## 2 Removal of Lead
### Removal of Lead using GO-Magnetite's
On increasing the adsorbent dosage from 250 mg/L to 550 mg/L, there was a significant enhancement in Pb(II) ions removal efficiency from 87 to 98%. No significant increase on further adsorbent dosage increasing was correlated with the dominance of the repulsive forces in the functional groups. Comparative results of three variables viz. adsorbent dosage, residual time and solution concentration have been depicted in Figure 5. Based on the results of experimental runs, independent variables 18.38 mg/L initial solution concentration, 550 mg/L adsorbent dosage and 83 min adsorbent residual time were optimized which not only may be helpful to reduce the cost of operating treatment process of an industry but also may also reduce the time in achieving the desired performance. [PERSON] et al. reported the preparation of magnetic cobalt ferrite-reduced graphene oxide (CoFe\({}_{2}\)O\({}_{4}\)+rGO) nanocomposite to absorb the Pb(II) ions from aqueous solution [218]. CoFe\({}_{2}\)O\({}_{4}\)+rGO nanocomposite was prepared as reported in literature and used for metal ions adsorption [219; 220]. In brief, iron(III) nitrate and cobalt (III) nitrate solutions were drop wise added to the ultrasonicated GO suspension under vigorous stirring. pH 12 was adjusted using 5% NaOH aqueous solution and hydrazine hydrate solution was added slowly to GO suspension. Reaction mixture was stirred for 5 h at 80 \({}^{\circ}\)C and cooled to room temperature. Purification was carried out using magnet followed by repeatedly washing with deionized water and absolute ethanol and dried at 50 \({}^{\circ}\)C for 24 h under vacuum. CoFe\({}_{2}\)O\({}_{4}\)+rGO was characterized with the help of XRD where the CoFe\({}_{2}\)O\({}_{4}\) nanoparticles were found in correspondent with the previous report and the presence of XRD peak 20 at 26.5\({}^{\circ}\) confirmed that CoFe\({}_{2}\)O\({}_{4}\)-rGO was well crystallized. Low zeta potential indicated the availability of entire negatively-charged functional groups environment from pH 4 to 10 for the better adsorption of heavy metal ions and CoFe\({}_{2}\)O\({}_{4}\)-rGO was found to be well dispersed in water pertaining a black suspension in aqueous solution. 1-ethyl-3(3-hydroxyethylaminopropyl) carbondiimide hydrochloride and N-hydroxylsuccinimimde were added at pH to activate carboxylic functionalities of GO. Magnetic chitosan and activated GO was suspended using ultrasonication for 10 min and stirred for 2 h at 60 \({}^{\circ}\)C. The precipitate was washed with NaOH and then with water repeatedly until the pH 7 was obtained. MCGO product was collected using magnet and dried under vacuum at 50 \({}^{\circ}\)C. The magnetic fluid was coated onto chitosan to accelerate the separation through an improved surface area and reduce the dose requirement for the adsorption of Pb(II) ions. The adsorption amounts and adsorption rates were calculated from the concentration difference of the solution used before and after the adsorption process using following equations:  
\[Q=\frac{(C_{0}-C_{e})V}{W} \tag{3}\]  
\[E=\frac{C_{0}-C_{0}}{C_{0}}\ x\ 100\% \tag{4}\]  
where \(C_{0}\) and \(C_{e}\) are the initial and the equilibrium concentrations of metal ions in mL/L, respectively; W is the amount of an adsorbent used, in grams; and V is the volume of metal ion solution in liter. Since, the adsorption is very sensitive to pH variations, adsorption capacity of MCGO was determined at varying pH from 1.0 to 7.0. At low pH, excessive competitive H\({}^{+}\) ions concentration inhibits the adsorption of Pb(II) ions and usually adsorption of heavy metal ions do not occur at low pH. Pb(II) ions adsorption capacity increased with the increasing pH from 1-5 and was measured 50.23 mg/g at pH 5. In acidic media, the slight decrease in uptake was attributed to amino group protonation, which may hinder complex formation. Pb(II) ions adsorption onto MCGO was obtained maximum within first 30 min. and no significant alteration was observed after 1 h which indicated that optimum adsorption time for Pb(II) ions.