a b s t r a c tGalvanic couples composed of zero-valent iron and activated carbon (Fe 0 /AC) were investigated for As(V) removal from water. The effects of Fe 0 to AC mass ratio (FCR), solution pH, ionic strength and co-existing anions (phosphate, carbonate, silicate, nitrate, chloride and sulfate) and humic acid (HA) on As(V) removal were evaluated. The results showed that the optimum mass ratio was 1:1, and Fe 0 /AC with this ratio was more effective for As(V) removal than Fe 0 and AC alone at pH of 7 and ion strength of 0.03 M NaCl. The enhanced performance for As(V) removal was fulfilled through an accelerated corrosion process of Fe 0 , which meant more corrosion products for efficient As(V) removal. The As(V) removal followed a pseudo-first order reaction. The rate constants (k) for 1:1 Fe 0 /AC and Fe 0 alone were 0.802 and 0.330 h −1 , respectively. Potentiodynamic polarization scans further confirmed that Fe 0 corrosion was promoted when Fe 0 was coupled with AC. Except silicates, other co-existing anions promoted As(V) removal. No reduction form of As (As(III) or As(0)) could be detected on iron corrosion products (ICPs) and in solutions. Identified ICPs included poorly crystallized lepidocrocite (␥-FeOOH) and magnetite/maghemite (Fe 3 O 4 /␥-Fe 2 O 3 ) for both of Fe 0 /AC and Fe 0 systems. In conclusion, the Fe 0 /AC couple exhibited higher As removal performance than that of Fe 0 alone from water.
In order to explain the field dependence of the steady-state electric birefringence of disk-shaped particles, a new orientation function was derived on the basis of the permanent dipole, saturable and unsaturable induced moment (PD-SUSID) mechanism. In this derivation, the covalent andor ionic polarizability anisotropy (Aa") responsible for the unsaturable induced dipole moment (Aa"E) was considered to be negative. This is the assumption that the plane of a disklike particle is oriented parallel to the direction of applied external field at infinitely high fields. Typical curves of the theoretical orientation function O@,p,,p,y") were graphically illustrated, and special features thereof were elaborated upon. The theoretical curves revealed some interesting characteristics associated with increasing field strengths; e.g., the theoretical orientation function plotted against the second power of field strength showed a positive maximum in certain cases, even if no permanent dipole moment was present. Comparison was made between the theoretical curves and the electric birefringence data experimentally measured up to 0.8 kV/cm for montmorillonite particles suspended in 1 x mol/dm3 NaCl aqueous solution at 25 "C. The results indicated that the newly derived PD-SUSID orientation function for disklike particles reproduces the field strength dependence of the experimental data of the clay particle quite well.
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