Advanced Materials Research Vols. 71-73

Abstract: Macrocystis pyrifera was used for the recovery of Zn2+ and Cd2+ from slightly acidic solutions (i.e., pH 4). Sorption isotherms were obtained from mono- and bi-component solutions. For the study of metal desorption, EDTA, HNO3 and Ca(NO3)2 were used as eluents. Metal release (Ca2+, Mg2+, K+ and Na+) was monitored in order to evaluate ion exchange mechanisms. After metal sorption/desorption steps the sorbent was characterized using SEM-EDAX analysis. SEM-EDAX analysis also allowed identifying the presence of elements such as Si, Al, Co, Ag, S, P, and Fe in the cell wall. Zinc desorption was almost complete when using 0.1 M nitric acid solution and the sorbent was not significantly damaged by the acidic treatment. Cadmium was completely removed from loaded sorbent when using EDTA, but at the expense of a partial degradation of the biomass as evidenced by the decrease in the intensity of the C and O peaks (SEM-EDAX).

Abstract: This work evaluated kinetic and adsorption physicochemical models for the biosorption process of lanthanum, neodymium, europium, and gadolinium by Sargassum sp. in batch systems. The results showed: (a) the pseudo-second order kinetic model was the best approximation for the experimental data with the metal adsorption initial velocity parameter in 0.042-0.055 mmol.g-1.min-1 (La < Nd < Gd < Eu); (b) the Langmuir adsorption model presented adequate correlation with maximum metal uptake at 0.60-0.70 mmol g-1 (Eu < La < Gd < Nd) and the metal-biomass affinity parameter showed distinct values (Gd < Nd < Eu < La: 183.1, 192.5, 678.3, and 837.3 L g-1, respectively); and (c) preliminarily, the kinetics and adsorption evaluation did not reveal a well-defined metal selectivity behavior for the RE biosorption in Sargassum sp., but they indicate a possible partition among RE studied.

Abstract: We investigated and evaluated metal up-take in three common dominant plants namely Ageratina adenophora, Eupatorium odoratum and Phoenix acaulis from three proposed bauxite mine sites in Araku valley, Vishakhapatnam, India. The concentrations of Cr, Cu, Pb and Zn varied from 14.41 to 87.73 mg/kg, 3.39 to 25.09 mg/kg, 2.48 to 17.39 mg/kg and 5.77 to 50.81 mg/kg, respectively. The variables studied showed significant spatial heterogeneity (General Linear Model, ANOVA, P < 0.05) among sites and metals. Transportation index (Ti) for Zn was >1 for all the species. The pH seemed to have the greatest effect on the solubility / retention of metals in soils thus, enhancing accumulation of metals.

Abstract: X-Rays Absorption Fine Structure Spectroscopy (XAFS) is an analytical technique that can be used as a probe to characterize almost all elements, even if they appear in diluted or non-crystalline systems. This is due to the fact that the absorption probability of X-rays has a unique feature for each element, and is modulated by the chemical and physical state of that element, as well as by its neighborhood. This paper presents a brief description of the X-rays absorption phenomenon and the analytical technique involving this phenomenon, as well as the application of XAFS in biosorption studies. For more details on XAFS theory, refer to [1].

Abstract: Genetic determinants for heavy metal resistance could be exploited in the design of bioprocesses for environmental cleanup. The removal of Ni(II), Co(II), Cr(VI) and Mn(II) was investigated using Serratia marcescens strains C-1, C4, 16 and Kluyvera sp. Nic3 isolated from nickel deposits in Moa, Holguín (Cuba). The high nickel and cobalt resistance of S. marcescens C-1 is based on the NreB- genetic determinant ncrABC, which encodes histidine-rich proteins, NcrA, NcrB and NcrC. NcrC is a Ni(II)/Co(II) uptake protein. In this work the presence of ncrAB fragment in S. marcescens C4, 16 and Kluyvera sp. Nic3 was determined by PCR. ncrAB fragment was efficiently amplified from genomic DNA of the strains C4 and 16 but not from strain Nic3. Strains C4, 16 and C-1 showed the highest resistance to Ni(II) and Co(II). The Ni(II)/Co(II) removal capacities of C4, 16 and C-1 strains were two times higher than that by Nic3 (12.88 mg of Ni(II)/g of biomass and 9.77 mg of Co(II)/g of biomass). Uptake of Cr(VI) and Mn(II) was not observed for any of these strains. pH value has an important influence on the Ni(II) and Co(II) removal capacity of S. marcescens C-1. Additional studies are currently in progress aimed to check the metal removal efficiency of strain C1 in batch reactors.

Abstract: Perceived environmental problems of nuclear fuel fabrication, use and treatment limit the acceptability of nuclear power as an alternative to fossil fuels. This applies to nuclear fuel processing and reprocessing but contamination also occurs at source via run-offs from current and historic mining activities. The price of uranium (U3O8) in the1990s was US$10/lb but is currently US$ 58/lb, peaking in 2007 at US$135/lb. With the potential global expansion of nuclear power as an alternative to fossil fuels the market and strategic values of U will rise. A new biotechnology was demonstrated for efficient recovery of U from minewaters as pure hydrogen uranyl phosphate (HUP) but an economic assessment (discounting the value of U) showed that the limitation as a waste treatment process was the cost of the phosphate feed supplement which contained 1 mol/mol phosphate. We describe the use of phytic acid (inositol phosphate; 6 mol phosphate/mol), a ubiquitous plant waste, to support the removal of uranium as HUP by an immobilised cell reactor and shift the focus from away bioremediation to value product manufacturing from wastes, and resource efficiency.

Abstract: The recovery of phosphorus from sewage sludge incineration ash as well as the separation of heavy metals from ash was investigated by using the biotechnological process of bioleaching and bioaccumulation of released phosphorus by newly developed population of bioleaching bacteria, Acidithiobacillus sp. strains, and polyphosphate (poly-P) accumulating bacteria, the AEDS-population (Acidithiobacillus sp. enriched digested sludge). The biologically performed solubilization of phosphorus from sewage sludge incineration ash is accompanied by the release of toxic metals. Therefore a combined process to separate phosphorus from heavy metals by achieving a plant available phosphorus-enriched product and a metal depleted ash was designed. Leaching experiments were conducted in laboratory scaled leaching reactor containing a bacterial stock culture of Acidithiobacillus sp.. Next step was the enhancement of P-recovery in combining bioleaching with simultaneous bio-P-accumulation by AEDS-population. The uptake of phosphorus in biomass reaches up to 66 % of the mobilized phosphorus by bioleaching. The combined biologically performed technology of phosphorus leaching and separation from toxic metals by simultaneous bioaccumulation developed in this study is a promising process for economical and ecological recovery of phosphorus from waste solids.

Abstract: Biological scorodite is produced at 80°C and 1g L-1 As5+, using iron oxidizing bacteria Acidianus Sulfidivorans, with a molar ratio Fe/As of 1 and without the use of seeds. We investigated the effect of high ferrous concentration, Fe/As higher than 1, and the use of foreign seeds (gypsum) on biological scorodite crystallization. The use of high ferrous concentrations resulted in a retardation of the time of crystallization due to the high concentration of ferric produced by a high biological oxidation. However, ferrous biological oxidation might be controlled to avoid this effect. The use of seeds did not improve the kinetics of crystallization. Nonetheless, a high arsenic removal rate was observed in the presence of seeds probably as a result of the formation of less stable scorodite.

Abstract: Unique properties of biogenic Mn oxides were applied to a fundamental study of separation and recovery of rare earth elements. Selective sorption of Ce3+ over La3+ ions was achieved at neutral pH values using biogenic Mn oxides produced by Paraconiothyrium sp. WL-2 strain. The selective coefficient for Ce3+ (αCe) was much greater with biogenic and synthetic Mn oxides than those for La3+ (αLa). Ce3+ ions were oxidized to CeO2 by Mn(III, IV) in Mn oxides under anaerobic conditions resulting in the release of Mn2+ ions, while La3+ ions were sorbed without a redox reaction. With an increase in coexisting La3+ ions, sorption of Ce3+ on both Mn oxides was significantly suppressed, especially with synthetic Mn oxides. The edges of the structure are competitive sites because of fewer numbers of vacant sites in synthetic Mn oxide layers. The preferential sorption on the edge sites of Mn oxides is in the order of La3+ > Ce3+. These phenomena can be expanded to separation and recovery of other rare earth elements from natural and anthropogenic sources.

Abstract: The aim of this research was the selection of bacterial strains resistant to mercury, as well as to demonstrate their capacity to reduce mercury in solution when they are inoculated in pure and mixed cultures. Samples of soil from informal mining gold sites in Peru were collected and fifteen mercury resistant bacteria were isolated. Strains RM6, RM7, RM9, RM11, RM12 and RM13 were selected for their capacity to reduce mercury in solution. The six bacterial strains belong to the genus Pseudomonas. Inoculated in pure cultures, these strains reduce mercury in solution although in different percentages: RM9, RM11 an RM12 reduce 93% to 97% of the mercury, while strains RM6, RM7 y RM13 reduce 80% to 85%. The consortium of all six bacterial strains showed a mercury reduction of 84%. Approximately 91% of mercury in solution was reduced in 1 hour and this reaction was not associated to bacterial growth. Using specific primers, the merA gene was amplified from genomic DNA of the bacterial strains, which would suggest the activity of the mer operon as a mechanism of mercury resistance. Due to their ability to reduce mercury in solution, it is advisable to carry out more research on the selected strains since they could be useful in future bioremediation processes.