The Effect of Coal Fly Ash Treatment with NaOH on the Characters

and Adsorption Mechanism toward Methyl Violet in The Solution

Widi Astuti et al

Abstract. The Coal fly ash (CFA) generated by coal-based thermal power plants is mainly composed of some oxides having high crystallinity including quartz, mullite and unburned carbon. In this study, the effect of CFA crystallinity toward its adsorption capacity and adsorption mechanism for methyl violet in the

solution was investigated. CFA having various crystallinity was obtained by refluxing it with sodium hydroxide (NaOH) solution at various concentrations, temperature and reflux time. To evaluate the effect of crystallinity of treated CFA on the adsorption capacity and adsorption mechanism, adsorption of MV solution

with treated CFA was carried out. The research shows that the reflux of CFA with NaOH solution leads to the crystallinity of quartz and mullite in CFA decreased. The decrease is proportional with the concentration increasing, the temperature elevation, and the longer time. The reflux using NaOH solution with high

concentration (> 3 M) in addition causes a decrease in the crystallinity of quartz and mullite, also results in the formation of hydroxysodalite. The decrease of the CFA crystalllinity gives an increase MV adsorbed. Adsorption of MV on treated CFA is a chemisorption.

many articles are present on net about fly ash treated with NaOH. Attached ine may be useful.

Flyash has a spherical and glassy stucture (d32 about 35 microns) . There are no internal pores so specific surface area is in order units  m2/g (compare with valu of 400-800 for regular adsorbents. From this reason it  is very difficult to measure adsorbed amount (it is very small) which is significantely affected by the capillary condensation. Increase in adsobed amount will be mostly due to  the capilarry condensation in scevices between particles in the points of their contact. What is important: we can expect signiffivant changes in electrical resistance od flyash particle layer after NaOH treatment due to Na ionts remaining after the treatment in mentioned scevices points of particle contact.

Fly ash by itself produces an alkali slurry when washed. This has caused crystallisation challenges in fly ash wet scrubbing partly due to gypsum formation. 

I am not sure why you would want to treat it with NaOH? If you can explain, we may be able to provide a better answer.

This might help,

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