Smelters pollution control

The absorption of sulfur dioxide in alkaline (even weakly alkaline) aqueous solutions affords sulfites, bisulfites, and metabisulfites. The chemistry of the interaction of sulfur dioxide with alkaline substances, either in solution, slurry, or soHd form, is also of great technological importance in connection with air pollution control and sulfur recovery (25,227,235—241). Even weak bases such as 2inc oxide absorb sulfur dioxide. A slurry of 2inc oxide in a smelter can be used to remove sulfur dioxide and the resultant product can be recycled to the roaster (242). 

Double-Absorption Plants. In the United States, newer sulfuric acid plants ate requited to limit SO2 stack emissions to 2 kg of SO2 per metric ton of 100% acid produced (4 Ib /short ton Ib = pounds mass). This is equivalent to a sulfur dioxide conversion efficiency of 99.7%. Acid plants used as pollution control devices, for example those associated with smelters, have different regulations. This high conversion efficiency is not economically achievable by single absorption plants using available catalysts, but it can be attained in double absorption plants when the catalyst is not seriously degraded. 

The ICS/SCS control system has been used for control of emissions from nonferrous smelters. Discuss at least one such active system in terms of its success or failure. Discuss the reasons why the interstate air pollution control region concept has failed in the United States. 

Barbaris and Betterton, 1996) are also slightly above baseline concentrations, probably because of inputs from smelters, power plants, and soil dust. In most industrialized countries, sources of airborne arsenic are limited as a result of air-pollution control measures. Unless significantly contaminated, atmospheric precipitation contributes little arsenic to surface waters. 

In April of 1970 a source test of the 600-foot stack was carried out by the Bay Area Air Pollution Control District (I). The results which were given in Ibs/day are presented in Table II normalized to As to make meaningful comparisons with the diurnal data of this experiment. The qualitative agreement between stack and ambient air data further implicates the smelter as the source of the episodes on these three days. 

Pollution control and waste disposal now represent large operating and capital cost items for most lead smelters and refineries, and will increase in importance as more stringent environmental legislation is applied. In the USA, for instance, necessary environmental expenditures have probably raised operating costs in the secondary lead industry on average by more than a quarter in recent years, and capital costs by at least as much. 

The proper management of dust collection follows a basic rule of any pollution control technology, namely that it is best to deal with a dust suspension as near to its source as possible, rather than after it has been diluted with gas from other sources. Thus, fume from a smelter should be treated in hoods immediately over the smelter, rather than in the general exhaust from the smelter building. 

The ban on the use of leaded gasoline in the 1970s produced one of the most successful episodes in the search for the control of air pollutants. As already noted, the concentration of lead in the air dropped dramatically and to very low levels within a matter of years after the ban was put into place. Currently, efforts to control lead emissions focus on improving the methods used to remove lead from air and water wastes of smelters, metal processing plants, and other such plants. The most common systems currently used are variations of traditional waste control techniques in which physical devices (such as baghouses) or chemical systems (such as precipitation reactions) are used to extract particles of lead from wastes. 

Control and reduction of ambient air pollutants in the United States has met with varying degrees of success. Unleaded gasoline now accounts for 99% of all gasoline sales. This change has virtually eliminated mobile sources as emitters of lead and reduced ambient lead levels by more than 75%. Likewise, stationary point sources of lead emissions, primarily industrial smelters, have dropped by more than 90% over the past three decades, although significant... 

Reasons for differences in estimates of industry performance are varied. High estimates of emissions are typically related to the nse of estimates of emission factors for lead smelters that were derived prior to the development of modern technologies for the control of air and water pollution. Emission estimates will also differ with respect to the fate that is presumed for lead contained in different waste streams. For example, lead within slags or other process wastes is nsually managed so as to prohibit undesirable levels of environmental contamination. In the absence of waste-management practices, high levels of environmental dispersion might resnlt. 

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