Wet precipitation

Rotary kilns and, to a lesser extent, Fluo-SoHds kilns are used to calcine a wet precipitated calcium carbonate filter cake in the kraft or sulfate paper-pulp process (15). Lime is regenerated for use as a causticization reagent in recovering caustic soda for pulp digestion. Losses in lime recovery are replaced by purchased lime (see Paper Pulp). 

Figure 13. Continuous-spray, parallel-plate type of wet precipitator.

Note. If the wet precipitate is heated directly, caking occurs which renders the complete oxidation of the carbonaceous matter very slow. If alkali metals were originally present, the ignited oxide must be washed with hot water, filtered, and re-ignited to constant weight. 

The tendency of acrylonitrile to partition between air and water is described by Henry s law constant (H). The value of H for acrylonitrile has not been determined experimentally, but has been calculated to be 8.8 x 10 5 atm-m3/mole (Mabey et al. 1982). This value indicates that acrylonitrile will occur in both air and water, tending to transfer between air and water phases only slowly. Cupitt (1980) estimated the half-time of acrylonitrile clearance from air in wet precipitation to be greater than 10 months. 

Amylose complexes (wet precipitates) were prepared with fluoro-benzene, 1,1,2,2-tetrachloroethane, 1,1,2,2-tetrabromoethane, bromo-form, and ferf-butyl alcohol. The conformation and packing of the amylose chains complexed with halogen-substituted hydrocarbons are the same as found in the complex with tert-butyl alcohol, namely,... 

PCB-153 at temperature 25 °C can be found in (Shatalov et al 2001). Modeling was performed at soil organic carbon content foe = 5% typical of usual chernozem. The wet precipitation flux was assumed equal to Jw = 10 cm/yr. 

Mirex has been detected in wet precipitation over rural areas at concentrations of less than 1 ng/L (ppt) (EPA 1981b). Rainfall samples collected at several sites in 1985-1986 as part of the Great Lakes Organics Rain Sampling Network contained from >0.2 to <0.5 ng/L (ppt) of mirex. Mirex was not detected consistently at many stations throughout the sampling period therefore, quantitative results for mirex were not presented (Strachan 1990). Air samples taken over southern Ontario in 1988 showed mirex in 5 of 143 samples, at an annual mean concentration of 0.35 pg/sol m (range, 0.1-22 pg/m ) with all of the positive samples detected in polluted environments (Hoff et al. 1992). 

Wet electrostatic precipitators (WESP) are used for removal of liquid contaminants such as sulfuric acid mist, aerosols, and particulate matter. The acid mist and aerosols are typically formed in a WGS by condensation of SO3. Unlike dry precipitators, wet precipitators do not require rapping to remove the dust. The collected mist and particulate matter form a liquid film that runs down a vertical collecting plate. In some cases, a continuous spray of liquid is used to prevent solids deposition on the collecting plates. 

Table 10 Average concentrations (pg/m3) of organochlorine pesticides in air samples and in wet precipitation (ng/L) in Big Creek watershed and at closest IADN sites (Sturgeon Point and Point Petre)...

The major objective of this chapter is to examine and synthesize the published literature with respect to sources and production of terrestrially derived DOC, its relationship with dissolved organic nitrogen (DON), and the mechanistic controls on their export from terrestrial ecosystems to surface waters. With the exception of wet precipitation (which is ranked by continental landmass), we have classified data for throughfall and soil solution under biome type. Where possible, we have shown mean and standard deviations of some biomes to illustrate the amount of variance within and between biomes. Relationships between DOC and DON are illustrated using only those studies that report both DOC and DON concentration. Because most research on DOC and DON has been accomplished in relatively undisturbed areas, particularly forests, this chapter concentrates on the aspect of diffuse-source allochthonous inputs to surface waters and not point-source inputs from urban and agricultural areas. Recent work by Westerhoff and Anning (2000), however, indicates that more research on effluent or point-source DOC as a contributor to riverine allochthonous inputs may be... 

FIGURE I Molecular weight distribution (thousands of daltons) of dissolved organic carbon in wet precipitation, throughfall, A and B horizon soil solution, and stream water at Hubbard Brook, New Hampshire. Source Adapted from McDowell (1982) and Cole et al. (1984). 

FIGURE 2 Dissolved organic matter (a) concentration (mgL-1) and (b) flux (kgha 1yr 1) in wet precipitation over continental landmasses. Source of data Mean values and standard deviations from data in Table I. 

From the data listed in Table 13.5 it can be seen that the Sauter mean diameter of the dried product, di2, is larger than that of the wet precipitate obtained under the same reaction conditions by about 10%, or by 0.15 pm. An obvious fact is that no matter whether at the bottom of the dryer or in the cyclone or in the bag filter, the recovery of the finer particles must be lower than that of the larger particles. These differences between the recoveries of particles of different sizes must lead to an increased mean diameter of the product. If this fact is taken into account, the sizes of the particles can be considered to be stable enough during the final treatment of the precipitate, without coalescence of particles occurring. 

The results of the spray drying experiment of the wet precipitate show that the particle sizes of particles in the product produced in the present investigation are stable, and no coalescence of particles during the final treatment of the reacted wet-precipitate is observed. 

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