Arsenic removal by natural and chemically modified water melon rind in aqueous solutions and groundwater

Contamination of groundwater with toxic arsenic (As) has become an emerging health and environmental problem around the world, which has seen significant attention amongst the scientists for development of new sorbents to remediate As-contaminated water. Here, we explored the arsenate (As(V)) and arsenite (As(III)) sorption to natural water melon rind (WMR), xanthated WMR and citric acid-modified WMR in aqueous solutions, and determined potential of the most potent sorbent for As removal in groundwater. Xanthated WMR (X-WMR) showed relatively higher As(V) and As(III) removal than the citric acid modified WMR (CA-WMR) and natural WMR. The maximum As(III) (99%) and As(V) (98%) removal was obtained at pH 8.2 and 4.6, respectively, by X-WMR at 4 mg L⁻¹ initial As(V) and As(III) concentrations and sorbent dose of 1 g L⁻¹. Langmuir isotherm model best fitted (R² of up to 0.96) the data both for As(III) and As(V) sorption to X-WMR. Sorption kinetics of As(V) and As(III) was well described (R² of up to 0.99) by the pseudo second-order model on surface of the X-WMR. Thermodynamic investigations revealed that As(V) and As(III) sorption was endothermic and spontaneous. The FTIR spectroscopy depicted the presence of different surface function groups (–OH, –COOH, S-bearing (C=S, S=O and S–S)) which were involved in As(V) and As(III) sequestration on the sorbents examined here. Significantly, X-WMR showed (up to 49%) greater As(III) and As(V) sorption than that of natural WMR. Our results demonstrated that X-WMR efficiently removed 94%–100% (n = 16) of As from As-contaminated drinking well water which possessed detectable concentrations of some anions (e.g., SO₄, CO₃, HCO₃). This study highlights that the X-WMR has potential to remove As, notably As(III), from solutions and drinking water, and might be utilized as a reactive medium for the treatment of As-contaminated water.