Redox conditions and biochar pyrolysis temperature affecting As and Pb biogeochemical cycles and bacterial community of sediment from mining tailings.

Despite the widespread use of biochar for soil and sediment remediation, little is known about the impact of pyrolysis temperature on the biogeochemistry of arsenic (As) and lead (Pb) and microorganisms in sediment under reducing conditions. In this study, we investigated the effects of pyrolysis temperature and the addition of glucose on the release and transformation of As and Pb, as well as their potential effects on the bacterial community in contaminated sediments. The addition of biochar altered the geochemical cycle of As, as it favors specific bacterial groups capable of changing species from As(V) to As(III) through fermentation, sulfate respiration and nitrate reduction. The carbon quality and content of N and S in solution shaped the pH and redox potential in a way that changed the microbial community, favoring Firmicutes and reducing Proteobacteria. This change played a fundamental role in the reductive dissolution of As and Pb minerals. The addition of biochar was the only efficient way to remove Pb, possibly as a function of its sorption and precipitation mechanisms. Such insights could contribute to the production or choice of high-efficiency biochar for the remediation of sediments subjected to redox conditions.

Zinc speciation and desorption kinetics in a mining waste impacted tropical soil amended with phosphate.

Mining is an important component of the Brazilian economy. However, it may also contribute to environmental problems such as the pollution of soils with zinc and other potentially toxic metals. Our objective was to evaluate changes in the chemical speciation and mobility of Zn in a soil amended with phosphate. Soil samples were collected from a deactivated mining area in the state of Minas Gerais, Brazil, and amended with NH4H2PO4 saturated with deionized water to 70 % of maximum water retention and incubated at 25 ± 2 °C in open containers for 60 days. The soil was chemically and mineralogically characterized, and sequential extraction, desorption kinetics, and speciation were carried out using synchrotron bulk-sample and micro-X-ray Absorption Near-Edge Structure (XANES/µ-XANES) spectroscopy at the Zn K-edge, and X-ray fluorescence microprobe analysis (µ-XRF). The combination of µ-XRF and µ-XANES techniques made it possible to identify Zn hotspots in the main species formed after phosphate remediation. The best fit combination for bulk XANES and µ-XANES was observed in Zn-montmorillonite, Zn-kerolite, Zn-ferrihydrite, and gahnite. In the course of phosphate treatment, gahnite, Zn layered double hydroxides (Zn-LDH), Zn3(PO4), and ZnO were identified by bulk XANES, while Zn-ferrihydrite, Zn-montmorillonite, and scholzite were identified by µ-XANES. Zinc in the phosphate-amended soil had the strongest partial correlations (r' > 0.05) with Ni, Co, Fe, Cr, Mn, Si, P, Cd, Pb, and Cd, while the unamended soil showed the strongest correlation with Cu, Pb, Fe, and Si. The application of NH4H2PO4 altered Zn speciation and favored an increase in Zn desorption. The most available Zn contents after phosphate amendment were correlated with the release of exchangeable Zn fractions, associated with carbonate and organic matter.

Pristine and biochar-supported nano zero-valent iron to immobilize As, Zn and Pb in soil contaminated by smelting activities.

Nano zero-valent iron (nZVI) is one of the most studied nanomaterials for environmental remediation during the past 20 years. However, few studies have focused on nZVI combination with other materials (e.g., biochar) for enhancement of soil remediation. In this study, pristine nZVI and a composite of wood sawdust biochar (BC) and nZVI (nZVI-BC) were added to a highly contaminated soil to compare their efficacy in immobilizing available arsenic (As = 28.6 mg kg-1), zinc (Zn = 1707 mg kg-1), and lead (Pb = 6759 mg kg-1). Sediment quality guidelines were used to evaluate the extent of soil contamination and ascertain its source. The mineralogy of soil and slags were assessed by X-ray Diffractometry Spectroscopy (XRD), and the geochemical fractions of Pb, Zn, and As were obtained by chemical sequential extractions. The average Pollution Load Index (PLI) was 10.66, indicating elevated multi-elemental contamination. Contamination Factor (CF) values for As, Zn, Pb, cadmium (Cd), and copper (Cu) were all higher than 6 which implies extreme contamination. Secondary minerals frequently found in Pb/Zn smelter sites, such as cerussite and anglesite, were detected in the slags through XRD. Pb and Zn were mainly bound to carbonates and residual fractions in soil and presented a high risk considering the sediment quality guidelines, sequential extraction results, and XRD analysis. The treatment with nZVI-BC was more effective than pristine nZVI on concurrently decreasing 97% of available As, 84% of Pb and 81% of Zn compared to control. The application of nZVI-BC is a promising green and sustainable remediation technique for soils contaminated with potentially toxic elements of distinct chemical behavior.

Temporal changes in arsenic and lead pools in a contaminated sediment amended with biochar pyrolyzed at different temperatures.

Globally, tons of soils and sediments are experiencing degradation due to the presence of high concentrations of potentially toxic elements (PTEs), such as arsenic (As) and lead (Pb), in areas in the vicinity of metal mining activities. The addition of biochar to contaminated sediments is a promising in situ remediation approach, and the effects of pyrolysis temperature and biochar aging are important factors for the immobilization and fate of PTEs. In this study, we evaluated the temporal changes in pools of As and Pb in sediment amended with biochars produced from sugarcane (Saccharum officinarum) pyrolyzed at 350 (BC350), 550 (BC550), and 750 °C (BC750). Biochars were aged by natural process (without additional acid or heat), and changes in As and Pb pools were evaluated every 45 days until completing 180 days of incubation. Changes in the As and Pb pools were extracted with water (bioavailable), magnesium chloride (exchangeable), nitric acid (active geochemical fraction), and exchangeable Mehlich-3 (associated with organic matter). As and Pb available contents have increased over time. BC750 was more effective in reducing the bioavailable and exchangeable As contents, while BC550 and BC350 were more effective in reducing the contents of bioavailable and exchangeable Pb.

Indaziflam sorption-desorption and its three metabolites from biochars- and their raw feedstock-amended agricultural soils using radiometric technique.

This study aimed to characterize the effect of amending soils with biochars derived from soybean residues, sugarcane bagasse, and wood chips on the sorption-desorption of indaziflam and indaziflam-triazinediamine (FDAT), indaziflam-triazine-indanone (ITI), and indaziflam-carboxylic acid (ICA) metabolites applied to soils from three Midwestern U.S. states, a silt loam and a silty clay loam. Biochars produced from different feedstock were used as soil amendments and compared with raw feedstock. Sorption-desorption experiments of indaziflam and its three metabolites were performed using the batch equilibration method and analyzed for 14C activity by liquid scintillation counting (radiometric technique). In all soils, the use of organic amendments promoted greater sorption and less desorption of indaziflam and ITI. The addition of biochar to soils promoted greater sorption of the four tested chemical products compared with the corresponding raw materials. Among the biochars, grape wood chips showed greater potential in sorb indaziflam and ITI. In general, none of the biochars affected the sorption and desorption of FDAT and ICA. Characterization of biochar to be used as a soil amendment (immobilizer) is highly recommended prior to field addition to optimize the sorption process and to prevent increased soil and water contamination of indaziflam and its metabolites following biochar addition.

In situ barium phytoremediation in flooded soil using Typha domingensis under different planting densities.

The management of initial planting density can be a strategy to increase barium phytoextraction from soil, reducing the time required for soil decontamination. To delimit the ideal planting density for barium (Ba) phytoremediation using Typha domingensis, we conducted a 300-day experiment in an area accidentally contaminated with barite. Four initial planting densities were tested: 4, 8, 12, and 16 plantsm-2 (D4, D8, D12, and D16 treatments, respectively). Plant development was evaluated periodically, and the phytoextraction efficiency was determined at the end of the trial. The initial planting density affected Ba phytoremediation by T. domingensis monoculture. Phytoextraction potential was better represented by the mass-based translocation factor (mTF) than the concentration-based translocation factor. D16 promoted the highest final number of plants and biomass production, but the mass of Ba in the aerial part did not differ among D8, D12, and D16. D4 resulted in more Ba accumulated belowground than aboveground (6.3 times higher), whereas D12 and D16 achieved the greatest mTFs. Higher absorption of Ba from soil can be achieved using less T. domingensis individuals at the beginning of the treatment (D4 and D8) but with high accumulation in belowground tissues. We conclude that the D8 density is considered the most appropriate if considering the phytoextraction potential and field management facilitated using fewer plants.

Successive sewage sludge fertilization: Recycling for sustainable agriculture.

Sewage sludge (SS) is widely used in agriculture in several countries around the world. However, the impact of successive applications of SS on soil and the risks of nutrient leaching are often neglected. In this study, corn was grown on a constructed wetland for four crop cycles (two years), in which the wetland was subjected to successive SS applications. The objective of this study was to evaluate how the successive applications of SS affect the availability and leaching of nutrients in the soil profile, after two years of cultivation. Experiments were performed using a randomized block design with repeated measurements in time, that is, soil was sampled in each harvest. Six treatments were tested: four fertilizations based on sewage sludge, resulting from biological and anaerobic treatment, calculated to provide 25 (SS25), 50 (SS50), 75 (SS75), and 100% (SS100), of the N required for corn production (140 kg ha-1); a mineral fertilization (NPK) (140 kg ha-1 N, 70 kg ha-1 of P2O5 and 40 kg ha-1 of K2O) and a control (without fertilization). The results showed that four consecutive applications of SS100 for two years caused significant accumulation of nutrients and organic matter in the superficial layers of the soil. The electrical conductivity and the concentration of NO3- in the soil solution were higher than those permitted by Brazilian legislation. The adoption of domestic SS in Brazilian agriculture can be a viable alternative in the search for an environment-friendly and economically feasible method for SS disposal.