Utilizing Thermally Regenerated Diatomaceous Earth from Spent Diatomaceous Earth to Remove Lead Ions from Wastewater

This study describes a method of removal of lead ions (Pb²⁺) in wastewater using thermally regenerated diatomaceous earth formed from spent diatomaceous earth (SDE) under 400 and 800 °C (SDE-400 °C and SDE-800 °C, respectively). SDE is generated as an industrial waste from raw diatomaceous earth (RDE or simply called DE) used in food processing and brewery industries. This study reveals the effectiveness and efficiency of SDE as an adsorbent for removing Pb²⁺ from aqueous solutions with respect to adsorbent dosage and the contact time. A well-organized porous structure with some particles on the surface is shown by the surface morphology of the SDE dry form as determined by field emission scanning electron microscopy (FE-SEM). Surface area (BET) analysis of DE and the dry form of SDE was carried out at liquid nitrogen temperature, and discovered that DE has a higher specific surface area and total pore volume of 3.70m² g^–1 and 0.015 cm³ g^–1, respectively, than those of SDE dry form, in which the values were 2.22 m² g^–1 and 0.010 cm³ g^–1. The optimal conditions for Pb²⁺ adsorption onto SDE were identified. The adsorbent dosage of 50mg and contact time of 180 min at a pH of 4.8, sustained for 50 mL of lead solution at 25 °C, produced the maximum adsorption. The equilibrium results of the investigated systems were interpreted using the Freundlich and Langmuir adsorption isotherm models. With the maximum adsorption capacities of 92.60, 163.93, 208.33, and 322.58mg g^–1 of Pb²⁺, the Langmuir model best fitted the adsorption properties of Pb²⁺ on DE (or RDE), SDE, SDE-400 °C , and SDE-800 °C. Due to the presence of chemisorption, the present study further suggests that SDE-800 °C is a more advantageous application of SDE as an effective material for the application in removal of Pb²⁺ from aqueous solutions for industrial wastewater treatment than the other three adsorbents.