RESUMO O intemperismo de alguns minerais silicáticos em rochas moídas pode ocorrer em alguns dias de cultivo e gerar diferentes propriedades físico-químicas, com benefícios potenciais a solos tropicais. Objetivou-se investigar a infuência da rizosfera do milho (Zea mays L.) nos produtos do intemperismo e na capacidade de troca de cátions da biotita-Mg da biotita xisto e biotita-Fe da biotita sienito. Um experimento em vasos foi conduzido de forma que plantas e rochas moídas foram avaliadas por sete ciclos de cultivo sucessivos. Os nutrientes ferro e potássio foram adquiridos da biotita xisto e da biotita sienito durante o cultivo. O intemperismo das biotitas promovido pela rizosfera causou mudanças mineralógicas. A mudança mais expressiva nos padrões da difração de raios-X ocorreu na fração com partículas < 53 µm, mas as frações 53-300 µm também mudaram. A alteração na biotita-Mg, que possui menor relação Fe/Mg nos sítios octaedrais que a biotita-Fe, foi responsável pelo maior aumento na capacidade de troca de cátions nas frações < 300 µm. Entretanto, o processo de intemperismo da biotita-Fe, a qual apresenta alta relação Fe/Mg nos sítios octaedrais, não aumentou a capacidade de troca de cátions.

ABSTRACT The weathering of some silicate minerals in crushed rocks may occur in a few days of cropping and generate different physicochemical properties, with potential benefits to tropical soils. This study aimed to investigate the infuence of maize (Zea mays L.) rhizosphere on the weathering products and on the cation exchange capacity of Mg-biotite from biotite schist and Fe-biotite from biotite syenite. An experiment was carried out in pots, so that plants and crushed rock materials could be evaluated during seven successive growth cycles. The nutrients iron and potassium were taken up from biotite schist and biotite syenite during cropping. The weathering of both biotites promoted by the rhizosphere caused mineralogical changes. The most expressive change in the X-ray diffraction patterns occurred in the < 53 µm particle size fraction; however, the 53-300 µm fractions also changed. The alteration in the Mg-biotite, which has a lower Fe/Mg relation in octahedral sites than the Fe-biotite, was responsible for the most expressive cation exchange capacity increase in the fractions < 300 µm. However, the Fe-biotite weathering process, which presents a higher Fe/Mg relation in octahedral sites, did not increase the cation exchange capacity.

Abstract In the bentonite industry - exploration and beneficiation - ore quality control has been traditionally carried out using the swelling parameter, denominating those that swell as naturally sodium bentonites and those that do not as naturally non-sodium bentonites. However, the properties of the bentonites can vary due to the quantity and cationic type of montmorillonite. The variation in those properties cannot always be predicted, because there is still no consolidated and convenient method for clays mineralogical quantification. A quantification via PXRD using the Rietveld method is only reliable when all the crystalline structures of the mineral phases are known. This is not the case for bentonites, since the montmorillonite shows turbostratic disorder that leads to extremely wide and asymmetric non-basal reflections that are not considered in the available structural models. Thus, in this work, is generate a calibrated hkl model for a Brazilian montmorillonite applying the combined Rietveld-Le Bail-Internal Standard method developed by Paz et al. (2018). The study concluded that the combined method is a good choice for the mineralogical quantification of the bentonites, handling turbostratic disorder of montmorillonite, since the develop hkl phase model showed good results in mixtures with >50% montmorillonite content (greater precision and reproducibility).

RESUMO As bauxitas metalúrgicas da região de Paragominas-PA (norte do Brasil) comumente apresentam uma alta quantidade de caulinita. Durante a lixiviação da bauxita nas condições de processo Bayer, este mineral reage com NaOH formando indesejavelmente sodalita, o qual é insolúvel e, portanto, descartada com o resíduo sólido, causando significativa perda do agente lixiviante. Neste trabalho foi dada a atenção a dois tipos principais de sodalita formadas em função de diferenças na concentração caustica e tempo de reação. Assim, o processo hidrotérmico foi conduzido em temperatura de 150 °C, concentração caustica variando de 2,5 à 5,0 M e tempo variando de 60 à 420 min. Os resultados mostraram que estas variáveis afetam tanto a velocidade da transformação da caulinita em sodalita como a cristaloquímica desta fase, resultando na formação de dois tipos de sodalita: 1) sodalita básica tetrahidratada, fase mais estável formada inicialmente e remanescente em todas as condições do processo; e 2) hidrosodalita, a qual é a fase secundária, menos estável e observada apenas nas condições intermediárias. Esta última fase é mais desejável no contexto Bayer devido a menor quantidade de NaOH consumida. Observou-se que o favorecimento da formação desta fase depende de maiores tempos, concentração caustica e quantidade de caulinita.

ABSTRACT Metallurgical bauxites from Paragominas-PA region (northern Brazil) commonly exhibit high amounts of kaolinite. During caustic leaching of bauxite in the Bayer process conditions, this mineral reacts with NaOH and undesirable sodalite is formed, which is insoluble and therefore discarded with the solid residue, causing significant losses of the leaching agent. In the present work, an attention was given to two main types of sodalite formed as function of differences in caustic concentration and residence time. Thus, the hydrothermal process was carried out at temperature of 150 °C, caustic concentration ranging from 2.5 to 5.0 M and time varying from 60 to 420 min. Results showed that these variables affect both the speed of kaolinite to sodalite transformation as the crystal chemistry of the two main types of sodalite phases formed: 1) tetrahydrate basic sodalite, which is the more stable phase initially formed and that remains during all process conditions; and 2) hydrosodalite, which is the secondary phase, less stable and observed only in intermediate conditions. This last phase is more desirable in the Bayer context due the less amount of NaOH consumed. The favoring of this phase formation depends on the long time, caustic concentration and the amount of kaolinite.

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.

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.