Performance of bentonite clays in the removal of cadmium and copper cations in fixed bed columns.

A adsorção tornou-se um processo de separação bastante atraente nos últimos tempos, principalmente após a descoberta de novos adsorventes. Mas para que se possa projetar e otimizar equipamentos de adsorção, é imprescindível a caracterização do adsorvente e o conhecimento da dinâmica de adsorção dos componentes em sistema experimental. Neste trabalho foi analisado a adsorção de Cu2+ e Cd2+, individualmente, de efluente sintético em coluna de leito fixo e tendo como adsorventes argilas bentoníticas (denominadas Bofe e Verde-Lodo), provenientes de Boa Vista – PB. Os métodos de caracterização utilizados foram Fluorescência de Raios-X (XRF), Análise Térmica Diferencial (DTA), Termogravimetria (TG), Microscopia Eletrônica de Varredura (MEV) e Fisissorção de N2 (método de BET). A coluna de leito fixo construída em acrílico possuía 13,3cm de altura e 1,4cm de diâmetro interno. Através da técnica de planejamento experimental com 3 pontos centrais foi possível um estudo mais abrangente dos fatores operacionais. Foram utilizados os modelos de Langmuir, Freundlich, BET e GAB no ajuste dos dados de equilíbrio. De acordo com a caracterização, as argilas bentoníticas estudadas apresentaram composição química de acordo com a maioria das argilas deste grupo. A presença de água nos espaços interlamelares das argilas, foi confirmada por Análise Térmica Diferencial (DTA) e Termogravimetria (TG). As curvas TG, das argilas Bofe e Verde-Lodo indicaram uma perda de massa de 12,15% e 14,3% respectivamente. A argila Bofe, calcinada a 500°C, apresentou área superficial 83,18m2/g, enquanto que a argila Verde-Lodo, calcinada a 500°C, apresentou uma área de 51,9m2/g. Mediante análise das curvas de ruptura obtidas em todos os sistemas de adsorção, a variável que mais influenciou foi a concentração inicial de alimentação. Os resultados finais dos planejamentos experimentais mostraram que: a adsorção de Cu2+ sobre a argila Bofe apresentou bom desempenho sob diâmetro de partícula 0,46mm e concentração inicial de Cu2+ 50ppm; a adsorção de Cd2+ sobre a argila Bofe apresentou bom desempenho sob diâmetro de partícula 0,65mm e concentração inicial de Cd2+ 100ppm; a adsorção de Cd2+ sobre a argila Verde-Lodo apresentou bom desempenho sob diâmetro de partícula 0,46mm, concentração inicial de Cu2+ 250ppm e vazão de 4mL/min. O Cu2+ não foi removido pela argila Verde- Lodo. Os dados de equilíbrio de adsorção do Cd2+ e Cu2+ sobre a argila Bofe foram melhor ajustados pelo modelo de Langmuir. Os dados de equilíbrio de adsorção do Cd2+ sobre a argila Verde-Lodo foram melhor ajustados pelo modelo de GAB. Palavras Chave: adsorção, argila bentonítica, leito fixo, remoção de metais.The adsorption became a separation process more attractive in the last times, mainly after the discovery of new adsorbents. In order to be possible to project and to optimize the adsorption equipments, it is indispensable the characterization of the adsorbent and the knowledge of the adsorption of the components dynamics in a experimental system. In this work it was analyzed the adsorption of Cu2+ and Cd2+ cations, individually, from the synthetic effluent in fixed bed column and having the bentonite clays (be called Bofe and Verde Lodo ones), originating from the Boa Vista-PB town. The characterization methods that were used in the work are the following ones: X-ray Fluorescence (XRF), Differential Thermal Analysis (DTA), Thermogravimetry (TG), Scanning Electron Microscopy (SEM) and Nitrogen Physissorption to determine the B. E. T. surface area of the samples. The fixed bed column that was built in acrylic had height of 13.3 cm and internal diameter of 1.4 cm. From the experimental projection technique with three central points it was possible to realize a more including study of the operational factors. Were utilized to adjust the balance data the following models: Langmuir, Freundlich, BET and GAB. In agreement with the characterization, the studied bentonite clays presented chemical composition in agreement with the most clays of their group. The presence of water in the interlamellar spaces of the clays, it was confirmed by DTA and TG. The Bofe and Verde-Lodo TG curves indicated a weight loss of 12.15 wt.% and 14.3 wt.% respectively. The Bofe clay, calcined at 500°C, presented surface area of 83.18m2/g, while the Verde-Lodo clay, which was calcined at 500°C, showed a surface area of 51.9m2/g. From the rupture curves obtained in all the adsorption systems, the incognita that most influences is the initial feeding concentration. The experimental projections last results showed that: the Cu2+ adsorption on the Bofe clay presented good performance under particle diameter of 0.46mm and Cu2+ initial concentration of 50ppm; the Cd2+ adsorption on the Bofe clay presented good performance under particle diameter of 0.65mm and Cd2+ initial concentration of 100ppm; the Cd2+ adsorption on the Verde-Lodo clay presented good performance under particle diameter of 0.46mm, Cu2+ initial concentration of 250ppm and flow of 4mL/min. The Verde-Lodo clay did not remove the Cu2+ cation. The adsorption balance data of the Cd2+ and Cu2+ cations on the Bofe clay were better adjusted through the Langmuir model. The adsorption balance data of the Cd2+ cation on the Verde-Lodo clay were better adjusted through the GAB model. Key Words: adsorption, bentonitic clay, fixed bed, metals removal

Ni-W alloys and their anticorrosive properties: Ni removal efficiency from galvanic wastewater by electrodeposition

The electroplating industrial wastewater is an environmental issue due to the high metal concentration and difficulty in disposing of the final residue generated by the formation of sludge when using the precipitation method. In this context, we propose to remove nickel from wastewater from the jewelry industry wastewater to obtain corrosion-resistant Ni-W alloys by the electroplating process. The concentration of nickel removed from the effluent was quantified by ultraviolet-visible (UV/vis) spectroscopy indicating removal close to 40 %. X-ray Diffraction (XRD) patterns showed the crystallinity of the deposits, as well as the Scanning Electron Microscope (SEM) with the Energy-Dispersive X-Ray Spectroscopy (EDX) technique determined homogeneity and the composition with 76 wt.% Ni/24 wt.% W for the optimized alloy. Besides, corrosion resistance tests by linear polarization indicated an Rp value of 29,199 Ω m236COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESsem informaçã

Anticorrosive Zn–Ni alloys: An alternative for the treatment of electroplating industry wastewater

Substrate protection coatings are widely applied in the industry. Zn–Ni alloys have less potential for corrosion, thus preserving the steel substrate by corroding first. In this sense, this study used nickel-rich electroplating industry wastewater to produce Zn–Ni alloys under different conditions, analyzing the zinc sulfate concentration, electric current density, and rotating cathode in the deposition. The nickel removal kinetics showed a reversible and first-order behavior. The alloys with a composition of 2 wt.% nickel, according to energy-dispersive X-ray spectroscopy analysis, were more anti-corrosive with polarization resistance of 1276.7 Ω cm2, than the alloys containing 5 wt.% nickel. Electrochemical impedance spectroscopy proved that alloys containing 2 wt.% nickel were more resistant to corrosion and indicated the formation of a porous oxide layer. Besides, the micrographs of the alloys containing 2 wt.% nickel showed homogeneity without cracks and nodular grains, unlike the alloys with 5 wt.% nickel, which had cracks and were heterogeneous. The X-ray diffraction diffractograms showed different structures according to the amount of Ni. Thus, the deposition of metals from wastewater is an alternative to conventional treatments and avoids the use of synthetic baths16CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informaçã

The influence of Ni and Co concentration in the electroplating bath on Ni‐Co‐W alloys properties

In this study, we evaluated the influence of nickel and cobalt concentrations in an electrochemical bath for a ternary Ni‐Co‐W coating alloy electrodeposition. The X‐ray diffraction indicated formation of amorphous coating alloys for higher Co concentration and a crystalline coating alloys for higher Ni concentration. Statistical evaluation showed a mathematical model connecting the increase of alloy deposition efficiency and the Ni and Co concentration in the electrochemical bath. Corrosion tests indicated that coating alloys with higher Ni concentration, which are crystalline alloys, showed higher polarization resistance (in NaCl 0.1 mol/L) indicating that composition can influence the corrosion resistance more than the crystallinity96612841289FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informaçã

Influence of current density and w concentration on co–w alloys used as catalysts in electrodes for Li–O2 batteries

In this study, we verified the influence of tungsten (W) concentrations and current density for the electroplating of the cobalt–tungsten (Co–W) alloy on two substrates (nickel foam and steel mesh). The statistical evaluation showed a mathematical model that related the efficiency of deposition with the parameters analyzed. The efficiency varied from 0 to 60.05% for the nickel foam and 0 to 64.39% for the steel mesh. Scanning electron microscopy showed that to increase the current density made the surface less uniform, due to the size of the grains formed and X-ray diffraction pointed to the formation of amorphous coating alloys. Electrodeposition of the alloy in the steel mesh occurred with greater contribution by forced convection, as opposed to the nickel foam that had a smaller contribution, according to the effects of fluid dynamics. The Co–W alloys evidenced by energy-dispersive X-rays spectroscopy were tested in the cell with a constant pressure of O2 and presented an alternative for the use of catalysts in Li–O2 batteries73511031112CAPES - Coordenação de Aperfeiçoamento de Pessoal e Nível Superior001This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. The authors thank the Espaço da Escrita—Pró-Reitoria de Pesquisa/UNICAMP for the language services provide

Continuous adsorption of silver and copper by Verde-lodo bentonite in a fixed bed flow-through column

Several studies have been conducted to evaluate and to improve wastewater treatment. Among the contaminants in wastewater, toxic metals stand out and their removal by adsorption process is of great interest. Silver and copper binary adsorption on bentonite was evaluated in the present work, using a fixed bed dynamic system. Initially, a fluid dynamic study was performed with different flow rates and efficiency and mass transfer parameters were analyzed. Using the optimum flow rate, the effects of initial concentration and molar fraction were investigated according to the same parameters, besides metals removal. Next, two adsorption and desorption cycles were performed using nitric acid as eluent. Regenerated clay, after elution with nitric acid, was characterized in order to verify morphology, thermal stability, functional groups and crystal structure171613621FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP2013/00732-1; 2013/25212-

Effects of tungsten and cobalt concentration on microstructure and anticorrosive property of cobalt-tungsten alloys

The replacement of chrome coatings for materials that maintain the same properties has become the Co-W alloy relevant. In this context, we proposed to evaluate the effects of the Co and W concentration in the electrolytic bath on the faradaic efficiency, morphology, and anticorrosive property of the Co-W alloy. The diffractograms indicated a tendency to amorphization when the W concentration increased from 0.1 to 0.3 M, and the faradaic efficiency achieved values close to 70%. Alloy surfaces demonstrated a homogeneous composition according to the energy-dispersive X-ray mapping. The increase of Co and W concentration promoted the formation of rounded structures and reduced the space between the microcracks. Moreover, the high concentration of these promoted greater corrosion resistance with a corrosion current density of 1.83 µA cm−220COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESsem informaçã

Adsorption and desorption processes for copper removal from water using different eluents and calcined clay as adsorbent

In this work, the copper removal in fixed-bed of Bofe calcined clay was realized, in which the adsorption and desorption of copper ions, the time of equilibrium and kinetic curves were investigated. Different types of eluents were utilized for calcined clays bed regeneration. Desorption tests were performed using a NaCl solution at 1% and seawater both at pH 3. The results indicated that the regeneration of the bed with NaCl/HCl or saline water at pH 3 is very efficient and the elution was verified as 50%. Also, it was observed an increase in removal after exposure of the bed to the eluent. The highest adsorption capacities of copper were ≈0.3 mmol/g, on the Bofe calcined clay. The equilibrium time increased from 120 min to 400 min considering the first to the last cycle. During the regeneration process, the mass-transfer zone decreased almost linearly from 9.8 to 3.4 cm with the use of NaCl and from 9.9 to 6.7 cm with seawater. In addition, those eluents provide the ideal breakthrough behavior. The recovery efficiency of the water showed that the desorption of copper ions with NaCl or seawater is feasible and has great potential39097CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informaçã