Complexes minerals-carboxylic acids

The processes that govern the formation of ash particles are complex and only partially understood (Figure 7.12). The mineral matter in pulverized coal is distributed in various forms some is essentially carbon-free and is designated as extraneous some occurs as mineral inclusions, typically 2-5 pm in size, dispersed in the coal matrix and some is atomically dispersed in the coal either as cations on carboxylic acid side chains or in porphyrin-type stmctures. The behavior of the mineral matter during combustion depends strongly on the chemical and physical state of the mineral inclusions. 

The starting material is an 18 electron nickel zero complex which is protonated forming a divalent nickel hydride. This can react further with alkenes to give alkyl groups, but it also reacts as an acid with hard bases to regenerate the nickel zero complex. Similar oxidative addition reactions have been recorded for phenols, water, amines, carboxylic acids, mineral acids (HCN), etc. 

The interpretation of the infrared and Raman spectra of solid salts of amides has been the subject of much disagreement. One must first distinguish solid complexes of amides with carboxylic acids from salts with strong mineral acids. In the first, the interaction is... 

Metal complexation by carboxylates is, on the other hand, an important mechanism to exclude uptake of toxic elements, such as Al3+, in plant species and cultivars adapted to acid mineral soils. The release is restricted to the apical root zones, which are most susceptible to the toxic effects of aluminum (Ma, 2000 Brimecombe et al., 2007). 

Carbonates are one plausible sohd source for metal ions which display similar dissolution/complexation barriers for various ions (that is, different COj salts, e.g. of Fe(II), Mg, Cu, Zn or Mn(II), are similarly soluble in water (pKs 11 Mizerski 1997)) and form mixed crystals among each other. In addition, the products of chemical evolution, with HCOOH, many higher carboxylic acids with or without amino groups being prominent in yields (Lemmon 1970), are usually acidic and thus would dissolve carbonates readily. Contrary to carbonates, other kinds of minerals like phosphates. 

This partially oxidized material contains 4.2-5.4 mmol g of carboxylic acid functional groups, which account in part for its generally acidic character, its charge distribution as a function of pH, its complexation of metal ions, and its interaction with mineral surfaces in the environment. Phenolic hydroxyl groups are present at concentration of —1.5-1.8 mmol g in FAs, HAs, and NOM. The ratio of carboxyl-to-phenolic groups is thus —3 1, which is significantly greater than the ratio of 2 1 that is commonly used in some mathematical models of the acidity of these materials. 

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