Acid consumption alkalinity

Under certain conditions, there is a stoichiometric relationship between the p and m values of a water and the concentration of hydrogen carbonate ions, carbonate ions and hydroxyl ions. For this reason, the p and m values may be used to determine the concentration of these ions indirectly and also to calculate the so-called carbonate hardness. 

Note also the remarks in Chapter 1 on local investigations, which are repeated in part here.  

The acid consumption (alkalinity) of a water is defined as the quantity in mmol/1 of a strong acid which is consumed during titration to achieve certain pH values or until certain indicators change colour. If titration is carried out electrometrically up to pH 8.3 or if phenolphthalein is used 

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In most ores, sufficient Fe is already present. For some ores, it is necessary to add metallic iron. In practice, the oxidation potential of the solution can be monitored and controlled using the Fe /Fe ratio. Very high leaching efficiencies with H2SO ate common, eg, 95—98% dissolution yield of uranium (39). If acid consumption exceeds 68 kg/1 of ore treated, alkaline leaching is preferred. The comparative costs of acid, sodium hydroxide, and sodium carbonate differ widely in different areas and are the determining factor. 

The authors assumed that the precipitation of these metal sulfides was controlled by the hydrolysis reaction of TAA promoted by proton in the acidic conditions. However, the hydrolysis of TAA observed in acidic and alkaline ranges is a much slower process than observed in the precipitation of these metal sulfides (7-12), and it may not be accelerated by consumption of S2 ions because of its irreversible nature. In addition, the reaction virtually finished with a great part of the starting metal ions and TAA left unreacted. Also, it has already been verified that the probability of direct reaction of TAA with metal ions is zero or at least negligible from its strong dependence of pH in reactivity (7). Thus, it seems reasonable to consider that the main path is the release of S2 ions from TAA according to the following reaction scheme with the production of acetonitrile (7,13) as found in the reaction of TAA with Cd2+ ions in an alkaline media ... 

Acid atmospheric deposition causes acidification of waters and soils if the neutralization of the acids by weathering is too slow. Biologically mediated redox processes are important in affecting the H balance. Among the redox processes that have a major impact on H" production and consumption are the synthesis and mineralization of biomass. Any uncoupling of linkages between photosynthesis and respiration affects acidity and alkalinity in terrestrial and aquatic ecosystems (Table 15.1). 

Electrorefining can be carried out in acidic or alkaline medium. The acid electrolytes consist of sulfuric acid and stannous sulfate, with additives such as creosulfonic or phenolsulfonic acids and glue to modify deposit formation on the cathodes. The alkaline electrolytes consist of potassium or sodium stannite and free alkali. When compact cathode deposits are required, alkaline electrolytes are inferior to acid sulfate or halogen solutions in terms of electric energy consumption, productivity, cathode morphology, and operating temperature [82, 83]. 

Modem membrane systems are compact and modular, in addition to their high selectivity (that can provide substance concentrations as low as parts per billion) and low energy consumption. Therefore, membrane units can relatively easily be introduced on existing production sites. Furthermore, modem membranes present high resistance to heat, to acid and alkaline conditions, to a number of other aggressive chemicals and to micro-organisms. Membrane processes do not destroy pollutants, they only separate them into a concentrate. It is possible to... 

The overall lifespan of a membrane is governed by the membrane chemical resistance and its antifouling property. Common membrane-cleaning processes employ acidic and alkaline solutions for removing salt precipitates and organic foulants, respectively, to recover the membrane permeability and other performances, which are important to minimize the energy consumption and operating costs (Li and... 

Direct attack by hot 70—80 wt % hydrofluoric acid, sometimes with nitric acid (qv), is effective for processiag columbites and tantalo-columbites. Yields are >90 wt%. This method, used in the first commercial separation of tantalum and niobium, is used commercially as a lead-in to solvent extraction procedures. The method is not suited to direct processiag of pyrochlores because of the large alkaU and alkaline-earth oxide content therein, ie, ca 30 wt %, and the corresponding high consumption of acid. 

The pulp and paper industry and potable and wastewater treatment industry are the principal markets for aluminum sulfate. Over half of the U.S. aluminum sulfate produced is employed by the pulp and paper industry. About 37% is used to precipitate and fix rosin size on paper fibers, set dyes, and control slurry pH. Another 16% is utilized to clarify process waters. The alum sold for these purposes is usually Hquid alum. It is frequendy acidic as a result of a slight excess of H2SO4. Aluminum sulfate consumption by the pulp and paper industry is projected to remain constant or decline slightly in the near term because of more efficient use of the alum and an increased use of alkaline sizing processes (13). 

In all cases, water and carbonic acid, the latter of which is the source of protons, are the main reactants. The net result of the reaction is the release of cations (Ca " ), Mg ", K", Na" ) and the production of alkalinity via HCO. When ferrous iron is present in the lattice, as in biotite, oxygen consumption may become an important factor affecting the weathering mechanism and the rate of dissolution. 

On the other hand, it has been demonstrated that the addition of CO2 to greenhouses iacreases the growth rate of plants so that an iacrease ia the partial pressure of CO2 ia the air could stimulate plant growth making possible shorter growing seasons and iacreased consumption of carboa dioxide from the air. CO2 is also used ia water-treatmeat appHcatioas. Because it is significantly safer than mineral acids, it can be used to reduce the alkalinity of treated water. 

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