Thallium mining from industrial wastewaters enabled by a dynamic composite membrane process

Abstract

Thallium (Tl) is a rare but highly toxic element. Mineral exploitation and utilization lead to a risk of thallium (Tl) leakage to the aqueous environment, greatly threatening human health. In this study, we propose a novel Tl wastewater treatment process based on a regenerable adsorptive membrane to achieve Tl removal and recovery from industrial wastewaters. Specifically, a composite membrane was fabricated using Prussian blue (PB) and a commercial polyvinylidene fluoride (PVDF) membrane. The as-fabricated PB/PVDF composite membrane exhibited an outstanding Tl removal efficiency (> 95%) at various operating conditions (i.e., a permeate flux ≤ 140 L m−2 h−1, pH from 3 to 11, and an initial Tl concentration from 50 to 1000 µg/L). Moreover, coexisting heavy metal ions (e.g., Pb2+, Cu2+, Cd2+, Ni2+, and Zn2+) had little interference with the Tl removal efficiency of the PB/PVDF composite membrane. Hydraulic backwash was applied to recover PB-Tl composite particles as a high content source of Tl (92.2 ± 11.4 mg of Tl per gram of composite), while the backwashed PVDF membrane can be reused for the fabrication of the PB/PVDF composite membrane. A simplified economic analysis suggests that chemical cost for synthesizing the consumable Pb in the proposed dynamic composite membrane process was only ∼ 6.1% of the value of recovered Tl, highlighting the vast potential of the proposed process for Tl removal and recovery from industrial wastewaters.