Roberto de Freitas Neves

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.

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.

Application of bauxite waste from amazon region in the heavy clay industry

In this work, a method was developed for the application of red mud, an alkaline leaching waste, from a bauxite processing plant located in northern Brazil (Amazon region) as starting material for heavy clay products. Samples were prepared by pressing blends of red mud and clay, which were then fired at temperatures from 900 oC to 1190 oC. Characterization was carried out by chemical analysis, differential thermal analysis (DTA) and X-ray diffraction (XRD), and the following ceramic properties were evaluated: water absorption, linear shrinkage and flexural strength. In order to evaluate the Na+ stability in the dense ceramic, leaching tests were also carried out on the specimens after sintering process. Results indicated that samples with 50 and 70 wt% of red mud are proper for being used in the production of ceramic bodies, due to its excellent properties, mainly high mechanical resistance and low water absorption, showing thus, an option to minimizing the environmental impacts caused by the aluminum industry.

Color and shade parameters of ultramarine zeolitic pigments synthesized from kaolin waste

Ultramarine pigments were successful synthesized from zeolite A obtained from kaolin waste. This waste has been used as an excellent source of silicon and aluminum for zeolite synthesis because of its high kaolinite concentrations and low contents of other accessory minerals. The cost is naturally less than the industrialized product. Color additives (Sulfur and Sodium Carbonate) were mixed with different proportions of zeolite A and further calcined for 5 h at 500 °C. They were characterized by XRD and XRF in addition to visual classification by color and shade. These products show colors from blue to green at different shades, both influenced by the amount of additives and cooling rate after calcination. Thus, a different quantity of the same additives in the same zeolitic matrix provides an increase in the color intensity. Cooling rate after calcination induces the color change which is substantially important in the pigments production.

Synthesis of Zeolitic Materials Using as a Source of SiO2 and Al2O3 Calcined Kaolin Waste

This paper has as main objective synthesize zeolitic materials in hydrothermal conditions using as the predominant source of Si and Al a waste in powder generated from kaolin processing industries for paper-coating from the Brazilian Amazon region, thus transforming a material of low commercial value in another with higher added value, and can thus be used in future in adsorption and catalysis. For this were tested compositions of the mixture with different molar ratios of Na2O/Al2O3 and SiO2/Al2O3 considering the effects time-temperature of crystallization. The starting material and the phases formed as synthetic products were characterized by XRD, SEM and FTIR. The results show that the methodology developed with metakaolinite from a thermically activated kaolin waste at 700 º C for 2h reacting in alkaline medium in the presence of an additional source of silica, zeolitic phases were obtained with structure FAU-type and GIS-type in the samples synthesized.

Mg-BENTONITE IN THE PARNAÍBA PALEOZOIC BASIN, NORTHERN BRAZIL

Bentonite deposits are rare in Brazil and most of their production comes from a single region. A new bentonite occurrence, the Formosa bentonite from northern Brazil, is described here. The occurrence is associated with altered Mesozoic volcanic rocks of the Parnaíba Sedimentary Basin, one of the largest continental flood basalt (CFB) provinces on Earth. The purpose of the present study was to evaluate the physical and chemical properties of a new smectite-bearing deposit in Brazil. Analysis has shown that the major mineral present in the Formosa bentonite is a dioctahedral smectite along with minor amounts of hematite, K-feldspar, and kaolinite. Quartz is absent. A Li+-saturation test (Hofmann-Klemen treatment) revealed a montmorillonite smectite; large interlayer-Mg2+ contents revealed by N2 adsorption/desorption and cation exchange capacity results suggested a Mg-bentonite. This characterization helped to explore the structure-functionality (reactivity) relationship and to develop index tests for industrial applications and the research of new materials.Use of this material as a desiccant-grade bentonite is envisaged (desiccant-grade bentonites contain Mg2+ and/or Ca2+ as the dominant exchangeable cations), or it could be activated with Na+ for use in many industrial applications (e.g. as a drilling fluid or for pelletizing iron ore). The large areal occurrence of the flood basalts suggests the possibility of very large deposits of these bentonites, a promising new exploration target for this class of industrial minerals in northern Brazil.