*2.5.2 pH test*

For pH test, 10 mg of the adsorbent were used in 10 ml samples of the metal solutions at a concentration of 20 ppm of the metal solutions at pHs of 5, 7 and 9. With the pH corrected, the solutions were placed in the Thermo Scientific shaker model 4360 for 24 hours. After 24 hours of stirring, the samples were centrifuged in a CIENTEC CT-6000R centrifuge for 3 minutes at 5500 rpm (4058 g) for aliquot withdrawal, for further dilution in 2% nitric acid, and analysis by ICP-MS Nexion 300D PerkinElmer (USA).

#### *2.5.3 Kinetic test*

The metallic solution of 10 ml to 20 mg.L−1 was added to 10 mg of the adsorbent material (biomass of banana peel and rice). Soon after, the solutions had the pH corrected to 7 and placed in a Thermo Scientific model 4360 agitator, with variations in contact time of the biomass with the metallic solution: 0.5, 2, 4, 6, 12 and 24 hours. After the stirring time, the samples were centrifuged through CIENTEC CT-6000R for 3 minutes at 5500 rpm (4058 g) for aliquot extraction, dilution (2% HNO3) and analysis of ICP-MS NexION 300D PerkinElmer (USA). The kinetic adsorption data were adjusted with the models of pseudo-first order [12] (Eq. (5)) and pseudo-second order [13] (Eq. (6)) models:

$$q\_t = q\_e \left(\mathbf{1} - e^{-k\_1 t}\right) \tag{5}$$

$$q\_t = \frac{k\_2 q\_e^2 t}{1 + k\_2 q\_e t} \tag{6}$$

where qe and qt are the amounts of adsorbent (mg g−1) in equilibrium and at time t (min), respectively. k1 (min−1) and k2 (g mg−1 min−1) are the equilibrium adsorption rate constants for pseudo-first and pseudo-second order adsorption, respectively.

*Removal of Copper and Lead from Water in the Mariana Mining Disaster Using Biomass… DOI: http://dx.doi.org/10.5772/intechopen.99668*
