Phosphate interaction with calcined form of Mg-Al-CO3 hydrotalcite in aqueous solutions

Abstract

In this study the sorption removal of phosphates from aqueous solutions was investigated. The sorbent used was Mg-Al-CO3 hydrotalcite with a molar ratio of 2:1 calcined at 450 oC. The retention capacity of cLDH was 2.88 mmol P/g. The sorption can be characterized by a kinetic model of the pseudo-second order. Laboratory tests proved the existence of two steps – fast and slow. The fast step is associated with regeneration of the layered structure accompanied by surface adsorption of phosphates and is applied within the first 1.5 to 2 hours. Its rate is controlled by diffusion mechanisms. If abundance of phosphates is present in the solution, the slow step follows, i.e., phosphate intercalation into the interlayer, and eventually precipitation of aluminium phosphate occur. Different sorption mechanisms significantly influence desorption of phosphates.