Copper xanthate

Thioacids have a most disagreeable odour and slowly decompose in air. Their boiling points are lower than those of the coiTcsponding oxygen counterparts and they are less soluble in water, but soluble in most organic solvents. An important dithioacid is dithiocarbonic acid (HO—CS2H). Whilst the free acid is unknown, many derivatives have been prepared such as potassium xanthate giving a yellow precipitate of copper xanthate with copper salts ... 

The copper sulfide formed on the surface of the sphalerite mineral reacts readily with the xanthate, and forms insoluble copper xanthate, which makes the sphalerite surface hydro-phobic. Such a reaction for activating sphalerite occurs whenever the activating ions are present in the solution. It is thus necessary to deactivate sphalerite (to prevent the occurrence of natural activation) in the case of some ores. With lead-zinc ores, for example, natural activation occurs due to Pb2+ in solution... 

The structure of the methylxanthate analogue, (Ph3P)2Cu(S2COMe), is also known and this essentially adopts the same structure as described above (127). The remaining copper xanthate structures are mixed-metal species. 

Dithiodi(thioformates [bi(ethyl xanthates) [) 800 The potassium alkyl xanthate is dissolved in water and cooled in ice while a rapid stream of air containing 5-10 % of chlorine is led through until treating a sample of the liquid with copper sulfate no longer gives a precipitate of copper xanthate. The precipitate or oil produced is separated, taken up in ether, dried, recovered, and distilled. 

Lipid-soluble metal complexes such as copper xanthates (from mineral flotation plants), copper 8-hydroxyquinolinate (agricultural fungicide) or alkyl-mercury compounds are particularly toxic forms of heavy metals because they diffuse rapidly through a biomembrane and carry both metal and ligand into the cell. ... 

A sequence of ATR spectra for a chalcocite (CU2S) electrode in the presence of 10 " M KEX at increasing potentials is shown in Fig. 1.31a [514]. The spectra observed from —0.25 V were attributed to Cu(I)EX (Fig. 7.23). The potential dependence of the VasCOC band, the flotation recovery, and the current are shown in Fig. 1.34b. After correcting for the difference in the EX concentration in the flotation test (a concentration of 1.9 x 10 M implies a cathodic shift of the flotation curve by 0.043 V), the onset of the flotation is seen to coincide with the appearance of the IR signal and the first two peaks in the voltammogram. Thus the spectra suggest that the maximum flotation may be a result of the formation of multilayers of Cu(I)EX, and the current peaks can be attributed to different mechanisms of copper xanthate formation. However, a closer inspection of the spectra shown in Fig. 1.31a reveals a number of differences from the spectrum of bulk Cu(I)EX, which were ignored by the authors. At potentials below -1-0.05 V,... 

Leppinen etal. also found a good correlation between FTIR spectra and voltammograms for the ethyl xanthate/chalcocite system, with the spectrum of chemisorbed xanthate being similar to that for bulk copper xanthate. 

Figure 19 shows the reflectance spectra reported by Leppinen etal for the interaction of ethyl xanthate with chalcopyrite. The peaks at 1240 and 1260 cm" are characteristic of dixanthogen, and the spectra indicate that this species was the initial surface product. Copper xanthate has characteristic peaks near 1190 cm" and it can be seen from Fig. 19 that this compound is deposited additionally at the higher potentials applied. This order of product formation is as expected from studies of chalcopyrite oxidation (see Section VII. 1). Leppinen et found that the development of FTIR intensity correlated with the growth of voltammetric currents. No evidence was reported for adsorption of xanthate at lower potentials than dixanthogen deposition as would be expected from the UV-vis results of Richardson and Walker." The absence of a clearly discernible xanthate spectrum in the potential range expected for chemi-... 

Figure 27 presents the flotation recovery curves of Richardson and Walker" for chalcocite, bomite, chalcopyrite, and pyrite. The results for chalcocite are similar to those shown in Fig. 25. The onset of flotation of bornite and chalcopyrite was found" to coincide with the potentials at which UV-vis spectroscopy showed xanthate to begin to be abstracted from solution. This indicated that attachment of xanthate to the surface was responsible for inducing flotation for both minerals. As pointed out in Section VII, these potentials are below the values at which copper xanthate or dixanthogen are formed but correspond to values at which chemisorption is expected.

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