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Synergistic torrefaction and co-combustion of rice husk and spent coffee grounds: Thermo-kinetics, ash morphology, and waste-to-energy implications
(2026-09-01)
Pambudi, Suluh
;
Jongyingcharoen, Jiraporn Sripinyowanich
;
Saechua, Wanphut
Combining silica-rich agricultural residues such as rice husk (RH) with energy-dense food-processing waste like torrefied spent coffee grounds (TSCG) offers a circular strategy to exploit the complementary advantages of each biomass while improving fuel performance and combustion reliability. Therefore, the objective of this study is to systematically investigate the co-combustion behavior, kinetic performance, and ash morphology of RH and TSCG blends using thermogravimetric analysis across multiple blend ratios and heating rates. Optimal co-combustion characteristics were observed for blends containing 40–60% RH, demonstrated by comprehensive combustion index values up to 6.02 × 10–6%2 min–2 °C–3 and flammability indices exceeding 0.72 × 10–4% min–1 °C–2. Furthermore, these blends exhibited low activation energies during dehydration (150–161 kJ mol⁻¹), devolatilization (143–175 kJ mol⁻¹), and char oxidation (89–134 kJ mol⁻¹). Notably, these blends exhibit high carbon conversion efficiency, leading to a relatively low residual ash content (10.25–14.36%). Synergistic effects, characterized by experimental mass loss exceeding theoretical predictions by up to 2%, were confirmed above 300 °C. This synergistic behavior is attributed to the interaction between oxygenated volatiles released from RH and the catalytic effects of alkali and alkaline earth metals present in TSCG, along with the stabilizing role of silica in mitigating ash-related issues. Additionally, increasing the proportion of TSCG promoted earlier ignition (T<inf>i</inf> reduced to 213 °C) but prolonged the char combustion stage, resulting in higher burnout temperatures of up to 678 °C. Morphological and elemental ash analysis revealed that moderate Si content in 40–60% RH blends contributed to thermal stability while suppressing alkali-induced slag formation. Collectively, these results demonstrate that co-combustion of RH with TSCG significantly enhances combustion reactivity, promotes kinetic synergy, and improves thermal stability. These findings highlight the potential of RH–TSCG blends as efficient and environmentally sustainable fuels for bioenergy applications by utilizing readily available local biomass residues.
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Adsorption of silver, thorium and nickel ions from aqueous solution onto rice husk
(2021-10-01)
Zafar, Shagufta
;
Khan, Muhammad Imran
;
Shanableh, Abdallah
;
Ahmad, Saleem
;
Manzoor, Suryyia
In this article, adsorption of metal ions such as silver (Ag(I)), thorium (Th(IV)) and nickel (Ni(II)) from aqueous solution onto rice husk (RH) was performed at room temperature. Adsorption of these metal ions (silver, thorium, and nickel) onto RH was demonstrated by using Fourier trans-form infrared spectroscopy and energy-dispersive X-ray. Morphology of RH was investigated before and after adsorption of these metal ions onto it by using scanning electron microscopy. The effect of different operational parameters (contact time, initial concentration of metal ion solution, weight of RH, pH, and temperature) on the percentage removal of these metal ions was explored in detail and compared. Experimental data for adsorption of these metal ions onto RH was sub-jected to Langmuir and Freundlich isotherm models. Results showed that adsorption of silver and thorium fitted well to Langmuir isotherm model (R2 > 0.99) whereas adsorption of Ni(II) fitted well to Freundlich isotherm model (R2 > 0.99). Adsorption kinetics study demonstrated that adsorp-tion of these metal ions onto RH from aqueous solution fitted well to pseudo-second-order model. Adsorption thermodynamics investigation represented that adsorption of these metal ions onto RH was endothermic process. The values of Gibb’s free energy were –6.53 to –9.17 kJ/mol for Ag(I), –1.11 to –3.57 kJ/mol for Th(IV) and –0.89 to –1.40 kJ/mol for Ni(II). The negative values of Gibb’s free energy for these metal ions suggested that the adsorption process was spontaneous in nature. The regeneration of RH and recovery of these metal ions were also studied.
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Kinetic, equilibrium, and thermodynamic studies for adsorptive removal of cobalt ions by rice husk from aqueous solution
(2020-11-01)
Zafar, Shagufta
;
Khan, Muhammad Imran
;
Rehman, Hafeez Ur
;
Fernandez-Garcia, Javier
;
Shahida, Shabnam
Herein, batch adsorptive removal of cobalt ions (Co(II)) from aqueous solution was studied at room temperature. Adsorption of cobalt ions onto rice husk (RH) was confirmed by utilizing Fourier transform infrared, scanning electron microscopy, and energy diffraction energy-dispersive X-ray analysis. The effect of contact time, mass of RH, initial concentration of cobalt ion solution, tem-perature, and pH on the percentage discharge of Co(II) was revealed. The nonlinear models such as pseudo-first-order model, pseudo-second-order model, intraparticle diffusion model, and Elovich model were utilized to study kinetics for adsorptive removal of cobalt ions (Co(II)) from aqueous solution. Results showed that experimental data fitted well to nonlinear pseudo-second-order kinetic model. Nonlinear isotherms such as Langmuir, Freundlich, and Dubinin–Radushkevivh (D–R) were used to reveal experimental data of cobalt ion adsorption onto RH. Results represented that experimental data fitted well to nonlinear isotherms. Adsorption thermodynamic study showed that adsorption of Co(II) onto RH was an endothermic and spontaneous process. Moreover, desorp-tion of cobalt ions was also revealed. Therefore, RH could be utilized as a good adsorbent for the removal of Co(II) from aqueous solution at room temperature.

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