Combined Fenton process and sulfide precipitation for removal of heavy metals from industrial wastewater:Bench and pilot scale studies focusing on in-depth thallium removal

Thallium (Tl) in industrial wastewater is a public health concern due to its extremely high toxicity. However, there has been limited research regarding Tl removal techniques and engineering practices to date. In this investigation, bench and pilot studies on advanced treatment of industrial wastewater to remove Tl to a trace level were conducted. The treatment process involved a combination of hydroxide precipitation, Fenton oxidation, and sulfide precipitation. While hydroxide precipitation was ineffective for Tl^+ removal, it enabled the recovery of approximately 70%-80% of Zn as Zn hydroxide in alkaline conditions. The Fenton process provided good Tl removal (>95%) through oxidation and precipitation. Tl was then removed to trace levels (< 1.0 μg/L) via sulfide precipitation. Effective removal of other heavy metals was also achieved, with Cd < 13.4 μg/L, Cu < 39.6 μg/L, Pb < 5.32 μg/L, and Zn < 357 μg/L detected in the effluent. X-ray photoelectron spectroscopy indicated that T12S precipitate formed due to sulfide precipitation. Other heavy metals were removed via the formation of metal hydroxides during hydroxide precipitation and Fenton treatment, as well as via the formation of metal sulfides during sulfide precipitation. This combined process provides a scalable approach for the in-depth removal of Tl and other heavy metals from industrial wastewater.