Acid Flooding

In the above reactions both MgO and CaO are the oxide ion donor and hence act as bases, whereas Si02 and S03 are the oxide-ion acceptor and hence act as acids. Ultimately, the Lux-Flood acid and base react to form magnesium silicate (MgSi03) and calcium sulphate (CaS04) salts respectively. 

Lux-Flood acid-base properties of dissolved oxides. 

In silicate melts and other nonprotonated solvents, the Bronsted-Lowry equation is not applicable and is conveniently replaced by the Lux-Flood acid-base definition (Lux, 1939 Flood and Forland, 1947), according to which free oxygen 0 replaces A basic oxide is one capable of furnishing oxygen ions, and an acidic oxide is one that associates oxygen ions ... 

As described in chapter 6, the main factors determining the solubility of a given element in a silicate melt are the Lux-Flood acidity of its oxide and the relative proportions of the cations of different field strengths (cation charge over squared sum of cation plus ligand radii ZIA ) or charge densities (cation charge over ionic radius Z/r). 

Ray et al. [77] used an indirect method based on AAS for the determination of sulfide in flooded acid sulfate soils. Hydrogen sulfide, evolved during the anaerobic metabolism of sulfate, is readily converted into insoluble metal sulfides, chiefly iron sulfide, in flooded acid sulfate soils. A method for determining sulfide is based on the precipitation of the sulfide as zinc sulfide and subsequent determination by methylene blue formation or iodine titrimetry. 

Ray et al. [77] have also described a method for determining sulfide in soil extracts involving the precipitation of zinc sulfide by the action of zinc on the hydrogen sulfide-flooded acid sulfate soil, and then indirect determination of sulfide by determining the zinc in the precipitate and also the zinc remaining in solution, after the precipitation by AAS. Over 85% of the sulfide was recovered in this procedure. 

Sethunathan N. 1973. Degradation of parathion in flooded acid soils. J Agric Food Chem 21 602-604. 

In these melts, the concept of acidity of Lux-Flood [343] (L-F) is applied. A Lux-Flood acid is defined as an oxide ion acceptor leading to the formation of the conjugate base ... 

In oxide melts the solvent system corresponds to the Lux-Flood acid/base... 

Lux-Flood acidities of oxides are important in reactions taking place in silicate melts, for example in glass manufacture. The values correlate well with other aspects of acid-base behaviour, for example that manifested in aqueous chemistry (see Topics B2 and F7). Acidity of EO generally... 

Since the process of complexation between the melt anion and different cations of close radii proceeds to practically equal degrees, one may assume that for a set of oxides dissolved in the same ionic solvent the solubility value should be dependent on the degree of acidic cation-anion interaction which is the Lux-Flood acid-base equilibrium. In this case, the constant of the... 

Although the increase in pH of acid soils is obtained by soil reduction in alkaline soils, a relatively stable pH is obtained after a few weeks of flooding, primarily due to the buffering capacity of carbon dioxide. Ponnamperuma (1972, 1981) observed the following empirical relationship for flooded acid soils ... 

Wahid, P. A. and A. Sethunathan. 1979. Involvement of hydrogen sulfide in the degradation of parathion in flooded acid sulphate soil. Nature (London), 282 401-402. 

It is well known that flocculation of asphaltenes in petroleum reservoirs, wells and surface separation-upgrading facilities pose technical problems and increase the cost of production and processing of crudes. Field conditions conducive to precipitation of asphaltenes include natural depletion, miscible flooding, caustic flooding, acid stimulation and gas-lift operations. Asphaltene precipitation is particularly important problem in miscible flooding since it can reduce permeability, affect well injectivities and productivities, alter rock wettability characteristics and even cause plugging of producing wells. ... 

Ionic melts as media for Lux-Flood acid-base reactions may be divided into two types on the base of constitutional (i.e., being a part of main components of the melt) oxygen ions oxygen-less and oxygen-containing ones. Let us consider some features of acid-base interactions in the mentioned melts. ... 

Wahid, P.A. and N. Sethunathan. Involvemerrt of Hydrogen Sulfide in the Degradation of Parathion in Flooded Acid Sulphate Soil, Nature (London), 282(5737) 401-402 (1979). 

Stability range of most melts, including chlorides. This occurs in nitrates themselves, of course, as a limiting reaction (but see below). Such electrochemical behavior might be rationalized in terms of the Lux-Flood acid-base formalization for many years the reduction of nitrate ions was written ... 

Apart from nitrate ions, the direct reduction of carbonate, phosphate, and silicate anions have all been reported. Some controversy surrounds the electroreduction of sulfate ions water may be implicated in this process. Inman and Wrench could only induce cathodic electroactivity of sulfate ions dissolved in a chloride melt by release of SO3, the conjugate acid, with a stronger Lux-Flood acid, metaphosphate, P03. While the alkali metal and alkaline earth sulfates, carbonates, and nitrates are clearly ionic, borate, phosphate, and silicate melts are highly polymerized. In such systems, the mobile cations move freely about the anion lattice network, which comprises a temperature- and compositional-dependent equilibrium between ion fragments of variable chain length. Inman and Franks observed kinetically limited electroreduction processes in a phosphate melt, as might be expected if only the smallest fragments of the dynamic polymer equilibrium are electroactive. 

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