Decomposition of flotation reagents in solutions containing metal ions. Part III: Comparison between xanthates and dithiocarbamates

Abstract

With an increasing concern on environment and health, the issue of decomposition of various mining reagents which generates harmful impacts need to be timely handled. DTC (Dithiocarbamate), which play a similar role as xanthate in flotation as collector, was under investigation in this study using the systematic method developed for xanthate (Part I) to understand the effects of metal ions on the decomposition.It was found that DTC and xanthate have similarities with respect to decomposition: Cu2+ suppresses while Fe3+ promotes its decomposition; with an increase in the alkyl chain length, decomposition becomes weaker. With the same alkyl chain length, DTC decomposes less than xanthate. These observations can be explained by the molecular structures of the reagent anion and the derivatives such as dimer and metal complex (similar to xanthate, DTC forms cuprous or ferric DTC and di-DTC when interacting with Cu2+ or Fe3+). The longer the alkyl chain, the stronger the -CS2 moiety attaches to the R2N- in DTC or the RO- in xanthate, so the lower the decomposition of xanthate or DTC is. The -CS2 moiety attaches to the R2N- in DTC stronger than that to the RO- in xanthate, making xanthate decompose more than DTC. A proposed order of easiness for the -CS2 moiety to break up from xanthate or DTC is: cuprous complex < dimer < reagent anion < ferric complex by comparing molecular structures of the compounds formed by the reagent and metal ions. Thus, Cu2+ suppresses while Fe3+ promotes the decomposition. Investigation of the binding energy to break the -CS2 moiety from the molecules is necessary for future studies.