Preparation of Iron-Loaded Maritime Pine Tannin Resins for Arsenic Uptake from Water

Tannin materials have been reported as efficient adsorbents toward several compounds. Here, an iron-loaded maritime pine tannin resin was produced and applied for arsenic removal from water. The production of the adsorbent started with tannin extraction in alkaline aqueous solution (optimal conditions: 60 min, 90 °C, and 7.5% w/w NaOH), yielding 143 ± 7 mg of formaldehyde-condensable phenols per g of bark used. After gelification (maximum efficiency of 80%), the resin was oxidized in nitric acid solution at 50 °C and loaded with iron (1250 mg-Fe L⁻¹ at pH 2). This chemical modification was done to enhance the affinity to As. The resultant product had an iron content of approximately 20 mg-Fe g⁻¹. Samples of this resin with different particle sizes were evaluated for As(III) and As(V) uptake. Within the conditions studied, the removal efficiencies were quite modest but potentially improvable. Both Langmuir and Freundlich models described well the adsorption data of As(V). The maximum adsorption capacity, predicted by the Langmuir model, was 0.3 ± 0.1 mg g⁻¹.