Preparation and adsorption kinetics and thermodynamics of sodium humate‐modified diatomite

Abstract

Diatomaceous earth has been used as a nonorganic carrier to prepare a sodium humate modified diatomaceous space using the sol‐gel method. X‐ray diffraction, field emission scanning electron microscopy, transmission electron microscope, the Brunauer–Emmett–Teller (BET) method, and other methods were used to characterize its physio‐chemical properties. The effects of sodium humate/diatomite on the pH of tetracycline in water, the dosage of adsorbent, and pollutant temperature on the adsorption effect were studied. The results show that after alkali modification, the porous structure of diatomite remains undamaged, and the specific surface area of the modified sample is increased to 12.712 m2/g, and the average pore diameter is reduced to 146.19 nm. Adding 20‐mg sodium humate/diatomite into 100‐mL tetracycline wastewater with an initial concentration of 20 mg/L, and pH of 5 at a temperature of 55°C, the adsorption capacity reaches 75.1 mg/L, and the removal rate reaches 78.3%. The quasi‐second‐order kinetic model was fitted by regression and found to have R2 > 0.99, indicating that the adsorption process was one of surface adsorption. It is a process that involves initially rapid adsorption and then slowly reaching equilibrium. As an adsorption thermodynamics model, the Temkin, Redlich‐Peterson and Koble‐Corrigan models can explain humic acid sodium/diatomite behavior in the adsorption of tetracycline in water (each with R2 ≥ 0.99), and the effects of surface behavior in multilayer adsorption and electrostatic attraction on uneven heterogeneous adsorption.