PH of activated carbons

Radioiodine Testing of Nuclear-Grade Gas-Phase Adsorbents pH of Activated Carbon... 

The Equilibrium pH of activated carbon at various surface loadings... 

Standard Test Method for pH of Activated Carbon, ASTM D3838-80, ASTM International, West Conshohocken, PA, 1999. 

About 250 ml of a reaction mixture obtained by the electrolytic reduction of nitrobenzene in sulfuric acid solution and containing about 23 grams of p-aminophenol by assay is neutralized while at a temperature of 60° to 65°C, to a pH of 4.5 with calcium carbonate. The calcium sulfate precipitate which forms is filtered off, the precipitate washed with hot water at about 65°C and the filtrate and wash water then combined. The solution is then extracted twice with 25 ml portions of benzene and the aqueous phase is treated with 0.5 part by weight, for each part of p-aminophenol present, of activated carbon and the latter filtered off. The activated carbon is regenerated by treatment with hot dilute caustic followed by a hot dilute acid wash, and reused a minimum of three times. 

Figure 2), significant reduction also took place although the activity was lower than that observed with KOH (the same number of K equivalents were used). This drop in activity is due to the difference in initial pH of the carbonate solution (as compared with the KOH solution) which would be governed by dissolved C02, a variable that changes as the reaction proceeds. 

Voudrias, E.A. "Effects of Activated Carbon on Free and Combined Chlorine with Phenols" Ph.D. Thesis University of Illinois, Urbana, 1985. 

F. 1,4,7,10,13,16-Hexaazacyclooctadecane (6). A 3-1., threenecked, round-bottomed flask is equipped with mechanical stirrer, nitrogen inlet, and addition funnel. In the flask are placed 200 g. (0.169 mole) of cyclic hexamine 5 and 500 ml. of concentrated (97%) sulfuric acid. The stirred mixture is held at 100° for 70 hours and then cooled in ice as 1300 ml. of anhydrous ethyl ether is slowly added. The precipitated polyhydrosulfate salt is filtered under nitrogen and washed with anhydrous ethyl ether (Note 7). The salt is then stirred in 200 ml. of water and cooled in ice as 71 ml. of aqueous 50% NaOH is added to neutralize the solution. Three grams of activated carbon are added, and the solution is heated to 80° and filtered through Celite. The filtrate is cooled in ice and reacidified to pH 1 by adding 42 ml. of concentrated sulfuric acid. The white, non hygroscopic tris(sulfuric acid) salt of 6 that precipitates is collected and washed with 95% ethanol. 

Each column was 35 cm in diameter and contained 0.126 kg of above resin. The filtrate (5300 L) was passed with rate 19 L/minute. Then the columns were washed with deionized water, 1 N sulfuric acid to pH 1.2-1.5, and at last eluted with 4x100 L water. About 200 L of column effluent was alkalifed to pH 6.4 with 10% sodium hydroxide. The 1-st column effluent was mixed with 1200 g of activated carbon, the second effluent was mixed with 850 g of coal (1 g coal per 1 g dissolved product). The mixture was thoroughly stirred and filtered. Each coal precipitate was washed 3x10 L with water and 200 L 15% water acetone. 

Two major strategies can be used for the recovery and purification of CPC. One strategy involves the use of activated carbon or the use of a nonionic resin. Because of the high selectivity of the resin, CPC is preferentially adsorbed over penicillin N or the contaminating biosynthetic precursor molecules. Most of the penicillin N is removed in the pH 2.0 acidification step. An additional anion- and cation-exchange step usually results in high-quality CPC. A large fraction of the CPC is converted to 7-ACA and derivatized to semisynthetic cephalosporins. 

FIGURE 8.35 Comparative cyclic voltammograms of a-Mn02/CNTs composite and of activated carbon (Maxsorb, Kensai, SBET = 3487 m2 g-1) obtained with a three-electrode cell in 2 mol L"1 KNOs (pH = 6.4). (Adapted from Khomenko, V., et al., J. Power Sources, 153, 183, 2006.)... 

The fructose level of the output of each of these columns can be controlled by varying the reaction time (flow rate), temperature and pH. Once conversion is complete the liquor is pumped through beds of activated carbon and then evaporated to the proper solids level, generally 71% or 80% dry solids as previously described. 

The removal of organics (typically measured by total organic carbon or TOC), is an adsorption process. The surface of activated carbon is both hydrophobic and oleophilic, conditions favorable for good removal of TOC. The capacity for organics is a function of temperature, pH, nature of the organic, and concentration such that accurate capacity predictions are not possible. However, typically 25% to 80% of TOC is removed through a carbon filter. 

Adsorption This is the most widely used of the physical-chemical treatment processes. It is used primarily for the removal of soluble organics with activated carbon serving as the adsorbent. Most liquid-ph ase-activated carbon adsorption reactions follow a Freundlich Isotherm [Eq. (22-25)]. 

In the same vein, key strategies for the selective removal of DOM (typically a mixture of acidic macromolecules ionized at circumneutral pH values see Section 6.1.3) with activated charcoal include tailoring this by attaching species with a high affinity for DOM, and developing a positively charged basic surface. Zeolites are also common adsorbents, and their action is much more specific than that of activated carbon since zeolites capture pollutants in cages of specific sizes. 

Cobalt(II) sarcophaginates were oxidized to imines and amides. In the presence of activated carbon, oxygen, and cobalt(II) ions at pH 8.5, the [Co(diAMsar)]3+ cation was oxidized first to imine and then through carbinolamine and amide to diamide sarcophaginate ... 

A general conclusion can be inferred from these observations The number of copper ions adsorbed on active carbon depends on the nature and quantity of the surface acid-base and iono-radical functionalities as well as on the pH equilibria in the external solution. Possible dominant interactions between metal ions and various modified surfaces of active carbon could be considered ... 

The interest in adsorption of molybdenum stems primarily from its use as a carbon-supported catalyst [22]. The use of activated carbon for the removal of Mo-99 (used in nuclear medicine) has also been reported ] 158]. Only hexavalent Mo is stable under a wide pH range and in the absence of other complexing agents. At pH > 8, the dominant species is M0O4-, while at very low pH there is precipitation of the hydrated oxide between these two extremes polymeric anions are formed [123,159]. 

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