Sweet sorghum (Sorghum bicolor (L.) moench), a crop that is grown by subsistence farmers in Zimbabwe was used to extract silica gel in order to assess its possible use as a raw material for the production of silica-based products. The gel was prepared from sodium silicate extracted from sweet sorghum bagasse ash by sodium hydroxide leaching. Results show that maximum yield can be obtained at pH 5 and with 3 M sodium concentration. The silica gel prepared at optimum pH 5 had a bulk density of 0.5626 g/cm 3 and anestimated porosity of 71.87%. Silica gel aged over 10 h had improved moisture adsorption properties. X-ray fluorescence (XRF) determinations show that the silica content in the ash is 40.1%. Characterization of sweet sorghum ash and silica gels produced at pH 5, 7 and 8.5 by Fourier Transform Infrared spectroscopy gave absorption bands similar to those reported by other researchers.Transmission electron micrographs show that silica prepared under optimum conditions is amorphous and consisted of irregular particles. Sweet sorghum proved to be a potential low cost raw material for the production of silica gel.

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This work was carried out in collaboration between all authors. Author NM designed the study, performed the statistical analysis, wrote the protocol, and wrote the first draft of the manuscript and managed literature searches. Authors LC, DS, MM managed the analyses of the study and literature searches. All authors read and approved the final manuscript.

The study seeks to determine the most significant factors affecting arsenic and chromium enrichment using novel P-ZrO2CeO2ZnO nanoparticles/alginate beads in order to minimize the total number of runs needed to successfully run the experiment. The effects of interactions between factors were also evaluated so that the optimum conditions which are not affected by the other factors are chosen for the experiments. The most significant factors on arsenic and chromium enrichment were screened for by using a half-factorial design, followed by the optimization of significant factors using the full-factorial design, and the interaction between factors was determined using ANOVA and interaction plots. The most significant factors for chromium recovery were sample volume, eluent flow rate, and sorbent dosage. For both chromium and arsenic recovery, interactions occurred between sample volume, dosage, and pH. The optimum conditions chosen for the experiment that gave favourable results for both metal ions were sample volume 5 mL, dosage 40 mg, pH = 7 and eluent flow rate 1 mL/min. This study showed that a preliminary screening step for the most significant factors for arsenic and chromium enrichment helps to reduce the number of total runs, and for the same experiment interactions between factors were present; hence, it is necessary to take this into account during the experimental design.