Search Documents

By A J. Ryan

The Ernest Henry copper-gold Mineral Resource is the major asset heldby Ernest Henry Mining Pty Ltd, comprising A$6.4 billion of containedmetal. The case history presented below describing the evolution andevaluation of this resource generally observes best industry practice and is a good example of effective due diligence in the resource delineation and estimation process. Early reconciliation data from mine production confirms the accuracy and validity of the resource estimate, providing valuable assurance to the mine owners.

Jan 1, 1998

By Roger Favreau, Patrice Favreau

The article reviews the aspects which contribute to the quality of the results from a blast with explosives, namely a good floor, no large blocks, easy mucking, and explains the mechanisms of the blasting process which decide on the quality of these aspects for a given blast method, and how these mechanisms can be simulated from basic principles. It proposes that good fragmentation size distribution can also be important if the rock is going to a crusher, e. g. for the ore in a mine and for the rock excavated in a quarry.

Jan 1, 2012

By Zvi Rivlin

Classical nucleation theory states that in first order phase transformations, such as liquid to solid transition, nucleation of the product phase starts with the formation of small, unstable clusters (embryos). When the thermodynamic barrier to nucleation is overcome, the embryos grow and attain a critical size, beyond which they are stable, i.e. they become nuclei. If nucle- ation does not occur, the parent, liquid phase remains in metastable equilibrium. At temperature lowers, undercooling increase and atomic mobility decreases. The viscosity change in the undercooled liquid may result in the formation of glassy state. As demonstrated in previous papers [I-21, in solidification involving surface nucleation of the product phase, as the case is in rapid quenching by melt-spinning, both nucleation temperature and nucleation time depend upon the number of atoms available at the isothermal surface in contact with the substrate. As a result of the thinness of the melt-spun ribbons, the embryo clusters that form at the freezing temperature may not be supplied by the amount of atoms necessary for their growth to critical nuclei sizes. In such extreme conditions, the liquid does not crystallize, it forms a metallic glass. A numerical simulation method is proposed for the reactions involved in embryo cluster formation and growth, at the atomic level. The simulation enables the caIcuIation of either the nucleation or the glass transition temperatures. Calculations made for the well-known glass forming CuZr and FeB systems afford prediction of the geometrical and thermodynamically conditions necessary for the formation of either crystalline or amorphous ribbons in melt-spun ribbons.

Jan 1, 1994

By Ruichen Ren, Xu Han, Caixia Li, Zengchuan Yue

In this paper, the size-density distribution of coarse middling coking coal (CMCC) with different grinding fineness and flotation concentrates was investigated. Then, the flotation behaviors and liberation characteristics of different size-density fractions in ground CMCC were analyzed, and the different size-density fractions were divided into five categories: mostbeneficial, secondary-beneficial, poorly liberated, insignificant-pollution, and serious-pollution. Based on the content of particles with different liberation characteristics, an evaluation index of the liberation characteristic of ground CMCC, namely, the liberation perfection index (LPI), was proposed. The results indicated that grinding changed the size-density composition of CMCC, which affected the flotation performance. Insufficient grinding and overgrinding were not beneficial to flotation. Insufficient grinding caused a higher content of poorly liberated particles and a lower content of most-beneficial particles. Overgrinding increased the content of serious-pollution particles and reduced the content of most-beneficial particles. The size order of the LPI values of different ground CMCC was consistent with the flotation efficiency, and the LPI values of the other two similar samples were overall positively correlated with their flotation performance, suggesting that the method is universal.

Feb 14, 2023

By A Gerson, S Miller, R Smart, J Thomas

Environmental Geochemistry International (EGi) and the Ian Wark Research Institute (IWRI) collaborated in a three-year Australian Minerals Industry Research Association (AMIRA) research project (Project Number P387A) focussed on the prediction and kinetic control of acid mine drainage. As part of this project, single addition, and sequential net acid generation (NAG) testing was carried out on sulfide mineral samples. The test samples comprised a range of synthetic waste materials prepared using a quartz bulk and controlled quantities of the commonly occurring sulfide minerals; pyrite (FeS2), pyrrhotite (Fe7S8), arsenopyrite (AsFeS), chalcopyrite (CuFeS2), chalcocite (Cu2S), covellite (CuS), bornite (Cu5FeS4), galena (PbS) and sphalerite (ZnS). NAG test results clearly show that there are significant differences between the acid forming potential of sulfide minerals. The NAG test results for each mineral were compared with theoretical acidity values (NAPP*). The NAPP* calculation was based on stoichiometric oxidation reactions assumed for each of the sulfide minerals. Sequential NAG values for pyrite corresponds closely to predicted NAPP* values, confirming the assumption that pyrite oxidation occurs according to the stoichiometry assumed. For the pyrite sample with 5 wt per cent S, two NAG stages were sufficient for all of the sulfur to be released to solution. Since sulfides in waste materials will generally be dominated by pyrite, results also confirm the validity of including NAG testing for ARD evaluation of most waste rock. NAG testing confirms that of the sulfide minerals examined, only pyrite, pyrrhotite, arsenopyrite and chalcopyrite are acid producing, ie able to produce leachate with a pH less than 4.5. In the case of sphalerite, galena, bornite, chalcocite and covellite the pH of the final NAG solution was greater than 4.5. The significant differences between the acid forming potential of different sulfide minerals could lead to overestimation of acid producing potentials based on NAPP values calculated from total per cent S alone, ie assuming all S is present as pyrite. The oxidation of galena during the NAG test resulted in the consumption of acid. The examination of the galena surface by X-ray photoelectron spectroscopy (XPS) after oxidation in peroxide solution indicated the presence of polysulfide. The reaction of sulfide to polysulfide is acid consuming, thus explaining the net acid consuming behaviour of galena in the NAG test. This reaction pathway may provide a possible explanation for the lower than expected acid production observed for some of the other sulfide minerals examined.

Jan 1, 2003

By J. A. S. Tenorio, K. S. Barros, D. C. R. Espinosa

Considering the risks involving the use of cyanide, other complexing agents have been evaluated for the treatment by electrodialysis of the effluent of brass electrodeposition and among them, EDTA is interesting since it has been already tested for many years to separate ions. The main objective of the present paper was to evaluate the occurrence of fouling and scaling on the surface of the anion-exchange membrane HDX 200 by the construction of chronopotentiometric curves and speciation diagrams in different conditions (pH between 10–12 and proportion of cupric ions of 30%, 50%, 70%). According to the results, the chronopotentiometric curves did not show additional inflexion points typical for the cases which occurs fouling and scaling for the pH values evaluated, which is in accordance with the speciation diagrams of the solutions constructed with the aid of Hydra-Medusa software. Hence, the pH and the proportion of cupric ions did not show influence on the curves behavior.

Mar 1, 2018

By U. Atici, R. Comakli

"Understanding rock properties is of vital importance in mining and civil engineering. Rock properties are generally determined through laboratory tests, which require a large number of uniformly shaped samples and technicians who use indirect methods to determine rock properties. The texture coefficient (TC), which represents various textural parameters including the size, shape, orientation, and relative proportions of grains and the matrix, is an efficient means for indirectly evaluating the mechanical behaviour of rocks. In this study, 12 different rocks (ten granites, one diorite, and one gabbro) were collected and their engineering properties. including specific gravity, porosity, P- and S-wave velocities, Schmidt rebound hardness, uniaxial compressive strength, and elasticity modulus, were investigated. Relationships between TC and these measured properties were assessed. Statistically significant (at the 95% confidence level) correlations were found between the TC and compressive strength, elasticity modulus, sound velocity (both compression and shear waves for dry and saturated samples), but no significant correlation was found with Schmidt rebound hardness. The results suggest that it is possible to use the relationships between TC and the mechanical properties of rocks in rock classification. IntroductionIn every aspect of rock engineering, knowing rock properties is essential for determining and predicting the behaviour of rocks and rock masses. Mechanical properties of rocks are important parameters in mining, geology, and engineering, and they are affected by textural characteristics such as grain size, grain shape, cement type, degree of cementation, mineral content, and the ratio of the grain area to the matrix area. The effects of textural properties on the physical and mechanical properties of rocks have been investigated for a long time, and previous studies revealed close relationships between single parameters related to rock texture and mechanical properties of rocks (Akesson et al. 2001; Gunsallus and Kulhawy 1984; Merriam, Rieke, and Kim, 1970: Onodera and Kumara 1980; Prikryl 2006; Ulusay, Tureli, and Bider, 1994; Tugrul and Zarif 1998). Rock properties are usually determined using mechanical tests, which require uniformly shaped and relatively large samples. However, it is not always possible to obtain such samples. Furthermore, rocks with similar textural and structural properties may exhibit different mechanical behaviour. Howarth and Rowlands (1987) developed a texture coefficient (TC) that expresses all the main textural parameters of a rock in a single dimensionless quantity based primarily on statistical assessment. The TC makes it possible to understand the effects of a rock’s textural properties on its mechanical properties using thin sections instead of large, uniform samples. Ersoy and Waller (1995) investigated the relationship between strength and TC for limestone, sandstone, and siltstone; they also examined the effect of rock properties and TC on drilling performance. Ozturk, Nasuf, and Bilgin (2004) explored the relationship between rock quality and TC by evaluating the uniaxial compressive strength (UCS) values of limestone, basaltic andesite, and tuff. Gupta and Sharma (2012) evaluated TCs as well as the petrophysical and mechanical properties of quartzite from the lower and higher Himalayas and found a strong relationship between TC and UCS. Similarly, Ozcelik, Bayram, and Yasitli (2013) investigated the relationship between TC and various parameters in marble by applying the statistical analyses developed by Ozturk, Nasuf, and Kahraman (2014)."

Jan 1, 2019

By Y. T. M. Ocsa, V. O. Tenorio

This research is the result of a geotechnical study carried out in a natural slope in an Open Pit mine in Southern Peru, highlighting earthquakes as an important cause of instability within the case study presented. This leads to analyze the stability of a slope, according to the safety factor and thus consider a future construction in its environment according to the identified requirements. There are known disasters at national and international level that involve human lives because of the lack of analysis of slope stability conditions, which based on the results will allow to control and to take adequate corrective measures. These mass movements are classified whether they are soils or rocks, considering the mechanism and type of rupture, as well as the presence of water, the speed and magnitude of the movement. The movement problems are due to factors of inherent nature and constitute a reason to perform a calculation study to analyze and estimate the safety factor of each of the evaluated cases

Mar 2, 2022

By D. Hinton, M. McCawley, R. C. Lantz, F. Pisano, C. Stanley

"INTRODUCTION Aerosols (5 um have not been shown to be consistently generated and characterized in inhalation chambers. Particle deposition in the lungs however may occur with particles as large as 25 um(1). Therefore, in order to closely simulate the atmosphere of an underground coal mine where the distribution is bimodal, with modes at S and 15 um (2), particles much greater than <1 um must be characterized for uniform mixing and size distribution within these chambers. The Hazelton Animal Exposure Chamber has been chosen because it has been best characterized for smaller particles (<1 um) (3), and is the major type used by most inhalation toxicology institutes such as Lovelace Inhalation Toxicology Institute and Battelle Northwest Laboratory.BACKGROUNDPreviously published studies on the inhalation of solid aerosols have attempted to characterize the distrition of particles of <2 um in diameter. There are no published reports of extensive work characterizing either the size distribution of particles <1 um or the concentration throughout the exposure chamber (Table 1).Table 1 shows the variability and sizes of several aerosols <1 um in diameter used in five previous chamber studies.Discussion of Previous StudiesThe study done by Bauermash, Bryan, Dickinson, and Burke (4)stated two major concerns in the development of the 6.5 ft. diameter chamber. The first was that a quantity of animals could be exposed to the same concentration regardless of the location of the animal, and second was that the chamber could be easily cleaned and decontaminated. The solution to the first concern required a circular chamber with the contamination air entering the chamber somewhere along the central axis. The animals could then be changed during exposure time so that each animal was exposed throughout the total volume."

Jun 1, 1988

By Hector Carreon

During fretting, high points or asperities of the mating surfaces adhere to each other and small particles are pulled out, leaving minute, shallow pits and powdery debris. Sometimes these surface conditions are neglected, but they are important in some application such as the aerospace industry. In this research work, non-contacting and contacting thermoelectric power techniques are performed in fretted 7075-T6 and Ti-6Al-4V samples. It has been found that the contacting and non-contacting thermoelectric power measurements are associated directly with the subtle material variations such as work hardening and residual stresses due to plastic deformation produced in the fretting zone but surface topography. Therefore, both techniques could be used for a global characterization of the most relevant fretting induced effects. Potential of these techniques to monitor subsurface changes in other severe surface plastic deformation processes are clearly envisaged.

Jan 1, 2015

This study explores two evolving 3D surveying technologies, photogrammetry and laser scanning, and applies them to deformation monitoring of rock faces and mine highwalls. A quantitative analysis focused on 3D coordinate determination is performed. Furthermore, a qualitative assessment directed at the practicality and viability of each system operating near a rock face or in a mining operation is undertaken to reveal one systemÆs deficiencies over the other. Two photogrammetric and four laser scanning surveys aimed at optimising accuracy and precision within a short period of data acquisition are conducted on the rock face at Organ Pipes National Park, Keilor, Victoria. The accuracy and repeatability of each survey is determined using a combination of iWitness photogrammetric, and Cyclone laser scanning software. The 3D coordinates of targets placed on the rock face are determined by triangulation and resection principles within a bundle adjustment. The coordinates determined by each system are then compared in a 3D transformation. Controlled deformation conditions are established to determine the precision to which each system can detect movement in the rock face. An object of known dimensions is placed on the rock face to simulate deformation. The relative orientation of images taken for the pre- and post-deformation photogrammetric surveys provide an overall 3D point accuracy of 1.255 mm and 1.804 mm respectively. A 3D transformation shows discrepancies of less than ¦22 mm (RMS) between the geometry of the photogrammetric and laser scanning models. Both systems are able to detect the simulated deformation to a precision of 50 mm. This work also identifies how to obtain millimetre accuracy for 3D coordinate determination of rock faces, thereby providing a quality data set for surveyors, geotechnical engineers and mine geologists. Photogrammetry is shown to be a mobile, time and cost-effective technique that is more amenable to mining operations than terrestrial laser scanning. However, both systems demonstrate that they are capable of detecting movements that may lead to failures in the rock face, and possibly endangering human life. The implications are significant for surveyors, geotechnical engineers and mine geologists working in mining operations where enhanced safety conditions, increased productivity and lower operational costs are important considerations.

Jan 1, 2009

By Mary Cunningham

The EPA and DOE have collaborated on a series of studies to evaluate the effectiveness of treatment technologies at stabilizing bulk elemental mercury and wastes containing high concentrations (i.e., with greater than 260 mglkg total mercury) and multiple forms of mercury. The data from these treatment demonstrations are intended to help EPA to determine if regulatory revisions to allow a stabilization alternative for high-mercury subcategory wastes are warranted. In addition to mercury-contaminated wastes, the disposal of bulk elemental mercury is of concern because of the excess quantity of mercury in the Defense Logistics Agency (DLA) stockpile, as well as other potential sources of excess elemental mercury. The studies evaluated the effectiveness of several technologies at: I) stabilization of mercury in a "hard-to-treat" matrix; and 2) conversion of elemental mercury into a stable waste form for disposal. A surrogate waste was designed for the study on high-mercury wastes, which included an organic form of mercury, elemental mercury, and several mercury salts in an inorganic matrix. The surrogate waste and the bulk elemental mercury were treated by the vendors, and the treated waste forms evaluated for mercury Icachability, using both the TCLP and an automated, constant-pH leaching protocol. Constant pH leaching was conducted at pH 2,4,6,8 10 and 12 for 14 days at each pH. The leaching data demonstrate that the stability of the mercury in three treated waste forms varies widely across the pH range tested. Clearly, the stability of mercury in these treated waste forms will be highly dependant on the disposal conditions. The combination of site-specific disposal conditions and appropriate treatment technology must be considered as decisions are made about disposal of high-mercury wastes.

Jan 1, 2003

By Moonkyung Chung

Static pile load tests were performed in order to evaluate bearing capacities and mechanical behaviors of three different pile types: (1) steel-concrete composite drilled shaft with rebar reinforcements inside the concrete, (2) steel-concrete composite drilled shaft without rebar, and (3) conventional drilled shaft (reinforcement concrete pile). The material elastic moduli obtained from pile load tests of steel-concrete composite drilled shafts with and without rebar reinforcement were found out to be similar. On the other hand, the elastic modulus of steel-concrete composite drilled shafts is almost twice as high as that of the conventional drilled shaft. The ultimate strengths of the steel-concrete composite drilled shaft with rebar, the steel-concrete composite drilled shaft without rebar, and the conventional drilled shaft were 9,810, 7,848, and 4,414kN, respectively. The results of these load tests reveal that the ultimate strengths of the steel-concrete composite drilled shaft with reinforcement and that without reinforcement are 2.22 times and 1.78 times greater that that of the drilled shaft. The structural failures of the steel-concrete composite drilled shafts occurred either at the boundary between tip of steel casing and rock-socketed concrete.

Jan 1, 2010

By W. J. Adams

It is recognized that within life cycle assessment that the eco-toxicity potentials (TPs) derived for metals require additional research to improve their reliability. Current models used to develop TPs do not include important fate process for metals such as speciation and bioavailability. Toxicity potentials are standard values used in LCA to enable a comparison of potential toxic impacts between substances. Huijbrechts (2001) calculated toxicity potentials for 181 substances utilizing the USES model for six impact categories, i.e. freshwater aquatic ecotoxicity, marine aquatic ecotoxicity, freshwater sediment ecotoxicity, marine sediment ecotoxicity, terrestrial ecotoxicity and human toxicity (not considered here). Marine ecotox potential for metals is typically high using this approach, whereas most open ocean metal concentrations are very low. A sensitivity analysis of the USES-LCA model was undertaken using copper as an example. Results indicate: fate processes on the global scale are driving the marine water and sediment TPs for copper most; the second most important fate parameter is sedimentation from the water and burial in deep sediment layers; inclusion of speciation and bio-availability processes would be very beneficial; more accurate estimates of input parameters should be used, and the PNECwater and PNECsediment and all partition coefficients for metals should be updated in the model.

Jan 1, 2007

By Taghi Sherizadeh, Kutay E. Karadeniz, Dogukan Guner, Samuel Nowak

Underground mining environments bring occupational health and safety issues with some severe dangers such as mine disasters like explosions. During such events, miners might escape using main access openings, or find a safe haven like refuge alternatives (RAs) to wait and be rescued and evacuated to the surface. In this paper, RAs are explained with their early and current applications. A classification as permanent and portable is explained depending on the conditions and their abilities. This classification is followed by the utilization and survivability of RAs with the requirements and recommendations of the main mining countries. Based on the utilization and survivability constraints, basic human requirements, waiting for a rescue team, and the required physical specifications of RAs during the events are analyzed in detail for various countries with their regulations. Among these, the specification, resistance to the explosion, is discussed in particular, and the studies in the literature are examined in terms of structural deformation. The highest deformed zones, the beneficiation of reinforcing steel components such as stiffeners, and the simulation approaches are investigated through this review.

Sep 24, 2022

By H. D. Yu

In this paper, an evaluation about the process mineralogy of the rich iron mine in Mongolia with comprehensive methods is given; this provides foundation of the comprehensive recovery of iron and cobalt in the ore. The research shows that the iron?s grade is 61.23%, Co?s grade is 0.02%, the ore is rich iron ore and its Co content also reaches border mining grade. For the ore, if want get high grade iron concentrate powder, must identify the mineral composition and the occurrence of iron and take into ac-count the recovery of Co content as associated resources. Chemical phase analysis results show that 86.35% of iron exists in magnetite, which means that the theoretical recovery ratio of iron is close to 86%. Minerals spectrum analysis confirmed that the magnetite containing a small amount of Mg, Al, and other impurities, the actual iron minerals to 70.28%, which means that theoretically iron grade iron concentrate only close to 70.28%. Based on the result of iron chemical phase analysis, by investigating the liberation of sulfide minerals and gangue, the recovery index of iron can be forecasted, when grinding fineness is 35%, 45%, 55% and 65% bellow 0.074mm,theoretical content of Fe in iron concentrate separately is 67.71%,67.88%,68.78%,and 69.43%,accordingly the theoretical recovery of Fe is 87.38%,87.05%,86.92% and 86.63%. From the perspective of process mineralogy, the forecast mineral beneficiation indicators show that the ore is easy sorting ore, iron processing operations have higher recovery rate, but wants sorting of high-grade iron ore concentrate still need appropriate grinding fineness. Furthermore, associated element Co, existing mostly in pyrite and pyrrhotite, is valuable in the ore. Pyrite and pyrrhotite have ideal liberation under grinding, so cobalt can be easily enriched in sulfide concentrate.

Jan 1, 2014

By Joseph C. Buchen

IN principle, production of salt from sea water is a simple operation. Sea water is trapped in ponds, the sun and wind cause evaporation of the water, and what is left is principally salt. Commercial production of solar salt, however, requires a careful consideration of many factors. Obviously, sufficient evaporation must take place throughout the making season to produce an economically adequate crop. Other factors are density of soil, contour of ground, height of ground above sea level, minimum dilution from fresh-water streams, and distance from market. Unfortunately, in the United States the localities of greatest evaporation, allowing for the other factors, are not the most suitable for the manufacture of sea salt by solar evaporation. The south end of San Francisco Bay most

Jan 1, 1937

By CRO CRO

Elk Valley Coal?s Cheviot Project is located in the Alberta foothills south of the town of Hinton. The mine has been in operation now for the 3 years. The start up and subsequent operation of the Cheviot project has been directly influenced by the Cardinal River Mine. As the Cardinal River Mine was winding down due to reserve depletion in 2004, the price of seaborne traded metallurgical coal jumped to record levels and customers began aggressively seeking new sources of supply. Several months later, the owners of Elk Valley Coal decided to begin mining at the Cheviot mining area, extending the life of the area?s operations by over 25 years. The Cheviot Project had been delayed by low coal prices, ownership changes and a complicated and lengthy regulatory process fueled in large measure by stiff opposition from a number of major environmental organizations. Chief to the startup of the project was the construction of a 23-kilometer-long haul road that would connect the new coal measures to the existing Cardinal River processing and rail facilities. Construction of this road was completed with the first coal truck making its first trip in October 2004. This paper will look at some of original assumptions, the actual mining experiences and the lessons that were learned while moving from the drawing board to the current development as it exists today.

May 1, 2007

By E. Naesgaard, Brian E. Hall, A. Amini, Advanced Geosolutions, A. Azizian

"A 2 km section of the Evergreen Line Rapid Transit Project is supported on improved ground consisting of cement deep soil mix (CDSM) panels because of highly variable and challenging soil conditions, especially the potential for seismic liquefaction-induced lateral spreading. CDSM was used as an alternative approach in place of driven piles for reducing the seismic lateral spreading displacements. An additional significant aspect of obtaining owner acceptance for CDSM was demonstrating that both seismic and non-seismic performance would equal or exceed that of using driven piles. It was recognized that, to demonstrate adherence to the seismic performance requirements, seismic design should be based on dynamic analyses (using FLAC) to estimate likely displacements and stresses/strains in the CDSM panels. One focus of the analyses was investigating the potential for cracking of the CDSM panels and the resulting displacements. This was simulated using the Ubiquitous-Joint and UBCSAND constitutive models.INTRODUCTIONThe Evergreen Line Rapid Transit Project (ELRT) is an 11 km extension of the SkyTrain system through Burnaby, Coquitlam and Port Moody in the Lower Mainland of British Columbia, Canada (Figure 1). The ELRT project is being delivered through a Design/Build/Finance model by Evergreen Rapid Transit Construction (EGRT), an SNC-Lavalin Inc. company, to the Province of British Columbia (the Province).This paper discusses the ground improvement design for a 2 km section of the alignment through Port Moody, a historic city at the head of Burrard Inlet. The alignment is located in a right-of-way of restricted width with many pinch points close to residential and commercial properties, and directly adjacent to the Canadian Pacific Railway (CPR) mainline tracks. The ground slopes from south to north across the alignment towards Burrard Inlet at inclinations of up to about 6%. Design and construction of the Port Moody section was subcontracted to SNC-Lavalin Constructors (Western) Inc. (SLCW) and SNCLavalin/ Graham Construction Joint Venture (SGJV). Construction included single- and double-track slab guideways, pocket track (where up to four to six tracks were present), and Moody Centre Station."

Jan 1, 2015

By N. S. Dalal, X. Shi

"Electron spin resonance (ESR) spectroscopy has been employed to· examine the role of tetraperoxochromate( V) ions (Cro:-) and other Cr(V) species in the generation of hydroxyl (OH) radicals in the reaction of Cr(VI) with H2O 2 in biological media. In contrast to earlier suggestions, the present ESR studies using crystalline K3CrO8 as a source of Cro:- show that decomposition of Cro:- in water or in H2O 2 does not generate significant amounts of OH radicals. Addition of NADH to a solution containing Cro:- yields a Cr(V)-NADH complex, which readily reacts with H2O 2 to generate OH radicals. Similar results obtained from several other biological reductants, including vitamin B2 , indicate that a vacant coordination site on a Cr(V) complex facilitates its reaction with H2O 2 to generate ""OH radicals. We thus suggest that in biological media, reaction [3] instead of [1] or [2] is the major pathway for the OH radical generation: While the carcinogenic potential of Cr(Vl)-based compounds has been well established via epidemiologic and animal studies (1), the underlying biochemical mechanism is still not well understood (2). In a recent development, however, Kawanishi et al. (3) have reported that hydroxyl (OH)2 radicals might be the key species in the mechanism of Cr(VI) toxicity. As to the mechanism of the ""OH radical formation they suggest that Cr(VI) reacts with cellular hydrogen peroxide (H2O 2) to form the tetraperoxochromate(V) (Crog-) ions, which decompose to produce hydroxyl radicals. It was also suggested (3) that the ""OH radicals thus produced cause genotoxicity via DNA base modification and deoxyribose phosphate backbone alterations. More recently Aiyar et al. (4) reported the detection of OH radicals in the reaction of Cr(VI) with H2O 2 in biological media, including the reaction of ""OH radicals with deoxyguanosine to generate 8-hydroxydeoxyguanosine adducts, confirming that ""OH radicals could indeed play a significant role in the mechanism of Cr(VI) toxicity. However, the mechanism for the ""OH generation was not clarified, although the role of Crog- ions as possible precursors was mentioned, somewhat along the lines suggested by Kawanishi et al. (3). The possibility of the participation of Crog- in the ""OH generation has also been indicated by Sugiyama et al. (5), since they mention that vitamin B2 enhances the formation of""OH radicals in the reaction of Cr(VI) with H2O 2 because of the generation of Crog- in the reaction."

Jan 1, 1990