Assessing the environmental impacts of mild extraction for biogenic silica recovery

Abstract

As rice consumption continues to increase, large amounts of by-products from rice production are being generated. In South Korea, these rice production by-products account for 70% of all agricultural by-products, with around 6.57 million tonnes of rice straw being produced annually. Despite the prevalence of rice straw, the majority of it is either incinerated on-site or left unattended, resulting in air pollution and greenhouse gas emissions. Consequently, there is a necessity to develop recycling technologies for rice straw. The utilisation of biogenic silica has garnered attention due to its potential to enhance the recycling of rice straw and mitigate the environmental risks associated with chemical-based silica. However, current biogenic silica extraction methods, including direct combustion, the acid leaching method, and alkali extraction, require substantial amounts of chemicals, necessitate high energy consumption, and generate voluminous wastewater. These environmental limitations create significant barriers to the practical application of biogenic silica recovery. Therefore, it is necessary to develop mild extraction methods that minimise chemical usage and energy input, which is critical for sustainable silica recovery and rice straw utilisation. In this study, alkaline hydrogen peroxide (AHP) was proposed as a mild extraction method for biogenic silica recovery. AHP, a solution of hydrogen peroxide (H2O2) mixed with an alkaline medium (NaOH and KOH), has been demonstrated to provide an alkaline environment for silica extraction and an oxidative environment for the decomposition of organic matter. Thus, AHP enables the production of high-purity silica without the need for additional incineration. To prove the hypothesis, the efficiency of AHP-based extraction (H2O2 9% and KOH 0.4 M) was compared with that of conventional methods. Furthermore, a life cycle assessment (LCA) was conducted to compare the environmental impacts of H2O2 consumption in the mild extraction process and energy input in conventional processes.