Effects of Leaching Method and Ashing Temperature of Rice Residues for Energy Production and Construction Materials

Abstract

Escalating demands for infrastructure materials and energy worldwide necessitate exploration of means to efficiently utilize resources to support growing consumption. This work evaluates the potential symbiotic relationship between cultivation of an agricultural product (namely, rice), energy conversion, and utilization of bioash in the production of cement-based materials to improve the sustainability across multiple industries. Primarily, leaching methods of biomass that benefit energy conversion are evaluated as a means to simultaneously improve ash properties for use in cement-based materials. Specifically, this study considers water leaching and H3PO4 leaching of rice hulls and rice straw, which were subsequently ashed at three different temperatures, 600, 850, and 1100 °C. The effects of leaching on the ash characteristics, on the performance of ash-cement mortars, and on the greenhouse gas (GHG) emissions from both the mortars and energy produced are quantified. Findings showed that while acid leaching led to higher GHG emissions for electricity generation, leaching decreased concentrations of undesirable alkali metals and chlorides in the ash. Regardless of treatment and ashing temperature, the inclusion of bioash delayed the early strength development of the cement-based mortars. Yet, several permutations of treatment, feedstock type, and ashing temperature were found to contribute to the later-age strength development of cement-based materials while reducing related GHG emissions. Specifically, after 28 days of curing, mortars containing 15% cement replacement with unleached ash prepared at 600 °C had 1–5% lower compressive strength, and after 56 days, mortars with leached rice hull ash prepared at 600 °C had 5–6% lower compressive strengths. Further, the use of unleached and water-leached ashes in mortar led to reductions in GHG emissions up to 15%. Hence, this work shows that pretreatment methods applied to rice biomass residues may contribute to desirable cobenefits for energy and materials production.

Technical, economic, and environmental feasibility of rice hull ash from electricity generation as a mineral additive to concrete

“…The likely reason for these shifts in properties is that the RHA could be acting as a pozzolan that contributes to later-age strength, but less so to early strength. Other works have demonstrated that, at 56 days, strength loss can be much less (~ 1–5%) for rice hulls 25 . With grinding, RHA has been shown to become more reactive 33 .…”

“…It has a long history of utilizing rice hulls, a byproduct of rice milling, to generate renewable electricity, and the resulting RHA has potential to be used as an SCM. Further, the research community has previously investigated the potential of RHA as an SCM and its environmental and economic feasibility 23 – 25 . Hu et al 26 showed that mixing RHA with cement reduced embodied CO 2 emission and energy consumption while sustaining the required compressive strength and sulfate resistance, and the comprehensive data analysis by Ozturk et al 27 concluded that it is possible to decrease CO 2 emissions by 25% and increase the cost efficiency of concrete by 65% by using RHA and other pozzolanic materials at optimal conditions.…”

Achieving net zero greenhouse gas emissions in the cement industry via value chain mitigation strategies

“…These ashes can be a by-product of biomass energy generation, thus concurrently benefiting another sector. 98 However, biomass must be burned to produce ashes, leading to low embedded carbon content and minimal CO 2 storage through their use. More recently, microbial-induced CaCO 3 precipitation, originally examined to patch cracks through mineral formation by microorganisms, 99 has been explored for the intent of forming fully bioderived cements.…”

Opportunities and challenges for engineering construction materials as carbon sinks

“…Environmental impact assessment methods are the most robust way to quantitatively assess the potential of CO2uptake materials. Forms of environmental impact assessment are frequently applied to examine the potential for new technologies to contribute to GHG emissions mitigation (e.g., [135][136][137][138]). For such assessments, it is crucial that consistent scoping, accounting methods, consideration of uptake time horizons, carbon-storage periods, and emissions during life cycle stages be considered to ensure net-sequestration.…”