Xanthate interaction with pyrite in the presence of Pb and diethylenetriamine (DETA, NH2-CH2-CH2-NH-CH2-CH2-NH2) was investigated by cyclic voltammetry, open-circuit potential measurements, an ex-situ spectroelectrochemical technique, and zeta potential measurement. Uptake of xanthate was promoted by the presence of Pb. The only xanthate product detected was dixanthogen. Xanthate adsorption on Pb-contaminated pyrite was suppressed by DETA, but relatively large concentrations were required. Addition of DETA decreased the open-circuit potential and increased the zeta potential in the absence or presence of Pb ions, indicating adsorption of DETA. The mechanism of depression of DETA may be a combination of competition with xanthate for adsorption sites and creation of reducing conditions which retard oxidation of xanthate to dixanthogen;