The adsorption of causticized cassava starch on coal‐washery effluent solids in relation to flocculation

Abstract

AbstractThe adsorption of causticized cassava starch on coal‐washery effluent (‘blackwater’) solids was investigated with a view to establishing how such factors as pH, starch concentration, aging and presence of complexing agent affect the extent and nature of the adsorption process. Also, the effect of starch concentration on the flocculation behavior of the blackwater slurry was studied.The adsorption process does not exhibit a Langmuir type behavior but produces a characteristic S‐shaped curve and is essentially unaffected by pH except in the highly alkaline range (pH > 10.0), where a marked decrease in adsorption density occurs. Based on the data generated in this study and the results of studies on the electrokinetic properties of starch and blackwater solids reported in the literature, it is postulated that the adsorption mechanism is predominantly controlled by hydrogen bonding aided by hydrophobic interactions.The flocculation studies established that high reagent (starch) concentration leads to low settling rates and the reasons for this phenomenon are discussed.