Adsorption Removal of Arsenic From Water Using Iron Hydroxide Loaded Cellulose Beads
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Arsenic contamination in groundwater has posed global challenges to drinking water supply. Due to the awareness of its toxicity and chronic effects on human health, removal of arsenic from water using adsorptive materials has been extensively studied. Iron-based composite materials are a group of promising adsorbents due to their high affinity to arsenic species. In the present research, iron hydroxide loaded bead cellulose adsorbents have been synthesized through a one-step hydrolysis and coating procedure using five different loading percentages ranging from 3.8% to 21.7% in terms of mass of iron. Adsorption kinetics at various concentrations of arsenite (As(III)) and arsenate (As(V)) were tested in batch experiments. The adsorption competition by coexisting phosphate and sulphate and the regeneration performance were also investigated. The adsorption kinetics were modeled using the Pseudo-second-order kinetics equation and the calculated equilibrium concentrations and adsorption capacities were used to build the adsorption isotherms, which were then fitted using Langmuir and Freundlich equations. The Langmuir adsorption capacity (in terms of mg arsenic per g dry mass of bead) of As(III) increased from 49.9 mg/g to 92.0 mg/g when the iron content increased from 3.84% to 17.7%, followed by a slight decrease to 86.1 mg/g when the iron content continued increasing to 21.7%. The adsorption capacity for As(V) showed a linear increasing, reaching 26.9 mg/g, with the increase of iron content. The coexisting PO43- of 5 mg P/L and 500 mg SO42-/L reduced the equilibrium adsorption capacity for As(III) by 14.5% and 24.4%, respectively. After two cycles of regeneration by 2.0 M NaOH solutions, the adsorbent showed 99.2% of the original adsorption capacity for As(III). The breakthrough behavior of As(III) and As(V) were investigated in packed bed column experiments. To determine the dispersion coefficients of arsenic in the column, the breakthrough curve of methylene blue as a tracer was obtained and modeled using the equilibrium convection diffusion equation. The estimated dispersion coefficient was 1.9 cm2/h at a flow rate of 361.4 cm/h for As(III) and 2.9 cm2/h at 561.1 cm/h for As(V), respectively. Parameters controlling the breakthrough behavior of arsenic were then estimated by fitting the Two-sites nonequilibrium convection diffusion equation to the experimental data using the Stanmod modeling package. The results showed that almost all the adsorption sites (96.46% for As(III) and 99.56% for As(V)) were at nonequilibrium adsorption state. The first order kinetics controlled the adsorption of As(III) and As(V) in the column at a rate of 0.0017 h-1 and 0.0018 h-1, respectively. The estimated partition coefficient for As(III) and As(V) was 99812.7 L/kg and 200721.8 L/kg, respectively.