Why is activated carbon acidic?

This is related to the activation process of activated carbon. There are processes such as alkaline activators, metal salt activation, and physical activation.

I have some basic knowledge of activated carbon, as I have been in contact with suppliers in Ningxia~ Activated carbon can be acidic or alkaline. . . It is mainly used for removing different types of gases. If the exhaust gases emitted by your company are acidic, you can choose alkaline activated carbon; the same applies in reverse! During the production process of activated carbon, it is created by spraying a solution onto the activated carbon or by using an impregnation method.

I agree with the views of those above: acidic ones are used to absorb alkaline substances； Conversely, alkaline activated carbon adsorbs acidic substances.

I have a slight understanding from everyone’s explanations. I wonder, if it is acidic activated carbon, what methods can be used to remove its acidity? I want activated carbon under neutral conditions. :)

Just make your requests directly to the manufacturer, and they will provide activated carbon that meets the requirements

1. Process of producing activated carbon: (1) The material used for activated carbon is mostly coconut shells or coal; it can also be made from wood and resin, among other materials. (2) Before becoming activated carbon, these materials undergo a high-temperature carbonization process; at temperatures of 400 to 600 degrees, the raw materials are completely carbonized, and the resulting carbonized material contains 50% to 80% carbon. (3) These carbonized materials are then heated in a high-temperature furnace, which is the process of activating the activated carbon. During this activation phase, steam and air are introduced into the high-temperature furnace to remove impurities from the pores of the activated carbon, thereby increasing its porosity. (4) Finally, there is granular activated carbon, which is processed into cylindrical or powdered activated carbon. 2. The pH of activated carbon is normally between 8 and 10; it is only between 6 and 8 after a pickling process (such as immersion in hydrochloric acid). 3. The pores of activated carbon can be generally divided into three types: (1) Macropores: with pore sizes ranging from about 10-4 mm to 1 mm; their functions include adsorbing large molecules, providing insulation, soundproofing, and trapping bacteria and microorganisms. (2) Mesopores: The pore size ranges from about 10-6 mm to 10-4 mm, and their functions include adsorbing larger molecules, deodorizing, decolorizing, and adsorbing chemicals. (3) Micropores: The pore size is around 10-6 mm or less; their function is similar to that of mesopores, except that they can adsorb smaller molecules. Additional note: Micropores are not necessarily better; it depends on what they are used for. If it is to be used in a filter, micropores are not suitable because they become saturated very easily. 4. Activated carbon can be regarded as an adsorbent; it can also function as a desorbent. Therefore, after activated carbon removes pollutants and has not been replaced, it acts as a desorbent. It can thus be used to absorb pollutants in water tanks or as a desorbent in base fertilizers, but it is necessary to replace it after it has absorbed pollutants. Addition: This is completely correct. So, it’s not about using more activated carbon; rather, it’s important to replace it frequently. It is recommended that the dosage for a 3-foot tank not exceed 1.5 liters. If there are many organisms in the tank and a large amount of food is provided, changing the water every two months is sufficient. 5. The impact of activated carbon on the pH level of the tank can be disregarded, unless you use an entire layer of activated carbon as the bottom substrate, in which case its effect would be even more significant than that of TK active bottom substrates. 6. For activated carbon used in aquariums, it is recommended to use coconut shell activated carbon; either granular or cylindrical form is acceptable, but powdered form is not suitable, as it causes the water to turn black. It’s not clear what type of adsorbent should be used in such cases. 7. To determine the quality of activated carbon, the simplest method is to use a transparent cup filled with water and drop some activated carbon into it. The higher the porosity, the faster it will sink and continue to produce bubbles; therefore, whether it is new or old, as long as it is dry, this method can be used to assess its quality simply. Additional note: The higher the temperature used in the production process of activated carbon (the higher the quality), the more complete the carbonization process, which results in a very low specific gravity of around 0.38~0.4. The lower the grade, the greater its density (around 0.48–0.55), and it will sink more quickly; however, this is true under the condition that the raw materials and particle sizes remain unchanged. 8. Another way to determine whether activated carbon is still effective is to use a certain amount of new activated carbon and conduct an adsorption test using colored water. For example, use a mineral water bottle, take out the activated carbon from the bottle’s cap (the amount of activated carbon can be determined by oneself), add clean water to the bottle (the amount can be adjusted as desired, but not too much), then add the activated carbon to the bottle. Add a few drops of yellow dye or methyl blue, etc. (the amount can be adjusted as desired, but not too much). After shaking or allowing it to stand for a certain period of time, remove the solution from the bottle (make sure there is no activated carbon left in it); this is Solution A. Repeat the above steps again, but this time without adding activated carbon and only with the chemicals, to obtain solution B that has not been treated with activated carbon. Finally, the used activated carbon can be used for experimental comparison; by determining whether the color of the water in the bottle falls between that of Solution A or Solution B, it is possible to determine whether the activated carbon still has an effective effect. It is important to keep the amount of activated carbon added, the amount of water, the amount of chemical used, and the shaking time constant. Additional notes: 1. The pores in activated carbon can be generally classified into large, medium, and small pores; each piece of activated carbon contains all three types of pores. Which type constitutes the largest proportion depends on the raw material used and the manufacturing conditions. 2. Coconut shell activated carbon is recommended because it has a high adsorption capacity; its specific density (apparent specific gravity) is usually below 0.45 g/ml, and its ash content is generally below 5%. The lower the specific gravity and ash content of the activated carbon, the fewer inorganic salts and impurities it contains, resulting in a higher proportion of pores and thus an improved adsorption capacity. In contrast, coal-based activated carbon has relatively higher specific gravity and ash content, though this is not always the case if it has been specially treated in advance. The activated carbon used for solvent adsorption that I’ve come across is mostly made from coconut shells; that’s why I recommend using coconut-shell activated carbon. In fact, it’s also fine to use coal-based activated carbon, as it’s cheaper as well, provided it isn’t carbon that has been recycled from factories, since who knows what residues might still be present in it. 3. In the production process of activated carbon, temperature control in the activation furnace is extremely important, as the temperature level determines the adsorption capacity and degradation rate of the activated carbon. Higher temperatures make it easier for the activated carbon to turn into ash, but they also enable more effective removal of the substances that have been adsorbed. Factors affecting the efficiency of activated carbon filtration and its usage methods: The adsorption capacity of activated carbon is related to factors such as water temperature and water quality. The higher the water temperature, the stronger the adsorption capacity of activated carbon ； When the water temperature exceeds 30°C, the adsorption capacity reaches its limit and may gradually decrease. When the water quality is acidic, the adsorption capacity of activated carbon for anionic substances decreases relatively ； When the water quality is alkaline, the adsorption capacity of activated carbon for cationic substances decreases. Therefore, unstable pH of water quality can also affect the adsorption capacity of activated carbon. 　　The adsorption principle of activated carbon is that a balanced surface concentration is formed on the surface of its particles, which then allows organic impurities to be adsorbed into these particles; the adsorption efficiency is very high at the beginning of use. However, over time, the adsorption capacity of activated carbon decreases to varying degrees, and its adsorption efficiency also declines as a result. If the water in the aquarium is turbid and contains high levels of organic matter, the activated carbon will quickly lose its filtering capacity. Therefore, activated carbon should be cleaned or replaced regularly. 　　The size of activated carbon particles also affects the adsorption capacity. Generally speaking, the smaller the activated carbon particles, the larger the filtration area. Therefore, powdered activated carbon has the largest total surface area and the best adsorption capacity, but it can easily flow into the aquarium with water, making it difficult to control, which is why it is rarely used. Granular activated carbon has poor flowability due to its granular structure, which prevents impurities such as organic matter in water from clogging the activated carbon filter layer; it boasts strong adsorption capacity and is easy to handle and replace. 　　The adsorption capacity of activated carbon is proportional to the time it spends in contact with water; the longer the contact time, the better the quality of the filtered water. Note: The filtered water should flow out of the filter layer slowly. The new activated carbon should be washed thoroughly before its first use; otherwise, ink-black water will flow out. Before placing the activated carbon in the filter, a layer of sponge 2–3 cm thick should be placed at the bottom and top; this serves to prevent large particles such as algae from penetrating inside. After 2–3 months of use, if the filtering efficiency declines, it is necessary to replace the activated carbon with fresh material, and the sponge layer should also be replaced regularly. The adsorption capacity of activated carbon is influenced by factors such as water temperature and water quality. The higher the water temperature, the stronger the adsorption capacity of activated carbon ； When the water temperature exceeds 30°C, the adsorption capacity reaches its limit and may gradually decrease. When the water quality is acidic, the adsorption capacity of activated carbon for anionic substances decreases relatively ； When the water quality is alkaline, the adsorption capacity of activated carbon for cationic substances decreases. Therefore, unstable pH of water quality can also affect the adsorption capacity of activated carbon. The adsorption principle of activated carbon is that a balanced surface concentration is formed on the surface of its particles, which then allows organic impurities to be adsorbed into these particles; the adsorption efficiency is very high at the beginning of use. However, over time, the adsorption capacity of activated carbon decreases to varying degrees, and its adsorption efficiency also declines as a result. If the water in the aquarium is turbid and contains high levels of organic matter, the activated carbon will quickly lose its filtering capacity. Therefore, activated carbon should be cleaned or replaced regularly. The size of activated carbon particles also affects the adsorption capacity. Generally speaking, the smaller the activated carbon particles, the larger the filtration area. Therefore, powdered activated carbon has the largest total surface area and the best adsorption capacity, but it can easily flow into the aquarium with water, making it difficult to control, which is why it is rarely used. Granular activated carbon has poor flowability due to its granular structure, which prevents impurities such as organic matter in water from clogging the activated carbon filter layer; it boasts strong adsorption capacity and is easy to handle and replace. The adsorption capacity of activated carbon is proportional to the time it spends in contact with water; the longer the contact time, the better the quality of the filtered water. Note: The filtered water should flow out of the filter layer slowly. The new activated carbon should be washed thoroughly before its first use; otherwise, ink-black water will flow out. Before placing the activated carbon in the filter, a layer of sponge 2–3 centimeters thick should be placed at the bottom and top; this serves to prevent large particles such as algae from penetrating inside. After 2–3 months of use, if the filtering efficiency declines, it is necessary to replace the activated carbon, and the sponge layer also needs to be replaced regularly. The efficiency of activated carbon depends on many factors; the shorter the time since the aquarium was set up, the more frequently the activated carbon needs to be replaced (about once a month). In aquariums that have been in use for a longer period, the activated carbon can remain effective for a longer time (over about four months). It is best to place the activated carbon in a mesh bag and then tie it tightly to secure it. Bags filled with activated carbon can be placed in an external filter or in the tank of a drip filter. If necessary, it is possible to force all the water flow through activated carbon, but in some cases this increases the resistance to the operation of the filter and reduces its efficiency. However, since the effect of activated carbon is very slow, it is recommended to allow only a partial flow of water to pass through the activated carbon filter, so as not to affect the filter’s resistance. The advantage of this method is that aerobic and anaerobic bacteria can grow simultaneously in the filter; the aerobic bacteria carry out oxidation processes, while the anaerobic bacteria break down nitrates into nitrogen in the anaerobic zones created by the activated carbon. Therefore, over time, the activated carbon filtering material shifts from chemical filtration properties to biological filtration properties.

The effect of solution pH on adsorption must be considered in conjunction with the effects of activated carbon and the adsorbate (solute). The pH value of the solution controls the degree of dissociation of acidic or basic compounds; when the pH reaches a certain range, these compounds dissociate, which affects their adsorption. The pH value of the solution also affects the solubility of the adsorbate (solute), as well as the charge state of the adsorbate (solute) on colloidal substances. Since activated carbon can adsorb hydrogen and oxygen ions in water, it affects the adsorption of other ions. The efficiency of activated carbon in adsorbing organic pollutants from water generally decreases as the pH value of the solution increases; when the pH is above 9.0, adsorption is difficult, while the lower the pH, the better the effect. In practical applications, the optimal pH range is determined through experimentation. Reference: http://www.ccdup.com/articleview/2006-11-30/article_view_440.htm

For the 5th floor: :lol Neutral activated carbon is available; just tell them it’s base carbon. . . . Don’t go to such trouble!

The acidity or alkalinity of activated carbon is determined by the method and process used in its production; you can simply discuss with the supplier the properties you need, which is very convenient.

So there are so many rules involved here!