Biosorption of uranium and thorium

Selected samples of waste microbial biomass originating from various industrial fermentation processes and biological treatment plants have been screened for biosorbent properties in conjunction with uranium and thorium in aqueous solutions. Biosorption isotherms have been used for the evaluation of biosorptive uptake capacity of the biomass which was also compared to an activated carbon and the ion exchange resin currently used in uranium production processes. Determined uranium and thorium biosorption isotherms were independent of the initial U or Th solution concentration. Solution pH affected the exhibited uptake. In general, lower biosorptive uptake was exhibited at pH 2 than at pH 4. No discernible difference in uptake was observed between pH 4 and pH 5 where the optimum pH for biosorption lies. The biomass of Rhizopus arrhizus at pH 4 exhibited the highest uranium and thorium biosorptive uptake capacity (g) in excess of 180 mg/g. At an equilibrium uranium concentration of 30 mg/liter, R. arrhizus removed approximately 2.5 and 3.3 times more uranium than the ion exchange resin and activated carbon, respectively. Under the same conditions, R. arrhizus removed 20 times more thorium than the ion exchange resin and 2.3 times more than the activated carbon. R. arrhizus also exhibited higher uptake and a generally more favorable isotherm for both uranium and thorium than all other biomass types examined.     

Biosorption of uranium by magnetically modified Rhodotorula glutinis

Adsorption of uranium from aqueous solution onto the magnetically modified yeast cell, Rhodotorula glutinis, was investigated in a batch system. Factors influencing sorption such as initial solution pH, biomass dosage, contact time, temperature, initial uranium concentration and other common cations were analyzed. Sorption isotherm, kinetic and thermodynamic studies of uranium on magnetically modified R. glutinis were also carried out. The temperature dependent equilibrium data agreed well with the Langmuir model. Kinetic data obtained at different temperatures were simulated using pseudo-first-order and pseudo-second-order kinetic models, the pseudo-second-order kinetic model was found to describe the data better with correlation coefficients near 1.0. The thermodynamic parameters, ΔH°, ΔS° and ΔG° were calculated from the sorption data gained at different temperatures. These thermodynamic parameters showed that the sorption process was endothermic and spontaneous. All results indicated that magnetically modified R. glutinis can be a potential sorbent for uranium wastewater treatment.     

Biosorption of uranium by Myxococcus xanthus

This paper deals with uranium biosorption by Myxococcus xanthus biomass in which dry biomass, accumulating up to 2.4 mM of uranium g⁻¹, is demonstrated to be a more efficient biosorbent than wet biomass. For uranium concentrations of 0.1–0.3 mM, between 95.79% and 95.99% of the uranium was taken up from the solution. Dry biomass biosorption was found to be relatively rapid, reaching equilibrium after 5–10 min. In addition, the pH influenced biosorption, pH 4.5 promoting maximum uptake. It was also established that the biosorbed uranium is located on the cellular wall and within the extracellular mucopolysaccharide of this microorganism. Furthermore, using sodium carbonate as a desorbent agent, 80.82% of the biosorbed uranium could be recovered. The results obtained indicate the possible utilization of M. xanthus biomass to solve some problems of the water contaminated by uranium.     

Biosorption of uranium(VI) by Aspergillus fumigatus

Aspergillus fumigatus removed uranium(VI) very rapidly and reached equilibrium within 1 h of contact of biomass with the aqueous metal solution. Biosorption data fitted to Langmuir model of isotherm and a maximum loading capacity of 423 mg U g^–1 dry wt was obtained. Distribution coefficient as high as 10,000 (mg U g^–1)/(mg U ml^–1) at a residual metal ion concentration of 19 mg l^–1 indicates its usefulness in removal of uranium(VI) from dilute waste streams. Optimum biosorption was seen at pH 5.0 and was independent of temperature (5–50°C ). Initial metal ion concentration significantly influenced uptake capacity which brought down % (w/w) uranium(VI) removal from 90 at 200 mg U l^–1 to 35 at 1000 mg U l^–1. Presence of 0.84 mmol Fe²⁺, Fe³⁺, Ca²⁺ and Zn²⁺ had no effect on uranium(VI) biosorption unlike Al³⁺ (0.84 mM) which was inhibitory.     

Biosorption of lead and nickel by biomass of marine algae

Screening tests of different marine algae biomas types revealed a high passive biosorptive uptake of lead up to 270 mg Pb/g of biomass in some brown marine algae. Members of the order Fucales perfomed particularly well in this descending sequence: Fucus > Ascophyllum > Sargassum. Although decreasing the swelling of wetted biomass particles, their reinforcement by crosslinking may significantly affect the biosorption performance. Lead uptakes up to 370 mg Pb/g were observed in crosslinked Fucus vesiculosus and Ascophyllum nodosum. At low equilibrium residual concentrations of lead in solution, however, ion exchange resin Amberlite IR-120 had a higher lead uptake than the biosorbent materials. An order-of-magnitude lower uptake of nickel was observed in all of the sorbent materials examined. (c) 1994 John Wiley & Sons, Inc.     

Biosorption of uranium by lake-harvested biomass from a cyanobacterium bloom

The aim of this work was to study some basic aspects of uranium biosorption by powdered biomass of lake-harvested cyanobacterium water-bloom, which consisted predominantly of Microcystis aeruginosa. The optimum pH for uranium biosorption was between 4.0 and 8.0. The batch sorption reached the equilibrium within 1 h. The isotherm fitted the Freundlich model well. Although the Langmuir model fitted the experiment data well at pH 3.0, 5.0 and 7.0, it did not fit at pH 9.0 and 11.0 at all. This implies that different biosorption mechanisms may be involved at different pH values. 0.1 N HCl was effective in uranium desorption. The results indicated that the naturally abundant biomass of otherwise nuisance cyanobacterium bloom exhibited good potential for application in removal of uranium from aqueous solution.     

Biosorption of lead phosphates by lead-tolerant bacteria as a mechanism for lead immobilization

The study of metal-tolerant bacteria is important for bioremediation of contaminated environments and development of green technologies for material synthesis due to their potential to transform toxic metal ions into less toxic compounds by mechanisms such as reduction, oxidation and/or sequestration. In this study, we report the isolation of seven lead-tolerant bacteria from a metal-contaminated site at Zacatecas, México. The bacteria were identified as members of the Staphylococcus and Bacillus genera by microscopic, biochemical and 16S rDNA analyses. Minimal inhibitory concentration of these isolates was established between 4.5 and 7.0 mM of Pb(NO₃)₂ in solid and 1.0–4.0 mM of Pb(NO₃)₂ in liquid media. A quantitative analysis of the lead associated to bacterial biomass in growing cultures, revealed that the percentage of lead associated to biomass was between 1 and 37% in the PbT isolates. A mechanism of complexation/biosorption of lead ions as inorganic phosphates (lead hydroxyapatite and pyromorphite) in bacterial biomass, was determined by Fourier transform infrared spectroscopy and X-ray diffraction analyses. Thus, the ability of the lead-tolerant isolates to transform lead ions into stable and highly insoluble lead minerals make them potentially useful for immobilization of lead in mining waste.     

Biosorption of uranium by Pseudomonas aeruginosa strain CSU: characterization and comparison studies

Pseudomonas aeruginosa strain CSU, a nongenetically engineered bacterial strain known to bind dissolved hexavalent uranium (as UO(2) (2+) and/or its cationic hydroxo complexes), was characterized with respect to its sorptive activity (equilibrium and dynamics). Living, heat-killed, permeabilized, and unreconstituted lyophilized cells were all capable of binding uranium. The uranium biosorption equilibrium could be described by the Langmuir isotherm. The rate of uranium adsorption increased following permeabilization of the outer and/or cytoplasmic membrane by organic solvents such as acetone. P. aeruginosa CSU biomass was significantly more sorptive toward uranium than certain novel, patented biosorbents derived from algal or fungal biomass sources. P. aeruginosa CSU biomass was also competitive with commercial cation-exchange resins, particularly in the presence of dissolved transition metals. Uranium binding by P. aeruginosa CSU was clearly pH dependent. Uranium loading capacity increased with increasing pH under acidic conditions, presumably as a function of uranium speciation and due to the H(+) competition at some binding sites. Nevertheless, preliminary evidence suggests that this microorganism is also capable of binding anionic hexavalent uranium complexes. Ferric iron was a strong inhibitor of uranium binding to P. aeruginosa CSU biomass, and the presence of uranium also decreased the Fe(3+) loading when the biomass was not saturated with Fe(3+), suggesting that Fe(3+) and uranium may share the same binding sites on biomass. Although the equilibrium loading capacity of uranium was greater than that of Fe(3+), this biomass showed preference of binding Fe(3+) over uranium. Thus, a two-stage process in which iron and uranium are removed in consecutive steps was proposed for efficient use of the biomass as a biosorbent in uranium removal from mine wastewater, especially acidic leachates. (c) 1996 John Wiley & Sons, Inc.     

Biosorption of uranium by cross-linked and alginate immobilized residual biomass from distillery spent wash

Residual biomass from a whiskey distillery was examined for its ability to function as a biosorbent for uranium. Biomass recovered and lyophilised exhibited a maximum biosorption capacity of 165–170?mg uranium/g dry weight biomass at 15?°C. With a view towards the development of continuous or semi-continuous flow biosorption processes it was decided to immobilize the material by (1) cross-linking with formaldehyde and (2) introducing that material into alginate matrices. Cross-linking the recovered biomass resulted in the formation of a biosorbent preparation with a maximum biosorption capacity of 185–190?mg/g dry weight biomass at 15?°C. Following immobilization of biomass in alginate matrices it was found that the total amount of uranium bound to the matrix did not change with increasing amounts of biomass immobilized. It was found however, that the proportion of uranium bound to the biomass within the alginate-biomass matrix increased with increasing biomass concentration. Further analysis of these preparations demonstrated that the alginate-biomass matrix had a maximum biosorption capacity of 220?mg uranium/g dry weight of the matrix, even at low concentrations of biomass.     

Biosorption of cadmium and lead ions by ethanol treated waste baker's yeast biomass

The biosorption of cadmium and lead ions from artificial aqueous solutions using waste baker's yeast biomass was investigated. The yeast cells were treated with caustic, ethanol and heat for increasing their biosorption capacity and the highest metal uptake values (15.63 and 17.49 mg g(-1) for Cd(2+) and Pb(2+), respectively) were obtained by ethanol treated yeast cells. The effect of initial metal concentration and pH on biosorption by ethanol treated yeast was studied. The Langmuir model and Freundlich equation were applied to the experimental data and the Langmuir model was found to be in better correlation with the experimental data. The maximum metal uptake values (qmax, mg g(-1)) were found as 31.75 and 60.24 for Cd(2+) and Pb(2+), respectively. Competitive biosorption experiments were performed with Cd(2+) and Pb(2+) together with Cu(2+) and the competitive biosorption capacities of the yeast biomass for all metal ions were found to be lower than in non-competitive conditions.     

Biosorption of lead by cotton shells powder: Characterization and equilibrium modeling study

Lead (Pb) is a toxic heavy metal causing serious health risks to humans and animals. In the present study, cotton (Gossypium hirsutum L.) shells powder was used as adsorbent for the treatment of synthetic Pb-contaminated water. The batch scale biosorption capacity of cotton shells powder was evaluated to study the effects of Pb concentrations, adsorbent doses and contact time at constant pH (6) and temperature (25?°C). Results revealed that sorption of Pb increased (q?=?0.09–9.60?mg/g) with increasing Pb concentration (1–15?mg/L) and contact time (15–90?min) while decreasing adsorbent dose (1–0.1?g/100?mL). The maximum Pb removal (90%) was achieved at Pb concentration (1?mg/L), contact time (90?min) and adsorbent dose (1?g/100?mL). Freundlich isotherm model proved best fit for Pb sorption (R²?=?0.99). The cotton shells powder has microporous structure confirmed by SEM, and has BET surface area (45 m²/g) and pore size (2.3 µm). These surface moieties along with various functional groups (C-H, C-O, C=O, O-H, S=O) confirmed by FTIR analysis might involve in Pb removal by complexation and ion exchange mechanisms. The cotton shells powder biomass could be considered as promising adsorbent for the removal of Pb from contaminated water.     

Biosorption of lead and copper from aqueous solutions by pre-treated crab and arca shell biomass

Sorption potential of pretreated crab and arca shell biomass for lead and copper from aqueous media was explored. The effects of pH, initial concentration, biosorbent dosage and contact time were studied in batch experiments. Effects of common ions like sodium, potassium, calcium and magnesium on the sorption capacity of pretreated crab and arca biomasses were also studied. At equilibrium, the maximum uptake by crab shell biomass was 19.83+/-0.29 and 38.62+/-1.27 mg/g for lead and copper, respectively. In case of arca shell biomass the maximum uptake capacity was 18.33+/-0.44 mg/g and 17.64+/-0.31 mg/g for lead and copper, respectively. Combined effect of all the common ions up to 50 microg/ml concentration was negligible for both the metals using both biomasses. Sorption isotherms were studied to explain the removal mechanism of both elements by fitting isotherms data into Lagergren, Freundlich and Langmuir equations.     

Biosorption of Fe3+ from aqueous solution by a bacterial dead Streptomyces rimosus biomass

The iron biosorption capacity of a Streptomyces rimosus biomass treated with NaOH was studied in batch mode. After pretreatment of biomass at the ambient temperature, optimum conditions of biosorption were found to be: a biomass particle size between 50 and 160 μm, an average saturation contact time of 4 h, a biomass concentration of 3 g/l and a stirring speed of 250 rpm. The equilibrium data could be fitted by Langmuir isotherm equation. Under these optimal conditions, 122 mg _Fe/g_biomass were fixed.     

Flotation of Streptomyces pilosus after lead accumulation

The flotation of Streptomyces pilosus was studied in the absence and presence of adsorbed Pb(II) ions on the cell walls and with and without using sodium dodecylsulfate (SDS) as collector. Adsorption of SDS onto the organism in the absence and presence of Pb(II) ions was also investigated. It was found that in the absence of adsorbed Pb(II), very little flotation took place with or without the presence of SDS although SDS adsorbed to some extent on the organism. The presence of Pb(II) on the bacterium's cell walls significantly increased flotation even in the absence of the collector. Addition of SDS, however, further increased both flotation rate and recovery.     

Biosorption of lead, cadmium and mercury by immobilized Microcystis aeruginosa in a column

Immobilized Microcystis aeruginosa in a flow-through sorption column was evaluated for the potential to remove Pb²⁺, Cd²⁺ and Hg²⁺ from aqueous solutions. M. aeruginosa showed high affinity for the three heavy metals with removal efficiency of 90% for Cd²⁺ and Hg²⁺, and 80% for Pb²⁺ at saturation conditions. Competitive sorption experiments conducted in paired and ternary systems indicated that Pb²⁺ was sequestered preferentially over Cd²⁺ and Hg²⁺. The presence of Cd²⁺ interfered only slightly with the uptake of Hg²⁺, as Pb²⁺ and Hg²⁺ did with Cd²⁺. In contrast, Hg²⁺ sorption was affected by Pb²⁺ to a great extent. Desorption with 1 M HCl was completed within 25 min with high efficiency and effectiveness for the three metals. The results of this study indicate that M. aeruginosa is to be a potential biosorbent material except when Hg²⁺ and Pb²⁺ are in the same contaminated solution.     

Biosorption of lead and nickel by living and non-living cells of Pseudomonas aeruginosa ASU 6a

The optimum conditions for biosorption and bioaccumulation of lead and nickel were investigated by using a tolerant bacterial strain isolated from El-Malah canal, Assiut, Egypt, and identified as Pseudomonas aeruginosa ASU 6a. The experimental adsorption data were fitted towards the models postulated by Langmuir and Freundlich isotherm equations. The binding capacity by living cells is significantly lower than that of dead cells. The maximum biosorption capacities for lead and nickel obtained by using non-living cells and living cells were 123, 113.6 and 79, 70 mg/g, respectively. The biosorptive mechanism was confirmed by IR analysis and from the identification nature of acidic and basic sites. Moreover, the postulated mechanism was found to depend mainly on ionic interaction and complex formation.     

Biosorption of cadmium,copper and lead by isolated mother cell walls and whole cells of Chlorella fusca

Using a new method for the isolation of released mother cell walls of Chlorella fusca, the biosorption of cadmium, copper and lead by purified cell wall isolates and whole cell suspensions was comparatively characterized. In all cases whole cells accumulated more metal ions than isolated cell walls. Both the Langmuir and Freundlich isotherm models were suitable for describing the short-term adsorption of cadmium, copper and lead by cell walls and the cadmium and copper adsorption by whole cells. However, neither model could sufficiently explain the lead accumulation by whole cells. The feasibility of a practical use of whole cells or isolated cell walls as biosorbents is discussed.     

Biosorption of lead, cadmium, and zinc by Citrobacter strain MCM B-181: characterization studies

The biosorption process for removal of lead, cadmium, and zinc by Citrobacter strain MCM B-181, a laboratory isolate, was characterized. Effects of environmental factors and growth conditions on metal uptake capacity were studied. Pretreatment of biomass with chemical agents increased cadmium sorption efficiency; however, there was no significant enhancement in lead and zinc sorption capacity. Metal sorption by Citrobacter strain MCM B-181 was found to be influenced by the pH of the solution, initial metal concentration, biomass concentration, and type of growth medium. The metal sorption process was not affected by the age of the culture or change in temperature. Equilibrium metal sorption was found to fit the Langmuir adsorption model. Kinetic studies showed that metal uptake by Citrobacter strain MCM B-181 was a fast process, requiring <20 min to achieve >90% adsorption efficiency. The presence of cations reduced lead, zinc, and cadmium sorption to the extent of 11. 8%, 84.3%, and 33.4%, respectively. When biomass was exposed to multimetal solutions, metals were adsorbed in the order Co2+ < Ni2+ < Cd2+ < Cu2+ < Zn2+ < Pb2+. Among various anions tested, only phosphate and citrate were found to hamper metal sorption capacity of cells. Biosorbent beads prepared by immobilizing the Citrobacter biomass in polysulfone matrix exhibited high metal loading capacities. A new mathematical model used for batch kinetic studies was found to be highly useful in prediction of experimentally obtained metal concentration profiles as a function of time. Metal desorption studies indicated that Citrobacter beads could, in principle, be regenerated and reused in adsorption-desorption cycles. In an expanded scale trial, biosorbent beads were found to be useful in removal/recovery of metals such as lead from industrial wastewaters.     

Uranium and lead accumulation in cells of Streptomyces sp.

Lead and uranium were accumulated equally well both in the viable and dry biomass of Streptomyces sp. The process occurred in less than 5 min. Uranium was accumulated selectively from a polymetallic solution containing U, Pb, Cu, Zn, Ni, Co. The optimum pH for the process was 5.0, and the concentration of each metal in the solution was 10(-3) M. Under these conditions, the dry biomass of Streptomyces amounting to 1 mg/cm3 accumulated over 60% of the uranium in the solution. With the same amount of cell wall preparation it was possible to remove from the solution ca. 90% of U. In this case, the accumulated uranium reached 21% of the sorbent dry mass. Electron micrographs show that lead accumulated in Streptomyces cells is mainly concentrated in the cell wall structures although in the case of uranium this is not so clear.