Cobalt ion removal from aqueous solutions by coal fly ash

Cobalt ions, which are commonly found in low concentrations in industrial wastewater, are toxic, biocumulative, and hard to degrade. Therefore, the removal of these heavy metal ions from wastewater is highly important. The removal of Co(II) from aqueous solutions using untreated and alkali-modified coal fly ash was studied. The results for untreated fly ash show that the pseudo-second-order kinetic equation better fits the observed adsorption progress. The Langmuir and Freundlich isotherms could describe the reaction efficiently, and the maximum adsorption capacity for Co(II) was 237 mg.g(-1) at 20 degrees C. Pretreating the fly ash with an alkali solution decreases the adsorption capability, possibly by destroying the zeolite structure. When the ratio of the fly ash dose and Con concentration is between 40 and 60, the removal rate of Co(II) at a concentration of 20 mg.L-1 reaches 99.95%.