Carbon-based recovery systems

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S0 3, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach Hquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH NO, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and cosdy ore particle/leach hquor separation step. 

Heterogeneous hydrogenation catalysts can be used in either a supported or an unsupported form. The most common supports are based on alurnina, carbon, and siUca. Supports are usually used with the more expensive metals and serve several purposes. Most importandy, they increase the efficiency of the catalyst based on the weight of metal used and they aid in the recovery of the catalyst, both of which help to keep costs low. When supported catalysts are employed, they can be used as a fixed bed or as a slurry (Uquid phase) or a fluidized bed (vapor phase). In a fixed-bed process, the amine or amine solution flows over the immobile catalyst. This eliminates the need for an elaborate catalyst recovery system and minimizes catalyst loss. When a slurry or fluidized bed is used, the catalyst must be separated from the amine by gravity (settling), filtration, or other means. 

Phenyl (Cohesive Technologies), the polymer-based Oasis HLB (Waters), the Cyclone (Cohesive Technologies), and the porous graphitized carbon-based Hypercarb (ThermoHypersil, Cheshire, UK) Cohesive s 2300 system was the HTLC component. Merck s monolithic reversed-phased Chromolith Speed ROD (RP-C18 (50 x 4.6 mm) served as the analytical column. The Oasis HLB, Cyclone TFC, and Hypercarb yielded the best retention capacity and good elution efficiency and volume. Recovery was 42 to 94% with a sample volume of 10 mL. Run time was 14 min. LODs were 0.4 to 13 ng/L for most compounds. 

A method which might ensure safety in the recovery system is based on a partial or total replacement of the air within the pipelines by a gas containing no oxygen that does not form explosive mixtures with alcohol-ether, e.g. by nitrogen or carbon dioxide from exhaust gases. This method, however, proved too expensive, and was not carried beyond small scale tests. 

Objective observations of the odor assist in the survey of a situation. Most vapors are characterized by an odor, and the sense of smell is without a peer for revealing the presence of any and all vapors even though it may not furnish individual identification. Inasmuch as minute quantities of a vapor (often less than 1 ppm) give a perceptible odor, it follows that the complete absence of odor can be considered as establishing the absence of any and all foreign vapors. Hence, in an air-recovery system, the complete absence of odor provides acceptable proof of satisfactory purification. This, however, is based on the assumption that carbon monoxide is not present. It is also reported that some war gases have no identifying odor. 

Determination. GC two different SFE systems are compared high temperature method in some cases yields a more exhaustive extraction, but also less clean extracts whereas medium temperature may sometimes cause problems with quantitative recoveries, but it yields very clean extracts The use, advantages and disadvantages of silica sorbents, polymeric, functionalized, carbon-based and mixed available sorbents are discussed Determination. LC—MS best conditions, extraction solvent methanol—acetone (1 1, v/v) temperature 50°C pressure 1500 psi two static cycles recoveries >10%. LOD between 1 to 5 /ag/kg loss of volatile molecules is produce at elevated temperatures Determination GC-MS Best conditions extractant methanol temperature lOffC, pressure 100 atm combined with 15 min static and then 10 min dynamic recovery 111% (RSD 4%) and 106% (RSD 5%) extraction efficiency of the PLE was compared with conventional Soxhlet and bath ultrasonication GC-MS an extraction time of 1 h was employed. 

Carbon dioxide analysers, based on heat capacity, electrical conductivity or partial pressure measurements, but especially on IR light absorption, are therefore used at various points in industrial processes. Carbon monoxide and dioxide are the species most commonly analysed for by the last of the above-mentioned detection techniques, which is also employed in a variety of processes [6], namely (a) control of the hydrogenation of plant oils in order to avoid production of unwanted trans isomers (b) measurement of sugars and CO2 In soft drinks (c) measurement of moisture (d) determination of CO2 In Industrial environments (e) determination of isocyanates In the production of polyurethane (f) determination of methane In argon from nuclear plants (g) control of the efficiency of solvent clean-up and recovery systems. 

Yield of Organic Residue. A high yield of organic residue adversely affects the cost of leaching the pulping base from the solid product as well as the thermal balance of the over-all recovery system. However, it was found in the laboratory (using the methylene blue adsorption test) that if the residue were produced at 750°C. or higher, it showed excellent adsorptive properties, similar to commercial activated carbons. The optimum yield of the residue appears to depend therefore on the size of the accessible market for this material. 

Designing an activated carbon system should be based on pilot data for the particular system and information obtained from the activated carbon producer. The basic engineering and the erection of the system should be done by an experienced engineering company. Solvent recovery systems would also necessitate the specification of condenser duties, distillation tower sizes, holding tanks and piping and valves. Designing of a solvent recovery system requires the following information (Table 22.1.7). 

W.N. Tuttle, Recent developments in vacuum regenerated activated carbon based hydrocarbon vapour recovery systems. Port Technology International, 1, pp. 143-146,1995. 

Incorporation of nonvolatile monomers, such as the sulfonated monomers, can be a problem. The sulfonated monomers must be converted to a soluble form such as the amine salt. Nonvolatile monomers are difficult to recover or purge from the reaction medium. Monomer recovery systems based on carbon adsorption have been developed. However, the usual practice is to maximize the single-pass conversion of these monomers. 

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