Palm kernel shell (PKS) core fibers, an agricultural waste, were chemically modified using N(3chloro2hydroxypropyl) trimethylammonium chloride (CHMAC) as a quaternizing agent. The potential of quaternized palm kernel shell (QPKS) as an adsorbent for fluoride in an aqueous solution was then studied. The quaternized palm kernel shell (QPKS) core fibers were characterized using Fourier transform infrared spectroscopy (FTIR) and a scanning electron microscope (SEM). The effect of various factors on the fluoride sequestration was also investigated. The results showed that with an increase in the adsorbent amount and contact time, the efficiency of fluoride removal was improved. The maximum fluoride uptake was obtained at pH 3 and a contact time of 4 h. The adsorption behavior was further investigated using equilibrium isotherms and kinetics studies. The results from these studies fit well into Freundlich, RedlichPeterson, and Sips isotherm's with a coefficient of determination (R2) of 0.9716. The maximum fluoride removal was 63%. For kinetics studies, the pseudo second order was the best fit for fluoride, with an R2 of 0.999. These results suggest that QPKS has the potential to serve as a lowcost adsorbent for fluoride removal from aqueous solutions.

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In this research, the adsorption potential of quaternized palm kernel shell (QPKS) to remove F− from aqueous solution was investigated using fixed-bed adsorption column. Raw palm kernel shell waste was reacted with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHMAC) in order to modify the surface charge. The effects of inlet F− concentrations (2–12 mg/l) and QPKS bed height (2–10 cm) with optimum pH (pH = 3) on the breakthrough characteristics of the adsorption system were determined. In the fixed-bed column, breakthrough time increases with increasing bed height due to increasing amount of active site on adsorbents to adsorb the fluoride ion. Decreasing trend of breakthrough values was obtained with increasing initial fluoride concentration due to greater driving force for the transfer process to overcome the mass transfer resistance in the column. The adsorptions were fitted to three well-established fixed-bed adsorption models, namely, Thomas, Yoon–Nelson, and Adams–Bohart models. The results fitted well to the Thomas and Yoon–Nelson models with correlation coefficient, R2 ≥ 0.96.

Rice straw is an abundant resource in Asian countries, for instance, Malaysia and India. Rice straw is a major agricultural waste product, which caused disposal issue in areas. Residue burning crops was adopted for the farmers to dispose of rice straw after harvest in order to prepare seedbed preparation for next season. An alarming air pollution report impacted by open burning of rice straw contributes to global warming. Commercialization of silica is an alternative method to dispose of agro-waste residues. The main objective of this research is to extract silica from rice straw. The amorphous silica was derived by first digesting rice straw with Soda AQ solution by varying NaOH concentration from 5 wt% - 25 wt% and 0.1 wt% anthraquinone (AQ) to dissolve silica content and acid precipitation at pH 7 to obtain silica gel. Other parameters such as the effect of digestion temperature (60 °C to 90 °C), digestion time (1 hour to 3 hours), and Soda AQ to rice straw impregnation phase ratio (150:5 to 500:5). The optimum effects of parameter had yielded 74.11 % of silica and it was demonstrated by Soda AQ with NaOH concentration 20 wt% and 0.1 wt% AQ, temperature of 75 °C, digestion time of 3 hours and the ratio 200:5 of Soda AQ to rice straw. Characterization of rice straw was performed by using Fourier Transforms Infrared Spectroscopy (FTIR). The commercialization of silica had the potential to be utilized as construction materials and silica gel that aids to absorb moisture.