Degradation of Thiol Collectors Using Ozone at a Low Dosage: Kinetics, Mineralization, Ozone Utilization, and Changes of Biodegradability and Water Quality Parameters

Abstract

Ozonation at a high O3 dosage can achieve high efficiencies in removing flotation reagents but it has a low ozone-utilization rate. The ozonation of potentially toxic thiol collectors (potassium ethyl xanthate (EX), sodium diethyl dithiocarbamate (SN-9), O-isopropyl-N-ethyl thionocarbamate (Z-200) and dianilino dithiophoshoric acid (DDA)) was investigated in an ozone-bubbled reactor at a low O3 dosage of 1.125 mg/(min·L). The degradation kinetics, mineralization, ozone utilization, changes of biodegradability, and water quality parameters were studied, and the degradation behaviors of four collectors were compared. Thiol collectors could be effectively degraded with a removal ratio of >90% and a mineralization ratio of 10‒27%, at a low O3 dosage. The ozonation of thiol collectors followed the pseudo first-order kinetics, and rate constants had the order of kSN-9 > kEX > kZ-200 > kDDA. The Z-200 and DDA were the refractory flotation reagents treated in the ozonation process. After ozonation, the biodegradability of EX, SN-9, and DDA solutions was remarkably raised, but the biodegradability of Z-200 only increased from 0.088 to 0.15, indicating that the Z-200 and its intermediates were biologically persistent organics. After ozonation, the solution pH decreased from 10.0 to 8.0‒9.0, and both the conductivity and oxidation-reduction potential increased. The ozone utilization ratio in decomposing thiol collectors was above 98.41%, revealing almost complete usage of input O3. The results revealed that thiol collectors could be effectively degraded by O3, even at a low dosage, but their degradation behaviors were quite different, due to intrinsic molecular properties.