Methods for the determination of carbon black in soil, determination of soil organic carbon

Method for determining carbon black in soil: The structure of carbon black is expressed by the degree to which carbon black particles aggregate into chains or grapes. Carbon black, which is composed of a condensate consisting of the size and shape of the conglomerate and the number of particles in each condensate, is called high-structure carbon black.

At present, the oil absorption value is commonly used to represent the structure, and the larger the oil absorption value, the higher the carbon black structure, which is easy to form a space network channel and is not easy to destroy. The high-structure carbon black particles are fine, the network chain is tightly packed, the specific surface area is large, and the unit mass particles are large, which is conducive to the formation of chain conductive structure in the polymer, among which acetylene carbon black is the best among many carbon black varieties. Carbon black particles with a wide particle size distribution are more likely to impart electrical conductivity to polymers than carbon black particles with a narrow distribution, and this phenomenon is statistically explained.

Carbon black with a wide particle size distribution, a small number of large diameter particles need a huge number, and the smaller diameter particles are compensated, and the carbon black with the same average particle size distribution has a larger total number of particles than the carbon black with a narrow distribution.

Most of them are geometrical studies of conductive particle contact. According to this theory, the larger the amount of carbon black filling, the greater the density of carbon black particles or carbon black particle aggregates in the dispersed state, the smaller the average distance between the particles, the higher the probability of contact with each other, and the more conductive pathways formed by carbon black particles or carbon black particle aggregates. The greater the polarity of the polymer and carbon black composition blending system of different polarities, the greater the critical volume fraction of carbon black, which means that the conductivity of the system decreases, because the surface of carbon black contains strong polar groups, the matrix polarity is large, and the action is enhanced, and the strength increases, but it hinders the agglutination of the conductive particles themselves, resulting in poor conductivity.

However, in the blending system composed of multi-component matrix resin and carbon black, due to the different polarity of different matrices, the filled carbon black will produce segregation, and the conductivity depends on the concentration and distribution state of carbon black particles in the segregated phase, and also depends on the proportion of polymers in the segregated phase.

The soil is dried at a high temperature (such as 300 degrees Celsius) in a vacuum oven, and the volatile substances and organic compounds with low molecular weight are removed, and then sintered with oxygen at 500 degrees Celsius to calculate the weight loss, which is the amount of carbon black.

Methods for the determination of soil organic carbon:

1. The classical determination methods include dry burning method (high-temperature electric furnace burning) or wet burning method (potassium dichromate oxidation).

The CO2 released is generally weighed with soda lime absorption, or absorbed with standard barium hydroxide solution, and then titrated with standard acid.

When the above methods are used to determine soil organic carbon, it also includes the elemental carbon and inorganic carbonates in the soil. Therefore, when calcareous soil organic carbon is determined, CaCO3 must be removed first. CaCO3 can be removed by sulfurous acid treatment prior to the assay, or by additionally determining the inorganic carbon and total carbon content, subtracting the inorganic carbon from the total carbon result.

Both the dry and wet burning methods for the determination of CO2 can decompose all soil organic carbon without being affected by reducing substances, and can obtain accurate results, which can be used as standard methods for verification. Because the determination requires some special instruments and equipment, and it is very time-consuming, this method is not used in general laboratories.

2. The combination of high-temperature electric furnace burning and gas chromatography device makes an automatic carbon and nitrogen analyzer.

It has been used in soil analysis, but due to the limitations of the instrument, it has not been widely adopted.

3. Capacity analysis method.

Although there are differences in the oxidants used in the various volumetric methods, their concentrations or specific conditions, the basic principles are the same.

Soil organic carbon (SOC) is an important indicator to characterize the change of soil fertility, which profoundly affects the physical, chemical and biological properties of soil, and is the basis for high and stable crop yield and sustainable agricultural development.

1. Volumetric method (external heating method) potassium dichromate oxide oil bath heating method to determine soil organic matter content.

2. The potassium dichromate volume method for the determination of organic matter in the soil is to use the highly oxidizing potassium dichromate sulfuric acid solution to undergo a redox reaction with the organic carbon in the soil, and there is a quantitative relationship between them. The remaining potassium dichromate is then titrated with a standard reducing agent (ferrous sulfate).

3. Visual colorimetry. Determination principle. A series of standard reference substances of different concentrations were made with different concentrations of glucose standard solution, and potassium dichromate was used to oxidize soil organic matter, and the color of the oxidized solution was correlated with the organic matter content, and the results were directly obtained by colorimetric control with the standard control.

4. The principle of calcination method (gravimetric method) determination. The amount of soil organic matter was calculated by measuring the change in soil weight before and after burning.

5. Photometric colorimetry. Determination principle. This method is used for spectrophotometric determination of soil organic matter using ferrous sulfate as a standard solution.

The water-soluble organic carbon (WSOC) in the soil complex refers to the organic components in the soil sample that can be dissolved in the aqueous phase at room temperature and pH.

Assay method DAO:

1. Quantitatively weigh the soil sample (such as g, depending on the organic matter content in the soil) and put it in a 150ml triangular bottle, add 50ml of distilled water to prepare a series of samples with different water-soil ratios;

2. Continuous oscillation for 5h;

3. The supernatant was obtained by suction filtration with a filter membrane;

4. Shimadzu TOC-5000A total organic carbon tester was used to determine the organic carbon content in the serum;

5. Calculate the WSOC content g and adsorption coefficient k::in the soil sample according to the following formula

c=(g w)/(k w+v )

where c is the concentration of organic carbon in the extract (mg g), g is the original content of water-soluble organic matter in the soil (mg g), w is the solid weight of the soil (g), k is the adsorption coefficient (l g), and v is the volume of the aqueous phase (i).

The water-soluble organic carbon du (WSOC for short) in soil refers to the water phase of BAI in soil samples that can be dissolved in water at room temperature and natural pH conditions.

of organic components.

Assay method:

1. Quantitatively weigh the soil sample (such as g, depending on the organic matter content in the soil) and put it in a 150ml triangular bottle, add 50ml of distilled water to prepare a series of samples with different water-soil ratios;

2. Continuous oscillation for 5h;

3. The supernatant was obtained by suction filtration with a filter membrane;

4. Shimadzu TOC-5000A total organic carbon tester was used to determine the organic carbon content in the serum;

5. Calculate the WSOC content g and adsorption coefficient k::in the soil sample according to the following formula

c=(g w)/(k w+v )

where c is the organic carbon concentration in the extract (mg g) g is the original content of water-soluble organic matter in the soil (mg g) w is the solid weight of the soil (g), k is the adsorption coefficient (l g), v is the volume of the aqueous phase (i) In the left task, the upstairs answer is good. Just quote below.

Pls have you found a way to find a way.

Assay step: Air-dried soil samples (air-dried soil samples through a sieve with potassium dichromate.

concentration of 5 ml), concentrated sulfuric acid.

at 170-180 degrees Celsius.

(in an oil bath, the water bath can only reach 100 degrees Celsius), keep boiling for 5 minutes, wait for cooling, pour the cooking liquid into a triangular bottle and add 3-5 drops of phenanthrene indicator, with standard ferrous sulfate.

Titration, the color of the solution from orange (or yellow-green) through green, gray-green, mutation to brown-red is the end point.

Principle: Mainly according to the potassium dichromate under the action of concentrated sulfuric acid can convert the carbon-containing organic matter in the soil into CO2, in this process will consume a part of potassium dichromate, the remaining potassium dichromate is titrated with ferrous sulfate, and the remaining amount x is calculated. The amount of potassium dichromate that reacts with organic matter (5-x) ml is known.

Converted into the mol number of potassium dichromate in the reaction fishing, the mol concentration of organic matter C in the soil (12g mol) can be calculated, and the carbon content can be calculated.