Sorption and desorption characteristics of organic phosphates of different structures on aluminium (oxyhydr)oxides

Abstract

Summary Sorption and desorption characteristics of four organic phosphates ( OPs ) with different molecular sizes and structures (glycerophosphate, GP ; glucose‐6‐phosphate, G6P ; adenosine triphosphate, ATP ; myo ‐inositol hexakisphosphate, IHP ) and inorganic phosphate ( P i ) on three aluminium ( A l) (oxyhydr)oxides (amorphous A l( OH ) 3 , boehmite and α‐ Al 2 O 3 ) were investigated. The maximum sorption amounts of OPs and P i increased with decreasing crystallinity of the minerals on a per mass basis: α‐ Al 2 O 3 < boehmite < amorphous A l( OH ) 3 . With an exception of IHP sorption on amorphous A l( OH ) 3 , the maximum surface area‐based sorption densities increased with decreasing molecular weight ( MW ) of OPs and P i : IHP < ATP < G6P < GP < P i . Despite having the largest MW , IHP had greater sorption amounts on amorphous A l( OH ) 3 than the other OPs because of the transformation of surface complexes to surface precipitates. Sorption kinetics of OPs was first a rapid sorption followed by a long and slow sorption process. Of the three Al (oxyhydr)oxides, amorphous A l( OH ) 3 had the greatest first rapid sorption density and initial sorption rate of OPs within 5 minutes, both factors decreasing with increasing MW of OPs . The initial desorption percentages of OPs by KCl generally increased with decreasing MW of OPs , whereas the maximum desorption percentages of OPs by citrate were four to five times those achieved with KCl . Overall, strong specific sorption of OPs occurs on the surface of Al (oxyhydr)oxides, and molecular structure and size of OPs , as well as crystallinity and crystal structure of the minerals, are the key factors affecting the interfacial reactions and environmental behaviour of OPs .