Effectively eliminating lead and cadmium from industrial wastewater using a biowaste-based sorbent

Abstract

Toxic heavy metals, such as Pb(II) and Cd(II), pose serious environmental and health risks, stressing the urgent demand for innovative and sustainable techniques to reduce their adverse effects. This study investigates the use of sugar beet biowaste as an eco-friendly biosorbent for the removal of Pb(II) and Cd(II) from aqueous solutions, in both laboratory and industrial effluents. Characterization through scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, and energy-dispersive X-ray spectroscopy revealed the formation of stable hydrocerussite and otavite, confirming chemisorption. Approximately 95% of the employed biowaste is composed of calcium (Ca), carbon (C), and oxygen (O). The zeta potential was measured at − 17.5 mV with a point of zero charge at pH 8.0, and the total surface area of the biosorbent was approximately 7.72 m² g⁻¹, with a Langmuir surface area of 11.563 m² g⁻¹ and a pore volume of 0.028 cm³ g⁻¹. Various parameters, such as the metal concentration, biosorbent dosage, pH, temperature, and contact time, were optimized, achieving maximum removal of Pb(II) and Cd(II) within 60 min at pH 12 and 328 K. Sorption followed a pseudo-second-order kinetic model (R² = 0.99) and the Freundlich isotherm (R² = 0.98), with high sorption capacities of 466.5 mg g⁻¹ for Pb(II) and 505.6 mg g⁻¹ for Cd(II). Thermodynamic analysis indicated that the sorption process is spontaneous, thermodynamically favorable, and endothermic. The biowaste effectively removed heavy metals and demonstrated removal efficiencies exceeding 85% for most heavy metals in industrial effluent samples from Alexandria and Ain Sokhna. Sorption capacity ratio values close to 1 indicate effective Pb(II) and Cd(II) uptake with minimal interference, even in the presence of methylene blue dye. Comparative analysis revealed that the untreated biosorbent was more efficient than typical biosorbents, and an economic cost evaluation revealed that processing the biosorbent costs 1.05 USD/kg, highlighting its potential as a sustainable and economically viable option for industrial effluent treatment and supporting broader environmental goals.