2.2. Adsorbates
All the chemicals used in this study were of analytical grade. A
stock solution of nickel (1000 mg/L) was prepared by weighing
4.955 g of Ni(NO3)2.6H2O. Similarly, stock solution of zinc was also
prepared by weighing 4.397 g of ZnSO4.7H2O. Initial solutions with
different concentrations of Ni(II) and Zn(II) were prepared by proper
dilution from stock of 1000 mg/L of Ni(II) and Zn(II) solutions.
Standard solution of Ni(II) and Zn(II) from Sisco Research Laboratories
(India) were used for calibration of atomic absorption
spectrometer.
2.3. Batch adsorption studies
The adsorption of Ni(II) and Zn(II) ions onto the MBRC and MBAC
of M. baccifera was investigated in batch mode adsorption equilibrium
experiments. All batch experiments were carried out in 250 mL
conical flasks containing 100 mL metal solution.
The effect of pH on the sorption capacity of MBRC and MBAC for Ni
(II) and Zn(II) removal was evaluated in the range of 2.0–7.0. The pH
of each metal solution was adjusted to the required pH value by
using 1 N HNO3 or 1 N NaOH. Then 0.1 g of dried adsorbent was added
into the metal solution. The reaction mixture was shaken for 6 h at
150 rpm, 29±1 °C, this is enough to attain adsorption equilibrium.
Similarly, adsorbent dose (0.1–0.5 g), contact time (15–360 min), and
initial metal concentration (30.0–70.0 mg/L) for raw and activated
charcoals were also conducted. At the end of the experiment, the
solutions were separated from the adsorbent by centrifuging at
10,000 rpm for 8 min. The concentrations of metal in the solutions
were analyzed using Flame Atomic Absorption Spectrometer (GBC
932 plus, Australia). The wavelength of 288 nm was used for the
analysis of the metal. The instrument was calibrated with a standard
solution within a linear range and a correlation coefficient (R2) of
0.995 to 1.0 was obtained. In order to reproduce the results, the
experiments were conducted in triplicate and the average values were
used for the data analysis.