Waste Valorization From the Burning of Rice Husk

Abstract

Rice production generates large volumes of residual rice husk, fact that leads to serious accumulation issues. Rice is a plant that contains a high amount of sílica, mainly in its husk. A large amount of rice husk is used as fuel in the rice milling process, or for the production of electricity in cogeneration systems. In these processes the rice husk ash (RHA) obtained has different characteristics from those produced under controlled conditions: presents high-carbon content and a part of silica in crystalline state. When burnt, large quantities of ash are obtained (each ton of paddy produces aprox. 40kg of ash). The rice husk ash has about 90% silica. The morphology of the silica is very dependant on the burning conditions; if it is not amorphous (crystalline), it can harm the human organism, causing silicosis, modifications of the genome and even cancer. Therefore, this paper presents the development of a pretreatment of the rice husk with HCl for the purpose of obtaining amorphous rice husk ash, and a methodology to obtain an amorphous pozzolanic mineral admixture (ARHA) for cement from the ashes as well. Microstructure and the influence of the milling time on the pozzolanic activity index of the ash obtained are studied. Also, a part of the cement in pastes and mortars was substituted by the ARHA in order to study its influence in the resistance to compression, resistance to bending, water demand and the alkali-silica reaction. The results obtained with the ARHA are compared with those obtained without rice husk ash, and with normative requirements, , proving the viability of the substitution of a portion of the clincker by the ARHA when elaborating pozzolanic cement. Originality