The regeneration characteristics of various red mud granular adsorbents (RMGA) for phosphate removal using different desorption reagents

Abstract

In this research, various red mud granular adsorbents (RMGA), which were made from red mud – a kind of waste residue from the alumina industry, were manufactured under different sintering temperatures (ST). For the purpose of investigating the regeneration characteristics of them for phosphate removal, systematic experiments were carried out, including adsorption, desorption (using different desorption reagents) and resorption tests. When RMGA were desorbed by HCl solutions, the desorption efficiencies were relatively higher due to acid erosion, but the corresponding resorption capacities became small owing to extraction of effective components. Although RMGA rarely released phosphate in desorption process when being desorbed by deionised water, it performed well on resorption of phosphate afterwards. It was assumed that the lower pH in resorption process, which was caused by the reductive release of CaO into solution, contributed to a weaker competition of OH − on phosphate resorption. When NaOH solution was employed as the desorption reagent, resorption capacities of RMGA were relatively larger and increased with the increase of NaOH concentration, because OH − might ameliorate the chemical composition on the surface of RMGA potentially. In addition, several RMGA manufactured under lower ST obtained larger resorption capacities than their original adsorption capacities, because of the comparatively unstable crystal structure which led to a stronger amelioration on them.