Abstract

Ferric groundwater treatment residual (Fe-GWTR) collected from a Finnish groundwater treatment plant were recovered for use after acid dissolution as an iron source for an inorganic-organic hybrid material. Acid dissolution, performed with 1 mol/L hydrochloric acid and mixing for one hour at room temperature, was determined as the optimal condition based on a high Fe concentration and low concentration of interfering elements. Peat modification was conducted at pH values of 3, 5 and 7 with both a commercial iron reagent (FeCl3·6H2O) and Fe-GWTR solution for comparison. A modification pH of 3 resulted in the highest vanadium removal efficiency for both iron sources. The isoelectric point (pHIEP) of Fe-GWTR-modified peat at pH 3 (Fe-GWTR-P3) was found to be 5.0. After modification, it was confirmed that BET surface area and pore volume of the peat were enlarged. Maximum capacity was found to be around 16 mg/g with a 24-hour contact time at pH 4 and a good fit was achieved with the Redlich-Peterson isotherm model. The kinetic data followed the Elovich equation, which refers to the chemisorption mechanism. According to intra-particle diffusion and Boyd models, the adsorption was a two-step diffusion process, with intra-particle diffusion being the slowest step. This study demonstrates that Fe-GWTR could safely be used as an iron source for biomass modification, and Fe-GWTR-P3 could be used as a low-cost and effective sorbent for vanadium-containing wastewater treatment.