Simultaneous adsorption of phosphate and diclofenac by Li/Al layered double hydroxides loaded on modified wheat straw

Abstract

Various organic and inorganic pollutants co-exist in wastewater, including highly concerning emerging organic pollutants like diclofenac (DCF) and nutrient pollutants like phosphate. Their simultaneous adsorption can be an attractive and simple solution if an appropriate adsorbent could be provided. In this study, a new composite material (Li/Al-MWS) was obtained by loading Li/Al layered double hydroxides (Li/Al-LDH) on wheat straw which had been modified with the quaternary amino group and was applied to adsorb both phosphate and DCF. The results showed that within the pH range of natural water, Li/Al-MWS can highly adsorb both pollutants in large quantities, and the adsorption capacity was not compromised with coexisting Cl⁻ and NO₃⁻, but was significantly influenced by SO₄²⁻. The adsorbent exhibited good reusability for both pollutants even after six cycles. This is attributed to the grafting of the quaternary amino group in the straw skeleton and the Li/Al-LDH loaded on its surface, which provides a large number of active sites for the adsorbent. The adsorption mechanism of phosphate and DCF adsorption onto Li/Al-MWS was analyzed in detail and verified by material characterization. In addition, the fixed-bed column result demonstrated that Li/Al-MWS is potentially an effective adsorbent for simultaneous removal of nutrients and organic pollutants from tertiary wastewater.