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Biohydrometallurgy in Turkish gold mining: First shake flask and bioreactor studies
Abstract
The first laboratory tests on biooxidation and cyanidation of gold ores in Turkey were carried out using samples of the Copler Gold Mine. Over a 3 year R&D test period, mixed bacterial/archaeal cultures improved biooxidation of the Copler ore. The highest sulphide oxidation of 87.35% over 432 h was achieved in shake flasks in the presence of the mixed culture (MODM: Sulfolobus acidophilus and Sulfolobus thermosulfidooxidans). Bioreactor tests resulted in greater dissolution rates for iron and arsenic than did shake-flask tests, which led to a greater extent of sulphide oxidation within a shorter period of time. The maximum sulphide oxidation in the bioreactor tests was 97.79% after 240 h when the EXTM (Acidianus brierleyi and Sulfolobus metallicus) mixed culture was used. After the biooxidation experiments with solids contents of 10% and 20% (w/v), the gold recovery from the oxidised ore was lower than that achieved in the presence of 5% solids (w/v) because the extent of sulphide oxidation was reduced as the pulp density increased. A strong correlation between the sulphide oxidation and gold recovery was also established. The highest gold recovery of 94.48% was achieved during cyanidation from the biooxidised ore produced from the experiment conducted using the EXTM mixed culture.
... The culture temperatures were set at 35˚C for stimulating the growth of mesophiles, and 45˚C for activating thermophiles, and the stirring speed was 150 rpm. Norris nutrient medium was a solution containing deionized water and 0.4 g/L (NH 4 ) 2 SO 4 , 0.4 g/L K 2 HPO 4 , 0.5 g/L MgSO 4 .7H 2 O (Ciftci and Akcil 2013). ...
... The cyanide consumption after the second hour continues probably due to the dissolution of other components which still present in the ore. Ciftci and Akcil (Ciftci and Akcil 2013) also reached the conclusion that the percentage of gold dissolution is proportional to the extent of sulfide ore biooxidation. In the experiments conducted by Olson et al. 2006, the positive effect of the biooxidation process on increasing the efficiency of the cyanidation process has been presented (Olson et al. 2006). ...
Acid mine drainage (AMD) is one of the challenging environmental issues in sulfidic mines. These hazardous solutions generally contain a mixture of indigenous iron- and sulfur-oxidizing microorganisms that could be used as a source for biotechnological purposes. In this study, the ability of an AMD from a sulfide-bearing gold mine to biooxidize its high-grade pyritic gold ore was investigated and its efficiency was compared with iron- and sulfur-oxidizing microorganisms from a microbial culture bank. Experiments were conducted at 35 and 45 ̊C, initial pH values of 1.5 and 2 in a Norris culture medium prepared from deionized and saline local waters. The effects of some critical parameters including the initial pH and the concentrations of ferrous or ferric sulfate were investigated on the efficiency of the biooxidation process and gold extraction. The results showed that the AMD microorganisms had a greater ability to oxidize the sulfide ore than the microorganisms from the microbial bank. The addition of ferrous and ferric sulfates increased the efficiency of biooxidation, while high concentrations of these ions caused the formation of inhibitory precipitates (jarosite) and decreased gold extraction. The results showed that biooxidation using the AMD medium in the saline local water increased the extraction of gold from 73 to 99%. It can be concluded that the application of AMD for the treatment of refractory gold sulfide ores could be an efficient solution for increasing gold extraction and reducing environmental problems.
... A mixed culture of moderate thermophiles dominates at these conditions [28]. The BIOX process developed by Gencor, operated at 40-45ºC with moderate thermophiles, is used by most of the stirred tank operations [12]. Mesophilies such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirilum ferriphilum are the most commonly used microbes in the process of bioleaching [15]. ...
... It has been stated that the mixed culture of extreme thermophiles has some advantages over other mixed culture, such as faster chemical oxidation kinetics, decreasing the cost of cooling, and a more complete oxidation [2,12]. However, the bio-oxidation efficiencies with MC3 were not the highest at different pulp densities. ...
Bio-oxidation is an effective technology for treatment of refractory gold concentration. However, the unsatisfied oxidation rate and long residence time, which cause the lower cyanide leaching rate and gold recovery, is a key factor to restrict the application of traditional bio-oxidation technology. In this study, the oxidation rate of refractory gold concentration and the adaption of microorganism were analyzed to evaluate a new developed two-step pretreatment process, which includes a high temperature chemical oxidation step and a subsequent bio-oxidation step. The oxidation rates and recovery rates of gold were improved significantly after two-step process. The results showed that the highest oxidation rate of sulfide sulfur could reach to 99.01 % with extreme thermophiles microbial community when pulp density was 5 %. Accordingly the recovery rate of gold was elevated to 92.51%. Meanwhile, the results revealed that moderate thermophiles performed better than acidophilic mesophiles and extreme thermophiles whose oxidation rates declined drastically when pulp density increased to 10 % and 15 %. The oxidation rates of sulfide sulfur with moderate thermophiles were 93.94 % and 65.73 % when pulp density increased to 10 % and 15 %, respectively. All these results indicated that the two-step pretreatment increased the oxidation rate of refractory gold concentration and is a potential technology to pretreat the refractory, meanwhile, due to the sensitivity of microbial commuinty under different pulp density, the optimization of microbial community in bio-oxidation is necessary in industry.
... 由于极度嗜热菌的硫化物氧化更彻底， 氧化渣的氰化物消耗极大降低，降低了生产成本 [15,16] . [30,31] . 另外，提高矿浆浓度时，预氧化体系中积累的有 害金属离子浓度也会相应增加，微生物的氧化活性受到 影响 [30,32] . ...
... [30,31] . 另外，提高矿浆浓度时，预氧化体系中积累的有 害金属离子浓度也会相应增加，微生物的氧化活性受到 影响 [30,32] . 相同矿浆浓度下，不同温度混合菌的铁、硫 氧化脱除率中度嗜热混合菌最高，嗜中温混合菌次之， 极度嗜热混合菌最低. ...
In order to enhance the efficiency of bio-oxidation of Axi gold concentrate, the effects of three mixed bacteria cultures and two-step treatment approach on the intensification of bio-oxidation were studied. The results revealed that the optimum mixed culture was moderate thermophiles, the oxidation rates declined drastically with increasing of pulp density. The extraction rates of iron and sulfur were 98.35% and 91.90% at 2% pulp density, when the pulp density was elevated to 15%, the extraction rates of iron and sulfur declined to 50.25% and 49.51%, respectively. The two-step treatment could further improve the efficiency of pretreatment with moderate thermophiles, the extraction rates of iron and sulfur boosted to 64.93% and 65.73% at 15% pulp density after the two-step treatment, which was equivalent to the result obtained at 10% pulp density with normal bio-oxidation process.
... The cyanide consumption after the second hour continues probably due to the dissolution of other components which still present in the ore. Ciftci and Akcil [11] also reached the conclusion that the percentage of gold dissolution is proportional to the extent of sul de ore biooxidation. In the experiments conducted by Olson et al. 2006, the positive effect of the biooxidation process on increasing the e ciency of the cyanidation process has been presented [20]. ...
Acid mine drainage (AMD) is one of the challenging environmental issues in sulfidic mines. These hazardous solutions generally contain a mixture of native iron- and sulfur-oxidizing microorganisms which could be used to a source for biotechnological aims. In this research, the ability of an AMD of a sulfide-bearing gold mine was investigated for the biooxidation of a high-grade pyritic gold ore and its efficiency was compared with iron- and sulfur-oxidizing microorganisms from a microbial culture bank. The experiments were conducted at 35 and 45 ̊C, initial pH values of 1.5 and 2 in a Norris culture medium prepared from deionized and saline local waters. The effects of some critical parameters including, initial pH, and the concentrations of ferrous or ferric sulfate were investigated on the efficiency of the biooxidation process and gold extraction. The results showed that the AMD microorganisms had a more ability to oxidize the sulfide ore than the microorganisms from the microbial bank. The addition of ferrous and ferric sulfates increased the biooxidation efficiency, while high concentrations of these ions caused the formation of inhibitory precipitates (jarosite) and decreased gold extraction. The results showed that biooxidation using the AMD medium in the saline local water increased the extraction of gold from 73–99%. It can be concluded that the application of AMD for the treatment of refractory gold sulfide ores could be an efficient solution for increasing gold extraction and reducing environmental problems.
... The biooxidation of refractory gold concentrates by mesophilic cultures with high percent solids is better comparing to the moderate and extreme-thermophilic mixed cultures (Ciftci and Akcil 2010). However, extremophiles showed better oxidation performance with 5% solids (Ciftci and Akcil 2010;Ciftci and Akcil 2013). ...
In nature, microorganisms developed at various places and adapted to the various weather and geological conditions. Microorganisms participate in geological transformations leading to the dissolution of some minerals and conversion to others. While some microorganisms with their metabolic activity increase the mobility of metals, others cause precipitation of metals and the formation of new minerals. These biogeochemical interactions found practical application in the recovery of metals. In the article, the proposals for improvement of existing engineering commercial processes for recovery of metals are given which can enable the formation of nanogold and nanogold compounds.
Key points
• Amino acids in pretreatment can increase the dissolution of the layer around the gold.• Amino acids in the complexing stage can increase gold leaching.• After the complexing stage, the bionanosynthesis of gold and its compounds is possible.Graphical abstract
... It has been proposed that the oxidation rate of sulfide by ferric ion increases as temperature rises (Li et al., 2009). Though the optimal temperature of extremely thermophiles is higher than the mesophiles and moderate thermophiles, the cell walls of extremely thermophiles are not strong enough as compared to the mesophiles and moderate thermophiles if the pulp density is higher than 5%, which results in the disruption of microbial cells due to shear and stress caused by stirring (Ciftci and Akcil, 2010;Ciftci and Akcil, 2013). The regeneration of ferric ion as oxidizing agent in the process of bio-oxidation would be hindered. ...
A two-stage chemical-biological oxidation approach, which applied a high temperature chemical oxidation stage prior to the bio-oxidation stage, was employed to accelerate the bio-oxidation rate of Axi gold concentrate with pyrite as the main sulfide phase. The extraction levels of Fe and S were 67.0% and 72.9% in the traditional one-stage bio-oxidation approach, while the values were elevated respectively to 78.0% and 79.6% with the two-stage approach. Accordingly, the extraction rate of gold was increased from 83.6% to 90.3% when subjected to the two-stage approach. The intensification mechanism of the two-stage approach was carried out by using Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM- EDX), X-ray photoelectron spectroscopy (XPS) and particle size analysis. The results indicated that pyrite on the surface of the concentrate was partly oxidized and particle size of the concentrate diminished after the first stage (chemical oxidation), which would facilitate the subsequent bio-oxidation process.
... Nowadays, more and more new biological approaches are being studied to recover gold from refractory gold-bearing sulfide ore [5,[34][35][36]. Although biometallurgy is environmentally friendly, it has not been applied on a large scale because its production cycle is too long and the environmental requirements of bacteria are strict [37,38]. ...
The technological mineralogy of a gold deposit located in North-Western province of Zambia was carried out by using X-ray fluorescence spectroscopy (XRF), X-ray diffraction spectroscopy (XRD), and scanning electron microscope (SEM). The results showed that gold was highly dispersed in gold-bearing minerals such as pyrite, arsenopyrite, and some gangues in the form of natural gold and electrum. The gold grade in the mineral was 15.96 g/t and the particle size distribution of gold was extremely uneven. Most of the gold particles were less than 10 μm and wrapped with gold-bearing minerals, making it difficult to achieve liberation during grinding. According to the characteristics of the refractory gold deposit, the gravity–flotation combined beneficiation process was used to recover the liberated coarse gold and the fine gold in the sulphides. The closed-circuit experiments obtained excellent indicators. The grade and recovery of gold in the gravity separation concentrates reached 91.24 g/t and 57.58%, respectively. The grade and recovery of gold in the flotation concentrates were 49.44 g/t and 33.36%, respectively. The total recovery of gold was 90.94%. The gravity–flotation combined beneficiation pretreatment process provided a feasible method for the refractory gold ore and ensured the effective recovery of gold.
... cyanide) (van Aswegen et al. 2007). While this process was originally operated with mesophilic microbes, extremely thermophilic archaea can enhance the dissolution of sulfidic ores and consequently improve downstream yields (Lindström, Sandström and Sundkvist 2003;van Aswegen et al. 2007;Astudillo and Acevedo 2009;Ciftci and Akcil 2013). ...
Although the extremely thermophilic archaea (Topt ≥ 70°C) may be the most primitive extant forms of life, they have been studied to a limited extent relative to mesophilic microorganisms. Many of these organisms have unique biochemical and physiological characteristics with important biotechnological implications. These include methanogens that generate methane, fermentative anaerobes that produce hydrogen gas with high efficiency, and acidophiles that can mobilize base, precious and strategic metals from mineral ores. Extremely thermophilic archaea also have been a valuable source of thermoactive, thermostable biocatalysts, but their use as cellular systems has been limited because of the general lack of facile genetics tools. This situation has changed recently, however, thereby providing an important avenue for understanding their metabolic and physiological details and also opening up opportunities for metabolic engineering efforts. Along these lines, extreme thermophilic archaea have recently been engineered to produce a variety of alcohols and industrial chemicals, in some cases incorporating CO2 into the final product. There are barriers and challenges to them reaching their full potential as industrial microorganisms but, if these can be overcome, a new dimension for biotechnology will be forthcoming that strategically exploits biology at high temperatures.
The substantial arsenic (As) content present in arsenic-containing bio-leaching residue (ABR) presents noteworthy environmental challenges attributable to its inherent instability and susceptibility to leaching. Given its elevated calcium sulfate content, ABR exhibits considerable promise for industrial applications. This study delved into the feasibility of utilizing ABR as a source of sulfates for producing super sulfated cement (SSC), offering an innovative binder for cemented paste backfill (CPB). Thermal treatment at varying temperatures of 150, 350, 600, and 800°C was employed to modify ABR’s performance. The investigation encompassed the examination of phase transformations and alterations in the chemical composition of As within ABR. Subsequently, the hydration characteristics of SSC utilizing ABR, with or without thermal treatment, were studied, encompassing reaction kinetics, setting time, strength development, and microstructure. The findings revealed that thermal treatment changed the calcium sulfate structure in ABR, consequently impacting the resultant sample performance. Notably, calcination at 600°C demonstrated optimal modification effects on both early and long-term strength attributes. This enhanced performance can be attributed to the augmented formation of reaction products and a densified microstructure. Furthermore, the thermal treatment elicited modifications in the chemical As fractions within ABR, with limited impact on the As immobilization capacity of the prepared binders.
Biohydrometallurgy waste (BW) was used as sulfate sources for supersulfated cement (SSC) production with the aim of providing an alternative binder for cemented paste backfill (CPB). Additives, including carbide slag (CC), Al2(SO4)3 (AlS) and Na2SO4 (NaS), were used to modify the binder properties, when considering the poor mechanical strength at the early curing ages. The reaction kinetics of binder modified by additives were studied via isothermal calorimeter test; mechanical strength and hydration products modifications due to the addition of additives were also explored. Additionally, arsenic (As) leaching from the binders was tested and the immobilization mechanism was explored using density functional theory (DFT) calculation. The results showed that the addition of CC increased the early strength strongly, but higher amount of CC restricted the strength development after curing for a long time; NaS presented marginal influence on the binder properties. The coupling addition of 25 wt% CC and 1 wt% AlS showed the best performance; the compressive strength after curing for 3 and 28 days reached around 13.67 MPa and 36.97 MPa, which was increased by about 47.69% and 18.34%, respectively, compared to the control sample. The superior performance was attributed to the generation of more reaction gels, especially ettringite (AFt). Rising in the AFt content contributed to better immobilization effects on As, because that it led to lower pore volume and permeability; besides, AFt showed higher immobilization effects according to the DFT calculation.
This work focuses on constructing a bio-electro-hydrometallurgical platform to efficiently recover cobalt (Co), lithium (Li), and manganese (Mn) from the cathode active materials (CAMs) of spent lithium batteries. A bioleaching process and selective adsorption by PC-88A/TOA-modified granular activated carbon were both incorporated into an electrokinetics approach to achieve excellent recycling performance. The technical feasibility was comprehensively investigated in terms of four aspects, including the domestication of microorganisms, the evaluation of the bioleaching process, the equilibrium adsorption of the adsorbent, and the electrokinetic recovery. Potential sulfur-oxidizing bacteria were screened and domesticated to a high concentration of pyrite pulp. The voltage gradient and the remediation time both had obvious influences on the recovery of the target elements in the electrokinetic process. Maximum recoveries of 91.45%, 93.64% and 87.92% for Co, Li, and Mn, respectively, were achieved from the CAMs of spent lithium-ion batteries via the electrokinetics process. The indirect oxidation of pyrite provided the necessary reductants for the platform. The transformation of sulfur (S) to H2SO4 as a result of bio-oxidation by bacteria strains supplied additional H⁺ ions to facilitate the reduction reaction, and acid dissolution mitigated the drawbacks caused by the uneven distribution of pH in the electrokinetics process.
Cobalt (Co) recycling from the spent LIBs not only favors the ecological protection also meets the supply chain of Co in the international market. In this research, a three-dimensional microbial-fuel-cell (3D-MFC) two-chamber system with granular activated carbon (GAC) microelectrodes was constructed to remove and recover Co from the stripping cobalt sulfate solution. The 3D bio-electrochemical (BE) system exhibited the largest voltage output and power production at 12th day during the acclimation, achieving the maximum power densities (W/m³) of 6.24, 10.29, 14.52, 12.59, and 8.78, respectively. The GAC prepared at 500 °C achieved highest removal and recovery efficiencies of Co in the 3D-MFC system. The maximum removal efficiency of 98.47%, the recovery efficiency of 96.35%, the power density of 11.34 W/m³, and the columbic efficiency of 28.74% were obtained in the orthogonal experiments. The influence of the operating time on the removal and recovery of Co was more obvious than the electro-output of the system. The addition of ammonium carbonate to the 3D-MFC systems clearly increased the precipitation of Co. The stacking of GAC particles in MFC had strengthened the adsorption of Co ions by intensifying the acidic-alkaline pathways during the 3D BE process. The removal and recovery of Co ions from the stripping solution in the 3D-MFC experiments were mainly achieved by the electromigration, electrostatic adsorption of GAC, and chemical precipitations of cobalt hydroxide and cobalt carbonate. A continuous process was suggested for the 3D-MFC application integrating to the traditional recovery procedure of Co from the spent LIBs at the pilot scale.
A defined mesophilic consortium including an iron oxidizing bacterium and a sulfur oxidizing bacterium was constructed to evaluate its ability for bioleaching a flotation concentrate from Andacollo mine in Neuquén, Argentina. Experiments were performed in shake flasks with a pulp density of 10% (w/v), using a basal salt medium containing ferrous iron at pH 1.8. The leaching solutions were analyzed for pH, redox potential (using specifics electrodes), ferrous iron (by UV-Vis spectrophotometry) and metal concentrations (by atomic absorption spectroscopy). The results showed that the consortium was able to reduce the refractory behavior of the concentrate, allowing 91.6% of gold recovery; at the same time, high dissolution of copper and zinc was reached. These dissolutions followed a shrinking core kinetic model. According to this model, the copper solubilization was controlled by diffusion through a product layer (mainly jarosite), while zinc dissolution did not show a defined control step. This designed consortium, composed of bacterial strains with specific physiological abilities, could be useful not only to optimize gold recovery but also to decrease the leachates metallic charge, which would be an environmental advantage.
The laboratory tests of biooxidation and cyanidation were carried out by using samples of the complex refractory gold ore from China. The elemental composition was 16.8 % iron, 18.6 % sulfur, 4.88 % arsenic，2.30 % carbon and 3.49 % antimony. Gold is assayed at 46 g/t. The arsenic oxidation of 88.11 %，carbon removal rate of 32.34 % and antimony oxidation of 23.92 % over 16d was achieved in shake flasks in the presence of the mixed culture (HQ0211: Thiobacillus ferrooxidans Leptospirillum ferrooxidans and Thiobacillus thiooxidans). The continuous bioreactor tests resulted in greater dissolution rates for arsenic, carbon and antimony, which led to a greater extent of sulphide oxidation within a shorter period of time. The maximum oxidation of arsenic and antimony was 90.72 % and 40.09 % respectively and the removal rate of carbon is 63.48% after 8d in the continuous bioreactor tests. After bioleaching, the gold recovery of the oxidation residue was 98.02 % with the cyanidation method, which was showed the biological pretreatment was applicable to the complex refractory gold ore.
We adapted a mixed culture of acidophiles to high arsenic concentrations to confirm the possibility of achieving more than 70% biooxidation of refractory gold concentrates containing high arsenic (As) concentration. The biooxidation process was applied to refractory gold concentrates containing approximately 139.67 g/kg of total As in a stirred tank reactor using an adapted mixed culture of Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. The percentage of the biooxidation process was analyzed based on the total As removal efficiency. The As removal was monitored by inductively coupled plasma (ICP) analysis, conducted every 24 h. The results obtained with the adapted culture were compared with the percentage of biooxidation obtained with a non-adapted mixed culture of A. ferrooxidans and A. thiooxidans, and with their respective pure cultures. The percentages of biooxidation obtained during 358 h of reaction were 72.20%, 38.20%, 27.70%, and 11.45% for adapted culture, non-adapted culture, and pure cultures of A. thiooxidans and A. ferrooxidans, respectively. The adapted culture showed a peak maximum percentage of biooxidation of 77% at 120 h of reaction, confirming that it is possible to obtain biooxidation percentages over 70% in gold concentrates containing high As concentrations.
In this study, cyanidation experiments on massive sulfide sample was investigated. The grade of precious metals (Au and Ag) in the ore are 4.2 g/t and 311.9 g/t. Also, the average grade of other elements are As-1751.6, Sb-619.7, Zn-781.4, Cu-454.6, Pb-101.8, Hg-324.3, and Bi-0.6 (all assays are in g/t). The first objective of test work focused on the determination of conditions for extracting gold from the ore ground to −75 μm. Different influential parameters such as cyanide concentration, particle size fraction, pH and leaching time have been comprehensively investigated. The optimum parameters were -25μm for size fraction, 2000 mg/L for cyanide concentration, pH=11 and 24hrs cyanidation time. The results showed that highest gold and silver leaching efficiencies were 76.88% and 59.63% in optimum condition. In addition, roasting as a pretreatment in temperature of 700oC in 2 hrs was evaluated. Cyanidation test on the roasted ore in optimized conditions decreased the gold and silver leaching efficiencies reached from 76.88% and 59.63% to 85.97% and 67.57%, respectively. In addition, the antimony extraction increased from 23.73% to 43.10%.
Cueva de Villa Luz (a.k.a. Cueva de las Sardinas) in Tabasco, Mexico, is a stream cave with over a dozen H2S-rich springs rising from the floor. Oxidation of the H2S in the stream results in a abundant, suspended elemental sulfur in the stream, which is white and nearly opaque. Hydrogen sulfide concentrations in the cave atmosphere fluctuate rapidly and often exceed U.S. government tolerance levels. Pulses of elevated carbon monoxide and depleted oxygen levels also occassionally enter the cave. Active speleogenesis occurs in this cave, which is forming in a small block of Lower Cretaceous limestone adjacent to a fault. Atmospheric hydrogen sulfide combines with oxygen and water to form sulfuric acid, probably through both biotic and abiotic reactions. The sulfuric acid dissolves the limestone bedrock and forms gypsum, which is readily removed by active stream flow. In addition, carbon dioxide from the reaction as well as the spring water and cave atmosphere combines with water. The resultant carbonic acid also dissolves the limestone bedrock. A robust and diverse ecosystem thrives within the cave. Abundant, chemoautotrophic microbial colonies are ubiquitous and apparently act as the primary producers to the cave's ecosystem. Microbial veils resembling soda straw stalactites, draperies, and 'u-loops' suspended from the ceiling and walls of the cave produce drops of sulfuric acid with pH values of <0.5-3.0 ±0.1. Copious macroscopic invertebrates, particularly midges and spiders, eat the microbes or the organisms that graze on the microbes. A remarkably dense population of fish, Poecilia mexicana, fill most of the stream. The fish mostly eat bacteria and midges. Participants in an ancient, indigenous Zoque ceremony annually harvest the fish in the spring to provide food during the dry season.
The extraction of copper from chalcopyrite has for centuries been limited to pyrometallurgical methods. Smelting of chalcopyrite is an efficient process but costly both in terms of capital investment, operating costs and environmental compliance. Biological extraction appeared as an appealing alternative. Unfortunately, traditional mesophilic biological extraction methods have met with little success. The chalcopyrite quickly becomes passivated and unacceptable copper extractions are achieved. It was not until the adoption of thermophilic systems that the biological leaching of chalcopyrite became a reality. Several questions remain as to the applicability of the thermophilic system for chalcopyrite; can the system operate auto-thermally; can high extraction rates be achieved; is the process sensitive to mineralogy or grade; and can the precious metals be recovered? GeoBiotics, LLC has embarked on an extensive program to develop the GEOCOAT ® bioleaching system to chalcopyrite ores. This program encompasses mathematical heap modeling, laboratory amenability and column tests, and large scale field trials. The GEOCOAT ® process involves the coating of concentrates onto a suitable substrate, usually barren rock, then stacking the coated material in a conventional heap fashion. The heap is irrigated with acidic solutions containing iron and nutrients while low pressure ambient air is applied at the heap base. To-date, copper extractions in excess of 97% have been achieved in approximately 140 days. Excellent gold extractions have been achieved from the biooxidation residue by cyanidation. Modeling indicates that obtaining thermophilic temperatures within the GEOCOAT ® heap is not a problem. Development is continuing, focusing on the heap design parameters and additional copper concentrates including enargite. Plans are now underway for the first large scale field test in the fall of 2002.
The origin of a rational (scientific) approach to extraction of metal values from ores with the aid of microorganisms (bioleaching) is traced. The removal by microbiological means of ore constituents that interfere with metal extraction (biobeneficiation), an outgrowth from bioleaching, is also traced. © 2004 SDU. All rights reserved.
Acidic biofilms present on cave walls in the sulfidic region of the Frasassi Gorge, Italy, were investigated to determine their microbial composition and their potential role in cave formation and ecosystem functioning. All biofilm samples examined had pH values Thiobacillus and Sulfobacillus. An acid-producing strain of Thiobacillus sp. also was obtained in pure culture. Stable isotope ratio analysis of carbon and nitrogen showed that the wall biofilms are isotopically light, suggesting that in situ chemoautotrophic activity plays an important role in this subsurface ecosystem.
Microbial mats of coexisting bacteria and archaea date back to the early Archaean: many of the major steps in early evolutio probably took place within them. The earliest mats may have formed as biofilms of cooperative chemolithotrophs in hyperthermophil settings, with microbial exploitation of diversifying niches. Anoxygenic photosynthesis using bacteriochlorophyll could hav allowed mats, including green gliding bacteria, to colonize anaerobic shallow–water mesothermophile habitats. Exploitatio of the Calvin–Benson cycle by purple bacteria allowed diversification of microbial mats, with some organisms in more aerobi habitats, while green sulphur bacteria specialized in anaerobic niches. Cyanobacterial evolution led to more complex mat and plankton, allowing widespread colonization of the globe and the creation of further aerobic habitat. Microbial mat structur may reflect this evolutionary development in broad terms, with anaerobic lower levels occupied by archaeal and bacterial respirers fermenters and green bacteria, while the higher levels contain aerobic purple bacteria and are dominated by cyanobacteria.
A possible origin of eukaryotes is from a fusion of symbiotic partners living across a redox boundary in a mat. The geologica record of Archaean mats may be present as isotopic fingerprints: with the presence of cyanobacteria, mats may have had a nearl modern structure as early as 3.5 Ga ago (1 Ga=109 years).
This paper presents an overview of the various methodologies used in the recovery of gold from secondary sources. Gold recovery is interesting due to its vast industrial applications, high market prices and extensively used precious metal, the sanctuary value attributed to gold during international political and economical crises, and the limited resource of this metal may explain the recent increasing gold share value. The state of art in recovery of gold from spent sources by pyrometallurgy; hydrometallurgy; bio-hydrometallurgy techniques is highlighted in this paper. This article also provides an overview of past achievements and present scenario of recovery studies carried out on the use of some promising methods which could serve as an economical means for recovering gold. The present review also highlights the used varieties of leaching, cementing, reducing agents, peeling, coagulants, adsorbents, agglomeration solvents, ion exchange resins and bio-sorbents in real situations and hopes to provide insights into recovery of gold from spent sources. Evaluation of lucrative and environmentally friendly technologies to recover gold from primary and secondary spent sources was made in this study.
The thin-layer leaching process originally conceived and developed for leaching oxide ores has been successfully adapted to bacterial leaching of mixed and secondary sulphide ores. The process is currently being applied at the Socicdad Minera Pudahuel Lo Aguirre Plant. About 3000 ton of ore per day are being processed to produce 14000 ton of high-grade copper cathodes per year, in a closed circuit integrated with SX-EW. Changes in the soluble copper grade of the ore from about 1.8C4 to (I.6% have occurred during the last years, which have been compensated by an equivalent increase in the insoluble copper grade. In addition, ore from satellite ore bodies has resulted in acid consumption variations ranging from 611 to 120 kg H2SO4 per ton of ore. The main sulphide mineralogical species are chatcocite and bornite, with small amounts of chalcopyrite and covellite. An intensive research program in columns and large-scale heaps has been carried out to define the operating conditions which assure adequate bacterial growth and bacterial activity towards the sulphides. Agglomerated ores with 1.7 2.5% Cur and (I.3-0.6%: Cus, with the insoluble copper mainly present as chalcocite bornite, were leached at a flow rate of 0.2 1 min1 mu2 with a SX-Raffinate solution containing (in g-1) 5–10 H2SO4, 2–4 FeT, 1–3 Fe+3, 0.5 Cu, as well as impurities resulting from a closed circuit operation. Copper recoveries of 75 85% CuT were obtained after 180–250 days of total leaching time, depending on the copper grade, the mineralogical composition, and the acid consumption of the ore. Important bacterial activity was detected. About 10 3−105 bacteria ml−1 were measured in effluent solutions. Iron oxidation rates of 7–100μg Fe2+ h−1 g−1, measured from respirometric tests on agglomerated ore, suggest that an adsorbed biomass of about 107-108 bacteria g−1 must also be present. Further applications of the bacterial thin-layer leaching process to Cerro Colorado and Qucbrada Blanca ores in North Chile are being studied.
Bacteria are small, prokaryotic, microorganisms that are ubiquitous in surface and subsurface terrestrial and aquatic habitats. Prokaryotes comprise two Domains (Superkingdoms) in the biological taxonomic hierarchy, the Bacteria and the Archaea. They exhibit remarkable diversity both genetically and metabolically even within the same microenvironment and they are thought to play a major role in the deposition and weathering of minerals in the earth’s crust. The synthesis of minerals by prokaryotes can be grouped into two canonical modes: 1) biologically induced mineralization (BIM) and 2) biologically controlled mineralization (BCM) (Lowenstam 1981; Lowenstam and Weiner 1989). In this chapter, we focus on biologically induced mineralization.
Minerals that form by biologically induced mineralization processes generally nucleate and grow extracellularly as a result of metabolic activity of the organism and subsequent chemical reactions involving metabolic byproducts. In many cases , the organisms secrete one or more metabolic products that react with ions or compounds in the environment resulting in the subsequent deposition of mineral particles. Thus, BIM is a presumably unintended and uncontrolled consequence of metabolic activities. The minerals that form are often characterized by poor crystallinity , broad particle-size distributions, and lack of specific crystal morphologies. In addition , the lack of control over mineral formation often results in poor mineral specificity and/or the inclusion of impurities in the mineral lattice. BIM is, in essence, equivalent to inorganic mineralization under the same environmental conditions and the minerals are therefore likely to have crystallochemical features that are generally indistinguishable from minerals produced by inorganic chemical reactions. In some cases, the metabolic products diffuse away and minerals form from solution. However , bacterial surfaces such as cell walls or polymeric materials (exopolymers) exuded by bacteria, including slimes, sheaths, or biofilms, and even dormant spores, can act as important sites for the adsorption of ions …
My perceptions of the biohydrometallurgical field span four decades and stem from being a professional microbiologist conducting academic research and research for process development and applications. My experiences have given me an appreciation for knowledge gained through fundamental research and the transfer of this knowledge to development of commercial scale applications of microbial processes. The symposia series for international activities in biohydrometallurgy has been a major factor in advancing knowledge and applications for microbial bioleach systems. The first international biohydrometallurgy meeting was held in Braunschweig, Germany in 1977. This was the predecessor for the International Biohydrometallurgy Symposia. As evident from the Symposia, advances in development and applications of biohydrometallurgy technologies follow an evolutionary, rather than revolutionary progression from demonstration of knowledge at the laboratory scale to engineering commercial plants.
Stable carbon and nitrogen isotope data, complemented with other geochemical parameters, were used to identify the sources of organic matter that support the food web of an anchialine cave ecosystem in the northeastern Yucatan Peninsula, Mexico. Anchialine caves, common along tropical karstic and volcanic coastlines, are completely or partially inundated by highly stratified layers of fresh and marine waters. Stable isotope data from the cave fauna, the particulate organic matter (POM) from the cenote pool and from the cave, the forest soil and the cave sediments indicated that at least 3 sources of nutritive organics could support the anchialine food web. These sources were: (1) soil from the overlying forest; (2) freshwater algae from adjoining open water pools; and (3) chemoautotrophic nitrifying bacteria living in the cave. Production of nitrate and a decrease in O-2 along the halocline provided geochemical evidence of nitrification. Stable nitrogen isotope data defined 2 to 2.5 trophic levels in the food web. Furthermore, it was found that troglobitic (cave-limited) species residing in the water column are capable of preferentially feeding on specific organic reservoirs. This study presents the first extensive description of the ecological and biogeochemical relationships of the anchialine cave ecosystem.
Two deep-sea gastropods, Ifremeria nautilei and Alviniconcha hessleri, collected on a hydrothermal site of the North Fiji Basin (Southwestern Pacific) were analysed for polar and neutral lipids using gas-liquid chromatography/mass spectrometry. A high level of monounsaturated fatty acids (MUFAs) and a low level of omega 3 series polyunsaturated fatty acids (PUFAs) indicated that nutrition of both gastropods was related to a food web based mainly on bacterial supply. From differences in MUFA distribution between the 2 gastropods, it appeared that most of the energy requirements of A. hessleri were supplied by sulfur-oxidizing endobacteria whereas I. nautilei probably had a mixotrophic diet based on endogenous as well as exogenous bacteria. Given the relatively high level of linoleic acid, which represented from 2 to 8% of the phospholipid fatty acids, hydrothermal gastropods did not appear to be depleted in omega 6 PUFAs. It was hypothesized that they obtain linoleic acid from a pathway different to that in heterotrophic marine molluscs. In contrast to omega 6 PUFAs, both hydrothermal gastropods appeared to be depleted in omega 3 PUFAs, indicating the limited importance of photosynthesis-based food supplies. Some non-methylene-interrupted dienes, particularly 20:2 omega 9,15 which represented from 9 to 18% of the phospholipid fatty acids, may be synthesized by deep-sea symbiotic molluscs in order to restore the depleted omega 3 PUFAs considered as essential for animals. Gills of both gastropods had high levels of neutral lipids, mainly MUFAs that may have originated from degradation of endobacterial phospholipids.
Larrea tridentata (creosote bush) is a plant that grows abundantly in the desert environment. This desert plant has been found naturally growing in heavy-metal contaminated soils. Previous experiments showed that the inactivated biomass of creosote bush was able to adsorb Cu(II) ions from aqueous solutions. The copper-binding capacity of the bush biomass that grows in heavy-metal uncontaminated soils was higher than the biomass that grows in heavy-metal contaminated soils. Experiments were performed to determine the ability of creosote bush biomass (grown in heavy metal uncontaminated soils) to adsorb Pb(II), Cd(II), Zn(II), Cr(III), Cr(VI), and Ni(II) ions from aqueous solutions. Batch pH profile experiments for these metal ions showed that the metal ion binding was different for every metal tested but increased as the pH was raised from 2.0 to 6.0. The metal ion uptake by the roots, stems, and leaves was quite fast. Binding capacity experiments showed a more significant binding capacity for lead(II) and chromium(III) ions and in general, the leaves bound more metal ions than the stems and roots. A great portion of the metal ions adsorbed by the creosote's roots, stems, and leaves was desorbed by treatment with 0.1 M HCl (up to 99% in some cases). Biomass of creosote bush may prove to be useful to remove and recover metal ions from contaminated waters.
Siliceous precipitates from portions of an 11-m-long core drilled through a relict Yellowstone hot-spring deposit provide valuable insights into the diagenetic facies in this hydrothermal environment. Most of the core consists of relatively low-temperature siliceous sinter containing abundant plant, diatom, and microbial fossilized remains derived from the distal debris apron and discharge channel/flowpath of the hot spring. A few intervals contain stromatolitic horizons analogous to modern, siliceous pool-margin and discharge channel/flowpath facies. Despite the abundance of silicified microbial remains (e.g., silicified stromatolitic horizons as well as individual filamentous microbes, diatoms), distinctive organic biomarkers are not preserved in the core. The apparent lack of distinctive organic biomarkers is attributable to pervasive diagenetic alteration in the presence of high-temperature, chemically reactive fluids. Numerous diagenetic features have been superimposed on the siliceous sinter, especially considering the relatively shallow depths of burial. The uppermost interval (0 to 1.2 m) consists of highly porous siliceous sinter (opal-A) and interbedded travertine. Amorphous manganese oxides and sparry calcite cements are present and are irregularly distributed throughout this interval. Below is a diagenetic facies (4.8 to 5.3 m) that consists of opal-CT and minor chalcedony. The most pervasive diagenetic alteration in the core is the 6.8 to 11.2 m depth interval, where abundant zeolites (mordenite, heulandite), bladed cristobalite lepispheres, chalcedony cements, and calcite veins are present. Judging by the assemblage of plant and diatom remains, most of this pervasive alteration is superimposed on relatively low-temperature siliceous sinters and is likely the result of migration of hot waters through this interval. The paragenesis of all these intervals is very complex, involving numerous episodes of mineral precipitation and dissolution. This diagenetic alteration is facilitated by the porous nature of the siliceous sinter, thermal convection of superheated fluids or steam, strongly oxidizing spring waters, and fluctuating hydrochemical regimes. Rapid dissolution and/or replacement of organic matter indicates that standard morphological means (e.g., petrographic identification of body fossils) may be the best method by which to identify that organisms were previously present in ancient hot-spring accumulations.
Calcite moonmilk, which is a cave deposit formed of calcite crystals and mater, is found in many caves in the Italian Alps. These modern and ancient deposits are formed of fiber calcite crystals, 50-500 nm wide and 1 to > 10 mu m long, and polycrystalline chains that have few crystal defects. Radiocarbon dating indicates that most moonmilk deposits in these caves are fossil and that for most precipitation ceased similar to 6400 cal years BP, at the end of the mid-Holocene Hypsithermal, In the caves of the Italian Alps, the optimal conditions for formation of calcite moonmilk are: (1) a temperature range of 3.5-5.5 degrees C, (2) low discharge volumes of seepage waters that are slightly supersaturated (SICAL = 0.0 to similar to 0.2), and (3) relative humidity that is at or close to 100%. Microbial activity apparently did not play an active role in the formation of the calcite moonmilk, Conditions for moonmilk formation are typically found in caves that are located beneath land surfaces, which are soil covered and support a conifer forest. Precipitation of the fiber calcite crystals apparently involved very slow how of slightly supersaturated fluids. The fact that moonmilk appears to form under a narrow range of environmental conditions means that this cave deposit has potential as a paleoclimatic indicator in high alpine karst areas.
Cave development in the Madison aquifer of the Black Hills has taken place in several stages. Mississippian carbonates fi rst underwent eogenetic (early diagenetic) reactions with interbedded sulfates to form breccias and solution voids. Later sub-aerial exposure allowed oxygenated meteoric water to replace sulfates with calcite and to form karst and small caves. All were later buried by ~2 km of Pennsylvanian– Cretaceous strata. Groundwater fl ow and speleogenesis in the Madison aquifer were renewed by erosional exposure during Laramide uplift. Post-Laramide speleogenesis enlarged paleokarst voids. Most interpretations of this process in the Black Hills invoke rising thermal water, but they fail to account for the cave patterns. Few passages extend downdip below the present water table or updip to outcrops. None reaches the base of the Madison Limestone, and few reach the top. Major caves underlie a thin cover of basal Pennsylvanian–Permian Minnelusa Formation (interbedded quartzarenite and carbonates). Water infi ltrating through the Minnelusa Formation dissolves car-bonates in a nearly closed system, producing low pCO 2 , while recharge directly into Madison outcrops has a much higher pCO 2. Both are at or near calcite saturation when they enter caves, but their mixture is undersaturated. The caves reveal four phases of calcite deposition: eogenetic ferroan calcite (Mis-sissippian replacement of sulfates); white scalenohedra in paleovoids deposited during deep post-Mississippian burial; palisade crusts formed during blockage of springs by Oligocene–Miocene continental sediments; and laminated crusts from late Pleisto-cene water-table fl uctuations. The caves reveal more than 300 m.y. of geologic history and a close relationship to regional geologic events.
Hydrothermal simulation experiments were performed with contemporary sediments from Lake Chapala to assess the source of the lake tars. The precursor-product relationships of the organic compounds were determined for the source sediments and their hydrous pyrolysis products. The pyrolysis products contained major unresolved complex mixtures of branched and cyclic hydrocarbons, low amounts of n-alkanes, dinosterane, gammacerane, and immature and mature hopane biomarkers derived from lacustrine biomass sources. The results support the proposal that the tar manifestations in the lake are not biodegraded petroleum, but were hydrothermally generated from lacustrine organic matter at temperatures not exceeding about 250 °C over brief geological times.
The chalcopyrite bioleaching mechanism was studied to determine its direct or indirect nature. At the same time, a study of possible causes that diminish the dissolution rate and inhibit the attack of this sulphide mineral was carried out. An electrochemical study of the mineral was also performed, which included the elimination or dissolution of possible diffusion barriers formed on the mineral surface.Results of these studies showed that the oxidation state of the dissolved iron (Fe3+) was fundamental to chalcopyrite bioleaching because Fe3+ controlled the relative rate of the oxidation reactions. In addition, the attack of chalcopyrite was controlled by elemental sulphur and intermediate, nonstoichiometric, copper sulphides forming on the chalcopyrite surface, which are less reactive than the original sulphide. Intermediate sulphides caused an important barrier effect at low temperature (35 °C). At higher temperature (68 °C), these intermediate sulphides do not constitute a diffusion barrier due to their dissolution.Microbial attachment to the pyritic phase of the copper ore was related to the dissolution rate of the mineral due to the liberation of Fe2+ after the attack of the pyrite by contact bioleaching.It was concluded that the bioleaching of chalcopyrite concentrate is a cooperative effort involving the simultaneous contact bioleaching of the pyritic phase of the mineral, possibly by an indirect mechanism via thiosulphate, and the indirect bioleaching of chalcopyrite, probably by a mechanism by way of polysulphide and elemental sulphur.
An efficient and simple method for the vacuum impregnation of stone is described, based on the formation of an airtight jacket around the object allowing a vacuum to be applied to the surface and acting as a wick for the consolidating material. /// Une méthode simple et efficace pour l'imprégnation sous vide de la pierre est décrite, basée sur la formation d'une enveloppe étanche à l'air autour de l'objet permettant d'appliquer le vide à la surface et agissant comme une mèche pour le matériel de consolidation. /// Ein wirksames und einfaches Verfahren zur Vakuumimpregnierung von Stein wird beschrieben, das auf der Bildung eines luftdichten Mantels um den Gegenstand basiert, welcher die Aufbringung eines Vakuums auf die Oberfläche erlaubt und als Docht für das Konsolidierungs-material wirkt.
Stromatolites are sedimentary structures produced by the sediment-trapping, binding and/or precipitation activity of microbial communities, in particular by photosynthetic cyanobacteria. They occur today in a wide range of aquatic habitats, both marine and non-marine, from shallow subtidal to supratidal and in lakes, streams and thermal springs. Although uncommon today, stromatolites were widespread in the past, and are the most conspicuous fossils in Precambrian rocks. It has been suggested that microbes played a major role in the development of the banded-iron formations that are widespread in Precambrian rocks, and that they played a crucial role in the formation of atmospheric oxygen. -from Authors
A broth containing the sulfate reducing bacterium Desulfovibrio desulfuricans was used to treat samples of reagent calcium sulfate, gypsum-rock specimens, fragments from a marble monument with a black weathering crust rich in gypsum, and a marble monument with similar crust. Calcite was found to have formed on all treated surfaces suggesting that this microbe has the potential to clean crusted marble monuments whilst also regenerating calcite, the parent mineral of the marble. /// Un bouillon de culture contenant une bactérie réductrice des sulfates, le Desulfovibrio desulfuricans, a été utilisé pour traiter des échantillons de sulfate de calcium, des spécimens de pierre en gypse, des morceaux provenant d'un monument de marbre recouverts d'une croûte noire de vieillissement riche en gypse, et un monument de marbre avec une croûte semblable. Il s'est formé de la calcite sur toutes les surfaces traitées, suggérant que cette bactérie peut nettoyer les monuments de marbre recouverts d'une croûte, tout en régénérant le calcite qui est le principal constituant du marbre. /// Calciumsulfate, gipshaltige Gesteine sowie gipsreiche schwarze Verwitterungskrusten von zwei Denkmälern aus Marmor wurden mit einer Desulfovibrio desulfuricans Kultur in Nährbouillon behandelt. Die Bakterien reduzieren Sulfate. Die Untersuchungen ergaben, daß sich auf allen behandelten Oberflächen Calcit (Calciumcarbonat) gebildet hatte. Dies scheint die Möglichkeit zu eröffnen, mit Hilfe dieser Bakterien Objekte aus Marmor zu reinigen. Der gebildete Calcit ist wiederum der Hauptbestandteil von Marmor.
Lipases, hydrolytic enzymes that act on glycerol-ester bonds, are often used in conservation for their ability to degrade aged oil films, as a non-toxic and often less aggressive alternative to highly polar organic solvents and/or alkaline mixtures. One such enzyme has been used to remove layers of an aged acrylic resin (Paraloid B72) in two instances, a fifteenth-century tempera painting on panel and a nineteenth-century oil painting on canvas. A plausible mechanism for the action of the enzyme is discussed.
A method for oil recovery enhancement by stimulating the growth of indigenous microbial populations in sandstones by nutrient injection was investigated. Incremental oil recovery from the cores ranged from 10–38% of the original oil in place. Volumetric and microscopic sweep efficiency was improved by the microbial selective plugging process. Biogenic gas production accompanied the oil produced from the cores. The combination of stratification correction, gas production, and pressure increase assisted in recovery of previously trapped oil.
Abstract Pyritic stromatolite, a rich pyrite ore, is scattered as reef masses in sedex deposits of the Proterozoic Yanshan rift trough. The pyritic stromatolite consists of a core and alternating concentric rims of light colloidal pyrite and dark organic materials. The concentric rims are cemented together by trichomes highly similar to the trichomic microorganisms inhabiting substantively around the black chimneys on the current sea beds while the core is composed chiefly of groups of thermophilous sulphur bacteria. Biomarkers for the molecules of pyritic stromatolite include pristane, phytane, regular isoprenoids paraffin, methyl-heptadecyl, and so on. This study reveals the existence of methane-yielding bacteria in the pyritic stromatolite and reflects the evolution of thermophilous thallophyta.
Long pulsation of mineralizing thermal solutions venting up along contemporaneous faults in rift troughs contributed greatly not just to the reproduction of thermophilous organisms living around the vents, but to their adsorption of Fe2+ from the solutions in a reducing environment. Pyritic stromatolite constantly took shape through metabolism and reduction of these organisms. Owing to the uneven development of the organic communities close to the vents or the hydrothermal plumes, pyritic stromatolite occurred eventually as scattered reef masses. This mineralizing mechanism may be summarized as the following procedure: flowing of hydrothermal fluids associated with submarine exhalatio→adsorption and metabolism of thermophilous micro-organisms→reduction of organic materials→formation of deposits of pyritic stromatolite.
Natural precipitates of metastable polymorphs of CaCO 3 , such as vaterite, are rarely found in nature however, they have been widely synthesized in laboratory under particular conditions (ie, supersaturated solutions, relative high temperatures, etc.). By SEM and XRD we recognize vaterite spherulites from culturable microbial colonies isolated from hypogean environments. Spherical bodies (~10 w in diameter), probably composed of vaterite, occur in submilimetric microbial mats and biofilms on volcanic substrates (Saint Callixtus Catacombs, Rome, Italy) and karstic caves (Altamira, Candamo, and Tito Bustillo caves, Spain, and Grotta dei Cervi, Italy) where cyanobacteria and actinomycetes are the major microbial components. These particles form beneath dense biofilms, where particular physicochemical conditions are developed by the microbial activity. Natural biofilms seems to generate microenvironments favoring the formation and preservation of metastable CaCO 3 polymorphs. This also shows a major role of microbes in processes of low-temperature alteration of different hypogean rock-substrates.
Modern microbial mats and microbialites are described from basaltic sea caves on the island of Kauai, HI. The mats grow on the ceilings and walls in the photic zone of several open caves where fresh water seeps out of the rock. Scanning (SEM) and transmission electron microscopy (TEM) showed that the active mats are dominated by filamentous and nonfilamentous cyanobacteria in the surface layers and heterotrophic bacteria in deeper layers. Energy dispersive X-ray analysis revealed that copious amounts of extracellular polymeric substances (EPS) are rich in Mg, Si, O, and Ca, likely concentrated from solution. Petrographic microscopy and electron microprobe analysis of the mineralized microbialites showed textures reminiscent of stromatolitic laminations, consisting mainly of alternating calcium carbonate (calcite and aragonite) and magnesium-rich silicate (kerolite). Thin coatings rich in magnesite, hydromagnesite and monohydrocalcite surround the microbialites on the rock surfaces and are likely inorganic in origin. Within the mats, minerals tend to form and concentrate within, or around, dense matrices of EPS. Microenvironments with geochemical conditions favorable for mineral crystallization likely develop in the mats as a result of the mucilaginous extracellular material and the development of bacterial microcolonies. In addition, copious amounts of extracellular polymers bind ions from solution and provide nucleation sites for mineral crystallization and growth. This combination of biological and inorganic processes can explain the occurrence of the secondary minerals in these caves, as well as the stromatolitic textures of the microbialites.
The 16S rDNA genes of an apparently pure culture of a psychrophilic and strict barophilic bacterium (WHB 46) were studied by PCR-mediated amplification and cloning into phage M13 mp18. Sequence analysis of five individual clones revealed the presence of two different 16S rDNA types. The homology value of 90% indicates that culture WHB 46 is actually composed of two closely related species (WHB 46-1 and 46-2). Both strains are members of the γ-subdivision of proteobacteria. Analysis of a sixth clone (WHB 46-1/2) leads to the conclusion that it represents a 16S rDNA hybrid molecule assembled during the PCR reaction. This hypothesis was confirmed by secondary structure analysis of the chimeric rDNA. The appearance of such hybrid molecules point to a potential risk in studies on the diversity of bacterial populations by analysis of rDNA pattern via PCR-mediated amplification because they suggest the existence of organisms that do not actually exist in the sample investigated.
The influence of different concentrations of base metal ions, such as Cu2+, Zn2+ and Fe3+, when present either alone or in different possible binary and ternary combinations in a 9K medium, on the ferrous ion oxidation ability of Thiobacillus ferrooxidans was studied. Levels and degree of toxicity of these ions have been quantified in terms of toxicity index (TI). Copper and zinc tolerant strains of the bacteria were developed through serial subculturing and their activity tested in the presence of the above metal ions in comparison with the behavior of wild unadapted cells under similar conditions. Copper tolerant strains (25 g/L Cu2+) were found to be more efficient in the bioleaching of both copper and zinc concentrates than wild unadapted strains, while zinc tolerant strains (40 g/L Zn2+) exhibited better leaching efficiency only in the bioleaching of sphalerite concentrates. The significance and relevance of multi-metal ion tolerance in Thiobacillus ferrooxidans has been highlighted with respect to bioleaching of sulphide mineral concentrates.
Ribonucleotide sequences were determined for 5S rRNAs purified from 31 type cultures and freshly isolated strains representing species of the eubacterial family Vibrionaceae. These were compared with published 5S rRNA sequences for 11 other species of rRNA superfamily I (Vibrionaceae, Enterobacteriaceae) for the purpose of constructing a phylogenetic taxonomy of the Vibrionaceae. Sequence data were compiled and analyzed, using single, average, and complete linkage clustering methods, resulting in the generation of evolutionary trees. Results of this study indicate a good correlation between the taxonomy of the Vibrionaceae established using conventional and molecular genetic data and evolutionary relationships deduced from 5S rRNA sequences. However, several species, including V. anguillarum, V. pelagius, V. damsela, V. fischeri, V. logei, V. psychroerythrus, V. marinus, and Plesiomonas shigelloides require reconsideration of their taxonomic status, based on the new information obtained in this study. Furthermore, the genus Aeromonas appears to be sufficiently distantly related to the Vibrionaceae to warrant exclusion from the family Vibrionaceae. We propose a restructuring of the family Vibrionaceae along phylogenetic lines, and establishment of two new genera Listonella and Shewanella, and a new family Aeromonadaceae.
Demand for nickel, largely driven by the Chinese stainless steel market, currently exceeds production, causing an unprecedented rise in the price of nickel and renewed interest in bioleaching technology for the processing of low grade nickel sulfide ores and concentrates. Although nickel inhibits bacterial physiological functions such as iron- and sulfur-oxidation, some bacteria adapt readily to high concentrations. In pilot‐scale continuous reactors, mixed microbial populations grew actively over many months in the presence of up to 400 mM nickel (23 g/L). The results of bench-scale test work have been sufficiently encouraging to prompt pilot- and demonstration-scale trials in heaps and agitated tanks in Australia, China, Finland and South Africa in recent years. The first commercial implementation of nickel sulfide heap leaching is likely to be the operation at Talvivaara, Finland.
Jarosite [KFe3(SO4)2(OH)6] is a mineral that is common in acidic, sulphate-rich environments, such as acid sulphate soils derived from pyrite-bearing sediments, weathering zones of sulphide ore deposits and acid mine or acid rock drainage (ARD/AMD) sites. The structure of jarosite is based on linear tetrahedral–octahedral–tetrahedral (T–O–T) sheets, made up from slightly distorted FeO6 octahedra and SO4 tetrahedra. Batch dissolution experiments carried out on synthetic jarosite at pH 2, to mimic environments affected by ARD/AMD, and at pH 8, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)2), suggest first order dissolution kinetics. Both dissolution reactions are incongruent, as revealed by non-ideal dissolution of the parent solids and, in the case of the pH 8 dissolution, because a secondary goethite precipitate forms on the surface of the dissolving jarosite grains. The pH 2 dissolution yields only aqueous K, Fe, and SO4. Aqueous, residual solid, and computational modelling of the jarosite structure and surfaces using the GULP and MARVIN codes, respectively, show for the first time that there is selective dissolution of the A- and T-sites, which contain K and SO4, respectively, relative to Fe, which is located deep within the T–O–T jarosite structure. These results have implications for the chemistry of ARD/AMD waters, and for understanding reaction pathways of ARD/AMD mineral dissolution.
In this paper the possible use of fungicides as a preventive measure during the restoration of works of art is considered.The efficacy of 8 fungicides, already widely experimented with in other sectors, was tested after 28 days, on three types of textiles, commonly used in restoration operations.The interaction between the fungicides and the textiles was evaluated through changes in the degree of reflectance, measured before and after artificial ageing, in the presence and absence of ultraviolet radiation.Finally conclusions are drawn on the possible use during restoration of these fungicides, also taking into consideration their known toxicity factors.
The iron-oxidizing bacterium ThiobaciUus ferrooxidans is the most important microorganism in mineral leaching. It plays the dominant role in bioextractive processes because of its ability to oxidize both iron and reduced sulfur compounds. T. ferrooxidans is also an important microorganism in acid rock/mine drainage, a serious environmental problem. In this article, the current status of this bacterium is described with particular emphasis on the biomining industry.
3 Abstract: In a study to assess the impact of dredging on heavy metal contamination, surface water was monitored for over one year, from December 1997 to December 1998. Samples were collected twice before dredging, in December 1997 and in June 1998, corresponding to dry and raining seasons respectively. Samples were also collected immediately after dredging in July 1998 and were monitored in August, September and December 1998. Samples were collected analysed from five stations within the study area, station 1-5. Station 1 was in the dredged canal, which was originally a side branch of the Warri River tributary. In the Warri River tributary, Station 2 was 500m upstream and Station 3 was 1000m upstream of the mouth of the dredged canal, whilst Stations 4 and 5 were respectively 500m and 1000m downstream of it. Stations 3 and 5 represented the reference situation to which possible dredging effects could be compared. Prior to dredging, the concentration of heavy metals in the surface water samples of Warri River occurred in traces; lead (0.01-0.28 mg l̄ ), 1 zinc (0.04-1.02 mg l̄), copper (0.00-0.17 mg l̄), iron (0.22-0.88 mg l̄), chromium (0.00-0.03 mg l̄) and cadmium 1 1 1 1
The potential contribution of microbial metabolism to the magnetization of sediments has only recently been recognized. In the presence of oxygen, magnetotactic bacteria can form intracellular chains of magnetite while using oxygen or nitrate as the terminal electron acceptor for metabolism1. The production of ultrafine-grained magnetite by magnetotactic bacteria in surficial aerobic sediments may contribute significantly to the natural remanent magnetism of sediments2-4. However, recent studies on iron reduction in anaerobic sediments suggested that bacteria can also generate magnetite in the absence of oxygen5. We report here on a sediment organism, designated GS-15, which produces copious quantities of ultrafine-grained magnetite under anaerobic conditions. GS-15 is not magnetotactic, but reduces amorphic ferric oxide to extracellular magnetite during the reduction of ferric iron as the terminal electron acceptor for organic matter oxidation. This novel metabolism may be the mechanism for the formation of ultrafine-grained magnetite in anaerobic sediments, and couldaccount for the accumulation of magnetite in ancient iron formations and hydrocarbon deposits.
The sequence of events relating to the geologic history of cave development in the Guadalupe Mountains, New Mexico, traces from the Permian to the present. In the Late Permian, the reef, forereef, and backreef units of the Capitan Reef Complex were deposited, and the arrangement, differential dolomitization, jointing, and folding of these stratigraphic units have influenced cave development since that time. Four episodes of karsification occurred in the Guadalupe Mountains: Stage 1 fissure caves (Late Permian) developed primarily along zones of weakness at the reef/backreef contact; Stage 2 sponge work caves (Mesozoic) developed as small interconnected dissolution cavities during limestone mesogenesis; Stage 3 thermal caves (Miocene?)formed by dissolution of hydrothermal water: Stage 4 sulfuric acid caves (Miocene-Pleistocene) formed by H2S-sulfuric acid dissolution derived hypogenically from hydrocarbons. This last episode is reponsible for the large caves in the Guadalupe Mountains containing gypsum blocks/rinds, native sulfur, endellite, alunite, and other deposits related to a sulfuric acid spelcogenetic mechanism.
The sulfuric acid speleogenesis (SAS) model was introduced in the early 1970s from observations of Lower Kane Cave, Wyoming, and was proposed as a cave-enlargement process due to primarily H2S autoxidation to sulfuric acid and subaerial replacement of carbonate by gypsum. Here we present a reexamination of the SAS type locality in which we make use of uniquely applied geochemical and microbiological methods. Little H2S escapes to the cave atmosphere, or is lost by abiotic autoxidation, and instead the primary H2S loss mechanism is by subaqueous sulfur-oxidizing bacterial communities that consume H2S. Filamentous ''Epsilonproteobacteria'' and Gammaproteobacteria, characterized by fluorescence in situ hybridization, colonize carbonate surfaces and generate sulfuric acid as a metabolic byproduct. The bacteria focus carbonate dissolution by locally depressing pH, compared to bulk cave waters near equilibrium or slightly supersaturated with calcite. These findings show that SAS occurs in subaqueous environments and potentially at much greater phreatic depths in carbonate aquifers, thereby offering new insights into the mi- crobial roles in subsurface karstification.
Summary A method for cultivatingSpirulina platensis in domestic raw sewage, coupled with pisciculture and water reclamation in an integrated recycling system, has been standardized. The alga is grown in an indigenously designed open-air pilot production unit consisting of 4 concrete basins with a total surface area of 450 m2. The harvesting and processing methods are based on simple filtration and sun drying. Extensive bench and field experiments have made it possible to produce pure blooms of AfricanSpirulina in sewage, using sodium bicarbonate and nitrate, and employing a fertilizing schedule which replenishes nitrogen withdrawn from the medium by the alga. Although urea and several ammoniacal nitrogen sources have been tried, the best source of protein-inducing nitrogen for mass cultivation ofSpirulina appears to be nitric nitrogen.
Measured profiles of the submerged portion of the steep cliffs that ring Harrington Sound, Bermuda, show that they are undercut as much as 4 to 5 m by a notch whose flat roof coincides closely with the level of extreme low tides. Nips, intertidal indentations with sloping roofs, are not present. Because of the largely subtidal position of the notch, the morphology of the undercut region, and the restricted wave energy, wave cutting is ruled out and bioerosion is proposed as the mechanism of undercutting. Bioerosion is suggested as a term for the removal of consolidated mineral or lithic substrate by the direct action of organisms.
Observations of the emerged and submerged carbonate coastline of Bermuda reveal that organisms of many types alter the exposed rock surface from the upper reaches of the spray zone to depths well below sea level by processes that vary with degree of exposure, tidal range, rock type, organic community, and probably other ecological variables. A series of experiments with common rock‐destroying organisms has been initiated.
Experiments in the laboratory and under natural conditions show that Cliona lampa, a boring sponge, is capable of removing as much as 6 to 7 kg of material from 1 m ² of carbonate substrate in 100 days. This corresponds to an erosion rate of calcarenite of more than 1 cm/year. If previous estimates are correct (that 90% of the boring by C. lampa is mechanical and not chemical), then 5 to 6 kg of fine‐grained carbonate detritus can be supplied from 1 m ² of sponge‐infected substrate in 100 days.
Recognizing microbial imprints in the morphology of calcium carbonate minerals that form in very supersaturated solutions containing a high level of dissolved inorganic carbon (DIC) is challenging. To better define criteria for this purpose, we have analyzed the influence of sulfate-reducing bacterium Desulfovibrio desulfuricans strain G20 on the morphology of calcite in such solutions. G20 does not induce large shifts of pH or alkalinity under these conditions, but its uptake of millimolar sulfate and lactate decreases the number of anhedral crystals and stimulates growth of subhedral spar crystals relative to the abiotic controls. In addition, organic compounds associated with the basal growth medium, purified exopolymeric substances produced by G20 and lypopolysaccharide, stimulate the growth of anhedral crystals and crystals with rounded edges at low supersaturation index (SI) of calcite. The effect of organic compounds is reduced at higher SI, where rhombohedral habits dominate. Our results suggest that the local production and uptake of kinetic inhibitors within microbial biofilms may be an important control on calcite morphology in supersaturated solutions.
Phytokarst is a distinctive landform resulting from a curious type of biologic erosion. Filamentous algae bore their way into limestone to produce black-coated, jagged pinnacles marked by delicate, lacy dissection that lacks any gravitational orientation. Ordinary rainfall-produced karst and littoral karst are characterized by flat-bottomed pans and vertically oriented flutes, thus differing from phytokarst. Algae attack by dissolving calcite preferentially to dolomite.