Novel process for organic wastewater treatment using aerobic composting technology: Shifting from pollutant removal towards resource recovery.

In this study, an organic wastewater treatment process based on aerobic composting technology was developed in order to explore the transition of wastewater treatment from pollutants removal to resource recovery. The novelty of the process focuses towards the microbial metabolic heat that is often ignored during the composting, and taking advantage of this heat for wastewater evaporation to achieve zero-discharge treatment. Meanwhile, this process can retain the wastewater's nutrients in the composting substrate to realize the recovery of resources. This study determined the optimum condition for the process (initial water content of 50 %, C/N ratio of 25:1, ventilation rate of 3 m3/h), and 69.9 % of the total heat generated by composting was used for wastewater treatment under the condition. The HA/FA ratio of composting substrate increased from 0.07 to 0.53 after wastewater treatment, and the retention ratio of TOC and TN was 52.3 % and 61.7 %, respectively, which proved the high recycling value of the composting products. Thermoduric and thermophilic bacteria accounted for 44.3 % of the community structure at the maturation stage, which played a pivotal role in both pollutant removal and resource recovery.

Geochemical distributions of natural radionuclides in surface soils and sediments impacted by lead-zinc mining activity.

This study investigated the distribution features of uranium-238 (238U), radium-226 (226Ra), thorium-232 (232Th), and potassium-40 (40K) and evaluated the associated environmental radiological hazards of the topsoil and river sediments in the Jinding lead-zinc (Pb-Zn) mine catchment from Southwest China. The activity concentrations of 238U, 226Ra, 232Th, and 40K ranged from 24.0 ± 2.29-60.3 ± 5.26 Bq.kg-1, from 32.5 ± 3.95-69.8 ± 3.39 Bq.kg-1, from 15.3 ± 2.24-58.3 ± 4.92 Bq.kg-1, and from 203 ± 10.2-1140 ± 27.4 Bq.kg-1, respectively. The highest activity concentrations for all these radionuclides were primarily found in the mining areas and decreased with increasing distance from the mining sites. The radiological hazard indices, including radium equivalent activity, absorbed gamma dose rate in the air, outdoor annual effective dose equivalent, annual gonadal dose equivalent, and excess lifetime cancer, revealed that the highest values were observed in the mining area and downstream, specifically in the vicinity of the ore body. These elevated values exceeded the global mean value but remained below the threshold value, suggesting that routine protection measures for Pb-Zn miners during production activities are sufficient. The correlation analysis and cluster analysis revealed strong associations between radionuclides such as 238U, 226Ra, and 232Th, indicating a common source of these radionuclides. The activity ratios of 226Ra/238U, 226Ra/232Th, and 238U/40K varied with distance, suggesting the influence of geological processes and lithological composition on their transport and accumulation. In the mining catchment areas, the variations in these activity ratios increased indicated the impact of limestone material dilution on the levels of 232Th, 40K, and 238U in the upstream region. Moreover, the presence of sulfide minerals in the mining soils contributed to the enrichment of 226Ra and the removal of 238U caused those activity ratios decreased in the mining areas. Therefore, in the Jinding PbZn deposit, the patterns of mining activities and surface runoff processes in the catchment area favored the accumulation of 232Th and 226Ra over 40K and 238U. This study provides the first case study on the geochemical distributions of natural radionuclides in a typical Mississippi Valley-type PbZn mining area and offers fundamental information on radionuclide migration and baseline radiometric data for PbZn deposits worldwide.

Phosphate interactions with iron-titanium oxide composites: Implications for phosphorus removal/recovery from wastewater.

Understanding the interactions between phosphate (P) and mineral adsorbents is critical for removing and recovering P from wastewater, especially in the presence of both cationic and organic components. To this end, we investigated the surface interactions of P with an iron-titanium coprecipitated oxide composite in the presence of Ca (0.5-3.0 mM) and acetate (1-5 mM), and quantified the molecular complexes and tested the possible removal and recovery of P from real wastewater. A quantitative analysis of P K-edge X-ray absorption near edge structure (XANES) confirmed the inner-sphere surface complexation of P with both Fe and Ti, whose contribution to P adsorption relies on their surface charge determined by pH conditions. The effects of Ca and acetate on P removal were highly pH-dependent. At pH 7, Ca (0.5-3.0 mM) in solution significantly increased P removal by 13-30% by precipitating the surface-adsorbed P, forming hydroxyapatite (14-26%). The presence of acetate had no obvious influence on P removal capacity and molecular mechanisms at pH 7. At pH 4, the removal amount of P was not obviously affected by the presence of Ca and acetate. However, acetate and high Ca concentration jointly facilitated the formation of amorphous FePO4 precipitate, complicating the interactions of P with Fe-Ti composite. In comparison with ferrihydrite, the Fe-Ti composite significantly decreased the formation of amorphous FePO4 probably by decreasing Fe dissolution due to the coprecipitated Ti component, facilitating further P recovery. An understanding of these microscopic mechanisms can lead to the successful use and simple regeneration of the adsorbent to recover P from real wastewater.

A critical review on adsorptive removal of antimony from waters: Adsorbent species, interface behavior and interaction mechanism.

Antimony (Sb) has raised widespread concern because of its negative effects on ecology and human health. The extensive use of antimony-containing products and corresponding Sb mining activities have discharged considerable amounts of anthropogenic Sb into the environment, especially the water environment. Adsorption has been employed as the most effective strategy for Sb sequestration from water; thus, a comprehensive understanding of the adsorption performance, behavior and mechanisms of adsorbents benefits to develop the optimal adsorbent to remove Sb and even drive its practical application. This review presents a holistic analysis of adsorbent species with the ability to remove Sb from water, with a special emphasis on the Sb adsorption behavior of various adsorption materials and their Sb-adsorbent interaction mechanisms. Herein, we summarize research results based on the characteristic properties and Sb affinities of reported adsorbents. Various interactions, including electrostatic interactions, ion exchange, complexation and redox reactions, are fully reviewed. Relevant environmental factors and adsorption models are also discussed to clarify the relevant adsorption processes. Overall, iron-based adsorbents and corresponding composite adsorbents show relatively excellent Sb adsorption performance and have received widespread attention. Sb removal mainly depends on chemical properties of the adsorbent and Sb itself, and complexation is the main driving force for Sb removal, assisted by electrostatic attraction. The future directions of Sb removal by adsorption focus on the shortcomings of current adsorbents; more attention should be given to the practicability of adsorbents and their disposal after use. This review contributes to the development of effective adsorbents for removing Sb and provides an understanding of Sb interfacial processes during Sb transport and the fate of Sb in the water environment.

Emergent thallium exposure from uranium mill tailings.

Thallium (Tl) pollution caused by the exploitation of uranium (U) mines has long been neglected due to its low crustal abundance. However, Tl may be enriched in minerals of U ore because Tl has both sulfurophile and lithophile properties. Herein, a semi-dynamic leaching experiment combined with statistical analysis, geochemical speciation and multi-characterization provided novel insight into the distinct features and mechanisms of Tl release from uranium mill tailings (UMT). The results showed that particle size effects prevail over the pH on Tl release, and surface dissolution is the pivotal mechanism controlling Tl release based on Fick's diffusion model. The study revealed that long-term leaching and weathering can lead to the increased acid-extractable and oxidizable fractions of Tl in UMT, and that the exposure and dissolution of Tl-containing sulfides would largely enhance the flux of Tl release. The findings indicate that UMT containing (abundant) pyrite should be paid particular attention due to Tl exposure. Besides, critical concern over the potential Tl pollution in universal U mining and hydrometallurgical areas likewise may need to be seriously reconsidered.

Critical insight and indication on particle size effects towards uranium release from uranium mill tailings: Geochemical and mineralogical aspects.

Uranium (U) is both chemically toxic and radioactive. Uranium mill tailings (UMTs) are one of the most important sources of U contamination in the environment, wherein the mechanisms that control U release from UMTs with different granularities have not yet been well understood. Herein, the release behaviours and underlying release mechanisms of U from UMTs with five different particle size fractions (<0.45, 0.45-0.9, 0.9-2, 2-6 and 6-10 mm) were studied with a well-defined leaching test (ANS 16.1) combined with geochemical and mineralogical characterizations. The results showed that the most remarkable U release unexpectedly emerged from UMT2-6 mm; in contrast, the smallest particle size UMT<0.45 mm contributed to the least U release. The predominant mechanism of U release from UMT2-6 mm was the oxidative dissolution of U-bearing sulfides, while abundant gypsum present in UMT<0.45 mm inhibited U release. The study highlights the importance of combined geochemical and mineralogical investigation when performing leaching tests of mineral-containing hazardous materials such as UMTs with consideration of particle size effects. The findings also indicate that elevating the content of gypsum and avoiding the oxidation of sulfides can effectively help immobilize and minimize the residual U release from the UMTs.

Phosphorous Retention and Release by Sludge-Derived Hydrochar for Potential Use as a Soil Amendment.

To solve both the problems of P deficiency in arable soil and excessive waste sludge disposal, we evaluated hydrothermal carbonization of sludge with the aim of recycling sludge P resources for soil amendment. In contrast with pyrochars obtained through pyrolysis, hydrochars generated from hydrothermal carbonization often feature variable properties and therefore require detailed characterization. In this study, sludge-derived hydrochars were evaluated to determine their P content and fractionation, release and availability of P, and P adsorption and desorption behavior. We also assessed changes in P availability after soil was amended with the hydrochars. Our results showed that the chars were rich in total P (up to 25,175 mg kg), but most of the free fractions were transformed to bound fractions, thereby reducing the available P concentrations. However, available P content was >417 mg kg, which was far higher than soil demand. The hydrochars shifted from releasing to adsorbing P adsorbent when the environmental P concentration increased above 20 mg L. The hydrochars showed a high phosphate adsorption capacity (up to 23,815 mg kg) and the adsorbed P could be readily released. The addition of 1% P-laden hydrochar significantly enhanced the soil available P content by 8.93 mg kg. These findings have important implications for further development of hydrochar-based P carriers as a slow-releasing fertilizer.

Mechanism of uranium release from uranium mill tailings under long-term exposure to simulated acid rain: Geochemical evidence and environmental implication.

To date, there is not sufficient knowledge to fully understand the occurrence, transport and fate of residual uranium (U) from uranium mill tailings (UMT). Herein this study investigated different U release behaviors from natural UMT (without grinding) under four simulated acid rain (pH = 2.0-5.0) compared with controlled scenario (pH = 6.0) for 25 weeks. The results showed that the most notable U release was observed from UMTpH2.0, followed by UMTpH3.0 whereas a nonlinear relationship between pH and U release was observed from UMTpH4.0-6.0. The divergence of U release behaviors was attributed to the presence of minerals such as calcite and clinochlore. Autunite, a secondary mineral formed after leaching, might regulate U release in UMTpH3.0-6.0. Fick theory model revealed the shift of U release mechanism from surface dissolution to diffusion transport for UMTpH2.0, UMTpH3.0 and UMTpH5.0 at varied stage, whereas UMTpH4.0 and UMTpH6.0 displayed univocal dissolution and diffusion mechanism, respectively. This study highlights the necessity of performing long-term leaching tests to detect the "shift event" of leaching kinetics and to better understand the mechanism of U release influenced by mineralogy of the natural UMT under simulated acid rain conditions, which is conducive to developing UMT management strategies to minimize the risk of U release and exposure.

Provenance of uranium in a sediment core from a natural reservoir, South China: Application of Pb stable isotope analysis.

As part of ongoing environmental investigations of U mining impacts, forty-two sediment samples of a nearly-half-meter-long sediment core retrieved from a natural reservoir near an active uranium (U) mining site, South China were analyzed to quantify the extent of U release and identify U release mechanism within the riverine catchment. Enrichment levels of U was dispersed not only in the surface sediments but also in deep sediments across the depth profile. Further analysis by SEM-EDS and XRD indicated that U partitioning in the depth profile was possibly controlled by complicated interplay of leaching and precipitation cycles of U-bearing minerals. Even with the relative complexity of U dispersal processes within the catchment, the Pb isotopic fingerprinting techniques allowed quantification of source inputs of the sediments by using a binary mixing model. The results revealed that along the depth profile, only 6%-50% of the sediment material is anthropogenically derived from the U ore tailing, with the other predominant proportions originated from geogenically natural weathering of granitic bedrocks. This study highlights the use of Pb isotopes as a powerful tool for quantitatively fingerprinting the sources of U dispersal in the sediment core, and natural-occurring U contamination that may become a hidden geoenvironmental health hazard in this area.

Incorporation of Cadmium and Nickel into Ferrite Spinel Solid Solution: X-ray Diffraction and X-ray Absorption Fine Structure Analyses.

The feasibility of incorporating Cd and Ni in hematite was studied by investigating the interaction mechanism for the formation of CdxNi1-xFe2O4 solid solutions (CNFs) from CdO, NiO, and α-Fe2O3. X-ray diffraction results showed that the CNFs crystallized into spinel structures with increasing lattice parameters as the Cd content in the precursors was increased. Cd2+ ions were found to occupy the tetrahedral sites, as evidenced by Rietveld refinement and extended X-ray absorption fine structure analyses. The incorporation of Cd and Ni into ferrite spinel solid solution strongly relied on the processing parameters. The incorporation of Cd and Ni into the CNFs was greater at high x values (0.7 < x ≤ 1.0) than at low x values (0.0 ≤ x ≤ 0.7). A feasible treatment technique based on the investigated mechanism of CNF formation was developed, involving thermal treatment of waste sludge containing Cd and Ni. Both of these metals in the waste sludge were successfully incorporated into a ferrite spinel solid solution, and the concentrations of leached Cd and Ni from this solid solution were substantially reduced, stabilizing at low levels. This research offers a highly promising approach for treating the Cd and Ni content frequently encountered in electronic waste and its treatment residues.

Medical geology of arsenic, selenium and thallium in China.

Arsenic (As), selenium (Se) and thallium (Tl) are three trace metals (metalloids) of high concern in China because deficiency or excess expose can cause a range of endemic diseases, such as endemic arsenism, selenosis, Keshan disease (KD), Kashin-Beck disease (KBD) and thallotoxicosis. These specific endemic diseases were attributable for overabundance or deficiency (mainly referring to selenium) of these three elements in the local environment as a result of natural geochemical processes and/or anthropologic activities. The geochemistry and human health impacts of these three trace elements have been intensively studied since the 1970s in China, in terms of geochemical sources, distribution, transportation, health impact pathways, and prevention/remediation measures. Endemic arsenism in China are induced from the exposures of high As in either drinking water or domestic combustion of As-rich coals. Both endemic selenium deficiency and selenosis occurred in China. The KD and KBD were related to the deficiency of Se in the low-Se geological belt with Se contents in soil less than 0.125mg/kg stretching from northeast to southwest of China. Endemic selenosis occurred in areas with high Se concentrations in soils derived from the Se-enriched black carbonaceous siliceous rocks, carbonaceous shale and slate. Endemic Tl poisoning occurred in southwestern China due to Tl contamination in local drinking water and vegetables surrounding the Tl-rich sulfide mineralized areas. Some measures have been taken to control and remedy the endemic diseases with significant effects in reducing health risk and damage of As, Se and Tl. However, the states of the endemic diseases of As, Se and Tl in China are still serious in some areas, and substantial research efforts regarding the health impacts of these elements are further required. This paper reviews the progress of medical geology of As, Se and Tl in China, and provides with some outlooks for future research directions.