Comparative Efficiency of Rice Husk Biochar and Magnesium/Aluminum Layered Double Hydroxide for Lead Removal from Aqueous Solution

Document Type : Research Paper

Authors

1 Department of Soil Science and Engineering, Faculty of Crop Sciences, Sari Agricultural Sciences and Natural Resources University, Sari, Iran

2 Academic member/ Sari Agricultural Sciences and Natural Resources University, Sari, Iran

3 Department of Soil Science and Engineering, Faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, Ardabil, Iran

Abstract

Lead contamination of water resources as an environmental challenge requires the development of highly efficient decontamination methods such as the use of efficient, non-toxic and low-cost adsorbents. This study was conducted to compare the performance of rice husk biochar (RHB) and layered double hydroxides (Mg/Al-LDH) in removing lead from aqueous solutions. In this study, biochar was prepared from the pyrolysis of rice straw and stubble residues at 500°C under limited oxygen conditions and magnesium/aluminum layered double hydroxides at a ratio of 2:1 by co-precipitation method. The evaluation of parameters including adsorption kinetics, isotherm, and the initial solution pH on lead adsorption was performed. According to the results, kinetic studies showed that lead adsorption by RHB and LDH reached equilibrium in 60 and 240 min, respectively and the pseudo-second-order kinetic model showed high ability to predict the adsorption kinetics. with the increasing of initial solution pH, lead adsorption by both adsorbents increased.  The Langmuir models showed high ability to predict the lead adsorption behavior by the adsorbents. The maximum lead adsorption capacity by RHB and LDH was 297.83 and 173.46 mg/g, respectively. The results of this study confirm that rice husk biochar can be considered a superior, low – cost, non – toxic and environmentally friendly option for the decontamination of lead from aquatic environments due to the high accessibility of active sites and stable performance over a wide pH range.

Keywords

Main Subjects

Introduction

Lead contamination of water resources poses a significant environmental challenge, necessitating the development of highly efficient, non-toxic, and low-cost remediation methods. The utilization of advanced adsorbents represents a promising solution for the removal of heavy metals. This study was conducted to evaluate and compare the efficacy of two distinct adsorbents: rice husk biochar (RHB), a sustainable carbonaceous material, and magnesium/aluminum layered double hydroxide (Mg/Al-LDH), a synthesized nanomaterial, for the adsorption of lead (Pb(II)) from aqueous solutions.

Materials and Methods

Rice husk biochar (RHB) was prepared through the pyrolysis of rice straw and husk residues at 500 °C under limited oxygen conditions. Magnesium/aluminum layered double hydroxide (Mg/Al-LDH) with a Mg/Al molar ratio of 2:1 was synthesized using the co-precipitation method at a constant pH. Batch adsorption studies were performed to evaluate the lead removal efficiency. The parameters investigated included adsorption kinetics (0-1440 min), adsorption isotherms (0-300mg/L), and the effect of the initial pH (4-10) of the solution on adsorption capacity. The initial pH was adjusted using dilute solutions of HNO₃ or NaOH. The concentration of residual lead in the solutions was measured using atomic absorption spectrometry (AAS) or inductively coupled plasma optical emission spectrometry (ICP-OES). The surface morphology of RHB and layered double hydroxide (Mg/Al-LDH) was characterized using scanning electron microscopy (SEM), and the mineral structure of rice husk biochar and layered double hydroxide (Mg/Al-LDH) adsorbents was characterized using X-ray diffraction.The Experimental data were fitted to four adsorption models: Langmuis, Freundlich, Temkin, and Dubinin-Radushkevich, and four kinetic models including pseudo-first order, pseudo-second order, Elovitch, and intraparticle diffusion. Parameters such as removal efficiency, apparent energy of adsorption, and separation factor were calculated.

Results

SEM imaging revealed that the RHB possesses a highly porous and heterogeneous structure, which is conducive to high adsorption capacity by providing abundant binding sites. The kinetic studies indicated that the adsorption of lead onto RHB and LDH reached equilibrium within 60 and 240 minutes, respectively. The adsorption data for both adsorbents were best fitted by the pseudo-second-order kinetic model, suggesting that chemisorption was the primary rate-controlling mechanism. The adsorption capacity of both RHB and LDH for lead was highly dependent on the initial pH of the solution, with removal efficiency increasing as the pH rose. This trend is attributed to reduced competition between H⁺ ions and Pb²⁺ ions at higher pH values. The equilibrium adsorption data were accurately described by the Langmuir isotherm model, indicating monolayer adsorption onto homogenous surfaces. The maximum Langmuir adsorption capacities were calculated to be 297.83 mg/g for RHB and 173.46 mg/g for LDH.

Conclusion

The results of this study confirm that RHB biochar can be considered a superior and environmentally friendly option for the removal of lead pollution from aquatic environments due to the high accessibility of active sites and stable performance over a wide pH range.

Funding

The study was funded by the Sari University of Agricultural Scinces and Natural Resources, Sari, Iran, and Grant No. 1402-12-101.

Authorship contribution

All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

Declaration of Generative AI and AI-assisted technologies in the writing process

The author declares that no generative AI or AI-assisted technologies were used in the preparation of this manuscript.

Data availability statement

The data supporting the findings of this study are available from the corresponding author upon reasonable request.

Acknowledgements

The authors would like to thank the University of Agricultural Scinces and natural Resources for financial support anf also thank the anonymous reviewers for their valuable suggestions in manuscript revision.

Ethical considerations

The authors avoided data fabrication, falsification, and plagiarism, and any form of misconduct.

Conflict of interest

The authors declare no conflict of interest.

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Iranian Journal of Soil and Water Research
Volume 57, Issue 1
March 2026
Pages 85-105

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