FR2757272A1 - Evaluating nature and quantity of mineral particles such as asbestos in fluid - Google Patents

Abstract

A known mass or volume of fluid is filtered to obtain a solids residue, which is then progressively heated in a closed vessel under reduced pressure while monitoring the temperature (100) and pressure (101). Blips (101a-101c) in the pressure curve at specific temperatures indicate that different minerals in the residue are releasing their gaseous constituents, whereby the minerals are identified, and the amplitudes of the blips indicate the respective quantities present. Also claimed is a vessel with an electric heater, pressure reducing means and internal temperature and pressure monitors feeding signals to a processor which identifies minerals by comparing the temperatures at which pressure blips occur with pre-recorded data. Also claimed is apparatus for measuring the amount of asbestos in air or water comprising means to heat the filter residue under vacuum and measure the pressure blip at the temperature where the water content of the asbestos is desorbed. Preferably the residue is heated from 400 to 800 deg C at a pressure below 10-2, preferably 10-4 Pa, while monitoring temperature and pressure at a frequency of 0.01-10 Hertz. Prior to the monitoring the residue is calcined at a lower temperature, under vacuum or atmospheric pressure, to eliminate organics. The vessel has a volume less than 100, preferably less than 10 cm<3>.

Description

METHOD AND DEVICE FOR MEASURING THE QUANTITY OF
MINERAL PARTICLES PRESENT IN A FLUID
The present invention relates to a method and a device for measuring the concentration of asbestos or of a solid mineral compound (in particular a hydrated calcium and / or magnesium silicate), present in the air, in water. or more generally in a fluid.

The technical field of the invention is that of the analysis and control of pollution.

This invention falls within the field of preventing the risks of pulmonary fibrosis induced by prolonged inhalation of this type of material.

An objective of the invention is to allow the evaluation, for example by comparison with a reference value, of the content of an essentially mineral compound, solid, mixed in a fluid, in a reliable, simple, inexpensive manner, easy and quick to implement.

An objective of the invention is to allow such measurements outside a laboratory, for example on the site of a site for the deflocking (that is to say the removal) of asbestos from a building.

Currently a method used to calculate the concentration of asbestos in the air is counting by Scanning Electron Microscopy coupled with chemical analysis by energy dispersion of X-rays. This analytical protocol has the drawback of requiring a "heavy" device. which cannot be installed on the actual sampling site. This remoteness of the dosing system from the sampling site induces high response times (that is to say a duration of obtaining results which is long) which is hardly compatible with the requirements of a deflocking site.

Any exceeding of the safety standards can, by this method, be known by the workers of the deflocking site only after several hours or days, and therefore does not make it possible to check compliance with health and safety standards on the site. construction site.

The object of the present invention is in particular to make it possible to determine the concentration of asbestos at the sampling site and to provide, in a short time (of the order of a few minutes or tens of minutes), quantitative information on the concentrations of the various types of asbestos found in the air or water
Although the invention is particularly suitable for detecting and measuring the quantity of asbestos fibers in the air, the invention can be used to detect the presence, determine the nature and quantify the quantity of other particles. solids or dust of mineral origin, liable to give rise to thermodesorption (that is to say desorption under the effect of temperature) or to the formation of a gas phase of species previously chemisorbed to "mark" them. particles.

The solution to the problem posed consists in providing a device for measuring the quantity of asbestos particles present in the air or in the water which comprises:
- a vacuum thermolysis means of a filtrate comprising the particles
asbestos,
- a means for locating in temperature a pressure signal generated by the
vacuum thermodesorption of the water constituting the asbestos particles
present in the filtrate.

According to one aspect, the invention consists in using a method for evaluating the nature and the quantity of solid mineral particles present in a fluid, in which
- a volume and / or a predetermined mass of said loaded fluid is taken
said particles,
- Separating, for example by filtration, a filtrate consisting of the compounds or
solid materials present in said predetermined volume (or mass) of the
fluid,
- Said filtrate is placed in a sealed container placed near the site of
sampling of the filtrate or on said site,
- said container is closed and connected to a vacuum device,
- said container is placed under negative pressure and heated to effect a
combustion (or calcination or thermolysis) to obtain a desorption of a
at least part of the species chemisorbed or constituting said particles
mineral solids; we measure the pressure in the container and we
increases the temperature of the container appreciably regularly, and during this phase of temperature increase, the increases in the pressure prevailing in the container are detected and, at each significant increase in the pressure, the temperature or temperature range is recorded, as well as the amplitude of the increase in the pressure prevailing in the container, - one deduces from the temperature (s) corresponding to each of the significant increases in pressure, the nature of the solid mineral particles, by comparison with data ( which are previously recorded) of characteristic temperatures of chemical desorption of species and, from the amplitude of the corresponding pressure increase, the quantity of mineral particles in said filtrate is deduced, and from said quantity the concentration of said solid particles is deduced minerals in said fluid.

According to preferred embodiments of the method - said fluid consists essentially of atmospheric air or water; said essentially mineral solid particles are asbestos fibers, dehydroxylation (ie water desorption) temperatures are measured and / or detected; - The thermolysis is carried out in a temperature range between 400 and 800 C; the analysis container is placed under ultra-high vacuum, and the (absolute) pressure prevailing inside the container is preferably maintained at a value less than or equal to 10-4 millibars or 10-2 Pascal, for example at a pressure less than or equal to 10-6 millibars, ie approximately 10-4 Pascal; - prior to the high temperature thermolysis operation for the desorption of chemisorbed species, a preliminary calcination or combustion step of the filtrate is provided, at a temperature below the temperature maintained during the subsequent thermodesorption operation, in with a view to removing part of the substances (in particular organic) present in said filtrate, which calcination or preliminary combustion operation is carried out at atmospheric pressure or else under vacuum; - During the high temperature thermodesorption operation, the temperature and the pressure prevailing inside the container are measured at a sampling frequency of between 0.01 hertz and 10 hertz;
According to another aspect, the invention consists in providing a device for determining the nature and the quantity of particles of mineral origin present in a fluid, which comprises:
- means for separating or preferably filtering said fluid
loaded with said particles to obtain a filtrate,
- a sealed container suitable for receiving the filtrate,
- a device (such as a pump) for depressurizing the container, which
is connected to said container,
- a container heater,
- a pressure sensor in the container, and a pressure sensor
temperature in the container,
- an organ for regulating the temperature and the pressure prevailing in the
the container,
- electronic means for recording the signals delivered by said
temperature sensor and said pressure sensor,
- a means of comparing temperatures (or signals
corresponding) for which there are increases
significant pressure with previously recorded data of
characteristic chemidesorption temperatures of contained species
in said solid mineral particles.

According to preferred embodiments of the device: - said fluid is essentially constituted by atmospheric air or water, said particles are essentially constituted by asbestos fibers - the volume of said container is less than 100 cm3, preferably less than or equal to 10 cm3; the device comprises a computer comprising said electronic pressure and temperature recording means and comprising said comparison means, which device further comprises heating means
electrical resistance of said container; The depressurization organ is a
vacuum pump able to maintain in the container, a pressure of the order of 10
at 10-4 Pascal.

According to a particular aspect, the invention is based on the analysis of the signal from
thermodesorption of the constituent hydroxides of each type of asbestos during the
vacuum calcination of a filtrate obtained under standard flow conditions
and time.

Indeed, under the generic term of asbestos one finds mainly in industrial asbestos used in Europe the following three minerals
- chrysotile Mg3Si2O5 (OH) 4
- crocidolite Na1.38K0.13Ca0.17Fe2 + 0.48Mg3.06Fe3 + 1.66Al0.05 (Si7.94Al0.06) O22 (OH) 2
- amosite Fe2 + 2 (Fe2 + Mg) 5Si8022 (OH) 2
These last two varieties of asbestos are much less used than chrysotile but their better chemical resistance (chrysotile already dissolves in weak acids) may explain why they are more difficult to eliminate from the human body.

Due to a different texture (absence of a central channel) crocidolite and amosite do not have the same physical adsorption properties as chrysotile and their chemical nature does not prepare them for the same chemisorption properties either. On the other hand, these three types of asbestos possess, due to the presence of the hydroxyl radical (OH), a water of constitution whose departure, at a sufficiently high temperature, corresponds to the collapse of the crystalline structure. The mass of water of constitution possessed by each of these samples is deduced from the chemical formula given above. The result of an exact calculation of the percentage by mass of the constituent water desorbed, with reference to the mass of the mineral, is
- 13.04% for chrysotile
- 2.12% for crocidolite
- 1. 60% for amosite;
Moreover, the temperature at which this departure of water of constitution occurs (by desorption) must be able to be considered as a specific property of each of these fibers, provided that the experimental conditions of the heat treatment (composition and pressure of the atmosphere surrounding gas, heating rate, thermal decomposition detection system) are effectively well controlled.

To carry out this check, the use of a very high sensitivity thermodesorption device is proposed. This very high sensitivity is imposed by the very small quantities of material to be detected (a few tens of micrograms). The proposed experimental protocol has five main steps:
step n "1: Introduction of the filtrate into the device,
step n "2: Preliminary thermolysis (either in air or under vacuum) at a temperature below the temperature characteristic of the dehydroxylation of the desired asbestos,
step 3: Putting the analysis cell under ultra-high vacuum (from 104 to 10 6 mbar depending on the desired sensitivity),
step n "4: Controlled heating up to a temperature higher than the previous characteristic temperatures with simultaneous detection of the signal (pressure peak) revealing the thermodesorption, in the predetermined temperature slots,
step n "5: Triggering of an alarm if the admissible threshold is exceeded.

Optionally, the device envisaged can be coupled to a quadrupolar mass spectrometer so as to analyze the chemical nature of the gases produced by thermolysis. This arrangement makes it possible to ensure that the recorded signal does not come from another mineral compound such as a carbonate, the calcination of which produces carbon dioxide.

Furthermore, a preliminary marking of the asbestos fibers with a substance (such as an alcohol) giving rise to a specific chemisorption, can be used to increase the sensitivity of the thermodesorption signal.

The calculation of the asbestos concentration can be made on the basis of the following considerations
a - The quantity of water released during the decomposition of asbestos is calculated either from the height (amplitude) of the thermodesorption peak, or by integrating this peak, according to the formula

where n H20 is the quantity of water released during thermodesorption
V is the volume of the reactor
R the gas constant
T, and Tf the initial and final temperatures of the pressure peak
p the measured pressure
T the measured temperature
b - The temperature range at which the thermodesorption is observed (T, and T) is specific to the variety of asbestos (under given experimental conditions).

c - The quantity of asbestos present in the furnace (or container) is then calculated according to the formula
ncomp = 100 / Xcomp * n H20
where xCOmp is the percentage of water of the compound considered (13.04% for chrysotile)
nCOmp the quantity of matter of the considered compound (in moles)
A preliminary determination or estimation of the average size of the fibers makes it possible to go back to the number of fibers.

Knowing the sampling conditions (volume of air sampled), it is then possible to calculate the concentration of each of the types of asbestos and to trigger an alarm if the measured rate exceeds the permitted threshold (either on one of these varieties). , or for the whole).

The result given is both quantitative and qualitative.

In addition, the present invention has the advantage of having recourse to a fairly rapid thermal analysis. The vacuum and heat treatment operations can be done in about ten minutes or even less. The processing of the pressure and temperature signals being carried out by computer in an almost instantaneous manner, which responds well to the objectives set.

Finally, all the components of this transportable analysis system are compact enough to allow installation and use on site,
The components of a preferred device are
- A pump ensuring a residual pressure of around 10.6 mbar,
- A heating device making it possible to impose a temperature program on the sample (to make it possible to correlate the phenomenon of thermodesorption and the temperature),
- A reactor capable of receiving the filter and / or the filtrate and of being heated,
- A temperature measuring device (chromel-alumel thermocouple for example),
- A pressure sensor capable of sensitively measuring pressures of the order of 10 1 to 10-6 mbar, for example consisting of a PIRANI type gauge, of the
PENNING, ionization or even quadrupolar,
- Power supplies for the various measuring devices as well as the oven,
- A system for acquiring temperature and pressure signals,
- An oven temperature profile programming system,
- A system for integrating and calculating the concentration of the different types of asbestos present,
- An alarm system triggered from the result of the concentration calculation.

By way of example, to detect a fiber concentration of 25 asbestos fibers per liter of air, a filtrate is taken by pumping and filtering the air with a flow rate of 10 liters per minute for 15 minutes, i.e. a total volume of pumped and filtered air 150 liters.

The resulting filtrate comprises 3750 fibers which represents (for cylindrical fibers of one micron in diameter, 10 microns in length and unit mass of the order of 2.510.11 grams) a total mass of asbestos in the filtrate of 1 10 -7 grams approximately.

In the case of the chrysotile variety, the loss of water (by mass) by thermodesorption represents approximately 13% of the overall mass of asbestos, ie here 0.01 g of water.

This quantity of water occupies a volume of 10-5 cm3 under standard conditions of temperature and pressure (the worst case since the gaseous molar volume is then only 22.4 liters mol, it is greater under vacuum. and at high temperature).

If the device (i.e. the container and its connection circuit to the pump) has a total volume of 1 cm3, the pressure rise (given by the calculation of the ratio of the volume of water to the total volume) will be of 1 on2 mbar.

If the device has a total volume of 100 cm3 pressure rise will be no more than 10-4 mbar.

Such low pressure rises can be measured by the aforementioned gauges which can be obtained in France, for example from the companies
ALCATEL, LEYBOLD or EDWARDS.

The many advantages provided by the invention will be better understood from the following description which refers to the appended drawings, which illustrate, without any limiting nature, preferred embodiments of a method according to the invention.

FIG. 1 schematically illustrates the main steps of a method according to the invention.

FIG. 2 illustrates in schematic view the main constituents of a device according to the invention.

With reference to FIG. 2, the device comprises a reactor or container 4 inside which is placed a sample 1 to be analyzed obtained by filtration of a fluid whose asbestos concentration is to be controlled.

A temperature sensor 8 such as a thermocouple is provided inside the reactor 4 which is housed in a furnace 2 equipped with electrical resistances 3 to enable the reactor 4 to be heated; the reactor is connected by means of a connector 5 and a pipe 7 to a pump 18 for drawing off the volume of the container with a vacuum; a pressure sensor 6 is placed on the pipe 7 to measure the pressure prevailing in said pipe and in said reactor.

The device comprises a computer 9 equipped with a member 10 for controlling and programming the temperature prevailing in the reactor 4; to this end, the module 10 receives the signal 14 delivered by the thermocouple 8 corresponding to the temperature prevailing in the container and in response emits a signal 16 for controlling the operation of the electric resistances 3 for heating the furnace 2.

The computer 9 is further equipped with a module 11 for controlling and recording the pressure in the container; to this end, the module 11 receives the signal 15 emitted by the pressure sensor 6 and controls the operation of the pump 18 by control signals 17.

The computer 9 comprises a module 12 for calculating the concentration of each type of asbestos as a function of the pressure data prevailing in the container which are transmitted to it by the module 11, as well as the temperature data prevailing in the reactor 4 which are transmitted to it by the temperature control and programming module 10.

An alarm module 13 connected to the calculation and analysis module 12 can also be provided.

With reference to FIG. 1, the x-axis represents time, the y-axis located on the left in the figure represents the pressure, and the y-axis located on the right in the figure represents the temperature prevailing in the container. where the sample subjected to thermolysis is placed with a view to effecting the desorption of the constituent or chemisorbed species of the material whose concentration is to be measured.

In this figure, the dotted curve 100 represents the internal temperature variations of the container as a function of time and the continuous line curve 101 represents the pressure variations inside the container as a function of time.

In a preliminary step 50 of the process, the operation of the pump is activated to change the pressure prevailing in the container from atmospheric pressure to a working pressure 40 which is for example of the order of 103 to 104
Pascal; at the end of this first step 50, the heating means of the reactor are activated, which cause an increase in the temperature 100 and correspondingly in the pressure 101 prevailing in the container; this second calcination or thermolysis step 51, which is prior to the main thermolysis step, makes it possible to eliminate pollutants or parasites contained in the sample or filtrate such as for example water, organic products and / or species physisorbed by the material to be analyzed; the temperature prevailing in the container during this preliminary calcination step 51 may be of the order of 200 to 300 ° C., for example.

This preliminary calcination step 51 can be carried out either under a relative vacuum, which can in particular make it possible to use the pressure signal 101, to determine the end of the preliminary calcination of the pollutants present in the filtrate, corresponding to the drop in the pressure, the reactor evacuating pump being during this phase in operation, for example substantially permanent alternately, this preliminary calcination step 51, can be carried out under an oxidizing atmosphere (for example in air), the presence of oxygen making it possible to facilitate the calcination of the polluting products present in the filtrate.

At the end of this preliminary calcination step 51, the heating means are activated to switch to a higher temperature range and simultaneously the pressure in the container is brought back to the reference value 40.

The next step is the main step of thermolysis of the sample with a view to detecting the peaks corresponding to the desorption of the characteristic species of the material to be analyzed, and corresponding to a phase of regular rise in temperature by a value 30 initial to a final value 31, between the times marked 21 and 22; during this period or step appear (as shown in FIG. 1) three peaks 101 a, 101 b, 101 c on the timing diagram of the pressure 101 prevailing in the container; these peaks correspond to instants marked respectively 23, 24, 25 and to respective temperatures marked 33, 34, 35; according to the method, the appearance of these peaks of the pressure signal is detected, the temperature values 33, 34, 35 corresponding to each of these peaks are recorded and the respective amplitude 43, 44, 45 of these three peaks is also recorded or substantial variations in the pressure signal.

By analysis, and by comparison with tables of temperature data characteristic of thermodesorption, one deduces from the temperatures 33, 34, 35 the nature of the desorbed species, and one deduces from the amplitudes 43, 44, 45 the respective concentrations of the three species corresponding respectively. at each of the three peaks of the pressure signal, knowing the chemical composition of the material sought and the concentration of which in the sample is to be determined.

Claims (10)

1. Method for evaluating the nature and quantity of solid particles minerals present in a fluid, in which: - there is a filtrate (1) consisting of the solid compounds present in a predetermined volume or mass of the fluid, in a container (4), - said container is placed under vacuum (40) and heated to effect thermolysis in order to obtain a desorption of at least part of the species chemisorbed or constituting said solid particles mineral, - measuring the pressure (101) prevailing in the container and increasing substantially regularly the temperature of the container and, during this phase of temperature increase, we detect the increases of the pressure in the container, and the temperature is recorded (100) or temperature range, as well as the amplitude (43, 44, 45) of the increase (101a, 101b, lolo) of the pressure prevailing in the container, - we deduce from the temperature (s) (33, 34, 35) corresponding to each of the pressure increases, the nature of the solid particles mineral, by comparison with previously recorded data characteristic desorption temperatures, and we deduce from the amplitude of the corresponding pressure increase the quantity of particles minerals in said filtrate, and the concentration of said solid mineral particles in said fluid. 2. The method of claim I wherein said fluid is essentially consisting of atmospheric air or water, wherein said essentially mineral solid particles are asbestos fibers, and in which dehydroxylation temperatures are measured and detected. 3. Method according to any one of claims 1 or 2 wherein one performs thermolysis in a temperature range of 400 to 800 "C. 4. Method according to any one of claims 1 to 3 wherein it is evacuates the analysis container, and preferably the pressure inside the container at a value less than or equal at 10-4 millibars or approximately 10.2 Pascal, and for example at a pressure less than or equal to 10.6 millibars or approximately i 104 Pascal. 5. Method according to any one of claims I to 4 wherein prior to the thermolysis operation, a step of calcination or preliminary combustion of the filtrate, at a temperature lower than the temperature maintained during the subsequent operation of thermodesorption, in order to eliminate the organic substances present in said filtrate, which calcination or combustion operation preliminary is carried out at atmospheric pressure or in a vacuum, and wherein, during the high temperature thermodesorption operation, the temperature and pressure inside the container are measured with a sampling frequency between 0.01 hertz and 10 hertz. 6. Device for determining the nature and quantity of particles of mineral origin present in a fluid, which comprises: - a sealed container (4) capable of receiving a filtrate (1) consisting of solid compounds present in a predetermined volume or mass fluid, - a member (18) for depressurizing the container, - a member (2, 3) for heating the container, - a sensor (6) of the pressure prevailing in the container, and a sensor (8) the temperature in the container, - a means (9, 10, 11) for recording the signals delivered by said temperature sensor and said pressure sensor, - a means (12) for comparing the temperatures at which are observed significant increases in pressure, with data previously recorded characteristic desorption temperatures. 7. Device according to claim 6 wherein said fluid is essentially constituted by atmospheric air or water and in in which said particles consist essentially of fibers asbestos. 8. Device according to any one of claims 6 or 7 wherein the volume of said container is less than 100 cm3, preferably less than or equal to 10 cm3. 9. Device according to any one of claims 6 to 8 which comprises a computer comprising said comparison means, which device further comprises means for electric resistance heating of said container, and in which the depressurization member is capable of maintain a pressure in the order of 10.2 to 10-4 Pascal in the container. 10. Device for measuring the quantity of asbestos particles present in the air or in the water which comprises; - a means of thermolysis (53) under vacuum of a filtrate comprising the asbestos particles, - a means for identifying the temperature of a pressure signal (101) generated by the vacuum thermodesorption of water constituting the asbestos particles.