Foreword

With the increasing demand for industry, energy, and transportation, the problem of atmospheric pollution has become increasingly prominent. Among them, heavy metals that enter the atmosphere in different forms become one of the most important pollutants in the air. It is estimated that more than 9,000 tons of five kinds of lead, mercury, cadmium, chromium, and arsenic in the air will be emitted in the country in one year. Non-ferrous metal smelting, lead storage batteries, recycled lead, coal-fired power plants, cement, iron and steel smelting, Chemicals production and other industries are the major sources of heavy metal pollution. Among them, non-ferrous metal smelting enterprises and coal-fired power plants are the major sources of mercury emissions. In addition, tail gas, tire friction, and brake friction are also important sources of pollution. Atmospheric heavy metals are present in suspended particles, and the dynamic diameter of particles is from 0.1 μm to 100 μm. Usually suspended particles of 50 μm or more settle in the atmosphere in minutes or hours. However, suspended particles less than 10 μm, especially less than 2.5 μm, do not easily settle. They can float in the atmosphere for days or even years, and can migrate hundreds or even thousands of kilometers.

Heavy metal pollutants in the air damage buildings, form soils, and cross-contamination of surface water systems through wind, rain, and snow. Heavy metals that enter the water body undergo a series of physical and chemical reactions such as oxidation, dissolution, desorption, complexation, and bio-methylation that produce water-soluble metal salts that diffuse with the flow of water. When the physical and chemical conditions of the basin change, these metal salts may be reduced, precipitated, adsorbed, and precipitated in the soil. Respiratory organs of different diameter particles are: 10 ~ 100 μm, nasal cavity; 2.5 ~ 10 μm, nasopharyngeal area; 0.1 ~ 2.5 μm, bronchus and lungs; 0.1 μm or less, heavy metal elements have strong migration, Enrichment and concealment, through the air, water, food chain and other ways into the human body, significant biological toxicity, easy to cause chronic poisoning, with carcinogenic, teratogenic and mutagenic effects on the immune system has a certain impact, a serious threat to human health.

At present, the Ministry of Environmental Protection has officially issued the relevant standards for the determination of inorganic elements in ambient air particles - energy dispersive X-ray fluorescence spectrometry, which shows that energy dispersive X-ray fluorescence spectrometers can easily, quickly and accurately analyze atmospheric particulate matter in samples. The heavy metal content.

Energy Dispersion X Fluorescence Spectrometer Analysis Principle

When the primary X-rays generated by the X-ray tube are irradiated to the surface of a uniform and uniform particle, the atoms of the test element contained in the sample are excited to emit characteristic X-rays. After being received by the detector, the light signal is converted into an analog electrical signal. The analog-to-digital converter converts the analog electrical signal into a digital signal and sends it to a computer for processing. The X-ray intensity of the element feature is obtained by dedicated software, and the content of the element to be measured is calculated according to the corresponding mathematical model of the spectral peak intensity and content of the element feature.

EDX4500H Energy Dispersion X Fluorescence Spectrometer Introduction

EDX 4500H X Energy Dispersive Fluorescence Spectrometer utilizes XRF detection principle to achieve fast, accurate and non-destructive analysis of various elemental components. The main feature of this instrument is the use of intelligent vacuum system, which can have good excitation effect on light elements such as Si, P, S, Al, Mg, etc. The XRF technology can be used to accurately analyze the heavy elements of atmospheric particulate matter enrichment in atmospheric filtration. The analysis of membrane enrichment content has the characteristics of non-destructiveness, rapidness, accuracy, etc., effectively improving the detection time and work efficiency.

Figure 1 EDX4500H Energy Dispersive X-ray Fluorescence Spectrometer

Performance characteristics

High-efficiency, ultra-thin window X-ray tube, the indicators have reached the international advanced level

Using digital multi-channel technology, it can achieve ultra-high count rate, improve test efficiency and accuracy

SDD silicon drift detector, good energy linearity, energy resolution, peak-to-back ratio and energy spectrum characteristics

Low-energy X-rays excite the test element and have good excitation effect on light elements such as Si and P

Intelligent vacuum pumping system shields the influence of air and greatly expands the scope of testing

Automatic spectrum stabilization device ensures the consistency of instrument work

High signal-to-noise ratio electronic circuit unit

Automatically switch collimators and filters for different samples, eliminating the need for manual operations

Decompose spectrum to decompose spectral peaks so that the measured results of the measured elements have equal analytical accuracy

Multi-parameter linear regression method to significantly suppress absorption and enhancement effects between elements

The LCD screen shows the important parameters of the instrument (tube pressure, tube flow, vacuum degree) at a glance

Technical Parameters

Product Model:EDX 4500H

Product Name: Energy Dispersive X Fluorescence Spectrometer

Measurement element range: from sodium (Na) to uranium (U)

Element content analysis range: ppm-99.99% (different elements, different analysis range)

Simultaneous analysis of elements: one-time measurement of dozens of elements

Measurement time: 30 seconds - 200 seconds

Detector energy resolution: 145±5 eV

Tube pressure: 5KV-50KV

Tube flow: 50μA-1000μA

Measurement object status: powder, solid, liquid

Input voltage: AC 110V/220V

Ambient temperature: 15°C-30°C

Humidity: 35%-70%

Sample chamber volume: 320mm×100mm

Dimensions: 660mm×510mm×350mm

Weight: 65Kg

Standard configuration

High-efficiency thin window X-ray tube

SDD silicon drift detector

Digital multi-channel technology

Optical path enhancement system

High signal to noise ratio electronic circuit unit

Built-in high-definition camera

Automatic Switching Collimators and Filters

Automatic spectrum stabilization device

Triple security protection model

Reliable overall steel structure

90mm × 70mm status display LCD screen

Vacuum pump

Atmospheric particulate collection and preparation

 Ambient air particulate sampling point settings should meet the relevant requirements of HJ664. The sampling process should be performed according to the particle sampling requirements in HJ/T194. When the target element content is low or PM10 (PM2.5) samples are collected, the sampling volume can be increased appropriately. Unorganized emission particulate sample collection Set monitoring points according to the relevant requirements in HJ/T55. Others are consistent with the collection requirements for ambient air samples. The collection of two types of particulate samples should meet the requirements of the relevant standards issued by the Ministry of Environmental Protection.

The heavy metal detection process in atmospheric particles is shown in Figure 2. First, the air and the carried particulate matter are pumped into the cutter by a flow control pump. The particulate collection mainly depends on the cutting head of the sampler, and the PM10 sampler cut point is 10 μm. The capture efficiency of 10 μm particles is more than 50%, and then the particles are captured by a certain size of sampling filter. Commonly used sampling membranes are quartz filter, PTFE filter, polycarbonate filter (PC ) Etc. After a period of time, the sample was collected and collected. After the sampling was completed, the filter was removed with a tweezers and stored in a dry, clean, numbered sample box.

Figure 2 Atmospheric heavy metal collection and detection process

In this experiment, a quartz filter membrane was used. The diameter of the filter membrane (0.4-0.8 μm) was 47 mm, the particle cutter (PM10), and the gas flow rate was controlled at 1 m3/h, and the sample was sampled for 24 hours. The numbers are 1#, 2#, ... 7#. The collected samples were stored dry for testing.

Formulation and Analysis of Heavy Metal Curves of Atmospheric Particulates

     Set the appropriate measurement conditions, use EDX4500H energy dispersive X-ray fluorescence spectrometer to scan the standard filter material, establish the calibration working curve of the content and intensity of the test element, and then measure the unknown sample of the atmospheric particulate filter.

Fig. 3 Pb element working curve of atmospheric particles in EDX4500H

Fig. 4 Fluorescence analysis of an enriched filter X by an atmospheric particle of EDX4500H

Table 1 Analytical results of atmospheric heavy metal membrane EDX4500H in a certain area Unit: μg/m3

At present, the “Ambient Air Quality Standard” GB3095-2012 stipulates that the annual average concentration limit of Pb element is 0.5 μg/m3. Because Pb belongs to the more toxic metal, its concentration limit is lower among various heavy metals. The instrument detected that the content of Pb in the sample #4 exceeded the standard, up to 2.955 μg/m3, and the Fe element content was also high, reaching 1.062 μg/m3. In addition, Fe and Zn, the most common heavy metal contaminants in the atmosphere, were detected in each sample.

The results show that the particulates in the atmosphere can be collected by the quartz filter and the standard calibration curve can be used to directly analyze the content of atmospheric heavy metals in the unknown sample. This method does not require digestion, and the measurement time of each sample only takes a few minutes. The instrument satisfies the requirements of the relevant standards for the "Determination of inorganic elements in ambient air particles - energy dispersive X-ray fluorescence spectrometry" implemented by the Ministry of Environmental Protection on July 1, 2017.

Accessories: Installation and Operating Environment of the Instrument

First, the overall design of the laboratory:

According to the characteristics of sample testing and sample preparation, each sub-compartment shall be established. Sample testing rooms and sample preparation rooms shall be established. Scientific equipment shall be arranged and placed, power lines shall be arranged, and reasonable lighting, natural ventilation and lighting shall be provided.

Schematic diagram: The sample testing room is as follows. For specific requirements, see the instrument installation conditions below.

Second, the working environment requirements

2.1 Ambient temperature: 10°C-35°C

2.2 Relative humidity: less than 70%

2.3 Power supply: AC 220V (If the power grid fluctuates ≥ 10%, a special AC voltage regulator (1kw or more) is required.

2.4 Room: No corrosive gas, no mechanical vibration, no electromagnetic field interference.