1. Iodine value (400 ~ 1300): refers to the amount of iodine adsorbed by activated carbon in 0.02N12 / KL aqueous solution. The iodine value is related to the pore surface area with a diameter greater than 10A. The iodine value is one of the criteria for judge the price of activated carbon.

2. Butane value: Butane value is the amount of butane adsorbed per unit weight of activated carbon after saturated air and butane pass through the carbon bed at a specific temperature and specific pressure.

3. Ash content (6-16): There are two types of ash of activated carbon, one is surface ash and the other is internal ash content. Normally, the ash of activated carbon refers to internal ash.

4. Water content (<5): It is a measure of how much water is contained in carbon, that is, the percentage of the weight of water adsorbed in activated carbon.

5. Hardness: The hardness value refers to the resistance of the granular activated carbon to the decay movement of the steel ball in the RO-TAP instrument. Hardness is an indicator for measuring the mechanical strength of activated carbon.

6. Carbon tetrachloride CTC (%): The carbon tetrachloride value is an indicator of the total pore volume, which is measured with a saturated CCI4 gas flow of zero degrees Celsius through a 25 degree carbon bed. That is, the adsorption function of activated carbon depends on the carbon tetrachloride value. The measurement method is to use activated carbon to adsorb carbon tetrachloride, and the measured result is the adsorption rate of activated carbon. Generally, the highest carbon tetrachloride value of activated carbon is 80. Activated carbon manufacturers in Beijing and Hebei have more than 80% to reach 60%.

7. Molasses value:  The molasses value is a method to measure the relative decolorization ability of activated carbon in boiling molasses solution. The molasses value is interpreted as a surface area with a pore diameter greater than 28A. Because molasses is a mixture of multiple components, this parameter must be tested in strict accordance with the instructions. The molasses value is obtained by calculating the ratio of the optical density of the filter by treating the molasses liquid with a standard sample of activated carbon and a sample of activated carbon to be tested.

8. Bulk weight (400-600): Bulk weight is a method of measuring the quality of a specific amount of carbon. By gradually adding activated carbon to a graduated drum to 100cc, and measuring its mass. This value is used to calculate the amount of activated carbon needed to fill a specific adsorption device. Simply put, the bulk weight is the weight of activated carbon per unit volume.

9. Particle density – The particle density is the weight of the particulate carbon per unit volume, excluding the particles and the space between cracks greater than 0.1 mm.

10. Methythioninium Chloride (100-300):   The Methythioninium Chloride value refers to the number of milligrams of Methythioninium Chloride absorbed when a solution of 1.0 g of carbon and a concentration of 1.0 mg / L of Methythioninium Chloride reaches equilibrium.

11. Wear value

The wear value is an index for measuring the wear resistance of activated carbon. The wear value of granular activated carbon indicates that the particles reduce the resistance of the particles during the treatment process. It is calculated by determining the ratio of the average diameter of the final particles to the average diameter of the original particles.

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Hardness/abrasion number is a measure of the activated carbon’s resistance to attrition. It is an important indicator of activated carbon to maintain its physical integrity and withstand frictional forces. There are large differences in the hardness of activated carbons, depending on the raw material and activity levels.

A variety of tests are available for the evaluation of the mechanical strength of granular activated carbon. In these tests the change in particle size distribution or the amount of fines produced is determined. Different mechanical strength test methods measures different aspects of strengths and can thus mathematically not be related to one another. The most common test method is Hardness number followed by abrasion number.

Mechanical strength: Hardness and abrasion number

• The Hardness number (DSTM 20) measures the external integrity against wearing along exterior and breakage of small points of activated carbon. It is expressed as a percentage of loss on a particular sieve after shaking granules under certain conditions.
• The abrasion number (AWWA B604) measures the structural strength of granular activated carbon. It is a measure of the ability of the particle to stand up to shear forces caused by particles rubbing together or particles rubbing against another surface such as a column wall or supporting screen. It is measured by shaking granules with steel balls in a container under certain conditions and expressed as a percentage reduction in Mean Particle Diameter (mpd).

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Iodine Number
Iodine adsorption is used to measure the effectiveness of activated carbon. During this test, activated carbon is added to a liquid holding a specific amount of iodine. The carbon is mixed thoroughly until it has dissolved into the solution. After a few minutes, the solution is filtered into another container, removing the charcoal particles and allowing the liquid to pass through. The iodine number is a gauge of the amount of iodine removed from the liquid. Essentially, the higher the number, the more iodine was removed.

Many carbons preferentially adsorb small molecules. Iodine number is the most fundamental parameter used to characterize activated carbon performance. It is a measure of activity level (higher number indicates higher degree of activation,) often reported in mg/g (typical range 500–1200 mg/g). It is a measure of the micropore content of the activated carbon (0 to 20 Å, or up to 2 nm) by adsorption of iodine from solution. It is equivalent to surface area of carbon between 900 and 1100 m²/g. It is the standard measure for liquid-phase applications.

Iodine number is defined as the milligrams of iodine adsorbed by one gram of carbon when the iodine concentration in the residual filtrate is at a concentration of 0.02 normal (i.e. 0.02N). Basically, iodine number is a measure of the iodine adsorbed in the pores and, as such, is an indication of the pore volume available in the activated carbon of interest. Typically, water-treatment carbons have iodine numbers ranging from 600 to 1100. Frequently, this parameter is used to determine the degree of exhaustion of a carbon in use. However, this practice should be viewed with caution, as chemical interactions with the adsorbate may affect the iodine uptake, giving false results. Thus, the use of iodine number as a measure of the degree of exhaustion of a carbon bed can only be recommended if it has been shown to be free of chemical interactions with adsorbates and if an experimental correlation between iodine number and the degree of exhaustion has been determined for the particular application.

Pore Diameter 
The diameter of the pores on and inside activated carbon will make a significant difference in how the materials performs. Pore diameter can determine the specific use of a carbon, as activated carbon with more micropores (smaller pores) can be effective for removing low concentrations of organic matter found in water. Activated carbon with both small and large pores are very versatile and can be used to remove both chlorine and a wide variety of organic matter at the same time.

Surface Area
The surface area is another important property that is often cited on activated carbon. Depending on the raw material, the activation process, and other factors, the surface area will vary, giving the charcoal more or less adsorption potential. Surface area for activated carbon is often measured using a BET nitrogen adsorption test.

Density 
Density will affect the volume activity. Generally, a higher density will indicate a higher-quality activated carbon. There are numerous ways to define density, including real density, which is the density excluding the voids of the material, as well as particle density, which is the measured density of the carbon particles alone. There is also wetted density, apparent density, bed or bulk density, and tamped density. All of these density measurements provide specific data on activated carbon performance.

Tannin

Tannins are a mixture of large and medium size molecules. Carbons with a combination of macropores and mesopores adsorb tannins. The ability of a carbon to adsorb tannins is reported in parts per million concentration (range 200 ppm–362 ppm).

Methylene blue

Some carbons have a mesopore (20 Å to 50 Å, or 2 to 5 nm) structure which adsorbs medium size molecules, such as the dye methylene blue. Methylene blue adsorption is reported in g/100g (range 11–28 g/100g).

Dechlorination

Some carbons are evaluated based on the dechlorination half-life length, which measures the chlorine-removal efficiency of activated carbon. The dechlorination half-value length is the depth of carbon required to reduce the chlorine level of a flowing stream from 5 ppm to 3.5 ppm. A lower half-value length indicates superior performance.

Apparent density

The solid or skeletal density of activated carbons will typically range between 2000 and 2100 kg/m³ (125–130 lbs./cubic foot). However, a large part of an activated carbon sample will consist of air space between particles, and the actual or apparent density will therefore be lower, typically 400 to 500 kg/m³ (25–31 lbs./cubic foot).^[19]

Higher density provides greater volume activity and normally indicates better-quality activated carbon. ASTM D 2854 -09 (2014) is used to determine the apparent density of activated carbon.

Hardness/abrasion number

It is a measure of the activated carbon’s resistance to attrition. It is an important indicator of activated carbon to maintain its physical integrity and withstand frictional forces. There are large differences in the hardness of activated carbons, depending on the raw material and activity levels.

Ash Content 
Ash content is an important measurement for activated carbon and can drastically change the effectiveness and specific use for the product. Ash in the activated carbon reduces the speed and reliability of reactivation and metal oxides can be released from charcoal with high ash content, resulting in discoloration when used to purify water. Carbon with high ash content is not good for fish tanks, as they can lead to heavy metal poisoning in the aquatic life, including fish and coral species. The type of ash can vary as well. For example, activated carbon made from coconut shells often has a higher concentration of alkali earth metals, while carbon made from coal is often loaded with heavy metals.

Ash reduces the overall activity of activated carbon and reduces the efficiency of reactivation. The metal oxides (Fe₂O₃) can leach out of activated carbon resulting in discoloration. Acid/water-soluble ash content is more significant than total ash content. Soluble ash content can be very important for aquarists, as ferric oxide can promote algal growths. A carbon with a low soluble ash content should be used for marine, freshwater fish and reef tanks to avoid heavy metal poisoning and excess plant/algal growth. Standard method D 2866-2011 is used to determine the ash content of activated carbon.

Mesh
The size of granular activated carbon (activated carbon that is in the form or a powder or fine grains) is measured using a Mesh system. It is measured by shaking a sample of the granulated carbon through a series of fine sieves. Imagine sieves like a window screen only much finer, with far smaller holes between the wires. Using a system that measures how much of the carbon passes through the screens, the activated carbon can be measured for general size.

Molasses Number 
The molasses number for activated carbon is a measurement of the charcoal’s effectiveness for removing large molecules. This is done by allowing the activated carbon to adsorb a molasses solution. The higher the molasses number, the better the activated charcoal is at removing these large molecules.

Some carbons are more adept at adsorbing large molecules. Molasses number or molasses efficiency is a measure of the mesopore content of the activated carbon (greater than 20 Å, or larger than 2 nm) by adsorption of molasses from solution. A high molasses number indicates a high adsorption of big molecules (range 95–600). Caramel dp (decolorizing performance) is similar to molasses number. Molasses efficiency is reported as a percentage (range 40%–185%) and parallels molasses number (600 = 185%, 425 = 85%). The European molasses number (range 525–110) is inversely related to the North American molasses number.

Molasses Number is a measure of the degree of decolorization of a standard molasses solution that has been diluted and standardized against standardized activated carbon. Due to the size of color bodies, the molasses number represents the potential pore volume available for larger adsorbing species. As all of the pore volume may not be available for adsorption in a particular waste water application, and as some of the adsorbate may enter smaller pores, it is not a good measure of the worth of a particular activated carbon for a specific application. Frequently, this parameter is useful in evaluating a series of active carbons for their rates of adsorption. Given two active carbons with similar pore volumes for adsorption, the one having the higher molasses number will usually have larger feeder pores resulting in more efficient transfer of adsorbate into the adsorption space.

Carbon tetrachloride activity

Measurement of the porosity of an activated carbon by the adsorption of saturated carbon tetrachloride vapour.

Particle size distribution

The finer the particle size of an activated carbon, the better the access to the surface area and the faster the rate of adsorption kinetics. In vapour phase systems this needs to be considered against pressure drop, which will affect energy cost. Careful consideration of particle size distribution can provide significant operating benefits. However, in the case of using activated carbon for adsorption of minerals such as gold, the particle size should be in the range of 3.35–1.4 millimetres (0.132–0.055 in). Activated carbon with particle size less than 1 mm would not be suitable for elution (the stripping of mineral from an activated carbon).

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The ability of activated carbon to remove contaminants is determined not by its weight or volume, but its Adsorption capacity, i.e., the amount of impurity removed by a given amount of activated carbon.

The higher this capacity, the more contaminants removed per, let’s say, cubic foot, the less carbon needed to perform a particular job. In the manufacture of activated carbons, a wide variety of raw materials and widely varying quality specifications are used.

While the raw material itself determines many of a carbons physical properties, its adsorption capacity is dependent on a precise and carefully controlled steam activation process

Quality is also an issue with reactivated carbons. The ability to decontaminate and reactive spent carbon to near virgin capacity is dependent not only on proper operation of the reactivation furnace but its close and careful monitoring (e.g., thermal degradation and the build up of inorganic ash constituents are common problems with carbons that are repetitively recycled).

The carbon manufacturing industry and ASTM have developed two critical tests that not only measure the quality of both virgin and reactivated carbon products but also predict its cost effectiveness:

The IODINE A D S O R P T I O N T E S T ( A S T M D4607) for measuring the LIQUID PHASE of activated carbons produce IODINE A D S O R P T I O N NUMBERS from 800 to 1250 mg/gr. (the higher the number the greater the capacity).

The CARBON T E T R A C H L O R I D E A D S O R P T I O N T E S T ( A S T M D3467) for the VA P O R P H A S E o f activated carbons produces CARBON T E T R A C H L O R I D E A D S O R PTION NUMBERS ranging from 45 to 70 percent by weight

When buying either virgin or reactivated carbon products, make sure that these adsorption numbers are specified. Then compare these to CARBTROL’s to insure the best activated and reactivated carbon value for your money.

CARBTROL’S NUMBERS:

Liquid Phase Virgin Carbon – CSL – Iodine Number

– 1100 mg/gr. (average) !

Vapor Phase Virgin Carbon – CSV – Carbon Tetrachloride Number

– 60-65% (average) !

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Iodine and molasses numbers measure pore size distribution.  Iodine number is a relative measure of pores at sizes of 10 to 2 Angstroms. It is reported in milligrams of elemental iodine adsorbed per gram of GAC and determines the area available on the GAC to adsorb low molecular weight organics.

Molasses number measures the degree a GAC removes color from a stock solution. It measures pores greater than 28 Angstroms. These are the pores responsible for removing larger molecular weight organics such as tannins.

Abrasion numbers represent the relative degree of particle size reduction after tumbling with a harder material. No reduction is rated 100, complete pulverization is zero.

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Molecular weight:
As the molecular weight increases, the activated carbon adsorbs more effectively because the molecules are lea soluble in water. However, the pore structure of the carbon must be large enough to allow the molecules to migrate within. A mixture of high and low molecular weight molecules should be designed for the removal of the more difficult species.

pH:
Most organics are less soluble and more readily adsorbed at a lower pH. As the pH increases, removal decreases. A rule of thumb is to increase the size of the carbon bed by twenty percent for every pH unit above neutral (7.0).

Contaminant concentration:  The higher the contaminant concentration, the greater the removal capacity of activated carbon. The contaminant molecule is more likely to diffuse into a pore and become adsorbed. As concentrations increase, however, so do effluent leakages. The upper limit for contaminants is a few hundred parts per million. Higher contaminant concentration may require more contact time with the activated carbon. Also, the removal of organics is enhanced by the presence of hardness in the water, so whenever possible, place activated carbon units upstream of the ion removal units. This is usually the case anyway since activated carbon is often used upstream of ion exchange or membranes to remove chlorine.

Particle size:
Activated carbon is commonly available in 8 by 30 mesh (largest), 12 by 40 mesh (most common), and 20 by 50 mesh (finest). The finer mesh gives the best contact and better removal, but at the expense of higher pressure drop. A rule of thumb here is that the 8 by 30 mesh gives two to three times better removal than the 12 by 40, and 10 to 20 times better kinetic removal than the 8 by 30 mesh.

Flow rate:
Generally, the lower the flow rate, the more time the contaminant will have to diffuse into a pore and be adsorbed. Adsorption by activated carbon is almost always improved by a longer contact time. Again, in general terms, a carbon bed of 20 by 50 mesh can be run at twice the flow rate of a bed of 12 by 40 mesh, and a carbon bed of 12 by 40 mesh can be run at twice the flow rate of a bed of 8 by 30 mesh.  Whenever considering higher flow rates with finer mesh carbons, watch for an increased pressure drop!

Temperature:
Higher water temperatures decrease the solution viscosity and can increase die diffusion rate, thereby increasing adsorption. Higher temperatures can also disrupt the adsorptive bond and slightly decrease adsorption. It depends on the organic compound being removed, but generally, lower temperatures seem to favor adsorption.

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Healing properties of Activated Carbons:

• Detox: By binding with organic chemicals from pesticides, plastics, and other pollutants.
• Detox: By binding with viruses and bacteria.
• Gentle on the colon and does not damage the mucus lining of the intestines.
• De- bloats by binding to gases.
• Facilitates digestion.
• May help lower cholesterol, triglycerides and lipids found in the blood.
• Helps relieve constipation.
• Helps with acne.
• Kills parasites like Candida.
• Removes the toxins in the human body. (The toxins are eliminated through feces).
• Helps with food poisoning

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Physical Adsorption – During this process, the adsorbates are held on the surface of the pore walls by weak forces of attraction known as Van Der Waals Forces or London dispersion forces.

Chemisorption – This involves relatively strong forces of attraction, actual chemical bonds between adsorbates and chemical complexes on the pore wall of the activated carbon.

Key Properties of Activated Carbon

Surface Area – Generally, higher the internal surface area, higher the effectiveness of the carbon. The surface area of activated carbon is impressive, 500 to 1500 m2/g or even more; a spoonful of activated carbon easily equates the surface area of a soccer field.

It is in the activation process that this vast surface area is created. The most common process is steam activation; at around 1000°C steam molecules selectively burn holes into the carbonized raw material, thus creating a multitude of pores inside the carbonaceous matrix. In chemical activation, phosphoric acid is used to build up such a porous system at a lower temperature.

Total Pore Volume – Refers to all pore spaces inside a particle of activated carbon. It is expressed in milliliters per gram (ml/g), volume in relation to weight. In general, the higher the pore volume, the higher the effectiveness. However, if the sizes of the molecules to be adsorbed are not a good match to the pore size, some of the pore volume will not be utilized. Total pore volume (T.P.V.) differs by raw material source and type of activation method.

Pore Radius – The mean (average) pore radius, often measured in angstroms, differs by activated carbon type.

Pore Volume Distribution – Each type of carbon has its own unique distribution of pore sizes. They’re referred to as micropores (small), mesopores (medium) and macropores (large). Carbons for adsorbing many types of gas molecules are microporous. The best carbons for decolorization have a higher distribution of mesopores.

• Micropores r < 1nm
• Mesopores r 1-25nm
• Macropores r > 25nm
  _{nm = nanometer}  

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The physical size, or mesh size, of a carbon must be considered in relation to the flow rate in the system it is to be used. Naturally, the smaller the carbon’s mesh size, the greater its resistance to flow. Thus, it is usual to select the smallest mesh size carbon that will satisfy the pressure drop limitations of the system.

Ash Content

Ash content is less important except where the carbon is used as a catalyst support since certain constituents of the ash may interfere or destroy the action of precious metal catalysts. Ash content also influences the ignition point of the carbon—this may be a major consideration where adsorption of certain solvents is concerned.

Density

The density of carbon is, of course, of great importance to many users in estimating the weight required to fill a vessel.

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CTC activity, density and ash content are interrelated and provide a simple means of manufacturing control. As quality, or degree of activation increases, CTC activity and ash content increase and density decreases.

Furthermore, CTC activity being equal, coconut carbons show higher density and lower ash content than coal based carbons. Wood based carbons show much lower density than either coal or coconut carbons but ash contents midway between coal and coconut carbons.

Thus, these properties are not only a means of controlling quality during manufacture but may also assist in determining the raw material and quality of an unknown carbon.

CTC activity, density, hardness, mesh size and raw material information will enable selection of a suitable carbon for most common applications (excepting those utilizing chemisorption as the prime mechanism).

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