In order to reduce the total number of experiments for achieving the best conditions for Cr(VI) uptake using
Araucaria angustifolia (named pinhão) wastes as a biosorbent, three statistical design of ...experiments were carried out. A full 2
4 factorial design with two blocks and two central points (20 experiments) was experimented (pH, initial metallic ion concentration—
C
o, biosorbent concentration—
X and time of contact—
t), showing that all the factors were significant; besides, several interactions among the factors were also significant. These results led to the performance of a Box–Behnken surface analysis design with three factors (
X,
C
o and
t) and three central points and just one block (15 experiments). The performance of these two statistical designs of experiments led to the best conditions for Cr(VI) biosorption on the pinhão wastes using a batch system, where: pH 2.0;
C
o
=
1200
mg
l
−1 Cr(VI);
X
=
1.5
g
l
−1 of biosorbent;
t
=
8
h. The maximum Cr(VI) uptake in these conditions was 125
mg
g
−1. After evaluating the best Cr(VI) biosorption conditions on pinhão wastes, a new Box–Behnken surface analysis design was employed in order to verify the effects of three concomitant ions (Cl
−, NO
3
− and PO
4
3−) on the biosorption of Cr(VI) as a dichromate on the biosorbent (15 experiments). These results showed that the tested anions did not show any significant effect on the Cr(VI) uptake by pinhão wastes. In order to evaluate the pinhão wastes as a biosorbent in dynamic system, a glass column was fulfilled with pinhão wastes (4.00
g) as biosorbent, and it was fed with 25.0
mg
l
−1 Cr(VI) at pH 2.0 and 2.5
ml
min
−1. The breakpoint was attained when concentrations of effluent of the column attained the value of 0.05
mg
l
−1 Cr(VI) using 5550
ml of the metallic ion solution. In these conditions, the biosorbent was able to remove completely Cr(VI) from aqueous solution with a ratio of Cr(VI) effluent volume/biosorbent volume of 252.3.
A new sorbent was synthesized by anchoring 7-amino-4-azaheptyltrimetoxisilane, freshly prepared, to silica gel, producing 7-amino-4-azaheptyl anchored silica gel (AAHSG). This material was ...characterized by infrared spectroscopy (IR), elemental analysis (CHN), and nitrogen adsorption-desorption isotherms. Isotherms of the adsorption of Fe3+, Fe2+ and Cu2+ on AAHSG were recorded, which indicated that Fe3+ presents a higher affinity by the sorbent. Therefore, AAHSG was successfully employed as a sorbent in a simple flow system for the preconcentration of Fe3+ in natural water samples, such as, river water, lagoonwater, springwater, stream water, well water and two water reference materials (NIST-SRM 1640, NIST-SRM 1643d). The obtained preconcentration factor was 82.2, and the detection limit achieved was 5.9 ng ml-1. The recovery of spiked water samples ranged from 95.0 - 103.1%.
The 1,3-diaminepropane-3-propyl-anchored silica gel (DAPPS) was successfully employed as a sorbent in a spectrophotometric flow system for the preconcentration of Cu
2+ in digests of biological ...materials (maize powder, soybean, citrus leaves, corn stalks) as well as water samples (river, stream, streamlet, springwater and well). The system presented a minicolumn packed with DAPPS, where the sample solution was passed through it for a period of time, and subsequently, an eluent solution, stripped-out the retained analyte which was further determined with DDTC at 460
nm.
The better preconcentration conditions utilized were: 120
s loading, 60
s elution, 30
s regeneration of the column, loading flow rate 6.5
ml
min
−1, buffer solution for the preconcentration and regeneration of the column-borate buffer pH 8.5, elution flow rate 2.3
ml
min
−1, time of elution 60
s, eluent composition, 0.4
mol
l
−1 HNO
3. Under these conditions, the preconcentration factor obtained was 36, and the detection limit achieved was 8.4
ng
ml
−1 in water samples and 0.84
μg
g
−1 in biological material. The maximum adsorption capacity of DAPPS to Cu
2+ was 0.49
mmol
g
−1 (31.1
mg
g
−1) obtained in a batch system.
The recovery of copper in the water samples ranged from 96.9 to 102.4% and in the biological materials ranged from 97.0 to 102.6%.
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