Insight into the relationship between the mineralogical characteristics and adsorption properties toward pollutants of oil shale semi-coke

Abstract

It is urgent and indispensable to develop the sustainable approach to realize the resource utilization of the industrial solid wastes. In this study, the oil shale semi-coke obtained from Yaojie, Longkou, Wangqing and Huadian were selected to study the relationship between the mineralogical characteristics and adsorption properties of oil shale semi-coke toward pollutants of Pb2+, Cd2+, and PO43-. The results indicated that the sample of Yaojie was mainly composed of quartz (55.1 %) and kaolinite (29.3 %) defined as silicate type, while the one of Longkou was a typical carbonate type with high calcite content of 29.7 % equaled the amount of quartz. Due to the unique mineralogical properties of quartz, kaolinite and calcite, the involved raw oil shale semi-coke had a poor adsorption capacity to the model pollutants. By contrast, the calcined samples exhibited good adsorption properties toward three pollutants, especially the samples derived from Longkou, in which the samples prepared at 600℃ and 800℃ presented the maximum capacity toward Pb2+ (257.03 mg/g), Cd2+ (131.72 mg/g) and PO43- (129.53 mg/g), respectively, which was higher than most of the reported similar adsorbents. Furthermore, the adsorption kinetics and isotherm of the heat-treated oil shale semi-coke from Longkou for Pb2+, Cd2+ and PO43- conformed to the quasi-second order kinetic model and Langmuir isothermal adsorption model, respectively. Due to the synergistic effect of the functional groups adsorption, mineral precipitation and ion exchange of the heat-treated samples, the adsorbates of PO43-, Cd2+, and Pb2+ were well adsorbed and then transformed into CaHPO4·2 H2O, CdCO3, PbCO3, Pb3(CO3)2(OH)2, respectively.