Acid-neutralizing capacity surface waters

Lien, L. Raddum, G. G. Fjellheim, A. Henriksen, A. A Critical Limit for Acid Neutralizing Capacity in Norwegian Surface Waters, Based on New Analyses of Fish and Invertebrate Responses, Sci. Tot. Environ. 

Sullivan T. J., Driscoll C. T., Gherini S. A., Munson R. K., Cook R. B., Charles D. F., and Yatsko C. P. (1989) Influence of aqueous aluminum and organic acids on measurement of acid neutralizing capacity in surface waters. Nature 338, 408-410. 

Alkalinity is a measure of the acid-neutralizing capacity of the solution. It is measured by titrating the solution to pH 8.3 to determine phenol-phthalein alkalinity and to a pH near 4.5 (see Greenberg et al. (1992) for exact values) to determine total alkalinity. Note that most values reported as alkalinity are total alkalinity. Alkalinity is also reported as mg CaCOs/L equivalent, which can be interpreted as the equivalent amount of calcite needed to consume the amount of acid titrated. Because bicarbonate is usually the predominate anion in most non-marine surface waters and shallow groundwater, total alkalinity values are sometimes interpreted as a reflection of the bicarbonate concentration of the solution. This interpretation should be applied with caution because several other kinds of anions, including hydroxide, organic acids, phosphates, silicates, carbonate, and borate, contribute to the measured alkalinity. 

Ecologically, accidental releases of solution forms of hydrochloric acid may adversely affect aquatic life by including a transient lowering of the pH (i.e., increasing the acidity) of surface waters. Releases of hydrochloric acid to surface waters and soils will be neutralized to an extent due to the buffering capacities of both systems. The extent of these reactions will depend on the characteristics of the specific environment. 

The application of ion exchangers to dextrose process liquors involved considerable experimental work because of a number of factors which do not enter into their application to water purification. The accumulation of fats and proteins on the resin surfaces must be guarded against by proper clarification of the liquors to be treated. Such accumulation may result from precipitation as the neutralization progresses, and may soon destroy the effective acid-removing capacity of the anion exchange resin. This difficulty can effectively be eliminated by prior precipitation of thfe refinery residue from the acid liquor by bentonite, a colloidal clay of opposite electrical charge to the colloids,21 followed by filtration. 

Acid rain primarily affects sensitive bodies of water, that is, those that rest atop soil with a limited ability to neutralize acidic compounds (called buffering capacity ). Many lakes and streams examined in a National Surface Water Survey (NSWS) suffer from chronic acidity, a condition m which water lias a constant low (acidic) pH level. The survey investigated tlie effects of acidic deposition in over 1,000 lakes larger than 10 acres and in thousands of miles of streams believed to be sensitive to acidification. Of the lakes and streams surveyed in the NSWS, arid rain has been determined to cause acidity in 75 percent of the acidic lakes and about 50 percent of tlie acidic streams. Several regions in the U.S. were identified as containing many of the surface waters sensitive to acidification. They include, but are not limited to, the Adirondacks. the mid-Appalachian highlands, the upper Midwest, and the high elevation West. 

Acid atmospheric waters can reduce the pH of surface waters with low neutralization capacity. For example, in Scandinavian lakes and rivers, acidification caused by acid atmospheric precipitations results in the killing of fish species, trout and salmon. Apart from the reduced abundance of fish, acid atmospheric waters also unfavourably affect the soil composition (soil becomes poor in cations, replaced by hydrogen ions), as well as the growth of plants. They also cause significant corrosion of concrete, mortar, iron and other metals. Because of this property, low mineralization and irregularity of precipitation, atmospheric waters are very seldom used directly for water supplies. In some cases atmospheric waters can be an important source of nitrogen compounds for agriculture. 

The formation of the M-PILCs involved the use of a suspension of <2pm STx-1 montmorillonite (Source Clay Minerals Repository, University of Missouri), which had been acid washed (2M HCl), neutralized and exchanged three times with 4M NaCl. This clay mineral has a cation exchange capacity of approximately 84 meq/l(X)g, and a surface area of about 83.3 m2/g (Van Olphen and Fripiat 1979). The hydrolyzed metal solutions were added dropwise to vigorously stirred suspensions (ca. 1% w/w) of the Na-STx-1 (or vice versa), to solution loadings of ca. 10 meq metal/g STx-1. The suspensions were then washed with distilled water by centrifugation until testing with silver nitrate revealed the supernatant fluid to be negative for chloride ions. 

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