Method for treating dust collected on dust filter of continuous dust monitoring device for analysis

Abstract

The present invention provides a method of treating dust collected on a dust filter of a continuous dust monitoring device for FTIR or XRD analysis, the method comprising: contacting the dust filter with a liquid carrier to selectively remove dust from the dust filter, thereby producing a slurry containing dust in the liquid carrier; and filtering the slurry through a filtration unit comprising a silicon-free polymer filter element, thereby retaining dust on the polymer filter element.

Description

[0001] This application claims priority to Australian Provisional Patent Application No. 2022901987 filed on July 15, 2022, the contents of which should be understood to be incorporated into this specification by reference. Technical Field

[0002] The present invention generally relates to providing a method of processing dust collected on a dust filter of a continuous dust monitoring device for subsequent FTIR or XRD analysis. The present invention also relates to a method of analyzing dust collected on a dust filter of a continuous dust monitoring device by FTIR or XRD analysis, in particular determining the crystalline silica content of the dust. The present invention is particularly suitable for analyzing dust collected by a personal dust monitor (PDM) comprising a tapered element oscillating microbalance (TEOM), and it will be convenient to disclose the present invention in conjunction with this exemplary embodiment. Background Art

[0003] Exposure to respirable crystalline silica (RCS) is a recognized risk factor for silicosis and lung cancer. Therefore, in industrial workplaces where RCS hazards exist, such as coal mines, respirable dust sampling is necessary to monitor the dose and composition of respirable dust in the air breathed by workers. Traditionally, this has been done using gravimetric sampling techniques.

[0004] Conventional gravimetric personal samplers direct a known volume of air from within the worker's breathing zone through a cyclone separator (which excludes larger non-respirable particles) and then through a filter containing a removable filter membrane to retain the respirable dust portion. After the desired period of use, the filter membrane is removed from the sampler, and the mass of the respirable dust per unit volume of air is calculated using the measured mass of the retained dust. The dust retained on the filter membrane is then subjected to laboratory analysis to determine its crystalline silica (quartz) content. Typically, the polymer filter membrane is first ashed to reduce interference from organic matter in the dust sample, and the ash is then re-deposited on another filter membrane suitable as a substrate for Fourier transform infrared (FTIR) and / or X-ray diffraction (XRD) analysis methods. Industry standard methods for gravimetric sampling and analysis have been established by regulatory agencies, such as the National Institute for Occupational Safety and Health (NIOSH, a U.S. government agency), which specifies methods 7603 and 7500 for FTIR and XRD analysis of crystalline silica in coal dust in its Manual of Analytical Methods.

[0005] A significant disadvantage of conventional gravimetric sampling is that it does not provide immediate feedback on dust exposure risk. To this end, significant resources have been invested in developing continuous dust monitoring devices that provide real-time monitoring of dust exposure. The most successful methods use resonant mass monitoring techniques, such as the Conical Element Oscillating Microbalance (TEOM), in which the dust filter of the monitoring device is oscillated in the sampling device at its natural resonant frequency. As the mass of the filter increases due to dust capture, the resonant frequency of the oscillating filter decreases. The correlation is used to calculate and track the amount of dust deposited on the filter in real time.

[0006] An example of a commercially available continuous dust monitoring device is the PDM3700 Personal Dust Monitor (PDM) available from Thermo Scientific. Figure 1 The TEOM unit of such a device schematically depicted in FIG. 1 comprises an inlet 100 through which air 102 containing respirable dust particles is sucked in. A dust filter 104 located in an inlet chamber 106 is mounted on a conical tubular element 108, which is fixed to a base 110 at its opposite ends. Thus, the conical tubular element can oscillate at a natural resonant frequency in the direction indicated by arrows 112a, 112b. The PDM electronics controls and measures the oscillations, for example, via the interaction of electromagnetic drivers 114a, 114b with magnets 116a, 116b.

[0007] The dust filter 104 includes a hollow polymer body 118 configured to receive the tapered tubular element 108, a glass fiber filter membrane 120, and a polymer retaining ring 122 that seals the filter membrane 120 to the edge of the body 118. The three components are welded together to form an integral assembly that can be mounted on and removed from the tapered tubular element 108.

[0008] In use, air is drawn into the PDM from the worker's breathing zone at a known flow rate, sized in a cyclone separator to remove coarse particles, and enters chamber 106 as air 102, passes through dust filter 104, and exits the TEOM unit via tapered tubular element 118 and outlet 122. Respirable dust in air 102 is retained on filter membrane 120, thereby increasing the mass of dust filter 104. The mass is monitored in real time by measuring the resonant frequency of tapered tubular element 108.

[0009] Personal dust monitors such as the PDM3700 are now in routine operation in many workplaces, including coal mines. While the real-time monitoring capabilities of these devices offer an advantage over conventional gravimetric samplers, they have the distinct disadvantage that the crystalline silica content of dust retained on the filter cannot be analyzed by conventional FTIR and XRD analysis methods such as NIOSH methods 7603 and 7500. Since both the amount and composition of respirable dust particles are important factors, the use of PDM devices to date has not been able to provide a complete picture of dust exposure risk.

[0010] This problem arises from the construction and composition of the dust filter assemblies used in PDM devices. As described above, commercially available PDM dust filters are not suitable for ashing because the materials of construction are durable, including glass fibers and fluoropolymers present in the filter membrane, and the mass of the multi-component filter assembly is significantly greater than the removable polymer filter sheets used in conventional gravimetric sampling methods. The silicon-based components in the dust filter (including glass fibers) will also contaminate the ash and therefore may confound any analysis of crystalline silica in the dust.

[0011] A previous attempt to solve the problem is described in U.S. Pat. No. 7,947,503. The method described therein attempts to modify the dust filter assembly ( Figure 1 Item 104) of the invention, so that all components are suitable for ashing. Therefore, the filter membrane ( Figure 1 Item 120 in the PP filter body is made entirely of nylon or other organic polymers. Inorganic components such as TiO2 pigment are also removed from the polypropylene filter body and retaining ring ( Figure 1 It is stated that a sample of the respirable dust retained on the improved dust filter can be analyzed by ashing the entire filter assembly and then subjecting the ash to conventional FTIR or XRD analysis.

[0012] However, this approach still has a number of significant disadvantages. First, the dust filter includes structural polymer components that require extended time to ashed. Second, the total mass of the multi-component dust filter is very high compared to the mass of the retained dust, so the residual ash from the filter is more likely to cause errors in the dust analysis performed on the ash. Third, the conditioning filter membrane ( Figure 1The competing technical requirements of item 120 in PDM are challenging. These requirements include: (i) a composition that is completely ashing and free of inorganic contents that could confound subsequent analysis, (ii) a membrane structure that is sufficiently strong to span the hollow body without support other than a retaining ring, and (iii) excellent dust filtration and dust retention capabilities during sampling. The method described in U.S. Patent 7,947,503 has not been commercially successful, and alternative PDM filters are not available to replace currently used glass fiber filters. Therefore, there is a continuing need for methods of analyzing dust collected in PDM that do not rely on redesign of the dust filter assembly.

[0013] Additionally, in some cases, it is desirable to avoid completely ashing dust samples. Ashing procedures used in standard analytical methods such as NIOSH Methods 7603 and 7500 are time consuming and must often be performed in off-site analytical laboratories. Results generated using the above standard laboratory analyses are typically not available for days to weeks after sampling, which delays timely and effective intervention in engineering controls for dust exposure. Earlier results can be obtained without unacceptable impact on accuracy by performing direct filter analysis of the sampled dust (e.g., using a field-based FTIR method). However, dust filters of continuous dust monitoring devices such as the PDM3700 are inherently unsuitable for direct filter analysis because the bulky filter assemblies block IR beam transmission and the glass fiber filters contain silica, which can confound RCS analysis. In addition, three-dimensional PDM filter assemblies, whether commercially available or modified as described in U.S. Patent 7,947,503, are physically incompatible with analytical instruments configured to receive planar substrates.

[0014] Therefore, there is a continuing need for new methods of treating dust collected on dust filters of continuous dust monitoring devices for FTIR or XRD analysis which at least partially address one or more of the above-mentioned disadvantages, or provide a useful alternative.

[0015] The reference herein to a patent document or other matter cited as prior art should not be taken as an admission that the document or matter is known or that the information it contains was part of the common general knowledge as at the priority date of any claim. Summary of the invention

[0016] According to a first aspect, the present invention provides a method for treating dust collected on a dust filter of a continuous dust monitoring device for FTIR or XRD analysis, the method comprising: contacting the dust filter with a liquid carrier to selectively remove dust from the dust filter, thereby producing a slurry comprising dust in the liquid carrier; and filtering the slurry through a filtration unit comprising a silicon-free polymer filter element, thereby retaining the dust on the polymer filter element.

[0017] This advantageously provides a robust method for analyzing the composition of dust collected by a continuous dust monitoring device, such as a personal dust monitor (PDM) equipped with a glass fiber filter. The collected dust is transferred in a representative and selective manner to a substrate that is inherently suitable for subsequent analysis by FTIR or XRD. Therefore, there is no need to redesign the dust filter, and in fact the method of the present disclosure is compatible with glass fiber based dust filters already used in commercial PDMS for mining environments. The inventors have found that more than 80% by weight of the dust collected on such a dust filter can be recovered on a polymer filter element and therefore analyzed to determine its crystalline silica content. In addition, the dust can be analyzed without interference from silicon (e.g. from the glass fibers) or other inorganics present in the dust filter, because the selective transfer of the dust to the silicon-free polymer filter element avoids contamination of the dust sample with components of the dust filter.

[0018] The methods disclosed herein advantageously allow the user to combine the results of the compositional analysis of the sampled dust with the pre-existing advantages of real-time quality monitoring provided by a continuous dust monitoring device. In at least some embodiments, the analysis of dust transferred to the non-silicon polymer filter element can be implemented using existing equipment and procedures in analytical laboratories that already serve many workplaces. In some embodiments, the dust transferred to the non-silicon polymer filter element is analyzed by a direct filter analysis method. This is more suitable for field implementation and can allow for a fast turnaround time for component analysis, which better complements the inherently fast (real-time) monitoring of dust quality exposure provided by a continuous dust monitoring device.

[0019] In some embodiments of the first aspect, the method further comprises analyzing dust present on the polymer filter element by FTIR or XRD analysis. In other embodiments, the method further comprises ashing the polymer filter element to produce an ash containing the dust, and analyzing the ash by FTIR or XRD analysis. In either case, analyzing the ash by FTIR or XRD analysis can include quantifying the amount of crystalline silica in the dust.

[0020] According to a second aspect, the present invention provides a method for analyzing dust collected on a dust filter of a continuous dust monitoring device by FTIR or XRD analysis, the method comprising: contacting the dust filter with a liquid carrier to selectively remove dust from the dust filter, thereby producing a slurry containing dust in the liquid carrier; filtering the slurry through a filtration unit comprising a silicon-free polymer filter element, thereby retaining the dust on the polymer filter element; and analyzing the dust retained on the polymer filter element by FTIR or XRD analysis.

[0021] In some embodiments of the second aspect, the dust is analyzed when the dust is present on the polymer filter element. In other embodiments, analyzing the dust comprises ashing the polymer filter element to produce an ash containing the dust, and analyzing the ash by FTIR or XRD analysis. In either case, analyzing the ash by FTIR or XRD analysis can include quantifying the amount of crystalline silica in the dust.

[0022] In some embodiments of the first and second aspects, the dust is coal dust.

[0023] In some embodiments of the first and second aspects, the dust filter comprises silicon, which is optionally at least partially present in glass fibers.

[0024] In some embodiments of the first and second aspects, the continuous dust monitoring device is a personal dust monitor (PDM) comprising a tapered element oscillating microbalance (TEOM).

[0025] In some embodiments of the first and second aspects, the polymer filter element is composed of one or more organic polymers. The one or more organic polymers may include at least one selected from the group consisting of polyvinyl chloride, polyvinyl chloride-acrylic copolymer, polyolefin, nylon, polyester and cellulose.

[0026] In some embodiments of the first and second aspects, the polymer filter element is ashing.

[0027] In some embodiments of the first and second aspects, the polymer filter element is a planar sheet that is removably insertable into the filtration unit.

[0028] In some embodiments of the first and second aspects, the liquid carrier is an organic solvent. The organic solvent can be an alcohol, such as isopropanol.

[0029] In some embodiments of the first and second aspects, contacting the dust filter with the liquid carrier includes backwashing the liquid carrier from an opposite side of the dust filter through the dust filter to a dust receiving side of the dust filter.

[0030] In some embodiments of the first and second aspects, at least 70 wt. % or at least 80 wt. % of the dust collected on the dust filter is retained on the polymeric filter element.

[0031] Where the terms "comprises", "comprising" and "containing" are used in the specification (including claims), they should be interpreted as specifying stated features, integers, steps or components, but not excluding the presence of one or more other features, integers, steps or components, or combinations thereof.

[0032] Other aspects of the invention appear from the following detailed description of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the present invention will be described herein by way of example only with reference to the accompanying drawings, in which:

[0034] Figure 1 A Conical Element Oscillating Microbalance (TEOM) unit of a commercially available personal dust monitor is schematically depicted, including its removable dust filter.

[0035] Figure 2 Schematically depicts backwashing with a liquid carrier according to some embodiments of the present invention. Figure 1 A dust filter as seen in FIG. 1 is a device for selectively removing dust from a dust filter.

[0036] Figure 3 is a graph comparing measurements of respirable crystalline silica content in coal dust (i) recovered from a dust filter of a continuous dust monitoring device of the present disclosure by solvent backwashing and (ii) recovered from a gravimetric personal sampler. DETAILED DESCRIPTION

[0037] The present invention relates to a method for treating dust collected on a dust filter of a continuous dust monitoring device for FTIR or XRD analysis. The method comprises the step of contacting the dust filter with a liquid carrier to selectively remove dust from the dust filter, thereby producing a slurry comprising dust in the liquid carrier. In a further step, the slurry is filtered through a filter unit comprising a silicon-free polymer filter element, thereby retaining the dust on the polymer filter element. The dust retained on the polymer filter element can then be analyzed by FTIR or XRD analysis, in particular to determine the crystalline silica content of the dust.

[0038] Dust continuous monitoring device

[0039] The method of the present disclosure is directed to processing dust collected in a continuous dust monitoring device. As used herein, a continuous dust monitoring device refers to a dust sampling device that provides real-time feedback on the quality of the collected dust. Thus, a continuous dust monitoring device is different from a conventional gravimetric sampling device that does not have real-time monitoring capabilities.

[0040] In some embodiments, the continuous dust monitoring device is a personal dust monitoring device, such as a personal dust monitor (PDM), such as the PDM3700 available from Thermo Scientific. Such a device is configured to be worn by a user and to sample representative air from the user's breathing space. However, the methods disclosed herein also extend to devices that are not configured for personal use, such as wall-mounted units or any other continuous dust monitoring device for real-time monitoring of dust in the air.

[0041] The continuous dust monitoring device may be equipped with a resonant frequency microbalance which monitors the mass of dust collected on the dust filter by measuring the resonant frequency of the dust filter as it vibrates. An example of a suitable resonant frequency microbalance is a tapered element oscillating microbalance (TEOM).

[0042] Optionally, the continuous dust monitoring device may include a cyclone separator to size select the dust particles so that dust particles close to the respirable dust fraction are collected on the dust filter. Other well-known components of the continuous dust monitoring device are also contemplated, including pumps, sensors, electronics, etc.

[0043] Dust filter

[0044] The dust to be processed is collected on a dust filter of the continuous dust monitoring device. As used herein, a dust filter includes a porous filter membrane for capturing and retaining dust and any associated components, which together form an integral filter unit that is inserted into the continuous dust monitoring device and removed therefrom after a monitoring cycle. The dust filter may include a porous membrane, and the dust filter is configured to pass a gas stream (usually air) for analysis through the porous filter membrane so that dust particles carried by the gas are retained in the porous membrane.

[0045] In some embodiments, the dust filter is non-ashable. This means that it cannot be ashed using standard equipment and procedures for dust analysis, such as those described in NIOSH methods 7603 and 7500. The dust filter may be non-ashable because it includes durable materials of construction, such as fiberglass and / or fluoropolymers.

[0046] In some embodiments, the dust filter contains silicon, for example in glass fibers present in the filter membrane. In some embodiments, the dust filter contains other inorganic components, for example inorganic pigments such as TiO2. The presence of silicon and other inorganic materials in the dust filter may confound conventional analysis of dust collected on the dust filter, and the methods of the present disclosure avoid or at least mitigate these difficulties.

[0047] In some embodiments, Figure 1As shown, the dust filter includes a hollow polymer body 118 configured to receive the tapered tubular element 108; a glass fiber filter membrane 120; and a polymer retaining ring 122 that seals the filter membrane 120 to the edge of the body 118. These three components can be welded together to form an integral assembly 104 that can be mounted on and removed from the tapered tubular element 108 of the continuous dust monitoring device.

[0048] dust

[0049] The dust collected on the dust filter may be any dust that may be collected in a continuous dust monitoring device, and in particular any airborne dust that includes respirable particles that present potential health issues when inhaled. In some embodiments, the dust includes or may include crystalline silica, such as quartz.

[0050] In some embodiments, the dust is coal dust, such as found in the air in coal mines. In other embodiments, the dust is generated in facilities used for mineral or stone mining or manufacturing.

[0051] Contacting the dust filter with a liquid carrier to selectively remove dust

[0052] The method of the present disclosure comprises the step of contacting a dust filter with a liquid carrier to selectively remove dust from the dust filter, thereby producing a slurry comprising dust in the liquid carrier. Typically, before performing the steps, the dust filter is first separated from the continuous dust monitoring device.

[0053] The liquid carrier can generally be any liquid carrier that can penetrate the dust filter membrane and carry the dust particles out of the filter. Typically, the liquid carrier is an organic solvent, preferably with a low standard boiling point (<100° C.), so that the solvent can be effectively removed from the dust by evaporation. The liquid carrier should have a suitable polarity to penetrate the dust filter membrane and carry the dust particles (e.g., including coal and silica particles) out of the filter. Suitable liquid carriers include alcohols, such as isopropanol, ethanol, and the like. In some embodiments, the liquid carrier is isopropanol, which is used as a dust carrier in other dust analysis methods such as NIOSH methods 7603 and 7500.

[0054] The dust filter is contacted with a liquid carrier under conditions suitable for selectively removing dust from the dust filter. It is generally important for subsequent analysis that the dust removed from the filter is not contaminated by the filter material (e.g., glass fiber). The inventors have found that if the dust filter is immersed in a liquid carrier and subjected to ultrasonic treatment to facilitate dust removal, there is a risk of such contamination. Therefore, in some embodiments, the dust filter is contacted with a liquid carrier to remove dust without ultrasonic treatment of the filter.

[0055] Dust may be removed from the dust filter by any suitable method that avoids unacceptable contamination of the dust sample, such as by flushing or washing the dust filter with a liquid carrier, or gently agitating the dust filter in a liquid carrier.

[0056] In some embodiments, the liquid carrier is backwashed through the dust filter from the opposite side of the dust filter to the dust receiving side of the dust filter, i.e., opposite to the airflow during dust sampling. The inventors have found that the method can be used to recover a high proportion of dust retained on the dust filter without contamination.

[0057] In an exemplary embodiment, Figure 2 As shown, the dust filter 104 with the dust retained thereon is removed from the PDM and clamped in an inverted configuration over a container 202 (e.g., a beaker). The dust filter 104 is generally as referred to herein. Figure 1 The present invention relates to a method for preparing a PDMS filter 104, which thus comprises a glass fiber filter membrane 120 (in which the collected dust is retained) and a hollow polymer body 118. The dust filter 104 is then connected to a syringe pump 204 via a thin flexible tube 206, which is frictionally sealed to the orifice of the hollow polymer body 118 (or above), and the orifice of the hollow polymer body 118 is configured to receive the tapered tubular element of the TEOM of PDMS. Isopropyl alcohol 208 is then dispensed from the syringe pump 204 at a suitable flow rate. Isopropyl alcohol enters the dust filter 108 from the opposite side 150, is evenly distributed in the pores of the filter membrane 120, and carries the dust particles out of the filter membrane at the dust receiving side 152 of the dust filter. Droplets 210 of isopropyl alcohol with dust particles fall from the dust filter and are collected in the beaker 202 as a slurry 212.

[0058] The flow rate of isopropyl alcohol backwashed through the dust filter is selected to avoid excessive pressure in the filter membrane, which may cause the glass fibers to fall off. For a dust filter configured for use with a PDM3700 device, a suitable flow rate is about 1-2 ml / min. The total volume of isopropyl alcohol backwashed through the filter should be sufficient to recover all removable dust from the dust filter. High recoveries from dust filters configured for use with a PDM3700 device have been obtained by passing 1-2 ml of isopropyl alcohol through the dust filter.

[0059] Filter slurry

[0060] The method of the present disclosure includes the step of filtering the slurry through a filtration unit comprising a silicon-free polymer filter element, thereby retaining the dust on the polymer filter element.

[0061] Filtration units suitable for filtering dust slurries in liquid carriers are well known in the art of dust analysis, such as specified in NIOSH methods 7603 and 7500. Thus, the filtration unit can be a vacuum filtration unit comprising a porous glass base (optionally 25 mm, optionally a Millipore XX1012502 porous glass base), a filtration vacuum bottle configured to receive the porous glass base (optionally a Millipore XX1012506 vacuum filtration funnel) and a glass funnel configured to be clamped onto the porous glass base (optionally a custom glass funnel similar to the Millipore XX1002514 glass funnel but with an inner diameter of approximately 8-10 mm).

[0062] As used herein, a non-silicon polymer filter element comprises a filter membrane suitable for capturing and retaining dust in a slurry, the filter membrane being completely free of silicon or containing a negligible amount of silicon that does not interfere with subsequent analysis of the dust. Typically, the non-silicon polymer filter element is configured as a planar sheet of a thin film material that is removably insertable into a filter unit. In the above-mentioned filter unit, such a filter element is placed on a porous glass base and is held in place when a glass funnel is clamped onto the porous glass base.

[0063] In some embodiments, the silicon-free polymer filter element is composed of one or more organic polymers. In other words, it does not contain other materials of construction. Suitable organic polymers include those of the following: (i) organic polymers that can be ashed, for example, under the conditions listed in NIOSH methods 7603 and 7500; and / or (ii) organic polymers that are compatible with subsequent FTIR or XRD analysis by direct filter analysis methods. Non-limiting examples of suitable organic polymers may include polyvinyl chloride (PVC), polyvinyl chloride-acrylic copolymers, polyolefins, nylon, polyester, cellulose, etc. Examples of particularly suitable materials include PVC and vinyl chloride-acrylonitrile copolymers.

[0064] It will be appreciated that the silicon-free polymer filter element should be porous enough to enable filtration. Thus, in some embodiments, the polymer filter element comprises fibers of one or more organic polymers. The polymer filter element may be a nonwoven membrane comprising these fibers.

[0065] In some embodiments, the polymer filter element as a whole is ashing, e.g., under the conditions set forth in NIOSH methods 7603 and 7500, thus allowing subsequent FTIR or XRD analysis of the dust via ashing and redeposition. In some embodiments, the polymer filter element is a suitable substrate for FTIR or XRD analysis, e.g., as also described in NIOSH methods 7603 and 7500.

[0066] Suitable silicon-free polymer filter elements include PVC filter membranes (eg, having a pore size of 5 μm) and vinyl chloride-acrylonitrile copolymer membranes (eg, having a pore size of 0.45 μm).

[0067] The slurry containing dust in a liquid carrier can be dispersed in the slurry before filtering. For example, the slurry can be ultrasonically treated to ensure that the dust is fully dispersed. The slurry containing dust can be filtered under conditions suitable for providing high transfer and uniform distribution of dust particles onto the polymer filter element. For example, after pouring the slurry from the slurry container into the filter unit, the slurry container can be rinsed with a further amount of liquid carrier and the rinse liquid can then be added to the filter unit. In addition, the filter unit can be rinsed with a further amount of liquid carrier to carry any dust particles captured on other surfaces to the polymer filter element.

[0068] After filtering the slurry, the polymer filter element with the dust retained thereon may be dried to evaporate the liquid carrier and then weighed to determine the mass of dust redeposited on the polymer filter element.

[0069] By carefully applying the two-step method disclosed herein, it has been found that at least 70% by weight or at least 80% by weight of the dust collected on the dust filter can be recovered on the polymer filter element. Such recovery is sufficient to obtain a representative analysis of the respirable dust particles collected in the continuous dust monitoring device.

[0070] Analytical methods

[0071] The method of the present disclosure may include one or more further steps of analyzing the dust on the polymer filter element. In particular, the dust may be analyzed by FTIR or XRD methods to determine the amount of crystalline silicon dioxide (quartz) in the dust.

[0072] In some embodiments, the polymer filter element on which dust is retained is first ashed to produce ash for analysis. Therefore, the polymer filter element should be selected to have high ashing property and ensure that any residual ash does not interfere with subsequent dust analysis. Ash is then analyzed by FTIR or XRD analysis, which may involve redepositing ash on a filter membrane suitable as a substrate in a selected analytical instrument. Such analytical methods are well known in the field of dust analysis, such as described in NIOSH methods 7603 (FTIR analysis) and 7500 (XRD analysis). Advantageously, the embodiments of the present invention that rely on ashing can therefore be realized in a laboratory that has been certified for such analysis using established analytical methods.

[0073] In other embodiments, a polymer filter element having dust retained thereon is subjected to direct filter FTIR or XRD analysis. In other words, the dust is analyzed while still present on the polymer filter element. For this method, the polymer filter element should be selected based on its compatibility with the desired analytical method. Advantageously, this method can sufficiently reduce analytical complexity to allow on-site implementation, rather than sending dust samples to an external analytical laboratory. The simpler method can also facilitate faster turnaround times, so that the compositional analysis of dust samples can be better matched with the inherently rapid (real-time) monitoring of dust quality provided by a continuous dust monitoring device. Therefore, if a worker is exposed to a high overall dust hazard based on mass and composition, appropriate intervention can be carried out at an early stage.

[0074] The inventors have demonstrated that direct filter FTIR analysis can be used to accurately characterize the crystalline silica content of different respirable coal dust samples collected on a PDM, once transferred to a suitable filter membrane according to the present disclosure.

[0075] Example

[0076] The present invention is described with reference to the following examples. It should be understood that the examples are illustrative and not limiting of the invention described herein.

[0077] Example 1. Dust sampling

[0078] Paired sampling was performed in parallel using two types of respirable dust samplers to obtain dust of similar composition collected on the filter of each sampler. One sampler was a Thermo Scientific personal dust monitor (PDM3700) with a glass fiber filter (PDM filter). The other was a conventional gravimetric personal sampler (Casella Apex 2) with a PVC filter of 25 mm in diameter (pore size 5 μm). The air inlets of the two samplers were connected to a dust collection chamber. A mixture of coal powder less than 125 μm and a respirable quartz standard (SRM 1878a) was fed into the chamber by compressed air to form dust of the desired concentration in the chamber. The mixture of coal powder and different silica contents was sampled for different durations to obtain dust samples collected by filters with different dust loads and different silica contents.

[0079] Example 2. Flushing PDM dust filter

[0080] The dust filter (as described in Example 1) with coal dust collected thereon was removed from the PDM3700 and clamped in an inverted configuration (dust receiving side down) over a beaker (25 ml), as shown. Figure 2As shown. During this procedure, no dust was detached from the filter. The dust filter was then connected to a syringe pump filled with isopropanol (reagent grade) via a flexible hose. The syringe pump was then operated at a flow rate of 2 ml / min for 1 minute in order to backwash the isopropanol through the dust filter. It was observed that the liquid was injected throughout the filter membrane, carrying and dispersing the dust particles from the membrane into droplets, which fell into the beaker. However, the flow rate was kept at a low value so that the membrane was not exposed to high pressure, which could cause the sample to be contaminated by the filter fibers.

[0081] Example 3. Filtration of slurry containing dust from a PDM dust filter

[0082] The dust removed from the dust filter in Example 2 was then recovered on a PVC filter (25 mm diameter, 5 μm pore size) suitable for filter FTIR analysis by modifying the procedure in the NIOSH Manual of Analytical Methods Method 7603 ("NIOSH 7603"). This involved the following steps:

[0083] (1) Add 3 ml of isopropanol to the dust slurry collected in the beaker to provide a total volume of about 5 ml of slurry. Place the beaker in an ultrasonic bath to fully disperse the dust particles in the solvent.

[0084] (2) Prepare a vacuum filtration device for filtering the dust slurry after ultrasonic dispersion. The filtration device consists of a 25mm sintered glass base (Millipore XX1012502) and a 125ml side arm filter bottle (XX1012506) and a custom funnel similar to Millipore XX1002514 but with an inner diameter of 9.5mm. Apply vacuum to the device and then place a 25mm glass fiber filter on the sintered glass base. Two separate polyvinyl chloride (PVC) filters are placed on the glass fiber filter. First, use a microbalance to weigh the top PVC filter so that the redeposition mass of the dust can be calculated by subtraction. The filter funnel is placed on a porous glass base, a clamp is applied and the vacuum is turned off.

[0085] (3) Add 3 ml of isopropanol to the funnel. Once the ultrasonic dispersion is complete (step 1), add the dispersed dust slurry to the funnel. Then rinse the beaker twice with 3 ml of isopropanol and add the rinse to the funnel. Apply vacuum and complete the filtration.

[0086] (4) Disassemble the filtration apparatus and remove the top PVC filter. Place the filter, which retains the dust from the filtration step, in an oven at 50°C for 15 minutes to evaporate all the isopropyl alcohol. Remove the PVC filter from the oven and allow it to cool to ambient temperature. Weigh the PVC filter and calculate the mass of dust redeposited on the PVC filter by subtracting its initial mass.

[0087] Example 4. Filtration of a slurry containing dust from a conventional gravimetric personal sampler (Comparative Example)

[0088] A 25 mm PVC filter containing dust collected in a conventional weight personal sampler (Example 1) was placed in a beaker and 5 ml of isopropanol was added. The dust was thus removed from the PVC filter and dispersed in isopropanol by ultrasonic treatment by placing the above beaker in an ultrasonic bath. After ultrasonic treatment, the PVC filter used for dust sampling was taken out of the beaker. The dust was then filtered and redeposited on a new PVC filter according to steps (2) to (4) of Example 3. The mass of redeposited dust was calculated by weighing the blank PVC filter before redeposition and the filter with redeposited dust after redeposition.

[0089] The purpose of separating and re-depositing the gravimetrically sampled dust is to compare the quartz analysis results of coal dust processed according to the present disclosure and coal dust recovered from conventional gravimetric samples collected in parallel sampling. Both samples are expected to have the same silica concentration (wt %) in the collected dust.

[0090] Example 5. Filter FTIR analysis

[0091] Direct filter FTIR analysis was performed on the redeposited dust on the PVC filter (as prepared in Examples 3 and 4) to determine the silica content. The FTIR analysis method is similar to that used in NIOSH 7603, which uses an 800 cm -1 The peak height is about 820cm -1 Up to 670cm -1 A ThermoScientific Nicolet iS50 FTIR spectrometer with an IR beam spot size of approximately 8 mm diameter was used. The circular area of ​​redeposited dust was approximately 9.5 mm in diameter. The PVC filter was positioned in the sample holder using an IR viewer to ensure that the IR beam was centered over the redeposited dust area.

[0092] result

[0093] Four sets of dust samples of different compositions collected by paired sampling on the dust filters of a personal dust monitor (PDM) and a gravimetric personal sampler (GPS) in Example 1 were processed for analysis according to Examples 2 and 3 (PDM dust) and Example 4 (GPS dust). Both methods achieved high dust recoveries, greater than 80% in most cases.

[0094] The recovered samples were then analyzed for silica content using the method of Example 5, and the results are shown in Table 1 below. The quartz content in each set of dust samples collected by paired sampling was very similar. The comparative analysis shows that treating dust from a personal dust monitor by flushing the filter with a solvent and filtering the resulting slurry, as disclosed herein, is an effective sample preparation method for subsequent evaluation of silica content.

[0095] Table 1

[0096]

[0097] Multiple parallel sets of PDM (according to Examples 2 and 3) and gravimetric samples (according to Example 4) with various dust loadings (0.3-2.2 mg) and silica concentrations (1.0-4.5 wt%) were also processed using the developed method and analyzed by FTIR (according to Example 5). Figure 3 As shown, the measured levels of RCS in the PDM samples were very close to the RCS levels of conventional gravimetric samples ("Casella samples") collected in parallel. The differences in silica levels measured between the PDM and gravimetric samples were less than 10%, with most variations below 5%. The FTIR technique is highly sensitive for silica quantification, and some samples measured had RCS levels as low as 5-10 micrograms.

[0098] Example 6. Comparison of dust removal methods

[0099] The redeposited dust produced by the methods of Examples 2 to 3 (ie, by solvent backwashing and filtration) was carefully analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis. Negligible glass fiber contamination was observed in the redeposited PDM dust samples.

[0100] Using a different approach, the dust filter (as described in Example 1) on which coal dust was collected was removed from the PDM3700, immersed in isopropanol and ultrasonicated (the beaker was placed in an ultrasonic bath for 1-2 minutes) to separate the dust from the filter membrane into the isopropanol. The resulting slurry was then filtered through a PVC filter using the apparatus described in Example 3 to recover the dust. Good dust recovery was obtained. However, significant contamination of glass fibers from the dust filter was observed in the redeposited PDM sample. Combined SEM-energy dispersive X-ray (EDX) analysis identified silica dust particles and glass fibers in the redeposited dust sample.

[0101] The results showed that the backwashing method was very effective in recovering dust from dust filters containing glass fibers without being contaminated by silicon-containing impurities (such as glass fibers) present in the dust filters.

[0102] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It should be understood that the invention includes all such variations and modifications that fall within the spirit and scope of the invention.

Claims

1. A method for treating dust collected on a dust filter of a continuous dust monitoring device for FTIR or XRD analysis, the method comprising: contacting the dust filter with a liquid carrier to selectively remove the dust from the dust filter, thereby producing a slurry comprising the dust in the liquid carrier; and The slurry is filtered through a filter unit comprising a silicon-free polymer filter element, thereby retaining the dust on the polymer filter element.

2. The method of claim 1 further comprising analyzing the dust present on the polymer filter element by FTIR or XRD analysis.

3. The method of claim 1, further comprising ashing the polymer filter element to produce ash containing the dust, and analyzing the ash by FTIR or XRD analysis.

4. A method as claimed in claim 2 or claim 3, wherein analyzing the ash by FTIR or XRD analysis includes quantifying the amount of crystalline silica in the dust.

5. The method according to any one of claims 1 to 4, wherein the dust is coal dust.

6. The method of any one of claims 1 to 5, wherein the dust filter comprises silicon.

7. The method of claim 6, wherein the silicon is present in glass fibers.

8. The method of any one of claims 1 to 7, wherein the continuous dust monitoring device is a personal dust monitor (PDM) comprising a tapered element oscillating microbalance (TEOM).

9. The method of any one of claims 1 to 8, wherein the polymer filter element is composed of one or more organic polymers.

10. The method of claim 9, wherein the one or more organic polymers include at least one selected from the group consisting of polyvinyl chloride, polyvinyl chloride-acrylic copolymer, polyolefin, nylon, polyester, and cellulose.

11. The method of any one of claims 1 to 10, wherein the polymer filter element is ashing.

12. The method of any one of claims 1 to 11, wherein the polymer filter element is a planar sheet that is removably insertable into the filtration unit.

13. The method of any one of claims 1 to 12, wherein the liquid carrier is an organic solvent.

14. The method of claim 13, wherein the organic solvent is an alcohol.

15. The method of any one of claims 1 to 14, wherein contacting the dust filter with the liquid carrier comprises backwashing the liquid carrier through the dust filter from an opposite side of the dust filter to a dust receiving side of the dust filter.

16. The method of any one of claims 1 to 15, wherein at least 70% by weight of the dust collected on the dust filter is retained on the polymer filter element.

17. A method for analyzing dust collected on a dust filter of a continuous dust monitoring device by FTIR or XRD analysis, the method comprising: contacting the dust filter with a liquid carrier to selectively remove the dust from the dust filter, thereby producing a slurry comprising the dust in the liquid carrier; filtering the slurry through a filter unit comprising a silicon-free polymer filter element, thereby retaining the dust on the polymer filter element; and The dust retained on the polymer filter element was analyzed by FTIR or XRD analysis.

18. The method of claim 17, wherein the dust is analyzed while present on the polymer filter element.

19. The method of claim 17, wherein analyzing the dust comprises ashing the polymer filter element to produce ash containing the dust, and analyzing the ash by FTIR or XRD analysis.

20. The method of any one of claims 17 to 19, wherein analyzing the ash by FTIR or XRD analysis comprises quantifying the amount of crystalline silica in the dust.

21. A method as claimed in any one of claims 17 to 20, wherein the dust is coal dust.

22. The method of any one of claims 17 to 21, wherein the continuous dust monitoring device is a personal dust monitor (PDM) comprising a tapered element oscillating microbalance (TEOM).

23. The method of any one of claims 17 to 22, wherein the polymer filter element is composed of one or more organic polymers.

24. The method of claim 23, wherein the one or more organic polymers include at least one selected from the group consisting of polyvinyl chloride, polyvinyl chloride-acrylic copolymer, polyolefin, nylon, polyester, and cellulose.

25. The method of any one of claims 17 to 24, wherein the polymer filter element is ashing.

26. A method as claimed in any one of claims 17 to 25, wherein the polymer filter element is a planar sheet which is removably insertable into the filter unit.

27. The method of any one of claims 17 to 26, wherein the liquid carrier is an organic solvent.

28. The method of claim 27, wherein the organic solvent is an alcohol.

29. The method of any one of claims 17 to 28, wherein contacting the dust filter with the liquid carrier comprises backwashing the liquid carrier through the dust filter from an opposing side of the dust filter to a dust receiving side of the dust filter.

30. The method of any one of claims 17 to 29, wherein at least 70% by weight of the dust collected on the dust filter is retained on the polymeric filter element.

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