In the present experimental study, the efficiency of permeable reactive barriers (PRBs) containing organic material mixed with zero-valent iron, fly ash or red mud to remove heavy metals from leachates was assessed. Upflow laboratory column experiments were carried out to assess system efficiency in terms of Cu, Zn, Ni and Mn removal. The initial concentration of each metal ion in the feed was 50 mg/L. X-ray diffraction as well as scanning electron microscopy and energy dispersive spectrometry were used to identify new mineral phases and to identify metal removal mechanisms. Results and analyses show that sorption and precipitation of metals as sulphides, hydroxides and other hydrated phases are the dominant metal removal mechanisms.