Evaluation of the effect of flow on the adsorptive process of Pb2+ ion in a fixed bed column using prepared adsorbent from agro-industrial residue
Carolaine de Oliveira Lima Silva, Giovanna Amaral Jorge Correia Guedes, Alex Leandro Andrade de Lucena, Marina Nunes dos Santos Silva, Marta Maria Menezes Bezerra Duarte
Department of Chemical Engineering, Federal University of Pernambuco, Postcode: 50670-420, Brazil
Abstract
The disposal of effluents contaminated with metals in the environment, without proper treatment, tends to cause serious risks to the ecosystem and public health, as these have a cumulative and toxic effect. Bearing in mind that conventional treatments have low efficiency for removing metal ions, studies looking at alternatives have been carried out. Therefore, this work the objective to evaluate the influence of flow rate on the adsorption process of Pb2+ ions in a fixed bed using adsorbent prepared from peanut shells (CAH3PO4). The CAH3PO4 is characterized by the presence of oxygenated, phenolic and carboxylic groups, a mesoporous structure and a pHPZC equal to 7.2. Initially, fixed-bed columns were built in borosilicate glass, packed with CAH3PO4. The solutions containing Pb2+ ions percolated through the bed, in an upward flow, and samples were collected at the top of the column at pre-established times. The flow rates evaluated were 3, 6 and 9 mL?min-1. The results obtained demonstrated that as the flow rate increases from 3 to 9 mL?min-1, higher adsorptive capacity values are obtained, 15.6% greater, despite the resistance to mass transfer increasing as indicated by the value of ZTM. In this way, the work demonstrates the potential use of CAH3PO4 in the removal of Pb2+ ions from aqueous media in continuous systems.
Keywords: Adsorption; Metal ions; Fixed bed; Peanut shell.
1. Introduction
The growth of urban occupation and industrial development has promoted an increase in the presence of heavy metals in aqueous media [1]. The dumping of effluents contaminated with harmful metal ions, without adequate treatment, poses serious risks to the ecosystem and health, due to their cumulative effect and toxicity [2].
Among the metals present in wastewater, lead (Pb) deserves to be highlighted as it is frequently found in effluents from batteries, metal alloys and coating industries[3,4]. The exposure or consuming these metallics ions can trigger multiple adverse biological effects on the human body, such as neurological disorders, depression, intelligence deficits and muscular atrophy[5].
In view of these harmful effects CONAMA Resolution Nº 430/2011 establishes conditions and standards for the discharge of effluents into receiving bodies, defining the maximum limit of lead ions as 0.5 mg·L-1[6].
In this way, the need for processes aimed at removing this ion from effluents before their disposal in a receiving body is highlighted. Among the treatments applied to remove metals from aqueous media, adsorption is one of the most efficient, versatile as well as easy to operate[7].
Large-scale adsorption tends to be more viable in continuous systems than in finite baths, due to its operational flexibility, high efficiency and low maintenance requirements [8]. Thus, aiming to increase the sustainability of the adsorptive process, studies have been carried out with the aim of using agricultural waste as precursors for the production of adsorbents, due to their abundance, effectiveness and renewable origin[9,10].
Among agro-industrial waste, peanut shells stand out, since in Brazil peanut (Arachis hypigaea Linn) is one of the main oilseeds cultivated in the country, reaching 893.2 thousand tons in the 2022/2023 harvest [11]. The peels represent Around 30% of the legume, and are 80% fiber, which makes it suitable for applications such as fuel in boilers, animal feed ingredients, among others. However, the quantity produced exceeds existing demand, making it possible to use the peels in the production of adsorbents, reintegrating them into the production chain[12].
In view if the above, the objective of this work is to evaluate the effect of flow rate on the fixed bed adsorption process of Pb2+ ions by peanut shells chemically activated with phosphoric acid.
2. Methodology
Stock solutions of 1000 mg?L-1 (4.8 mmol?L-1) were prepared from Pb(NO3)2 (Dinâmica, 99%). The working solutions were obtained by diluting the stock solutions. The tests were carried out at pH 5, considering that in previous studies by the research group[13] it was found that at this pH there is no precipitation of ions, thus allowing the evaluation of only the adsorptive process. All reagents used to adjust pH and carry out the tests were of analytical grade.
The ion levels were quantified before and after the experiments in the Flame Atomic Absorption Spectrophotometer (Varian, AA 240 FS - Fast Sequencial Atomic Absorption Sprectrometer) at a wavelength of 261.4 nm. The analytical curve presented a linear range between 0.025 and 2.25 mmol·L-1 with a linear correlation coefficient (r) greater than 0.99, coefficient of variation (CV%) equal to 5%, limit of detection and limit of quantification of 0.004 and 0.014 mmol·L-1, respectively. The adsorbed amount of the Pb2+ ion (adsorptive capacity q) was calculated by Equation 1.
In which: q (mmol?g-1) the adsorption capacity of the adsorbent; C (mmol?L-1) the adsorbate concentration at the column outlet; C0 (mmol?L-1) the initial concentration at the column inlet; ms (g) the amount of adsorbent in the bed; Q (mL?min-1) the volumetric flow rate of the fluid phase.
The peanut shells were obtained from commercial establishments in the metropolitan region of Recife-PE/Brazil. The Chemical activation of the peanut shells with phosphoric acid followed the procedure described by Santos et al. (2022)[12]. The prepared adsorbents were macerated, with the aid of a mortar and pestle, and classified in particle size of 0.15-0.21 nm using a series of Tyler sieves.
2.1 Fixed bed column adsorption tests
The tests were carried out in a borosilicate glass fixed bed column (30 x 0.3 cm), packed with CAH3PO4. In order to obtain the fluid travel times in the system, ultrapure water was pumped in an upward flow in the column previously in each experiment. The mass/volume of solution ratio, initial concentration and minimum contact time adopted in this work were based on data obtained in finite bath tests.
The solutions were pumped, with the aid of a peristaltic dosing pump (Milan, model 202), in an upward flow, traveling through the adsorptive bed at room temperature (25 ± 2ºC). Sample collection was carried out at the top of the column, at pre-established times.
The tests to evaluate the influence of flow on the adsorptive process were carried out by varying the flow of the feed solution by 3, 6 and 9 mL?min-1, f or solutions with a concentration of 2.0 mmol·L-1. Finally, to obtain the value of the Mass Transfer Zone (MTZ), the methodology developed by Geankoplis (2003)[13] was used. For this, the calculation of useful time, total time and total and useful heights is taken as a basis so that the MTZ can then be determined.
3. Results and discussion
The rupture curves obtained to study the effect of flow rate (3, 6 and 9 mL·min-1) on the removal of Pb2+ ion from aqueous solutions by CAH3PO4 in a fixed bed column are shown in Figure 1.
It can be seen from Figure 1 that, as the flow rate increased, the rupture curves became steeper, with a reduction in the rupture time (tr) and saturation time (ts) of the bed. At the highest flow rate, there was a decreased in ts of 15,4% in relation to the flow rate of 3 mL·min-1. According to Gama et al. (2022)[14], this can be attributed to the shorter residence time of the fluid in the bed and greater contact with the adsorbent.
The calculated values ??for tr, ts, q and MTZ in the evaluated flows are shown in Table 1.
Table 1. Values of tr, ts, q and MTZ for the study of the feed flow of Pb2+ ions in a fixed bed column.
Flow rate (mL·min-1) | tr (min) |
O Encontro Brasileiro sobre Adsorção (EBA) é um evento reconhecido que ocorre a cada dois anos desde 1996, alternando entre cidades do Nordeste e Sul/Sudeste do Brasil. O objetivo principal do evento é fornecer um espaço para discussões entre a comunidade científica, acadêmica e empresarial, nacional e internacional, que esteja interessada na área de adsorção, promovendo assim o intercâmbio de ideias e resultados de pesquisas.
Maceió/AL, novembro de 2024. Comissão Organizadora 15º Encontro Brasileiro sobre Adsorção - EBA
Comissão Organizadora: Prof. Dr. Lucas Meili (Presidente da Comissão Organizadora) Prof. Dr. Amaro Gomes Barreto Jr. Prof. Dr. Daniel Pinto Fernandes Prof. Dr. João Batista Rocha Maia Neto Prof. Dr. Rodolfo Junqueira Brandão Dra. Pollyanna Vanessa dos Santos Lins Dra. Rafaela Gabriel
Comitê Científico:
Email do evento:
Comissão organizadora:
Prof. Dr. Lucas Meili (Presidente da Comissão Organizadora) (lucas.meili@ctec.ufal.br) Prof. Dr. Amaro Gomes Barreto Jr. Prof. Dr. Daniel Pinto Fernandes ( daniel.fernandes@ctec.ufal.br) Prof. Dr. João Batista Rocha Maia Neto (joao.maia@ctec.ufal.br) Prof. Dr. Rodolfo Junqueira Brandão (rodolfo.brandao@ctec.ufal.br) Dra. Pollyanna Vanessa dos Santos Lins ( polly_lins91@hotmail.com) Dra. Rafaela Gabriel Comitê Científico:
Patrocínio: DpUnion Instrumentação Analítica e Científica Parceiros: Universidade Federal de Alagoas (UFAL) Centro de Tecnologia (CTEC/UFAL) Fundação Universitária de Desenvolvimento de Extensão e Pesquisa (FUNDEPES) Secretaria de Estado da Ciência, da Tecnologia e da Inovação (SECTI) Centro de Inovação do Jaraguá Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de Alagoas (FAPEAL) Não há edições anteriores 
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