Silica extraction from rice hull ash through the sol–gel process under ultrasound

Abstract

Rice is among the main foods produced in the world and is part of the daily diet of most families. The main waste from rice processing is rice husk (RH), which has been used as biomass for energy generation through combustion. In this process, rice husk ash (RHA) is generated as a residue, and its silica (SiO 2 ) content varies from 85-98%. The present work describes the study of the extraction of silica from RHA by the ultrasoundassisted sol-gel method. An experimental design based on the Response Surface Methodology (RSM) with the symmetrical, second-order Rotational Central Composite Design (RCCD) was applied to determine the best extraction conditions considering extraction time and molar ratio (n) as variables = n NaOH / n Silica ). These optimal conditions were then applied to three ash samples, two obtained by the combustion process in a boiler furnace, with a mobile grate system (RHAC 1 and RHAC 2 ), and one obtained by the pyrolysis process (RHAP) carried out in a xed bed reactor. Results showed that a molar ratio of 4.4, and an extraction time of 107 minutes were the best extraction conditions, leading to a yield of 73.3% for RHAP, 43.9% for RHAC 1 , and 31.1% for RHAC 2 . It was found that the extraction yield and textural properties of the silica obtained depend on the characteristics of the ash used. The silica extracted from RHAC 1 presented a surface area of 465 m 2 .g − 1 , mesopores of 4.69 nm, purity greater than 95%, and an ultra-ne granulometric distribution, reaching nanoparticle dimensions, characteristics comparable to commercially available silicas.

Green Synthesis of Silica Nanoparticles (Si-NPs) from Palm Oil Fuel Ash (POFA) and its Application to Purification Water: A Review

“…Research indicates that SiO2 content rises with the increasing fineness of POFA, with silica finding applications across various industrial sectors [35]. Silica sees widespread utilization in diverse fields, including fertilizer, pest management, insulation, adsorbent materials [33], catalysts, and environmentally sustainable concrete or cement [12].…”

“…The ash produced from the steam boiler/boiler in the palm oil mill comes from the inner shell of the oil palm and the flesh of the fruit, which contains high levels of silica (SiO2). The high silica content in palm oil mill ash has the potential to be extracted and used as a source of SiO2 [33] [14]. Research on the synthesis of silica from agricultural wastes, one of which is POFA, has been conducted extensively.…”

“…For example, the sol-gel technique has many advantages, including being easy and cost-effective, operating at low processing temperatures, requiring minimal energy, and producing nano-silica with high purity and quality [39]. Palm Oil Boiler Ash Ball-milling 24.79 [28] Palm Kernel Shell Ash Sol-gel process 50-98 [25] Additionally, this method is safe, environmentally friendly, and cost-effective [33]. The ball milling method used to produce silica nanoparticles from POFA is influenced by ball milling.…”

Synthesis and Characterization of Silica and Silica Cellulose from Natural Materials as Matrix for Various Sensor Applications: A Mini Review

“…Silica can be obtained or manufactured synthetically by extracting from the abundant amounts found in nature. The synthesis of silica and cellulose-silica from natural resources involves diverse methods such as sol-gel [30,31], acid leaching [32,33], and alkaline extraction [34,35]. and other techniques, each offering unique advantages in material design and application [9].…”