A Comprehensive Review on Production, Properties and Sustainable Applications of Rice Husk Ash

Rice husk ash is a valuable material produced from the thermal processing of rice husks, which generate over 100 million tonnes of waste annually worldwide. This review examines the production methods, chemical and physical properties, applications, and challenges associated with rice husk ash utilization across various industries. The production methods analyzed include uncontrolled burning, controlled combustion, fluidized bed combustion, gasification, and pyrolysis. Processing conditions, particularly combustion temperature, significantly influence the final properties of rice husk ash. The optimal temperature range of 500-700°C produces ash with predominantly amorphous silica content ranging from 80 to 95 percent, which provides excellent pozzolanic reactivity. The study evaluates key applications in construction, where rice husk ash serves as a supplementary cementitious material that enhances concrete strength and durability at replacement levels of 10-20 percent. Additional applications include high-purity silica extraction, ceramic manufacturing, environmental remediation through wastewater treatment and heavy metal adsorption, and soil amendment for agricultural improvement. Emerging applications in nanotechnology and advanced materials demonstrate the expanding scope of rice husk ash utilization. The environmental benefits are substantial, including agricultural waste reduction, lower carbon dioxide emissions compared to conventional cement production, and contribution to circular economy principles. However, several barriers limit widespread adoption. These include high variability in ash quality depending on rice variety and processing conditions, absence of standardized production protocols, limited infrastructure in rice-producing regions, and insufficient regulatory frameworks. Current research trends show increasing focus on geopolymer concrete, digital fabrication applications, and high-value silica products. Successful implementation requires coordinated efforts to develop quality standards, optimize processing technologies, establish efficient supply chains, and create supportive policies. Future research should prioritize process optimization for consistent quality, development of application-specific standards, exploration of high-value nanotechnology applications, and comprehensive techno-economic assessments to guide industrial adoption.