Yingtai: Application of Vacuum Freeze-Drying Technology in Soil Environmental Research
1. Soil Testing Contents
Since 2022, the third national soil survey has entered its third year. The Ministry of Agriculture and Rural Affairs recently announced that the national soil survey has been launched in various regions, with more than 1.6 million samples collected, accounting for over 60% of all sampling points. According to the plan, the "comprehensive check-up" of the soil will complete all field surveys and sampling by the end of November this year, with the final survey results expected to be formed by 2025. Soil testing is a process that analyzes and evaluates various substances in the soil. It is an important task in agriculture, environmental protection, land development, and pollution remediation. The contents of soil testing include:
1. pH Value: This indicator measures the acidity or alkalinity of the soil. Soils with a pH value greater than 7 are alkaline, while soils with a pH value less than 7 are acidic.
2. Organic Matter Content: This reflects the fertility and water-holding capacity of the soil and includes fresh organic matter, microorganisms, simple organic compounds, humus, and partially decomposed organic matter.
3. Nutrient Content: This includes the levels of key nutrients such as nitrogen, phosphorus, and potassium, which are crucial for plant growth and development.
4. Microelements Content: This includes the levels of essential microelements for plant growth, such as iron, zinc, copper, manganese, chromium, boron, and others.
5. Soil Structure: This describes the size and arrangement of soil particles, affecting soil aeration, permeability, and root growth.
6. Moisture Content: The moisture content in the soil is critical for plant growth and irrigation management.
7. Soil Texture: This refers to the relative proportions of sand, silt, and clay in the soil, which influences water retention, aeration, and root growth.
8. Heavy Metal Content: This indicates the presence of heavy metals such as cadmium, lead, mercury, etc., and helps determine if the soil is polluted.
Regular soil testing allows for monitoring soil trends and helps adjust soil management practices to protect the health of the environment and ecosystem.
2. Soil Freeze-Drying Method and Advantages
Due to the instability, poor reproducibility, and high element loss rates in fresh soil or sludge samples, as well as the complexity of their composition, it is difficult to ensure whether the gases emitted by the soil could impact human health. Moreover, post-testing storage poses another challenge. Therefore, direct testing is generally avoided. Typically, soil samples are first dried and then ground, sieved, or processed in other ways for analysis. The freeze-drying method, as a common soil drying technique, has become widely adopted in laboratories. The principle behind it is to freeze the soil sample at low temperatures, causing the liquid water in the sample to turn into ice without expanding in volume. Then, under low-temperature vacuum conditions, the water sublimates and is removed through the vacuum system, keeping the soil sample dry. The freeze-drying method offers many advantages:
1. After freeze-drying, the soil sample typically has a moisture content of less than 5%, and can be reduced to as low as 0.01%, which is conducive to subsequent processing and analysis.
2. After freeze-drying, the soil sample becomes brittle and porous, making it easier to grind using a specialized grinder.
3. The vacuum freeze-dryer requires no constant monitoring of the sample. Once the parameters are set, it can operate continuously, with app alerts notifying users in case of any issues, greatly enhancing drying efficiency.
4. The equipment allows for a large sample volume. A professional freeze-drying unit can process multiple soil samples in one day, meeting the needs for sample pre-treatment.
5. The freeze-drying method can use external freeze-drying bottles to prevent cross-contamination between different batches or within the same batch of samples.
This technique is especially advantageous for soil environmental research, ensuring high-quality sample preparation for accurate analysis.
