Sabine Willscher

A comparative study of As(III) and As(V) in aqueous solutions and adsorbed on iron oxy-hydroxides by Raman spectroscopy

The sorption of the arsenite (AsO(3)(3-)) and the arsenate (AsO(4)(3-)) ions and their conjugate acids onto iron oxides is one of main processes controlling the distribution of arsenic in the environment. The present work intends to provide a large vibrational spectroscopic database for comparison of As(III) and As(V) speciation in aqueous solutions and at the iron oxide - solution interface. With this purpose, ferrihydrite, feroxyhyte, goethite and hematite were firstly synthesized, characterized in detail and used for adsorption experiments. Raman spectra were recorded from As(III) and As(V) aqueous solutions at various pH conditions selected in order to highlight arsenic speciation. Raman Scattering and Diffuse Reflectance Infrared Fourier Transform (DRIFT) studies were carried out to examine the respective As-bonding mechanisms. The collected data were curve-fitted and discussed according to molecular symmetry concepts. X-ray Absorption Near Edge Spectroscopy (XANES) was applied to confirm the oxidation state of the sorbed species. The comprehensive spectroscopic investigation contributes to a better understanding of arsenic complexation by iron oxides.

Biomining: Metal Recovery from Ores with Microorganisms

Biomining is an increasingly applied biotechnological procedure for processing of ores in the mining industry (biohydrometallurgy). Nowadays the production of copper from low-grade ores is the most important industrial application and a significant part of world copper production already originates from heap or dump/stockpile bioleaching. Conceptual differences exist between the industrial processes of bioleaching and biooxidation. Bioleaching is a conversion of an insoluble valuable metal into a soluble form by means of microorganisms. In biooxidation, on the other hand, gold is predominantly unlocked from refractory ores in large-scale stirred-tank biooxidation arrangements for further processing steps. In addition to copper and gold production, biomining is also used to produce cobalt, nickel, zinc, and uranium. Up to now, biomining has merely been used as a procedure in the processing of sulfide ores and uranium ore, but laboratory and pilot procedures already exist for the processing of silicate and oxide ores (e.g., laterites), for leaching of processing residues or mine waste dumps (mine tailings), as well as for the extraction of metals from industrial residues and waste (recycling). This chapter estimates the world production of copper, gold, and other metals by means of biomining and chemical leaching (bio-/hydrometallurgy) compared with metal production by pyrometallurgical procedures, and describes new developments in biomining. In addition, an overview is given about metal sulfide oxidizing microorganisms, fundamentals of biomining including bioleaching mechanisms and interface processes, as well as anaerobic bioleaching and bioleaching with heterotrophic microorganisms.

Nocardiopsis metallicus sp. nov., a metal-leaching actinomycete isolated from an alkaline slag dump.

A taxonomic study was carried out on a metal-mobilizing, alkaliphilic bacterium from an alkaline slag dump, strain KBS6(T). The strain produced substrate and aerial mycelia. Growth occurred in the pH range 7.0-10.5, with an optimum at pH 8.5. A salt concentration of up to 10% was tolerated, and various organic substrates were used for growth. The results of a 16S rDNA sequence comparison revealed that strain KBS6(T) belongs to the genus Nocardiopsis. DNA-DNA hybridization with the two closest relatives, Nocardiopsis exhalans and Nocardiopsis prasina, gave similarity values of 18.2 and 44.1%, respectively, which indicated that strain KBS6(T) represents a novel species of the genus Nocardiopsis. This is consistent with the morphological, physiological and chemotaxonomic data. Because of the ability of this micro-organism to solubilize metals, the name Nocardiopsis metallicus sp. nov. is proposed for strain KBS6(T) (= DSM 44598(T) = NRRL B-24159(T)), this being the type strain.

Studies on the leaching behaviour of heterotrophic microorganisms isolated from an alkaline slag dump

Abstract Eleven heterotrophic isolates from an alkaline slag dump, including nine bacteria strains, one fungus and one yeast isolate, were investigated for their ability to leach alkaline siliceous material. The efficiencies of these isolates were compared with those of chemical processes. Under defined experimental conditions, all the organisms demonstrated leaching capability, but, in general, the bacteria were more effective than the fungus or the yeast. The bacteria strains leached up to 38% of the manganese and up to 46% of the magnesium and were more selective than chemical processes. Scanning electron microscopy (SEM) analysis of the solid material after leaching showed considerably more surface erosion of the biologically leached material than observed in the control experiments. The possible long-term risks originating from uncontrolled leaching in alkaline waste dumps, as well as the participation of microbial activity in weathering processes of mineral materials, are briefly discussed.

Microbial Leaching of Metals from Printed Circuit Boards

Electrical and electronic equipment (EEE), e.g. printed circuit boards, contain substantial amounts of metals, e.g. Cu, Pb and Sn. The objective of this work was to investigate the bioleaching of a material, originating from a technical waste processing facility, as one possible way of a complete separation of the metals from the polymer carrier. During the leaching experiments the mechanism of the leaching process was investigated, and biofilms and precipitates were analyzed by microscopical (SEM) and spectroscopical methods (EDX, XRF, XRD). The enhanced formation of exopolymer layers seems to promote the precipitation of secondary mineral particles beneath and the sorption of particles from the suspension on the layer surface.

Phytoremediation as an Alternative Way for the Treatment of Large, Low Heavy Metal Contaminated Sites: Application at a Former Uranium Mining Area

Large sites with a low contamination of metall(oid)s were in the past a problem for remediation measures – the “traditional” processes were too expensive for an application on such expanded areas. Phytoremediation can be an alternative for such low contamination problems. In Germany, a research project is performed on this subject, in cooperation of the University of Jena and the TU Dresden. The field site is a former U mining area. Until 1991, a low grade U ore dump for sulfuric acid leaching was located on this site. After the close-down of the U mining in East Germany in 1991, the dump material was removed. Now, a phytoremediation test field is constructed on top of this site for the capture of the remained contaminants coming up by capillary forces. The paper pictures the phytoremediation in general, the research project and gives some first preliminary results.

Underground Degradation of Lignite Coal Spoil Material by a Mixed Microbial Community under Acid Mine Drainage Conditions

In a field study, biogeochemical processes in a large lignite coal spoil area with moderate AMD generation were investigated. Underneath this area, large amounts of groundwater are impacted by degradation and transformation processes of coal remainders in the former open pit mining area. An investigation was performed to find out the sources for the ground and surface water contaminations of larger areas. Samples were taken from different places and different depths of the coal spoil area and were investigated for different metabolic groups of microorganisms. As a result, fungi are able to degrade humic matter in coal spoil heaps in a first step to oligomers. Other microorganisms do a further degradation of first intermediates in a commensalic community. Streptomycetes do a cleavage of lignocelluloses, strepto- and other actinomycetes also degrade cellobiose and xylose related parts of the humic coal spoil matter. The different members of the microbial community exist in different “floors” of the spoil area: fungi and most Actinomycetes prefer the oxic zone, whereas degraders of aromatic and heterocyclic compounds can also exist in the capillary and ground water zones; here more frequently Arthrobacter, Pseudomonas, Rhodococcus and Mycobacterium strains were detected. Ferric iron formed in biooxidation of pyrite seems to play an important role as a catalyst for oxic as well as anaerobic degradation of complex organic matter in the underground. A complex linkage between microbial Fe-, S-, C- and N-cycles was figured out on this site that induces a high and long-term impact on ground water contamination in this area.

Field Scale Phytoremediation of Soils Contaminated with Heavy Metals and Radionuclides and Further Utilization of the Plant Residues

Phytoremediation is applied to a site in the former uranium mining area of Ronneburg in Eastern Thuringia, Germany, slightly contaminated with heavy metals and radionuclides (HM/R). In a joint research project, remediation of HM/R-contaminated sites is investigated and concepts for the subsequent utilization of the contaminated plant residues are developed. To minimize HM/R-accumulation in soil and to reduce groundwater contamination a combination of phytostabilization and phytoextraction methods is applied and lysimeter experiments are performed to demonstrate the reduction of seepage water rate and load. The final utilization of HM/R loaded plant residues after harvests was studied by biogas and ethanolic fermentations and by combustion of the plant material. The fate of HM/R in the different by-products was investigated.

Environmental Impact after 30 to 60 Years of Remediation: Microbial Investigation of Hard Coal Mining Dumps in Germany

Important groups of microbes were investigated in three hard coal mining dumps in Saxonia/ Germany. In the particular dumps, different chemophysical and geochemical conditions are existing, depending on the kind of remediation up to six decades ago. Thiobacillus denitrificans, iron and sulfate reducers, and general aerobic heterotrophs and fungi were counted by MPN and CFU methods. Samples were taken from drilling cores in different depths out of the dumps, from seepage-, surface- and ground waters and from sediments. Similarities and significant differences were found between the microbial populations of the three dumps, depending on the appropriate environmental conditions. As a result, enhanced counts of T. denitrificans were detected at all three sites, originating from fertilizers (agricul-ture, gardens) and atmospheric precipitations. Sulfate reducers and aerobic heterotrophic microorganisms are suited indicators for the ongoing biogeochemical processes in the dumps

Microbial and Geochemical Characterization of an Acid-Generating Hard Coal Tailings Dump in Saxonia/ Germany

An enhanced entry of heavy metals and metalloids into ground and surface water was observed in the historical hard coal mining areas of the districts of Zwickau and Lugau/ Oelsnitz in Saxonia, Germany. Heavy metals and metalloids like Mn, Co, Ni, Zn, As and Cd are enriched in the surface waters of the district. This environmental impact is observed even though a recultivation of some of the dumps occurred partially already 50 years ago. In this study, preliminary microbial and geochemical characterizations of samples from drilling cores in different depths of a dump site, of surface and ground water samples, and of sediments are described. Thiobacillus denitrificans appeared to be a dominating species in these moderately acidic environment especially where there is nitrate infiltration and inflow, respectively, due to agricultural use of the adjacent area. Some of the sediment samples also contained high counts of iron- and sulfate-reducing bacteria due to the organic detritus on the sediment surface.