Reducing Heavy Metal Element from Coal Bottom Ash by Using Citric Acid Leaching TreatmentAhmad Asyari Yahya, Noorwirdawati Ali, Nur Liyana Mohd Kamal, Shahiron Shahidan, Salmia Beddu, Muhd. Fadhil Nuruddin and Nasir ShafiqMATEC Web Conf., 103 (2017) 01004DOI: https://doi.org/10.1051/matecconf/201710301004