One-step treatment of hydrometallurgical wastewater of photovoltaic laminates with ferrite process under weak alkali conditions: Regulation, precipitation characteristics, and mechanism

The metal ions contained in the hydrometallurgical wastewater from decommissioned photovoltaic laminates are harmful to the environment. A high-efficiency ferrite one-step strategy is proposed to regulate and treat these metal ions under weak alkaline conditions. The optimal experimental conditions (pH = 8, n(Fe 3+ ):n(Fe 2+ ) = 1, n(Fe 2+ ):n(Me) = 7.5, t = 10 min, T = 55 °C) resulted in a 99.04 % removal of metals from wastewater. The residual concentration of metals complies with the emission standards of China. Through XRD, XPS, SEM and TEM characterization of the precipitate, it was determined that the main components were ferrites. Cu 2+ is introduced into the spinel lattice to form CuFe 2 O 4 , which is the key to achieving one-step stability, whereas other metal ions are stably encapsulated and removed in a composite form. The TEM and vibrating sample magnetometry characterization showed that the precipitate had a large specific surface area and high saturation magnetization. Under a 1500 Gs magnetic field, the sedimentation rate was increased by 80 % compared to natural sedimentation, achieving rapid solid-liquid separation. The removal of multiple metals from the waste liquid undergoes two stages: the formation and doping of ferrite, and the stable encapsulation of metal compounds by ferrite. The resulting composite precipitates exhibit high stability and have potential applications in adsorption, wave absorption, catalysis, and various other fields after drying. This provides a green, circular and efficient approach for the treatment, disposal, and resource utilization of photovoltaic modules during the decommissioning stage.