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.