What is activated carbon used in water treatment?

Activated carbon is a commonly used adsorbent, catalyst, or catalyst carrier, and has a wide range of applications in water treatment. So how to choose activated carbon? Let's analyze together!

What is activated carbon

Activated carbon is a type of microcrystalline carbon material made of carbon containing materials with a black appearance, well-developed internal pore structure, large specific surface area, and strong adsorption capacity. It is a commonly used adsorbent, catalyst, or catalyst carrier. Activated carbon can be divided into wood activated carbon, fruit shell activated carbon, animal bone/blood activated carbon, mineral activated carbon, synthetic resin activated carbon, rubber/plastic activated carbon, regenerated activated carbon, etc. according to the source of raw materials; Activated carbon can be divided into powder, granular, irregular granular, cylindrical, spherical, and fibrous shapes according to its appearance. The application of activated carbon is extremely extensive, involving almost all sectors of the national economy and people's daily lives, such as water purification, gold extraction, sugar decolorization, drug injection extraction, blood purification, air purification, and human safety protection.

The principle of activated carbon

1. Filtering principle

Activated carbon filter is the process of intercepting suspended pollutants in water, and the intercepted suspended solids fill the gaps between activated carbon. The pore size and porosity of the filter layer increase with the increase of activated carbon particle size. The coarser the particle size of activated carbon, the greater the space it can accommodate suspended solids. It is manifested as an increase in filtration capacity, pollutant holding capacity, and pollutant interception capacity. At the same time, the larger the pore size of the activated carbon filter layer, the deeper the suspended solids in the water can be transported to the next layer of activated carbon filter layer. With sufficient protective thickness, the suspended solids can be more intercepted, making the middle and lower layers of filter layer better play a interception role, and increasing the unit's pollutant interception capacity.

Strictly speaking, the ability of activated carbon to retain suspended solids comes from the surface area provided by activated carbon. When the flow rate is low, the filtration capacity of the unit mainly comes from the screening effect of activated carbon, while when the flow rate is high, the filtration capacity comes from the adsorption effect on the surface of activated carbon particles. During the filtration process, the larger the particle surface area provided by activated carbon, the stronger the adhesion to suspended solids in water.

2. Adsorption principle

According to the different forces between activated carbon molecules and pollutant molecules during the adsorption process, adsorption can be divided into two categories: physical adsorption and chemical adsorption (also known as active adsorption). In the process of adsorption, when the force between the activated carbon molecule and the pollutant molecule is Van der Waals force (or electrostatic attraction), it is called physical adsorption; When the force between the activated carbon molecule and the pollutant molecule is a Chemical bond, it is called chemisorption. The adsorption strength of physical adsorption is mainly related to the physical properties of activated carbon, and is basically independent of the chemical properties of activated carbon. Since Van der Waals force is weak and has little impact on the structure of pollutant molecules, this force is the same as the cohesion between molecules, so physical adsorption can be compared to condensation. The chemical properties of pollutants remain unchanged during physical adsorption.

Due to the strong Chemical bond, which has a great impact on the structure of pollutant molecules, chemical adsorption can be regarded as a chemical reaction, which is the result of the chemical interaction between pollutants and activated carbon. Chemisorption generally includes electron pair sharing or Electron transfer, rather than simple perturbation or weak polarization, and is an irreversible chemical reaction process. The fundamental difference between physical adsorption and chemical adsorption lies in the forces that generate adsorption bonds

The adsorption process is the process of pollutant molecules being adsorbed onto the solid surface, and the free energy of molecules will be reduced. Therefore, the adsorption process is a Exothermic process, and the heat released is called the heat of adsorption of the pollutant on the solid surface. Due to the different forces of physical adsorption and chemical adsorption, they exhibit certain differences in adsorption heat, adsorption rate, adsorption activation energy, adsorption temperature, selectivity, number of adsorption layers, and adsorption spectra. Activated carbon adsorption technology has been used for refining and decolorization in industries such as pharmaceuticals, chemicals, and food in China for many years. It was used for Industrial wastewater treatment since 1970s. Production practice has shown that activated carbon has excellent adsorption ability for trace organic pollutants in water, and it has good adsorption effects on industrial wastewater such as textile printing and dyeing, dye chemical industry, food processing, and organic chemical industry. In general, it has a unique ability to remove organics represented by BOD, COD and other comprehensive indicators in wastewater, such as synthetic dyes, surfactants, phenols, benzene, organic chlorine, pesticides and Petrochemical. Therefore, the activated carbon adsorption method has gradually become one of the main methods for secondary or tertiary treatment of industrial wastewater.

Adsorption is a slow process in which a substance adheres to the surface of another substance. Adsorption is an interface phenomenon that is related to changes in surface tension and surface energy. There are two types of driving forces that cause adsorption, one is the repulsive force of solvent water on hydrophobic substances, and the other is the affinity attraction of solids to solutes. The adsorption in wastewater treatment is mostly the result of the combined action of these two forces. The specific surface area and pore structure of activated carbon directly affect its adsorption capacity. When selecting activated carbon, it should be determined through experiments based on the water quality of the wastewater. For printing and dyeing wastewater, it is advisable to choose carbon species with well-developed transition pores. In addition, ash content also has an impact. The smaller the ash content, the better the adsorption performance; The closer the size of adsorbate molecules is to the pore diameter of carbon, the easier it is to be adsorbed; The concentration of adsorbate also has an impact on the adsorption capacity of activated carbon. Within a certain concentration range, the adsorption capacity increases with the increase of adsorbate concentration. In addition, water temperature and pH value also have an impact. The adsorption capacity decreases with the increase of water temperature.

Selection of Activated Carbon for Water Treatment

A good activated carbon must have characteristics such as large adsorption capacity, long service life, high mechanical strength, low ash content, easy flushing, and good effluent quality. It can not only remove odors and odors, improve color, but also has a high removal rate for various toxic and harmful substances in water, such as chlorine, phenol, mercury, lead, arsenic, chloride, detergent, pesticide, fertilizer, and other pollutants.

The specific main technical indicators are as follows:

1. Particle size (10-24 mesh 2.0-0.8mm): ≥ 95% indicates that generally, the smaller the particle size of activated carbon, the larger the specific surface area, which means the better the adsorption effect. However, the smaller the particle size, the greater the loss and the more dust.

2. Iodine adsorption value: ≥ 1000mg/g indicates that generally speaking, the higher the iodine adsorption value, the stronger the adsorption capacity of activated carbon.

3. Specific surface area: 1000-1200m2/g Explanation: If 1 gram of activated carbon is taken and all the pore walls inside are unfolded into a plane, this area will reach 1000 square meters (i.e. specific surface area is 1000g/m2)! The main factor affecting the adsorption capacity of activated carbon depends on the degree of development of its internal pore structure. The larger the specific surface area, the better the adsorption effect of activated carbon.

4. Methylene blue decolorization capacity: ≥ 10mL/g Description: decolorization capacity.

5. Wear resistance strength: ≥ 95% indicates the performance of wear resistance or friction resistance; The higher the strength, the better the performance of activated carbon.

6. Drying loss: ≤ 10% indicates that drying loss refers to moisture content. The lower this value, the better the quality of activated carbon.

7. Burning residue: ≤ 3% indicates that the lower the value of burning residue and ash content, the better the quality of activated carbon.

8. Filling specific gravity: 0.48--0.55g/mL Description: The filling specific gravity and density refer to the smaller the density, the better the adsorption capacity of activated carbon.

9. PH value: 6-8

The above is what Hongjie Water brings to you about "What is activated carbon in water treatment?" I hope it can help you!

Shenzhen Hongjie Water Technology Co., Ltd. is an integrated high-tech enterprise specializing in product development, production, sales, engineering design, installation and commissioning, technical consultation, and sales of supporting materials in the field of industrial water treatment and drinking water treatment. Main products: design, manufacturing, installation, commissioning and maintenance of water treatment equipment such as pure water equipment, Ultrapure water equipment, reverse osmosis equipment, GMP purified water equipment, EDI deionized water equipment, domestic sewage equipment, industrial wastewater equipment, softened water equipment and reclaimed water reuse equipment.