Photocatalytic Reduction and Crystallization Hybrid System for Removal and Recovery of Lead (Pb)

The heavy metal lead (Pb) is toxic to humans, animals, and plants and shows persistence and is nondegradable in aquatic media. A novel method has been proposed using photocatalysis (PC) and reduction crystallization (RC) for efficient removal and recovery of lead (Pb) from the aqueous phase. Using photocatalysis, maximum removal of lead ions (Pb2+) was 79.6% under optimized conditions (2 g L–1 TiO2, pH 5.3, and 35 W cm–2 UV light intensity). However, reduction crystallization removed 90% lead ions (Pb2+) using hydrazine hydrate as a reduction agent with optimized parameters (pH 10 and temp 80 °C). To achieve maximum removal as well as recovery of toxic lead, both methods, photocatalysis and reduction crystallization, were combined, removing 98.2% of lead ions (Pb2+) from the aqueous phase. The recovered precipitates and photocatalysts (TiO2) were analyzed using scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) techniques after applying processes at optimized conditions. The EDS spectrum showed that the recovered precipitates and TiO2 contained the lead (Pb) element. The XRD peak analysis showed that precipitates contained lead having the crystallite size of around 90 nm, whereas the XRD spectrum of recovered titanium dioxide indicated additional peaks at specific angles, showing lead deposition on the TiO2 surface. The rate of photocatalytic removal of lead ions (Pb2+) followed the Langmuir–Hinshelwood equation of the first order.