FAQ

Activated carbons are processed forms of carbon and are one of the most significant adsorbent materials due to their highly developed porosity, large surface area ranging from 500 to 3000 m2/g, variable characteristics of surface chemistry, and high degree of surface reactivity. It has capability to selectively adsorb thousands of organic and inorganic pollutants, remove colour and impurities from liquids and gases, used in the separation of chemical compounds and in the recovery of solvents.

Adsorption is a surface phenomenon which is characterized by the adhesion of molecules (or ions and atoms) to the surface of a solid or liquid. The molecules get accumulated only at the surface and do not enter the bulk of the adsorbing material. The substance which gets adsorbed is called adsorbate and the substance which adsorbs is called the adsorbent. Some of the well-known adsorbents include Activated Carbon, Alumina gel, Silica gel, Zeolites and Graphite. The reverse process which involves the removal of adsorbed substance from the Adsorbent media is known as desorption. The process of Absorption is a bulk phenomenon. In absorption, the substance gets uniformly distributed throughout the bulk of the solid or liquid. The substance which gets absorbed is called absorbate and the substance which absorbs is called the absorbent.

Commercially activated carbon basically uses precursors such as petroleum residues, wood, coal, peat and lignite which are very expensive and non-renewable. Therefore, in recent years, people have been focusing on the activated carbon preparation based on agricultural waste and lignocelluloses materials which are effective and very inexpensive, such as coconut shell, wood, corn cob, hazelnut shell, pruning mulberry shoot, olive stone, Jojoba seed, Chinese fir sawdust, hazelnut bagasse , kenaf fiber , bamboo , rice husk , petai , groundnut shell, paper mill sludge, prosopis (Prosopis juliflora), coconut husk, Jatropha husk, tamarind wood , pistachio-nut, sugarcane bagasse, jackfruit peel , and many others.

Characteristics of Activated Carbon depend on the physical and chemical properties of the raw materials as well as method of activation. In all activated carbon producer, coconut shell has been proven to produce top grade active carbon charcoal which got great performance owing to its high carbon content, exceptional porosity, resistance to breakage .

Most of the activated carbons are produced by a two-stage process, viz., carbonization followed by activation. The first-stage, carbonization, is to enrich the carbon content and to create an initial porosity and the second-stage, activation process, helps in enhancing the pore structure. Activated carbons may be obtained by physical activation (with steam or gaseous CO2) or chemical activation by strongly reacting chemicals, such as ZnCl2, H3PO4 and alkali-metal hydroxides (NaOH and KOH). Physically activated carbons exhibit good Adsorption Characteristics and are environmental friendly as no chemical is involved in the process, further, they are cost effective as they do not involve an extra step in washing away the chemicals agents after the activation step. Chemically activated carbons have good thermal stability, characteristic porous structure, and large internal surface area and porous volume.

Activated Carbon has been widely used as an adsorbent for separation, purification, decolourization and deodorization, water purification and pollution treatment, air and gas purification, its finds its use in food and pharmaceutical industries, gas storage, catalysis, metal extraction, chromatographic separation, trapping mercury, fuel cells and many other applications. Carbon adsorption has numerous applications in industrial processes; such as spill cleanup, groundwater remediation, drinking water filtration, air purification, volatile organic compounds removal, gasoline dispensing operations, and other processes. The importance and relevance of activated carbon to an ever growing society cannot be overemphasized considering its enormous uses.

• Removal of Chlorine and Chloramines from drinking water
• Removal of organic pollutant and bio-refractive substances
• Reducing the amount of DBP (Disinfection by-product)
• Removal of objectionable odour.
• Removal of Poly aromatic hydrocarbons (PAHs)
• Phenolic Compounds Removal
• Oil Separation and Removal
• Heavy metal ions Removal
• Reducing Quantity of Lead
• Removal of Organic dyes like Methylene blue, levafix red and remazon blue.
• Treating and purification of oleo chemicals
• Purification of organic chemicals like fumaric acid, malefic acid and amino acids like methionine, lysine and phenyl alanine
• Removal of pharmaceutically active compounds
• Removal of Agrochemicals and pesticides;
• Removal of Petroleum Refinery waste like Hydrogen Sulphide, Hydrogen Compounds, phenol (P), p-chlorophenol
(PCP) and p-nitrophenol (PNP)
• Adsorption of the gold-cyanide complex (dicyanoaurate ion) in carbon-in-pulp (CIP) and carbon-in-leach (CIL) systems, or in carbon-in-column (CIC) systems.
• Adsorption of Organic species originating from Flotation ,Oils, degreasers etc., from leaking glands, washing of equipment, trackless mining oil deposits, etc. , Humic and Fulvic acids originating from plant material (vegetation, wood etc) that compete directly with gold.
• Controlling the airborne emissions containing bad and hazardous odours, harmful compounds etc.
• Removal of contaminants, Protection of Catalysts, Purification of final gaseous products etc. in industrial Gas purification processes.
• Removal of colorants like mealonoidins, polyphenols from apple and grape juices
• Suppress the straw taste from the malt- beer.
• Prevention of turbidity during ageing process of Whisky
• Removal of congeners like Fusel oils and Aldehydes.

After a certain use interval, Activated carbon becomes exhausted and there is a significant drop in the effectiveness of its adsorption. Regeneration, often referred to as reactivation, is a method of thermally processing the activated carbon to destroy the adsorbed components contained on its surface. It is a process which restores the adsorptive capacity of the Activated Carbon. In regeneration, the adsorbed components are almost completely removed, and yielding a regenerated carbon that can again function as an adsorbent.

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Gold Recovery Process

Activated Carbon finds its best use in the process of recovery of gold from a gold cyanide complex form (dicyanoaurate). The processes that are dedicated to this mechanism of Gold Adsorption is the CIL (Carbon in Leach) and CIP (Carbon in Pulp) process. Cyanide is a reagent that is used to leach gold from its ore and form a gold cyanide complex, a solution form, gold is then adsorbed onto the Activated carbon which is a renowned adsorbent that has a highly porous structure, and an appreciable kinetic adsorption characteristics. CIL process is where, the Activated Carbon is added to leach tanks and the process of leaching and adsorption takes place in the same tank. CIP process differs from the CIL process in a way that, it is a sequential process, where, there are tanks that are dedicated separately for each of the leaching process and the adsorption process. The Activated Carbon that is loaded with gold and some organic and inorganic impurities is transferred to elution where is it subjected to sequence of cold wash to remove the impurities, followed by washing with solvent to extract the gold from the adsorbed media. Studies have confirmed that extraction of gold cyanide complex is strongly enhanced by the presence of KCl (Potassium Chloride) and CaCl2 (Calcium Chloride) electrolytes in the adsorption medium (Activated Carbon), furthermore, the recovery rate is increased by increasing the acidity of the Adsorption medium.

Impregnated carbons offer additional capabilities through (a) Optimization of existing properties of an AC (b) Synergism between Activated Carbon and the impregnating agent (c) The availability of a large internal surface area, where the carbon surface is replaced by the surface of another material (as in a coating) Some of the benefits include, Impregnation with phosphoric acid is used for the removal of ammonia vapours from the atmosphere. Impregnation with potassium iodide promotes the oxidation of hydrogen sulphide to sulphur. Silver-impregnated activated carbon for the removal of bromide, iodide and Natural Organic Matter and Nitrogen Oxide. Sulphur Impregnation for mercury removal. Amine-impregnated activated carbons have higher adsorption capacity for CO2. Copper impregnated activated carbon for the treatment of sulphurous waters.

Activated carbons are classified in many ways, although a general classification can be made based on their physical characteristics, as powdered activated carbon, granular activated carbon, extruded activated carbon or pressed pellets activated carbon, impregnated carbon, polymer coated carbon and other types.

Each grade of Activated Carbon is used in specific applications. Powdered activated carbons are added directly to process units, granulated carbons are used for deodorization and for the separation of components in flow systems, extruded activated carbons are mainly used for gas phase applications, impregnated carbons are used for specific applications in air pollution control and polymer coated carbons are useful for hemoperfusion.

There are Commercial grades of activated carbon which are available for specific use in vapour-phase applications. The granular form of activated carbon is typically used in packed beds through which the contaminated air flows until the concentration of contaminants in the effluent from the carbon bed exceeds an acceptable level.

Properties of activated carbon are: its specific surface area, iodine index, molasses index, tannin index, methylene blue index, butane index, carbon tetrachloride index, De- chlorination half-value length, density, hardness number, ash content, porosity and particle size distribution. The indexes give an idea of the kind of pore a certain carbon has.

The contact time refers to the amount of time that a particular type of contaminant is in contact with the surface area of the Activated carbon adsorbent. Thus, contact time would differ for various Applications based on the type of Adsorbent, Concentration of the contaminant, temperature, PH etc. The contact time plays a vital role in deciding the kinetics of the Adsorption media.

Water pollution is gaining equal importance along with climate change as the most intricate environmental turmoil for the 21st century. Today, the percolation of textile effluents into the waterways and ecosystems has become a major issue that requires immediate attention. With the renaissance of activated carbon, there has been a steadily growing interest in this research field. While Activated Carbon is effective in removing organic dyes like Methylene blue, levafix red and remazon blue, there is scope for expanding of adsorption science in dye treatment for accruing the worldwide environmental benefit.

The pH has a very important effect for adsorption processes in the liquid phase. The pH indeed has an influence on surface chemistry and on surface charge. Activated Carbon with a more neutral pH has been found to outperform in its characteristic adsorption capacity when compared to a lower pH. A lower pH renders the Absorbent to be corrosive.

The activation process is the preparation stage of activated carbon where pore development takes part, with the available methods being classified either as physical activation or as chemical activation. While physical activation methods result in the preparation of microporous solid with large surface area but poor mass transfer rate, chemical activation methods allow the development of mesoporosity that enhances mass transfer rates of pollutants. It is important to note that the selected activation temperature and the activating agent in the chemical activation play a key role on the preparation yield as well as on the texture properties and surface chemistry of the resulting activated carbons

Carbon air filter help to get rid of strong odours or harmful gases in our home, in air purification systems, activated carbon filters can be used along with HEPA filters to eliminate impurities like dust, lint, mold spores, smoke, household chemicals and Volatile Organic compounds.

Steam Activation is widely preferred owing to the fact that Steam Activation does not introduce any harmful chemicals to the Adsorbent. It helps in providing adsorbent which is highly porous, which has high resistance to breakage and an Activated carbon that has an ideal Adsorption kinetics. It is highly Cost effective considering the price of Chemical agents and additional washing step involved in the Chemical Activation process.

It is a measure of the micro pore content of the activated carbon. Iodine number is a widely used parameter for activated carbon testing for its simplicity and a rapid assessment of adsorbent quality. It gives an estimate of its surface area and porosity. The iodine number is defined as the milligrams of iodine adsorbed by one gram of Activated Carbon. ASTM D4607 Standard Test Method for Determination of Iodine Number of Activated Carbon is designed to quantitatively characterize the adsorption capacity of activated carbons that have a high adsorption capacity.

Activated Carbon has been used in the treatment of overdoses or poisoning, due to its properties of detoxification. Though there has not been scientifically conclusive evidence, Activated Carbon is believed to assist in kidney functioning by filtering out the undigested toxins. It helps in Teeth whitening and oral health owing to its antibacterial, antifungal characteristics. It has been playing a role in the cosmetic industry as it draws dirt, dust, chemicals and bacteria from the surface of the skin.

Hybridized value added Activated Carbon, numerous research studies have reported remarkable physical, chemical, thermal, conductivity, porosity, and mechanical (stiffness and strength) properties of such type of AC. The scale of the reinforcement and filled phase of the AC has changed from micrometers to nanometers. This create opportunities to increase the potential applications of AC hybrid materials of the development of fundamentally unique new materials for chemical conversion, environmental, and fuel storage applications.