Polluted gypsum

K. Schneider, Mopping-up Pollution , Gypsum, Lime and Building Products, April, 1996, 23. 

By analogy, many waste industrial acids are neutralized by limestone, but in the case of sulphuric acid, this results in large accumulations of polluted gypsum. Geochemical engineering concepts can circumvent this problem in two different ways ... 

Common pollutants in a titanium dioxide plant include heavy metals, titanium dioxide, sulfur trioxide, sulfur dioxide, sodium sulfate, sulfuric acid, and unreacted iron. Most of the metals are removed by alkaline precipitation as metallic hydroxides, carbonates, and sulfides. The resulting solution is subjected to flotation, settling, filtration, and centrifugation to treat the wastewater to acceptable standards. In the sulfate process, the wastewater is sent to the treatment pond, where most of the heavy metals are precipitated. The precipitate is washed and filtered to produce pure gypsum crystals. All other streams of wastewater are treated in similar ponds with calcium sulfate before being neutralized with calcium carbonate in a reactor. The effluent from the reactor is sent to clarifiers and the solid in the underflow is filtered and concentrated. The clarifier overflow is mixed with other process wastewaters and is then neutralized before discharge. 

Ongwandee, M. and Morrison, G.C. (2008) Influence of ammonia and carbon dioxide on the sorption of a basic organic pollutant to carpet and latex-painted gypsum board. Environmental Science and Technology, 42 (15), 5415-20. 

World sulfur reserves. The earth s crust contains about 0.6% S, where it occurs as elemental S (brimstone) in deposits associated with gypsum and calcite combined S in metal sulfide ores and mineral sulfates as a contaminant in natural gas and crude oils as pyritic and organic compounds in coal and as organic compounds in tar sands (Tisdale and Nelson, 1966). The elemental form commonly occurs near active or extinct volcanoes, or in association with hot mineral spings. Estimates by Holser and Kaplan (1966) of the terrestrial reservoirs of S suggest that about 50% of crustal S is present in relatively mobile reservoirs such as sea water, evaporites, and sediments. The chief deposits of S in the form of brimstone and pyrites are in Western European countries, particularly in France, Spain, Poland, Japan, Russia, U.S.A., Canada, and Mexico. World production of S in the form of brimstone and pyrites was approximately 41 Tg in 1973 other sources accounted for about 8 Tg, making a total of 49 Tg (Anon, 1973). Byproduct S from sour-gas, fossil fuel combustion, and other sources now accounts for over 50% of S used by western countries, as shown in Fig. 9.1. This percentage may increase as pollution abatement measures increase the removal of SO2 from fossil fuel, particularly in the U.S.A. Atmospheric S, returned to the earth in rainwater, is also a very important source of S for plants. 

Figures 1,2, and 3 are provided to illustrate one protocol often used to evaluate sink materials [20,32,42-47] however, other methods are also used. For example, Krebs and Guo [48] reported on a unique method involving two test chambers in series. The first chamber is injected with a known concentration of a pollutant (in this case, ethylbenzene). The outlet from the first chamber provides a simple first-order decay that is injected into the inlet of the second chamber that contains the sink material (gypsum board). Thus, this method exposes the sink test material to a changing concentration typical of many wet VOC sources. The sink adsorption rate and desorption rate results are comparable to one-chamber tests and are achieved in a much shorter experimental time. Kjaer et al. [31] reported on using a CLIMPAC chamber and sensory evaluations coupled with gas chromatography retention times to evaluate desorption rates. Finally, Funaki et al. [49] used AD PAG chambers and exposed sink materials to known concentrations of formaldehyde and toluene and then desorbed the sinks using clean air. They reported adsorption rates as a percentage of concentration differences.

For most pollutants, fleecy materials (e.g., carpet) are stronger sinks (i.e., higher k ) than smooth materials (e.g., vinyl and PVC flooring, gypsum board)... 

The main characteristic features of these ecosystems are related to the continental climate and low precipitation, precipitationipotential (and actual) evapotranspiration (PTE). P PE ranges between 0.6-0.3. In accordance with the given climatic conditions, the soils of steppe ecosystems (Chernozems, Kastanozems, Solonetzes) are characterized by the presence of a few buffer layers, such as humus, carbonate, and gypsum that makes them insensitive to actual and potential loads of pollutants. 

Another advantage of SCR on FGD is that mercury remains on the SCR catalyst as Hg +. Gypsum is thus not contaminated with mercury. The Hg + may be easily removed by washing the catalyst with water. When placing the SCR unit downstream a FGD unit, compounds such as N-S compounds and Hg2Cl2 may pollute the water of the FGD [140]. 

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