Efficient determination method of free silicon dioxide

Abstract

The invention discloses an efficient determination method of free silicon dioxide, which at least comprises the following steps: respectively pretreating and weighing a dust sample to prepare a suspension; diluting the suspension step by step to prepare to-be-filtered liquid, and filtering the to-be-filtered liquid through filter paper; the filter paper is transferred to a filtering cavity for cleaning and filtering, part of the peripheral wall of the filter paper is suspended relative to the filtering cavity, so that part of the peripheral wall of the filter paper is free of contact blocking of a cavity wall, water is added into the funnel-shaped filter paper, and the water penetrates through the filter paper to generate filtrate which is converged through a suspended space between the peripheral wall of the filter paper and the filtering cavity or flows downwards; dynamically monitoring the pH value of the filtrate, and stopping adding water until the pH value of the filtrate is greater than or equal to 7; and drying and carbonizing the filter paper, cooling, weighing, and calculating the content of free silicon dioxide in the dust sample. Part of the peripheral wall of the filter paper is suspended relative to the filter cavity, so that the cleaning and filtering steps can be effectively accelerated, and the experimental efficiency of measuring the content of free silicon dioxide in dust by a pyrophosphoric acid method is further improved.

Description

Technical Field

[0001] The invention belongs to the field of detection technology, and particularly relates to a high-efficiency determination method for free silicon dioxide. Background Art

[0002] Mining, stone, coal, wood and other industries will produce dust during the processing and production process. The free silica in the dust has adverse effects on human health. Therefore, the free silica content is the main indicator for evaluating the harmful nature of dust. The state stipulates that work environments involving dust must be dust-proofed and monitored.

[0003] At present, the free silicon dioxide content in dust is detected by the pyrophosphate method specified in GBZ / T 192.4-2007 Determination of Dust in Workplace Air Part 4: Free Silica Content. The pyrophosphate method has relatively low requirements for laboratory equipment and instruments. The main instruments are glass containers (such as beakers, conical flasks, etc.), crucibles, stirring glasses, funnels, filter paper, heating furnaces, etc., which are all very common laboratory equipment and have the advantages of low experimental cost and high accuracy. However, the pyrophosphate method also has obvious disadvantages. It involves multiple filtering and cleaning operations, which results in the cost of the measurement experiment being mainly concentrated in labor costs and time costs.

[0004] In order to solve the above problems, a patent document with publication number CN117949350A discloses a method for determining the content of free silicon dioxide in dust, which method comprises the following steps: (1) drying the dust to be tested to obtain a dust sample; (2) drawing a standard curve; (3) dissolving a dust sample with a mass of G in hydrofluoric acid, standing and centrifuging, and detecting the obtained supernatant using an ICP-MS instrument to determine the total silicon content in the detected dust sample; (4) mixing a dust sample with a mass of G with an acid solution (phosphoric acid or pyrophosphoric acid mixed solution), stirring and mixing at 240 to 320° C., cooling, filtering and centrifuging, and detecting the supernatant using an ICP-MS instrument to determine the silicon content in the detected dust sample; (5) determining the content of free silicon dioxide in the dust sample based on the mass G of the dust sample, the total silicon content and the silicon content.

[0005] The above-mentioned prior art has the advantages of simple operation, rapidity and accuracy in the determination of the free silica content in dust. However, the purchase cost of the ICP-MS instrument is relatively high, and it is often not within the laboratory's purchase plan. Secondly, the pyrophosphate method is the detection method adopted by most laboratories. The above-mentioned prior art experimental steps are quite different from the pyrophosphate method. For experimental personnel who have already mastered the pyrophosphate method, the laboratory needs to re-train the experiments, thereby incurring training costs. The applicant has been deeply engaged in laboratory technical services for many years and believes that it is necessary to carry out research and development and improvement on the experimental operation of the pyrophosphate method, while controlling the cost of technical improvements as much as possible, reducing labor costs and shortening the experimental cycle. Summary of the invention

[0006] In view of the problems in the related art, the present invention proposes an efficient determination method of free silicon dioxide to overcome the above technical problems existing in the existing related art.

[0007] The technical solution of the present invention is achieved in this way:

[0008] An efficient method for determining free silicon dioxide comprises at least the following steps:

[0009] (1) pre-treating and weighing the dust samples respectively, then mixing with at least a pyrophosphoric acid solution to form a suspension, heating and then cooling;

[0010] (2) diluting the suspension of step (1) stepwise to prepare a filtrate, filtering the filtrate through a funnel-shaped filter paper, and retaining the silicon dioxide in the filtrate in the filter paper;

[0011] (3) transferring the filter paper of step (2) to a filter cavity for cleaning and filtration, wherein the funnel-shaped filter paper has a wide end and a narrow end. After being placed in the filter cavity, the filter paper is kept in an upright state with the narrow end facing downward, and a portion of the outer peripheral wall of the filter paper is suspended relative to the filter cavity. Water is added to the funnel-shaped filter paper, and the highest water level is set between the position of the filter paper two-thirds away from the narrow end and the wide end. When the filtrate passes through the filter paper to generate a filtrate, the filtrate converges or flows downward through the suspended space between the outer peripheral wall of the filter paper and the filter cavity, and the pH of the filtrate is dynamically monitored until the pH of the filtrate is ≥7, then the addition of water is stopped;

[0012] (4) Place the cleaned filter paper in a container of known weight, dry and carbonize it, and weigh it again after cooling to calculate the free silica content in the dust sample.

[0013] In the experimental operation of the pyrophosphate method, the filter paper with retained silica needs to be repeatedly washed and filtered until the pH is ≥ 7. This step is generally to fit the filter paper in a funnel, and place a beaker under the funnel to receive the filtrate. Since the other side of the liquid is close to the inner wall of the funnel after passing through the filter paper, it is difficult for the filtrate to converge or flow downward, which leads to a long experiment time. In the present invention, part of the outer peripheral wall of the filter paper is suspended relative to the filter cavity, so that part of the outer peripheral wall of the filter paper is not blocked by the contact of the cavity wall, and the filtrate passing through the filter paper can converge or flow downward as quickly as possible, while the remaining outer peripheral wall of the filter paper is The invention can effectively speed up the step of cleaning and filtering the filter paper to neutrality in the pyrophosphate method by fitting with the filter cavity to maintain the shape, thereby improving the experimental efficiency of the pyrophosphate method for determining the free silicon dioxide content in dust. At the same time, the improvement scheme of the invention can be achieved by customizing a funnel of a specific shape (such as a funnel with a convex or concave inner surface, etc.), customizing a support structure for suspending the filter paper and then placing it in an existing funnel in the laboratory for use, etc. Compared with the prior art, the improvement cost is lower, the original pyrophosphate method experimental steps are maintained, there is no need to re-conduct experimental training, and there is almost no training cost.

[0014] Preferably, in step (3), the speed of adding water is greater than the water filtering speed of the filter paper, so that the funnel-shaped filter paper can accumulate a certain amount of water over a period of time, which can fully soak and clean the silica on the filter paper, thereby improving the accuracy of the measurement experiment.

[0015] Since the filter paper itself is a material with poor mechanical strength and toughness, and the filter paper is completely soaked with the filtrate when placed in the filter cavity, it is relatively soft and easily damaged. More importantly, the filter paper is specifically designed in the present invention so that part of the outer peripheral wall is suspended relative to the filter cavity during cleaning and filtration in step (3). If the suspended position of the filter paper is impacted by the water flow when water is added, it is easy to cause deformation, damage, tearing and other problems. Therefore, the design of the water adding speed of the present invention is particularly important. More preferably, in step (3), the water adding speed is 0.1-1.0 m / s. This speed design not only avoids damaging the filter paper, but also has the effect of avoiding liquid splashing as much as possible.

[0016] More preferably, in step (3), water is added in the form of a spray to reduce the impact force of the water flow on the filter paper when adding water, avoid the water flow concentrating on a certain position of the filter paper, and at the same time make the water flow as comprehensively and evenly as possible on the inner surface of the filter paper, thereby improving the cleaning effect of step (3).

[0017] Preferably, the inner surface of the filter cavity is adapted to the funnel-shaped filter paper, the bottom of the filter cavity has a through leakage hole, the inner surface of the filter cavity is provided with at least one outwardly recessed flow guide groove, the filter paper is in a suspended state corresponding to the outer peripheral wall of the flow guide groove, and the remaining outer peripheral wall of the filter paper is in contact with the cavity wall of the filter cavity;

[0018] At least one end of all the guide grooves is directly or indirectly connected to the water leakage hole.

[0019] Preferably, the sum of the slot areas of all the guide grooves is smaller than the remaining inner surface area of ​​the filter cavity without the guide grooves. As mentioned above, the completely soaked filter paper is very soft and fragile, and there needs to be sufficient fitting area between the filter cavity and the filter paper so that the filter paper can maintain an ideal shape. At the same time, if the area of ​​the guide groove is too large, the filter paper will have too many unsupported peripheral walls hanging in the air, which is prone to deformation, damage, tearing and other problems under the impact of water.

[0020] Preferably, in step (3), the water used to wash the filter paper is distilled water, and the temperature of the distilled water is set to T, 80°C≤T≤250°C.

[0021] Preferably, in step (3), the filter paper is cleaned and filtered by an automatic filter.

[0022] The automatic filter comprises a rotating drive source, a rotating platform, a lifting drive source, a filtering platform, a water supply pipeline, a drainage pipeline, a weighing module, a pH sensor and a controller;

[0023] The rotation driving source is connected to the rotating table and drives the rotating table to rotate at a specific angle. The rotating table is provided with N evenly distributed filter paper containers (N≥2), and one filter paper container is one filter cavity;

[0024] The rotating platform is provided with N supporting openings evenly distributed on the circumference and adapted to the filter paper container, the width of each supporting opening being larger than the water leakage hole and smaller than the maximum width of the filter paper container, and the supporting opening supports the filter paper container;

[0025] A filter platform is fixedly arranged below any of the supporting openings, the filter platform comprises a lifting piece for lifting the filter paper container and a weighing module installed at the bottom of the lifting piece, the weighing module is used to monitor and control the amount of water added so that the highest water level is located between the position of the filter paper two-thirds away from the narrow end and the wide end, the lifting drive source is directly or indirectly connected to and drives the lifting of the filter platform, and the filter platform lifts or puts down the filter paper container through the supporting opening;

[0026] The water supply pipe is arranged above the filter station, the water supply pipe is externally connected to a water source and is provided with a water valve, the water supply pipe is higher than the filter paper container in the vertical direction and the water outlet faces the inside of the filter paper container;

[0027] The drainage pipe receives the filtrate from the filter paper container held by the filter table, the probe of the pH sensor is installed in the drainage pipe, and the pH sensor dynamically monitors the pH of the filtrate.

[0028] Preferably, step (3) specifically comprises the following steps:

[0029] (3-1) placing filter paper in the filter paper container;

[0030] (3-2) starting the automatic filter, the controller controls the lifting drive source to drive the filter table to rise, and the filter table supports the filter paper container located above it;

[0031] (3-3) Adding water: After the lifting action is completed, the controller starts the water valve, and the water source delivers 80-250° C. distilled water to the filter paper through the water supply pipe until the target water volume is reached. The water level of the target water volume is located between the position of the filter paper two-thirds away from the narrow end and the wide end. The weighing module sends a weight signal to the controller that the target water volume has been reached, and the controller controls the water valve to be closed to stop adding water;

[0032] (3-4) Cleaning and filtration: The filtrate passing through the filter paper converges or flows downward along the guide groove, then flows to the leaking hole, and then flows into the drainage pipe, and flows through the probe of the pH sensor. The pH sensor detects the pH of the filtrate and sends it to the controller. If the pH is less than 7, the filtration is continued until the weighing module sends a weight signal of the preset minimum water volume to the controller. The controller starts the water valve and the water pump again, and adds water again until the target water volume is reached. And so on. The water adding operation is repeated until the pH sensor detects that the pH of the filtrate is ≥7, and the cleaning and filtration of one filter paper is completed;

[0033] (3-4) The filter paper container is re-placed on the supporting opening, and then the rotating drive source drives the rotating table to rotate, and another filter paper container is rotated to the top of the filter table, and the above steps (3-2) to (3-4) are repeated;

[0034] The rotating table stops working when the number of rotations reaches N-1.

[0035] Preferably, the water leakage hole is opened at the bottom of the filter paper container, and the inner surface of the filter paper container is provided with a spiral guide groove and four arc-shaped guide grooves evenly distributed around the circumference, the spiral guide groove spirally extends downward from the upper part of the inner surface of the filter paper container to the water leakage port, the four arc-shaped guide grooves are formed by extending downward from the upper part of the inner surface of the filter paper container and intersecting with the spiral guide groove, and the lower ports of all the guide grooves are gathered and connected to the water leakage hole.

[0036] The inner diameter of the filter paper container is 1-9 cm, and the depth of the container is 0.5-5 cm. This size design enables the filter paper to be placed in the filter paper container and remain in an upright state with the narrow end facing downward.

[0037] Preferably, a wastewater receiving pan is installed below the rotating table, the water leakage holes of all the filter paper containers are located directly above the wastewater receiving pan, and the water outlet of the drainage pipe is directly or indirectly connected to the wastewater receiving pan.

[0038] Preferably, the lifting member is The structure comprises an upper plate and a lower plate, wherein the upper plate is inserted between the rotating table and the waste water tray, the top surface of the upper plate has a ring platform for supporting the bottom of the filter paper container, the lower plate is located below the waste water tray, and the lower plate is connected to the lifting drive source and the weighing module;

[0039] A drainage pipe is arranged between the upper plate and the waste water tray, and a drainage port is opened at a position of the upper plate corresponding to the water leakage hole, and the drainage port leads to the water inlet of the drainage pipe.

[0040] Preferably, a cavity cover is installed near the water outlet of the water supply pipe, the water supply pipe runs through the center of the cavity cover, the cavity cover is adapted to the open cavity of the filter paper container, and the water outlet of the water supply pipe is connected and communicated with a spherical spray nozzle;

[0041] In step (3-2), the open cavity of the lifted filter paper container is close to the cavity cover but not in contact with it, and the highest water drop point of the spherical spray nozzle is lower than the wide end of the filter paper.

[0042] Preferably, the water supply pipeline is externally connected to a water pump, a constant temperature heating water tank and the water valve, and the constant temperature heating water tank contains at least 5L of distilled water as the water source.

[0043] Preferably, the drainage pipe can also be connected to an external flushing water source for flushing the drainage pipe and the pH sensor probe located in the drainage pipe after each pH sensor detects pH, which can further improve the accuracy of the measurement.

[0044] Preferably, the following preparatory work is included before step (1):

[0045] The distilled water used for washing the filter paper is heated, the distilled water is heated at least 5 L at a time, and the distilled water is heated to 80° C. and kept warm;

[0046] Preparation of pyrophosphoric acid solution: Heat 85% (W / W) phosphoric acid solution to boiling, raise the temperature to 250°C until no bubbling occurs, cool, and store for later use.

[0047] Specifically, step (1) includes the following steps:

[0048] (1-1) The dust sample is placed in a closed environment at 105±3℃ and dried for 1.5 to 2.5 hours. After cooling slightly, it is stored in a dry container for later use.

[0049] If the particle size of the dust sample is large, the dust sample needs to be processed to a particle size of less than 0.3 μm (such as grinding with an agate mortar, etc.).

[0050] (1-2) Accurately weigh 0.1-0.2 g of dust sample into a container, record the mass G of the dust sample, add 15-20 ml of pyrophosphoric acid solution and 0.1-0.2 mg of ammonium nitrate powder, stir to make the dust sample completely wet, and prepare a suspension;

[0051] The suspension is quickly heated to 245-250°C and kept warm, stirred for 15-20 minutes, and the heated suspension is cooled to 40-50°C at room temperature. If the temperature exceeds 250°C, a jelly-like substance is easily formed, which affects subsequent filtration.

[0052] Specifically, step (2) includes the following steps:

[0053] (2-1) Stepwise dilution: Add 50-80° C. distilled water to the suspension in step (1) until the liquid volume is 40-45 ml, stir evenly while adding distilled water, and continue to add distilled water until the liquid volume is 150-200 ml to prepare a filtrate;

[0054] (2-2) Take a slow quantitative filter paper and fold it into a funnel shape, place it in the funnel and moisten it with distilled water to adhere to the wall;

[0055] (2-3) boiling the filtrate prepared in step (2-1), allowing it to stand for a while, and filtering it while it is hot after the suspension has settled slightly;

[0056] (2-4) After filtration, wash the container with 0.1 mol / L hydrochloric acid and transfer to filter paper.

[0057] Preferably, the specific operation of step (4) is: fold the filter paper after filtering and cleaning, put it into a container of known weight, the weight of the container is set as m1, and then place the container at 800-900°C for drying and carbonization for 30-35 minutes, cool it at room temperature for at least 30 minutes, and then place it in a dryer to cool for at least 1 hour, place it on a weighing device and weigh it to a constant weight, the weight is set as m2, and calculate the free silica content in the dust sample with reference to the following formula.

[0058] C=(m2-m1) / G×100

[0059] Where: C refers to the free silica content in the dust sample (%);

[0060] m1 refers to the mass of the container (g);

[0061] m2 refers to the total mass of the container and the filter paper sediment after carbonization (g);

[0062] G refers to the mass of the dust sample (g).

[0063] Preferably, the dust sample is sampled by using a filter membrane with a diameter of 75 mm to collect dust in the air at a sampling point at a large flow rate, or by collecting fresh settled dust at a breathing zone height at the sampling point, with a sampling weight of >0.1 g. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a structural schematic diagram of the present invention;

[0065] Figure 2 It is a schematic diagram of the guide groove structure of the filter cavity of the present invention;

[0066] Figure 3 It is a schematic diagram of the structure of the filter cavity, cavity cover, water supply pipeline and spherical spray nozzle of the present invention;

[0067] Figure 4 It is a cross-sectional view of the present invention (the water supply pipe and the spherical spray nozzle are omitted).

[0068] Reference numerals

[0069] 1. Filter paper container (filter cavity); 101. guide groove; 101a. spiral guide groove; 101b. arc-shaped guide groove; 102. water leakage hole;

[0070] 2. Rotating table; 201. Support opening;

[0071] 3. Wastewater receiving pan;

[0072] 4. Rotation drive source;

[0073] 5. Weighing module;

[0074] 6. Water supply pipe;

[0075] 7. Cavity cover;

[0076] 8. pH sensor;

[0077] 9. Drainage pipes;

[0078] 10. Lifting member; 1001. Upper plate portion; 1002. Lower plate portion;

[0079] 11. Lifting drive source;

[0080] 12. Spherical spray nozzle. DETAILED DESCRIPTION

[0081] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0083] Example 1

[0084] An efficient method for determining free silicon dioxide comprises the following steps:

[0085] A. Preparatory work

[0086] Preparation of pyrophosphoric acid solution: Heat 85% (w / w) phosphoric acid solution to boiling, raise the temperature to 250°C until no bubbling occurs, cool, and store for later use.

[0087] Start the constant temperature heating water tank and check whether there is at least 5L of distilled water in the water tank. The distilled water is heated at least 5L at a time. The distilled water is heated to 80°C and kept warm.

[0088] B. Measurement work

[0089] (1) Pre-treat and weigh the dust samples respectively.

[0090] (1-1) The dust sample is placed in an oven (constant temperature drying oven) at 105±3°C for 1.5 to 2.5 hours, cooled slightly, and stored in a desiccator for later use. The desiccator contains color-changing silica gel. The particle size of the dust sample is less than 0.3 μm.

[0091] (1-2) Use an analytical balance to accurately weigh 0.1000-0.2000 g of dust sample into a container (conical flask), record the mass G of the dust sample, add 15-20 ml of pyrophosphoric acid solution and 0.1-0.2 mg of ammonium nitrate powder, and stir to make the dust sample completely wet to obtain a suspension.

[0092] The suspension was placed on an adjustable electric furnace and rapidly heated to 245-250°C and kept warm. The temperature was monitored with a stirring rod with a thermometer and stirring was continued for 15-20 minutes. The heated suspension was cooled to 40-50°C at room temperature.

[0093] (2) diluting the cooled suspension in step (1) stepwise to prepare a filtrate, filtering the filtrate through filter paper, and retaining the silicon dioxide in the filtrate in the filter paper.

[0094] The specific steps include:

[0095] (2-1) Stepwise dilution: Add 50-80° C. distilled water to the suspension in step (1) until the liquid volume is 40-45 ml, stir evenly while adding distilled water, and continue to add distilled water until the liquid volume is 150-200 ml to prepare a filtrate;

[0096] (2-2) Take a slow quantitative filter paper and fold it into a funnel shape, place it in the funnel and moisten it with distilled water to adhere to the wall;

[0097] (2-3) placing the filtrate prepared in step (2-1) on an adjustable electric stove and boiling it, allowing it to stand for a while until the suspension settles slightly, and filtering it while it is hot;

[0098] (2-4) After filtration, wash the container with 0.1 mol / L hydrochloric acid and transfer it to filter paper. Rinse the sediment on the filter paper 3 to 5 times.

[0099] (3) The filter paper of step (2) is transferred to the filter chamber for cleaning and filtering. In this embodiment, the operation is specifically performed by an automatic filter, and the automatic filter can clean and filter eight filter papers at the same time.

[0100] The automatic filter comprises a rotating drive source 4, a rotating platform 2, a lifting drive source 11, a filtering platform, a water supply pipeline 6, a drainage pipeline 9, a weighing module 5, a pH sensor 8 and a controller.

[0101] The rotation driving source 4 is connected to the rotating platform 2 and drives the rotating platform 2 to rotate at a specific angle. The rotating platform 2 is provided with N filter paper containers 1 (N≥2) that are evenly distributed. In this embodiment, eight filter paper containers 1 are provided.

[0102] The inner surface shape of the filter paper container 1 is adapted to the filter paper folded into a funnel shape, the inner diameter of the filter paper container 1 is 1 to 9 cm (9 cm in this embodiment), and the container depth is 0.5 to 5 cm (5 cm in this embodiment).

[0103] The bottom of the filter paper container 1 has a through leakage hole 102 , and the inner wall of the filter paper container 1 is provided with at least one guide groove 101 recessed toward its outer wall, and at least one end of the guide groove 101 is directly or indirectly connected to the leakage hole 102 .

[0104] The total area of ​​the slots of all the guide grooves 101 is smaller than the remaining inner surface area of ​​the filter paper container 1 where no guide grooves 101 are provided.

[0105] Specifically in this embodiment, the inner surface of the filter paper container 1 is provided with a spiral guide groove 101a and four arc-shaped guide grooves 101b evenly distributed around the circumference. The spiral guide groove 101a spirally extends downward from the upper part of the inner surface of the filter paper container 1 to the water leakage port. The four arc-shaped guide grooves 101b are formed by extending downward from the upper part of the inner surface of the filter paper container 1 and intersecting with the spiral guide groove 101a. The lower ports of all the guide grooves 101 are gathered and connected to the water leakage hole 102.

[0106] The rotating table 2 is a disc-shaped structure, and is provided with a plurality of (eight) supporting openings 201 that are adapted to the filter paper container 1 and are evenly distributed around the circumference. The width of the supporting openings 201 is larger than the leakage hole 102 and smaller than the maximum width of the filter paper container 1. The supporting openings 201 support the filter paper container 1.

[0107] A wastewater receiving pan 3 is installed below the rotating platform 2 , and the water leakage holes 102 of all the filter paper containers 1 are located directly above the wastewater receiving pan 3 .

[0108] A filter platform is fixedly arranged below any of the supporting openings 201, and the filter platform includes a supporting member 10 for supporting the filter paper container 1 and a weighing module 5 (a commercially available weight sensor may be used) installed at the bottom of the supporting member 10, and the weighing module 5 is used to monitor and control the amount of water added so that the highest water level is located between the position of the filter paper two-thirds away from the narrow end and the wide end, and the accuracy of the weighing module 5 is not less than 1g. The lifting drive source 11 is directly or indirectly connected to and drives the lifting of the filter platform, and the filter platform lifts or puts down the filter paper container 1 through the supporting opening 201.

[0109] The lifting member 10 is The structure comprises an upper plate 1001 and a lower plate 1002, wherein the upper plate 1001 is inserted between the rotating table 2 and the waste water tray, the top surface of the upper plate 1001 has a ring platform for supporting the bottom of the filter paper container 1, and the lower plate 1002 is located below the waste water tray, and the lower plate 1002 is connected to the lifting drive source 11 and the weighing module 5.

[0110] A drainage pipe 9 is provided between the upper plate 1001 and the wastewater tray, and a drainage port is provided at the upper plate 1001 corresponding to the position of the water leakage hole 102, and the drainage port leads to the water inlet of the drainage pipe 9. The drainage pipe 9 receives the filtrate of the filter paper container 1 held by the filter table, and the probe of the pH sensor 8 is installed in the drainage pipe 9 for dynamically monitoring the pH of the filtrate of the filter paper, and the water outlet of the drainage pipe 9 is directly or indirectly connected to the wastewater receiving tray 3.

[0111] The rotary drive source 4 and the lifting drive source 11 of this embodiment may include conventional parts such as a motor, a gear set, a connecting shaft, and a gearbox. Switching the rotary motion of the motor to the lifting motion is a conventional technology in the field, which will not be described in detail here. Mechanical engineers in this field can design and increase or decrease the adaptability of parts according to the installation space of the specific equipment in actual applications. Specifically in this embodiment, the two drive sources are arranged under the wastewater table to make the final finished product structure more compact and beautiful.

[0112] A water supply pipe 6 is arranged above the filter station. The water supply pipe 6 is externally connected to the above-mentioned constant temperature heating water tank and is provided with a water valve and a water pump. The water outlet of the water supply pipe 6 is higher than the filter paper container 1 in the vertical direction and the water outlet faces the inside of the filter paper container 1.

[0113] A cavity cover 7 is installed near the water outlet of the water supply pipe 6, and the water supply pipe 6 runs through the center of the cavity cover 7. The cavity cover 7 is adapted to the open cavity of the filter paper container 1; the water outlet of the water supply pipe 6 is connected and communicated with a spherical spray nozzle 12.

[0114] Step (3) specifically includes the following steps:

[0115] (3-1) The filter paper is placed in a filter paper container 1 serving as a filter cavity. The funnel-shaped filter paper has a wide end and a narrow end. After being placed in the filter cavity, the filter paper is kept in an upright position with the narrow end facing downward. The filter paper is suspended relative to the peripheral wall of the guide groove 101, and the remaining peripheral wall is in contact with the cavity wall of the filter paper cavity.

[0116] (3-2) The automatic filter is started, and the controller controls the lifting drive source 11 to drive the filter table to rise. The filter table supports the filter paper container 1 located above it, and the open end of the filter paper container 1 is close to the chamber cover 7 but not in contact with it.

[0117] (3-3) Adding water: After completing the lifting action, the controller starts the water valve and the water pump. The constant temperature heating water tank transports 80°C distilled water to the filter paper through the water adding pipe 6 until the target water volume is reached. The speed of adding water is 0.1-1.0 m / s. The highest water drop point of the spherical spray nozzle 12 is lower than the wide end of the filter paper. The water level of the target water volume is located between the position of the filter paper two-thirds away from the narrow end and the wide end. The weighing module 5 sends a weight signal to the controller indicating that the target water volume has been reached. The controller controls the closing of the water valve and the water pump to stop adding water.

[0118] (3-4) Cleaning and filtration: The filtrate passing through the filter paper converges or flows downward along the guide groove 101, then flows to the leakage hole 102, and then flows into the drainage pipe 9, and flows through the probe of the pH sensor 8. The pH sensor 8 detects the pH of the filtrate and sends it to the controller. If the pH is less than 7, the filtration is continued until the weighing module 5 sends a weight signal of the preset minimum water volume to the controller. The controller starts the water valve and the water pump again, and adds water again until the target water volume is reached. And so on, the water adding operation is repeated until the pH sensor 8 detects that the pH of the filtrate is ≥7, and the cleaning and filtration of the filter paper is completed;

[0119] (3-5) The controller controls the lifting drive source 11 to drive the filter table to descend and reset, and the filter paper container 1 is replaced in the supporting opening 201. Then the rotating drive source 4 drives the rotating table 2 to rotate, and another filter paper container 1 is rotated to the top of the filter table, and the above steps (3-2) to (3-4) are repeated.

[0120] The rotating platform 2 stops working when the number of rotations reaches N-1. In this embodiment, the rotating platform 2 stops working when the number of rotations reaches seven.

[0121] (4) Place the cleaned filter papers into containers (crucibles) of known weight m1, dry and carbonize them, and weigh m2 again after cooling to calculate the free silica content in the dust sample.

[0122] The specific operation of step (4) is as follows: fold the filter paper after filtration and cleaning, put it into a container of known weight, the weight of the container is set as m1, and then place the container on a high-temperature electric furnace, dry and carbonize at 800-900°C for 30-35 minutes, cool at room temperature for at least 30 minutes, and then place it in a dryer (with built-in color-changing silica gel) to cool for at least 1 hour, place it on an analytical balance and weigh it to a constant weight, the weight is set as m2, and calculate the free silica content in the dust sample according to the following formula.

[0123] C=(m2-m1) / G×100

[0124] Where: C refers to the free silica content in the dust sample (%);

[0125] m1 refers to the mass of the container (g);

[0126] m2 refers to the total mass of the container and the filter paper sediment after carbonization (g);

[0127] G refers to the mass of the dust sample (g).

[0128] It should be noted that the drainage pipe 9 of this embodiment can also be connected to an external flushing water source to flush the drainage pipe 9 and the pH sensor 8 probe located in the drainage pipe 9 after each pH sensor 8 detects pH, which can further improve the detection accuracy.

[0129] Comparative Example 1

[0130] With reference to the standard "GBZ / T 192.4-2007 Determination of dust in workplace air Part 4: Free silicon dioxide content" (pyrophosphate method), the entire process was completed manually by laboratory staff, who placed the filter paper in the funnel to complete the cleaning and filtration of step (3).

[0131] Comparative Example 2

[0132] Compared with Example 1, the filter paper container 1 of this comparative example has a continuous and smooth inner surface and no guide groove design; the rest of the structure is the same as that of Example 1.

[0133] Comparative Example 3

[0134] Compared with Example 1, the water adding speed of this comparative example is 1.5 m / s; the rest of the structure is the same as that of Example 1.

[0135] Comparative Example 4

[0136] Compared with Example 1, this comparative example does not add water in the form of spraying, that is, the spherical spray nozzle 12 is not provided; the rest of the structure is the same as that of Example 1.

[0137] Comparative Example 5

[0138] Compared with Example 1, the guide groove 101 of the filter paper container 1 of this comparative example is transformed into a convex strip design; the rest of the structure is the same as that of Example 1.

[0139] 1. Accuracy of test results

[0140] Two dust samples were selected, numbered T1-T2. The dust samples were obtained by collecting dust in the air at a large flow rate using a filter membrane with a diameter of 75 mm at a sampling point. The sampling weight was greater than 0.1 g. The free silicon dioxide content was determined by referring to Example 1.

[0141] The accuracy and reliability of Example 1 were tested by quality control samples, and the reference value range of the quality control samples was: 18.9 to 22.2.

[0142]

[0143] It can be seen from the above table that the determination of the free silicon dioxide content in the dust sample in Example 1 is accurate, that is, the present invention can accurately determine the free silicon dioxide content in the dust sample.

[0144] (II) Total test time and filter paper status

[0145] -- Filter paper status Total time Example 1 The filter paper is not damaged during the filtration process 1h Comparative Example 1 The filter paper is not damaged during the filtration process 10h Comparative Example 2 The filter paper is not damaged during the filtration process 7h Comparative Example 3 Four filter papers were slightly damaged during the filtration process in step (3) -- Comparative Example 4 Two filter papers were slightly damaged at the bottom during the filtration process in step (3) -- Comparative Example 5 Five filter papers were slightly damaged or deformed during the filtration process in step (3) --

[0146] By comparing Example 1 with Comparative Example 1, it can be seen that the total time taken for Example 1 is much shorter than the total time taken for manual operation in Comparative Example 1, indicating that the present invention can effectively improve the speed of determining the free silicon dioxide content in the dust sample. Combined with the experimental results of Comparative Example 2, it can be seen that although the determination speed of Comparative Example 2 is faster than that of Comparative Example 1, it is still much slower than that of Example 1, indicating that although the automatic water adding equipment can increase the experimental speed, it is relatively limited. It also indicates that the improvement of the determination speed of the present invention is strongly related to the design of the suspended outer peripheral wall of the filter paper part.

[0147] Part of the filter paper in Examples 3, 4 and 5 is deformed or damaged during the cleaning process of step (3), which will seriously affect the accuracy of the test. Therefore, it is meaningless to count the total time, and only the number of damaged filter papers is recorded. The experimental results of Examples 3, 4 and 5 show that based on the design of the filter paper of the present invention in which the outer peripheral wall is suspended, the water adding speed, the water adding in the form of spraying and the size and shape design of the suspended area are very important. They are specific designs based on the core idea of ​​the present invention and the material characteristics of chronic quantitative filter paper.

[0148] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs may also change and modify the above implementation modes. Therefore, the present invention is not limited to the specific implementation modes disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. An efficient method for determining free silicon dioxide, characterized in that: At least the following steps are included: (1) pre-treating and weighing the dust samples respectively, then mixing with at least a pyrophosphoric acid solution to form a suspension, heating and then cooling; (2) diluting the suspension of step (1) stepwise to prepare a filtrate, filtering the filtrate through a funnel-shaped filter paper, and retaining the silicon dioxide in the filtrate in the filter paper; (3) transferring the filter paper of step (2) to a filter cavity for cleaning and filtration, wherein the funnel-shaped filter paper has a wide end and a narrow end. After being placed in the filter cavity, the filter paper is kept in an upright state with the narrow end facing downward, and a portion of the outer peripheral wall of the filter paper is suspended relative to the filter cavity. Water is added to the funnel-shaped filter paper, and the highest water level is set between the position of the filter paper two-thirds away from the narrow end and the wide end. When the filtrate passes through the filter paper to generate a filtrate, the filtrate converges or flows downward through the suspended space between the outer peripheral wall of the filter paper and the filter cavity, and the pH of the filtrate is dynamically monitored until the pH of the filtrate is ≥7, then the addition of water is stopped; (4) Place the cleaned filter paper in a container of known weight, dry and carbonize it, and weigh it again after cooling to calculate the free silica content in the dust sample.

2. The efficient determination method of free silicon dioxide according to claim 1, characterized in that: In step (3), the speed of adding water is greater than the water filtering speed of the filter paper.

3. The efficient determination method of free silicon dioxide according to claim 2, characterized in that, In step (3), water is added in the form of spraying at a speed of 0.1 to 1.0 m / s.

4. The method for efficiently determining free silicon dioxide according to any one of claims 1 to 3, characterized in that: The inner surface of the filter cavity is adapted to the funnel-shaped filter paper, the bottom of the filter cavity has a through leakage hole, the inner surface of the filter cavity is provided with at least one outwardly recessed flow guide groove, the filter paper is in a suspended state corresponding to the outer peripheral wall of the flow guide groove, and the remaining outer peripheral wall of the filter paper is in contact with the cavity wall of the filter cavity; At least one end of all the guide grooves is directly or indirectly connected to the water leakage hole.

5. The efficient determination method of free silicon dioxide according to claim 4, characterized in that: The total area of ​​the slots of all the guide grooves is smaller than the remaining inner surface area of ​​the filter cavity where no guide grooves are arranged.

6. The efficient determination method of free silicon dioxide according to any one of claims 1 to 3, characterized in that: In step (3), the water used to wash the filter paper is distilled water, and the temperature of the distilled water is set to T, 80°C≤T≤250°C.

7. The efficient determination method of free silicon dioxide according to claim 4, characterized in that: In step (3), the filter paper is cleaned and filtered by an automatic filter; The automatic filter comprises a rotating drive source, a rotating platform, a lifting drive source, a filtering platform, a water supply pipeline, a drainage pipeline, a weighing module, a pH sensor and a controller; The rotation driving source is connected to the rotating table and drives the rotating table to rotate at a specific angle. The rotating table is provided with N filter paper containers evenly distributed, N≥2, and one filter paper container is one filter cavity; The rotating platform is provided with N supporting openings evenly distributed on the circumference and adapted to the filter paper container, the width of each supporting opening being larger than the water leakage hole and smaller than the maximum width of the filter paper container, and the supporting opening supports the filter paper container; A filter platform is fixedly arranged below any of the supporting openings, the filter platform comprises a lifting piece for lifting the filter paper container and a weighing module installed at the bottom of the lifting piece, the weighing module is used to monitor and control the amount of water added so that the highest water level is located between the position of the filter paper two-thirds away from the narrow end and the wide end, the lifting drive source is directly or indirectly connected to and drives the lifting of the filter platform, and the filter platform lifts or puts down the filter paper container through the supporting opening; The water supply pipe is arranged above the filter station, the water supply pipe is externally connected to a water source and is provided with a water valve, the water supply pipe is higher than the filter paper container in the vertical direction and the water outlet faces the inside of the filter paper container; The drainage pipe receives the filtrate from the filter paper container held by the filter table, the probe of the pH sensor is installed in the drainage pipe, and the pH sensor dynamically monitors the pH of the filtrate.

8. The efficient determination method of free silicon dioxide according to claim 7, characterized in that: Step (3) specifically includes the following steps: (3-1) placing filter paper in the filter paper container; (3-2) starting the automatic filter, the controller controls the lifting drive source to drive the filter table to rise, and the filter table supports the filter paper container located above it; (3-3) Adding water: After the lifting action is completed, the controller starts the water valve, and the water source delivers 80-250° C. distilled water to the filter paper through the water supply pipe until the target water volume is reached. The water level of the target water volume is located between the position of the filter paper two-thirds away from the narrow end and the wide end. The weighing module sends a weight signal to the controller that the target water volume has been reached, and the controller controls the water valve to be closed to stop adding water; (3-4) Cleaning and filtration: The filtrate passing through the filter paper converges or flows downward along the guide groove, then flows to the leaking hole, and then flows into the drainage pipe, and flows through the probe of the pH sensor. The pH sensor detects the pH of the filtrate and sends it to the controller. If the pH is less than 7, the filtration is continued until the weighing module sends a weight signal of the preset minimum water volume to the controller. The controller starts the water valve and the water pump again, and adds water again until the target water volume is reached. And so on. The water adding operation is repeated until the pH sensor detects that the pH of the filtrate is ≥7, and the cleaning and filtration of one filter paper is completed; (3-4) The filter paper container is re-placed on the supporting opening, and then the rotating drive source drives the rotating table to rotate, and another filter paper container is rotated to the top of the filter table, and steps (3-2) to (3-4) are repeated; The rotating table stops working when the number of rotations reaches N-1.

9. The efficient determination method of free silicon dioxide according to claim 8, characterized in that: A cavity cover is installed near the water outlet of the water supply pipe, the water supply pipe runs through the center of the cavity cover, the cavity cover is adapted to the open cavity of the filter paper container, and the water outlet of the water supply pipe is connected and communicated with a spherical spray nozzle; In step (3-2), the open cavity of the lifted filter paper container is close to the cavity cover but not in contact with it, and the highest water drop point of the spherical spray nozzle is lower than the wide end of the filter paper.

10. The efficient determination method of free silicon dioxide according to claim 1, characterized in that: The step (1) comprises the following steps: (1-1) The dust sample is placed in a closed environment at 105±3℃ and dried for 1.5 to 2.5 hours. After cooling slightly, it is stored in a dry container for later use. (1-2) Accurately weigh 0.1-0.2 g of dust sample into a container, record the mass G of the dust sample, add 15-20 ml of pyrophosphoric acid solution and 0.1-0.2 mg of ammonium nitrate powder, stir to make the dust sample completely wet, and prepare a suspension; The suspension was rapidly heated to 245-250°C and kept warm, stirred for 15-20 min, and the heated suspension was cooled to 40-50°C at room temperature.

Images