Abstract:
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Abstract
The use of biosorption to complement conventional water treatment techniques has gained
widespread appeal partly due to the abundance of waste materials that can be used as low
cost biosorbents. However, some materials have not yet been exploited in this regard. This
research was aimed at evaluating the biosorption potential of Mangifera indica (mango) seed
shells that are readily available in several farming areas of the Limpopo and Mpumalanga
Provinces of South Africa.
In this work, powdered ethylenediaminetetraacetic acid (EDTA) functionalized biosorbent was
prepared from alkali treated biomass of waste mango seed shells. The influence of alkali
treatment and EDTA functionalization on the physicochemical properties of the biomass was
characterized using Fourier transform infra-red spectroscopy, X-ray diffraction and
thermogravimetric analysis. Results confirmed removal of hemicelluloses, conversion of
crystalline to amorphous cellulose and the introduction of carboxyl, ester and tertiary amine
groups from EDTA. Furthermore, the powdered biosorbent was immobilized using calcium
alginate for adaptation to column sorption.
The powdered biosorbents were tested for sorption of lead(II) ions using batch sorption
experiment. Through EDTA functionalization, improvement in sorption capacity for lead(II)
ions from 59.25 mg.g-1 to 306.33 mg.g-1 was realized. The Langmuir and Pseudo-nth order
models most suitably simulated the equilibrium and kinetics of sorption by both functionalized
and non-functionalized biomaterials. The calcium alginate immobilized biosorbent was
evaluated for non-specific sorption of ionic species of copper, chromium, nickel and iron from
electroplating wastewater through discontinuous column sorption experiments. Highest
copper, chromium, nickel and iron removal was 12.3%, 14.8%, 4.4% and 13.8% from nonacidified
samples at an initial pH of 3.4, and 15.5%, 18.7%, 13.7% and 17.3% from samples
acidified to an initial pH of 1.8. Repeated sorption-desorption cycles involving acidified
wastewater resulted in successive improvement in metal uptake against declining recovery
indicating irreversible binding on –COOH groups formed from –CH2OH groups through a
redox reaction involving reduction of chromium(VI) to chromium(III).
Keywords: Mangifera indica; biosorption; alkali treatment; carboxyl functionalization; calcium
alginate
