Role of grinding method on granular activated carbon characteristics

A coconut shell (AC1230CX) and a bituminous coal based (F400) granular activated carbon (GAC) were ground with mortar and pestle (MP), a blender, and a bench-scale ball milling unit (BMU). Blender was the most time-efficient for particle size reduction. Four size fractions ranging from 20 × 40 to 200 × 325 were characterized along with the bulk GACs. Compared to bulk GACs, F400 blender and BMU 20 × 40 fractions decreased in specific surface area (SSA, –23% and –31%, respectively) while smaller variations (–14% to 5%) occurred randomly for AC1230CX ground fractions. For F400, the blender and BMU size fraction dependencies were attributed to the combination of (i) radial trends in the F400 particle properties and (ii) importance of shear (outer layer removal) versus shock (particle fracturing) size reduction mechanisms. Compared to bulk GACs, surface oxygen content (At%-O1s) increased up to 34% for the F400 blender and BMU 20 × 40 fractions, whereas all AC1230CX ground fractions, except for the blender 100 × 200 and BMU 60 × 100 and 100 × 200 fractions, showed 25–29% consistent increases. The At%-O1s gain was attributed to (i) radial trends in F400 properties and (ii) oxidization during grinding, both of which supported the shear mechanism of mechanical grinding. Relatively small to insignificant changes in point of zero charge (pHPZC) and crystalline structure showed similar trends with the changes in SSA and At%-O1s. The study findings provide guidance for informed selection of grinding methods based on GAC type and target particle sizes to improve the representativeness of adsorption studies conducted with ground GAC, such as rapid small-scale column tests. When GACs have radial trends in their properties and when the target size fraction only includes larger particle sizes, manual grinding is recommended

Electoral coordination in anglophone Africa

Electoral coordination has been a primary concern for scholars of African politics, interested in topics such as ethnic conflict mitigation and democratisation, for decades. However, understanding of micro-level electoral coordination in Sub-Saharan Africa is generally still very limited. This study is the first to investigate voter coordination in Sub-Saharan Africa using constituency-level election results. Studying 20 single-member district elections during the period 1990–2010 in five Anglophone African countries (Botswana, Ghana, Kenya, Malawi and Zambia) demonstrates that many African elections continue to show low levels of electoral coordination. Using a multi-level regression analysis, the study shows that the most important explanation for low levels of coordination across Africa is high voter volatility. It is argued that insufficient information makes it hard for voters and candidates to act strategically. However, the level of democracy, which has been emphasised in earlier aggregate level research, does not significantly affect the level of coordination