Enhancing arsenic removal using Cu-infused biochar: Unravelling the influence of pH, temperature and kinetics

Arsenic contamination, at lower concentrations (up to 500 µg L-1), is an important environmental concern but has received limited attention. Adsorption capacities, kinetics and equilibrium phenomena are concentration dependent. Previous studies focused on higher arsenic concentrations associated with industrial discharges, failing to address arsenic contamination in drinking water. This study investigates arsenic adsorption using Eleocharis dulcis biochar loaded with CuO (EDB-CuO) at lower concentrations (up to 500 µg L-1). The synthesized biochar was characterized by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Point of Zero Charge (PZC) and Scanning Electron Microscopy (SEM). Batch adsorption experiments were conducted, varying time, concentration, temperature and pH. Results indicated that increasing temperature positively influenced arsenic adsorption onto EDB-CuO, while pH had an opposite effect, with maximum adsorption occurring at lower pH levels (2-3). The equilibrium time was established at 240 min for arsenate adsorption. Kinetic data best fitted the Ho and McKay’s plot and the Langmuir model calculated a maximum adsorption capacity of 26.1 mg g-1. Thermodynamic parameters, including enthalpy, entropy and activation energy, supported the conclusion that the arsenate adsorption process was spontaneous and chemisorptive. Column studies demonstrated remarkable adsorption retention performance (>88%) of the composite for arsenate removal over 8 h. Similarly, a fixed-bed column experiment was conducted to study the adsorption mechanism of arsenate on EDB-CuO by employing the Bohart-Adams, Thomas, and Clark models. The Clark model was found to best describe the arsenate removal mechanism. Additionally, recycling studies of arsenate from the loaded EDB-CuO surface were investigated up to 4 adsorption-desorption cycles. A small decrease was observed in the second cycle, from 92.06% removal to 85.15%, which further decreased in the third cycle (62.18%), and even more in the fourth cycle (30.8%).