Advances in Environmental Technology (Nov 2022)
Fabrication of highly reactive MgO-NPs-CaO-hydrous nanocomposite and its application for the removal of manganese from aqueous solution
Abstract
Elevated concentrations of manganese (Mn) in drinking water notoriously impart colour, metallic taste, and other (eco)-toxicological effects to the final water quality at different point of use (POU). Specifically, levels in the range of ≥100 to 300 µg/L are prevalently known to be of grave concern. Herein, the efficacy of the Mg-(OH)2-Ca-NPs nanocomposite, i.e., calcined dolomitic effects, and its application for the removal of Mn from contaminated river water was explored. The nanocomposite was synthesized through mechanochemical activation using vibratory ball milling and thermal activation to remove CO2 and other volatile impurities. The one factor at a time (OFAAT) modality was used to fulfil the objectives of this study, specifically the effects of contact time, dosage, and mixing speed. To substantiate that, experimental results, state-of-the-art analytical techniques, and geochemical modelling (PHREEQC) were used to substantiate the study results. The optimum conditions were observed to be 15 min of mixing, 0.5 g of dosage, and 200 rpm of mixing speed. The interaction of Mn containing aqueous solution with hydrated lime (Ca(OH)2) and magnesium oxide (MgO) as well as their nanocomposite, i.e., Mg-(OH)2-Ca-NPs nanocomposite, led to an increase in the pH that registered as ≥11.87, ≥10.17, and ≥11.35, respectively. The Mn removal efficiency registered as ≥72.4%, ≥91.8%, and ≥83% for the hydrated lime, MgO, and Mg-(OH)2-Ca-NPs nanocomposite, respectively, whilst their turbidities were recorded as ≤0.41 NTU, ≤3.50 NTU and ≤1.05 NTU. An increase in pH and other factors resulted in the attenuation of Mn as a different chemical species, i.e., birnessite, hausmannite, bixbyite, manganite, nsutite, pyrolusite, and rhodochrosite. Ca2+, Mg2+, and Mn2+ were predicted to exist as divalent species in aqueous solution. The nanocomposite demonstrated superior performance compared to individual materials. As such, findings from this study confirmed the performance and effectiveness of the Mg-(OH)2-Ca-NPs nanocomposite on the removal of Mn from real river water. This will go a long way in curtailing the impacts of Mn in drinking water and further afield.
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