Natural waters activated carbon

There are five major greenhouse gases that occur naturally water vapor, carbon dioxide, ozone, methane, and nitrous oxide. Human activity has in-... 

Ketterer, M., and Khourey, C. J. (1998). High-ptedsion determination of 020304U/ 020308U activity ratios in natural waters and carbonates by ICPMS. ASTM Spec. Tech. Pub., p. 120. 

The most common hydrophobic adsorbents are activated carbon and siUcahte. The latter is of particular interest since the affinity for water is very low indeed the heat of adsorption is even smaller than the latent heat of vaporization (3). It seems clear that the channel stmcture of siUcahte must inhibit the hydrogen bonding between occluded water molecules, thus enhancing the hydrophobic nature of the adsorbent. As a result, siUcahte has some potential as a selective adsorbent for the separation of alcohols and other organics from dilute aqueous solutions (4). 

Potable Water Treatment. Treatment of drinking water accounts for about 24% of the total activated carbon used in Hquid-phase apphcations (74). Rivers, lakes, and groundwater from weUs, the most common drinking water sources, are often contaminated with bacteria, vimses, natural vegetation decay products, halogenated materials, and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (75). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (76—78) for safety and palatability. 

Other Uses. The quantity of coal used for purposes other than combustion or processing is quite small (2,6). Coal, especially anthracite, has estabHshed markets for use as purifying and filtering agents in either the natural form or converted to activated carbon (see Carbon). The latter can be prepared from bituminous coal or coke, and is used in sewage treatment, water purification, respirator absorbers, solvent recovery, and in the food industry. Some of these markets are quite profitable and new uses are continually being sought for this material. 

Adsorption and Desorption Adsorbents may be used to recover solutes from supercritical fluid extracts for example, activated carbon and polymeric sorbents may be used to recover caffeine from CO9. This approach may be used to improve the selectivity of a supercritical fluid extraction process. SCF extraction may be used to regenerate adsorbents such as activated carbon and to remove contaminants from soil. In many cases the chemisorption is sufficiently strong that regeneration with CO9 is limited, even if the pure solute is quite soluble in CO9. In some cases a cosolvent can be added to the SCF to displace the sorbate from the sorbent. Another approach is to use water at elevated or even supercritical temperatures to facilitate desorption. Many of the principles for desorption are also relevant to extraction of substances from other substrates such as natural products and polymers. 

Adsorption — An important physico-chemical phenomenon used in treatment of hazardous wastes or in predicting the behavior of hazardous materials in natural systems is adsorption. Adsorption is the concentration or accumulation of substances at a surface or interface between media. Hazardous materials are often removed from water or air by adsorption onto activated carbon. Adsorption of organic hazardous materials onto soils or sediments is an important factor affecting their mobility in the environment. Adsorption may be predicted by use of a number of equations most commonly relating the concentration of a chemical at the surface or interface to the concentration in air or in solution, at equilibrium. These equations may be solved graphically using laboratory data to plot "isotherms." The most common application of adsorption is for the removal of organic compounds from water by activated carbon. 

Activation of zeolites is a dehydration process aceomplished by the application of heat in a high vacuum. Some zeolite crystals show behavior opposite to that of activated carbon in that they selectively adsorb water in the presence of nonpolar solvents. Zeolites can be made to have specifie pore sizes that will increase their seleetive nature due to the size and orientation of the molecules to be adsorbed. Moleeules above a specific size could not enter the pores and therefore would not be adsorbed. 

Some greenhouse gases occur naturally in the atmosphere, while others result from human activities. Naturally occurring greenhouse gases include water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases ... 

The following natural precursors have been selected for KOH activation coal (C), coal semi-coke (CS), pitch semi-coke (PS) and pitch mesophase (PM). An industrial activated carbon (AC) was also used. Activation was performed at 800°C in KOH with 4 1 (C KOH) weight ratio, for 5 hours, followed by a careful washing of the samples with 10% HC1 and distilled water. The activation process supplied highly microporous carbons with BET specific surface areas from 1900 to 3150 m2/g. The BET surface area together with the micro and the total pore volume of the KOH-activated carbons are presented in Table 1. The mean micropore width calculated from the Dubinin equation is designed as LD. 

Hydroxide and carbonate typically form insoluble precipitates with polyvalent cations in natural waters. The activity of both of these species increases with pH. The presence of surface functional groups that are capable of exchanging a proton creates pH dependent-charge, whereby the ionic character of the surface increases with pH [158,284,285]. 

Heijman SGJ, Verliefde ARD, Comelissen ER, Amy G, van Dijk JC (2007) Influence of natural organic matter (NOM) fouling on the removal of pharmaceuticals by nanoflltration and activated carbon filtration. Water Sci Technol Water Supply 7 17-23... 

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