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Adsorption of arsenic (V) and
arsenic (III) onto different uncalcined and calcined aluminium hydroxide
powder
Fine (1.5µm) and coarse (~100µm)
aluminium trihydroxide (ATH), gibbsitic in nature and low bulk density
(0.3g/cm3) gel aluminium hydroxides (basic aluminium sulfate,
BAS) were used as precursor material for obtaining various calcined products
at different temperatures up to 1200oC. These calcined products were used
for adsorption of As(III) and As (V) from aqueous media. As(III) and As(V) adsorptions were found effective for fine gibbsitic materials calcined
at 350oC and for coarse gibbsite particles calcined at 400oC. Similarly low
bulk density BAS calcined at different temperatures up to 900oC showed high adsorptibility for As(V) but As(III) separation was not effective.
Gibbsite when heated between 350oC –400oC transformed to boehmite while low
bulk density BAS remained amorphous up to 800oC and at 900oC it transformed
to η-alumina. It was found that chi and kappa forms of transition aluminas
formed by calcining gibbsite at 500oC and 1000oC respectively showed lower
adsorption efficiencies than boehmite phase. The
α-alumina obtained from
different sources showed different adsorptibility for As(V) and As(III).
Variation of temperature and pH showed dependency of adsorptribility on such
parameters. It was found further that degree of dehydroxylation had effect
on the adsorptibility. Total dehydroxylation such as in the case of
α-alumina, had no or less activity. Surface area showed beneficial effect on
adsorption. The crystalline phase, extent of dehydroxylation and
desulfurisation, surface area, starting precursor etc., were found to have
bearing on adsorption efficiency of a material. The As(III) adsorption
showed major dependency on surface area but As(V) adsorption showed
combined dependency on above parameters. |
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