The pH of fly ash is not a single fixed value; rather, it varies depending on factors such as the type of coal burned and the ash's chemical composition, particularly its calcium and sulfur content. Fly ash is typically classified into different categories based on its pH range.
According to research [23], fly ashes are categorized into specific pH ranges:
Classification of Fly Ash Based on pH
The reference [23] outlines the following classification based on pH value and calcium/sulfur ratio:
- Acidic Ash: These ashes exhibit a pH value ranging from 1.2 up to 7.
- Mildly Alkaline Ash: This category includes ashes with a pH typically between 8 and 9.
- Strongly Alkaline Ash: These ashes show a high pH, ranging from 11 to 13.
The classification is also influenced by the type of coal from which the ash is derived [23]. Therefore, to determine the specific pH of a given sample of fly ash, it is necessary to test it directly, as it will fall into one of these defined ranges.
| Fly Ash Classification | Typical pH Range |
|---|---|
| Acidic Ash | 1.2 – 7 |
| Mildly Alkaline Ash | 8 – 9 |
| Strongly Alkaline Ash | 11 – 13 |
This variation in pH is a key characteristic that influences how fly ash interacts with its environment and how it can be utilized, particularly in applications like concrete production or soil stabilization.
