Pristine Mineral Research Articles

Pengaruh Brand Trust, Word of Mouth dan Sales Promotion terhadap Keputusan Pembelian Air Mineral Pristine di Kota Semarang

This research aims to determine the influence of brand trust, word of mouth and sales promotion on purchasing decisions of Pristine mineral water in Semarang City. This research uses quantitative methods. The population of this research is the people of Semarang City who have purchased Pristine mineral water with a sample of 136 respondents. The sampling technique uses a purposive sampling method. Collection and research techniques were carried out through questionnaires and processed using SPSS 24. The results of this research show that brand trust has a positive and significant effect on purchasing decisions, word of mouth has a positive and significant effect on purchasing decisions, and sales promotion has a positive and significant effect on purchasing decisions.

The dissolution characteristics of cadmium containing birnessite produced from paddy crusts

The cadmium (Cd) accumulates in birnessite as it forms on the surface of paddy crusts (PC). The stability of Cd-containing birnessite is influenced by environmental factors, and destabilized birnessite releases dissolved Cd. We report the effects of pH, oxalic acid, and light on the dissolution of Cd-containing birnessite. We found that at pH 4.0, with light and 0.20 mol/L oxalic acid, the ratio of dissolved Cd and manganese (Mn) peaked after 24 h at 2978.0 μg/g and 326.8 mg/g, respectively. The three environmental factors affected the dissolution of Cd-containing birnessite in the following order: pH > oxalic acid > light. During dissolution process, Cd and Mn did not dissolve simultaneously, and the dissolved Cd/Mn ratio in the solution was significantly lower than that of the pristine mineral (33.5 × 10−3). Compared with Mn, Cd dissolution was inhibited by strong acidity (pH 4.0–5.0), and the dissolved Cd/Mn ratio was 5–10 × 10−3. Mild acidity (pH 6.0) was weakly inhibitory, with a Cd/Mn ratio of 6–15 × 10−3. In an alkaline (pH 8.0) oxalate environment, light illumination inhibited Cd dissolution, and the Cd/Mn ratio decreased over time due to the stability of the products formed by oxalate and carbonate, with Cd being more stable than those formed by Mn. Our findings would provide insights into the migration and transformation of PC-associated Cd in paddy fields.

Enhanced Cd2+ removal from aqueous solution using olivine and magnesite combination: New insights into the mechanochemical synergistic effect

In this study, an efficient stabilizer material for cadmium (Cd2+) treatment was successfully prepared by simply co-milling olivine with magnesite. Several analytical methods including XRD, TEM, SEM and FTIR, combined with theoretical calculations (DFT), were used to investigate mechanochemical interfacial reaction between two minerals, and the reaction mechanism of Cd removal, with ion exchange between Cd2+ and Mg2+ as the main pathway. A fixation capacity of Cd2+ as high as 270.61 mg/g, much higher than that of the pristine minerals and even the individual/physical mixture of milled olivine and magnesite, has been obtained at optimized conditions, with a neutral pH value of the solution after treatment to allow its direct discharge. The as-proposed Mg-based stabilizer with various advantages such as cost benefits, green feature etc., will boosts the utilization efficiency of natural minerals over the elaborately prepared adsorbents.

Mineral type and land-use intensity control composition and functions of microorganisms colonizing pristine minerals in grassland soils

Mineral surfaces in soil are an important interface for organic matter (OM) and nutrient cycling, with associated microorganisms contributing to the formation and turnover of mineral-associated OM (MAOM). However, the relevance of intrinsic (mineral type) versus extrinsic (land-use intensity) factors on the co-development of MAOM and microorganisms under natural conditions remains poorly understood. Mineral containers filled with mixtures of quartz-sand and pristine secondary minerals (goethite or illite) were exposed to 50 grassland topsoils of the Schwäbische Alb (Germany) along a land-use intensity gradient for five years. Mineral samples and soils were analyzed for organic carbon (OC) and nutrients (N and P), abundance and composition of major microbial groups based on phospholipid fatty acid profiles, as well as enzyme activities (β-glucosidase, β-xylosidase, N-acetylglucosaminidase, and acid phosphatase). Microorganisms colonized both mineral samples to the same extent, with goethite samples exhibiting greater MAOM accumulation and higher enzyme activities than illite samples. Both mineral samples differed from the overlying soils with greater relative abundances of fungi and Gram-negative bacteria and greater microbial acquisition of nutrients (N and P) relative to C as indicated by the stoichiometry of enzyme activities. Increasing land-use intensity was associated with decreasing C:N ratios and microbial abundances for goethite samples and increasing β-glucosidase activity for illite samples while the proportion of fungi was reduced in both mineral samples. We conclude that in the studied temperate grasslands the association of OM and microorganisms with secondary minerals is driven more by mineral type and reactivity than by differences in land-use intensity. The different minerals apparently formed distinct microhabitats with unique characteristics that differed in MAOM accumulation and microbial access to OC and nutrients, thus affecting microbial colonization and functionality.

Properties and adsorptive performance of candlenut shell and its porous charcoals for aqueous mercury(II) removal

The present work investigated the functional properties of candlenut shell particles (CSP), candlenut shell charcoal (CSC), and candlenut shell activated charcoal (CSAC) for Hg2+ removal. The highest Brunauer-Emmet-Teller (BET) surface area of 1183 m2/g and total pore volume of 0.674 cm3/g were achieved from the CSAC. The aqueous Hg2+ removal performance was evaluated via a continuous flow experiment at 25 °C. Although the CSP and CSC showed a relatively good adsorption performance, the CSAC presented superior adsorption properties to remove Hg2+ from water. Its pristine mineral constituents and large surface area corresponded to the highest adsorption capacity of 214.36 mg/g. These findings were confirmed by the energy-dispersive X-ray spectroscopy analysis (EDX) which was lineal substantiation for the Hg2+ adsorption onto the CSAC film. It appears feasible to use candlenut shell (CS) waste as an economical precursor for the high-grade bioadsorbent production and augmentation of agro-industrial waste management.

Catalytic pyrolysis of oily sludge with iron-containing waste for production of high-quality oil and H2-rich gas

Oily sludge (OS), as a kind of organic hazardous waste with complex components, is suitable for treatment by pyrolysis. To attain effective removal of petroleum hydrocarbons and explore synergistic disposal for multi-source solid wastes, the catalytic effects of steel slag (SS) and red mud (RM) were investigated in this work. They could reduce the activation energy, accelerate OS degradation and shift the degradation of petroleum hydrocarbons towards lower temperature. What’s more, RM with higher iron content worked better, gained more pyrolytic gas and higher H2 production as well. More pyrolytic gas production was obtained when RM addition was at a low proportion. However, excessive catalyst would play a certain inhibitory role. The addition of RM promoted oil recovery at low temperature (400–500 °C) but brought more gas originating from oil cracking at high temperature (600 °C). At 400 °C, the oil yield elevated continuously with prolonging retention time. Nevertheless, even if the retention time was long enough, the harmless disposal for OS could not be completed with the catalysis of RM. Finally, the pristine minerals in RM were co-pyrolysis with OS individually to explore catalytic contributions. Metal oxides could enhance the gas yield and reduce the oil yield. The order of catalytic capacities was Fe2O3＞CaO＞SiO2＞Al2O3. Fe2O3 promoted H2 production and conversion from heavy oil into light fuels. Besides, Fe2O3 was reduced into Fe3O4 with part of [O] shifting into oil. CaO, SiO2, and Al2O3 could reduce the oxygen content in the pyrolytic oil through their acid-base properties to improve the oil quality. This work summarized the functions of various components in RM, might provide inspiration for getting insight into the application of collaborative treatment of different solid wastes.

Effect of Different Doses of Phosgreen Fertilization on Chlorophyll, K, and Ca Content in Butterhead Lettuce (Lactuca sativa L.) Grown in Peat Substrate

Struvite is regarded as a promising phosphorus (P) fertilizer compared to commercial pristine mineral phosphorus fertilizers. The aim of this study was to determine the effect of Phosgreen fertilizer, with struvite as its phosphorus source, on the chlorophyll, potassium (K), and calcium (Ca) contents in lettuce grown in peat compared to superphosphate. The study was carried out as a pot experiment with different doses of P fertilization. The study presents the chlorophyll a, b, total (a + b) chlorophyll, and carotenoid contents of the lettuce plants. Significant differences in the chlorophyll a and b contents were observed between the different phosphorus applications, and this can have a direct impact on the crop yields. Significantly higher contents of both chlorophyll contents were observed under Phosgreen fertilization as well as the chlorophyll a + b content *. The results of the study on lettuce indicate a dependence of vitamin C content on phosphorus fertilizer, but with no significant increase under Phosgreen fertilization; the contents of K and Ca were not significantly dependent on the type of phosphorus fertilizer. Due to the favorable composition of Phosgreen, it may be recommended for use as a phosphorus fertilizer in the agriculture and horticulture sectors.

Ion exchange to immobilize Cd(II) at neutral pH into silicate matrix prepared by co-grinding kaolinite with calcium compounds

A novel silicate-based composite material was simply prepared by co-milling kaolinite and calcium compounds to endow the well studied clay minerals with active calcium for efficient removal of heavy metals. Batch experiments were carried out to investigate the main affecting factors such as raw material ratio, ball milling time, contact time, etc.. Even at a neutral solution pH, the silicate adsorbent exhibited excellent performance for the adsorption of Cd(II), reaching equilibrium in 30 min with a removal efficiency over 95%, and allowed a direct discharge of the treated solution without the need of acidic neutralization as usually used in the alkaline precipitation. A set of analytical methods including SEM/EDS and 29Si MAS NMR etc. were used to analyze the adsorption mechanism of Cd(II), revealing that the adsorption process was mainly dominated by ion exchange to accommodate Cd ions inside silicate matrix, accompanied with partial hydroxide precipitation, rather than normally reported surface adsorption on pristine minerals. Furthermore, the as-prepared adsorption material exhibited similar excellent immobilization capacity for multiple heavy metals including Cu(II), Zn(II), Ni(II), Cd(II) and Mn(II). These findings provide a novel concept for the activation of the widely available cheap silicate minerals by the same widely available cheap calcium compounds and high contribution may be expected on its potentials to the environmental purification of heavy metal pollution in water and soil.

Porous structure and adsorptive properties of activated carbon derived from Bambusa vulgaris striata by two-stage KOH/NaOH mixture activation for Hg2+ removal

Activated carbon with a large surface area was synthesized from Bambusa vulgaris striata via two-stage KOH/NaOH mixture activation. Functional properties of the produced activated carbon were investigated. Optimum conditions in activated carbon production were obtained from an impregnation ratio of char to KOH/NaOH mixture of 1:3 (w/w) at 800 °C, with a surface area and total pore volume of 1108 m2/g and 0.634 cm3/g, respectively. The optimized activated carbon was employed in mercury ion (Hg2+) adsorption through a continuous flow experiment at 25 °C. Its large surface area and pristine mineral elements were responsible for a high adsorption capacity of 312.7 mg/g. The results showed the superior feasibility of Bambusa vulgaris striata as a low-cost and abundant biomass precursor for the production of highly porous activated carbon that can be employed for Hg2+ removal. Hence, the produced activated carbon represents a promising adsorbent for the treatment of contaminated and polluted water as well as wastewater.

Earth-abundant ZnS/ZnO/CuFeS2 films for air purification and solar fuels production

Heterogeneous photocatalysis is one of the most viable solutions for environmental remediation, and it helps to overcome energy crisis by solar fuel generation with an environmentally friendly approach. Hence, the search for efficient, stable, and inexpensive photocatalysts is one of the most significant challenges that scientists currently face for the implementation of this technology on a larger scale. One alternative is to use naturally occurring semiconductor materials as photocatalysts because they are obtained at low cost and have great potential in environmental remediation and solar fuel generation. Therefore, in this study, an earth-abundant chalcogenide mineral (ZnS), which is obtained directly from nature, was used as raw material to fabricate thick films over glass substrates by the doctor-blade technique. Both materials (pristine and thick films) were evaluated as photocatalysts to remove CH2O a commonly volatile organic compound (VOC) gas pollutant found in indoor spaces from the air, and for solar fuel generation (H2, CH3OH, and HCOOH) from CO2 reduction under simulated visible light. Pristine mineral contained ZnS and traces of CuFeS2 as crystal phases of micrometer-sized particles with visible-light response. When the earth-abundant mineral was immobilized on glass substrates as a thick film, it exhibited ZnS/ZnO/CuFeS2 as crystalline phases with a hierarchical morphology formed by stacking several plate-like particles. The thickness of the film was 2.5 μm and it was rough. These properties favored high efficiencies for air purification because more than 55% of gas pollutant was removed after 90 min. In addition, the films exhibited photocatalytic activity toward CO2 reduction to produce solar fuels such as H2 (615 μmol/g), CH3OH (150 μmol/g), and HCOOH (1693 μmol/g) at 25 °C. The good photocatalytic performance of earth-abundant films was related to an efficient charge transfer among the components (ZnS/ZnO/CuFeS2) and an enhanced light absorption owing to hierarchical morphology. The stability of samples was confirmed after three consecutive cycles.

In Situ Growth of Transition Metal Nanoparticles on Aluminosilicate Minerals for Oxygen Evolution

Earth‐abundant and environmentally friendly aluminosilicate minerals can be one of the promising alternatives to develop cost‐effective energy conversion and storage devices. Herein, in situ growth of transition metal nanoparticles is proposed to modify two commonly available feldspar minerals, albite and microcline, for promoting electrocatalytic oxygen evolution reaction activity via a one‐step thermal reduction strategy. Three types of transition metal nanoparticles, namely, Ni, Co, and Fe, are selected to modify the albite or microcline surfaces. As expected, these modified products deliver enhanced catalytic activities compared to the pristine minerals. Particularly, Co‐modified microcline (C‐KASO) demonstrates the best performance that even outperforms the commercial RuO2 catalyst. This design by coupling low‐cost aluminosilicate minerals with active transition metal nanoparticles offers a new insight into directly utilizing the natural abundant resources to address the current energy crisis.

The mineralosphere\u2014interactive zone of microbial colonization and carbon use in grassland soils

To improve our understanding of early microbial colonization of pristine minerals and their group-specific C utilization, we exposed minerals (illite/goethite/quartz) amended with artificial root exudates (ARE, glucose, and citric acid) in grassland soils for a period of 24 weeks. FTIR spectra indicated that mineral-associated ARE were used within the first 2 weeks of exposure and were replaced by other carbohydrates derived from living or dead cells as well as soil-borne C sources transported into the mineralosphere after heavy rain events. Fungi and Gram-positive bacteria incorporated ARE-derived C more rapidly than Gram-negative bacteria. Gram-negative bacteria presumably profited indirectly from the ARE by cross-feeding on mineral-associated necromass of fungi and Gram-positive bacteria. The Gram-negative bacterial phyla Verrucomicrobia, Planctomycetes, Gemmatimonadetes, Armatimonadetes, and Chloroflexi showed a positive correlation with Gram-negative PLFA abundances. After 24 weeks of exposure in the grassland soils, abundances of soil microorganisms in the mineralosphere reached only 3.1% of the population density in soil. In conclusion, both bacteria and fungi slowly colonize new surfaces such as pristine minerals, but quickly assimilate artificial root exudates, creating an active microbial community in the mineralosphere.

Effects of Ni incorporation on the reactivity and stability of hausmannite (Mn3O4): Environmental implications for Mn, Ni, and As solubility and cycling

Trace metal structural impurities are common in Mn (II/III) oxides, yet their effects on the oxides' reactivity and stability have not been experimentally assessed. The present investigation quantifies such effects for the first time by measuring the extent of mineral dissolution of pristine and Ni-substituted hausmannite (MnIIMnIII2O4) (at 1 and 2 wt% Ni) in 8-h batch reactions at pH 5 with/without arsenite (As(III)). Ni substitution occurred at Mn(III) octahedral sites, causing noticeable structural modification in lattice parameters with a decrease in Jahn-Teller distortion, particularly at 2 wt%. In both acidic and reductive dissolution (with As(III)), the Ni-substituted hausmannite exhibited enhanced Mn release relative to the pristine mineral, with concurrent release of structural Ni increasing with substitution percentage. When As(V) release was normalized by surface area, Ni-substituted hausmannite showed a higher As(III) oxidation percentage than the pristine phase. Further, higher ratios of Mn(II):As(V) were observed in Ni-substituted hausmannite. As K-edge X-ray absorption spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy analyses indicated that As(III) oxidation lead to the formation of binuclear bidentate As(V) surface complexes. Enhanced reactivity of Ni-substituted hausmannite may be attributed to lowered mineral stability, which promotes accelerated mineral dissolution and increased structural Mn release, resulting in formation/exposure of highly reactive sites. Thus, structural impurities dictate the properties, reactivity, and stability of the Mn(II/III) oxides, affecting the level of dissolution and the extent of redox reactions, which together impact the fate and cycling of transition metals and metalloids in surface environments.

Ceramic abandonment. How to recognise post-depositional transformations

After they have been abandoned, ceramic materials may undergo substantial transformations, all of which may change their macroscopic aspect, mineralogy, chemical composition and microstructure. The intensity and pervasiveness of these transformations on both macro- and micro-scales depend to a great extent not only on their compositional and microstructural features but also on the chemical-physical characteristics of the post-depositional environment in which they were hosted. This contribution describes the main post-depositional transformations observed in ancient ceramics in relation to secondary phases precipitation, mineral dissolution, pristine mineral and amorphous phases transformations into new mineral phases, and chemical leaching and enrichment. The mechanisms responsible for these transformations are described, together with the characteristics which allow us to identify them according to the most common analytical approaches, in order not to introduce misleading interpretations concerning the study of the provenance and production technology of ancient ceramic materials.

Probing silicate weathering reactions in soils with B isotopes

The determination of the mechanisms and extent of soil mineral weathering can be challenging, and the caveats reside in 1) difficulty identifying minerals that are actually involved in weathering reactions, 2) non-stoichiometric release of cations during weathering processes due to coupled dissolution, precipitation and transformation reactions and, 3) impact of vegetation activity on elemental cycles in upper soil horizons.To better characterize mechanisms controlling mineral weathering in soils and trace the evolution of B concentration and isotope ratios during chemical weathering, quantitative mineralogical analyses were coupled to B isotopes in a group of minerals (biotite, muscovite, K-feldspar and albite). Samples were selected along an Alocrisol (Alumic Cambisol, WRB FAO) soil profile from the bedrock (at 130 cm depth) up to 20 cm depth, developed on granitic bedrock in the Breuil-Chenue forest (France). The samples consist of residual primary minerals associated with weathering secondary phases (vermiculite, kaolinite…) in varying proportions.The B isotopic compositions of the most pristine minerals span a very narrow range of values (around −31‰), whereas all secondary phases point to a much heavier value (around −16‰), regardless of mineralogy. Our results also show a mineral-dependent evolution of B concentration or isotopic composition as weathering progresses: no variation is observed during dissolution of K-feldspars; B behaves like a very mobile element in micas (biotite and muscovite), whereas it concentrates in weathered products derived from albite. However, rates of B concentrations and changes in isotopic compositions appear to be much faster than those inferred from mineralogy or major element concentrations determined by XRD and bulk chemical analyses, respectively. These results indicate that B is involved in very early weathering reactions and raises the question of its actual location in the structure of the various soil minerals as well as its pathway to solution.

Dimensional distribution control of elongate mineral particles for their use in biological assays

The aim of the present method is to reduce the dimensional variability of asbestos, elongate mineral particles, and other asbestiform minerals for use in biological assays. Here, the pristine mineral sample is filtered through two nylon meshes of different sizes to obtain a narrower dimensional distribution following a power law. Furthermore, we show that anoxic preparation, autoclaving and storage of the mineral prior to addition into biological cultures did not affect the mineral's chemical properties. This approach avoids the use of highly reactive chemicals modifying mineralogical characteristics and surface properties, which can affect to a major extent mineral toxicity as well as interactions between minerals and biological matter or biofluids. The method can be combined with additional selective approaches to further refine the dimensional range of the minerals. The advantages of this protocol over previous methods are:•Exclusive use of distilled water and 2-propanol, thus eliminating chemicals that can modify bulk or surface properties of the studied minerals.•Successful sterilization of the resulting mineral particles for use in biological assays without compromising mineralogical characteristics.•Applicability of this method across various types of asbestos, elongate mineral particles and, potentially, other hazardous minerals.

The mineralosphere – Succession and physiology of bacteria and fungi colonising pristine minerals in grassland soils under different land-use intensities

The mineralosphere is an important micro habitat in terrestrial ecosystems. How different groups of microorganisms colonise mineral surfaces and whether the level of grassland land-use intensity (LUI) modifies this micro-habitat is not well known, however. We exposed mesh containers filled with pristine soil minerals (illite/goethite) mixed with 13C labelled root litter of Dactylis glomerata and Lolium perenne in grassland soils of the “Schwäbische Alb” (Germany) to characterise the succession of different microbial properties in the mineralosphere. The use of sites within the Biodiversity Exploratories made it possible to select five sites of low LUI and five sites of high LUI. After 1, 2, 7, 12 and 31 months of exposure in the grassland soils, we used physiological, microbiological and isotopic methods to elucidate in situ colonisation patterns, carbon use and levels of extracellular enzyme expression by soil microorganisms associated with mineral surfaces. Microorganisms slowly colonised pristine mineral surfaces and established functionally distinct communities over time. Fungi colonised mineral surfaces to a greater extent than bacteria, reaching 13.2% of control soils compared to 3.2% by bacteria after 31 months. Fungi also reached pristine mineral surfaces earlier than bacteria, probably due to their hyphal growth strategies, and made immediate use of the added complex root litter substrate. This result is evident by the incorporation of up to 74% root litter-derived C into the fungus-specific PLFA (18:2ω6,9) compared to 51% root litter-derived C in the bacteria-specific PLFAs. Both bacteria and fungi associated with minerals remained in an active state (high biomass-specific respiration, high bacterial and fungal growth rates) throughout the experimental period. Grassland LUI and physico-chemical properties of the adjacent soil modified both quantity and quality of substrates available to soil microorganisms in the mineralosphere. Since 13C incorporation into microbial biomass was greater under low LUI than under high LUI, we conclude that microorganisms in low LUI sites had to rely on the added root material, while the carbon signal in microorganisms in the high LUI sites was diluted by alternative sources resulting from transport of dissolved organic carbon into the mineralosphere.

Structural properties of adsorbent phyllosilicates rule the entrapping ability of intercalated iron-phenanthroline complex towards thiols

Abstract The interaction of volatile organic sulfur derivatives, such as 1-heptanethiol (C7H16S), with clay minerals treated with a μ-oxo Fe3+-phenanthroline 1:1 complex results strongly affected by crystal chemical properties of pristine mineral phases. In particular, two sepiolite clays with different structural features demonstrated significantly different ability to immobilize the Fe3+-phenanthroline complex at two pH values (pH = 5.4 and pH = 2.3). The most effective binding was obtained with sepiolite with higher structural disorder at pH 5.4. Accordingly, the resulting hybrid material showed also the greatest efficiency in removal of thiol in gas phase. A direct correlation can be established between the adsorption of the Fe3+-phenanthroline complex and the gas binding process at room temperature. In fact, 1-heptanethiol entrapping occurs via redox reactions between Fe3+ and a first thiol molecule to give the reduced Fe2+-phenanthroline complex and disulfide, followed by the binding of further thiols to the reduced metal centre. The extremely high amount of thiol immobilized by the hybrid material also suggests the co-presence of a catalytic mechanism that guarantees the reoxidation of Fe+2 to Fe+3 and the restoration of redox reactions with thiol. Investigation and conclusions were supported by the several experimental techniques: elemental analysis, X-ray powder diffraction analyses, UV–Vis measurements, FT-IR and NMR spectroscopies, thermogravimetric analyses.

High-performance porous biochar from the pyrolysis of natural and renewable seaweed (Gelidiella acerosa) and its application for the adsorption of methylene blue

A high-performance porous biochar adsorbent prepared by facile thermal pyrolysis of seaweed (Gelidiella acerosa) is reported. The textural characteristics of the prepared seaweed biochar (SWBC) and the performance in the adsorption of methylene blue (MB) dye were evaluated. The batch experiment for the adsorption of MB was conducted under different parameters, such as temperature, pH, and initial concentration of MB in the range of 25–400 mg/L. The developed SWBC exhibited a relatively high surface area, average pore size, and pore volume of 926.39 m2/g, 2.45 nm, and 0.57 cm3/g, respectively. The high surface area and pristine mineral constituents of the biochar promoted a high adsorption capacity of 512.67 mg/g of MB at 30 °C. The adsorption isotherm and kinetics data best fitted the Langmuir and pseudo-second-order equations. The results indicate that SWBC is efficient for MB adsorption and could be a potential adsorbent for wastewater treatment.

Mercury Isotopic Fractionation during Pedogenesis in a Tropical Forest Soil Catena (French Guiana): Deciphering the Impact of Historical Gold Mining.

We used natural mercury (Hg) stable isotopes to investigate the Hg cycle in a rainforest soil catena (French Guiana) partially gold-mined during the early 1950s. Litterfall showed homogeneous Δ199Hg values [-0.18 ± 0.05‰, i.e., a modern gaseous elemental Hg (GEM) isotopic signature]. After litter decomposition, Hg bound to organic matter (OM) is mixed with Hg from pristine (-0.55 ± 0.22‰) or gold-mined (-0.09 ± 0.16‰) mineral materials. Negative Δ199Hg values in deep pristine mineral horizons (-0.60 ± 0.16‰) suggest the transfer of Hg bound to dissolved OM depleted in odd isotopes due to mass-independent fractionation during Hg abiotic reduction. Perennial palm tree leaves collected above gold-mined and pristine soil recorded contrasting Δ199Hg signatures likely resulting from GEM re-emission processes from soils and leaf surfaces. Upslope, soil δ202Hg signatures showed a negative shift (ε ∼ -1‰) with depth attributed to mass-dependent fractionation during Hg sorption and complexation onto iron oxides and dissolved OM. Downslope, higher δ202Hg values in soils resulted from hydromorphy [lower humification, greater Hg(II) reduction, etc.]. The unique Hg isotopic signatures of Amazonian soils probably result in multistep fractionation processes during pedogenesis (millions of years) and in a potentially different Hg isotopic signature of preanthropogenic background GEM.