UV185þ254 nm photolysis of typical thiol collectors: Decomposition efficiency, mineralization and formation of sulfur byproducts

Abstract

The decomposition of toxic flotation reagents upon UV185þ254 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 UV185þ254 nm photolysis. The degradation efficiencies and mineralization extents of collectors were assessed. The formation of CS2 and H2S byproducts was studied, and the mechanisms of collector degradation were proposed under UV185þ254 nm irradiation. The PEX, SDD and IET were decomposed with nearly 100% removal upon 75 min of UV185þ254 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 UV185þ254 nm irradiation, 15245% of carbon and 25275% of sulfur of collectors were completely mineralized, and the mineralization extent decreased in the order PEX . SDD . IET . DDA. The percentage of gaseous sulfur (CS2 and H2S) ranged from 0.48 to 4.85% for four collectors, showing the fraction of emitted sulfur byproducts was small. The aqueous CS2 concentration increased in the first 10220 min, and was decreased to a low level of 0.05-0.1 mg l21 at 120 min. Two mechanisms, i.e. direct UV254 nm photolysis and indirect oxidation with free radicals, were responsible for collector decomposition in the UV185þ254 nm photolysis.