Valuable Metals Extraction From Hydrocracking Spent Catalyst Using Citric Acid - Dewi Purnama Sari; Ahmad Tawfiequrahman; Himawan Tri Bayu Murti Petrus; Fika Rofiek Mufakir; Widi Astuti; Y Iskandar; D Bratakusuma (Seminar Nasional Teknik Kimia Kejuangan, 2018)