Sulfate deposition

Sulfates of sodium are iadustriaUy important materials commonly sold ia three forms (Table 1). In the period from 1970 to 1981, > 1 million metric tons were consumed aimuaHy ia the United States. Siace then, demand has declined. In 1988 consumption dropped to 890,000 t, and ia 1994 to 610,000 t (1,2). Sodium sulfate is used principally (40%) ia the soap (qv) and detergent iadustries. Pulp and paper manufacturers consume 25%, textiles 19%, glass 5%, and miscellaneous iadustries consume 11% (3). About half of all sodium sulfate produced is a synthetic by-product of rayon, dichromate, phenol (qv), or potash (see Chromium compounds Fibers, regenerated cellulosics Potassium compounds). Sodium sulfate made as a by-product is referred to as synthetic. Sodium sulfate made from mirabilite, thenardite, or naturally occurring brine is called natural sodium sulfate. In 1994, about 300,000 t of sodium sulfate were produced as a by-product another 300,000 t were produced from natural sodium sulfate deposits (4). 

RoUs and other relatively simple shapes make use of inert shields and thieves to avoid edge buildup and produce a more even plate thickness. For more compUcated shapes having deeper recesses thicker deposits from cyanide copper baths have been used as an undercoat to the copper sulfate deposit. Acid copper baths operate near 100% efficient over a wide current density range. The cathode efficiency is usuaUy slightly less than the anode efficiency, bringing about a slow increase in copper unless drag-out losses are high. 

Elemental sulfur in the caprock of salt domes w almost certainly produced 1 the anaerobic bacterial reduction of sedimentary sulfate deposits (mainly anhydrite or gypsum, p. 648). The strata are also associated with hydrocarbtms these are consumed as a source of energy by the anaerobic bacteria, which use sulfur instead of O2 as a t drogen acceptor to produce CaC03, H2O and H2S. The H2S... 

The back-pressure increase is to 7.5 inches for a similar thickness of calcium sulfate deposit... 

Calcium sulfate deposition is inhibited by the addition of sufficient soda ash. 

PCA 16 is available as Beldene 161/164 (50/35% w/w solids), Acumer 4161 (50%), and Polysperse (50%). These are low-phosphorus content materials that have found application in boiler FW formulations because of excellent sludge conditioning and particulate dispersion properties. The number 16 represents a 16 1 w/w ratio of acrylic acid and sodium hypophosphite, giving PCA 16 a MW range of 3,300 to 3,900. PCA 16 is particularly effective for the control of calcium carbonate and sulfate deposition. It is usually incorporated with other polymers in formulations and is approved for use under U.S. CFR 21, 173.310. 

Hirabayashi (1907) defined Kuroko as an ore which is a fine compact mixture of sphalerite, galena, and barite. This definition can be applied to black ore , but not to yellow ore or siliceous ore because these minerals are not abundant in these ores. Kinoshita (1944) defined Kuroko deposit as a deposit genetically related to the Tertiary volcanic rocks, consisting of a combination of Kuroko (black ore), Oko (yellow ore), Keiko (siliceous ore), and/or Sekkoko (gypsum ore) (Matsukuma and Horikoshi, 1970). The deposit is generally defined as a strata-bound polymetallic sulfide-sulfate deposit genetically related to Miocene bimodal (felsic-basaltic) volcanism (T. Sato, 1974). 

Kaolin minerals (kaolinite, dickite, nacrite), pyrophyllite and mica-rich mica/smec-tite mixed layer mineral occur as envelopes around barite-sulfide ore bodies in the footwall alteration zones of the Minamishiraoi and Inarizawa deposits, northern part of Japan (south Hokkaido) (Marumo, 1989). Marumo (1989) considered from the phase relation in Al203-Si02-H20 system that the hydrothermal alteration minerals in these deposits formed at relatively lower temperature and farther from the heat source than larger sulfide-sulfate deposits in the Hokuroku district. 

Fe) ratios of magnesite and dolomite occurring in hanging wallrocks are useful in the exploration for concealed volcanogenic massive sulfide-sulfate deposits. 

We saw in section 2.3.2 that present-day hot spring venting and sulfide-sulfate depositions have been discovered in back-arc basins in the Western Pacific. These intense hydrothermal activities indicate that seawater-volcanic rock interactions are taking place at these environments. 

Kuroko deposits, which are strata-bound massive sulfide-sulfate deposits, are well-known because (1) many studies have been done and many papers (more than 1,(K)0) have been published since the work by Ohashi (1919), (2) original ore textures are preserved due to the absence of metamorphism, and (3) geological and physicochemical environments of ore deposition were well-elucidated. Summaries of previous studies on Kuroko deposits have been published in the 1970s and early 1980s (Ishihara, 1974 Ohmoto and Skinner, 1983). However, no summary written in English after the early 1980s has been published, although considerable works on ore deposits have been carried out. 

Scale deposits are converted to dispersed particles which can be circulated out of the wellbore. A chelating agent such as ethylenediamine tetraacetic acid can aid in dissolving calcium sulfate deposits. Hydrochloric acid following the basic treatment can also be used to dissolve calcium sulfate (167). 

In theory, significant reduction in SO2 emissions should, over a long-term period and large areas, produce detectable reductions in the amount of wet sulfate deposition. 

Acid rain monitoring data in North America have been gathered by Environment Canada and stored in the National Atmospheric Chemistry (NatChem) Database, details of which can be found at www.airquality.tor.ec.gc.ca/natchem. Analysis of the deposition chemistry data has confirmed that wet sulfate deposition did indeed decline in concert with the decline in SO2 emissions in both eastern Canada and the... 

It is roughly estimated that there are more than 1,200,000 water bodies in eastern North America that are currently affected by acid deposition. A subset of these lakes has been sampled since early 1980s in order to monitor the changes in lake water chemistry induced by the declining sulfur dioxide emissions and wet sulfate deposition... 

Figure 10. Regional critical loads in eastern Canada (from RMCC, 1990). Different shaded areas show the critical loads of wet sulfate deposition (kg/ha/yr) that can be tolerated by lakes in those areas.

As applied to aquatic ecosystems in eastern Canada, critical load is defined as the amount of wet sulfate deposition that must not be exceeded in order to protect at least 95% of lakes in a region from acidifying to a pH level of less than 6.0 (Ro et al., 1997). 

After calculation and mapping of critical loads, the next step is to identify those areas where the critical loads were/are exceeded, i.e., where the wet deposition loading of sulfate exceeds the critical loads. In these areas of exceedance, lakes will continue to have pH values lower than 6.0 until such time that wet sulfate deposition decreases below the critical loads. 

The critical load exceedance pattern is shown across eastern Canada for the years 1980 and 1995. The differences in the exceedance patterns of 1980 and 1995 indicate that the area of exceedance, and the amount of exceedance in most areas, declined considerably in 15 years. By way of comparison, the 1995 area of exceedance is 61% lower than that in 1980, a clear illustration that the decline in annual sulfate deposition from 1980 to 1995 resulted in a large reduction to the number of lakes vulnerable to acid rain. In spite of the decline, there still exist in 1995 large areas in eastern Canada where the critical loads are exceeded. In 1995, this area was approximately 510,000 km2 and encompassed roughly 60,000 lakes. 

Figure 12 illustrates the year-to-year change in the total amount of wet sulfate deposition (non-sea-salt) that exceeded the critical loads in eastern Canada. 

Hundreds of thousands of square kilometers in eastern Canada, encompassing tens of thousands of lakes, will continue to receive wet sulfate deposition above the critical loads for aquatic ecosystems, even after the existing Canadian and USA SO2 emission control programs are fully implemented in the year 2010 ... 

Further SO2 emission reductions, estimated to be of the order of 75% beyond current reduction commitments, are required in both Canada and the United States to protect lakes in eastern Canada from sulfate deposition in excess of the critical loads. 

Jeffries, D. S., Lam, D. C. L. (1993). Assessment of the effect of acidic deposition on Canadian lakes determination of critical loads for sulfate deposition. Water Science Technology, 28, 183-187. 

Efforts to reduce acid deposition have had mixed results thus far. For example, measurements at five locations in Nova Scotia, New Brunswick, Newfoundland, and Labrador by Canadian researchers found that sulfate deposition dropped between 27 and 50 percent between 1980 and 1995. During the same time, however, there was a significant reduction in acid deposition at only one of the five monitoring sites. 

In the northeastern United States, sulfate deposition has also been reduced substantially since the 1980s. The average annual wet deposition of sulfates dropped in three environmentally sensitive areas (the Adirondacks, Mid-Appalachian, and Southern Blue Ridge mountains) by 26, 23, and 9 percent, respectively, from the period 1983-94 to the period 1995-98. That trend is also reflected in data collected from monitoring stations throughout the eastern United States, which show a 26 percent decrease in sulfate deposition between the two monitoring periods, 1983-94 and 1995-98. 

Similar trends were detected in a more limited study conducted by the Adirondack Lakes Survey Commission during the 1990s. The commission found a reduction of 92 percent in sulfate deposition in a selected sample of lakes in the Adirondack Mountains between 1992 and 1999, but an increase of 48 percent in nitrogen deposition in the same lakes. 

A major factor involved in determining the relationship between S02 emissions and sulfate deposition is the chemistry. As discussed above, the oxidation of S02 by OH in the gas phase generates H02 and hence OH in the presence of NO. The regeneration of OH means that the oxidation will not be oxidant limited in the gas phase, and hence a reduction in S02 might be expected to be accompanied by a corresponding decrease in the formation of H2S04. 

There are a number of held measurements that have addressed this relationship between the mandated reductions in S02 emissions in the United States and the subsequent changes in sulfate deposition downwind. For example, one analysis of the trends in the atmospheric concentrations of sulfate in the northeastern United States suggests that from 1977 to 1989, the sulfate concentration decreased by about 22-28% during which the emissions of S02 were estimated to have decreased by 25% (Shreffler and Barnes, 1996). 

Fay. J. A., Golomb, D. Kumar, S. 1985. Source apportionment of wet sulfate deposition in Eastern North America. Atmospheric Environment, 19, 1773-1782. 

In crystallizing salts from solution, it frequently happens that it is possible to obtain more than one hydrate. In all such cases, a perfectly definite temperature can be found above which the one hydrate will deposit, and below which the other one with a larger number of molecules of water of hydration appears. Thus, above 38°, zinc sulfate deposits crystals of the composition ZnS04 6H20, while crystals deposited below that temperature have the formula ZnS04-7H20. This is also called a transition point. 

Lake and Mountain Lake evaporative losses exceed precipitation in the west (Cedar and Mountain), but represent only about 60% of the precipitation falling in northern Wisconsin (Little Rock). Precipitation chemistry varies along the same gradient, with pH increasing from 4.6 in northern Wisconsin to 4.8 in northeastern Minnesota and 5.2 in western Minnesota. The corresponding values for wet sulfate deposition decrease from 15 kg/ha per... 

In distillation the water closest to the heating surface is hottest and it is there that calcium sulfate is least soluble. Thus, calcium sulfate deposits, forming an adhering film that increases the thermal resistance and decreases the heat flux. The scale is continuously deposited until the tubes are cleaned or become plugged. For scale deposition the local concentration must be at least saturated in calcium sulfate. At 100° C. this occurs in concentrated sea water at a concentration 3.1 times that of ordinary sea water. A plant has been successfully operated continuously without calcium sulfate deposition by taking only part of the available water from the sea water, so that the liquid in the evaporator is never more than 1.8 times the concentration of sea water and the wall temperature is below about 250° F. ( ). This imposes technical and economic limitations on distillation plants. Similar considerations hold for plants distilling brackish water containing calcium sulfate. 

Figure 8. Effect of velocity on calcium sulfate deposition...

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