Mineral matter cations

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. 

Soils also display a wide range of physico-chemical characteristics that influence the bioavailability of toxic metals to microorganisms, fauna, and plant roots. These characteristics include soil texture, organic matter, cation and anion type, pH, or alkalinity. The presence of colloidal clay minerals in soils greatly increases the... 

Radovic, Walker and Jenkins (14) studied the effect of various forms of mineral matter in chars on their reactivity in air. It was found that ion-exchangeable cations particularly Ca, greatly enhanced char reactivity whereas discrete mineral phases had no significant effect. A redox reaction was again postulated as the mechanism of catalysis by the ion-exchangeable cations. 

A number of processes affect the solubility characteristic of metal-hu-mate and metal-fulvate complexes in soils, as well as in natural waters. A major factor is the extent to which the complex is saturated with metal ions. Other factors affecting solubility include pH, adsorption of the complex to mineral matter (e.g., clay), and biodegradation. Under proper pH conditions, trivalent cations, and to some extent divalent cations, are effective in precipitating humic substances from very dilute solutions monovalent cations are generally effective only at relatively high particle concentrations. 

Dissolved mineral matter in soil is largely present as ions. Prominent among the cations are Ca, Mg, K, Na, and usually very low levels of Fe, Mn, and Al. The last three cations may be present in partially hydrolized form, such as FeOH, or complexed by organic humic substance ligands. Anions that may be present are HCO3, COj, HSO, SO, Cl, and F. In addition to being bound to... 

Biological exposure pathway of sulfur movement in soils of forest ecosystems is related to microbial transformation of sulfolipids. Back conversion of sulfate-S into organic matter immobilizes the anion and potentially reduces soil cation leaching. Processes of sulfur mineralization and incorporation proceed rapidly in response to several factors, including temperature, moisture, and exogenous sulfate availability in soils and water. 

The first of these environmentally-important parameters can be expressed as a partition coefficient. In aqueous solution many, but not all pesticide compounds exhibit strong affinity for soil organic matter or concentrate in the lipid phase of soil organisms. Some, notably the cationic group, also exhibit marked affinity for clay or other mineral surfaces. An overall partition (or distribution) coefficient (kD) can be defined ... 

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