Acidic deposition control standards

Polymaleic acid (PMA). The use of chemicals based on PMA and some derivatives has become standard practice for very brackish waters and seawater distillation processes around the world, where the TDS may reach 50,000 ppm TDS, or where total hardness levels exceed 500 to 1,000 ppm CaC03. Its use in RO systems is growing. However, PMA has limited dispersing properties and may need to be formulated with a dispersant chemical to provide satisfactory performance with some RO designs. It is claimed that PMA is also a successful silica deposit control agent and therefore may be incorporated into formulations where this is a problem. 

Earlier the standard industrial approach to prevention of calcium carbonate scaling by addition of sulfuric acid was described. Objectives were to reduce bicarbonate alkalinity, convert calcium carbonate to calcium sulfate, and regulate sulfate concentration by bleedoff. Corrosion inhibitors were added to protect system metals. A new approach to industrial cooling system treatment does not require addition of sulfuric acid. It involves application of phosphonate seques-trants, dispersants and special corrosion inhibitors, and provides deposit control equal to that obtainable when using sulfuric acid. Availability of phosphonate sequestrants makes possible combination scale control and corrosion inhibitors that can be used without the necessity of reducing cooling water alkalinity by acid feed. 

Selection of pollution control methods is generally based on the need to control ambient air quaUty in order to achieve compliance with standards for critetia pollutants, or, in the case of nonregulated contaminants, to protect human health and vegetation. There are three elements to a pollution problem a source, a receptor affected by the pollutants, and the transport of pollutants from source to receptor. Modification or elimination of any one of these elements can change the nature of a pollution problem. For instance, tall stacks which disperse effluent modify the transport of pollutants and can thus reduce nearby SO2 deposition from sulfur-containing fossil fuel combustion. Although better dispersion aloft can solve a local problem, if done from numerous sources it can unfortunately cause a regional one, such as the acid rain now evident in the northeastern United States and Canada (see Atmospheric models). References 3—15 discuss atmospheric dilution as a control measure. The better approach, however, is to control emissions at the source. 

The influence of a surface on an adsorbed species is well-accepted. The TA/Ni(l 10) system demonstrates how much the molecule can influence the behaviour of the surface. How far can an adsorbate like tartaric acid induce such effects Work by Switzer and co-workers on the electrodeposition of CuO films in the presence of tartaric acid showed that chirality could be induced in a normally achiral inorganic material [25]. In a standard electrochemical cell, a Au(OOl) crystal is placed in a solution containing Cu(II) ions, tartrate ions and NaOH. At a certain potential, CuO will deposit, as a thin-film on the Au Surface. Characterization by diffraction revealed that the deposited CuO film has no mirror or inversion elements, i.e. it is chiral. The chirality of the film is controlled by the chirality of the tartrate ions in the solution (/ ,/ )-tartrate yielding a chiral CuO(-lll) fihn while presence of (S,S )-tartrate produces the mirror Cu(l-l-l) enantiomorph. Switzer et al, by catalyzing the oxidation of tartaric acid, demonstrate that not only the bulk, but also the surface of the CuO film is chiral the CuO electrode surface grown in the presence of (/ ,/ )-tartrate is more effective at oxidizing (/ ,/ )-TA, while the surface deposited in the presence of (S,S )-tartrate is more effective at oxidizing (S,S )-TA. 

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