Coal ash is the residue that is produced during coal combustion for instance fly ash, bottom ash or boiler slag which was primarily produced from the combustion of coal. With growth in coal burning power station, huge amount of coal bottom ash (CBA) considered as hazardous material which are normally disposed in an on-site disposal system without any commercialization purpose. Previous researchers have studied the extraction of silica from agricultural wastes such as palm ash and rice husk ash (RHA) and CBA by using leaching treatment method. In this study, the weaker acid, citric acid solution was used to replace the strong acid in leaching treatment process. Result showed that the heavy metal content such as Copper (Cu), Zinc (Zn) and Lead (Pb) can be decrease. Meanwhile the silica can be extracted up to 44 from coal bottom ash using citric acid leaching treatment under the optimum reaction time of 60 minutes with solution temperature of 60°C and concentration of citric acid more than 2. © The Authors, published by EDP Sciences, 2017.