Jorge Carvalho de Lena

Adsorption of chromium (VI) ion from aqueous solution by succinylated mercerized cellulose functionalized with quaternary ammonium groups

Succinylated mercerized cellulose (cell 1) was used to synthesize an anion exchange resin. Cell 1, containing carboxylic acid groups was reacted with triethylenetetramine to introduce amine functionality to this material to obtain cell 2. Cell 2 was reacted with methyl-iodide to quaternize the amine groups from this material to obtain cell 3. Cells 2 and 3 were characterized by mass percent gain, degree of amination and quaternization, FTIR and CHN. Cells 2 and 3 showed degrees of amination and quaternization of 2.8 and 0.9 mmol/g and nitrogen content of 6.07% and 2.13%, respectively. Cell 3 was used for Cr (VI) adsorption studies. Adsorption equilibrium time and optimum pH for Cr (VI) adsorption were found to be 300 min and 3.1, respectively. The Langmuir isotherm was used to model adsorption equilibrium data. The adsorption capacity of cell 3 was found to be 0.829 mmol/g. Kinetic studies showed that the rate of adsorption of Cr (VI) on cell 3 obeyed a pseudo-second-order kinetic model.

Distribuição, fracionamento e mobilidade de elementos traço em sedimentos superficiais

The gold and iron mining activities in the Velhas River yield considerable amounts of suspended solids as well as metals to the hydrological system of the region. The risks were assessed by sequential extraction procedures. They were carried out in sediment samples, aiming to evaluate the presence of Co, Cr, Cu, Ni, Zn and As. Although being at high levels in some parts of the river (e.g. As 527 mg g-1 and Cr 475 mg g-1) they are associated with the residual fraction. Mobility factors were also calculated and show that these species are enriched along the river, e.g. for As 0.02 at the spring and 0.33 at the high course of the river.

Potencial poluidor de resíduo sólido da Samarco Mineração: estudo de caso da barragem de Germano

Samples of solid waste from the Germano Dam of Samarco Mineracao S.A were studied. This dam is located in the county of Mariana and it is mainly used to retain the waste resulting from the iron ore treatment at the Germano Plant. The waste was classified according to the ABNT Norms 10004, 10005, 10006 and 10007. as class III (inert) which was shown to be capable to retain heavy metals as well as chromium.

Evaluation of matrix effect on the determination of rare earth elements and As, Bi, Cd, Pb, Se and In in honey and pollen of native Brazilian bees (Tetragonisca angustula – Jataí) by Q-ICP-MS

Bees are considered the main pollinators in natural and agricultural environments. Chemical elements from honey and pollen have been used for monitoring the environment, the health of bees and the quality of their products. Nevertheless, there are not many studies on honey and pollen of native Brazilian bees. The goal of this work was to determine important chemical elements (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Lu and Yb) along with As, Bi, Cd, Pb, Se and In, in honey and pollen of native Brazilian bees, assessing analytical interferences from the matrix. A proposed analytical method was developed for these elements by quadrupole ICP-MS. Matrix effect was verified in honey matrix in the quantification of As, Bi and Dy; and in pollen matrix for Bi, Cd, Ce, Gd, La, Pb and Sc. The quality of the method was considered satisfactory taking into consideration the recovery rate of each element in the spiked solutions: honey matrix (91.6-103.9%) and pollen matrix (94.1-115.6%). The quantification limits of the method ranged between 0.00041 and 10.3μgL-1 for honey and 0.00041-0.095μgL-1 for pollen. The results demonstrate that the method is accurate, precise and suitable.

Evaluation of signal-to-background and Mg II/Mg I ratios as response for the optimization of rare earth elements determination by inductively coupled plasma optical emission spectrometry

Rare earth elements (REEs) is a peculiar group of chemical elements. Their determination in geological samples is important and complex due to their low concentrations and problems with spectral and non-spectral interferences. Herein, the operating conditions of an inductively coupled plasma optical emission spectrometer were optimized for the determination of REEs using experimental designs. The signal-to-background ratio (SBR) of the REEs emission signals and the Mg II/Mg I line intensity ratio were evaluated as response functions. According to the results obtained, three different sets of operating conditions were selected and classified as robust, semi‑robust and best SBR conditions. Limits of detection (LOD), SBR and relative standard deviation of the blank solution (RSDblank) were determined. The semi-robust condition (RF power of 1250 W and nebulizer gas flow rate of 0.90 L min-1) exhibited lower LOD and RSDblank than others tested operating conditions.

ADSORÇÃO DE As, Cu, Pb E Cr NA AVALIAÇÃO DA CAPACIDADE DE FIXAÇÃO DE METAIS POR RESÍDUO DE MINERADORAS DE FERRO

Two samples of residues from iron mining plants have been investigated for their retention capacity of As, Cu, Cr, and Pb. The sample with the higher content of iron oxides showed the highest capacity to retain metals. The adsorption affinity series changes from Pb>Cu>Cr»As to As>Pb>Cu>Cr or As>Cu>Cr>Pb, depending on the material and the concentration of the initial solution. In the competitive environment, the Pb adsorption decreases and the As, Cu and Cr adsorption increases. Sequential extraction procedures, carried out after adsorption batch experiments, showed that the most important adsorption process occurs in the oxide fraction and that the major part of the absorbed metal is remobilized from exchangeable and oxide fractions.

Coagulação/floculação de suspensões ricas em óxidos de ferro por sulfato de alumínio

The destabilization mechanism of suspensions of positively charged iron oxide particles by aluminum sulphate was investigated, aiming to evaluate the efficiency of the latter as a coagulant for natural surface waters from iron ore mining plants. Synthetic waters that simulate natural suspensions were used. The best coagulant dosage was found to be 100 mg/L at pH 4. The specific adsorption of hydrolysis products of aluminum salts on iron oxide particles and heterocoagulation processes involving differently charged substrates are proposed to explain the turbidity reduction of the suspensions.

Manganese Oxide Biominerals from Freshwater Environments in Quadrilatero Ferrifero, Minas Gerais, Brazil

Biogeochemical Mn cycling in aquatic environments is driven mostly by microbes, and includes reductive dissolution in anaerobic sediments as well as oxidation in aerobic regions. Oxidation is followed by precipitation, which occurs mainly on the extracellular structures of microorganisms. In this work, we studied the minerals precipitated on extracellular structures of native microorganisms from freshwater environments in Quadrilatero Ferrifero (Iron Quadrangle), Minas Gerais, Brazil, known to contain high levels of manganese. Light microscopy of biofilms and floating material showed diverse biomineralized structures. The most conspicuous were identified as the holdfasts of algae from the genus Ulothrix. Diatom frustules associated to manganese oxide precipitates were relatively common. In addition, both filaments and holdfasts produced by bacteria of the genus Leptothrix were found, as well as structures similar to those described as Siderocapsa and Metallogenium. Some previously unknown structures were also observed. Transmission electron microscopy of most of these structures showed the ‘crumpled tissue-paper’ morphology common in biomineralised manganese oxides. Energy-dispersive X-ray analysis (EDXA) showed that manganese and oxygen were the main components, along with minor amounts of Al, P, S, K, Ca and/or Ba. Our results bring new perspectives to the study of biomineralized manganese oxide structures from the environment. Moreover, they add information about the background of present-day microbial structures needed to better interpret fossilized microbial biominerals.

A qualidade das águas na região dos garimpos de topázio imperial na sub-bacia do rio da Ponte, Ouro Preto-MG

Around the Ouro Preto region, State of Minas Gerais Brazil, there is a significant presence of topaz prospecting. This activity is characterized by the use of rudimentary techniques without any tailing disposal control. Among the environmental impacts are: deforestation, tailing generation and accumulation, introduction of suspended fine particulate matter to the water and silting up of streams. In this work a hydrochemical study was carried out aiming to assess the water quality of the Ponte River and its tributaries. Water samples were analyzed for pH, Eh, dissolved oxygen, electrical conductivity, turbidity, alkalinity, chloride, sulfate, metals (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Sc, Sr, Ti, V, Y and Zn) and suspended particulate matter. The results show that the main problem in the area is the high turbidity values, which are associated with the presence of suspended solids introduced by the prospecting activity (reaching a concentration of up to 2.9 g.L-1). This fact represents an important facto, since it demonstrates that metals are being deposited in the aquatic atmosphere.

Avaliação de risco à saúde humana por contaminação natural de arsênio nas águas subterrâneas e nos solos da área urbana de Ouro Preto (MG)

Na avaliacao da exposicao humana a contaminacao natural por arsenio (As) das aguas subterrâneas e solos na area urbana da cidade de Ouro Preto, MG), nos bairros Piedade, Taquaral, Padre Faria, Alto da Cruz, Antonio Dias e Barra, foram estimados, para as criancas e adultos residentes nesses locais: (i) os valores das doses de ingestao diarias (DID) de As; (ii) os valores para os quocientes de risco (QRs) e (iii) o incremento da probabilidade de se desenvolver câncer ao longo da vida (RC), com teores medios de As encontrados nas aguas subterrâneas, variando entre 10 e 77 µg.L-1 e, nos solos, de 332,75 e 656 mg.kg-1.