Wednesday, November 15, 2006

Arsenite Removal from Water using Ferrate [Fe( VI)] in Combination with Ferric or Aluminum Salts.

Amita Jain, Florida A&M Univ, 109 South Perry Paige Bldg., Tallahassee, FL 32307

Arsenic is a highly toxic and carcinogenic element.  Drinking water is one of the major sources of arsenic exposure to humans.  In natural water, arsenic is primarily present in inorganic forms as oxyanions of trivalent arsenite [As(III)] and pentavalent arsenate [As(V)].  Several treatment technologies are available for the removal of arsenic from waters; however these technologies are effective for the removal of As(V) but not for As(III).  It would be more feasible and effective if As(III) can be converted into As(V) before its removal.  Ferrate seems to be a promising candidate for arsenite removal from water because of its high oxidizing power, selectivity, coagulant properties and the ability to form a non-toxic byproduct Fe(III).  The objective of this study is to evaluate the efficiency of ferrate or ferrate in combination with Fe(III) or Al(III) salts to remove arsenite from water.  The effect of phosphate, silicate and bicarbonate on the removal of arsenite was also evaluated.  Potassium ferrate was prepared by hypochlorite oxidation of ferric nitrate.  Batch experiments were conducted by adding various concentrations of ferrate (6.7-134 µM) and ferric chloride or aluminum chloride (13-127 µM) to the arsenite solution (6.7 µM).  After 24 h of equilibration, the sample was filtered using 0.2 µm pore size filter membrane.  Arsenic was analyzed by atomic absorption spectrometer using graphite furnace and hydride generation techniques.  Ferrate in combination with Al(III) was much more effective than with Fe(III) to remove arsenite below the maximum contaminant level of arsenic in drinking water (10 ppb).  It is conceivable that mixed Fe and Al phases provide more surface sites for arsenic adsorption than individual phase.  The competing anions studied had a detrimental impact on the removal of arsenic.