Adsorção de Mn (II) e Zn (II) em soluções aquosas usando perlita expandida revestida com quitosana

In this work, chitosan was used as a coating of pure perlite in order to increase the accessibility of the groups OH- e NH2+the adsorptionof ions Mn2+ e Zn2+.The characterization results of the expanded perlite classified as microporous and whose surface area 3,176 m2 g-1after the change resulted in 4,664 m2g-1.From the thermogravimetry(TG) it was found that the percentage of coating was34,3%.The infrared analysis can prove the presence of groups Si-OH, Si-O e Al-O-Siresulting from the perlite and C=O, NH2and OH characterization of chitosan. The experiments on experiments on the adsorption of Mn and Zn were performed in the concentration range of10 a 50 mgL-1and the adsorption capacity inpH 5,8 e 5,2 was 19,49 and 23,09 mgg-1to 25 oC,respectively.The adsorption data were best fitted to Langmuir adsorption model to Langmuir adsorption model for both metalionsisindicative of monolayer adsorption. The kinetics of adsorption were calculated from the equation of Lagergren fitting the model pseudo-second-order for all initial concentrations, suggesting that adsorption of ions Mn2+ and Zn2+ follows the kinetics of pseudo-second-order and whose constant Speedk2(g/mg.min) are 0,105 e 3,98 and capacity and maximum removal qe 4,326 e 3,348,respectively.In this study we used a square wave voltammetry cathodic stripping voltammetry to quantify the adsorbed ions, and the working electrode glassy carbon, reference electrode silver / silver chloride and a platinum auxiliary electrode. The attainment of the peaks corresponding to ions Mn2+ and Zn2+ was evaluated in and electrochemical cell with a capacity of 30 mL using a buffer system (Na2HPO4/NaH2PO4)at pH 4 and was adjusted with solutionsH3PO4 0,1molL-1and NaOH 0,1 molL-1and addition of the analyte has been a cathodic peak in- 0,873 Vand detection limit of2,55x10-6molL-1para Zn.The dough used for obtaining the adsorption isotherm was 150 mg and reached in 120 min time of equilibrium for both metal ions.The maximum adsorption for 120 min with Mn concentration 20 mgL-1 and Zn 10 mgL-1,was91, 09 e 94, 34%, respectively

Aplicação da tecnologia eletroquímica para a remoção e monitoramento de metais pesados em efluentes aquosos

Heavy metals are present in industrial waste. These metals can generate a large environmental impact contaminating water, soil and plants. The chemical action of heavy metals has attracted environmental interest. In this context, this study aimed to test t he performance of electrochemical technologies for removing and quantifying heavy metals. First ly , the electroanalytical technique of stripping voltammetry with glassy carbon electrode (GC) was standardized in order to use this method for the quantificatio n of metals during their removal by electrocoagulation process (EC). A nalytical curves were evaluated to obtain reliability of the determin ation and quantification of Cd 2+ and Pb 2+ separately or in a mixture. Meanwhile , EC process was developed using an el ectrochemical cell in a continuous flow (EFC) for removing Pb 2+ and Cd 2+ . The se experiments were performed using Al parallel plates with 10 cm of diameter (  63.5 cm 2 ) . The optimization of conditions for removing Pb 2+ and Cd 2+ , dissolved in 2 L of solution at 151 L h - 1 , were studied by applying different values of current for 30 min. Cd 2+ and Pb 2+ concentrations were monitored during electrolysis using stripping voltammetry. The results showed that the removal of Pb 2 + was effective when the EC pro cess is used, obtaining removals of 98% in 30 min. This behavior is dependent on the applied current, which implies an increase in power consumption. From the results also verified that the stripping voltammetry technique is quite reliable deter mining Pb 2+ concentration , when compared with the measurements obtained by atomic absorption method (AA). In view of this, t he second objective of this study was to evaluate the removal of Cd 2+ and Pb 2+ (mixture solution) by EC . Removal efficiency increasing current was confirmed when 93% and 100% of Cd 2+ and Pb 2+ was removed after 30 min . The increase in the current promotes the oxidation of sacrificial electrodes, and consequently increased amount of coagulant, which influences the removal of heavy metals in solution. Adsortive voltammetry is a fast, reliable, economical and simple way to determine Cd 2+ and Pb 2+ during their removal. I t is more economical than those normally used, which require the use of toxic and expensive reagents. Our results demonstrated the potential use of electroanalytical techniques to monitor the course of environmental interventions. Thus, the application of the two techniques associated can be a reliable way to monitor environmental impacts due to the pollution of aquatic ecosystems by heavy metals.

Aplicação e otimização de métodos eletroquímicos combinados para remoção e determinação de cromo hexavalente em efluentes simulados

Hexavalent chromium is a heavy metal present in various industrial effluents, and depending on its concentration may cause irreparable damage to the environment and to humans. Facing this surrounding context, this study aimed on the application of electrochemical methods to determine and remove the hexavalent chromium (Cr6+) in simulated wastewater. To determine was applied to cathodic stripping voltammetry (CSV) using ultra trace graphite electrodes ultra trace (work), Ag/AgCl (reference) and platinum (counter electrode), the samples were complexed with 1,5- diphenylcarbazide and then subjected to analysis. The removal of Cr6+ was applied electrocoagulation process (EC) using Fe and Al electrodes. The variables that constituted the factorial design 24, applied to optimizing the EC process, were: current density (5 and 10 mA.cm-2), temperature (25 and 60 ºC), concentration (50 and 100 ppm) and agitation rate (400 and 600 RPM). Through the preliminary test it was possible the adequacy of applying the CSV for determining of Cr6+, removed during the EC process. The Fe and Al electrodes as anodes sacrifice showed satisfactory results in the EC process, however Fe favored complete removal in 30 min, whereas with Al occurred at 240 min. In the application of factorial design 24 and analysis of Response Surface Methodology was possible to optimize the EC process for removal of Cr6+ in H2SO4 solution (0.5 mol.L-1), in which the temperature, with positive effect, was the variable that presented higher statistical significance compared with other variables and interactions, while in optimizing the EC process for removal of Cr6+ in NaCl solution (0.1 mol.L-1) the current density, with positive effect, and concentration, with a negative effect were the variables that had greater statistical significance with greater statistical significance compared with other variables and interactions. The utilization of electrolytes supports NaCl and Na2SO4 showed no significant differences, however NaCl resulted in rapid improvement in Cr6+ removal kinetics and increasing the NaCl concentration provided an increase in conductivity of the solution, resulting in lower energy consumption. The wear of the electrodes evaluated in all the process of EC showed that the Al in H2SO4 solution (0.5 mol.L-1), undergoes during the process of anodization CE, then the experimental mass loss is less than the theoretical mass loss, however, the Fe in the same medium showed a loss of mass greater experimental estimated theoretically. This fact is due to a spontaneous reaction of Fe with H2SO4, and when the reaction medium was the NaCl and Na2SO4 loss experimental mass approached the theoretical mass loss. Furthermore, it was observed the energy consumption of all processes involved in this study had a low operating cost, thus enabling the application of the EC process for treating industrial effluents. The results were satisfactory, it was achieved complete removal of Cr6+ in all processes used in this study.