Adsorption study of xanthates on PbSO 4 by titration microcalorimetry

Isoperibol (pseudo-adiabatic) titration microcalorimetry was used to study the adsorption of various xanthates [CH 3 (CH 2 ) n OCS 2 − ] at the PbSO 4 /aqueous solution interface. The effect of the xanthate alkyl chain length (1n–3n) on the adsorption heat was evaluated. Xanthate adsorption isotherms were also determined. Furthermore, the amount of SO 4 into the aqueous solution was quantified to correlate it with the xanthate uptake by PbSO 4 . The adsorption isotherms and the adsorption heat of the xanthates showed two steps. The first step occurred within a sub-monolayer xanthate coverage and was attributed to chemisorption of the xanthates exchanging surface hydroxyls to form CH 3 (CH 2 ) n OCS 2 Pb. Lead xanthate (CH 3 (CH 2 ) n OCS 2 ) 2 Pb multilayers formed in the second step, which was attributed to an ionic exchange chemical reaction between the xanthates and PbSO 4 (aq). In the chemisorption step, the heat was found to be independent of the xanthate alkyl chain length and to linearly decrease in magnitude with the xanthate adsorption. In the multilayer formation step, the magnitude of the integral heat increased with the chain length of the xanthate. Heat contributions due to both the alkyl chain length and the interaction between the xanthate polar group and PbSO 4 (aq) for the formation of lead xanthates are presented. Raman spectroscopy was used to characterize the lead xanthate multilayers on PbSO 4 .