How much do you know about activated carbon for sewage treatment?

Date:Apr 7,2017
Activated carbon is an excellent adsorbent, it is the use of charcoal, charcoal, shell and high-quality coal as raw material, the raw material crushing, sieving, catalyst activation, rinsing, drying and screening of a series of manufacturing processes through physical and chemical methods. Activated carbon has the dual characteristics of physical adsorption and chemical adsorption, which can selectively adsorb various substances in the gas phase and liquid phase, so as to achieve the purpose of decolorization, purification, disinfection, deodorization and decontamination.
 
Adsorption is the primary property of activated carbon. The activated carbon has the irregular arrangement of the graphite grains, and in the activation process, the pores of different shapes and sizes are produced between the crystallites. According to the IUPAC method: the micropore is less than 1.0nm, the mesopore 1~25nm, the pore is larger than 25nm. The pore volume of activated carbon microporous generally only 0 25~0. 9Ml/g, the pore number is about 1020 /g, about 500~1500 square meters for all microporous /g surface area, also known as high as 3500 square meters of /g ~5000. These pores, especially micropores, provide a large surface area.
 
More than 95% of the surface area of activated carbon is in the micropore, so micropore is an important factor to determine the adsorption performance of activated carbon. The pore volume is about 0 02~1.0mL/g, the specific surface area of up to several hundred square meters, can provide for the adsorption of micro channel into the pores, but also the direct adsorption of larger molecules. The pore volume of large holes is generally about 0.2 -0.5mL/ g, the specific surface area of about 0.5 square meters of ~2 /g, its role is to make the adsorbate molecules rapidly activated carbon internal small pores; the two is taken as the catalyst carrier as catalyst carrier, catalyst and only a small amount of precipitation in the micro hole, mostly in precipitation the hole and the hole.
 
(two) the main factors affecting the adsorption of activated carbon
 
Due to the adsorption process and the action principle of activated carbon water treatment involves more complex, so there are a lot of influence factors, the nature of water, the main pollutants are of the nature of the activated carbon and activated carbon treatment process principle and selection of operating parameters and operating conditions.
 
1 Properties of activated carbon
 
Activated carbon for water treatment should have three requirements: large adsorption capacity, adsorption speed, good mechanical strength. The adsorption capacity of activated carbon in addition to other external conditions, mainly related to the specific surface area of activated carbon, the specific surface area, a large number of micropores, can be adsorbed on the pore wall of the adsorption of more. The adsorption rate is mainly related to the particle size and pore size distribution. The activated carbon, which is used for water treatment, requires the transition pore (radius 2 0~100nm) is more developed, which is conducive to the diffusion of the adsorbate to the micro pores. The smaller the particle size of activated carbon, the faster the adsorption rate, but the head loss to increase, generally in the 8~30 range is appropriate. The mechanical wear resistance of activated carbon directly affects the service life of activated carbon.
 
2 Properties of adsorbate (solute or contaminant)
 
The adsorption capacity of the same activated carbon for different pollutants is very different.
 
(1) solubility
 
The solubility of the same species decreases with the increase of the chain, while the adsorption capacity increases with the increase of the series or the molecular weight. The smaller the solubility, the more easily adsorbed, such as activated carbon adsorption of organic acids from the water in the order of formic acid to acetic acid, propionic acid and butyric acid increased.
 
(2) molecular size and chemical structure
 
The size and chemical structure of adsorbate molecules also have a great influence on adsorption. Because the adsorption rate is affected by the internal diffusion velocity, the size of the adsorbate molecule is proportional to the pore size of the activated carbon, which is the most suitable for adsorption. In the homologues, the molecule is larger than the small molecule. Unsaturated bonds of organic matter is more saturated than the adsorption. Aromatic organic compounds are easier to adsorb than aliphatic organic compounds.
 
(3) polarity
 
Activated carbon can be regarded as a kind of non-polar adsorbent, the adsorption capacity of non-polar substances in water is greater than that of polar substances.
 
(4) adsorption concentration
 
When the concentration of adsorbate in a certain range, the adsorption capacity increases with the increase of concentration. As a result, the adsorption capacity of activated carbon to the adsorbate (solute) is also changed due to the change of the concentration of adsorbate.
 
3 solution pH
 
The influence of pH value of solution on adsorption should be combined with the influence of activated carbon and adsorbate (solute). The pH value of the solution controls the degree of dissociation of acidic or basic compounds. When the pH value reaches a certain range, these compounds will dissociate and affect the adsorption of these compounds. The pH value of the solution also affects the solubility of the adsorbate (solute), and the charge of the adsorbate (solute). As activated carbon can adsorb hydrogen and oxygen ions in water, it will affect the adsorption of other ions. The effect of activated carbon adsorption of organic pollutants from water, generally with the increase of the solution pH value, pH value higher than 9, not easy to absorb, the lower the pH value, the better the effect. In practical application, the optimum pH value range should be determined by experiment.
 
4 solution temperature
 
Because the liquid phase adsorption, the adsorption heat is small, so the solution temperature has little effect. Adsorption is exothermic reaction. The greater the heat of adsorption, the greater the influence of temperature on adsorption. On the other hand, the temperature has an effect on the solubility of the material, so it also has an effect on the adsorption. When activated carbon was used to treat wastewater, the effect of temperature on adsorption was not significant.
 
5 multi component adsorbate coexistence
 
When the water is treated by adsorption, the water is usually not a single pollutant, but a mixture of multiple pollutants. In the adsorption, they can be co adsorbed, promote each other or interfere with each other. In general, the adsorption of multi component adsorption

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Keywords for the information:How much do you know about activated carbon for sewage treatment? 

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