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By Robert Bissonette, Samir Sbai

A critical component of implementing autonomous systems is the ability to use information from a robust sensory and information system to make sound, predictable, and repeatable decisions to assure safety. This means that any such system would need to evaluate what objects (people, equipment, boulders, etc.) of interest exist in that environment (with relevant data about identity, trajectory, characteristics, etc.), project a future continuum of those objects (including considerations for variabilities), and make control intervention choices to minimize risk due to exposures in the present operational area. The components of an overall system would include: a) sensor and data fusion, b) probability projection of future states, c) generation and evaluation of alternate futures, and d) implementation of best course of action to reduce risk. The National Institute for Occupational Safety and Health (NIOSH) Spokane Mining Research Division (SMRD) is studying this framework for applications for autonomous mining equipment. This paper focuses on using information from the sensor fusion engine to generate a continuous projection of future and alternate states (b and c above) incorporating the factors of confidence, accuracy, tolerance, and other variabilities. We refer to this as Machine Situational Awareness (MSA).

Jun 25, 2023

By Akira Yazawa

In the field of pyrometallurgy, the equilibrium evaluation has recently become easy by use of thermodynamic software, but it is strongly desired to estimate the amounts of non-equilibrium minor components to simulate practical processes. However, simple physico-chemical technique can not be applied to evaluate practical non-equilibrium components for many reasons. As an engineering solution for postulated equilibrium system, the activity coefficient is modified and introduced as the simulation parameter referred to as the "adjustment coefficient." This modified thermodynamic calculations were adopted to various sulfide roasting processes where many solid phases are participating and the system is not necessarily in equilibrium. Successful simulation was realized by assigning suitable adjustment coefficients for minor components which form a pseudo solid solution in the calcine. Some examples from sulfation roasting and dearsenizing roasting were discussed. In the smelting system, the loss of copper in slag is caused by equilibrium and non- equilibrium reasons, that is, chemical dissolution and entrainment of copper in slag. The total copper content of slag was simulated by use of the adjustment coefficient for entrained copper.

Jan 1, 1998

By E. Sharifi, B. Komishke, R. Heffel, D. Schwartz

"The oil sands resources in Canada are one of the world’s largest hydrocarbon deposits. Processing of oil sands uses hot water to extract bitumen. The process generates tailings slurry that must be settled for final deposition. The tailings contain fine material, with poor water release characteristics which makes water recovery challenging. Polymer flocculants are added to assist in settling and dewatering the fine tailings. The amount of polymer addition is dependent on tailings characteristics, including the particle size distribution (PSD). If the PSD of the tailings is unknown, an excess amount of polymer needs to be added in the dewatering stage to flocculate the particles. Over flocculation also has a detrimental effect on the water release characteristics. Measuring the particle size distribution using an on-line analyzer could have major benefits over common laboratory methods as it provides online and fast insight into the process enabling the operators to implement required changes to minimize the reagent consumption, while achieving optimal flocculation. Online measurement of PSD using laser diffraction has long been used in base metals beneficiation processes. A series of test work using Outotec PSI500® particle size analyzer on oil sands samples from different operations have been conducted. Tests were performed by recirculating the slurry in closed circuit to simulate real plant conditions. This paper presents a summary of the results.INTRODUCTION Canada’s oil sands are the third largest reserves of crude oil in the world, with an estimated 165.4 billion barrels of recoverable oil (Government of Alberta 2016). Oil sands are a mixture of sand, water, clay and bitumen. Bitumen is a form of oil that is too heavy or thick to flow or be pumped without being diluted or heated. About 20% of bitumen reserves are close enough to surface to be mined. In mining methods, oil sand is transported from an open pit mine to the processing plant and bitumen is separated from solids and water. The separation process involves ore preparation, such as addition of hot water, steam and caustic (NaOH), followed by gravity separation and froth treatment (Masliyah et al. 2004). A general scheme of the extraction process is presented in Figure 1."

Jan 1, 2018

By Rodrigo Fina Ferreira, Jacek Kolacz, Luciana Gois, Neymayer Pereira Lima

The recent developments on the sensor detectors together with the higher capacity of the machines, due the high-speed computing recent advances, have made possible extending the application in the mining industry. The use of x-ray fluorescence, x-ray transmission and radiometric sensor based sorting can selectively remove gangue minerals in different size fractions for different minerals. This paper summarizes the potential application of SBS for an iron ore in three size fractions aiming to increase the %Fe after the removal of particles with main gangue minerals associated. Pilot plant tests were carried out with samples of iron ore in different size fractions and different content of hematite and gangues. The use of x-ray transmission sensor showed the possibility to increase the %Fe from about 63% to above 68% for particles below 80mm and 45mm, after the removal of low density particles. The presence of fines on the feed affected the performance of the SBS X-rays transmission machine, especially for the fine fraction feed. The mineralogical determination, carried out to know the association between hematite and gangue minerals, and the density of the particles on the feed, can be used to preview the quality of products of the x-transmission sorting process.

Oct 3, 2019

By Pedro A. Netto, Giulio R. Altoé, Sergio N. Monteiro, Ygor M. Moraes, Frederico M. Margem, Gabriel O. Glória

Since environmental issues are becoming more and more important Worldwide. Nowadays, Natural fibers are been used to substitute the synthetic ones. Although PALF fiber is an important natural fiber and its mechanical Properties surpass in various aspects some other lignocelluloses fibers, such few studies have been conducted with the fiber obtained from leaf of PALF plant. In order to better evaluate the mechanical properties and possible applications, this paper aims to improve the elastic modulus of the PALF fiber by Weibull statistics, by evaluating their mechanicals properties and possible applications. The fibers were divided in diameter intervals and the tensile strength and elasticity modulus were measured in each range. The fractured surface was examined using scanning electron microscopy. The results, interpreted by the Weibull statistical method, showed a correlation between the fiber elastic modulus and its diameter.

Jan 1, 2015

By D. Antonov

The physical and mechanical properties of coal play a important role in the planing and design of coal mines. However, due to the complexity conditions in situ and the influence of unknown factors, it is hard for people to evaluate the physical and mechanical properties of coal directly. In this research, uniaxial compressive stress was used to change the attribute of coal samples, and the ultrasonic measure technique was used to evaluate the physical and mechanical properties of coal. The results of laboratory test showed that there was a strong relation between uniaxial stress and velocity of ultrasonic wave. Sensitivity analysis with numerical simulation was used to define the relation between the physical-mechanical parameters of coal and ultrasonoc wave. With the dynamic analysis module of FLAC, three elastic and plastic models were built to model the coal samples. The modeling parameters were changed pro rata, and the correlation of coal and ultrasonic wave properties were summarized and presented. The result from this research will be base for further analysis of caving behavior of coal.

Jan 1, 2010

By L. Yuan, J. H. Rowland, R. A. Thomas, D. Bahrami

Blasting is the main method of production in many non-coal underground mining operations and produces multiple toxic gases as a result. The Mine Safety and Health Administration (MSHA) requires mine operators to measure the level of toxic gases in mines as frequently as necessary to ensure they are below regulatory safety limits. The current practice uses portable gas monitors to check the concentrations of toxic gases after a fixed post-blast time. This paper studies the application of a gas monitoring system in the return entry of a limestone mine to determine a safe re-entry time. The National Institute for Occupational Safety and Health (NIOSH) conducted such a monitoring program in a limestone mine from September 2016 through May 2018. NIOSH/PMRD (Pittsburgh Mining Research Division) is endeavoring to develop workplace solutions to improve detection of and reduce the risk of hazardous conditions. This study showed that the use of gas monitoring in the return air can be a useful tool at the mine operator’s disposal to detect and reduce the risk of hazardous conditions and also to reliably estimate the re-entry time. INTRODUCTION Underground miners are at risk of overexposure to toxic gases from various sources. Production blasting operations using explosives in underground mines are a source of multiple toxic gases that could be harmful and even fatal to humans if prolonged exposure occurs beyond the safe limits. According to Code of Federal Regulations, Title 30, Part 57.5002 [1], metal and nonmetal mine operators must conduct gas, mist, and fume measurements as frequently as necessary to determine the adequacy of control measures to protect miners from overexposure to harmful gases. MSHA will inspect mine operators’ activities to verify the evidence of such measurements [2,3]. Continuous gas monitoring in the return air is an effective way to make sure that toxic gas concentrations at the working areas are kept below the regulatory limits before the return of miners. Toxic gases can enter the mine atmosphere from different operations, such as welding, combustion, and blasting. The main gases produced from blasting are carbon monoxide (CO), carbon dioxide (CO2), nitric oxide (NO), and nitrogen dioxide (NO2). Other gases are produced in small amounts and, therefore, were not considered for this study. Related regulatory and recommended exposure limits of CO, NO, and NO2 gases are summarized in Table 1 [4].

Jan 1, 2019

By L. Yuan, J. H. Rowland, D. Bahrami, R. Thomas

Blasting is the main method of production in many non-coal underground mining operations and produces multiple toxic gases as a result. The Mine Safety and Health Administration (MSHA) requires mine operators to measure the level of toxic gases in mines as frequently as necessary to ensure they are below regulatory safety limits. The current practice uses portable gas monitors to check the concentrations of toxic gases after a fixed post-blast time. This paper studies the application of a gas monitoring system in the return entry of a limestone mine to determine a safe re-entry time. The National Institute for Occupational Safety and Health (NIOSH) conducted such a monitoring program in a limestone mine from September 2016 through May 2018. NIOSH/PMRD (Pittsburgh Mining Research Division) is endeavoring to develop workplace solutions to improve detection of and reduce the risk of hazardous conditions. This study showed that the use of gas monitoring in the return air can be a useful tool at the mine operator’s disposal to detect and reduce the risk of hazardous conditions and also to reliably estimate the re-entry time.

By E. M. R. Santos

Acid mine drainage (AMD) is a serious environmental problem in mining activities. Prediction is the first step for evaluate the potential of acid generation and there are some possible methods to estimate it. They are described as static tests, which examine the balance between acid producing and acid consuming materials, and kinetic tests, which attempt to predict drainage quality over time. Static methods are very simple and give a qualitative classification of the ores based on their potential to generate acid drainage. The characterization of ores to determine their acid producing potential is vital for the prevention of long term environmental liabilities. Laboratory tests were conducted under different methodologies to predict the acid producing potential of sulphide overburden, ore materials and tailings from a deposit of copper ore.

Jan 1, 1999

By D Laurence, L Ge

This paper demonstrates use of remotely sensed imagery in promoting sustainable mining. Remote sensing technology can be used during all phases of a mining project û from evaluating the resource, to making extraction more cost-effective, through to monitoring, mine closure and remediation. Use of the new generation of satellite platforms with the capability of acquiring satellite data with higher spectral and spatial resolution have the capability to emerge as essential indicator for sustainable development in the minerals industry. A life cycle approach to satellite imagery is discussed. The use of an imagery of the site prior to mining activity establishes the environmental baseline, guides mitigation measures and eventual help in suggesting remediation. Remote imagery provides the cost-effective means of monitoring reclamation, including the growth of planted vegetation, of the mine site and surrounding area. The latest advancements in satellite remote sensing are highlighted to meet the newer challenges of sustainable mining practices. Some of the worldwide successful remote sensing applications for the measurement and evaluation of the sustainable development impact of mining operations are described. Presently available source of imagery and its comparative advantages and disadvantages are provided as a guide. Finally, the limitations of this tool are indicated.

Jan 1, 2009

By T. A. Gray, L. M. Crayne, P. Glogowski, Trevits. M. A.

Of the 19 major mine fire events (including thermal events) that have occurred in the last 6 years (2000-2005), it is estimated that remotely constructed mine seals could have been used at 65% of the events to control or suppress the fire. Underground observations of seals that have been remotely installed during mine fire events show that they often do not fully achieve mine roof-to-floor and rib-to-rib closure. Unfortunately, the inability to reliably close the mine void has limited or precluded the regular use of this technology. The National Institute for Occupational Safety and Health is conducting full-scale underground experiments at the Lake Lynn Experimental Mine to identify and remedy existing remote sealing technology shortcomings, to develop novel technologies, and to transfer the new or improved technologies to the mining industry. This paper will discuss the remote mine seal testing program and will provide the results of the in-mine experiments. Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

By S. Paul Singh

"The long-term viability of seismically active and/or deep mining operations hinges upon the industry's ability to maintain profitability in a climate of increasingly difficult conditions, escalating operating costs and fluctuating metal prices. Within this context, it is prudent to explore mining techniques that could provide means for safer and more profitable extraction of seismically active and/or deep seated deposits that are vital to the long term survival of the industry.The first step was to examine Penetrating Cone Fracture (PCF) and other relevant concepts with the objective of semi-continuous mining in deep underground hard rock mines. This was followed by an assessment of the current conventional drilling and blasting practice. Thirteen blasts were monitored in five different seismically active workings of an operating deep mine. The main concerns during the current drill and blast practice were identified.On the basis of the literature review, three short round blasting techniques were short listed for further review. These techniques were evaluated based upon the available literature and discussions with the persons associated with their applications. Justification, requirements and major challenges for the application of short round blasting have been discussed in this paper. Suggestions for improving the current drilling and blasting practice have also been outlined.INTRODUCTIONRock fragmentation is the key to mineral excavation and production. Increasing working depths, environmental concerns and trends towards continuous mining necessitate the development of new and improved rock breakage methods.The excavation of hard rocks is still dominated by the sequential routine of face preparation, drilling, charging explosives, blasting, ventilating for fume and dust removal, mucking and roof support. Worse still, drilling and mucking require specialized equipment that fills the end of the heading so that no other operation can be performed and the equipment must be removed from the face to protect it from fly rock."

Jan 1, 2010

By Takuya Tani, Tomoyuki Aoki, Kazuo Saskai

"The authors have proposed a unique methodology in the evaluation of rock mass stiffness for the range of five to twenty meters ahead of the tunnel face, with the use of small diameter inclinometers. The inclinometers are installed at the tunnel crown at a pre-determined constant interval, about one meter behind the face in order to obtain the slight change in inclination angles during tunnel excavation. This method was developed as a daily control measurement such that the geological condition and its possible change ahead of the face could be detected early by monitoring the trend of inclination angles. This paper describes the results of the ground stiffness ahead of the tunnel face evaluated at a mountain tunnel construction site. This stiffness is evaluated automatically and displayed visually by the current system equipped with a result display screen, together with a warning message against a weak zone when detected. 1. INTRODUCTION In a conventional planning of a mountain tunnel, according to the Japanese Standard (JSCE, 2006) seismic refraction surveys from the ground surface are performed and tunnel support patterns are then designed based on the seismic wave velocity. The resolution of the velocity profile estimated by this technique, however, is poor as the tunnel overburden becomes large. The tunnel face is therefore often encountered by unforeseeable fault zones or weak rocks. Such an unpredictable weak zone occasionally causes the collapse of the tunnel face. Clarifying the forward geological information during excavation is hence significant for safe and well-controlled construction. According to the geological conditions ahead of a face, auxiliary methods typified by forepiling and face bolting could be preliminarily prepared for prompt execution. For the purpose of acquiring forward geological information, pilot borehole drilling and seismic reflection methods represented by the TSP (Tunnel Seismic Prediction) or HSP (Horizontal Seismic Profiling) are often applied. Those exploration are carried out near the tunnel face for a couple of days. This often leads to the interruption of excavation procedure and has no small effect on the construction schedule. On the other hand, some forward ground prediction methods in the daily control measurement have been developed e.g. by Schubert et al. (1995). In this method, tunnel displacements in the direction of the tunnel axis are used together with the crown settlements. We have tested their method at a few of our tunnel projects and found difficulty in the evaluation of the forward ground condition due to insufficient resolution of the axial displacement measured by a total station theodolite that we usually use for the tunnel measurement. We have therefore developed a novel methodology of monitoring slight inclination at the tunnel crown near the face, so that the forward ground conditions can be predicted and evaluated as part of a routine measurement procedure."

Jan 1, 2016

By Ehsan Moosavi, Kamyar Tolouei, Mehran Gholinejad

The literature defines rockbursts in slightly different ways based on their generation mechanisms, field phenomena, and degree of damage, but in a way that is almost consistent. Generally, a rockburst refers to seismic events that mainly happen in underground excavations, for purposes such as underground mining, road and railway tunnels, nuclear power, etc., and that are followed by the collapse and outburst of rocks. Long-term rockburst prediction can be abstracted as a classification problem mathematically, in which we can introduce deep learning to solve it. Further, using deep learning in rockburst prediction can overcome drawbacks such as subjectivity and inconsistency brought from previous traditional approaches. A rockburst data-set, was employed to evaluate the current method for predicting rockburst grade, and the good results of overall success rate were obtained. The results indicated that the proposed algorithms can speed up parameter optimization search, the proposed method is robust model and might hold a high potential to become a useful tool in rockburst prediction research.

Apr 26, 2022

By S. A. Villalobos, F. A. Villalobos, and L. E. Aguilera

Rockburst events have been a serious problem for many years in many mines worldwide, and in particular at El Teniente mine in Chile. El Teniente is the largest copper mine in the world, located in the Andes Cordillera where high stress levels are present due to intensing mining activity in addition to complex geology. Consequently, the study and management of the rockburst threat are necessary. In this work, the case of the Diablo Regimiento (DR) mine within El Teniente is studied. The energy capacity of dynamic support systems is determined for different tunnel geometries based on two kinetic methodologies, using data from DR. Initially, rockburst potential is determined by means of a stress analysis around different tunnel geometries through the boundary elements method. In the first methodology a yielding zone (YZ) is estimated for each excavation geometry using the finite element method FEM. The second methodology involves the definition and determination of a critical strain energy (SE) around each excavation geometry using a FEM numerical analysis. In both cases, peak particle velocity PPV is estimated by a scaling law, which is subsequently adjusted due to tunnel amplification effects. According to the results, and knowing the working energy capacity applied in DR mine, it was found that the values of energy capacity for the rock dynamic supports were better estimated by the YZ-PPV approach than by the SE approach.

Sep 1, 2022

"The main purpose of geometallurgy is to develop a model to predict the variability in the mineral processing performance within the ore body. Geometallurgical tests used for developing such a model need to be fast, practical and inexpensive and include as an input data relevant and measureable geological parameters like elemental grades, mineral grades and grain size. Important in each geometallurgical program is to define the number of samples needed to be sent for geometallurgical testing to enable reliable metallurgical forecast. This is, however, a complicated question that does not have a generic answer.To study the question on sampling a simulation environment was built including a synthetic ore body and sampling & assaying module. A synthetic Kiruna type iron oxide - apatite deposit was established based on case studies of Malmberget ore. The synthetic ore body includes alike variability in rock types, modal mineralogy, chemical composition, density and mineral textures as its real life counterpart. The synthetic ore body was virtually sampled with different sampling densities for a Davis tube testing, a geometallurgical test characterising response in magnetic separation. Based on the test results a forecast for the processing of the whole ore body was created. The forecasted parameters included concentrate tonnages, iron recovery and concentrate quality in terms of iron, phosphorous and silica contents.The study shows that the number of samples required for forecasting different geometallurgical parameters varies. Reliable estimates on iron recovery and concentrate mass pull can be made with about 5-10 representative samples by geometallurgical ore type. However, when the concentrate quality in terms of impurities needs to be forecasted, the sample number is more than 20 times higher. This is due to variation in mineral liberation and shows the importance of developing techniques to collect qualitative information on mineral and ore textures in geometallurgy."

Jan 1, 2016

By A. Salmoni, E. K. Gillin, T. Eger, A. Cann, P. Vi, M. Hunt

Kittusamy (Kittusamy & Buchholz, 2004) state that there have been few studies conducted to assess exposure to whole-body vibration (WBV) in the construction industry. They suggest that there is very little reliable data from the construction industry that characterizes exposure levels to various hazards including WBV or the health outcomes from such exposure and that there is a need for more exposure data. In a recent exploratory study of heavy construction equipment Cann (Cann, Salmoni, Vi, & Eger, 2003) looked at vibration levels for 14 different types of construction equipment. Eight of the 14 pieces of equipment tested exposed operators to levels of WBV that exceeded the recommended limits for an 8-hour period when comparing the measured VDV to the ISO 2631-1 standards. The purpose of the present research was not only to test a larger number of scrapers but also to investigate scraper operator exposure to whole body vibration (WBV) separately for each task. Methods 33 scrapers were evaluated for WBV in a variety of residential and road construction projects. Testing equipment consisted of triaxial accelerometers that allowed vibration data collection in all three orthogonal axes, with the x-axis positioned to measure vibration in the anterior-posterior direction, the y-axis in the medial-lateral direction, and the z-axis in the vertical direction. Root mean square accelerations (aRMS), vibration dose value (VDV), crest factor, and maximum transient vibration values (MTVV) were derived from this software and exported to an Excel™ spreadsheet for later data analysis. Test sessions for each piece of equipment lasted for approximately 20 minutes until at least three work cycles had been completed. Tasks included: idling while waiting for a bulldozer to push the scraper through the scraping phase, scraping, traveling loaded with dirt, dumping and traveling empty. Results Task breakdown by time reveals 25% of the work cycle was spent traveling fully loaded with dirt, 19% dumping, 21% traveling unloaded, 17% idling and 18% scraping. Calculation of aRMS vector sums gave values of 2.55 m/s2 during loaded transport, 2.46 m/s2 during dumping, 2.31 m/s2 during unloaded travel, 0.55 m/s2 during idling and 1.46 m/s2 during scraping (see Table 1). The highest acceleration values recorded were found in the z-axis during fully loaded transport reaching an average aRMS over three work cycles of 2.55 m/s2.

Jan 6, 2006

By G. M. Castillo

Newmont?s Phoenix mine started production in March of 2006. Due to the extreme hardness of the ore, the mill has struggled to meet throughput projections. Grinding studies showed that optimizing the existing circuit would not achieve budgeted throughput. These studies also showed that the pebble crusher was being underutilized due to the inability of the SAG mill to break the rock. The concept was developed to supplement the feed to the existing pebble crusher with a secondary crusher. Models of this process looked favorable so a portable crusher was installed to test the process. The temporary crusher was successful at increasing the throughput by 7% and based on the operating data, plans are currently being developed to install a permanent secondary crushing system in front of the SAG mill. This paper will review the results from the test crusher and the flow sheet for the permanent secondary crusher.

Jan 1, 2012

By C. D. Litton, I. E. Perera

This report presents the results of experiments to evaluate different types of mine fire sensors in an underground mine environment using a commercially available atmospheric monitoring system. To determine how well carbon monoxide (CO) and smoke sensors respond for purposes of fire detection, experiments were conducted using test fires of different mine combustibles and for both flaming and nonflaming combustion. The experiments were designed to assess the response of fire sensors to different contaminants and different contaminant levels produced from the test fires. The experiments were performed in the Safety Research Coal Mine at the U.S. National Institute for Occupational Safety and Health’s Bruceton Research Facility in the presence of an average ventilating air velocity of 1.6 m/s (315 fpm). Five fire sensor stations were located downstream of the test fire at fixed locations, with each sensor station consisting of four sensors: a CO fire sensor and three different smoke sensors, of which two were evaluated by the Mine Safety and Health Administration (MSHA) for intrinsic safety and the third was used extensively in underground mines overseas but not evaluated by MSHA for intrinsic safety. All four sensors were mounted near the center of the entry and in the upper onethird of the entry height. A UL-listed combination ionization and photoelectric smoke sensor was mounted near the roof at the first sensor station and its responses were compared against the responses of the four CO and smoke fire sensors. Sensor response data, contaminant travel times, and the impact of fire on the existing ventilation flow are discussed as they apply to earlywarning fire detection. Of significance in the analysis is the need for performance standards for mine fire sensors in order to provide for consistent and timely early warning of developing fires.

Jan 1, 2014

By Kevin Ashley

Because toxicities may differ for Cr(VI) compounds of varying solubility, some countries and organizations have promulgated different occupational exposure limits (OELs) for soluble and insoluble hexavalent chromium (Cr(VI)) compounds, and analytical methods are needed to determine these species in workplace air samples. To address this need, international standard methods ASTM D6832 and ISO 16740 have been published that describe sequential extraction techniques for soluble and insoluble Cr(VI) in samples collected from occupational settings. However, no published performance data were previously available for these Cr(VI) sequential extraction procedures. In this work, the sequential extraction methods outlined in the relevant international standards were investigated. The procedures tested involved the use of either deionized water or an ammonium sulfate/ ammonium hydroxide buffer solution to target soluble Cr(VI) species. This was followed by extraction in a sodium carbonate/sodium hydroxide buffer solution to dissolve insoluble Cr(VI) compounds. Three-step sequential extraction with (1) water, (2) sulfate buffer and (3) carbonate buffer was also investigated. Sequential extractions were carried out on spiked samples of soluble, sparingly soluble and insoluble Cr(VI) compounds, and analyses were then generally carried out by using the diphenylcarbazide method. Similar experiments were performed on paint pigment samples and on airborne particulate ?lter samples collected from stainless steel welding. Potential interferences from soluble and insoluble Cr(III) compounds, as well as from Fe(II), were investigated. Interferences from Cr(III) species were generally absent, while the presence of Fe(II) resulted in low Cr(VI) recoveries. Two-step sequential extraction of spiked samples with (?rst) either water or sulfate buffer, and then carbonate buffer, yielded quantitative recoveries of soluble Cr(VI) and insoluble Cr(VI), respectively. Three-step sequential extraction gave excessively high recoveries of soluble Cr(VI), low recoveries of sparingly soluble Cr(VI), and quantitative recoveries of insoluble Cr(VI). Experiments on paint pigment samples using two-step extraction with water and carbonate buffer yielded varying percentages of relative fractions of soluble and insoluble Cr(VI). Sequential extractions of stainless steel welding fume air ?lter samples demonstrated the predominance of soluble Cr(VI) compounds in such samples. The performance data obtained in this work support the Cr(VI) sequential extraction procedures described in the international standards.

Jan 1, 2009