UV(185+254 nm) photolysis of typical thiol collectors: decomposition efficiency, mineralization and formation of sulfur byproducts

The decomposition of toxic flotation reagents upon UV(185+254 nm) irradiation was attractive due to operational simplicity and no dosage of oxidants. In this work, the degradation of typical thiol collectors (potassium ethyl xanthate (PEX), sodium diethyl dithiocarbamate (SDD), O-isopropyl-N-ethyl thionocarbamate (IET) and dianilino dithiophoshoric acid (DDA)) was investigated by UV(185+254 nm) photolysis. The degradation efficiencies and mineralization extents of collectors were assessed. The formation of CS(2) and H(2)S byproducts was studied, and the mechanisms of collector degradation were proposed under UV(185+254 nm) irradiation. The PEX, SDD and IET were decomposed with nearly 100% removal upon 75 min of UV(185+254 nm) irradiation. The decomposition rate constants decreased in the order SDD > PEX > IET ≫ DDA, and the DDA was the refractory collector. After 120 min of UV(185+254 nm) irradiation, 15−45% of carbon and 25−75% of sulfur of collectors were completely mineralized, and the mineralization extent decreased in the order PEX > SDD > IET > DDA. The percentage of gaseous sulfur (CS(2) and H(2)S) ranged from 0.48 to 4.85% for four collectors, showing the fraction of emitted sulfur byproducts was small. The aqueous CS(2) concentration increased in the first 10−20 min, and was decreased to a low level of 0.05–0.1 mg l(−1) at 120 min. Two mechanisms, i.e. direct UV(254 nm) photolysis and indirect oxidation with free radicals, were responsible for collector decomposition in the UV(185+254 nm) photolysis.