Use of Rice Husk Ash as an Adsorbent in the Removal of Tartrazine Yellow and Methylene Blue From Aqueous Solutions - A Kinetic and Thermodynamic Study

Oct 28, 2026

Rice husk ash (RHA), a carbon-rich byproduct often applied as fertilizer, can cause residual carbon accumulation in soil. This study examines RHA chemically treated with NaOH (RHA-b) and H3PO4 (RHA-a) for adsorbing tartrazine yellow (anionic) and methylene blue (cationic) from aqueous solutions. Characterization identifies silanol groups and slit-like pore morphology. Kinetic results show faster equilibrium for MB than TY and pseudo-second-order behavior. Removal efficiency reaches 93% for MB and 54% for TY on RHA-b, with Langmuir isotherms providing the best fit. Thermodynamic analysis indicates spontaneous adsorption for all adsorbents, driven by enthalpy for TY and entropy for MB, with the highest spontaneity for MB on RHA.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages17

Reading Time43 min

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Introduction

Background on effluents and dyes

Adsorption of tartrazine yellow (TY) and methylene blue (MB)

Use of rice husk ash as an adsorbent in the removal of tartrazine yellow and methylene blue from aqueous solutions: A kinetic and thermodynamic study Uso da cinza da casca de arroz como adsorvente na remoção de amarelo de tartrazina e azul de metileno de soluções aquosas: Um estudo cinético e termodinâmico F. A. C. Biasuz 1 ; N. S. Leite 1 ; O. B. Garla 1 ; J. G. da S. de Andrade2*; S. L. F. Rosa3 ; F. R. de Carvalho 1 1Department of Technology, State University of Maringa, 87506-370, Umuarama-PR, Brazil 2Postgraduate Program in Chemical Engineering, State University of Maringa, 87020-900, Maringa-PR, Brazil 3Department of Mechanical Engineering, State University of Maringa, 87020-900, Maringa-PR, Brazil *[joaogabriel-andrade@hotmail.com](joaogabriel-andrade@hotmail.com) (Recebido em 27 de abril de 2025; aceito em 02 de março de 2026) Rice husk ash (RHA) is an abundant byproduct of the food industry. While frequently used as a fertilizer, this application can lead to the polluting accumulation of residual carbon in the soil. Research suggests that RHA can serve as a cost-effective alternative adsorbent to high-cost activated carbon. In this study, RHA was chemically treated with NaOH (RHA-b) and H3PO4 (RHA-a) to enhance the adsorption of the anionic dye tartrazine yellow (TY) and the cationic dye methylene blue (MB) . Structural analysis identified silanol groups and a slit-like pore morphology on the RHA surface.Kinetic studies revealed that equilibrium was reached faster for MB (180 minutes) than for TY (240 minutes), with experimental data best described by the pseudo-second-order kinetic model. RHA-b exhibited the highest removal efficiency, reaching 93% for MB and 54% for TY. Regarding isothermal studies, the Langmuir model provided the best fit for the experimental data. The maximum adsorption capacities were determined to be 20.21 and 19.92 mg g-1 for MB (RHA-a and RHA-b, respectively) and 3.29 and 9.29 mg g-1 for TY (RHA-a and RHA-b, respectively) . Thermodynamic parameters indicated that adsorption was a spontaneous process for all adsorbents, with the highest spontaneity observed for MB adsorption on RHA 􀀧Gºads = -34.5 kJ mol-1. Furthermore, spontaneity was driven by enthalpy in TY adsorption and by entropy in MB adsorption. Keywords: adsorption, rice husk ash, thermodynamics. A cinza de casca de arroz (RHA) é um subproduto abundante da indústria alimentícia. Embora comumenteutilizada como fertilizante, essa aplicação pode causar o acúmulo poluente de carbono residual no solo. Estudos indicam que a RHA pode atuar como adsorvente alternativo ao carvão ativado de alto custo. Nestetrabalho, a RHA foi tratada quimicamente com NaOH (RHA-b) e H3PO4 (RHA-a) para otimizar a adsorçãodo corante aniônico amarelo tartrazina (TY) e do catiônico azul de metileno (MB) . Estruturalmente, identificaram-se grupos silanol e morfologia de poros do tipo fenda na superfície da RHA. Os estudos cinéticos revelaram que o equilíbrio foi alcançado em 180 minutos para o MB e 240 minutos para o TY, com os dados experimentais sendo melhor descritos pelo modelo de pseudo-segunda ordem. ARHA-b apresentou a maior eficiência de remoção, atingindo 93% para MB e 54% para TY. Nos estudosisotérmicos, o modelo de Langmuir demonstrou o melhor ajuste aos dados. As capacidades máximas deadsorção obtidas foram de 20,21 e 19,92 mg g-1 para MB (RHA-a e RHA-b, respectivamente) e de 3,29 e 9,29 mg g-1para TY (RHA-a e RHA-b, respectivamente) . Os parâmetros termodinâmicos indicaram que aadsorção foi um processo espontâneo para todos os adsorventes, com maior espontaneidade registrada na adsorção de MB em RHA 􀀧Gºads = -34,5 kJ mol-1. Além disso, observou-se que a espontaneidade foi impulsionada pela entalpia na adsorção de TY e pela entropia na adsorção de MB. Palavras-chave: adsorção, cinza da casca de arroz, termodinâmica. 1. INTRODUCTION The rise in the world population has contributed to the expansion of industrial activities. Sa

FAQs

Why was rice husk ash (RHA) investigated as an adsorbent?

RHA is an abundant byproduct, and although it is often used as fertilizer, residual carbon accumulation in soil can be a concern. The study evaluates RHA as a cost-effective alternative adsorbent to activated carbon.

What kinetic model best described the adsorption data?

Equilibrium was reached faster for methylene blue than for tartrazine yellow, and the experimental data were best described by the pseudo-second-order kinetic model.

What do the thermodynamic results indicate about adsorption?

Thermodynamic parameters show adsorption is spontaneous for all adsorbents. For TY, spontaneity is driven by enthalpy, while for MB it is driven by entropy, with the highest spontaneity reported for MB on RHA (ΔG°ads = -34.5 kJ mol-1).

Oct 28, 2026

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