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Abstract Summary and Conclusion Rare earth elements are collection of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides plus scandium and yttrium. REEs are widely used in industry, agriculture, and medicine. REEs can enter the food chain, resulting in their intake by human. Thus, it has become increasingly important to know the behavior of these elements in the environment. The present study is stressed on samples from Magharet El Meyiah Formation of early Carboniferous age in southwestern Sinai. A total of (16) representative samples were collected to represent the lithologic variations from north (Budaa), middle (El Gor) and south (G. Farsh El Azraq) localities. This work aims to study the effects of fungal biomass on the solubilization of REEs, selective leaching and precipitation of some of trace elements, the effect of the REEs on the physical and chemical properties of the bio-cell walls and attempt to visualize if there is contribution of the isolated biomass on the concentration of the REEs in the study samples. To study the bioleaching of REEs from the collected rock samples in different localities, it is very important to identify and discuss the results and distributions of major, trace, rare earth and radioactive elements. Chemical analyses of the three carbonaceous shale samples from Budaa, El Gor and G. Farsh EL Azraq localities showed high content of SiO2 which represented by (av.= 51.1%, 66.3% and 62%) respectively , and moderate content of Al2O3 were recorded as (av. = 13.9%, 14.5% and 15.1%) respectively. The well noticed thing is the high loss on ignition for samples of the studied localities. The highest loss on ignition (61.1%) was recorded in Budaa (sample B.8). This high loss on ignition was found to affect on the process of bioleaching of the REEs as will be seen later. All the studied samples are generally depleted in their Pb and Ga contents and have moderate contents of (Ni, Cu, Zn, Rb, Y, Sr, V and Nb) which are lower than 100 ppm and high values of Zr content in El Gor, G. Farsh EL Azraq and Budaa localities (av. = 938, 921 and 560 ppm) respectively are attributed to the presence of zircon mineral. All studied samples of the examined localities are characterized by very high values of Ba content. The average values of this element are 2454, 2121 and 2604 ppm in the studied Budaa, El Gor and G. Farsh EL Azraq localities respectively. The whole studied samples are generally similar in their Cr and Rb contents. Carbonaceous shales show REEs content ranging between 200 ppm and 581 ppm with an average 366 ppm. The average of activity concentrations of 238U, 226Ra, 232Th radionuclides in the three localities are higher than that reported in UNSCEAR (2000) but have lower 40K contents. The 238U/235U ratios are nearly within the natural ratio (21.7) for investigated samples from the three localities. The 238U/226Ra and 238U/232Th ratios indicate U-migration-in these sedimentary rocks. Eight fungal genera were isolated from the studied samples. The most dominant were Aspergillus and Penicillium. The Aspergillus (A.) was identified as A. niger, A. flavus, A. terreus and A. ficuum whereas, Penicillium (P.) was P. aeruginosa, P. oxalicum, P. cyclopium and P. diversum. All of the tested fungi could grow in the presence of 1% ore concentration of the studied Budaa locality samples (B.4, B.8 and B.3). It was found that direct bioleaching process of REEs from the tested samples was more effective than indirect process for all tested microorganisms. The bioleaching percentages of REEs from the tested samples by Aspergillus sp. were more than Penicilium sp. whereas; A. niger was the superior followed by A. flavus. The obtained results showed that as the concentrations of REEs in the original samples decrease the bioleaching efficiency in the whole fungi increase. The reverse case was in the growth of fungus which increases with the increase of REEs concentrations except in A. terreus and P. oxalicum. The growth of Penicillium sp. in the presence of carbonaceous shale samples was higher than A. niger followed by A. flavus. The best leaching efficiency of REEs was occurred only when the final pH of the media became more acidic which reached to 4.24 for A. niger and 4.64 for A. flavus. Aspergillus niger and Aspergillus flavus were selected to study the factors affecting the bioleaching efficiency of REEs from the studied sample B.3, B.4 and B.8 from Budaa locality. The maximum leaching of REEs was obtained using 1% sample concentration by A. niger and followed by A. flavus reached to 86% and 60% respectively from the studied sample B.3. The bioleaching efficiency was observed to decrease by increasing the sample concentration in the growth medium. An important note was that at 1%, 5% and 7% ore concentrations and high REEs content for sample (B.4), the bioleaching efficiency of A. flavus was higher than that of A. niger. This means that A. flavus can work under stress of REEs content than A. niger. The maximum bioleaching efficiency of REEs using A. niger and A. flavus was obtained at 7 days of incubation and rapidly decreased after these days. The behavior deviated something from this result especially with A. flavus in the samples (B.8) with high carbon content which plays essential role in the leaching efficiency. A very important notice is that the A. niger did not affected by the high content of carbon in this sample, while A. flavus was affected as noticed after sample roasting at 1000 oC. The best leaching efficiency of REEs from ore samples by A niger and A. flavus was occurred at 30 oC. It was noticed that at lower temperature (20°C) or higher temperature (40°C and 45°C) the fungal bioleaching was highly decreased. The bioleaching efficiency was highly affected by initial pH of growth medium. However, the bioleaching of REEs was optimum at pH value 4. Optimum conditions of REEs bioleaching by A. niger and A. flavus on Budaa sample (B.3), reached 86% and 73%, respectively, were found at (1%) ore concentration, (7 days) incubation period, (30 °C) temperature and pH (4). The resulted optimum conditions for REEs solubilization by A. niger and A. flavus were applied on samples from the other studied locations having different REEs concentrations. The best bioleaching efficiency (91%) of REEs is found in El Gor sample (G.1) which has the lowest content of REEs concentrations. By using HPLC, the concentration of oxalic, citric and formic acids in the fermented liquor by A. niger were 1.068, 12.876 and 8.887 mg/ml, respectively whereas being oxalic (3.054) and citric (8.456) mg/ml for A. flavus. from the previous results it can be deduced that the citric and oxalic acids contents produced by A. niger was higher than that produced by A. flavus often at 7 days incubation period. This explains the higher REEs bioleaching efficiency of A. niger than A. flavus. With pulp density 1%, citric and oxalic acid concentrations increased to 21.844 and 28.967 mg/ml for A. niger and 6.688 and 23.683 mg/ml for A. flavus, while with increasing pulp density to 7%, the citric and oxalic acid concentrations decreased to 16.379 and 2.077 mg/ml for A. niger and 3.767 and 16.818 mg/ml for A. flavus. For REEs recovery, the oxalic acid was used for precipitation then the precipitate was analyzed by ESEMEDAX analysis. It is clearly evident that the total REEs concentrate includes La, Ce and Nd assays and 9.29, 39.06 and 16.58 %, respectively, while Pr and Sm assay 6.18 and 5.49 %, respectively. The product from bioleaching process of REEs by A. niger indicate selective nature of the fungi where the dissoluted and precipitated elements represent only the LREEs except Eu which is very low in the original sample. The XRD pattern of the precipitated REEs showed the presence of the chemical compound sodium neodymium carbonate hydrate NaNd(CO3)26H2O associating with other compound named Vanadyl phosphate ethanol (C4H12O2VOPO4). The last compound considered as an evidence for the reactions between fungi media and original sample. Vanadium is coming from the original sample which has 201 ppm. To optimize the relevant biosorption factors during bioleaching process by A. niger and A. flavus for the studied sample B.3. The highest biosorption efficiency of REEs obtained from 5% ore concentration of Budaa (B.3 sample) by A. flavus followed by A. niger reached to 21 and 18% respectively. A well noticed point is that the efficiency of A. flavus is higher than that of A. niger. This means that A. flavus can work under stress of REEs content than A. niger. The final pHs were increased with increasing concentrations in the growth media. Biosorption of REEs by both tested fungi was highly affected by contact time. The results showed the rapid increase of biosorption efficiency of REEs with time. However, best accumulation of REEs occurred at nine days of incubation for A. flavus and A. niger reached to 24 and 20% respectively. The biosorption of REEs by fungal biomass was slightly affected by different temperature from 37-45 oC, but lowest biosorption of REEs was occurred at 20 oC 12 and 9% respectively, while at 40 oC biosorption was reached to the highest value. At this temperature, A. niger biosorbed 20% from the total amount of REEs found in B.3 sample. On the other hand, A. flavus biosorbed 24% from the total amount of REEs found in B.3 sample. After 40 oC the amounts of REEs accumulation decreased. The pH seems to be the most important parameter in the biosorption process. The maximum REEs uptake wa observed at initial pH 7 for dry biomass of A. niger and A. flavus 20 and 24% respectively. The important morphological changes of A. niger were investigated by using microscopic examination which showed that the vesicle diameter of A. niger was decreased with increasing ore concentration in the growth media. Also, the primary stigmata appeared shorter than the control, whereas the secondary stigmata were found to disappear with increasing ore concentration. The conidial heads reduced in size and carrying little number of conidia which appear thicker than control in 1% and 7% ore concentration. Transmission electron microscope (TEM) analysis of A. niger grown on Dox agar media contains (0, 3, 5 and 9 %) ore concentration of B.3 showed that elements were accumulated and precipitated around cell wall and therefore it formed a black dense area around it. This dense area was increased with increasing ore concentration in the growth media. The thickness of cell walls was markedly increased at 5% ore concentration when compared to control. At 9 % ore concentration cell wall start to hydrolysis and cell large vacuole was formed due to metal ions entrance at (3% - 9%) ore concentration. The adsorption efficiency for different elements at 3% ore concentration can be arranged in descending order as follow Al ˃ Fe ˃ Si ˃ Ca ˃ Mn ˃ P ˃ U ˃ Co ˃ Cu ˃ S ˃ Ce ˃ K ˃ Ni ˃ Cl ˃ Zn whereas at 7% the adsorption efficiency arranged as follow Mn ˃ Fe ˃ K ˃ Co ˃ Ce ˃ P ˃ Ni ˃ Si ˃ Al ˃ Zn ˃ Na ˃ Ca ˃ Cu ˃ U. The adsorption efficiency for different elements at 3% ore concentration by A. flavus can be arranged in descending order as follow Fe ˃ Al ˃ Si ˃ Mn ˃ Na ˃ Zn ˃ Co ˃ Ni ˃ K ˃ U ˃ P ˃ Ca ˃ Ce ˃ Cu whereas at 7% the adsorption efficiency could be arranged as follow Fe ˃ Mn ˃ Al ˃ Ce ˃ Si ˃ P ˃ Zn ˃ K ˃ Co ˃ Nb ˃ Ca ˃ Ni ˃ S ˃ U ˃ Cu ˃ Cl. The main achieved goal in this work is the selectivity of Ce from REEs being in both fungal, whereas A. niger and A. flavus in 7% ore concentration adsorbed 6.84% and 7.01% of Ce, respectively. 5.2 Conclusion 1- Bioleaching and biosorption are two processes occur together at the same time with different optimum conditions. CHAPTER 5 Summary and Conclusion 203 2- The variation in the amount of leachability of REEs was depending on geochemical features and concentration of REEs in the ore. 3- The high loss on ignition is negatively affecting on the process of bioleaching of the REEs. 4- Acidolassies is the principal mechanism in the bioleaching of metals by microorganisms which produced organic acids such as citric and oxalic. 5- Some elements were leached from tested ore and affect on the soluble of REEs due to the toxic effect on the activate microorganisms. 6- The product from bioleaching process of REEs by A. niger indicate selective nature of the fungi where the dissoluted and precipitated elements represent only the LREEs. 7- Biosorption on the external cell surface is biomass defense system against toxic metals with producing an external polymeric layer to avoid metal penetration through the cell wall and still a life. 8- The Biosorption process of REEs by A. niger and A. flavus indicate selective nature of Ce from REEs being in both fungus. |