Dataset Information

Tailings after Iron Extraction in Bayer Red Mud by Biomass Reduction: Pozzolanic Activity and Hydration Characteristics.

ABSTRACT: Bayer red mud (BRM) is a kind of solid waste with high hematite content, and its effective utilization is difficult due to the special physicochemical properties. In this work, Fe₂O₃ in BRM was reduced to Fe₃O₄ by biomass, and iron concentrate and high activity tailings were obtained after magnetic separation. The pozzolanic activity and hydration characteristics of the tailings were systematically studied. The results showed that the relatively stable polymerization structures of Si-O and Al-O in BRM are destroyed under the effect of biomass reduction at 650 °C, and some fracture bonds and activation points are formed in the structures. The aluminosilicate phases in the BRM were easy to transform into the active substances of Si and Al. The pozzolanic activity of tailings is greatly improved, and its pozzolanic activity index is 91%. High polymerization degree of gel and ettringite are formed since more active substances and alkali in the tailings promote the hydration reaction of cement-based cementitious materials, which made cementitious materials have dense matrix, good mechanical properties, and environmental performance. This work has realized the full quantitative utilization of BRM and provided a feasible way for the resource utilization of BRM.

SUBMITTER: Wang Y

PROVIDER: S-EPMC8306629 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Mine wastes introduce anthropogenic weathering profiles to the critical zone that often remain unvegetated for decades after mining cessation. As such, they are vulnerable to wind and water dispersion of particulate matter to adjacent ecosystems and residential communities. In sulfide-rich ore tailings, propagation to depth of the oxidative weathering front controls the depth-variation in speciation of major and trace elements. Despite the prevalence of surficial mine waste deposits in arid regions of the globe, few prior studies have been conducted to resolve the near-surface profile of sulfide ore tailings weathered under semi-arid climate. We investigated relations between gossan oxidative reaction-front propagation and the molecular speciation of iron and sulfur in tailings subjected to weathering under semi-arid climate at an EPA Superfund Site in semi-arid central Arizona (USA). Here we report a multi-method data set combining wet chemical and synchrotron-based X-ray diffraction (XRD) and X-ray absorption near-edge spectroscopy (XANES) methods to resolve the tight coupling of iron (Fe) and sulfur (S) geochemical changes in the top 2 m of tailings. Despite nearly invariant Fe and S concentration with depth (130-140 and 100-120 g kg-1, respectively), a sharp redox gradient and distinct morphological change was observed within the top 0.5 m, associated with a progressive oxidative alteration of ferrous sulfides to (oxyhydr)oxides and (hydroxy)sulfates. Transformation is nearly complete in surficial samples. Trends in molecular-scale alteration were co-located with a decrease in pH from 7.3 to 2.3, and shifts in Fe and S lability as measured via chemical extraction. Initial weathering products, ferrihydrite and gypsum, transform to schwertmannite, then jarosite-group minerals with an accompanying decrease in pH. Interestingly, thermodynamically stable phases such as goethite and hematite were not detected in any samples, but ferrihydrite was observed even in the lowest pH samples, indicating its metastable persistence in these semiarid tailings. The resulting sharp geochemical speciation gradients in close proximity to the tailings surface have important implications for plant colonization, as well as mobility and bioavailability of co-associated toxic metal(loid)s.

Project description:Particulate and dissolved metal(loid) release from mine tailings is of concern in (semi-) arid environments where tailings can remain barren of vegetation for decades and, therefore, become highly susceptible to dispersion by wind and water. Erosive weathering of metalliferous tailings can lead to arsenic contamination of adjacent ecosystems and increased risk to public health. Management via phytostabilization with the establishment of a vegetative cap using organic amendments to enhance plant growth has been employed to reduce both physical erosion and leaching. However, prior research suggests that addition of organic matter into the oxic weathering zone of sulfide tailings has the potential to promote the mobilization of arsenate. Therefore, the objective of the current work was to assess the impacts of phytostabilization on the molecular-scale mechanisms controlling arsenic speciation and lability. These impacts, which remain poorly understood, limit our ability to mitigate environmental and human health risks. Here we report on subsurface biogeochemical transformations of arsenic and iron from a three-year phytostabilization field study conducted at a Superfund site in Arizona, USA. Legacy pyritic tailings at this site contain up to 3 g kg-1 arsenic originating from arsenopyrite that has undergone oxidation to form arsenate-ferrihydrite complexes in the top 1 m. Tailings were amended in the top 20 cm with 100, 150, or 200 g kg-1 (300-600 T ha-1) of composted organic matter and seeded with native halotolerant plant species. Treatments and an unamended control received irrigation of 360 ± 30 mm y-1 in addition to 250 ± 160 mm y-1 of precipitation. Cores to 1 m depth were collected annually for three years and sectioned into 20 cm increments for analysis by synchrotron iron and arsenic X-ray absorption spectroscopy (XAS) coupled with quantitative wet chemical and mass balance methods. Results revealed that > 80% of arsenic exists in ammonium oxalate-extractable and non-extractable phases, including dominantly ferrihydrite and jarosite. Arsenic release during arsenopyrite oxidation resulted in both downward translocation and As(V) attenuation by stable Fe(III)(oxyhydr)oxide and Fe(III) (hydroxy)sulfate minerals over time, highlighting the need for sampling at multiple depths and time points for accurate interpretation of arsenic speciation, lability, and translocation in weathering profiles. Less than 1% of total arsenic was highly-labile, i.e. water-extractable, from all treatments, depths, and years, and more than 99% of arsenate released by arsenopyrite weathering was attenuated by association with secondary minerals. Although downward translocation of both arsenic and iron was detected during phytostabilization by temporal enrichment analysis, a similar trend was measured for the uncomposted control, indicating that organic amendment associated with phytostabilization practices did not significantly increase arsenic mobilization over non-amended controls.

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Tailings after Iron Extraction in Bayer Red Mud by Biomass Reduction: Pozzolanic Activity and Hydration Characteristics.

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