3.1.4. Effect of initial pH
It is well documented that pH of the biosorption medium is an
important parameter affecting the uptake of heavy metals from
aqueous solutions by biosorbent. Fig. 4 summarizes the removal of
Cu(II), Ni(II) and Zn(II) by MOSB from aqueous solutions as a function
of pH. Itis observed thatthe biosorption ofthe metal ions Cu(II)
and Zn(II) increased dramatically with increase in initial solution
pH, reaching an optimum value at 3.5, i.e. sorption capacity then
tends to level off. The increase in biosorbed for Ni(II) is more gentle
initially and begins to increase sharply at pH 5 reaching maximum
at pH 7 (this trend is not so obvious in Fig. 4 unless the Ni(II) data
is plotted alone). The lower removal of the studied metal ions at
below optimum pH values can be attributed to the effective competitionbetweenhigher
concentrationof H+ or H3O+ andmetal ions
present in the form of M2+ or M(OH)+ according to their speciation
diagrams [21]. From these results, the MOSB is effective in removing
metal ions in wide pH range. The results have shown that the
powder of the MO seeds keeps its adsorption power at neutral pH
(i.e. pH 7). The elimination of the pH adjusting step for the adsorption
process on a large scale is favorable because it simplifies the
process and results total costs. Previous studies have shown that
the main component for water treatment in the MO seeds is protein
whose isoelectric point is about pH 10 and the properties such
as fluorescence [22], circular dichroism [23] and zeta potential [24]
are independent of pH in the range 4–9. Based on these results and
FTIR data reported, it is not surprising that the MOSB is effective in
such a wide pH range.
3.1.4. Effect of initial pHIt is well documented that pH of the biosorption medium is animportant parameter affecting the uptake of heavy metals fromaqueous solutions by biosorbent. Fig. 4 summarizes the removal ofCu(II), Ni(II) and Zn(II) by MOSB from aqueous solutions as a functionof pH. Itis observed thatthe biosorption ofthe metal ions Cu(II)and Zn(II) increased dramatically with increase in initial solutionpH, reaching an optimum value at 3.5, i.e. sorption capacity thentends to level off. The increase in biosorbed for Ni(II) is more gentleinitially and begins to increase sharply at pH 5 reaching maximumat pH 7 (this trend is not so obvious in Fig. 4 unless the Ni(II) datais plotted alone). The lower removal of the studied metal ions atbelow optimum pH values can be attributed to the effective competitionbetweenhigherconcentrationof H+ or H3O+ andmetal ionspresent in the form of M2+ or M(OH)+ according to their speciationdiagrams [21]. From these results, the MOSB is effective in removingmetal ions in wide pH range. The results have shown that thepowder of the MO seeds keeps its adsorption power at neutral pH(i.e. pH 7). The elimination of the pH adjusting step for the adsorptionprocess on a large scale is favorable because it simplifies theprocess and results total costs. Previous studies have shown thatthe main component for water treatment in the MO seeds is proteinwhose isoelectric point is about pH 10 and the properties suchas fluorescence [22], circular dichroism [23] and zeta potential [24]are independent of pH in the range 4–9. Based on these results andFTIR data reported, it is not surprising that the MOSB is effective insuch a wide pH range.
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