Adsorption of surfactant on pyrite and degradation of pyrene by pyrite-fenton reaction

Abstract

Adsorption of CPC on pyrite surface at pH 5 to 9 and electrolytes effect in the presence of 0.01~0.1 M NaCl at pH 5 and 7 with the measurement of zeta ($\zeta$) potential is investigated. It was observed that depending on pH condition, CPC adsorption could occur by only hydrophobically (positive surface charge) or using both hydrophobic and hydrophilic force (negatively surface charge). Regardless the nature of surface charge, presence of NaCl decreased adsorption by shielding effect. Positively $\zeta$-potential value showing no charge reversal confirmed the monolayer adsorption at positive surface condition while by giving a charge reversal; it suggested the existence of the double layer adsorption. In the presence of NaCl, $\zeta$-potential value of pyrite surface gave negative value confirming that counterions shielded pyrite surface. By measuring the CMC and degree of dissociation of counterions ($\alpha$) in micelles at different pH condition, it was studied that CMC did not affect the adsorption significantly while smaller and larger value of $\alpha$ is preferential for adsorption using tail groups and head groups, respectively. From PhreeqC analysis, it was studied that maximum adsorption occurred at pH 7 due to the metastable phase where pyrite started to saturate with solution. By introducing hydrogen peroxide ($H_2O_2$) while surfactant content polycyclic aromatic hydrocarbons (PAHs) like pyrene could be degraded efficiently by pyrite-Fenton reaction. Therefore, this study also focused on the mechanism of enhanced pyrene degradation by pyrite-Fenton reaction in the presence of NaCl. For this purpose, 10 ppm pyrene was solubilized in 1.8 mM of a cationic cetylpyridinium chloride (CPC) surfactant solution. Degradation kinetic experiment was performed using 3 g/L pyrite suspension with 0.42 mM hydrogen peroxide ($H_2O_2$) without and with 0.1 M NaCl. The value of first order kinetic rate constant was $0.029min^{-1}$ without NaCl and it was observed ...