The adsorption of colloidal particles by coal
The use of anthracite as a filter medium is gaining popularity throughout industry as evidenced by the fact that in recent years 1100 filter plants have been installed for clarifying water and other chemicals (51). Since little information is contained in the literature as to why anthracite has become so popular replacing the much used sand filters, this investigation was undertaken in an effort to determine the reason, if any, tor this popularity of use. A number of factors such as rank, chemical composition, size, shape, and surface condition or coal could possibly affect its adsorptive properties.
Tests were made in an effort to determine if any relationship existed between these factors and adsorptive properties. In the experiments tannin extract solution and viscose spinning bath solution were used as the adsorbate and coals varying in rank from anthracite to high volatile bituminous C, in sizes of -4 +8, -8 +10, -8 +16, -10 +16, -16 +20, -20 +30, and -30 +40, as the adsorbent. The tests were made with the coal in the form of the conventional filter bed (10 ± l in. depth) in l¼ diameter by 12" length Liebig condenser jackets with the direction of flow of the adsorbate, in the case of the tannin extract solution in an upward direction, at a rate of coverage of 500 to 2600 cm.²/min., at 24 ± 4°C, and the viscose spinning bath solution in a downward direction, at a velocity of 19 to 44 ml./min., at 35 ± 6°C.
The results of the experiments indicated that in the case of the tannin extract solution the coals were not effective to tannin extract solution clarification; while in the case of the viscose spinning bath solution the following conclusions were drawn:
l. As the size of anthracite was decreased from -4 .+8 to -30 +40 mesh (U. S. Standard Screen), thus decreasing the pore space diameter and increasing the surface area in the coal bed from 2740cm.², to 22,940 cm.², the amount of insoluble solids adsorbed was increased from 10.3 p.p.m. or 27.9% to 34.1 p.p.m. or 92.4% of insoluble solids in the testing solution.
In testing all coals in the size range of -8 +16 mesh (U. S. Standard Screen), the solids adsorbed per 1000 cm.² of coal surface increased from 9.7% to 14.7% as the porosity of the coal beds decreased from 52.3% to 47.2%.
In testing all coals in the size range of -8 +16 mesh (U. S. Standard Screen), no correlation of proximate chemical analysis or relative roughness with adsorptive power could be obtained.
The method of determining surface area used in this investigation is a satisfactory means of obtaining relative external surface area of coal particles of the sizes tested.