**2. Materials and methods**

The BGMA was collected along the coast of Tamil Nadu, India, near Chidambaram. It is cleaned and dried at room temperature with distilled water. It is then pulverised to 150–200 microns in size. For IR spectrum investigations of dried biomass and Ni(II) sorbed biomass in the range of 4000–400 cm<sup>1</sup> , a Fourier transform infrared (FT-IR) spectrometer (BRUKER FT-IR, ALPHA-T, GERMANY) was employed.

The synthetic Ni(II) solution is made with an analytical grade salt, Nickel(II) sulfate heptahydrate (NiSO47H2O). To make 1 L of solution for the stock purpose of *Removal of Divalent Nickel from Aqueous Solution Using Blue Green Marine Algae… DOI: http://dx.doi.org/10.5772/intechopen.103940*

1000 ppm, exactly 4.7852 g of NiSO4�7H2O is weighed and utilised. For stock solution preparation, double distilled water is employed. This stock solution is diluted to a concentration of 25–250 parts per million.

Each solution's pH is changed from 2 to 7. pH is adjusted with 0.1 N nitric acid (HNO3) and 0.1 N sodium hydroxide (NaOH) solutions. The amount of biomass put to the conical flask varies from 0.5 to 2.5 g (0.5, 1.0, 1.5, 2.0 and 2.5 g).

A 500 mL conical flask is used for the batch adsorption experiment. The starting concentrations of metal ions are 25, 50, 75, 100, 125, 150, 175, 200, 225, and 250 parts per million. Each 500 mL Erlenmeyer flask contains 400 mL of 25 ppm metal ion solution. Each Erlenmeyer flask receives 0.5, 1.0, 1.5, 2.0, and 2.5 g of BGMA, respectively. In all five flasks, the pH of the solution is kept at 2. The flasks are agitated at 120 rpm in a rotary shaker. There is a total of 24 hours of contact (shaking) time given. This is more than enough to attain the desired equilibrium (maximum adsorption). The starting and ultimate concentrations of the solution are determined using a double-beam Atomic Adsorption Spectrophotometer (AAS SL176-Elico Limited India). The % removal of metal ions is computed using Eq. (1) from the starting (Cin) and equilibrium final concentration (Ceq).

$$\% \text{Removal} = \frac{\text{C}\_{\text{in}} - \text{C}\_{\text{eq}}}{\text{C}\_{\text{in}}} \times 100 \tag{1}$$

Eq. (2) is used to compute the equilibrium metal uptake, qeq, using the starting (Ci) and equilibrium (Ceq) concentrations of the metal ion solution.

$$\mathbf{q}\_{\rm eq} = \frac{\mathbf{V}}{\mathbf{M}} \left( \mathbf{C}\_{\rm in} - \mathbf{C}\_{\rm eq} \right) \tag{2}$$

where V is the litre volume of the liquid sample and M is the gram weight of the adsorbent. In order to improve the pH value and biomass loading, the same operation is repeated with adjusting the solution pH as 3, 4, 5, 6 and 7. Similarly, 50 ppm, 75 ppm, 100 ppm, 125 ppm, 150 ppm, 175 ppm, 200 ppm, 225 ppm, and 250 ppm metal ion concentrations are used in the studies. For concordant results, experiments are repeated (**Table 1**).


#### **Table 1.**

*Experimental values of adsorption of Ni(II) onto BGMA.*

One parameter model (Henry's law), two parameter models (Henry's law with intercept, Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Hill-de Boer, Fowler-Guggenheim, Flory-Huggins, Halsey, Harkin-Jura, Jovanovic, Elovich and Kiselev), three parameter models (Hill, Redlich-Peterson, Sips, Langmuir-Freundlich, Fritz-Schlunder-III, Radke-Prausnits-I, Radke-Prausnits-II, Radke-Prausnits-III, Toth, Khan, Koble-Corrigan, Jossens, Jovanovic-Freundlich, Brouers-Sotolongo, Vieth-Sladek, Unilan, Holl-Krich and Langmuir-Jovanovic), four parameter models (Fritz-Schlunder-IV, Baudu Weber-van Vliet and Marczewski-Jaroniec) and five parameter model (Fritz-Schlunder-5) are used to examine the experimental facts and to discover its applicability for modelling purpose. The parameter values are predicted using the cftool kit available in MATLAB R2010a software. This toolkit aids in the estimation of model parameters, including the non-linear regression coefficient (R<sup>2</sup> ), Sum of Squares due to Error (SSE), and Root Mean Squared Error (RMSE).
