ON THE ROLE OF OIL WETTING IN THE CLEANING OF HIGH RANK COALS BY AGGLOMERATION

The wettability of three Spanish anthracites with a large mineral matt er content was studied by measuring the oil/water/coal contact angle w ith heptane and with crude and refined vegetable oils. The captive dro p method was used for this purpose. The contact angle was found to dep end on the coal, oil, and an interaction between coal and oil. Particl e agglomeration tests were conducted to determine the maximum recovery of organic matter for each combination of coal and oil. The maximum r ecovery was observed to correlate well with the three-phase contact an gle when heptane was employed as an agglomerant for the different anth racites. When vegetable oils were employed as agglomerants, the maximu m recovery was also observed to correlate well with the contact angle in half the cases. For the other half the recovery exceeded what would have been predicted by the contact angle. Therefore, for these cases the oil wettability of the coal seemed greater under dynamic condition s than under static conditions. (C) 1998 Elsevier Science Ltd. All rig hts reserved.