Icp oes 9820

To prepare the solutions, 0.05 g of T4 biosorbent (250 and 500 µm) was added to 200 mL of a multimetal solution (As, Cd, Pb and Zn) with concentrations of 1, 5, 10, 25, 50, 100, 125 and 150 mg/L; the pH of the solution was adjusted to 5.0 with 0.1 N NaOH and 0.1 N HNO₃; and the solutions were stirred at 150 rpm for 120 min at 20 °C. Then, the mixtures were filtered at 0.45 µm, and heavy metal concentrations were determined by ICP-OES 9820, Shimadzu, Kyoto, Japan, calibrated with As, Pb, Cd and Zn standards (Calibration solution traceable, Sigma-Aldrich, Taufkirchen, Germany). The analysis was performed in axial mode, with a sample exposure of 30 s and an argon gas flow of 10 L/min.
Two models have been tested: Langmuir and Freundlich in order to evaluate the biosorption efficiency of heavy metals studied.
$$\mathrm{Langmuir}: qe=\frac{\left(q_m·K_L·Ce\right)}{\left(1+K_L·Ce\right)}$$
$$\mathrm{Freundlich}: qe=K_F·C{e}^{1/n}$$
where $qe$ (mg g⁻¹) is the amount of metal adsorbed at equilibrium, $q_m$ (mg g⁻¹) is the maximum heavy metal biosorption capacity of the biosorbent, $K_L$ is the adsorption equilibrium constant of Langmuir, $Ce$ (mg L⁻¹) is the adsorbate equilibrium concentration and $K_{F }$ and $1/n$ are constants of Freundlich model.

To prepare the solutions, 0.05 g of T4 biosorbent (250 and 500 µm) was added to 200 mL of a multimetal solution (As, Cd, Pb and Zn) with a concentration of 25 mg/L. The pH of the solution was adjusted to 5.0 with 0.1 N NaOH and 0.1 N HNO₃, and the solutions were stirred at 150 rpm for 120 min at 20 °C. The solutions were withdrawn at 0, 5, 10, 20, 30, 45, 60, 90, 120, 180, 240 and 300 min. Then, the mixtures were filtered at 0.45 µm, and heavy metal concentrations were determined by ICP-OES 9820, Shimadzu, Kyoto, Japan, calibrated with As, Pb, Cd and Zn standards (Calibration solution traceable, Sigma-Aldrich, Taufkirchen, Germany). The analysis was performed in axial mode, with a sample exposure of 30 s and an argon gas flow of 10 L/min.
Pseudo-first order and pseudo-second order mathematical models were used to evaluate the adsorption kinetics.
$$\mathrm{Pseudo}\text{-}\mathrm{first} \mathrm{order}: qt=qe·\left(1-e^{k_1\ast t}\right)$$
$$\mathrm{Pseudo}\text{-}\mathrm{second} \mathrm{order}: qt=\frac{(k_2·q{e}^2·t)}{\left(1+k_2·qe·\mathrm{t}\right)}$$
where $qt$ (mg g⁻¹) is the amount of metal adsorbed at time t (min), $qe$ (mg g⁻¹) is the amount of metal adsorbed at equilibrium, and k₁ and k₂ are the constants of the pseudo-first and pseudo-second order models.

The cation exchange capacity (CEC) of natural and activated clay (HMB) was determined by the sum of the compulsive changes of Al, Ca, Mg, K, and Na, by Ba; the exchangeable cations were removed with a 0.1 mol/L BaCl₂ solution at a 1/12 (w/v) ratio of clay/BaCl₂ solution, which was stirred at 200 rpm for 1 h.
Then, it was centrifuged at 3000× g for 10 min and this operation was repeated three times. The supernatants were collected in a container, and the exchangeable ions (Al, Fe, Ca, Mg, Mn, K, and Na) were measured using an inductively-coupled plasma optical emission spectrometer, Shimadzu, model ICP-OES 9820 (Kyoto, Japan). Calibration curves were prepared for the ions under study, with a regression coefficient, R² > 0.995. Readings were performed in axial mode with an argon gas flow of 10 L/min with 30 s plasma exposure and 30 s rinses at 60 rpm between samples.

In total, 500 mg of the samples was digested at 180 °C for 20 min in an acid medium (12 mL of 65% nitric acid/3 mL of 37.7% hydrochloric acid) gauged with ultrapure water to 50 mL in a microwave digester, SCP Science brand, MiniWave model (Quebec, Canada). The digested samples were filtered at 0.45 µm and an aliquot was taken for metal quantification in an inductively coupled plasma optical emission spectrometer, Shimadzu brand, model ICP-OES 9820 (Kyoto, Japan). Calibration curves were previously prepared for the metals under study, with a regression coefficient R² > 0.995. Aliquots were analyzed in axial mode with 10 L/min argon gas flow and 30 s plasma exposure, with a 30 s rinse at 60 rpm between samples [79 (link)].