Regeneration of waste rolling oil via inorganic flocculation-adsorption process

Waste rolling oil (WRO) can be regenerated by inorganic flocculation-adsorption. Ferric hydroxide (Fe(OH)3) colloid prepared by the double decomposition reaction of FeCl3 and NaOH was selected as an inorganic flocculant. Fly ash, activated carbon, clay and silica gel were used as adsorbents to treat the WRO. Effects of different treatment conditions on the performance of the recycled oil were investigated. Results indicated that the recycled oil achieved optimum quality under the following conditions: flocculation time, 6 min; temperature, 60 °C; adsorption time, 20 min; and mass ratios of FeCl3-to-WRO, NaOH-to-FeCl3 and fly ash-to-WRO of 0.10, 3 and 0.03, respectively. NaOH combined with Fe(OH)3 effectively removed most macromolecular impurities, organic acids, lipids, and alcohols. Fly ash exerted the best adsorption rate and adsorption effect. In addition, physicochemical properties of the recycled oils were close to those of fresh oil.