This slide presentation outlines a study on the effect of pH, Phosphate, and vanadate on As(III/V) adsorption during coagulation-filtration with zirconium, titanium, and ferric salts. Specific objectives included: determining the feasibility of using zirconium and
titanium salts in comparison to ferric chloride as
coagulants for Arsenic removal;
studying the individual and combined effects of pH
and competing ions including
silica (0, 20 mg/L, NSFI water w/wo PO<sub>4</sub>), phosphate (0, 40 µg P/L, NSFI water w/wo SiO<sub>2</sub>), and
vanadate (0, 50 µg/L in NSFI water w/wo SiO<sub>2</sub> and PO<sub>4</sub>); and,
studying the toxicity characteristics of the sludges
using TCLP and California WET tests. Conclusions for As(III) indicated that: As(V) removal was pH dependent, and the
removal increased with decreasing pH for all
coagulants;
Fe(III) was a much better coagulant than
Ti(III), Ti(IV), and Zr(IV) at pH 6.5 and 8.5 for
As(V) removal. At pH 8.5, Fe(III),Ti(III), and
Ti(IV) were similar; Ti(III) was superior to the other
coagulants at pH 6.5 and 7.5, but at
8.5, the Fe and Ti coagulants were
similar in performance; and,
As(III) was oxidized to As(V) in the
presence of Ti(III). The oxidation
continued for several hours due to the
slow rate of formation of H<sub>2</sub>O<sub>2</sub> and
oxidation of As(III) by H<sub>2</sub>O<sub>2</sub>. Conclusions for competing ions indicated that: for As(V) and As(III), Silica competition significantly
reduced the adsorption, the detrimental effect of silica
increased with increasing pH, the presence of
phosphate lessened the detrimental effect of silica at all
pHs;
in the absence of silica, phosphate significantly reduced
the adsorption of As(V) at all pHs, and had a minor effect
on the adsorption of As(III) at pH 7.5 and 8.5, in the
presence of silica, phosphate significantly reduced As(V)
adsorption at pH 6.5 and 7.5, phosphate had no effect on
the adsorption of As(III) at any pH when SiO<sub>2</sub> was pres.; and,
in the absence of silica and phosphate, vanadate
significantly reduced the adsorption of As(V) at all pHs,
and had a minor effect on the adsorption of As(III) at pH
7.5 and 8.5. But in the presence of silica and phosphate,
vanadate did not have significant effect on the
adsorption of As(V) or As(III) at any pH. General conclusions indicated that: in-situ formed hydroxides had significantly
higher adsorption capacities compared
with the granular media, probably due to
high effective surface area of the
coagulants; and,
the settled liquid wastes contained less
than 0.5% dry solids and, defined as
TCLP extracts, easily passed the TCLP
and California WET tests. Includes figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 1.6 MB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 25 |
| Published : | 06/01/2006 |
