Chemical and mineralogical features related to the experimental generation of acid drainage in sulfide geomaterials

A drenagem ácida é um problema ambiental capaz de comprometer a qualidade dos recursos hídricos, que decorre da oxidação de sulfetos. A adoção de medidas corretivas ou preventivas depende de uma correta avaliação, não apenas do potencial de geração ácida, mas também da velocidade em que esse processo ocorre. Supõe-se que a cinética de oxidação dos sulfetos está na dependência das características químicas e mineralógicas das amostras, em particular do tamanho e da cristalinidade dos sulfetos presentes. Assim sendo, o presente trabalho foi conduzido com o objetivo de identificar as características químicas e mineralógicas que mais influenciam na dinâmica de geração ácida de amostras provenientes de ambientes geoquímicos distintos, bem como sugerir métodos rápidos para se avaliar a cinética de oxidação de sulfetos. Foram utilizadas amostras de substratos rochosos, em diferentes graus de intemperismo, contendo sulfetos provenientes de distintas províncias geológicas do Brasil, relacionadas à mineração de ouro, carvão, zinco, chumbo, níquel e urânio, além de um solo tiomórfico. As amostras de geomateriais, moídas a 0,149 mm, foram caracterizadas por meio de análises químicas incluindo pH, teores totais de elementos maiores e menores, potencial de acidificação, potencial de neutralização e balanço ácido-base. A caracterização mineralógica foi feita por difratometria de raios-x, espectroscopia Mössbauer, magnetização de saturação e microscopia eletrônica de varredura, com ênfase nos sulfetos. A cinética de oxidação dos sulfetos, presentes nas amostras, foi avaliada por meio de experimento de intemperismo simulado, em que as amostras foram submetidas à oxidação, em condições de laboratório, sob diferentes doses de H 2 O 2 e CaCO 3 , por um período de 357 dias. A solução em contato com as amostras foram drenadas a cada 21 dias, determinando-se o pH, acidez titulável e concentrações de S-sulfato, As, Cu, Cd, Fe, Mn, Ni, Pb e Zn, na solução de equilíbrio. Os resultados obtidos permitem concluir que o método do balanço ácido-base (BAB) não foi eficiente para se avaliar a capacidade de geração ácida de todas as amostras, em particular do substrato de rocha ultrabásica. Com exceção dos carbonatos e sulfetos, os demais minerais presentes nas amostras não apresentaram influência marcante na cinética de geração de drenagem ácida. A taxa de geração ácida foi determinada, primordialmente, pelo tamanho dos cristais dos sulfetos, sendo que a presença de pirita framboidal , pirrotita e marcassita imprimiu um ritmo particularmente acelerado na cinética de oxidação, em relação aos outros sulfetos. As expectativas de desenvolvimento de um método analítico capaz de simular a cinética de drenagem ácida, comum para amostras de naturezas geoquímicas distintas, foram pouco promissoras nas condições experimentais utilizadas.Acid drainage is an environmental problem that affects the quality of water, which arises from sulfide oxidation. Adopting corrective or preventive measures depends on a suitable evaluation of not only the acid generation potential, but also on the reaction kinetics. It is hypotesized that the kinetics of sulfide oxidation depends on the chemical and mineralogical characteristics of samples, especially the size and cristalinity of sulfides. Nevertheless, ranking those characteristics based on the relative importance is still a matter of debate. Thus, the present work was performed in order to identify the chemical and mineralogical features that influences the acid generation dynamics in samples from different geochemical environments, as well as to suggest fast methods to evaluate the kinetics of sulfide oxidation. Samples of rocky substrats, on diferents weatering grades, containing sulfides from different geological provinces of Brazil, related to the mining of gold, coal, zinc, lead, nickel and uranium, and a thiomorphic soil were used. The samples were characterized through chemical analyses including pH, total contents of major and minor elements, acidification potential, neutralization potential and acid-base accounting (ABA). The mineralogical characterization was made by X-ray difractometry, Mössbauer spectroscopy, magnetization saturation and scanning electronic microscopy, with emphasis in sulfides. The kinetics of sulfide oxidation in samples was evaluated through simulated weathering experiment by submitting the samples to the oxidation at in vitro conditions, under different doses of H 2 O 2 and CaCO 3 , during a 357 days period. The equilibrium solutions were drained every 21 days, in order to determine pH, tritable acidity and S- sulfate, As, Cd, Fe, Mn, Ni, Pb and Zn concentrations. The results showed that the ABA method was not efficient to evaluate the acid generation potential overall the samples, especially to the ultrabasic rocky substrat. Excepting the carbonates and sulfides, other minerals in the samples did not influence the kinetics of acid drainage generation. The acid drainage rate was primarily determined by the size of the sulfides crystals, and the xpresence of framboidal pyrite, pyrrhotite and marcasite promoted a particularly fast rate to the oxidation kinetics. Expectations for developing a common static method that simulates the kinetics of acid drainage, suitable for all samples of different geochemical natures, were poorly promising at these experimental conditions.Coordenação de Aperfeiçoamento de Pessoal de Nível Superio

Characterization of verdete rock as a potential source of potassium

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

Arkeologiska och förhistoriska världar: fält, erfarenheter och stenåldersplatser i sydvästra Skåne

The humic substances, major constituents of the organic matter of the substrates, play an important role in plant development, including: the availability of nutrients, the generation of negative charges (CEC) and the buffering effect. Based on this, this study aimed to use the molecular absorption spectroscopy in the ultraviolet-visible region (UV-VIS), the vibrational spectroscopy Fourier transform infrared (FTIR) and the elementary analysis CHN/O techniques to characterize the humic acid (HA) and fulvic acid (FA) fractions of the humic substances of five organic substrates, named as T1, T2, T3, T4, and T5, which were produced at the Federal University of Tocantins – Campus Gurupi. The molecular absorption spectra in UV-VIS and FTIR on the T1, T2, T3, T4 and T5 substrates showed humification, the formation of negative charges, which is related to the cation exchange capacity (CEC) and the complexation of metal ions that are considered nutrients. The biggest humification was shown for the T4 substrate, in function of its higher cabon-acid humic/carbon-acid fulvic ratio and the lower C/N ratio, allied to a negative charge generation, the low E4/E6 ratio found in the humic acid fraction. The complexation of metal nutrient ions indicates the greatest potencial of its use for seedlings production and the conservation of the chemical and physical properties of the organic substrate. The humic substances, major constituents of the organic matter of the substrates, play an important role in plant development, including: the availability of nutrients, the generation of negative charges (CEC) and the buffering effect. Based on this, this study aimed to use the molecular absorption spectroscopy in the ultraviolet-visible region (UV-VIS), the vibrational spectroscopy Fourier transform infrared (FTIR) and the elementary analysis CHN/O techniques to characterize the humic acid (HA) and fulvic acid (FA) fractions of the humic substances of five organic substrates, named as T1, T2, T3, T4, and T5, which were produced at the Federal University of Tocantins – Campus Gurupi. The molecular absorption spectra in UV-VIS and FTIR on the T1, T2, T3, T4 and T5 substrates showed humification, the formation of negative charges, which is related to the cation exchange capacity (CEC) and the complexation of metal ions that are considered nutrients. The biggest humification was shown for the T4 substrate, in function of its higher cabon-acid humic/carbon-acid fulvic ratio and the lower C/N ratio, allied to a negative charge generation, the low E4/E6 ratio found in the humic acid fraction. The complexation of metal nutrient ions indicates the greatest potencial of its use for seedlings production and the conservation of the chemical and physical properties of the organic substrate

Influência da qualidade da água de irrigação na dispersão da argila de Latossolos

O fenômeno de dispersão da argila do solo pode ser provocado pela qualidade da água de irrigação. Objetivou-se estudar o efeito da irrigação com água com diferentes condutividades elétricas (CE), combinadas com diferentes valores de Relação de Adsorção de Sódio (RAS), na dispersão da argila de solos, de diferentes mineralogias, do Estado de Minas Gerais. As amostras foram coletadas no horizonte B de solos das cidades de Viçosa, Belo Horizonte e Barroso, classificados como Latossolo Vermelho-Amarelo distrófico típico (LVA), Latossolo Vermelho perférrico típico (LV) e Latossolo Vermelho distroférrico típico (LVd) destacados, respectivamente, pela presença de argilominerais caulinita, hematita e gibbsita. Os tratamentos corresponderam à percolação, nos três solos, de soluções de NaCl e CaCl2 preparadas de forma a se obter seis diferentes valores de CE (20; 50; 100; 200; 400 e 800 mS m-1) e cinco de RAS (0, 5, 10, 20 e 40 mmol c L-1), em três repetições, dispostos em um delineamento em blocos casualizados. A aplicação das soluções foi feita em permeâmetros de coluna vertical e carga constante. A solução foi aplicada até o momento em que a CE do efluente se aproximou daquela da solução aplicada (C/C0 = 1,0). Para avaliar o efeito das soluções aplicadas na estrutura do solo, foram quantificados os teores de argila dispersa em água (ADA). Os valores de ADA nas amostras de solo submetido à percolação das diferentes soluções salino-sódicas (ADA-S) foram relacionados com a CE e a RAS da solução percolada, ajustando-se superfícies de resposta com este fim. O comportamento dos solos foi diferenciado, no que se refere à dispersividade da argila, o que estava associado à mineralogia, mas, também, ao grau de intemperismo do solo. O LVA apresentou comportamento não dispersivo em todos os tratamentos e, no geral, todas as soluções de percolação, notadamente as de maiores CE, independentemente dos valores de RAS, proporcionaram diminuição no teor de argila dispersa (ADA-S) nos solos LV e LVd

Soil-geomorphology interactions and paleoclimatic implications of an ornithogenic soil toposequence on Rata Island, Fernando de Noronha Archipelago, South Atlantic

The formation of highly phosphatized soils on sites of avian activity is a common feature of oceanic islands. We characterized a toposequence of phosphatic soils on Rata Island, to evaluate the soil genesis based on local topographic variations. For this purpose, four soils ranging from the upper hill down to the lowest landscape position on the island, representing a range of parent materials (basalt and calcareous sands), were analyzed. In the lowest landscape position a shallow Regosol was identified, strongly influenced by birds and marine sprays, developed on “karstified” Pleistocene calcarenites; the three other soils in the upper part of the toposequence are Ornithogenic Cambisols, ranging from a deep Cambisol profile on Basalt lava to intermediate Cambisols on mixed colluvial sediments of the basalt/ calcareous. The lowermost Regosol is associated with a rugged landscape with strong calcarenite dissolution and karstification. The soil phosphatization is clearly an inherited process of the Late Quaternary age, when climate conditions were different. Initial weathering took place in the last interglacial period, under wetter conditions during which the Tertiary basalts were strongly weathered, leaving corestones in a saprolitic, oxidized mass. In the late Pleistocene, a gentle surface distributed these weathering products along the pediment slopes as colluvial materials, whereas in the coastal areas aeolian processes formed large sand dunes composed of reworked calcareous sands from marine sources during a time of very low sea level. During this time, widespread bird activity accounted for secondary apatite formation on the surface of calcareous oolites. Finally, the Holocene warming was accompanied by increasing sea level, enhanced tropical weathering, Fe and Al mobility and variscite formation superimposed on degraded Ca-phosphates, forming two phase phosphatic aggregates

Thermal and chemical solubilization of verdete for use as potassium fertilizer

Thermal and chemical treatments were used to investigate the solubilization of potassium from verdete, a glauconitic rock. Fluxing agents were evaluated at distinct temperatures and proportions. Chemical dissolution of verdete was studied with increasing amounts of acids or bases at different temperatures and reaction times. In the calcination test, the presence of fluxing agents was critical to increasing the rock solubility, in addition to the effects of temperature and material ratios. The content of water-soluble K was 100, 100, 85, and 42% when using the salts LiCl, CaCl2.2H2O, Na2CO3, NaCl, respectively, as fluxing agents. The salts CaSO4, CaCO3 and Ca3(PO4)2 were ineffective as fluxing agents. In the chemical treatments, the reaction with the base NaOH was more efficient than the acids to solubilize K. It was possible to solubilize up to 60% of K from verdete with 4.0 mol L− 1 NaOH, at 150 °C for 120 min. Among the acids, H3PO4 was the most efficient, promoting solubilization of up to 42% K, with 4.0 mol L− 1 H3PO4, at 225 °C, for 120 min. When using the concentrated acid waste and shaking for 144 h, up to 75% of K could be solubilized from the rock. It was concluded that the heated treatments were most effective in solubilizing verdete, followed by the acid waste, which are processes required for the production of soluble potassium fertilizers from unconventional sources of low reactivity

Induction of a geochemical barrier for As, Fe and S immobilization in a sulfide substrate

Acid mine drainage (AMD) is an environmental concern due to the risk of element mobilization, including toxic elements, and inclusion in the food chain. In this study, three cover layers were tested to minimize As, Fe and S mobilization from a substrate from former gold mining, containing pyrite and arsenopyrite. For this purpose, different layers (capillary break, sealant and cover layer) above the substrate and the induction of a geochemical barrier (GB) were used to provide suitable conditions for adsorption and co-precipitation of the mobilized As. Thirteen treatments were established to evaluate the leaching of As, Fe and S from a substrate in lysimeters. The pH, As, Fe, S, Na, and K concentrations and total volume of the leachates were determined. Mineralogical analyses were realized in the substrate at the end of the experimental period. Lowest amounts of As, Fe and S (average values of 5.47, 48.59 and 132.89 g/lysimeter) were leached in the treatments that received Na and K to induce GB formation. Mineralogical analyses indicated jarosite formation in the control treatment and in treatments that received Na and K salts. However, the jarosite amounts in these treatments were higher than in the control, suggesting that these salts accelerated the GB formation. High amounts of As, Fe and S (average values of 11.7, 103.94 and 201.13 g/lysimeter) were observed in the leachate from treatments without capillary break layer. The formation of geochemical barrier and the use of different layers over the sulfide substrate proved to be efficient techniques to decrease As, Fe and S mobilization and mitigate the impact of acid mine drainage