Enhancing bauxite residue properties for plant growth: Gypsum and organic amendment effects on chemical properties of soil and leachate.

Here, we assess the effects of gypsum and local organic waste as amendments to non-weathered, filter-pressed bauxite residue (BR) to improve its properties and support plant growth. In addition, we monitored the leachate quality of the amended BR under progressive leaching that simulated precipitation conditions in Northern Brazil. Free-draining column tests consisting of BR amended with gypsum and organic waste, at 5% and 10% w/w, respectively, were leached for 8 weeks to assess the effects on the chemical composition of BR and the leachates. Adding gypsum to BR reduced the exchangeable sodium (Na) percentage (ESP) from approximately 79%-48%, whereas adding only organic waste had smaller effects on ESP (from ∼79% to âˆ¼ 70%). The mean leachate pH ranged from 8.7 to 9.4 for the gypsum, and organic waste amended BR, while this was 10.3 in the leachate of the unamended BR. The treatments had similar trends of electrical conductivity throughout the experiments and were below 2 dS/cm after 8 weeks, when ∼1.700 mm simulated precipitation had leached. Aluminium (Al), Arsenic (As), and Vanadium (V) concentrations in leachates of BR with gypsum, either alone or in combination with organic waste, were significantly lowered than in leachate of non-amended BR. By contrast, metal concentrations increased if organic waste was added to BR. We conclude that amending BR with gypsum, in combination with organic waste, significantly improves the chemical properties of the solid phase and achieved rehabilitation goals for SAR and EC of the leachates after 8 weeks of leaching. However, despite high leaching rates, rehabilitation goals for pH and ESP were not achieved with gypsum either alone or combined with organic waste.

The effects of soil organic matter on leaching of hexavalent chromium from concrete waste: Batch and column experiments.

Concrete is one of the most common building materials in the world and in accordance with the world's shift to a circular economy, there is a need of an increase in concrete reuse and recycling. One of the environmental concerns linked to concrete recycling is the leaching and spread of hexavalent chromium (Cr(VI)). In the present study the Cr(VI) leaching from crushed concrete waste and the effects of soil organic matter (SOM) on chromium (Cr) speciation has been investigated in realistic reuse scenarios by the means of batch shale tests and layered column tests. The effects of concrete properties (pH, grain size and age) on Cr(VI) leaching was also studied. Cr leaching from concrete alone is mainly in the form of Cr(VI), with the pH of the leachate being >10. The smaller the grainsize of the concrete, the higher the Cr(VI) concentration is in the leachate. There was no correlation between the age of the concrete and concrete leaching. When exposed to SOM the Total-Cr concentration in the leachate was reduced. The reduction increased with higher TOC level, with a 99% reduction at very high TOC (25%). The results indicate that Cr(VI) leaching from recycled concrete waste can be mitigated by exposing it to SOM in the desired recycling scenario.

Industrial byproducts for the soil stabilization of trace elements and per- and polyfluorinated alkyl substances (PFASs).

The present work was the first exploration of the use of industrial byproducts from iron and titanium processing as sorbents for the stabilization of soil contamination. The main aim was to test slag waste and iron-rich charred fossil coal ("Fe-char"), as sorbents for per- and polyfluorinated alkyl substances (PFASs), as well as lead (Pb) and antimony (Sb), in four soils from a firefighting training area (PFASs) and a shooting range (Pb and Sb). Adding slag (10-20%) to shooting range soils decreased the leaching of Pb and Sb up to 50-90%. Fe-char amendment to these soils resulted in a moderate reduction in Sb leaching (20-70%) and a slightly stronger effect on Pb (40-50%). The sorption is most likely explained by the presence of Fe oxyhydroxides. These are present in the highest concentrations in the slag, probably resulting in more effective metal binding to the slag than to the Fe-char. Fe-char but not slag proved to be a strong sorbent for PFASs (reducing PFAS leaching from the soil by up to 99.7%) in soil containing low total organic carbon (TOC; 1.2%) but not in high-TOC soil (34%). The sorption coefficient KD for Fe-char was high, in the range of 104.3 to 106.5 L/kg at 1 ng/L in the low-TOC soil. The KD value increased with increasing perfluorocarbon chain length, exceeding PFAS sorption to biochar in the low ng/L concentration range. This result indicates that the mechanism behind the strong PFAS sorption to Fe-char was mainly van der Waals dispersive interactions between the hydrophobic PFAS-chain and the aromatic π-electron systems on nanopore walls within the Fe-char matrix. Overall, this study indicates that industrial byproducts can provide sustainable and cost-effective materials for soil remediation. However, the sorbent needs to be tailored to the type of soil and type of contamination.

Occurrence and fate of antimony in plastics.

Antimony (Sb) is a technology critical element whose presence is ubiquitous in manufactured products, and in particular in plastics where it is used extensively as a flame retardant synergist for brominated compounds, as a catalyst for polyethylene terephthalate production, and as a pigment for colour. This study reviews the usage, regulations and fate of Sb in plastics by examining primary data on its production, applications, contents in and migration from manufactured objects, and presence in and release from waste, including the disposal and recycling routes for this material (i.e., non-controlled disposal, incineration, landfilling and recycling). Consumption of Sb and the relative apportioning of the metalloid between different uses in plastics change continuously and are largely driven by dynamic economic factors; accordingly, reference to secondary data or sources can be misleading. Since Sb is not recovered from plastics, its fate is entirely linked to the fate of plastics themselves which, as far as disposal and recycling are concerned, might be dictated by the presence of co-associated regulated substances such as brominated flame retardants. Significantly, because of the high leachability of Sb from bottom incineration ashes, the EU considers the metalloid as the most problematic substance regarding the potential reuse of this material.

Can biochar and designer biochar be used to remediate per- and polyfluorinated alkyl substances (PFAS) and lead and antimony contaminated soils?

Designer biochars can be used to remediate organic and inorganic contaminant polluted soils. Here, a waste timber biochar (BC), a coconut shell activated biochar (aBC) and a wood shrub iron enriched designer biochar (Fe-BC) were investigated. Per- and polyfluorinated alkyl substances (PFAS) contaminated soils with different total organic carbon (TOC) contents (1.6 and 34.2%) were amended with six doses of BC and aBC. Two shooting range soils (TOC 5.2 and 10.2%) contaminated with heavy metals (mainly Pb and Sb) were amended with four doses of BC and Fe-BC. An amendment of 20% BC reduced the PFOS leachate concentration by 86% for the low TOC soil but was not effective for the high TOC soil. An amendment of 1% aBC reduced PFOS leachate concentrations by over >96% for both soils. For the low TOC shooting range soil, a 20% amendment of BC reduced Pb and Sb leaching by 61% and 12%, respectively. An amendment of 20% Fe-BC to soil with low TOC reduced Pb and Sb leaching by 99% and 40%, respectively. The need for "designer" biochars using processes such as iron enrichment or activation should be considered depending on the TOC of the soil, the type of contaminants and remediation goals.

Sequestration of Antimony on Calcite Observed by Time-Resolved Nanoscale Imaging.

Antimony, which has damaging effects on the human body and the ecosystem, can be released into soils, ground-, and surface waters either from ore minerals that weather in near surface environments, or due to anthropogenic releases from waste rich in antimony, a component used in batteries, electronics, ammunitions, plastics, and many other industrial applications. Here, we show that dissolved Sb can interact with calcite, a widespread carbonate mineral, through a coupled dissolution-precipitation mechanism. The process is imaged in situ, at room temperature, at the nanometer scale by using an atomic force microscope equipped with a flow-through cell. Time-resolved imaging allowed following the coupled process of calcite dissolution, nucleation of precipitates at the calcite surface and growth of these precipitates. Sb(V) forms a precipitate, whereas Sb(III) needs to be oxidized to Sb(V) before being incorporated in the new phase. Scanning-electron microscopy and Raman spectroscopy allowed identification of the precipitates as two different calcium-antimony phases (Ca2Sb2O7). This coupled dissolution-precipitation process that occurs in a boundary layer at the calcite surface can sequester Sb as a solid phase on calcite, which has environmental implications as it may reduce the mobility of this hazardous compound in soils and groundwaters.

The mass flow and proposed management of bisphenol A in selected Norwegian waste streams.

Current initiatives for waste-handling in a circular economy favor prevention and recycling over incineration or landfilling. However, the impact of such a transition on environmental emissions of contaminants like bisphenol A (BPA) during waste-handling is not fully understood. To address this, a material flow analysis (MFA) was constructed for selected waste categories in Norway, for which the amount recycled is expected to increase in the future; glass, vehicle, electronic, plastic and combustible waste. Combined, 92tons/y of BPA are disposed of via these waste categories in Norway, with 98.5% associated with plastic and electronic waste. During the model year 2011, the MFA showed that BPA in these waste categories was destroyed through incineration (60%), exported for recycling into new products (35%), stored in landfills (4%) or released into the environment (1%). Landfilling led to the greatest environmental emissions (up to 13% of landfilled BPA), and incinerating the smallest (0.001% of incinerated BPA). From modelling different waste management scenarios, the most effective way to reduce BPA emissions are to incinerate BPA-containing waste and avoid landfilling it. A comparison of environmental and human BPA concentrations with CoZMoMAN exposure model estimations suggested that waste emissions are an insignificant regional source. Nevertheless, from monitoring studies, landfill emissions can be a substantial local source of BPA. Regarding the transition to a circular economy, it is clear that disposing of less BPA-containing waste and less landfilling would lead to lower environmental emissions, but several uncertainties remain regarding emissions of BPA during recycling, particularly for paper and plastics. Future research should focus on the fate of BPA, as well as BPA alternatives, in emerging reuse and recycling processes, as part of the transition to a circular economy.

Antimony (Sb) and lead (Pb) in contaminated shooting range soils: Sb and Pb mobility and immobilization by iron based sorbents, a field study.

Small-arm shooting ranges often receive a significant input of lead (Pb), copper (Cu) and antimony (Sb) from ammunition. The goal of the present study was to investigate the mobility, distribution and speciation of Pb and Sb pollution under field conditions in both untreated and sorbent-amended shooting range soil. Elevated Sb (19-349µgL(-1)) and Pb (7-1495µgPbL(-1)) concentrations in the porewater of untreated soil over the four-year test period indicated a long-term Sb and Pb source to the adjacent environment in the absence of remedial measures. Mixing ferric oxyhydroxide powder (CFH-12) (2%) together with limestone (1%) into the soil resulted in an average decrease of Sb and Pb porewater concentrations of 66% and 97%, respectively. A similar reduction was achieved by adding 2% zerovalent iron (Fe°) to the soil. The remediation effect was stable over the four-year experimental period indicating no remobilization. Water- and 1M NH4NO3-extractable levels of Sb and Pb in field soil samples indicated significant immobilization by both treatments (89-90% for Sb and 89-99% for Pb). Results from sequential extraction analysis indicate fixation of Sb and Pb in less accessible fractions like amorphous iron oxides or even more crystalline and residual mineral phases, respectively. This work shows that amendment with Fe-based sorbents can be an effective method to reduce the mobility of metals both in cationic and anionic form in polluted shooting range soil.

Short-term effect of the soil amendments activated carbon, biochar, and ferric oxyhydroxide on bacteria and invertebrates.

The aim of the present study was to evaluate the secondary ecotoxicological effects of soil amendment materials that can be added to contaminated soils in order to sequester harmful pollutants. To this end, a nonpolluted agricultural soil was amended with 0.5, 2, and 5% of the following four amendments: powder activated carbon (PAC), granular activated carbon, corn stover biochar, and ferric oxyhydroxide powder, which have previously been proven to sequester pollutants in soil. The resulting immediate effects (i.e., without aging the mixtures before carrying out tests) on the springtail Folsomia candida, the earthworm species Aporectodea caliginosa and Eisenia fetida, the marine bacteria Vibrio fischeri, a suite of ten prokaryotic species, and a eukaryote (the yeast species Pichia anomalia) were investigated. Reproduction of F. candida was significantly increased compared to the unamended soil when 2% biochar was added to it. None of the treatments caused a negative effect on reproduction. All amendments had a deleterious effect on the growth of A. caliginosa when compared to the unamended soil, except the 0.5% amendment of biochar. In avoidance tests, E. fetida preferred biochar compared to all other amendments including the unamended soil. All amendments reduced the inhibition of luminescence to V. fischeri, i.e., were beneficial for the bacteria, with PAC showing the greatest improvement. The effects of the amendments on the suite of prokaryotic species and the eukaryote were variable, but overall the 2% biochar dose provided the most frequent positive effect on growth. It is concluded that the four soil amendments had variable but never strongly deleterious effects on the bacteria and invertebrates studied here during the respective recommended experimental test periods.

Antimony (Sb) contaminated shooting range soil: Sb mobility and immobilization by soil amendments.

Antimony (Sb) in lead bullets poses a major environmental risk in shooting range soils. Here we studied the effect of iron (Fe)-based amendments on the mobility of Sb in contaminated soil from shooting ranges in Norway. Untreated soil showed high Sb concentrations in water extracts from batch tests (0.22-1.59 mg L(-1)) and soil leachate from column tests (0.3-0.7 mg L(-1)), occurring exclusively as Sb(V). Sorption of Sb to different iron-based sorbents was well described by the Freundlich equation (Fe2(SO4)3, log KF = 6.35, n = 1.51; CFH-12 (Fe oxyhydroxide), log KF = 4.16-4.32, n = 0.75-0.76); Fe(0) grit, log KF = 3.26, n = 0.47). These sorbents mixed with soil (0.5 and 2% w/w), showed significant sorption of Sb in batch tests (46-92%). However, for Fe2(SO4)3 and CFH-12 liming was also necessary to prevent mobilization of lead, copper, and zinc. Column tests showed significant retention of Sb (89-98%) in soil amended with CFH-12 (2%) mixed with limestone (1%) compared to unamended soil. The sorption capacity of soils amended with Fe(0) (2%) increased steadily up to 72% over the duration period of the column test (64 days), most likely due to the gradual oxidation of Fe(0) to Fe oxyhydroxides. Based on the experimental results, CFH-12 and oxidized Fe(0) are effective amendments for the stabilization of Sb in shooting range soils.

Treatment of air pollution control residues with iron rich waste sulfuric acid: does it work for antimony (Sb)?

Antimony (Sb) in air pollution control (APC) residues from municipal solid waste incineration has gained increased focus due to strict Sb leaching limits set by the EU landfill directive. Here we study the chemical speciation and solubility of Sb at the APC treatment facility NOAH Langøya (Norway), where iron (Fe)-rich sulfuric acid (∼3.6M, 2.3% Fe(II)), a waste product from the industrial extraction of ilmenite, is used for neutralization. Antimony in water extracts of untreated APC residues occurred exclusively as pentavalent antimonate, even at low pH and Eh values. The Sb solubility increased substantially at pH<10, possibly due to the dissolution of ettringite (at alkaline pH) or calcium (Ca)-antimonate. Treated APC residues, stored anoxically in the laboratory, simulating the conditions at the NOAH Langøya landfill, gave rise to decreasing concentrations of Sb in porewater, occurring exclusively as Sb(V). Concentrations of Sb decreased from 87-918µgL(-1) (day 3) to 18-69µgL(-1) (day 600). We hypothesize that an initial sorption of Sb to Fe(II)-Fe(III) hydroxides (green rust) and eventually precipitation of Ca- and Fe-antimonates (tripuhyite; FeSbO4) occurred. We conclude that Fe-rich, sulfuric acid waste is efficient to immobilize Sb in APC residues from waste incineration.

Antimony (Sb) and arsenic (As) in Sb mining impacted paddy soil from Xikuangshan, China: differences in mechanisms controlling soil sequestration and uptake in rice.

Foods produced on soils impacted by antimony (Sb) mining activities are a potential health risk due to plant uptake of the contaminant metalloids (Sb) and arsenic (As). Here we report for the first time the chemical speciation of Sb in soil and porewater of flooded paddy soil, impacted by active Sb mining, and its effect on uptake and speciation in rice plants (Oryza sativa L. cv Jiahua). Results are compared with behavior and uptake of As. Pot experiments were conducted under controlled conditions in a climate chamber over a period of 50 days. In pots without rice plants, flooding increased both the concentration of dissolved Sb (up to ca. 2000 µg L(-1)) and As (up to ca. 1500 µg L(-1)). When rice was present, Fe plaque developing on rice roots acted as a scavenger for both As and Sb, whereby the concentration of As, but not Sb, in porewater decreased substantially. Dissolved Sb in porewater, which occurred mainly as Sb(V), correlated with Ca, indicating a solubility governed by Ca antimonate. No significant differences in bioaccumulation factor and translocation factor between Sb and As were observed. Greater relative concentration of Sb(V) was found in rice shoots compared to rice root and porewater, indicating either a preferred uptake of Sb(V) or possibly an oxidation of Sb(III) to Sb(V) in shoots. Adding soil amendments (olivine, hematite) to the paddy soil had no effect on Sb and As concentrations in porewater.

Distribution, speciation and availability of antimony (Sb) in soils and terrestrial plants from an active Sb mining area.

Here, we present one of the first studies investigating the mobility, solubility and the speciation-dependent in-situ bioaccumulation of antimony (Sb) in an active Sb mining area (Xikuangshan, China). Total Sb concentrations in soils are high (527-11,798 mg kg(-1)), and all soils, including those taken from a paddy field and a vegetable garden, show a high bioavailable Sb fraction (6.3-748 mg kg(-1)), dominated by Sb(V). Elevated concentrations in native plant species (109-4029 mg kg(-1)) underpin this. Both chemical equilibrium studies and XANES data suggest the presence of Ca[Sb(OH)(6)](2), controlling Sb solubility. A very close relationship was found between the citric acid extractable Sb in plants and water or sulfate extractable Sb in soil, indicating that citric acid extractable Sb content in plants may be a better predictor for bioavailable Sb in soil than total acid digestible Sb plant content.