RESUMO
In this study, four Brazilian clays (Bofe, Verde-lodo, commercial Fluidgel, and expanded commercial vermiculite) were evaluated for their adsorptive capacity and removal percentage in relation to different toxic metals (Ni2+, Cd2+, Zn2+, and Cu2+). The best results were obtained by expanded vermiculite, with cadmium removal reaching values of 95%. The most promising clay was modified by the sodification process, and the metal cadmium was used to evaluate the ion exchange process. The clays expanded vermiculite (EV) and VNa-sodified vermiculite were evaluated by equilibrium study at 25, 35, and 45 °C. At 25 °C, EV obtained a maximum adsorption capacity of 0.368 mmol/g and sodified vermiculite 0.480 mmol/g, which represents an improvement of 30.4% in modified clay capacity. At 45 °C, the sodified vermiculite reached 0.970 mmol/g adsorption capacity. The Langmuir, Redlich-Peterson Freundlich, and Dubinin-Raduskevich models were adjusted to the results. Langmuir provided the best fit among the models. The thermodynamic quantities (ΔS, ΔH, and ΔG) demonstrated that the process is spontaneous and endothermic and the metal is captured by physisorption and chemisorption in the studied temperature range. For the ion exchange equilibrium, the binary Langmuir and binary Langmuir-Freundlich models were adjusted to the expanded vermiculite and sodified vermiculite isotherms, respectively. Both models were predictive. Thermal analysis indicated good heat resistance even after material modification. The apparent and real densities demonstrated that after each treatment or contamination, the clayey material undergoes contraction in its structure. An improved efficiency of the adsorbent was found after sodification.
Assuntos
Silicatos de Alumínio , Argila , Termodinâmica , Adsorção , Argila/química , Brasil , Troca Iônica , Silicatos de Alumínio/química , Poluentes Químicos da Água/química , Metais/químicaRESUMO
The organic xerogel (OX) was synthesized through sol-gel polymerization of formaldehyde and resorcinol in inverse emulsion using Na2CO3 as a catalyst. Meanwhile, OX containing sepiolite (OX-Sep) and vermiculite (OX-Ver) were prepared similarly to OX but adding clays during synthesis. All materials were mesoporous and presented spherical morphology, and the surface of these materials exhibited an acidic character because the concentration of acidic sites was higher than those of basic sites. Cd(II) adsorption from aqueous solutions onto OX, OX-Sep, and OX-Ver was examined, and the OX-Sep showed the highest adsorption capacity towards Cd(II) of 189.7 mg/g, being 1.5, 2, and 36 times higher than that of OX-Ver, OX, and Sep. The OX-Sep capacity for adsorbing Cd(II) was significantly lessened by decreasing the pH from 7 to 4 and raising the ionic strength from 0.01 N to 0.1 N. This trend was ascribed to electrostatic attraction between the Cd+2 in water and the negatively charged surface of OX-Sep. Besides, desorption studies at pH 4 showed that the average desorption percentage of Cd(II) adsorbed on OX-Sep was 80%. The characterization results and the effect of the operating conditions on the adsorption capacity proved that electrostatic attraction and cation exchange play a crucial role in the adsorption mechanism.
Assuntos
Silicatos de Alumínio , Cádmio , Microesferas , Adsorção , Cádmio/química , Silicatos de Alumínio/química , Silicatos de Magnésio/química , Poluentes Químicos da Água/química , Concentração de Íons de Hidrogênio , Géis/químicaRESUMO
Alum sludge (AS) is a by-product generated from drinking water treatment and produced in large amounts around the world. Its chemical composition makes this waste an emerging alternative source of silicon and aluminum for aluminosilicates or zeolite material production, which can add value to residues and contribute to the circular economy process on a global scale. In this sense, and considering the scarcity of information about AS, this review shows data collection about AS in different countries, including generation, chemical composition, and disposal information. The reuse of AS is discussed based on circular economy and the environmental gains derived from such approaches are highlighted, including the possibility of utilization with other residues (e.g., ash, bioproducts, etc). Moreover, this review shows and discusses the benefits and challenges of AS reuse in the synthesis process and how it can be a sustainable raw material for aluminosilicates and zeolite synthesis. The most common conditions (conventional or non-conventional) in zeolite synthesis from AS are mentioned and advantages, limitations and trends are discussed. The discussions and data presented can improve the AS management and reuse legislations, which certainly will collaborate with sustainable AS use and circular economy processes.
Assuntos
Compostos de Alúmen , Silicatos de Alumínio , Reciclagem , Esgotos , Purificação da Água , Zeolitas , Zeolitas/química , Silicatos de Alumínio/química , Compostos de Alúmen/química , Purificação da Água/métodos , Reciclagem/métodos , Eliminação de Resíduos Líquidos/métodosRESUMO
To assess the physical properties and topographical aspect of dental enamel's surface microhardness (KHN), surface roughness (Ra), and color parameters CIELAB (∆Eab*), CIEDE 2000 (∆E00), and whiteness index for dentistry (∆WID) after toothbrushing with experimental toothpaste formulations with the following mineral clay types: kaolin, Sparclay SGY, and Tersil CGY used as abrasive component. Scanning electron microscopy (SEM) was performed for topographical analyses purposes. A total of 96 bovine incisors were used in the experiment. They were divided into eight experimental groups (n = 12), namely: NC-negative control (no treatment), CT12-Colgate Total 12®, CMP-Colgate® Máxima Proteção Anticáries, K-kaolin experimental toothpaste, SGY-Sparclay SGY experimental toothpaste; CGY-Tersil CGY experimental toothpaste, SD-SiO2 experimental toothpaste, and CC-CaCO3 experimental toothpaste. All samples were subjected to mechanical brushing protocol with 5000 cycles and kept in artificial saliva with daily exchanges. KHN was analyzed through the mixed linear model for repeated measures over time. Ra was analyzed through nonparametric Kruskal Wallis and Dunn tests to compare the groups. Paired Wilcoxon test was run to compare experimental times. ∆WID, ∆Eab*, and ∆E00 were analyzed through Kruskal Wallis and Dunn tests. All analyses were performed in R* software, at 5% significance level. EXP_SGY recorded higher KHN than EXP_SiO2 and EXP_CaCO3, whereas EXP_K showed increased Ra in comparison to CMP (p = 0.0229). ∆Eab and ∆E00 were significantly higher in the CT12, EXP_SiO2, and EXP_CaCO3 groups than in the NC and EXP_K (p < 0.0001). There were no significant changes in ∆WID (p = 0.0852). According to SEM results, toothbrushing with experimental toothpastes added with mineral clay types did not have significant impact on enamel's polishing and smoothness. CLINICAL RELEVANCE: Mineral clays have a broad application in the cosmetic industry, and recently, they have been used in the formulation of vegan toothpaste.
Assuntos
Silicatos de Alumínio , Argila , Esmalte Dentário , Dureza , Escovação Dentária , Cremes Dentais , Cremes Dentais/química , Animais , Bovinos , Argila/química , Silicatos de Alumínio/química , Propriedades de Superfície , Microscopia Eletrônica de VarreduraRESUMO
The removal of dyes from effluents of textile industries represents a technological challenge, due to their significant environmental impact. The application of halloysite (Hal) and palygorskite (Pal) clay minerals as adsorbents for the removal of Congo red (CR) and methylene blue (MB) was evaluated in this work. The materials were applied both in natural and acid-treated forms, and characterized by XRD, XPS, SEM-EDS, FTIR, and N2 adsorption-desorption isotherm techniques to identify their properties and main active sites. The adsorbents showed potential to remove CR (> 98%) and MB (> 85%) within 180 min, using 0.3 g adsorbent and initial dye concentration of 250 mg L-1. Semi-empirical quantum mechanical calculations (SQM) confirmed the interaction mechanism between dyes and the adsorbents via chemisorption (- 69.0 kcal mol-1 < Eads < - 28.8 kcal mol-1), which was further observed experimentally due to the high fit of adsorption data to pseudo-second order kinetic model (R2 > 0.99) and Langmuir isotherm (R2 > 0.98). The use of Pal and Hal to remove dyes was proven to be economically and environmentally viable for industrial application.
Assuntos
Argila , Corantes , Compostos de Silício , Poluentes Químicos da Água , Adsorção , Argila/química , Corantes/química , Poluentes Químicos da Água/química , Compostos de Silício/química , Minerais/química , Azul de Metileno/química , Silicatos de Alumínio/química , Compostos de Magnésio/química , Cinética , Vermelho Congo/químicaRESUMO
Produced water (PW) generated by oil companies is a highly impacting waste that contains chemicals such as metals and organic and inorganic compounds. Given its polluting potential, PW requires effective treatment before being discharged into the environment. Conventional treatments have limited efficiency in removing PW toxicity, so alternative approaches must be developed and standardized. In this context, treatment with adsorbent materials like magnetized vermiculite (VMT-mag) is highlighted. This work aimed to evaluate the efficiency of treatment with VMT-mag in reducing PW toxicity to aquatic biota. For this purpose, three aquatic species (the midge Chironomus riparius, the planarian Girardia tigrina, and the crustacean Daphnia magna) were exposed to untreated PW and to PW treated with VMT-mag at laboratory conditions. The assessed endpoints included mortality, growth, emergence, and developmental time of C. riparius; mortality, locomotion, feeding, and head regeneration of G. tigrina; and intrinsic population growth rate (r) and reproductive output of D. magna. The results showed that all the species exposed to raw PW were impaired: C. riparius had delayed development, G. tigrina had reduced locomotor activity and delayed head regeneration, and D. magna had reduced reproduction and delayed intrinsic population growth rate (r). Most of the analyzed parameters showed that treatment with VMT-mag diminished PW toxicity. Therefore, using VMT-mag to treat PW may be the key to reducing the PW effects on aquatic organisms.
Assuntos
Silicatos de Alumínio , Indústria de Petróleo e Gás , Eliminação de Resíduos Líquidos , Águas Residuárias , Poluentes Químicos da Água , Animais , Silicatos de Alumínio/química , Organismos Aquáticos , Daphnia , Água/química , Poluentes Químicos da Água/química , Poluentes Químicos da Água/toxicidade , Águas Residuárias/química , Eliminação de Resíduos Líquidos/métodos , Testes de ToxicidadeRESUMO
BFS-MK-based alkali-activated materials are well established as an alternative for sustainable and green construction. This work aims to collaborate and encourage the use of biomass ashes, such as sugarcane bagasse ash (SCBA), as a precursor in alkali-activated materials (AAM). This ash is a rich source of aluminosilicate, which is a primary requirement for this application. In addition, this waste is still an environmental liability, especially in developing countries, and with a large volume of annual production. Thus, in this research, alkali-activated pastes (AA) were produced using sugarcane bagasse ash (SCBA), granulated blast furnace slag (BFS) and metakaolin (MK) as precursors. In addition, environmental gains were encouraged with energy savings, with no extra reburn or calcination steps in the SCBA. Thus, the precursors were characterized by laser granulometry, X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The pastes were produced by mixing the precursors with the activator, composed of a mixture of sodium hydroxide 8 mol/L and sodium silicate. Aiming to study the incorporation of SCBA, all samples have a precursor/activator ratio and a BFS/(BFS + MK) ratio constant of 0.6. The compressive strength analysis, FTIR, XRD, TGA, SEM and isothermal calorimetry analyses pointed out the occurrence of alkaline activation in all proposed samples for curing times of 7, 28 and 91 days. The sample GM0.6-BA0 (15% SCBA) achieved the highest compressive strength among the samples proposed (117.7 MPa, at 91 days), along with a good development of strength throughout the curing days. Thus, this work presents the properties of alkaline-activated pastes using SCBA as a sustainable and alternative precursor, seeking to encourage the use of raw materials and alternative waste in civil construction.
Assuntos
Álcalis/química , Silicatos de Alumínio/química , Biomassa , Celulose/química , Saccharum/químicaRESUMO
Helicobacter pylori can be found in the stomach of about half of the humans, and a large population can be associated with serious diseases. To survive in the stomach H. pylori increases the pH locally by producing ammonia which binds to H+ becoming ammonium. This work investigated the effects on the in-vitro growth of H. pylori of a natural cation-exchanger mainly composed (≈70%) of clinoptilolite and mordenite. The zeolitized material from Cuba was evaluated in its original form (M), as well as in its Na- (M-Na) and Zn-exchanged (M-Zn) counterparts. In the preliminary agar cup diffusion test, H. pylori revealed susceptibility only to M-Zn, with a direct relationship between concentration and width of inhibition halo. Further experiments evidenced that bacterium replication increases when ammonium is supplied to the growth medium and decreases when zeolites subtract NH4+ via ion exchange. Due to the multi-cationic population of its zeolites M was not effective enough in removing ammonium and, in the Minimum Inhibitory Concentration (MIC) test, allowed bacterial growth even at a concentration of 50 mg/mL. Inhibition was achieved with M-Na because it contained sodium zeolites capable of maximizing NH4+ subtraction, although the MIC was high (30 mg/mL). M-Zn evidenced a more effective inhibitory capacity, with a MIC of 4 mg/mL. Zinc has antimicrobial properties and H. pylori growth was affected by Zn2+ released from clinoptilolite and mordenite. These zeolites, being more selective towards NH4+ than Zn2+, can also subtract ammonium to the bacterium, thus enhancing the efficacy of M-Zn.
Assuntos
Silicatos de Alumínio/farmacologia , Antibacterianos/farmacologia , Helicobacter pylori/efeitos dos fármacos , Zeolitas/farmacologia , Zinco/farmacologia , Silicatos de Alumínio/química , Compostos de Amônio/metabolismo , Compostos de Amônio/farmacologia , Antibacterianos/química , Cuba , Helicobacter pylori/crescimento & desenvolvimento , Troca Iônica , Testes de Sensibilidade Microbiana , Sódio/química , Zeolitas/química , Zinco/químicaRESUMO
This study sought to analyze the effect of curing temperature on mechanical strength and microstructure of a copper tailing-based geopolymer via scanning electron microscopy (SEM), HCl extraction, nuclear magnetic resonance (NMR), and X-ray diffraction (XRD). The distribution of gel formed in geopolymers tended to be uniform with increasing curing temperature from 25 to 80 °C. Moreover, the percentage of Si sites in C-S-H and N-A-S-H gels increased from 62.08% to 78.94% and more tetrahedral [AlO4] was incorporated into the tetrahedron [SiO4] backbone, leading to an increase of compressive strength from 10.2 to 39.6 MPa. When the curing temperature was increased to 120 °C, the percentage of Si sites in C-S-H and N-A-S-H gel decreased to 69.52%, and the compressive strength decreased to 27.5 MPa. Moderately elevated curing temperature promoted the dissolution of aluminosilicate while curing temperatures above 80 °C hindered it. Excessive curing temperature led to a decrease in the geopolymer alkaline medium.
Assuntos
Silicatos de Alumínio/química , Materiais de Construção/análise , Cobre/química , Resíduos Industriais/análise , Gerenciamento de Resíduos/métodos , Força Compressiva , Microscopia Eletrônica de Varredura , Mineração , Propriedades de Superfície , Temperatura , Difração de Raios XRESUMO
The objective of this study was to evaluate the influence of hydrofluoric acid (HF) concentration, etching time, and application of phosphoric acid (PA) followed by neutralization with sodium bicarbonate on the bond strength between a feldspar ceramic and resin cement. Thus, 80 blocks (10 x 12 x 2 mm) of glass ceramic (VM - Vita Mark II - Vita Zahnfabrik) were made and randomly assigned to eight groups (n = 10) according to the factors: HF concentration (5 and 10%), etching time (60 and 120 s), and use of phosphoric acid (PA) (with and without). According to the experimental group, 37% PA (Condac, FGM) was applied after HF etching for 60s. Afterwards, samples were immersed in sodium bicarbonate for 1 min then in an ultrasonic bath in distilled water (5 min) for cleaning. After surface bonding treatment, cylinders (Ø = 2 mm; h = 2 mm) of dual resin cement (AllCem / FGM) were made in the center of each block. The samples were then stored in water (37ºC) for 90 days and submitted to the shear bond test (50 KgF, 1 mm/min). Failure analysis was performed by stereomicroscope and scanning electron microscopy. Data (MPa) were analyzed with 3-way ANOVA and Tukey's test. Only the factor "HF concentration" was significant (p = 0.02). Most failures were of cohesive in ceramic (40%) and mixed types (42.5%). The 10% HF resulted in higher shear bond strength value than the 5% HF. Surface cleaning with phosphoric acid followed by sodium bicarbonate and HF time (60 or 120 seconds) did not influence the resin bond strength to feldspar ceramic.