| 1. |
- Forslund, Anna-Lena, 1964-, et al.
(författare)
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Direct repeat-mediated deletion of a type IV pilin gene results in major virulence attenuation of Francisella tularensis
- 2006
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Ingår i: Molecular Microbiology. - : Wiley-Blackwell. - 0950-382X .- 1365-2958. ; 59:6, s. 1818-1830
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Tidskriftsartikel (refereegranskat)abstract
- Francisella tularensis, the causative agent of tularaemia, is a highly infectious and virulent intracellular pathogen. There are two main human pathogenic subspecies, Francisella tularensis ssp. tularensis (type A), and Francisella tularensis ssp. holarctica (type B). So far, knowledge regarding key virulence determinants is limited but it is clear that intracellular survival and multiplication is one major virulence strategy of Francisella. In addition, genome sequencing has revealed the presence of genes encoding type IV pili (Tfp). One genomic region encoding three proteins with signatures typical for type IV pilins contained two 120 bp direct repeats. Here we establish that repeat-mediated loss of one of the putative pilin genes in a type B strain results in severe virulence attenuation in mice infected by subcutaneous route. Complementation of the mutant by introduction of the pilin gene in cis resulted in complete restoration of virulence. The level of attenuation was similar to that of the live vaccine strain and this strain was also found to lack the pilin gene as result of a similar deletion event mediated by the direct repeats. Presence of the pilin had no major effect on the ability to interact, survive and multiply inside macrophage-like cell lines. Importantly, the pilin-negative strain was impaired in its ability to spread from the initial site of infection to the spleen. Our findings indicate that this putative pilin is critical for Francisella infections that occur via peripheral routes.
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| 2. |
- Abdel-Magied, Ahmed Fawzy, et al.
(författare)
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Hierarchical porous zeolitic imidazolate framework nanoparticles for efficient adsorption of rare-earth elements
- 2019
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 278, s. 175-184
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchical porous zeolitic imidazolate frameworks nanoparticles (ZIF-8 NPs) were synthesized at room temperature via a template-free approach under dynamic conditions (stirring) using water as a solvent. The ZIF-8 NPs were evaluated as adsorbents for rare earth elements (La3+, Sm3+ and Dy3+). Adsorption equilibrium was reached after 7h and high adsorption capacities were obtained for dysprosium and samarium (430.4 and 281.1 mg g(-1), respectively) and moderate adsorption capacity for lanthanum (28.8 mg g(-1)) at a pH of 7.0. The high adsorption capacitiese, as well as the high stability of ZIF-8 NPs, make the hierarchical ZIF-8 materials as an efficient adsorbent for the recovery of La3+, Sm3+ and Dy3+ from aqueous solution.
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| 5. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
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Isolation of rare earth element phosphate precipitate in the nitrophosphate process for manufacturing of fertilizer
- 2016
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Ingår i: IMPC 2016 - 28th International Mineral Processing Congress. - : Canadian Institute of Mining, Metallurgy and Petroleum. - 9781926872292
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Konferensbidrag (refereegranskat)abstract
- In the present study, the recovery of rare earth elements (REE) in the nitrophosphate process of fertilizer production is investigated. The apatite has been recovered from iron ore tailings by flotation. After digestion of apatite in concentrated nitric acid, Ca(NO3)2.4H2O is first separated by cooling crystallization and then the REEs are recovered by precipitation. Optimum conditions in these steps have been determined in a previous study. The precipitate mainly consists of CaHPO4.2H2O and REE phosphates. In the present study, selective dissolution and re-precipitation have been studied in order to obtain a precipitate that is more concentrated in REEs. The precipitate was selectively dissolved in nitric and phosphoric acid at different acidities (pH 6 to 0) with the liquid /solid ratio of 100 mL/g. It is shown that most of the CaHPO4.2H2O and other calcium containing compounds will be dissolved at pH 2 while the REE phosphates are not dissolved above a pH of approximately 2. Thus, by partial dissolution of the REE precipitate at pH 2.5 most of the solid calcium phosphates will be dissolved and the remaining solid phase, which is more concentrated in REEs, can be filtered off as a fairly concentrated REE solid mass and the liquor can be recycled back to recover more P nutrients. Alternatively, the REE enriched precipitate was dissolved completely in nitric acid and re-precipitated again by addition of ammonium hydroxide to pH 1.2. A chemical equilibrium software, MEDUSA (Puigdomenech, 2013) has been used to evaluate the experimental results and to estimate the optimum conditions for selectively dissolving the precipitate.
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| 6. |
- Alemrajabi, Mahmood, 1989-, et al.
(författare)
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Processing of a rare earth phosphate concentrate obtained in the nitrophosphate process of fertilizer production
- 2019
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Ingår i: Hydrometallurgy. - : Elsevier. - 0304-386X .- 1879-1158. ; 189
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Tidskriftsartikel (refereegranskat)abstract
- In this study, different processes have been developed and applied to treat a rare earth phosphate concentrate obtained within the nitrophosphate process of fertilizer production. Methods to remove impurities such as Fe and Ca have been investigated as well as to separate the phosphorous and thereby facilitate dissolution of the rare earth elements (REE). These methods include thermal treatment with sodium hydroxide and sodium double sulphate precipitation with and without alkaline conversion, followed by selective dissolution in different acids. The proposed processes were compared and analyzed from the perspective of introducing an appropriate intermediate product for further individual REE separation. The results have shown that after thermal treatment with NaOH at 400 °C, the phosphorous can be removed from the rare earth phosphate concentrate by water leaching. Investigation of different REE phosphate concentrates demonstrated that mixed Ca and REE phases, e.g. REEmCan(PO4)3m+2n/3 and CaHPO4 are less likely to dephosphorize than REE(PO4).nH2O and FePO4.H2O under these conditions. The recovery of REE to a mild acidic solution is limited by the presence of remaining phosphate ions and by the formation of REE oxide phases during the thermal treatment. The results also show that a solution containing 40 g/L REE; free of phosphorous, calcium and iron can be obtained after reprecipitation of the rare earth phosphate concentrate as sodium rare earth double sulphates followed by alkaline conversion with sodium hydroxide and dissolution in nitric acid.
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| 9. |
- Alemrajabi, Mahmood, 1989-
(författare)
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Recovery of Rare Earth Elements from an Apatite Concentrate
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rare earth elements (REE) are a group of 17 elements including lanthanides, yttrium and scandium; which are found in a variety of classes of minerals worldwide. The criticality of the application, lack of high grade and economically feasible REE resources and a monopolistic supply situation has raised significant attention in recovery of these metals from low grade ores and waste materials. In this thesis, the recovery of REE from an apatite concentrate, containing 0.5 mass% of REE, within the nitrophosphate route of fertilizer production has been investigated. Most of the REE (≥ 95%) content can be recovered into a phosphate precipitate with almost 30 mass% REE. Different processes have been developed to convert the REE phosphate precipitate into a more soluble form to obtain a solution suitable for further REE purification and individual separation. It has been shown that after reprecipitation of the REE phosphate concentrate as REE sodium double sulphate and then transformation into a REE hydroxide concentrate, a solution containing 45g/L REE free of Ca, Fe and P can be obtained. The results suggest that the apatite waste after processing of iron ore have the potential to be a very important source for REE in Europe and that the economy is strongly supported by the simultaneous extraction of phosphorous.The potential of using hollow fiber supported liquid membrane (HFSLM) extraction in individual and group separation of REE has been investigated. A hollow fiber supported liquid membrane plant in pilot scale has been operated according to the three main configurations: standard hollow fiber supported liquid membrane technology (HFSLM); hollow fiber renewal liquid membrane technology (HFRSLM) and emulsion pertraction technology (EPT). The standard HFSLM operation is more selective than HFRSLM and EPT, while higher metal transport rate is observed in EPT followed by HFRSLM and HFSLM. The HFRLM configuration helps to maintain the performance of the liquid membrane.
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| 10. |
- Alemrajabi, Mahmood, et al.
(författare)
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Recovery of rare earth elements from nitrophosphoric acid solutions
- 2017
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Ingår i: Hydrometallurgy. - : Elsevier. - 0304-386X .- 1879-1158. ; 169, s. 253-262
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, the recovery of rare earth elements (REEs) from an apatite concentrate in the nitrophosphate process of fertilizer production has been studied. The apatite concentrate has been recovered from iron ore tailings in Sweden by flotation. In the first step, the apatite is digested in concentrated nitric acid, after which Ca(NO3)2.4H2O is separated by cooling crystallization. The solution is then neutralized using ammonia whereby the REEs precipitate mainly as phosphates (REEPO4.nH2O) and together with calcium as REEn Cam (PO4)(3n + 2m) / 3. In this work, the degree of rare earth coprecipitation during seeded cooling crystallization of Ca(NO3)2.4H2O has been studied. The solubility of calcium nitrate tetrahydrate (Ca(NO3)2.4H2O) in acidic nitrophosphoric acid solutions in the temperature range of − 2 °C to 20 °C has been determined. For the neutralization step, it is shown that the calcium concentration and the final pH play an important role in determining the concentration of REEs in the precipitate. It is found that reaching maximum recovery of REE with minimum simultaneous precipitation of calcium requires careful control of the final pH to about 1.8. It is further observed that the precipitation yield of REEs and iron is favored by a longer residence time and higher temperature. Finally, the effect of seeding with synthesized REE phosphate crystals as well as a mixture of REE and Ca phosphates on the precipitation rate and the composition of the precipitate was studied.
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