itakpe, Nigeria's major iron mining town. The survey was conducted to establish a baseline pollution index for Fe and Zn in the Itakpe environment and to evaluate the role of foods as an exogenous source of these metals among the inhabitants. Exceedingly high levels of both metals characterized the staple food cultivars in the town.     

Effect of peroxide on neutralization-potential values of siderite and other carbonate minerals

To assess quantitatively the effect of peroxide addition to standard static tests of the neutralization potential (NP) of mine wastes, 10 specimens of carbonate minerals, including five of siderite (FeCO3) and two of rhodochrosite (MnCO3), were analyzed by electron microprobe. The compositions of the siderite span a range from 60 to 86 mol % Fe. Tests of NP for the siderite diluted with 80% (w/w) kaolinite gave values of 647 to 737 kg CaCO3 equivalent per Mg for determinations by the standard Sobek method. However, if it is assumed that the ferrous carbonate component of the mineral does not contribute to NP in field situations because oxidation of Fe(II) to Fe(III) and the subsequent hydrolysis of Fe(III) leads to the release of an equivalent amount of acid, then the calculated NP for the samples ranges from 110 to 390 kg CaCO3 equivalent per Mg. Two different methods involving the addition of peroxide to the test solutions were successful in bringing the measured NP values closer to the theoretical ones. By contrast, the tests with rhodochrosite indicated the Mn(II) to be stable. For long-term environmental planning, especially for wastes from metalliferous sulfide-poor deposits in which gradual dissolution of silicate and aluminosilicate minerals may be involved in attenuating the acidity, consideration in the overall NP budget needs to be given to the ferrous iron content of those minerals. The presence of Fe2+-bearing minerals, especially carbonates, in tested mine-waste materials may lead to overestimated Sobek NP values, thus increasing the risk of poor-quality drainage and the need for costly remediation.