Examination of metal sorting and concentration technology in landfill mining –with focus on gravity and magnetic force sorting–

The study focuses on the recovery of the minor metals contained in waste landfills. We have previously reported on the method of investigating the existing chemical morphology of each element in landfills, creating a high-concentration zone for a specific element, and non-destructively exploring the position of that within the block. In this study, a method for concentrating useful metals from landfills was examined, using samples taken from a concentrated zone. Specifically, the efficiency of physical sorting using gravity and a magnetic force was examined with samples collected from landfills mainly composed of incinerator ash. In the gravity sorting method, the resulting metal concentration is large when the heavy liquid specific gravity is 2.5 or 2.75 g/cm³ and above. Currently, sorting using a heavy liquid with a specific gravity of 2.75–3.0 g/cm³ is effective for increasing the metal concentration of the sample. Magnetic force sorting can efficiently separate metals and non-metals, and is effective as a pretreatment for a more advanced concentration stage. Various substances are mixed within the landfill waste, and several stages of sorting and concentration treatments are required to extract useful minor metals. A physical sorting method, such as the use of gravity or magnetic force is effective for the initial stage processing. Furthermore, when the metal to be extracted has been determined, a more effective concentration method based on the chemical form and characteristics of the target metal will be further examined for these pretreated samples.