The Production of Biogenic Silica from Different South African Agricultural Residues through a Thermo-Chemical Treatment Method

Ncamisile Nondumiso Maseko,Samuel Ayodele Iwarere,Jonathan Pocock,Annegret Stark,Dirk Enke,Denise Schneider,Susan Wassersleben

doi:10.3390/su13020577

Abstract

A thermo-chemical treatment method was used to produce biogenic amorphous silica from South African sugarcane and maize residues. Different fractions of South African sugarcane (leaves, pith, and fiber) were processed for silica production. The biomass samples were leached with either 7 wt% citric acid or 7 wt% sulfuric acid at 353 K for 2 h prior to being rinsed, dried and combusted using a four-step program ranging from room temperature to 873 K in a furnace. The characterization of the pre-treated biomass samples was conducted using thermogravimetric analysis (TG/DTA), X-ray fluorescence analysis (XRF) and elemental analysis (CHN), while the final products were characterized by XRF, X-ray diffraction (XRD), elemental analysis, nitrogen physisorption and scanning electron microscopy (SEM). Citric acid pre-treatment proved to be an attractive alternative to mineral acids. Amorphous biogenic silica was produced from sugarcane leaves in good quality (0.1 wt% residual carbon and up to 99.3 wt% silica content). The produced biogenic silica also had great textural properties such as a surface area of up to 323 m2 g−1, average pore diameter of 5.0 nm, and a pore volume of 0.41 cm3 g−1.

Highlights

Plants can either be classified as silica accumulators or silica non-accumulators
This study focuses on the valorization of South African maize and sugarcane residues for the first time to produce amorphous biogenic silica using a thermo-chemical method that utilizes an organic acid
This study demonstrates the production of biogenic silica with high purity

Summary

Introduction

Maize, and other types of Gramineae (grasses) fall under silica accumulators. Agricultural residues such as maize leaves or sugarcane leaves, pith, and fiber consist of cellulose, hemicellulose, lignin, as well as inorganic matter that is generally referred to as ash. Biogenic silica can be obtained, e.g., from diatomite. This procedure utilizes complex thermal and mechanical treatments that result in biogenic silica with impurities like CaO, FeO3 , and Al2 O3 [6]. The production of high-quality porous silica from silica accumulating plants has become an area of interest to most researchers [1,2,3,4,5]. For the production of silica from biomass, pre-treatment of the biomass by leaching prior

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Conclusion