Walter Antônio Pereira Abrahão

The role of Al-Goethites on arsenate mobility

The geochemical fates of Fe and As are so closely correlated that methods of As removal from contaminated water are in general based on the high affinity of this metalloid for Fe (hydr)oxides. Dissimilatory Fe reducing bacteria, however, play a fundamental role in catalysing the redox transformations that ultimately control the mobility of As in anoxic environments. The potential of Al-goethites in adsorbing As(V) compared with hematite, goethite, ferrihydrite, and gibbsite, and the stability of As retained by the Fe compounds under anoxic conditions were investigated in this study. The (hydr)oxides were synthesised, and adsorption isotherms and As(V) adsorption maxima at different pH were measured. Arsenic loaded samples were anaerobically incubated in the presence of Shewanella putrefaciens, and periodically sampled to evaluate the contents of soluble As and Fe. The As(V) adsorption maxima decreased in the following order: Fh > AlGt(13) > AlGt(20) > AlGt(23) > Gb > Hm > Gt. In terms of surface area, Gb, Gt, and Hm showed higher As(V) loading capacity than Fh, suggesting available reactive sites not fully occupied by arsenate on Fh. The same hypothesis can be considered for Al-goethites, as they showed even lower arsenate loading capacity per surface area. The presence of structural Al in the goethites enhanced considerably the As uptake capacity and stability under reducing conditions. Therefore, the Al-goethites showed good potential as adsorbents to remove As from water. S. putrefaciens cells were able to utilise both noncrystalline and crystalline Fe (hydr)oxides as electron acceptors, releasing As into solution. Al-goethites showed a decrease in Fe and As mobilisation as structural Al increased.

Occurrence of magnetite in the sand fraction of an Oxisol in the Brazilian savanna ecosystem, developed from a magnetite-free lithology

It is relatively well established from many pedogenetic studies that, in deeply weathered Oxisols from Central Brazil, magnetite or maghemite are either inherited or transformed from magnetite of the mafic parent material. However, no similar pedogenetic pathways have been reported in the literature for other lithologies, such as limestone and pelitic rocks (shales and slates) of the BambuGroup in Brazil. In these sedimentary, non- mafic lithologies, magnetic minerals are not likely to occur. Despite that, magnetic nodules were identified in a representative Oxisol pedon developed on this pedodomain, under savanna (Cerrado). Magnetic and non-magnetic fractions of nodules were separated with a hand magnet. Chemical and mineralogical compositions of these nodules were determined by conventional chemical methods, powder X-ray diffractometry (XRD), and 298 K M¨ ossbauer spectroscopy. For the magnetic fraction, containing up to 84 dag/kg of Fe2O3 but also relatively rich in Al, Ti, Cr, and Si, M¨ ossbauer measurements were also made at 4.2 K, without and with an externally applied magnetic field of 8 Tesla, and at 100 K. M¨ ossbauer results and structural Rietveld refinement of the XRD data consistently suggest that the iron oxide mineralogy corresponds to approximately equivalent proportions of hematite and a partially oxidised magnetite, containing 3 dag/kg of iron as FeO. Laboratory tests were conducted in an attempt to produce magnetic material by heating this non-magnetic fraction. The sample was wrapped in filter paper and heated at 300 ◦ C for 30 min, and the results were compared with the naturally occurring magnetic nodules. The saturation magnetisation value of the thermally treated sample was found to be σ = 7 J/T.kg, well below σ = 16 J/T.kg of the magnetic soil nodules. Mand XRD results indicate that the iron oxide mineralogy of this laboratory- produced magnetic sample also corresponds to a mixture of partially oxidised magnetite and hematite. Two other parts of the same non-magnetic, naturally hematite-rich precursor were mixed with charcoal, to act as reducing agent, and oven-heated at 450 ◦ C and 600 ◦ C, respectively, for 1 h, producing increasing reduction of the hematite to magnetite. These laboratory simulations support the model in which magnetite in these hematite-rich nodules was formed under the influence of seasonal burning regimes of the covering vegetation, followed by partial re-conversion of the magnetite particles to hematite under long-term atmospheric exposure to air. This model is consistent with a long-term, seasonal fire history, assumed for the genesis of the Cerrado ecosystem in the Central Brazil, although a wider validity for the entire BambuGroup area remains open. Additional keywords: M¨ ossbauer spectroscopy, Rietveld, iron oxides, BambuGroup.

Effects of Competing Anions and Iron Bioreduction on Arsenic Desorption

Dissimilatory iron-reducing bacteria play a fundamental role in catalysing the redox transformations that ultimately control the mobility of As in anoxic environments, a process also controlled by the presence of competing anions. In this study, we investigated the decoupling of As from loaded Al and Fe (hydr)oxides by competing anions in the presence of iron-reducing bacteria. Hematite, goethite, ferrihydrite, gibbsite and three aluminium-substituted goethites (AlGts) were synthesised and loaded with arsenate, followed by anaerobic incubation with different phosphate or carbonate-containing media in the presence of catalytic iron-reducing bacteria. Soluble Al, As, Fe and P contents were measured in aliquots by inductively coupled plasma optical emission spectrometry following periodical sampling. Shewanella putrefaciens cells were able to utilise both non-crystalline and crystalline Fe (hydr)oxides as electron acceptors, releasing Fe and As into solution. Phosphate and carbonate affected the Fe bioreduction, probably due to the precipitation of metastable mineral phases and also to phosphate-induced stabilisation on the hydroxide surfaces. Phosphate precipitation acted as a sink for As, thus limiting its mobilisation. The highest fraction of desorbed As by phosphate was observed for gibbsite, followed by AlGts. Similarly, gibbsite showed significant amounts of arsenate displaced by carbonate. In spite of its low crystallinity, ferrihydrite was the most efficient compound in retaining arsenate, possibly due to As co-precipitation. This study provides new insight into the management of As-contaminated soils and sediments containing Al-goethites and gibbsite, where the Fe activity may be too low to co-precipitate As-bearing vivianite. Thus, the dynamics of As(V) in flooded soils are significant in agriculture and environmental management.

Distribuição de freqüência de tamanho da fração areia e compacidade relativa de solos desenvolvidos de sedimentos do grupo geológico barreiras

The packing condition of the soil is important for providing direction for land management. In soils developed from recent sediments, the tendency to packing may be related to inherited characteristcs from sedimentation conditions. In a soil toposequence from sandy sediments of Barreiras geological group, in Caravelas city - Bahia, eight soil profiles were selected, five of them from a eucalypt plantation. The soils were allocated in five great groups: Fluvaquent (P1),Duraquod (P2, P8), Haplorthod (P3), Hapludult (P4, P5, P7) and Plintaquult (P6) according to the 7th approximation of USA soil taxonomy. Soil bulk density was determined in 41 horizons along with minimum and maximum soil bulk densities. Values of soil bulk densities were located between the two other densities, thereby obtaining the relative densities. The sand was subdivided into 21 size classes by standard sieves and the data were used to determine mean size, inclusive graphic standard deviation, inclusive graphic skewness and graphic kurtosis. It was observed that higher fine sand content combined with unsorted sand grains enhanced closer packing of soil particles, inducing increments of relative density in soil horizons more resistant to penetration.

Produção de mudas de alface em função de diferentes combinações de substratos

O substrato utilizado na producao de mudas exerce papel primordial, no desenvolvimento inicial da planta. Neste sentido, com o presente trabalho objetivou-se avaliar a producao de mudas de alface em funcao de diferentes combinacoes de substratos. O experimento foi implantado seguindo um delineamento inteiramente casualizado, com quatro repeticoes. Os 20 tratamentos foram dispostos em esquema fatorial 4x5; sendo o primeiro fator constituido por quatro substratos (PlantHort I, PlantHort II, PlantHort III e substrato comercial Plantmax®) e o segundo constituido de cinco niveis de casca de arroz carbonizada (0; 25; 50; 75; 100%). Foi utilizada a cultivar de alface Elba (Lactuca sativa L.). As sementes foram semeadas nos diferentes substratos contidos em bandejas de poliestireno expandido, com 128 celulas, na profundidade 0,5 cm. O aumento da porcentagem de casca de arroz carbonizada nos substratos avaliados apresentou comportamentos semelhantes em todas as caracteristicas avaliadas. Os substratos PlantHort I, PlantHort II, PlantHort III considerados alternativos, independentemente da proporcao adicionada de casca de arroz carbonizada proporcionaram maiores crescimentos em relacao ao substrato comercial Plantmax®.

Preliminary evaluation of acid mine drainage in Minas Gerais State, Brazil

A despeito da importância economica de atividades mineralogicas para o estado de Minas Gerais, perceber-se que elas causam significativo impacto ao ambiente. Drenagem acida e um dos aspectos ambientais considerados pela atividade em funcao de seus impactos. Ela tem origem a partir da oxidacao de sulfetos metalicos que acidificam as aguas, com possibilidade de mobilizar elementos toxicos e poluir os recursos hidricos. Este trabalho teve como objetivo realizar uma avaliacao preliminar do problema em Minas Gerais. O trabalho teve inicio a partir de um levantamento bibliografico junto a Fundacao Estadual de Meio Ambiente (FEAM) para identificar mineracoes cujo minerio esta associado a sulfetos. Amostras dos substratos foram retiradas para determinar o potencial de acidez (AP) e de neutralizacao (NP). AP foi avaliado por dois procedimentos: pelo teor total de sulfetos e pela oxidacao com peroxido seguida da titulacao acida. O NP foi avaliado pelo teor equivalente de carbonato de calcio. Lâminas petrograficas foram preparadas para a descricao mineralogica com enfase em sulfetos e carbonatos. O balanco acido-base (ABA) foi determinado pela diferenca entre AP e NP, enquanto o potencial de geracao de aguas acidas foi obtido pelo valor de ABA e o volume total de material de cada atividade mineraria. Os resultados permitiram identificar quatro substratos com potencial para gerar drenagem acida no estado de Minas Gerais. Juntas, estes materiais representam um potencial de geracao de cerca 3,14 a 10,37 bilhoes de metros cubicos de agua a pH 2,0 ou 31,4 a 103,7 bilhoes de metros cubicos de agua a pH 3,0. Estes valores significam custos entre US

Cover layers to the growth of trees and shrobs over a sulfide spoil from gold mining

7,8 e 25,9 milhoes para neutralizar a acidez com o uso de calcario. Estas estimativas sao provavelmente subavaliadas, uma vez que algumas mineracoes nao foram incluidas no levantamento e, para outras, as amostras superficiais podem nao representar a realidade. Uma avaliacao mais rigida do potencial de drenagem acida em nivel estadual requer estudos futuros. Estes estudos precisariam incluir um numero maior de amostras e mineradoras nao incluidas neste trabalho. Eles poderiam considerar, ainda, a cinetica de geracao de acidez por meio de procedimentos de intemperismo simulado.

Methods for evaluation of easily-reducible iron and manganese in paddy soils

This work was done at a gold mine company in Paracatu, MG, Brazil, and was conducted from March 2000 to November 2005. The substrate (spoil) studied was a phillite rock which contains sulfides such as pyrite and arsenopyrite. This study aimed to evaluate the survival and growth of plant species on different combinations of substrate layers over the spoil. These layers were a cover layer and a sealing layer, both deposited over the spoil. The treatment 1 had saprolite (B1) in the sealing layer (SL) and B1 with liming (B1L) in the cover layer (CL). The treatment 2 had B1 in SL and B1L + soil with liming (SoL) in the CL. The treatment 3 had B1 + SoL in the SL and B1L in the CL. The treatment 4 had B1 + SoL in the SL and B1L + SoL in the CL. The plant species used were Acacia farnesiana, A. holosericea, A. polyphylla, Albizia lebbeck, Clitoria fairchildiana, Flemingia sp., Mimosa artemisiana, M. bimucronata e Enterolobium contortisiliquum. Forty and 57 months after planting, collardiameter, height, and living plants were evaluated. The greatest survival rate was oobservedintreatmentwith B horizon of an Oxisoil in both layers, with 80 %. In general, M. bimucronata and A. farnesiana species showed the highest survival rate. The arsenic-content by Mehlich 3 in the cover layer ranged from 0.00 to 14.69 mg dm -3 among treatments. The experimental results suggest that layers combinations above the sulfide substrate allow the rapid revegetation of the spoil.

Characterization of verdete rock as a potential source of potassium

ABSTRACT Iron (Fe) and manganese (Mn) toxicity can be an important limitation to flooded rice cropping. Flooding causes several physical and chemical alterations that affect the dynamics of these elements in the soil environment. The objective of this study was to develop procedures of soil analysis, that enable the assessment of easily reducible Fe and Mn availability and uptake by plants. Surface samples (0–20 cm) of ten lowland soils from the State of Minas Gerais, Brazil, were used. The experiment consisted of a factorial randomized block design of ten soils and five liming levels, with five rice plants grown in pots containing 2 dm3 of soil with permanent flooding. The concentrations of Fe and Mn were evaluated in the soil solution and in the aerial parts of the rice plants. The air-dried samples were analyzed for Fe and Mn with sodium-citrate dithionite, ammonium oxalate, Melich-1, 0.1 mol L−1 HCl, ammonium acetate–EDTA, and DTPA–TEA extractants. The Fe concentration in the soil solution was most highly correlated with Melich-1 (r = 0.87), while DTPA–TEA showed the highest correlation with the amount of Fe in the plant (r = 0.62). For Mn, DTPA–TEA was the best predictor of both soil solution Mn and plant Mn (r = 0.87 and r = 0.80, respectively).

Valores de referência local e avaliação da contaminação por zinco em solos adjacentes a áreas mineradas no município de Vazante-MG

Potassium is a nutrient found at low levels in Brazilian soils, requiring large inputs of fertilizers to achieve satisfactory crop yields. Brazil has high external dependence and limited reserves of soluble K mineral, which is traditionally exploited for the production of fertilizers. On the other hand, it is common the occurrence in the country of potassium-rich silicate minerals which are not commercially exploited. This study aimed to characterize mineralogically and chemically samples of verdete rock separated into size fractions and evaluate its potential as potassium fertilizer. The mineral composition of verdete rock is based on glauconite, quartz and feldspar. The total K2O content in verdete rock ranged from 5.18 to 9.0 dag/kg. The K content extracted in water or 2% citric acid was 2.4% below the total of K, indicating low reactivity of verdete rock and limitations for direct use as K source. The processes of physical fractionation and sedimentation in water are inefficient to promote the concentration of K in the different verdete rock fractions. The total K content in some samples are considerable and may enable the use of this rock as raw material for production of more reactive potassium fertilizers.