Uranium (U) source, speciation, uptake, toxicity and bioremediation strategies in soil-plant system: A review.

Phosphogypsum (PG) is a massive industrial solid waste. In this paper, PG was purified by flotation method, and α-hemihydrate gypsum (α-HH) was prepared by the autoclaving method. The morphology of α-HH was adjusted by adding different doses of Maleic acid and Aluminium sulfate. The results showed that after flotation purification, the impurity content in PG was significantly reduced, the soluble phosphorus content decreased from 0.48 to 0.07%, the PG purity increased from 73.12 to 94.37%, and the PG whiteness risen from 19.4 to 40.5. Then the performance of α-HH prepared from PG before and after purification was compared. Fixing the amount of aluminium sulfate at 0.2 wt%, the reaction temperature at 140 °C, and the reaction time at 120 min, the average length/diameter ratio of α-HH crystals decreased from 7.2 to 0.6 as the amount of Maleic acid increased from 0 to 0.17 wt%. When the amount of Maleic acid was 0.13 wt%, the α-hemihydrate gypsum reached the best mechanical properties. The mechanical strength of high strength gypsum prepared from PG concentrate was significantly better than that of raw PG, indicating that flotation purification can effectively improve the performance of PG. In this study, a new method of PG purification and resource utilization was proposed. 

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The study on the effect of flotation purification on the performance of α-hemihydrate gypsum prepared from phosphogypsum

After nearly 20 years of exploration, various areas of the seafloor with hydrocarbon seepage have been discovered in the South China Sea (SCS). Through linking subsurface and seafloor biospheres, seeps have become natural laboratories to enhance our knowledge on the processes of hydrocarbon migration and associated hydrocarbon-based ecosystems in the marine environment. This review summarizes the distribution of macrofauna in the active seep areas of the SCS and describes the physiological characteristics of three groups of representative macrofauna (bathymodioline mussels, pliocardiine clams, siboglinid tubeworms). In addition, a comparison is made between the seep macrofauna of the SCS and the Northwest Pacific Ocean. Modes of energy transfer and microbial processes are elucidated by integrating trace element, stable isotope, and lipid biomarker data of macrofaunal soft tissues. Our aims are to provide an overview of the macro-ecology of the SCS seeps and to underscore aspects which desire more research efforts in the future. 

Macro-ecology of cold seeps in the South China Sea

The effect of humus on the remediation of arsenic (As)-contaminated soil by electrokinetic technology was investigated in this study. The results showed electromigration regulated the spread of As in soil and the addition of humus significantly promoted the release of As from the soil during electrokinetic remediation (EKR). The remediation efficiency was obviously enhanced by 20% when the added amount of humus was 4g. The removal efficiency was also improved with the increase of running time. The results of functional group analysis of humus indicated the presence of several oxygen-containing functional groups, which desorbed As from the soil particles under both acidic and base conditions. When the pH was 10, approximately 11.63% of bonded As was desorbed as free As, which was in favor of EKR. The main result of this work suggests that humus can be used as a green agent to improve the EKR technology.

Effect of humus on the remediation of arsenic-contaminated soil by electrokinetic technology

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The macrofaunal community in the Haima cold seeps of the South China Sea was investigated, and trophic relationships were evaluated using carbon and nitrogen stable isotope signatures (δ13C and δ15N). A total of 30 macrofaunal species were identified in this study, most of which were collected from the Gigantidas haimaensis mussel beds. Only four macrofaunal species were collected from the Calyptogena marissinica clam beds, where the environment may not be suitable for the survival of most macrofauna. The bush of slim tubeworms (Sclerolinum sp.) might be an important nursery ground for mussels. G. haimaensis was the predominant species, and its average δ13C and δ15N values were −52.7‰ and 0.6‰, respectively. Compared with the stable isotope signatures of particulate organic matter (POM), it suggested that the food source of macrofauna in the Haima cold seeps was mainly originated from chemosynthetic autotrophs. In the mussel bed, most of the macrofauna had a large δ13C isotopic distance compared with G. haimaensis, suggesting that G. haimaensis was not a direct food source for most cold-seep macrofauna in the mussel bed. The variation in stable isotope signatures of macrofauna might be attributed to different proportions of methanotrophic and thiotrophic endosymbionts. Neolithodes brodiei and Bathynomus jamesi showed the highest δ13C and δ15N values. However, the large isotopic distance indicated that N. brodiei and B. jamesi might just occasionally visit the cold-seep ecosystem and their food sources were mainly from the upper ecosystem relying on photosynthesis. Overall, our results suggested that there was no significant predator-prey relationship among these macrofaunal species in the Haima cold seeps. This study provided important baseline data of stable isotope signatures for further studies to elucidate the trophic interaction among seep organisms. 

A preliminary study of macrofaunal communities and their carbon and nitrogen stable isotopes in the Haima cold seeps, South China Sea

Heavy metal pollution by both uranium and arsenic has become a major environmental problem associated with uranium mining worldwide. At present, physical, chemical and biological technologies are available as the main remediation techniques. Among them, phytoremediation is relatively low cost, hinders more pollution and allows for fast recycling of the uranium as compared to other techniques. However, suitable phytoremediation depends critically on the better choice of plant species. In this study, field sampling of soils and plants surrounding a uranium mine was conducted, and atomic emission spectrometry of samples performed, in order to characterize the distribution of heavy metal pollution and to provide a scientific basis for the phytoremediation of uranium mining sites. Soil uranium concentrations were found to be highest in open-pit mine sites, followed by ore dressing investigation sites and also the river confluence sites. Uranium did not migrate from active mining areas and the highest uranium concentration measured 232.70 mg×kg-1. In contrast, arsenic regularly migrated downstream, with soil concentrations averaging 47.26 mg×kg-1, two times the limit set by the Three Grade Standard of Soil Quality in China (GB 15618-1995). Rumex nepalensis accumulated high levels of uranium, with a bioconcentration factor of 3.60 and a transfer factor of 3.61. Polygonum viviparum was able to accumulate arsenic, with a root transfer factor of 3.69, and also uranium as indicated by a bioconcentration factor greater than one. Thus, our investigations improved the understanding of the potential role of Polygonum viviparum and Rumex nepalensis involved in phytoremediation of uranium or uranium-arsenic pollution.

http://www.pjoes.com/pdf-103446-43013?filename=Characterization of.pdf

Characterization of Arsenic and Uranium PollutionSurrounding a Uranium Mine in SouthwesternChina and Phytoremediation Potential

Crystal modifier is a significant factor in preparation of α-hemihydrate gypsum (α-HH) from phosphogypsum (PG). The influence of maleic acid, reaction temperature, time, and solid–liquid ratio on the preparation of high-strength α-HH from PG was systematically studied herein. The optimum condition for α-HH prepared by hydrothermal autoclave method was pH of 4, temperature of 140 °C for 2.0 h with solid–liquid ratio of 4:5. Crystal modifier of maleic acid can effectively regulated the crystal morphology of α-HH. SEM–EDS and FTIR analysis suggested that maleic acid could preferentially absorbed on the top face of α-HH crystals that decreased the growth rate of α-HH along the c-axis, resulting in the morphology of α-HH crystals transformed to hexagonal prisms, and the regulatory mechanism was estimated by molecular dynamics (MD). When maleic acid (0.1%) was added, the obtained α-HH showed aspect ratio of 1.2, and the flexural and compressive strength of the hardened α-HH could reach to 14.79 and 46.24 MPa, respectively. All of these results will help to design long-term effectiveness of phosphogypsum recycling strategies.

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Facile preparation of high-strength α-CaSO4·0.5H2O regulated by maleic acid from phosphogypsum: experimental and molecular dynamics simulation studies

The spatial and seasonal distributions of stable carbon and nitrogen isotopes (δ13C and δ15N) in dominant zooplankton groups were investigated in Jiaozhou Bay. Zooplankton δ13C values ranged from −22.89‰ to −15.86‰, and δ15N values ranged from 3.18‰ to 13.57‰, respectively. The δ13C and δ15N values generally followed the order of small zooplankton < large calanoids < small Sagitta < large Sagitta. Spatial distribution patterns of zooplankton δ13C and δ15N values varied in different seasons. Our results suggested that the spatial variation of δ13C was mainly controlled by terrigenous organic matter (OM) input and phytoplankton biomass, but water temperature may have played a key role in the seasonal variation of δ13C. In spring, the high phytoplankton biomass might increase the δ13C value of small zooplankton in the inner bay. During other seasons, the δ13C values of zooplankton generally increased from the inner bay to the outer bay, which might be associated with the influence of 13C-depleted terrigenous OM carried by the river discharge. Small zooplankton stable isotope values were significantly correlated with that of particulate organic matter (POM). The influence of anthropogenic nutrient input on isotopic baseline can be cascaded to the zooplankton, and the effect might be weak at higher trophic levels. The Bayesian standard ellipse areas of dominant zooplankton groups were generally smallest in the winter, suggesting a narrow niche width during that time. The niche partition between small zooplankton, large calanoids, and Sagitta was most distinct in winter, and followed by summer. The relative trophic level of Sagitta ranged from 2.23 to 4.01, which generally declined from the inner bay to the outer bay during the spring, autumn, and winter seasons. High anthropogenic nutrient loading might reduce the difference in trophic niches among zooplankton groups. This study provided detailed information on the distribution of zooplankton δ13C and δ15N in a coastal bay, which will be useful for understanding the anthropogenic influence on the ecosystem structure and function.

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Ruofei Li

Papers

A preliminary study of macrofaunal communities and their carbon and nitrogen stable isotopes in the Haima cold seeps, South China Sea

Characterization of Arsenic and Uranium PollutionSurrounding a Uranium Mine in SouthwesternChina and Phytoremediation Potential

Facile preparation of high-strength α-CaSO4·0.5H2O regulated by maleic acid from phosphogypsum: experimental and molecular dynamics simulation studies

Spatial and Seasonal Variations in the Stable Isotope Values and Trophic Positions of Dominant Zooplankton Groups in Jiaozhou Bay, China

Spatial distributions of zooplankton stable isotopes and their trophic positions in a bay under serious anthropogenic influences: Daya Bay, China