Determination of metal-abundant high-density particles in municipal solid waste incineration bottom ash by a series of processes: Sieving, magnetic separation, air table sorting, and milling

Abstract

Valuable non-ferrous (NFe) metals are contained in municipal solid waste incineration (MSWI) bottom ash (BA). The applicability of an air table for separating NFe metal-abundant particles in MSWI BA (<8 mm) was studied. A stepwise separation procedure was developed based on the performance tests of the air table conducted by changing three variables (air injection, vibration, and end slope). As a result of the stepwise separation, six bulk density ranges (<0.7 to >1.1 g/cm³ at intervals of 0.1 g/cm³) were prepared from non-magnetic fractions with four size ranges (4-8, 2-4, 1-2, and 0.5-1 mm). The effectiveness of air table sorting was evaluated based on dry particle density and proportion of metals. NFe metals were obtained by sieving (>0.5 mm) after a ball mill process, confirming that NFe metals accounted for 3.2% of the < 8 mm MSWI BA. The highest particle density of each size fraction and the proportion of NFe metals in the fractions were 3.19 g/cm³ and 59.9% (4-8 mm), 2.97 g/cm³ and 28.8% (2-4 mm), 2.78 g/cm³ and 10.4% (1-2 mm), and 2.87 g/cm³ and 4.4% (0.5-1 mm). In the 0.5-2 mm particles, the highest density fraction contained 68.7% of the NFe metals, which were expected to be recovered by applying an air table separator to MSWI BA 0.5-2 mm.

Keywords: Air table; Bottom ash; Density; MSW; Metal recycling.