Carbon, as an adsorbent

Other hydrometaHurgical uses for resin have been smaH in comparison. Replacement of carbon as an adsorbent for gold [7440-57-5] from a cyanide [57-12-5] leached ore has been studied for many years, but remains in limited commercial use. A deterrent has been the failure to develop an efficient and... 

Serious science started in Russian empire in the middle of the XVIII century. The first known Russian scientist M.V. Lomonosov obtained (in the I750sJ experimental data on the preservation of the mass of substances in chemical reactions. T.E. Lovits discovered adsorption from solutions he used wood carbon as an adsorbent. Among other scientists, Lovits detected compounds using characteristic forms of their crystals. V.M. Severgin published a book on analysis of mineral raw materials. 

Carbon materials can be used in de-NO processes either as adsorbents, reduc-tants, or catalysts. The use of carbon as an adsorbent and/or reducing agent for NO c has been reviewed [ref. 109 and references therein], and falls outside the scope of the present review. Nevertheless, we discuss briefly some results and conclusions from more recent papers which are relevant in the context of carbon as a catalyst. 

A novel method to improve the amount of hydrogen that can be stored in composite cylinders involves cryo-compression of the gas. This depends on the fact that gases are denser at cryogenic temperatures than at ambient temperature. Also, they adsorb more readily on to materials with high surface areas. A medium-pressure composite cylinder (20—40 MPa) is filled with activated carbon as an adsorbent and then enclosed in an insulated jacket of liquid nitrogen (77 K). Compressed hydrogen is introduced into the cylinder where it cools, densifies, and is adsorbed on the surface of the carbon. The resultant storage capacity is several times that of the same cylinder at ambient temperature. 

Activated carbon is an adsorbent as described in Chapter 3, Footnote 93, and in Appendix A2. One of the first large-scale uses of activated carbon as an adsorbent was in military gas masks where complete removal of contaminants was essential. Another essential application is removal of mercury contained in emissions from coal-fired power stations, medical incinerators, and in produced natural gas at wellheads. A value provided in cleaning operations by activated carbon adsorbent is that multiple solvent components can be captured within the same apparatus... 

ZeoHte-based materials are extremely versatile uses include detergent manufacture, ion-exchange resins (ie, water softeners), catalytic appHcations in the petroleum industry, separation processes (ie, molecular sieves), and as an adsorbent for water, carbon dioxide, mercaptans, and hydrogen sulfide. 

Chemical Applications. Cesium metal is used in carbon dioxide purification as an adsorbent of impurities in ferrous and nonferrous metallurgy (qv) it can be used as a scavenger of gases and other impurities. 

Several techniques for VOC removal have been investigated such as thermal incineration, catalytic oxidation, condensation, absorption, bio-filtration, adsorption, and membrane separation. VOCs are present in many types of waste gases and are often removed by adsorption [1]. Activated carbon (AC) is commonly used as an adsorbent of gases and vapors because of its developed surface area and large pore volumes [2]. Modification techniques for AC have been used to increase surface adsorption and hence removal capacity, as well as to improve selectivity to organic compounds [3]. 

Activated Carbon (Charcoal). Activated carbon is commonly used as an adsorbent. It has a micro-... 

Cetyltrimethylammonium bromide, latex auxiliary. Also used as an adsorbent to measure the total surface area of carbon black. 

The concentrates were subsequently analysed for arsenic using Varian-Techtron AAS atomic absorption spectrophotometer fitted with a Perkin-Elmer HGA 72 carbon furnace, linked to a zinc reductor column for the generation of arsine (Fig. 5.3). A continuous stream of argon was allowed to flow with the column connected into the inert gas line between the HGA 72 control unit and the inlet to the furnace. Calcium sulfate (10-20 mesh) was used as an adsorbent to prevent water vapour entering the carbon furnace. The carbon tube was of 10 mm id and had a single centrally located inlet hole. 

The major potential application of active carbon fibers is as an adsorbent in environmental control, as outlined in the previous section. However, there is a number of smaller scale, niche applications that seem to be particularly suited to ACF. These emerging applications include the use of ACF in medicine [111 (see also 59,60),112], as capacitors [113-119] and vapor sensors [120], and in refrigeration [121]. The first two of these applications are summarized below. However, there are not many detailed, publicly-available sources describing any of these applications, partly for commercial reasons and partly because the technology is emerging, so any summary is necessarily limited in scope. 

Once the volatile prodiicts have been pyrolyzed, one is left with a material that is mostly carbon, and these are called coke (from coal) and charcoal (from wood). Coke was of course used in blast furnaces to make iron (the volatiles would make the process less reproducible in reducing Fc203) by our ancestors, while charcoal was used in soap (mainly the alkalis in the ash) and as an adsorbent. 

Elemental carbon has many important applications. The diamond is a precious gem, known to mankind for ages graphite is used as an electrode and has numerous other applications carbon-14 isotope is used in carbon dating and the isotope carbon-13 in tracer studies and NMR. Carbon black is used in paints, pigments and inks. Activated carbon is used as an adsorbent for purification of water and separation of gases. Coke is used for electrothermal reduction of metal oxides to their metals. These applications are discussed below in more detail. 

Carbonate-fluor-apatite accommodates large quantities of trace elements, mainly uranium, which are potential luminescence centers. It has been proposed that uranium may occur in phosphorites in the following forms as a separate uraninite phase as an adsorbed or structurally incorporated uranyl ion as a dominantly replacement for Ca +, to be structurally incorporated... 

Junk et al. (5) found that the Rohm and Haas procedure (29) did not clean the resin sufficiently for use as an adsorbent for recovering nanogram-per-liter amounts of organic materials. Junk s resin preparation and cleaning procedure started with backwashing the resin with water to remove fines, sodium chloride, and sodium carbonate. 

As an adsorbent, the new material has similar properties as the activated carbons but with better kinetic performance. 

Li, Q.-L., D.-X. Yuan, and Q.-M. Lin. 2004. Evaluation of multi-walled carbon nanotubes as an adsorbent for trapping volatile organic compounds from environmental samples. J. Chromatogr. A 1026 283-288. 

Therefore, MCM-41 is a possible adsorbent to substitute activated carbon for controlling VOCs [39,119,120], But, the adsorption equilibrium of VOCs on MCM-41 frequently shows very low adsorption capacity in the low-concentration region, owing to its mesoporous structure, which considerably limits the application of MCM-41 as an adsorbent for low-concentration VOC removal [39],... 

Another material that has recieved considerable attention in recent years is carbon [365]. Carbon can be used as an adsorbent for LC in one of several forms, such as pyrolytic carbon (either as such or as a thin layer covering silica particles), glassy carbon and... 

This form of carbon offers a two-fold advantage its large surface area is ideal to adsorb pollutants, and its redox potential is sufficiently low so as to reduce several metal ions to less-toxic oxidation states. For example, it can reduce chromate ions to Cr3+, where C02 is produced as a byproduct. Examples of its use as an adsorbent are given in Section 10.2.1. 

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