Factors affecting the sorption/desorption of arsenic on/from synthetic nanomaterials

A. VIOLANTE; M. PIGNA; R. M. TORRES SÁNCHEZ; M. DOS SANTOS AFONSO

Mar del Plata

Congreso; V. Congreso Iberoamericano de Física y Química ambiental 2008; 2008

UNSAM, CNE, FCEN UBA

Sorption/desorption reactions on/from inorganic sorbents control the concentration of arsenic in solution and influence its mobility and toxicity. These reactions are affected by many factors, such as pH, nature of the sorbents and presence and concentration of organic and inorganic ligands. In natural systems, dissolved organic and inorganic ligands may compete with arsenic for adsorption sites on mineral surfaces, facilitating its potential mobility.We studied the sorption/desorption of arsenate and arsenite on/from synthetic nanomaterials such as metal oxides (ferrihydrite, non crystalline aluminum hydroxide, mixed iron-aluminum oxide), double layered hydroxides (anionic clays), pillared clays and iron exchanged clays as affected by pH and presence of inorganic (phosphate, sulfate, selenate, selenite) and organic ligands (oxalate, citrate, malate, tartrate).Arsenate was adsorbed much more than arsenite on nanomaterials containing aluminum, whereas almost similar amounts of arsenate and arsenite were fixed on the sorbents containing iron. Anionic clays and iron oxides were the nanomaterials which showed the highest capacity to adsorb arsenic. The presence of foreign ligands prevented arsenic sorption. Phosphate, selenite, citrate, tartrate malate and oxalate inhibited (in the order listed) the sorption of arsenic or promoted its desorption, whereas sulfate and selenate had a negligible effect in preventing adsorption or in replacing arsenic previously sorbed onto the minerals. The sorption of arsenic was strongly influenced by the order of addition of organic and inorganic ligands and arsenate or arsenite on the sorbents. For example, we have found that phosphate prevented arsenate sorption onto selected sorbents much more when added before arsenate than when added as a mixture or after arsenate. Finally, the effect of selected anions in promoting arsenate or arsenite desorption from the sorbents under investigation was studied. The desorption of arsenic was affected by the surface properties of the sorbents, the nature and concentration of the inorganic or organic ligands, pH, surface coverage and residence time of arsenic onto the surfaces of the nanominerals.