(248e) Porous Iron Oxyhydroxide Having Dual Adsorption Site for Efficient Removal of Anions in Wastewater

Recently, harmful ion,
phosphoric acid ion, nitrate nitrogen and fluoride ion is contained so much in
agricultural effluent and industrial waste water.  This causes a serious
problem for the environmental protection of river and sea.  From these
situations, it is desired to develop an efficient adsorbent for various anions.
We try to develop a new cheap adsorbent having a high capacity for adsorbing
several anions selectively.  Iron oxyhydroxide was precipitated by dropping
NaOH aqueous solution into iron chloride aqueous solution under a strict control
kept at pH=5, and then calcinated at low temperature.  The internal surface
area of FeOOH prepared was over 200m²/g.  The FeOOH consisted of
beta-crystal and amorphous structures.  Various anions, F^-,
PO₄^3-, NO₃^- and
SO₄^2-, could be adsorbed by thus prepared porous
FeOOH.  The equilibrium amounts adsorbed by the porous FeOOH were several
ten times larger than those by conventionally used adsorbent.  For example,
more than 100 mg/g of phosphoric acid ion could be adsorbed.  In addition,
the FeOOH developed was the first adsorbent to adsorb fluoride ion completely in
the presence of other anions.  From several investigations, it was
clarified that the phosphoric acid ion adsorbed at the amorphous OH hydrogen
bond site, on the other hand, fluoride or nitrate ion adsorb to the tunnel site
of beta-crystal structure. We also confirm the ability of the FeOOH through the
long run experiment of actual wastewater using continuous adsorption equipment.
 Thus, it was clarified that the proposed adsorbent was effective for an
efficient treatment of anions in wastewater.