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.

Estimation of the potential of landfill mining and exploration of metal-enriched zones.

Since the Industrial Revolution, people have exploited natural resources to manufacture products. Many of the products have later been disposed of in landfills and the like. The aim of this study was to determine the contents and chemical forms of valuable rare metals in landfills and to identify the metal-enriched zones in landfills using non-destructive prospecting methods. Box experiments were performed using four mixtures of sand and iron sulfide particles, and excavated waste samples. Field prospecting studies were performed at an industrial landfill site. As a result, it is possible to establish a grading system for elements based on the maximum contents in the fill, and the condition in the fill is found to potentially affect the metal distribution. In addition, investigations for rare metals coexisting with iron sulfide were performed at each target site. This allowed zones with high rare metal contents in the fill to be identified in a non-destructive manner. Based on the above approach, a basic evaluation of a landfill site that could be used as an "urban mine" was accomplished.

Two-step extraction method for lead isotope fractionation to reveal anthropogenic lead pollution.

This study developed the 2-step extraction method which eluted the Pb adsorbing on the surface of sediments in the first solution by aqua regia and extracted the Pb absorbed inside particles into the second solution by mixed acid of nitric acid, hydrofluoric acid and hydrogen peroxide solution. We applied the method to sediments in the enclosed water area and found out that the isotope ratios of Pb in the second solution represented those of natural origin. This advantage of the method makes it possible to distinguish the Pb between natural origin and anthropogenic source on the basis of the isotope ratios. The results showed that the method was useful to discuss the Pb sources and that anthropogenic Pb in the sediment samples analysed was mainly derived from China because of transboundary air pollution.