Chemical recovery indicators

The gradient elution scheme is a scaled-up procedure originally described by Middleton (10) that has been extended to handle highly refractive materials such as coal liquids. This separation technique uses Alcoa F-20 alumina activated to a 5.5 wt % moisture level as the stationary phase. Details of this separation procedure are given elsewhere (2). This method separates SRC into 13 fractions and these fractions are listed in Table II along with some key chemical and physical descriptions of the cuts. The structural types indicated in Table II for Fractions 1-6 have been assigned based upon model compound studies and low resolution mass spectrometry (MS) (2), whereas the chemical types indicated for Fractions 7-13 are based upon IR observations and additional model compound studies. Recoveries in these separations are normally greater than 90%. 

The ACP system combines a sulfur dioxide scrubbing system based on spray dryer technology with a regeneration system based on a unique reduction step coupled to chemical recovery and Claus technologies. This combination results in an efficient and reliable process for application to sulfur dioxide pollution problems. The remainder of this paper discusses the details of the process and typical installation characteristics and also presents process economics which indicate that the ACP system is economically feasible a well as technically sound. 

An analysis of the scientific literature suggests that five thresholds can serve as indicators of chemical recovery (see Table 3.3). If chemical conditions in an ecosystem are above these thresholds, it is unlikely that the ecosystem has been substantially impaired by acidic deposition. Conversely, if chemical conditions are below these thresholds, there is a high likelihood that the ecosystem is vulnerable to acidic deposition. 

Table 3.3. Indicators of chemical recovery from acidic deposition...

According to the results of the computer model, the 1990 CAAA will have a positive effect on stream concentrations of sulfate at Hubbard Brook, but will not facilitate appreciable progress toward chemical recovery of key indicators of acidification stress, such as pH or ANC (see Figure 3.10). With... 

S deposition (Driscoll et al. 1995 Dillon et al. 1997 Dillon and Evans 2001 Lofgren et al. 2001). Furthermore, other measures of chemical recovery, particularly increases in lake pH and acid neutralizing capacity (ANC), have provided conflicting evidence. In a few cases (Webster and Brezonik 1995 Stoddard et al. 1998), they have indicated limited evidence of chemical recovery, while in many others (Clair et al. 1995 Houle et al. 1996 Dillon et al. 1997), there has been little or no change in these parameters despite declining S deposition. 

The values in parentheses indicate the maximum boundary condition for the quantity under consideration based upon the average historical chemical recovery of 78.42+5.38 percent. Propagation of the listed uncertainties in accordance with established statistical methods yields a relative systematic standard deviation (0 t/R) = 0.037. The frequency distributions for the chemical recoveries exhibited by two chemists are portrayed in Figure 6. The main point to be remembered from these two distributions is that no two individuals will have the same distribution of results. Establishing an a-priori LLD based upon the results of a single individual may not be applicable to other individuals. 

Figure 20-1 Simplified overview of a typical kraft process showing chemical pulping, oxygen delignification, pulp bleaching, and chemical recovery systems. Important mixing operations are indicated by the NAMF mixing icon.

Recovery studies were also conducted with woolen cloths, remaining bath liquor, and the distillate when permethrin was applied in a distilling apparatus (Bry et al., 1976). The bath concentration was 0.005% permethrin (wt/wt), and the applications were made at pH 4.5 and 100°C for 1 hour. Chemical analyses indicated that ca. 93% of the Al present in a bath was recovered. About 97% of the Al recovered was present on the cloth and the percent exhaust was ca. 90%. In additional studies conducted with no wool present in the distilling flask, ca. 97.5% of the Al available was recovered. About 99.5% of the Al recovered was still present in the bath liquor and ca. 0.5% was present in the distillate, indicating almost no loss due to steam distillation. 

FIG. 19-68 The schematic diagram showing the relationship between the physical and chemical properties of fine particles and their behavior in flotation. (G) and (R) refer to whether the phenomena affects grade and/or recovery. The arrows indicate the various factors contributing to a particular phenomena observed in flotation of fine particles (Fiierstenaii, 1980). 

Observed recovery in raptors has been slow owing to their lifecycle this is also an indication of the environmental movement and dispersal of endocrine disrupting chemicals from areas of intense agriculture to the aquatic environmental... 

Ihe implementation of the Resource Conservation and Recovery Act (RCRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (Superfund) has underscored a number of the weaknesses in our capabilities to measure the chemical characteristics of wastes. We are now being called upon to identify and quantify with unprecedented sensitivity hundreds of chemicals found in many types of materials within waste sites, near discharges of hazardous contaminants, and in the surrounding environments. Extrapolations from a limited number of measurements must indicate the general environmental conditions near waste sites. The measurements have to be made faster and cheaper than ever before, with the precision and bias of each measurement fully documented. Thus, the technical challenges facing the monitoring community are substantial. 

The 50.31 MHz 13C NMR spectra of the chlorinated alkanes were recorded on a Varian XL-200 NMR spectrometer. The temperature for all measurements was 50 ° C. It was necessary to record 10 scans at each sampling point as the reduction proceeded. A delay of 30 s was employed between each scan. In order to verify the quantitative nature of the NMR data, carbon-13 Tj data were recorded for all materials using the standard 1800 - r -90 ° inversion-recovery sequence. Relaxation data were obtained on (n-Bu)3SnH, (n-Bu)3SnCl, DCP, TCH, pentane, and heptane under the same solvent and temperature conditions used in the reduction experiments. In addition, relaxation measurements were carried out on partially reduced (70%) samples of DCP and TCH in order to obtain T data on 2-chloropentane, 2,4-dichloroheptane, 2,6-dichloroheptane, 4-chloroheptane, and 2-chloroheptane. The results of these measurements are presented in Table II. In the NMR analysis of the chloroalkane reductions, we measured the intensity of carbon nuclei with T values such that a delay time of 30 s represents at least 3 Tj. The only exception to this is heptane where the shortest T[ is 12.3 s (delay = 2.5 ). However, the error generated would be less than 10%, and, in addition, heptane concentration can also be obtained by product difference measurements in the TCH reduction. Measurements of the nuclear Overhauser enhancement (NOE) for carbon nuclei in the model compounds indicate uniform and full enhancements for those nuclei used in the quantitative measurements. Table II also contains the chemical... 

A) Recorded with 256 increments, 4 transients, and a recovery delay of 1 s. (B) Recorded with 256 increments, 8 transients, and a recovery delay of 0.2 s. The flip angle a was set to 90°. The typical F2 rows (at the 13C chemical shift of C-18, indicated by the horizontal arrows and depicted on the top of the spectra) show the signal enhancements. 

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