Mobility and retention of phenolic acids through a goethite-coated quartz sand column

In the present work, a natural mineral, such as quartz sand (NQS), was modified with a small amount of goethite to yield a goethite-coated quartz sand (GCQS) adsorbent that was used for depolluting water contaminated with a series of phenolic acids that have various numbers and positions of hydroxyl groups in the benzene ring. Thus, the transport and retention of gallic acid and its derivatives from water onto GCQS column were carried out at ambient temperature. Prior to the column adsorption experiments, the GCQS adsorbent was characterized with various methods such as X-ray diffraction, X-ray fluorescence, and scanning electron microscopy (SEM) coupled with X-ray microanalysis and zeta potential. The amount of adsorbed phenolic acid at the GCQS-water interface was found to be controlled by hydrogen bonding and electrostatic interactions, and it was tuned by varying parameters such as the aqueous phase pH, the ionic strength and the nature of inorganic ions. In addition, the effect of the number and the positions of hydroxyl groups (-OH) on the benzoic acid mobility was also examined. The data indicate that adding no more than 2.5 wt% of goethite to NQS shifts the solid Isoelectrical Point from 2.5 for pure NQS to 5.7 for GCQS and leads to a 16-fold increase in the maximum adsorbed amount of gallic acid. Moreover, the adsorbed amount of gallic acid was also found to decrease in the presence of inorganic anions in the order Cl- > NO3- > SO42- > H2PO4-, and to decrease as the ionic strength of the aqueous phase increases. This study brings new insight to the role of colloid and interface science for mineral processing and the environment.