Preparation and characterization of acid-leached diatomaceous earth for application in the treatment of oily wastewater

Abstract

This study evaluated the potential application of acid-leached diatomaceous earth in oily wastewater treatment. Acid-leached diatomaceous earth was prepared by treating diatomaceous earth using 2.2 M HNO3 to remove impurities. The leached diatomaceous earth was characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and Brunauer Emmett Teller (BET) analytical techniques to determine the crystallinity, elemental content, morphology and surface area, respectively. Response surface methodology (RSM) was employed to establish the optimum conditions on the treatment of oily wastewater using acid-leached diatomaceous earth. Elemental composition of acid-leached DE showed an increase in silica content reaching 91.57% from 78.98% and a decrease on elements such as CaO, K2O, MgO, and Fe2O3 associated with impurities such as carbonates and clay minerals. BET analysis showed an increase in pore volume and surface area from 60.88 to 68.71 Å and 15.02–22.40 m2/g following the acid leaching. The oil removal experiments revealed a maximum adsorption capacity of 124.16 mg/g and oil removal efficiency of 78.55% at an initial oil concentration of 3229.69 using 0.05 g adsorbent dosage and 119.20 min contact time. The adsorption kinetics data fitted better to pseudo-second order model (R2 = 0.98) of reaction kinetics indicating that adsorption occurred through chemisorption. The adsorption isotherms were described better by the Freundlich isotherms model (R2 = 0.87) indicating that adsorption occurred in a heterogeneous and multilayer surface. This study concluded that acid-leached DE has the potential for use in treatment of oily wastewater. However, further studies are encouraged to evaluate the regeneration and re-usability of the material.