Retention of amorphous silica in rice hulls at high temperatures

Abstract

Rice hulls contains around 20 wt% amorphous silica (rice hull silica). Rice hull silica containing no potassium impurity crystallized from amorphous silica to cristobalite at 1300 °C. When a small amount of MgO or a-Fe2O3 or Al2O3 were added to the rice hull silica, the rice hull silica crystallized to cristobalite at 1500°C. MgO a-Fe2O3 and Al2O3 diffused to silica as Mg2+, Fe3+ and Al3+ at high temperatures. These ions broke the SiO4 tetrahedron network, so that the amorphous state of rice hull silica was maintained. As sintering occurred at 1500°C in rice hull silica mixed with additives such as MgO, the melting of the silica particle surface by sintering made the SiO4 tetrahedrons to move easily, so that the rearrangement of SiO4 tetrahedrons occurred and amorphous silica in the rice hull silica crystallized to cristobalite at 1500°C.

Synergistic effects of silicon and phosphorus co-application on rice (Oryza sativa L.) growth, yield and nutrient use efficiency in saline soil

“…Apart from that, Si intensifies antioxidant activity or increase in cytokinins, salicylic acid, gibberellins or other plant growth hormones [60], that might augmented the TN production. Silicon is known to be accumulated in the epidermal cells of the rice hull [61], helping the synthesis of phytolith [62], that contribute to the mechanical strength [63], prevent pathogens and give protection from environmental stresses [64], resulted higher mature grains [29]; which eventually increased the FG production. Likewise some past investigations [21,52,64], in our study, the interaction effect of Si and P was also significant on FG and UFG production.…”

Circular Food Systems around the world: exploring concepts, ideas and opportunities

“…Presently, rice husk is largely regarded as a nuisance or worse; its disposal can be a challenging waste stream for millers (Kumar et al, 2016). When burned as a low-value fuel, it can even create ash that is carcinogenic due to the respiratory silica particles (Okutani et al, 2018) and still requires landfill of the residue. We argue that the present use of rice husk is relatively inefficient and difficult to scale.…”