Effects of polymers and metal ions on vacuum filtration of fine coal

Surface modification approaches have been investigated in vacuum filtration of column flotation froth products of high and low sulfur coal slurries. It was shown that vacuum dewatering of fine coal can be enhanced significantly in terms of both filtration rate and cake moisture by modifying surface properties of fine coal particles with polymeric flocculants and metal ions. As expected, use of cationic or anionic flocculants significantly increased filtration rate. Addition of 5 g/t cationic flocculant to the high sulfur clean coal slurry lowered cake moisture from 26% to 22.3% and increased cake thickness from 5 to 10 mm, however, use of 25 g/t cationic flocculant increased cake moisture to 26.3% at increased cake thickness of 24 mm. When cake thickness was maintained constant, use of anionic flocculant significantly reduced cake moisture. Cake moisture was reduced from 27.3% to 18.8% with the low sulfur coal using 25g/t anionic flocculant at cake thickness of 7 mm. Use of metal ions showed less significant effects on fine coal filtration. Mechanisms responsible for observed improvement in fine coal dewatering behavior have been discussed from the perspectives of filtration fundamentals.