UV185+254 nm photolysis of typical thiol collectors: decomposition efficiency, mineralization and formation of sulfur byproducts.

Pingfeng Fu,Gen Li,Xiaoting Wu,Xiaofeng Lin,Bolan Lei

doi:10.1098/rsos.190123

Abstract

The decomposition of toxic flotation reagents upon UV185+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 UV185+254 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 UV185+254 nm irradiation. The PEX, SDD and IET were decomposed with nearly 100% removal upon 75 min of UV185+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 UV185+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 (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 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 UV254 nm photolysis and indirect oxidation with free radicals, were responsible for collector decomposition in the UV185+254 nm photolysis.

Highlights

Froth flotation has become the most widely applied process for separating valuable minerals from ores in mines around the world
The photolysis of thiol collectors (PEX, sodium diethyl dithiocarbamate (SDD), IET and dianilino dithiophoshoric acid (DDA)) upon UV254 nm or UV185þ254 nm irradiation is shown in figure 2
To investigate the mineralization of thiol collectors under UV185þ254 nm irradiation, the concentrations of chemical oxygen demand (COD), total organic carbon (TOC) and SO422 ions were measured with the results shown in figure 4

Summary

Introduction

Froth flotation has become the most widely applied process for separating valuable minerals from ores in mines around the world. Thiol collectors, such as xanthates, dithiophosphates and dithiocarbamates, are important flotation reagents to render sulfide minerals hydrophobic and facilitate bubble attachments [1,2]. Nearly 50% of collectors dosed in flotation circuits would be discharged in wastewaters after the mineral flotation [3]. Some collectors and their byproducts are found to be toxic to soil microbes, biota, animals and human beings [4,5,6,7]. It has been of great concern to remove potentially toxic collectors from flotation wastewaters for the sustainable development of mining industry

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Conclusion