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|Title: ||Preparation and properties of granular ferric hydroxide as an adsorbent in potable water treatment|
|Authors: ||Newton, Nichola|
Granular ferric hydroxide
|Issue Date: ||2002|
|Publisher: ||© Nichola Newton|
|Abstract: ||Three iron oxide materials have been studied for uptake of three anions (arsenate,
phosphate and fluoride) and a cation (cadmium) from aqueous solutions.
Two of the materials were produced using original procedures developed
at Loughborough University. The former material was conditioned by
a controlled freeze-thaw procedure to enhance granularity and the latter was
air-dried at room temperature. Their capacities were compared with a commercially
available material supplied by GEH Wasserchemle, Germany. Pore size distributions and specific surface area values were determined by N2 analysis at 77 K. All samples possessed a reasonable specific surface area, in the range 200-300 m2/g and were mesoporous. Samples produced at Loughborough University also contained some macropores, evidence of a more amorphous
structure or lack of pH control during production. X-ray diffraction indicated that all samples had some b-FeOOH present and
that the chloride content and production pH affected the material crystallinity.
Crystallinity increased with increasing chloride content and a higher production
pH resulted in the presence of more than one phase.
Chemical characterisation was also completed on all three samples. The point
of zero net proton charge and isoelectric point for each material was obtained
by potentiometric batch titrations and zeta potential measurements respectively.
The difference in these values increased with a higher chloride content
and all samples studied possessed a positive surface at low pH and negative
surface at high pH. These parameters were not greatly affected by the background
electrolyte concentration, implying that the background electrolyte is
not specifically adsorbed. However, arsenate and phosphate appeared to be
specifically adsorbed as the isoelectric point decreased.
The uptake capacities for arsenate, phosphate. fluoride and cadmium of all
three samples were obtained by measuring batch isotherms at 25 degrees C. The
pH range was 4-9, using various initial concentrations up to a maximum of
approximately 30 uM. For all anionic species studied, the capacity decreased with increasing pH, and the reverse trend was noted for cadmium. The Langmuir model provided a
good fit for the anionic isotherms and the Freundlich model for the cationic
isotherms. The materials studied possessed a markedly higher capacity for
fluoride than arsenate and phosphate, with an intermediate capacity for cadmium.
This indicates that fluoride is attached to the surface via monodentate
(single) bonds, whilst both arsenate and phosphate are primarily attached to
the surface via bidentate (two) bonds. Cadmium is probably bound by both
The effect of competing anions on arsenic uptake capacity was determined using
mini-column experiments of binary (arsenate-fluoride, arsenate-Phosphate
and phosphate-fluoride) and ternary (arsenate-fluoride-phosphate) mixtures.
Arsenate removal was strongly affected by the presence of phosphate, but was only slightly lower in the presence of fluoride. (Continues...).|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Chemical Engineering)|
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