Rômulo Simões Angélica

Assessment of Mercury Levels in Soils, Waters, Bottom Sediments and Fishes of Acre State in Brazilian Amazon

Mercury in the aquatic biota and geologic materials in areas without anthropogenic sources has been stimulating the discussion about the possibility of natural Hg occurrence in the Amazon region. In this study the dispersion of Hg in different geologic materials as well as its relationship with high Hg levels, detected in some species of carnivorous fish consumed in the Rio Branco city, is evaluated. Bottom and suspended sediments, river water and fishes were sampled in the Acre and Purus Rivers and in some of their tributaries. Total mercury as well as physical and chemical characterization of the waters were done. Hg on top soil and upper horizons samples were also determined to evaluate the potential Hg accumulation in these materials. In addition the dominant minerals were determined by X-ray Diffraction analysis. Furthermore, ten samples of fossilized material were analyzed. The Hg analysis were carried out by CVAAS. The Hg mean levels in the bottom and suspensed sediments were 0.042 and 0.060 μg g-1, respectively. In the river water samples, the Hg levels were below the detection limit. The Hg mean values in the different soil samples were as follow: soil samples (0.077 μ g-1), lower (50–60 cm depth) horizons samples (0.117 μ g-1), ferruginous nodules within the clayey matrix (0.190 μ g-1) and fossilized material (0.379 μ g-1). In the fishes the Hg levels are high with mean of the 1.287 μ g-1 in the carnivorous species. These levels indicate a possible bioaccumulation of Hg mostly in the carnivorous fishes. Although low concentrations of Hg were found in the river waters, it is assumed here that the bioavailable Hg can is original large from the ferruginousnodules and fossilized materials.

Utilização de rejeito de caulim da Amazônia na síntese da zeólita A

Zeolita A e hidroxisodalita foram sintetizadas a partir de um rejeito industrial do processo de beneficiamento de caulim para papel, de industrias da regiao amazonica. Esse rejeito e composto essencialmente por caulinita e possui razao SiO2/Al2O3 igual a requerida para esses dois tipos de zeolitas. Dessa maneira, o processo de sintese passou por duas etapas: primeiramente o caulim foi submetido ao tratamento termico, atraves de calcinacao a 700 °C por 2 h, para transformacao de caulinita em metacaulinita. A metacaulinita obtida reagiu com NaOH em solucao, em condicoes hidrotermais, atraves de autoclavagem estatica, nas temperaturas de 80, 110 e 150 °C por 24 h. Os materiais de partida foram identificados e caracterizados por difracao de raios X (DRX) e microscopia eletronica de varredura (MEV) e os produtos sintetizados, por meio de DRX, MEV, analises termica diferencial e termogravimetrica, e espectroscopia de infravermelho. No processo realizado a 150 oC foi obtida uma mistura de zeolita A e hidroxisodalita. A 110 oC houve a formacao de zeolita A. Contudo, na menor temperatura de sintese (80 °C) nao houve formacao de material cristalino para as condicoes do processo estabelecidas.

Caracterização mineralógica e geoquímica e estudo das transformações de fase do caulim duro da região do Rio Capim, Pará

The Capim region (Para State, northern Brazil) is the most important kaolin district in the Amazon region, with the largest Brazilian reserves of high whiteness kaolin for the paper coating industry. The main ore (soft kaolin horizon) is located at a depth of about 20 m, being covered by a hard, iron-rich kaolin level, also called flint or semi-flint kaolin, besides a sandy-clay overburden. The beneficiation of this kaolin produces large volumes of wastes, composed mainly of coarse-grained kaolinite, deposited in basins that occupy extensive areas. The main objective of this work is to carry out mineralogical and geochemical studies of the hard kaolin, and to evaluate its thermal transformations through calcination up to 1500 oC. The results show a mineralogical composition dominated kaolinite. The evaluated thermal transformations allows us to describe a series of chemical reactions from kaolinite to metakaolinite and further development of spinel, cristobalite and mullite. For the two analyzed samples, such transformations can start at different temperatures as a result of the different chemical compositions, mainly the iron contents.

Assessment of Hg-contamination in soils and stream sediments in the mineral district of Nambija, Ecuadorian Amazon (example of an impacted area affected by artisanal gold mining)

Abstract The Nambija Mineral District (NMD) is located in the southeastern part of Ecuador, east of Zamora (Zamora Chinchipes country), Ecuadorian Amazon. In this district, Au occurrences have been know since colonial and pre-colonial times, but only after the early 1980s has intensive artisanal Au mining activity been developed. Currently, the different NMD Au occurrences continue to be exploited by artisanal operations and are difficult to control in the study area. The environmental impacts due to Au mining are a consequence of the illegal situation and deficiency in controlling the techniques of ore exploitation. The Au extraction is carried out by outdoor amalgamation, so the indiscriminate use of Hg by artisanal miners, associated with careless methods of tailings disposal, has caused occupational exposure and environmental degradation. The present study evaluated the geochemical dispersion and concentrations of local contamination of metallic Hg in soils, stream sediments and mine tailings in the NMD area. This article aims to contribute to the discussion of environmental changes caused by the artisanal Au mining in the Nambija district. A total of 82 samples (32 soil, 40 stream sediment and 10 mine tailings) were analyzed. The results were compared with the Hg levels in soil and stream sediments considered not to be contaminated in the Nambija mining area and in other areas where Hg is mined in the Amazon basin. In this work, mean total Hg (T-Hg) concentrations of 1.7 μg g−1 in soils and 2.7 μg g−1 in stream sediments have been found. Mercury values in the mine tailing samples revealed values ranging from 89 to 1555 μg g−1. The results found for Hg in the different analyzed materials pointed to contamination of the studied area by this metal, while soil erosion is responsible for an increase in stream sediments T-Hg concentrations in the different aquatic ecosystems of the Nambija Creek and Nambija River.

Síntese hidrotermal de sodalita básica a partir de um rejeito de caulim termicamente ativado

Basic sodalite was successfully synthesized by hydrothermal method using kaolin waste as source of Aluminum and Silicon. This waste is mainly composed by kaolinite and is produced in large amount by kaolin processing industries for paper coating from the Amazon region. Initially, the waste has been calcined at 700 oC for 2 h and then reacted with the following solutions: Na2CO3 and mixture of Na2CO3 + NaOH to 150 oC with autogenous pressure for 24 h. The raw materials and transformed materials were characterized by XRD, FTIR and SEM. In both studied media, well-crystallized, basic sodalite was the only phase synthesized, while in the literature usually a mixture of zeolites is obtained.

Use of industrial kaolin waste from the Brazilian Amazon region for synthesis of zeolite A

Abstract Production of kaolin for the paper-coating industry in the Brazilian Amazon region generates large amounts of waste, most of which is kaolinite. It is known that such materials can be used to synthesize zeolites. The use of kaolin waste for zeolite synthesis could, in principle, help social and economic development while providing valuable materials for industry. Additionally, there is a significant environmental appeal if such wastes could be used instead of new raw materials. This study focused on the production of zeolite A. Samples of the raw material were first calcined (700°C/2 h) to obtain metakaolinite for further reaction with NaOH solution. Different parameters were evaluated to optimize the synthesis conditions of zeolite A. The results showed that zeolite A with a large degree of structural order was generally obtained as the only zeolitic product. The following synthesis conditions were used: temperature 110°C, time 24 h and a Na/Al ratio of 1.36. Hydroxysodalite was also obtained under specific conditions.

Estabilidade térmica da zeólita A sintetizada a partir de um rejeito de caulim da Amazônia

Zeolita A foi calcinada nas temperaturas de 200, 400, 600, 800 e 1000 °C/2 h para estudar sua estabilidade termica. A sintese foi feita a partir de um rejeito de beneficiamento de caulim para a producao de papel de uma empresa mineradora localizada na regiao Amazonica. A caracterizacao da zeolita A calcinada nas diferentes temperaturas foi realizada por difracao de raios X e microscopia eletronica de varredura. A zeolita A permaneceu estavel ate 600 °C, havendo apenas variacoes nas intensidades dos picos em funcao da temperatura. A 800 °C o padrao de difracao apresentado pelo material continuava sendo da zeolita A mas com ausencia de alguns picos. A 1000 °C foi constatado que o produto de calcinacao era constituido de nefelina, mulita e provavelmente sodalita. Essa zeolita tambem foi aquecida em mais duas temperaturas, 900 e 950 °C, com o objetivo de confirmar os dois picos exotermicos observados em curva de analise termica diferencial. Os produtos de calcinacao nessas temperaturas eram constituidos de nefelina, sodalita e mulita.

Synthesis and characterization of zeolite NaP using kaolin waste as a source of silicon and aluminum

The synthesis of zeolite NaP using kaolin waste, from the Amazon region, as a predominant source of silicon and aluminum has been studied. The zeolitisation process occurred in hydrothermal conditions using static autoclaving and the effects of time, temperature, and the Si/Al ratio were investigated. The starting material and the phases formed as reaction products were characterized by XRD, SEM and FTIR. The results showed that pure zeolite NaP is hydrothermally synthesized, at 100 °C for 20 hours, using metakaolin waste material in alkaline medium in presence of additional silica. The XRD and SEM analyses indicate that the synthesized zeolite presents good crystallinity.

The geochemical association Au–As–B–(Cu)–Sn–W in latosol, colluvium, lateritic iron crust and gossan in Carajás, Brazil: importance for primary ore identification

Abstract Carajas, in the state of Para, eastern Amazon, is the most important mineral province in Brazil. Its high plateau landscape contrasts with the lowland domain of the Amazon region. It is developed on old lateritic formations and covered by dense tropical rain forest under a hot and humid tropical climate. The bedrock is made up of high-grade metamorphic terrain of Archean age, greenstone belts and post-tectonic granites. The laterite profiles are complex, partly transformed into yellow to red latosols on the plateau and colluvium on the slopes. The lateritic terrain hosts the gold rich gossans of the Igarape Bahia and Aguas Claras gold mines. Gold is found in red latosols, iron crust, gossans and colluvium. In order to investigate the capacity of these materials as geological sampling media and as indicators of primary ore, a multi-element geochemical survey was carried out at Aguas Claras. Seventy-four samples were analysed for 27 elements by AAS (Au, Cr, Cu, Mn, Ni, Pb and Zn), XRF (Cl, W), OES (B, Be, Ga, Mo, Sc, Sn, Sr, V, Y, Zr and Bi), AA–HG (As, Hg, Se and Sb), ICP–AES (Te), and the mineralogy identified by XRD. The supergene materials are mainly kaolinite, quartz, hematite, maghemite, gibbsite and some goethite. Dravite, muscovite, wolframite and chromite are accessory minerals. In the latosols, As, Au, B, Cr, Cu, Ga, Mo, Pb, Se, Sn, V, W and Zr are concentrated by a factor greater than three times compared to crustal abundance levels, whist gossan and colluviums contain more than ten times the crustal average levels of As, Au, B, Mo, Sn and W. Multivariate R-mode analyses distinguish several associations according to the nature of the supergene materials. The As–Cu–Mn–Pb–B–Au–W–F cluster corresponds to primary signatures still preserved in latosols, iron crust and colluvium; and the Cr–V–Ga–Mo–Ni–Zn–Se–Sc–Hg–Sn–Cl–Y–Zr cluster reflects the general laterite evolution. The latosols preserve the geochemical signature and signal of underlying primary ore, and, together with the colluvium, they can be used as good sampling media.

Geochemistry of rare-earth elements in surface lateritic rocks and soils from the Maicuru complex, Para, Brazil

Abstract The Maicuru area contains a typical alkaline/ultramafic rocks-carbonatite complex that is part of the Guyana Craton, northern Brazil, and exhibits thick lateritic profiles. Tops of profiles are hardened ferruginous horizons frequently called “iron crust” or “ferricrete” which gives rise to landforms called “iron-hat”. The area is being explored for titanium and phosphate resources by Docego, a subsidiary of Companhia Vale de Rio Doce (CVRD). This paper discusses rare-earth elements (REE) mineralization related to aluminum phosphates in Ti-rich surface laterites (iron crusts and lateritic soils) containing anatase over the Maicuru Complex. Some samples show total REE concentrations as high as 20.0 wt.% that is contained in crandallite-goyazite-florencite solid solutions, with the last end member predominant. Mean Σ REE contents are slightly greater in soils than in iron crusts. Chondrite-normalized plots for REE in soils and iron crusts reveal strong fractionations with high (La/Lu)N mean values, where the heavy rare-earth elements (HREE) are strongly depleted compared to light rare-earth elements (LREE), a pattern typical of carbonatite and alkaline rocks. Strong positive and negative Ce anomalies were observed in iron crust samples, but were less common in soils. Lateritic iron crusts distinctly differ from lateritic soils in geochemical properties. Lateritic iron crusts over mineralized rocks are enriched in Ti, Fe, P, REE and resistate minerals, but soils are not. Anomalous concentrations of REE in laterites strongly indicates the presence of phosphates in laterites and in parent rocks. The study illustrates the importance of understanding laterization processes for geochemical exploration in tropical terrains.