Synthesis of magnesium oxide from waste magnesium-rich Cucurbita pepo (pumpkin) seeds

Abstract

Recent studies have focused on the processing of biowaste to obtain added value and to reduce organic waste in the general stream. This study investigated the synthesis of magnesium oxide (MgO) from magnesium-rich Cucurbita pepo (pumpkin) seeds for a precursor solution as a reducing agent via an eco-friendly method for the first time. The pumpkin seeds were ashed at 550°C for 6 h and subjected to acid-leaching. Mg(OH)2 was then precipitated using an aqueous solution of 2.0 M NaOH. The Mg(OH)2 was then calcined at 550°C for 4 h to obtain MgO. Physicochemical properties (i.e. proximate analysis, elemental composition, electrical conductivity (EC), pH) and selected heavy metals (i.e. Pb, Fe, As, Cd, Cr, Hg, Cu, and Ni) analyses were conducted on the seed samples and as-synthesized MgO. X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR), citric acid test (CAT), and acid neutralization capacity (ANC) tests were techniques used to characterize the synthesized MgO. The results revealed the percentage yield of the MgO to be 23%. The pH of the as-synthesized MgO was recorded as 10.63. XRF studies showed that MgO made up 75.1% of the total weight synthesized. XRD results showed the presence of crystalline cubic structures of MgO. FTIR results showed a peak at 584 cm−1 which confirmed the formation of MgO. The produced MgO was highly reactive, with a CAT time of 2 s. The ANC of the MgO was high at 22.77 mol+/kg. Also, metal concentrations such as Fe, Cu, Cd, Ni, Pb, Hg, As, and Cr in MgO were below the WHO stipulated limits of 350, 36, 0.8, 35, 85, 0.03, 40, and 100, respectively. This implies its suitability for soil remediation purposes. Results indicate that the as-synthesized MgO from Cucurbita pepo (C. pepo) seeds could be used for several applications due to its high alkalinity, reactivity, and fast CAT time.