p. tajer mohammad ghazvini

Environmental hazards of wastewater containing metals, including lead, have attracted researchers' attention on their cleanup using novel methods such as bioremediation. In the present study, the biosorption ability of lead by Bacillus sp. Strain STG-83 was evaluated. Response surface methodology with central composite design by the Design Expert software was used to optimize parameters such as pH, biomass concentration, and initial lead concentration. The results showed that the quadratic model proposed by Design Expert software with a correlation coefficient of R2=0.9938 predicted the process behavior properly; lead biosorption by the bacteria was optimized at pH=4.5, initial concentration of lead 297.95 mg. L-1, and the amount of adsorbent 1 g.L-1, which is equal to 149.595 mg. g-1 dry weight. Also, the experimental data were fitted with Langmuir and Freundlich isotherms. The results showed that the Langmuir model is more suitable with R2=0.961. Kinetic studies showed that adsorption capacity reached its maximum value within 5 minutes. Ultimately, due to the valuable potential of this bacterium in rapid and high biosorption of lead, Bacillus sp. strain STG-83 is introduced as a valuable bacterial sorbent for lead bioremediation processes and performance of response surface methodology in modeling and optimizing lead biosorption process by Bacillus sp. strain STG-83 is confirmed.

Molybdenum metal with atomic number 42 belongs to the sixth group of the periodic table of elements. This element has many usages in various industries. The most important molybdenum mineral is molybdenite (MoS2 ). Different leaching methods are used for the extraction of molybdenum. One of the methods is bioleaching, which requires a high potential for extraction of molybdenum, in addition to applying other special leaching conditions. In this study, in order to use a bioleaching method for extraction of molybdenum from its mineral, the native thermophilic archaebacteria of Sulfolobus solfataricus and Acidianus ambivalens were isolated from the Narigan mine and registered on the NCBI site, also they were gradually adapted for resistance against to the high potential. The result of the adaptation was positive and archaebacteria were able to resist potentials higher than 1000 mV and had a good growth and proliferation rate. In the following, these archaebacteria have been used for the bioleaching of the Narigan ore for the extraction of molybdenum. Because molybdenum recovery has a strong dependency on the redox potential, recovery was increased to 80%. By increasing the potential from 400 mV to 1000 mV. While the molybdenum recovery was 43% by non-adapted bacteria against high potential.

One of the most important application of rhenium is its use in nuclear medicine.The recovery of rhenium via biosorption by micro-organisms, in contrast to other methods, has not been investigated yet. In the present study the biosorption of rhenium on Bacillus sp. MGG-83 in a batch of stirred system is reported, and its optimum condition has been determined. The optimum pH-value of the medium was found to be 2 for rhenium. The maximum biosorption of rhenium was obtained at a temperature between 35–40 0C. The rhenium take up increases by increasing the rhenium concentration, and for 250 mg/l the take up was 146.3 mg/g dry wt. The uptake of rhenium within 5 min of incubation is relatively rapid and the continuation of absorption behaves slowly thereafter. The reduction in the V/X0value causes an increase of the adsorbed rhenium and that is due to the increase of the adsorption surface area. The desorption of rhenium which has been carried out with 0.1 M sodium hydroxide at 25 0C was 55%.