Nanoclays and mineral derivates applied to pesticide water remediation.

Although pesticides are vital in agroecosystems to control pests, their indiscriminate use generates innumerable environmental problems daily. Groundwater and surface water networks are the most affected environmental matrices. Since these water basins are mainly used to obtain water for human consumption, it is a challenge to find solutions to pesticide contamination. For these reasons, development of efficient and sustainable remedial technologies is key. Based on their unique properties including high surface area, recyclability, environmental friendliness, tunable surface chemistry and low cost, nanoclays and derived minerals emerged as effective adsorbents towards environmental remediation of pesticides. This study provides a comprehensive review of the use of nanoclays and mineral derivatives as adsorbents for pesticides in water. For this purpose, the characteristics of existing pesticides and general aspects of the relevant clays and minerals are discussed. Furthermore, the study provides insightful discussion on the potential application of nanoclays and their derivatives toward the mitigation of pesticide pollution in the environment. Finally, the outlook and future prospects on nanoclay implications and their environmental implementation are elucidated.

Use of red mud activated at different temperatures as a low cost adsorbent of reactive dye / Uso de lama vermelha ativada em diferentes temperaturas como um adsorvente de baixo custo de corante reativo

ABSTRACT Red mud, a waste product generated during alumina extraction from bauxite, could be used as a low-cost adsorbent. Here, the effect of thermal treatment on the adsorption of Reactive Blue 19 (RB19) dye by red mud was compared with the adsorption capacity of untreated red mud. Thermal treatment of red mud at 500°C results in an increase in adsorption capacity from 357 mg g-1 (untreated red mud) to 416 mg g-1, under acidic conditions. Red mud samples thermally treated at 600°C and 800°C show a reduction in adsorption capacity, however, falling to 337 mg g-1, in acid medium. The change in the maximum adsorption capacity of red mud to RB19 following thermal treatment is associated with specific surface area. Red mud subjected to 500°C can be used for the treatment of water and wastewaters with a higher efficiency than untreated red mud, thus finding possible application in the textile industry.

RESUMO O resíduo de refino de bauxita (lama vermelha) é um resíduo importante gerado na produção de alumínio, podendo ser utilizado como adsorvente de baixo custo. Este estudo teve como objetivo investigar a influência do tratamento térmico na adsorção do corante azul reativo (RB19) por lama vermelha, comparando com a capacidade de adsorção de lama vermelha não tratada termicamente. O tratamento térmico da lama vermelha até 500°C resultou em aumento da capacidade de adsorção, variando seu valor de 357 mg g-1 (lama vermelha não tratada) a 416 mg g-1, em condições ácidas. No entanto, amostras de lama vermelha tratadas termicamente a 600 e 800°C mostraram uma redução na capacidade de adsorção, chegando a 337 mg g-1 em meio ácido. A mudança na capacidade máxima de adsorção de RB 19 na lama vermelha tratada termicamente está associada a valores de área superficial específica. Assim, é possível concluir que a lama vermelha tratada termicamente em 500°C pode ser utilizada para o tratamento de água e águas residuárias com maior eficiência do que a lama vermelha natural nas indústrias têxteis, contribuindo para novos insights sobre possíveis aplicações na indústria têxtil.

Factors and mass ratio analyses for Reactive Blue 19 dye decolorization using ozone: an experimental and analytical modelling approach / Análises de atributos e taxa mássica da descolorização do corante Azul Reativo 19 usando ozônio: modelagem experimental e analítica

ABSTRACT Dyes highly reduce sunlight penetration into the stream, and consequently affect photosynthesis and oxygen transfer into water bodies. An experimental and analytical modelling approach to Reactive Blue 19 (RB19) removal using ozone was carried out. For this purpose, factors and mass ratio analyses were assessed based on batch assays experiments. Removal efficiency increased from 64 to 94% when the dosage increased from 38.4 to 153.6 mg O3.L-1. Results showed that RB19 is more efficiently removed when initial pH is 7. The rate of RB19 removal decreased as the initial dye concentration increased. Kinetic studies showed that the ozonation of RB19 was a pseudo first-order reaction with respect to the dye, and the apparent rate constant declined logarithmically with the initial dye concentration. Mass ratio studies showed that, for the empirical analysis, the power law equation was adequate to describe mass ratio over time and the analytical analysis suggests that the process is influenced by mass transfer in the liquid film as well as in the bulk fluid.

RESUMO Os corantes reduzem significativamente a penetração da luz solar no corpo d'água e, consequentemente, afetam a fotossíntese e a transferência de oxigênio. Realizaram-se modelagens experimental e analítica da remoção do azul reativo 19 por ozônio. Para isso, avaliaram-se os atributos e a taxa mássica por ensaios em batelada. A eficiência de remoção foi de 64 para 94% quando a dose de ozônio aumentou de 38,4 para 153,6 mg O3.L-1. Os resultados mostraram que o azul reativo 19 é removido mais eficientemente em pH inicial da solução de 7. A taxa de remoção do azul reativo 19 reduziu à medida que a sua concentração inicial aumentou. Os estudos cinéticos mostraram que a ozonização do azul reativo 19 é uma reação de pseudoprimeira ordem em relação ao corante e a constante cinética aparente decai logaritmicamente com a concentração inicial de corante. A análise empírica indica que a taxa mássica ao longo do tempo pode ser descrita adequadamente por uma equação de potência, e os estudos analíticos sugerem que o processo é influenciado pela transferência de massa tanto no filme líquido quanto na massa líquida.

Adsorção de Cd 2+, Ni 2+ e Zn 2+ em soluções aquosas usando anidrita e lama vermelha / Adsorption of Cd2+, Ni2+ and Zn2+ in aqueous solutions using anhydrite and red mud

RESUMO Vários minerais e resíduos industriais têm sido estudados para uso como adsorvente, entre eles a lama vermelha e a anidrita. A lama vermelha é um resíduo insolúvel gerado em grande quantidade durante o processamento da bauxita. A anidrita é um sulfato de cálcio (CaSO4) cristalizado sob a forma rômbica e usada como matéria-prima na indústria. Nesta investigação, a capacidade de adsorção de Cd2+, Ni2+ e Zn2+ pela anidrita e pela lama vermelha foi avaliada usando isotermas de adsorção de Langmuir e Freundlich. Os materiais empregados apresentaram adsorção ≥75±1% para todos os metais em soluções aquosas com concentração de 0,5 mmol.25 mL-1. As isotermas baseadas no modelo de Langmuir foram as mais apropriadas para descrever o fenômeno de remoção de Cd2+, Ni2+ e Zn2+ para a anidrita e a lama vermelha, com valores de capacidade máxima de adsorção de 0,47 e 0,51 mmol.g-1 para o Cd2+, 1,18 e 1,56 mmol.g-1 para o Ni2+ e 0,84 e 1,47 mmol.g-1 para o Zn2+, respectivamente. Esses valores foram superiores a outros valores exibidos por materiais empregados como adsorventes descritos em estudos prévios.

ABSTRACT Various minerals and industrial waste have been studied for use as an adsorbent, in particular the anhydrite and the red mud. The red mud is an insoluble residue that is generated in large quantities during the processing of bauxite. The anhydrite is a calcium sulfate (CaSO4), crystallized as a rhombic way, and used as raw material in the industry. In this study, the Cd2+, Ni2+ and Zn2+adsorption capacity by anhydrite and by red mud was evaluated using adsorption isotherms obtained by the Langmuir and Freundlich models. The materials used showed adsorption ≥75±1% for all metals in aqueous solutions with a concentration of 0.5 mmol.25 mL-1. The Langmuir isotherm was more appropriate to describe the phenomenon of Cd2+, Ni2+ and Zn2+ removal, with highest adsorption capacity at 0.47 and 0.51 mmol.g-1 for Cd2+, 1.18 and 1.56 mmol.g-1 for Ni2+, and 0.84 and 1.47 mmol.g-1 for Zn2+, respectively. These values were higher than those ones obtained for other materials described in previous studies.

Adsorption of reactive dye on seawater-neutralised bauxite refinery residue.

This investigation has demonstrated the need for thermal treatment of seawater neutralised red mud (SWRM) in order to obtain reasonable adsorption of Reactive Blue dye 19 (RB 19). Thermal treatment results in a greater surface area, which results in an increased adsorption capacity due to more available adsorption sites. Adsorption of RB 19 has been found to be best achieved in acidic conditions using SWNRM400 (heated to 400°C) with an adsorption capacity of 416.7 mg/g compared to 250.0mg/g for untreated SWNRM. Kinetic studies indicate a pseudosecond-order reaction mechanism is responsible for the adsorption of RB 19 using SWNRM, which indicates adsorption occurs by electrostatic interactions.

Radionuclide concentrations in raw and purified phosphoric acids from Brazil and their processing wastes: implications for radiation exposures.

Radionuclides from the U and Th natural series are present in alkaline rocks, which are used as feedstock in Brazil for the production of raw phosphoric acid, which can be considered as a NORM (naturally occurring radioactive material). As a result of the purification of raw phosphoric acid to food-grade phosphoric acid, two by-products are generated, i.e., solid and liquid wastes. Taking this into account, the main aim of this study was to evaluate the fluxes of natural radionuclide in the production of food-grade phosphoric acids in Brazil, to determine the radiological impact caused by ingestion of food-grade phosphoric acid, and to evaluate the solid waste environmental hazards caused by its application in crop soils. Radiological characterization of raw phosphoric acid, food-grade phosphoric acid, solid waste, and liquid waste was performed by alpha and gamma spectrometry. The (238)U, (234)U, (226)Ra, and (232)Th activity concentrations varied depending on the source of raw phosphoric acid. Decreasing radionuclides activity concentrations in raw phosphoric acids used by the producer of the purified phosphoric acid were observed as follows: Tapira (raw phosphoric acid D) > Catalão (raw phosphoric acids B and C) > Cajati (raw phosphoric acid A). The industrial purification process produces a reduction in radionuclide activity concentrations in food-grade phosphoric acid in relation to raw phosphoric acid produced in plant D and single raw phosphoric acid used in recent years. The most common use of food-grade phosphoric acid is in cola soft drinks, with an average consumption in Brazil of 72 l per person per year. Each liter of cola soft drink contains 0.5 ml of food-grade phosphoric acid, which gives an annual average intake of 36 ml of food-grade phosphoric acid per person. Under these conditions, radionuclide intake through consumption of food-grade phosphoric acid per year per person via cola soft drinks is not hazardous to human health in Brazil. Considering these annual additions of (238)U, (226)Ra, (232)Th and (40)K, and since these radionuclide should be homogeneously distributed in the upper 10 cm of soils with an assumed apparent density of 1.5 g/cm(3), a maximum increase of 0.19 ± 0.03 Bq kg(-1) of soil is expected for (238)U and (234)U. Thus, the addition of solid waste as phosphate fertilizers to Brazilian agricultural soils does not represent a hazard to the ecosystem or to human health.