Adsorption of oil from waste water by coal: characteristics and mechanism

The work described here was focused on exploring the potential application of coal to purification of oily waste water. Coal was added to oily waste water as an adsorbent and then removed through a flotation process. This allowed economical and highly efficient separation of oil from the waste water. The absorption time, coal type, coal particle size distribution, pH value and oil concentration were investigated. The results indicate that oil absorption by a coal increases for a period of 1.5 h and then gradually tends toward an equilibrium value. It appears that the absorption capacity of anthracite is more than that of lean coal or lignite, given the same coal particle size distribution. The absorption capacity of a coarse coal fraction is less than that of finer coal, given the same of coal type. The absorption capacity of anthracite decreases slightly as the pH increases from 4 to 9. The adsorption of oil on anthracite follows the Freundlich isothermal adsorption law: given initial oil concentrations of 160.5 or 1023.6 mg/L the absorption capacity was 23.8 or 840.0 mg/g. The absorption mechanism consists of two kinds of absorption, a physical process assisted by a chemical one.