Iron Grit Research Articles

Valorisation of Metallurgical Waste for Inorganic Pigments Production

Four industrial wastes, namely, tionite (T), iron grit (IG), electroplating sludge (ES), and mill scale (MS), are typically disposed of in controlled hazardous landfills because of their toxic content, posing potential harm to human health and to the environment. At the same time, the chemical composition of these wastes, specifically the nature and content of transition metals, makes them potentially attractive for reuse in pigments manufacturing. This work details the study of these residues for producing coloured perovskites to be tested as inorganic pigments. The residues were mixed, in different proportions, and subsequently calcined to produce the required structures. The colouring potential was then assessed in a ceramic paste and in a transparent glaze. Leaching tests were carried out to verify the effective immobilisation of the hazardous species. Dark pigments were successfully obtained from the mixtures of T: ES: Co3O4, T: MS and T: IG. The crystalline phases present in T: ES: Co3O4 are nickel–chromium iron oxide spinel–Fe1.5Cr0.5NiO4 (without Co) or trevorite–Fe2NiO4 (with Co), titanium nickel oxide–TiNiO3 and titanite–CaTiSiO5. The mixtures T: MS and T: IG presented hematite (Fe2O3) and pseudobrookite (Fe2TiO5). Leaching tests confirmed the non-hazardous or inert character of the synthesized pigments. Products showed brownish or greyish hues, depending on the pigment added. T:75ES_1100, T:73ES:2Co_1100, T:75MS_1000, T:75MS_1100 and T:75IG_1000 pigments can effectively and safely be used to colour ceramic paste replacing partially or totally the commercial pigments.

Nano zerovalent Fe did not reduce metal(loid) leaching and ecotoxicity further than conventional Fe grit in contrasting smelter impacted soils: A 1-year field study

The majority of the studies on nanoscale zero-valent iron (nZVI) are conducted at a laboratory-scale, while field-scale evidence is scarce. The objective of this study was to compare the metal(loid) immobilization efficiency of selected Fe-based materials under field conditions for a period of one year. Two contrasting metal(loid) (As, Cd, Pb, Zn) enriched soils from a smelter-contaminated area were amended with sulfidized nZVI (S-nZVI) solely or combined with thermally stabilized sewage sludge and compared to amendment with microscale iron grit. In the soil with higher pH (7.5) and organic matter content (TOC = 12.7 %), the application of amendments resulted in a moderate increase in pH and reduced As, Cd, Pb, and Zn leaching after 1-year, with S-nZVI and sludge combined being the most efficient, followed by iron grit and S-nZVI alone. However, the amendments had adverse impacts on microbial biomass quantity, S-nZVI being the least damaging. In the soil with a lower pH (6.0) and organic matter content (TOC = 2.3 %), the results were mixed; 0.01 M CaCl2 extraction data showed only S-nZVI with sludge as remaining effective in reducing extractable concentrations of metals; on the other hand, Cd and Zn concentrations were increased in the extracted soil pore water solutions, in contrast to the two conventional amendments. Despite that, S-nZVI with sludge enhanced the quantity of microbial biomass in this soil. Additional earthworm avoidance data indicated that they generally avoided soil treated with all Fe-based materials, but the presence of sludge impacted their preferences somewhat. In summary, no significant differences between S-nZVI and iron grit were observed for metal(loid) immobilization, though sludge significantly improved the performance of S-nZVI in terms of soil health indicators. Therefore, this study indicates that S-nZVI amendment of soils alone should be avoided, though further field evidence from a broader range of soils is now required.

The rhizosphere of Salix viminalis plants after a phytostabilization process assisted by biochar, compost, and iron grit: chemical and (micro)-biological analyses.

Amendments, such as biochar, compost, and iron grit, used in phytostabilization studies, showed positive effects on soil physico-chemical properties, plant growth, and the microbial community. However, assisted phytostabilization studies do not always focus on the rhizosphere area where soil, plants, and microorganisms are affected by the amendments and plants and microorganisms can also interact with each other. The aims of this study were to evaluate the effects of amendment application on the exudation of organic acids by Salix viminalis plant roots, as well as the effects of amendments and plant development on the soil CHNS contents and the microbial community activity and diversity, assessed by measuring enzyme activities and using Biolog EcoPlatesTM tests and next-generation sequencing analyses. The results of the mesocosm experiment showed that soil C, H, and N contents were increased by amendment application, especially biochar and compost, while the one of S decreased. Enzyme activities, microbial activity, and diversity were also increased by the addition of amendments, except iron grit alone. Finally, the quantity of organic acids exuded by roots were little affected by amendments, which could in part explain the reduced effect of plant development on soil chemical and microbiological parameters. In conclusion, this study showed in particular that biochar and compost were beneficial for the soil CHN contents and the microbial community while affecting poorly Salix viminalis root exudates.

Field evaluation of one Cu-resistant somaclonal variant and two clones of tobacco for copper phytoextraction at a wood preservation site.

A Cu-resistant somaclonal tobacco variant (NBCu 10-8-F1, C1), its BaG mother clone (C3), and the FoP tobacco clone (C2) were cultivated at a wood preservation site on Cu-contaminated soils (239-1290mg Cu kg-1 soil range) and an uncontaminated control site (CTRL, 21mg Cu kg-1) to assess their shoot DW yields and potential use for bioavailable Cu stripping. The Cu concentration in the soil pore water varied between 0.15 and 0.84mgL-1. Influences of Cu exposure and soil treatments, i.e., untreated soil (Unt), soils amended with compost and either dolomitic limestone (OMDL) or zerovalent iron grit (OMZ), on plant growth and shoot ionome were determined. All transplants survived and grew even at high total soil Cu. Shoots were harvested after 3months (cut 1). Subsequently, bottom suckers developed and were harvested after 2months (cut 2). Total shoot DW yield (cuts 1 + 2) varied between 0.8 and 9.9t DW ha-1year-1 depending on tobacco cultivars, soil treatments, and soil Cu exposure. It peaked for all cultivars in the OMDL plots at moderate Cu exposure (239-518mgkg-1 soil), notably for the C2 plants. Cut 2 contributed for 11-43% to total shoot DW yield. Increase in shoot DW yield diluted shoot Cu concentration. At low Cu exposure, total shoot Cu removal peaked for the variant. At moderate Cu exposure, shoot Cu concentrations were similar in all cultivars, but total shoot Cu removal was highest for the C2 plants. At high Cu exposure (753-1140mgkg-1), shoot Cu concentrations peaked for the C2 plants in the Unt plots, the C1 and C2 plants in the OMZ plot, and the C3 ones in the OMDL plots. Shoot Cu removal (in g Cu ha-1year-1) ranged from 15.4 (C2 on the CTRL soil) to 261.3 (C2 on moderately contaminated OMDL soils). The C2 plants phytoextracted more Cu than the C1 and C3 ones in the Unt plots and in the OMDL plots at moderate Cu exposure. In the OMDL plots with high Cu exposure, shoot Cu removal was highest for the C1 plants. Soil amendments improved shoot Cu removal through increase in either shoot DW yield (OMDL-3-fold) or shoot Cu concentration (OMZ-1.3-fold). Increased shoot Cu concentration induced an ionome imbalance with increased shoot Al, Fe, B, and Mg concentrations and decreased P and K ones. Copper concentrations in plant parts varied in decreasing order: roots > leaves > inflorescence (cymes including seeds) > stem, whereas Cu removal ranked as roots > stem = leaves > inflorescence.

Amending an As/Pb contaminated soil with biochar, compost and iron grit: effect on Salix viminalis growth, root proteome profiles and metal(loid) accumulation indexes.

There is currently a large amount of research being done into the phytoremediation of polluted soils. Plant installation in contaminated soils may require the application of soil amendments, such as biochar, compost and/or iron grit, which can improve the soil conditions and reduce the metal (loid) phytoavailability and mobility. The beneficial effects of these amendments on soil properties, plant growth and metal (loid) accumulation ability have already been described, although their effect on the plants response machinery has been poorly studied. This study aimed to assess the effect of these amendments on Salix viminalis growth and metal (loid) accumulation, as well as elucidating associated molecular mechanisms. The results showed that the amendment applications improved plant growth by three fold, except for the biochar plus iron combination. It also revealed that metal (loid)s were not effectively translocated from the roots to the shoots (translocation factors <1), their bioaccumulation peaked in the roots, and increased in the presence of iron-based amendments. Corresponding proteomic profiles revealed 34 protein spots differentially represented and suggested that plants counteracted metal (loid)-induced oxidative stress after the addition of biochar and/or compost by eliciting proper defense and signaling pathways, and by redirecting the metabolic fluxes towards primary and secondary metabolism. However, they did highlight the occurrence of oxidative stress markers when the biochar plus iron amendment was applied, which could be both the cause and result of protein degradation impairment.

Quality of water recovered by treating acid mine drainage using pervious concrete adsorbent

In this paper, a batch experiment was conducted to evaluate the water quality obtained from using pervious concrete (PERVC) technology to treat acid mine drainage (AMD). The study proposes an innovative application of PERVC as a permeable reactive barrier liner in evaporation ponds. The effectiveness of PERVC adsorbent in removing heavy metals was compared with that of zero-valent iron (ZVI) of particle size 1.0 to 1.8 mm. The AMD used in the study was obtained from abandoned gold and coal mines. PERVC mixtures consisted of granite aggregate and ordinary Portland cement CEM I 52.5R (CEM I) or CEM I containing Class F 30% fly ash (30%FA) as a cement replacement material. ZVI was prepared from a mixture of silica sand and iron grit of specific sizes. PERVC and ZVI media were used to conduct batch reactor tests with AMD, for a period of 43 days at a ratio of 1 L of reactive material to 3 L of AMD. The quality of treated AMD was compared against effluent discharge standards. The contaminants Al, Fe and Zn were effectively removed by both PERVC and ZVI. Also, both adsorbents reduced Ni, Co and Cu to levels below those measured in raw AMD. However, PERVC was more effective in removing Mn and Mg while ZVI was ineffective. Although PERVC removed more heavy metals and with greater efficiency than ZVI, the PERVC-treated water showed high pH levels and exhibited elevated Cr6+ concentrations, owing to leaching from the cement and fly ash materials used in PERVC mixtures.

Influence of amendments on metal environmental and toxicological availability in highly contaminated brownfield and agricultural soils.

The immobilizing effects of wood biochar (BW2%) and iron grit (Z1%) applied alone or in combination (BW2% + Z1%) to agricultural (M750) and brownfield (MAZ) soils highly contaminated by metals were assessed in a greenhouse experiment. The results showed that Z1% and BW2% + Z1% were the most efficient amendments to reduce Cd, Cu, Pb, and Zn mobility, environmental availability, and phytoavailability in the M750 soil. The oxidation of Z1% allowed part of the Cu and Zn pools present in exchangeable or carbonate-bound forms (labile fraction) to complex in less mobile forms. In this soil, the metal chemical extractions (0.01 M CaCl2 and 0.05 M EDTA) and the DGT (diffusive gradient in thin films) devices to assess metal in soil solution and soil pore water (SPW) also highlighted the immobilizing characteristic of Z1%. In most cases, the addition of BW2% to Z1% (BW2% + Z1%) did not improve this effect, except for the dissolved Pb and Zn concentrations in the M750 soil solution. It was also observed that Cd, Pb, and Zn passed throughout DGT mimicking the biological cell membrane were reduced by all amendments of the M750 soil corroborating metal concentrations measured in rye grass shoots. In the MAZ soil, metals were less available as shown by their low extractability rate, low capacity of metal resupply from the solid phase to pore water, and low phytoavailability. The poor metal availability could be explained by the high levels of carbonate and organic matter contents in this soil. Nevertheless, a decrease of the Cu environmental availability and the Cu concentrations in rye grass shoots grown on the MAZ soil was also observed in the soil amended with Z1% alone or in combination with BW2%. From a health point of view, the most effective amendment to reduce human exposure through ingestion of soil particles for the M750 and MAZ soils was BW2% for Cd and BW2% + Z1% for Pb. However, the presence of rye grass minimized the amendments' beneficial effects.

Potential use of biochar, compost and iron grit associated with Trifolium repens to stabilize Pb and As on a multi-contaminated technosol

Vegetation cover can be used in the phytomanagement of polluted areas by adding value to abandoned sites and reducing the dispersion of pollutants by erosion. Appropriate amendments, that allow both efficient plant growth and the immobilization of contaminants in the soil must be chosen in order to optimize the efficiency of this process. We used a mining technosol mainly contaminated by arsenic (1068 mg kg−1) and lead (23387 mg kg−1) to study the effect of three amendments (biochar, compost and iron grit) on (i) physico-chemical properties of the soil and soil pore water, (ii) metal(loid) mobility, bioavailability and bioaccessibility (CaCl2 and Simple Bioaccessibility Extraction Test (SBET)), and (iii) the capability of Trifolium repens to germinate and grow. All the amendments used increased the pH and electrical conductivity of the SPW, resulting in a 90% decrease in the concentration of lead in the soil pore water (SPW). We also demonstrated a decrease in Pb phytoavailability. The amendments allowed the establishment of a plant cover, although the addition of iron grit alone did not allow any clover germination. For the Pontgibaud technosol, the combination of the three amendments resulted in a significant decrease in As and Pb concentrations in clover tissues, mainly in the aerial organs. The amendments also made it possible for some of them to halve the phytoavailable fraction of arsenic. However, for compost, both the As concentrations in the SPW, and the bioavailable fraction of As increased. All the amendments used had contrasting effects on the bioaccessible fractions of metal(loid)s. The most efficient amendment combination was the addition of 5% biochar and 5% compost.

Biochar effect associated with compost and iron to promote Pb and As soil stabilization and Salix viminalis L. growth

Soil pollution by metal(loid)s is one of the most significant problems in Europe. To remediate and potentially rehabilitate these contaminated sites, phytoremediation procedures are being put into place, often using amendments to help offset the extreme conditions of such soils. The aim of this study was to define the best amendment to use on the field. This was done by studying how the addition of three different amendments (biochar, compost and iron grit), alone or in combination, could affect: (i) soil physico-chemical properties, (ii) Salix viminalis growth, and (iii) metal(loid) stabilization. A 69 day-mesocosm study was thus set up using a former mine technosol, the three amendments applied alone or combined, and S. viminalis cuttings. The results showed that biochar and/or compost improved the soil fertility and the soil pore water characteristics, with reductions of acidity, metal(loid) mobility and toxicity, while iron grit amendment presented negative effects on such parameters. Such ameliorations allowed better plant growth and higher biomass production. In addition, stress indicators (leaf pigment content and root guaiacol peroxidase activity) showed a reduction in plant stress following biochar and/or compost application. Finally, among the different treatments, the use of compost or a biochar-compost combination showed better results in terms of improvement of soil conditions, increase in plant growth and reduced translocation of metal(loid)s towards upper parts, making these two treatments a valuable option for a field trial.

Stability of in situ immobilization of trace metals with different amendments revealed by microbial 13C-labelled wheat root decomposition and efflux-mediated metal resistance of soil bacteria

The aim of the present study was to prove the long-term efficiency of the amendments zerovalent iron grit, zeolite, and Divergan® for trace metal remediation in heavily contaminated soils and to attain a recovery of microbial functionality and diversity by remediation. For immobilization of the trace metals the amendments zerovalent iron grit, natural zeolite, and Divergan® were used. Trace metal total and mobile contents were determined and bacterial communities were assessed after a SIP experiment with 13C-labelled wheat root by Ion-Torrent Sequencing targeting the bacterial 16S rRNA gene and two trace metal resistant genes for copper and cadmium (copA and czcA gene).The results show that the remediation effect of the three amendments is still stable after five years. The mobile trace metal contents were significantly (≤0.001) reduced in all treatments, except the Cu content in the zeolite treatment. A higher diversity in active metabolizing and growing soil bacteria was observed in remediated soils as compared to the non-remediated control, especially for the Divergan® treatment. The bacterial genera Kribbella, Glycomyces, Inquilinus, Nocardioides, and Lysobacter are the most significantly enriched genera in the 13C fractions of the treated samples. The occurrence of bacterial families, which could be identified carrying efflux-mediated metal resistance genes for Cd/Zn and Cu, were reduced in the remediated soils as compared to the non-remediated control. The most abundant bacterial family for the copA and the czcA gene is Xanthomonadaceae. The pH-value and the trace metal concentration could be identified as key drivers of bacterial community composition, and functions in trace metal contaminated soils and remediated soils.

Impact of Redox Condition on Fractionation and Bioaccessibility of Arsenic in Arsenic-Contaminated Soils Remediated by Iron Amendments: A Long-Term Experiment

Iron-bearing amendments, such as iron grit, are proved to be effective amendments for the remediation of arsenic- (As-) contaminated soils. In present study, the effect of redox condition on As fractions in As-contaminated soils remediated by iron grit was investigated, and the bioaccessibility of As in soils under anoxic condition was evaluated. Results showed that the labile fractions of As in soils decreased significantly after the addition of iron grit, while the unlabile fractions of As increased rapidly, and the bioaccessibility of As was negligible after 180 d incubation. More labile fractions of As in iron-amended soils were transformed into less mobilizable or unlabile fractions with the contact time. Correspondingly, the bioaccessibility of As in iron-amended soils under the aerobic condition was lower than that under the anoxic condition after 180 d incubation. The redistribution of loosely adsorbed fraction of As in soils occurred under the anoxic condition, which is likely ascribed to the reduction of As(V) to As(III) and the reductive dissolution of Fe-(hydr)oxides. The stabilization processes of As in iron-amended soils under the anoxic and aerobic conditions were characterized by two stages. The increase of crystallization of Fe oxides, decomposition of organic matter, molecular diffusion, and the occlusion within Fe-(hydr)oxides cocontrolled the transformation of As fractions and the stabilization process of As in iron-amended soils under different redox conditions. In terms of As bioaccessibility, the stabilization process of As in iron-amended soils was shortened under the aerobic condition in comparison with the anoxic condition.

Wood-derived-biochar combined with compost or iron grit for in situ stabilization of Cd, Pb, and Zn in a contaminated soil

In situ stabilization of Cd, Pb, and Zn in an Austrian agricultural soil contaminated by atmospheric depositions from a smelter plant was assessed with a pine bark chip-derived biochar, alone and in combination with either compost or iron grit. Biochar amendment was also trialed in an uncontaminated soil to detect any detrimental effect. The pot experiment consisted in ten soil treatments (% w/w): untreated contaminated soil (Unt); Unt soil amended with biochar alone (1%: B1; 2.5%: B2.5) and in combination: B1 and B2.5+5% compost (B1C and B2.5C), B1 and B2.5+1% iron grit (B1Z and B2.5Z); uncontaminated soil (Ctrl); Ctrl soil amended with 1 or 2.5% biochar (CtrlB1, CtrlB2.5). After a 3-month reaction period, the soil pore water (SPW) was sampled in potted soils and dwarf beans were grown for a 2-week period. The SPW Cd, Pb, and Zn concentrations decreased in all amended-contaminated soils. The biochar effects increased with its addition rate and its combination with either compost or iron grit. Shoot Cd and Zn removals by beans were reduced and shoot Cd, Pb, and Zn concentrations decreased to common values in all amended soils except the B1 soil. Decreases in the SPW Cd/Pb/Zn concentrations did not improve the root and shoot yields of plants as compared to the Ctrl soil.

Long-term Cu stabilization and biomass yields of Giant reed and poplar after adding a biochar, alone or with iron grit, into a contaminated soil from a wood preservation site.

A 2-year pot experiment was carried out to examine the aging effect of biochar (B), alone or combined with iron grit (Z), on Cu stabilization and plant growth in a contaminated soil (964mg Cu kg-1) from a wood preservation site. The experiment consisted in 3 soil treatments, either planted with Arundo donax L. (Ad) or Populus nigra L. (Pn): (1) untreated Cu-contaminated soil (Ad, Pn); (2) Unt+1% (w/w) B (AdB, PnB), and (3) Unt+1% B+1% Z (AdBZ, PnBZ). After 22months, the soil pore water (SPW) was sampled and roots and shoots were harvested. The SPW compositions at 3 and 22months were compared, showing that the SPW Cu2+ concentration increased again in the PnB and PnBZ soils. Cultivation of A. donax enhanced the dissolved organic matter concentration in the SPW, which decreased its Cu2+ concentration but promoted its total Cu concentration in the Ad and AdB soils. Adding Z with B reduced both SPW Cu2+ and Cu concentrations in the pots cultivated by A. donax and P. nigra as compared to B alone. The B and BZ treatments did not enhance root and shoot yields of both plant species as compared to the Unt soil but their shoot Cu concentrations were in the range of common values.

Influence of biochars, compost and iron grit, alone and in combination, on copper solubility and phytotoxicity in a Cu-contaminated soil from a wood preservation site

Two biochars, a green waste compost and iron grit were used, alone and in combination, as amendment to improve soil properties and in situ stabilize Cu in a contaminated soil (964mgCukg−1) from a wood preservation site. The pot experiment consisted in 9 soil treatments (% w/w): untreated Cu-contaminated soil (Unt); Unt soil amended respectively with compost (5%, C), iron grit (1%, Z), pine bark-derived biochar (1%, PB), poultry-manure-derived biochar (1%, AB), PB or AB+C (5%, PBC and ABC), and PB or AB+Z (1%, PBZ and ABZ). After a 3-month reaction period, the soil pore water (SPW) was sampled in potted soils and dwarf beans were grown for a 2-week period. In the SPW, all amendments decreased the Cu2+ concentration, but total Cu concentration increased in all AB-amended soils due to high dissolved organic matter (DOM) concentration. No treatment improved root and shoot DW yields, which even decreased in the ABC and ABZ treatments. The PBZ treatment decreased total Cu concentration in the SPW while reducing the gap with common values for root and shoot yields of dwarf bean plants. A field trial is underway before any recommendation for the PB-based treatments.

Reduction of arsenic bioavailability by amending seven inorganic materials in arsenic contaminated soil

Seven inorganic amendment materials were added into arsenic (As) contaminated soil at a rate of 0.5% (w/w); the materials used were sepiolite, red mud, iron grit, phosphogypsum, ferrihydrite, iron phosphate, and layered double oxides (LDO). Plant growth trials using rape (edible rape, Brassia campestris L.) as a bio-indicator are commonly used to assess As bioavailability in soils. In this study, B. campestris was grown in a contaminated soil for 50 days. All of the inorganic amendments significantly inhibited the uptake of As by B. campestris. Following soil treatment with the seven aforementioned inorganic ammendments, the As concentrations in the edible parts of B. campestris were reduced by 28.6, 10.5, 8.7, 31.0, 47.4, 25.3, and 28.8%, respectively, as compared with the plants grown in control soil. The most effective amendment was ferrihydrite, which reduced As concentration in B. campestris from 1.84 to 0.97 mg kg−1, compared to control. Furthermore, ferrihydrite-treated soils had a remarkable decrease in both non-specifically sorbed As and available-As by 67 and 20%, respectively, comparing to control. Phosphogypsum was the most cost-effective amendment and it showed excellent performance in reducing the water soluble As in soils by 31% and inhibiting As uptake in B. campestris by 21% comparing to control. Additionally, obvious differences in As transfer rates were observed in the various amendments. The seven amendment materials used in this study all showed potential reduction of As bioavailability and influence on plant growth and other biological processes still need to be further explored in the long term.

Effects of iron-based amendments on soil structure: a lab experiment using soil micromorphology and image analysis of pores

Recent trends in soil green and sustainable remediation require an increased attention on environmental effects. The physical consequences of remediation practices on soil structure are very rarely investigated. A laboratory experiment was carried out by adding iron grit to a sand (S), a silt loam (L), and a clay (C) soil subjected to several wetting-drying cycles. The physical effects of the treatment on soil pore system were identified and quantified combining physical measurements on repacked samples with image analysis of pores on resin-impregnated soil blocks and micromorphological analysis on thin sections. A negligible reduction of total porosity (P) resulted in S, and a slight increase was observed in the L and C soils. However, an important impact on soil structure was identified in pore size range >10 μm for the L and C soils, with the formation of new pores related to the differential shrink-swell behavior between soil matrix and added iron grains. Different plasticity of these soils also played a role in planar pore formation. Effects of the addition of iron grit on soil pore system are strongly dependent on soil physical properties. The performed experiment showed that iron-based amendments can improve soil structure in low-plastic shrink-swell soil increasing porosity in the range of transmission pores (50–500 μm). This study showed the high potential of soil micromorphology and pore image analysis in order to evaluate the environmental impact of soil remediation practices.

Impact of trace metal contamination and in situ remediation on microbial diversity and respiratory activity of heavily polluted Kastanozems

Agriculturally used soils (Kastanozems) of experimental fields in the Mashavera Valley in southeast Georgia show various degrees of trace metal contamination (Cd, Cu, and Zn). Therefore, one part of the soils was remediated with iron grit. The effects of the remediation in comparison to nonremediated soils on microbial diversity and activity were analyzed with the single-strand conformation polymorphism (SSCP) and microbial respiratory activity. All topsoils were characterized by neutral to weakly alkaline pH values, high contents of Corg, and clay. The total contents ranged between 0.46 and 5.89 mg kg−1 for Cd, between 1.19 and 81.4 mg kg−1 for Cu, and between 210 and 976 mg kg−1 for Zn. Basal respiration was significantly (p ≤ 0.05) lower in the heavily contaminated soils as compared to the weakly contaminated and control soils. Phylogenetic analyses of the DNA bands found 40 operational taxonomic units with ≥98 % sequence identity. The phylum Acidobacteria dominated with 57.7 %. Other groups detected were Proteobacteria (α (2.8 %), β (8.5 %), γ (14.1 %), δ (4.2 %)), Bacteroidetes (5.6 %), Firmicutes (4.2 %), Actinobacteria (1.4 %), and Nitrospira (1.4 %). Furthermore, the results of the SSCP analysis and the Shannon–Weaver indices suggested that microbial diversity was lower in the heavily contaminated soils, but DNA band profiles of the remediated soils were in higher number than in the untreated soils. Due to the remediation, a recovery of the microbial diversity seems attainable.

Suitability of inorganic and organic amendments for in situ immobilization of Cd, Cu, and Zn in a strongly contaminated Kastanozem of the Mashavera valley, SE Georgia. I. Effect of amendments on metal mobility and microbial activity in soil

AbstractThe aim was to find an adequate, cost‐efficient in situ remediation technique for the Mashavera valley, a mining area in SE Georgia heavily contaminated with Cd, Cu, and Zn. A 12‐month experiment was conducted to test: iron grit, natural zeolite, biochar, and Divergan® (a scavenger) for soil melioration. The amendments were added in different concentrations to the topsoil of a Kastanozem. Mobile metal concentrations decreased with increasing concentrations of amendments in the sequence Divergan® &gt;&gt; iron grit ≈ natural zeolite &gt; biochar. In the same order amendments enhanced activities of soil microbial respiration, alkaline phosphatase, and dehydrogenase; microbial C also followed this trend. A sequential extraction confirmed a shift from easily mobilized to heavily bound fractions. The addition of 2% (w/w) of Divergan® was sufficient to lower mobile trace metal concentrations below German thresholds by chemisorption, and soil microbial activity was significantly increased. The effects of all other treatments were at a much lower level and not found suitable due to needed application rates.

Arsenic fractionation in mine spoils 10 years after aided phytostabilization

Aided phytostabilization using a combination of compost, zerovalent iron grit and coal fly ash (CZA) amendments and revegetation effectively promoted the biological recovery of mining spoils generated at a gold mine in Portugal. Selective dissolution of spoil samples in combination with solid phase characterization using microbeam X-ray absorption near edge structure (μXANES) spectroscopy and microbeam X-ray fluorescence (μXRF) mapping were used to assess As associations in spoils ten years after CZA treatment. The results show that As preferentially associates with poorly crystalline Fe-oxyhydroxides as opposed to crystalline Fe-(oxyhydr)oxide phases. The crystalline Fe(III)-phases dominated in the treated spoil and exceeded those of the untreated spoil three-fold, but only 2.6–6.8% of total As was associated with this fraction. Correlation maps of As:Fe reveal that As in the CZA-treated spoils is primarily contained in surface coatings as precipitates and sorbates. Arsenic binding with poorly crystalline Fe-oxyhydroxides did not inhibit As uptake by plants.

Heavy metal immobilization by cost-effective amendments in a contaminated soil: Effects on metal leaching and phytoavailability

The combination of revegetation and application of stabilizing soil amendments on heavy metal-contaminated soils is generally considered to be a promising alternative to expensive classical remediation techniques. Here, we simultaneously investigated the effects of six cost-effective amendments (CaCO3, iron grit, fly ash, manure, bentonite and bone meal) on Cd, Zn and Pb leaching and phytoavailability (assessed using white lupin, Lupinus albus L.). The Cd and Zn leaching was reduced by all amendments mainly due to alkalinity increase. The Pb leaching was strongly affected by the dissolved organic carbon (DOC) release. Therefore, bone meal and manure treatments, which highly increased DOC concentrations in leachates, increased the flow-weighted mean Pb concentrations by 2.3 and 16 times, respectively. Surprisingly, while iron grit induced strong Cd and Pb leaching reductions, this amendment doubled Cd and Pb concentrations in shoots of white lupin. Conversely, the addition of bone meal reduced Pb concentrations in shoots by 74%, probably because organo-Pb complexes (predicted using Visual MINTEQ) were largely dominant in solution. Overall, the addition of CaCO3 offered the best compromise as it successfully reduced both the leaching and the phytoavailability of the three considered metals. Our results demonstrate the efficacy of several amendments while stressing the need to measure simultaneously the leaching and the phytoavailability of metals induced by each amendment.