A granular Cu-modified chitosan biocomposite for sulfate removal from laboratory and groundwater sources

Addressing sulfate contamination from aqueous sources via adsorption presents challenges due to its high solubility and hydration characteristics. Herein, a Cu-modified granular chitosan-based adsorbent (CHP-Cu) was prepared, and its sulfate adsorption characteristics from both laboratory water sources and groundwater samples wereinvestigated. Batch equilibrium and dynamic (column) adsorption studies were conducted, focusing on environmentally relevant pH (ca. pH 7) conditions. Adsorbent characterization was accomplished via spectral techniques (IR, Raman, X-Ray Photoelectron spectroscopy), surface charge measurement, and thermogravimetry. The sulfate adsorption in laboratory water followed the Sips isotherm model (407 mg/g); the maximum adsorption capacity under dynamic column conditions reached 146 mg/ and was fitted with the Thomas and the Yoon–Nelson model. To investigate the role of Cu-coordination for sulfate removal, a brief comparison of the removal (%) in four well water samples was performed with three different granular composites (non-imbibed, Ca-imbibed, and Cu-imbibed). While non-imbibed and Ca-imbibed adsorbents showed low to negligible uptake, the Cu-imbibed adsorbent resulted in a considerable sulfate removal capacity from environmental water sources. The dynamic uptake capacity of CHP-Cu in well water samples showed that the matrix influences the dynamic uptake capacity, where the uptake increased from 120 mg/g (ca. 900 mg/L sulfate) to 134 mg/g (ca. 2100 mg/L sulfate), then 144 mg/g (ca. 2800 mg/L sulfate), and then to 153 mg/g (ca. 6800 mg/L sulfate).