# Application of Fly Ash as an Adsorbent for Removal of Air and Water Pollutants
## 4 Application of Fly Ash for Treatment of Pollutants
### Removing Water Pollutants
#### 4.2.2 Removal of Other Organic/Inorganic Components  
On the other hand, FA not only has the capacity to adsorb heavy metals from wastewater, but also has the ability to adsorb other organic/inorganic pollutants from wastewater, including to phosphorous, fluoride, boron, phenolic compounds, pesticides, dyes, etc. [5; 151]. Phosphorus is an indispensable element in living organisms. Phosphorus is required for the metabolism of organisms. Therefore, when the phosphorus chemical industry discharges phosphorus compounds into rivers, it will lead to the \"autrophication\" of water, which will lead to the rapid growth of algae and other plants, and absorb a large amount of free oxygen in the water, posing a great threat to the ecological environment. Many researchers [152; 153] have studied the use of FA to remove phosphorus from wastewater. [PERSON] et al. reported that mixture of sand with 5% of FA by weight can effectively reduce phosphorus concentration in water [151]. They showed that the FA has a good effect of adsorb or precipitate phosphate because of the FA contains a certain amount of calcium contents. The removal efficiency of phosphate is affected by pH conditions and calcium content in FA. In general, alkaline conditions for high-calcium FA, neutral pH levels for medium-calcium FA have a high ability to remove phosphate, and the low-calcium FA immobilized little phosphate at all pH values [154]. In addition, the iron contained in FA can also react with phosphate to cause phosphate to be precipitated. Using FA to remove phosphorus from wastewater is primarily due to the precipitation of phosphate with Ca\({}^{2+}\) ions in solution, and the weak physical interactions between the surface of FA and the phosphate [155]. [PERSON] et al. [156] found that a magnesia-loaded fly ash nanospheres (MLC) is an efficient adsorbent for adsorption of fluoride. The influence of temperature, initial fluoride concentration, pH of the solution, contact time, coexisting ions, and fly ash dosage on fluoride removal was respectively investigated. They indicated that when the pH of the solution is 3, MLC has the maximum adsorption of fluorine, which is mainly due to highly protonated MLC surface and the gradual increase in the attractive forces between the positively charged surface and the negatively charged fluoride ions. [PERSON] et al. [70] investigated the removal of boron from seawater and desalinated seawater on FA. They carried out several series of column and batch experiments and determined that there is a significant reduction of boron concentration in seawater after interaction with FA. Under suitable conditions (e.g., pH = 9, L/S = 1/10, reaction time > 6 h), more than 95% of boron was removed by FA. Phenolic compounds are one of the major pollutants in polluted water. Phenol will volatilize into the atmosphere or infiltrate underground, polluting the atmosphere, groundwater and crops when untreated phenolic wastewater is used to irrigate crops. Phenol, cresol and other volatile phenols have attracted wide attention. FA as a waste material can be used as adsorbents for the removal of phenolic compounds. [PERSON] et al. [157] and [PERSON] et al. [158] reported that the high adsorption capacity of FA was related to its high-surface-area, pore volume, porosity and higher unburned carbon content. Moreover, phenols  
Figure 15: Comparison of SEM images before (**a**) and after (**b**) heavy metal adsorption (adapted with permission from [26], Elsevier, 2018).  
have a strong hydroxyl functional group which interacts with the adsorbent surfaces, resulting in vertical alignment of the molecule on the surface. Therefore, phenol can be more adsorbed by FA because of the interaction between adsorbed molecules. Other researchers [159; 160] have demonstrated that FA also has the ability to remove pesticides, various dyes and pigments from wastewater. FA is low cost and more effective for adsorption of multiple harmful substances to be used widely in wastewater treatment.