NAMS 2002 Workshop - ICOM 2008

Nanofiltration and Reverse Osmosis III - Applications – 4
Friday July 18, 11:15 AM-11:45 AM, Maui
Nanofiltration of Ferric and Ferrous Cations in Acidic Solutions
X. Bernat (Speaker), ETSEQ, Universitat Rovira i Virgili, Terragona, Spain
F. Stüber, ETSEQ, Universitat Rovira i Virgili, Terragona, Spain
A. Fortuny, Universitat Politècnica de Catalunya, Barcelona, Spain
C. Bengoa, Universitat Rovira i Virgili, Terragona, Spain
A. Fabregat, ETSEQ, Universitat Rovira i Virgili, Terragona, Spain
J. Font, ETSEQ, Universitat Rovira i Virgili, Terragona, Spain - jose.font@urv.cat
Ferric and ferrous ions are used as catalyst in advanced oxidation processes, in
conjunction with hydrogen peroxide, to accelerate oxidation reactions for partially
mineralizing organic biorefractory substances. Fenton process, Fe/H2O2, is the
most popular technique based in this principle. As a result, homogeneous iron
leaves the oxidation step with the treated wastewater posing potential
environmental and economical problems. Nanofiltration is being studied and
applied as a promising technology to recover multivalent ions and organic
compounds from aqueous polluted streams achieving additionally partial
softening of these waters. Several mechanisms such as charge repulsion
between the membrane and the targeted compound and sieving are involved in
the mechanisms allowing the retention of the targeted ions or compounds. In
addition, several operating variables may affect the efficiency of the separation
process by lowering the permeate fluxes during the operation. The
transmembrane pressure, the pH, the hydrodynamic conditions, the presence of
other species and still others may influence the retention, the permeate rate and
the fouling during the filtration process. In this work, the recovery of ferrous and
ferric ions from aqueous solution by nanofiltration is presented. The experiments
were conducted in a commercial batch stirred filtration cell. The effect of several
operating variables on both the iron retention and the permeate flux were
studied. NF, NF90 and NF270 membranes (manufactured by Dow Filmtec) were
selected for this work as they are commercially available membranes that
possess different isoelectric points and charge densities on their surfaces. The
solutions to be treated were adjusted at pH 2, which is typical pH for effluents
treated by Fenton process. The effect of the transmembrane pressure, the
stirring speed, the presence of NaCl and the iron concentration on the iron
retention and permeate flux decline is illustrated. The results show that low
permeate flux decline was achieved and high Fe (III) retention (up to 99.9%) was
obtained with all the tested membranes, assuring the final quality of the permeate
and the possibility of reusing the retentate in the oxidation reactor. When
comparing Fe (III) and Fe (II) performance, a lower iron charge caused a
decrease of the iron retention due to the poorer charge repulsion phenomena
between the charged membrane surface and the Fe (II) ions. NF90, which is a
specially designed membrane for the recovery of iron, showed the highest Fe (III)