_Applied_  
_sciences_  
_Article_  
**Extraction and Characterization of Biogenic Silica Obtained**  
**from Selected Agro-Waste in Africa**  
**[PERSON] 1,2,*, [PERSON] 1, [PERSON] 1, [PERSON] 1,3 and [PERSON] 1,2**  
1 Department of Thermochemical Conversion, DBFZ Deutsches Biomassesforschungszentrum  
Gemeinutzige GmbH, Torgauer Strase 116, 04347 Leipzig, Germany; [PERSON]] (S.F. );  
[PERSON].S. ); [PERSON](H.B.D. ); [PERSON]] (M.N.) 2 Department of Agriculture and Environmental Science, University of Rostock, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany  
3 Institute of Chemical Technology, Universitat Leipzig, Limesstr. 3, 04103 Leipzig, Germany  
* Correspondence: [PERSON]@[PERSON]ADDRESS]; Tel. : +49-(0)341-2434-523  
**Featured Application: The synthesized biogenic silica can be considered in applications such as catalyst support, construction material, concrete and backing material. **  
**Abstract** Increased amounts of available biomass residues from agricultural food production are present widely around the globe. These biomass residues can find essential applications as bioenergy feedstock and precursors to produce value-added materials. This study assessed the production of biogenic silica (SiO\({}_{2}\)) from different biomass residues in Africa, including comrhusk, comrcob, yam peelings, cassava peelings and coconut husks. Two processes were performed to synthesize the biogenic silica. First, the biomass fuels were chemically pre-treated with 1 and 5% \(w/v\) citric acid solutions. In the second stage, combustion at 600 \(\lx@math@degree\)C for 2 h in a muffle oven was applied. The characterization of the untreated biomasses was conducted using Inductively coupled plasma--optical emission spectrometry (ICP-OES), thermal analysis (TG-DTA) and Fourier-transform infrared spectroscopy (FTIR). The resulting ashes from the combustion step were subjected to ICP, nitrogen physisorption, Energy dispersive X-ray spectroscopy (EDX) as well as X-ray diffraction (XRD). ICP results revealed that the SiO\({}_{2}\) content in the ashes varies between 42.2 to 81.5 wt.% db and 53.4 to 90.8 wt.% db after acidic pre-treatment with 1 and 5 \(w/v\)% acid, respectively. The relative reductions of K\({}_{2}\)O by the citric acid in yam peel was the lowest (79 wt.% db) in comparison to 92, 97, 98 and 97 wt.% db calculated for comrcob, cassava peel, coconut husk and comrhusk, respectively. XRD analysis revealed dominant crystalline phases of arcanite (K\({}_{2}\)SO\({}_{4}\)), sylvite (KCl) and calcite (CaCO\({}_{3}\)) in ashes of the biomass fuels pre-treated with 1 \(w/v\)% citric acid due to potassium and calcium ions present. In comparison, the 5 \(w/v\)% citric acid pre-treatment produced amorphous, biogenic silica with specific surface areas of up to 91 m\({}^{2}\)/g and pore volumes up to 0.21 cm\({}^{3}\)/g. The examined biomass residues are common wastes from food production in Africa without competition in usage with focus application. Our studies have highlighted a significant end-value to these wastes by the extraction of high quality, amorphous silica, which can be considered in applications such as catalyst support, construction material, concrete and backing material. **  
biogeric silica; African biomass fuels thermochemical conversion; ash characterization; combustion 4.0/. **  
**1. Introduction**  
Lignocellulosic residues, also known as biomass, have a pivotal role in the context of sustainable development due to their unique properties. They offer biodegradability, which contributes to a healthy ecosystem, as it can drastically reduce greenhouse gas emissions compared to fossil fuels [1,2]. The combustion of biomass fuels is perceived as carbon-neutral in many perspectives as it results in no net increase of greenhouse (GHG)emissions on a life-cycle basis. Plants are able to capture the same amount of CO2 through photosynthesis during the different stages of plant growth.