I am working on XRD of fly ash to know the effect of particle size on heavy metal release with pH variation.
There can be several effects with a different outcome:
1) the chemical form and stability of the oxides / metal compounds is strongly particle size dependent. Smaller particles are usually formed with a higher energy which results in other metal compounds compared with lower temperatures for larger particles. At high temperatures, reactions with CO2, O2, N2 etc. in the atmosphere are very common and metal oxides or compounds with high affinitiy to these atmospheric gases will form preferentially. These high temperature oxides or compounds are not necessarily highly soluble (often not). Due to the very rapid cooling rate of small particles, the high temperature oxides or compounds persist and are still present when the particles are cooled to low temperatures.
2) If the chemical form / surface phase of the metal compounds would be equal for large and small sized particles, the specific surface area determines the amount of released metals. Since this is larger for smaller particles, the released metals are larger (when normalized to mass) for smaller particles, but not when normalized to the surface area of the particles. This is however not true for the smallest particles (< 100 nm), which can have an additional driving force for dissolution due to the low ratio of surface to bulk atoms.
From my experience for metals, metal oxides or metal compounds, smaller size does not necessarily mean a higher metal release when normalized to the specific surface area - it depends on the physico-chemical form/phase, which is strongly dependent on the formation conditions and cooling rate. I also found that the metal release is not necessarily larger or smaller for different particle sizes, but depends strongly on the metal release mechanism - whether it is for example a protonation-induced dissolution, a complexation-induced dissolution, metal oxidation, or oxide reduction.
1. ion characterization
2. particles size distribution
3. All type of Solids ( Like TS, TVS, TSS, VSS, TDS, VDS )
Should be analysis.
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