Preparation Of Ce-Mn Binary Oxides Adsorbent For Arsenic And Phosphate Removal From Aqueous Solution

Arsenic (As) contamination in groundwater has long been a worldwide problem. As(Ⅲ) is much more toxic, more soluble, more mobile and therefore more difficult to be removed than As(Ⅴ). Phosphorus, as an essential nutrient element, may cause eutrophication if excessively existin water. As phosphorus and arsenic located near on the same host family, they have similar chemical structures and properties, therefore, the adsorption behavior of phosphorus and As (Ⅴ) is similar.To achieve higher arsenic removal, a pretreatment for As(Ⅲ) oxidation is therefore usually involved. A novel Ce-Mn binary oxide material which combined the oxidation property of manganese dioxide and the special adsorption features to As(Ⅴ) and phosphorus of cerium oxides, were developed aiming at simultaneously effectively removing both As(Ⅲ)、As(Ⅴ) and phosphorus from drinking water. A systematic investigation including optimization of preparation, characterization of adsorbent, evaluation of adsorption performance, arsenic and phosphorus removal mechanisms was conducted in present paper.The following results were obtained.1. The Ce-Mn binary oxide is aggregates of nanosized particles and is amorphous form. It has a high specific area of157m2·g-1and an isoelectric point of6.5.2. A novel Ce-Mn binary oxide material which combined the oxidation property of manganese dioxide and the special adsorption features to As(V) of cerium oxides, were prepared using a simultaneous oxidation and coprecipitation method. This adsorbent could effectively oxidize As(Ⅲ) to As(Ⅴ) and was effective for both As(Ⅴ) and As(Ⅲ) removal, the maximal adsorption capacities of As(Ⅴ) and As(Ⅲ) were57.5mg·g-1and93.5mg·g-1, respectively. Additionally, the aresnic adsorption on Ce-Mn binary oxide is pH-dependent, decreasing with an increase in solution pH. However, ionic strength has little effect on arsenic adsorption. The effects of coexisting anions on arsenic adsorption decrease in the order of:PO43->SiO32->CO32->SO42-.3. The Ce-Mn binary oxide has a excellent adsorption propriety. The Langmuir model is found to be more suitable for describing the adsorption behavior of phosphate and the maximal adsorption capacity is as high as28.6mg-g-1at pH7.0. The phosphate adsorption is quick and the kinetic data is well fitted by the pseudo second order model. Additionally, the phosphate adsorption on Ce-Mn binary oxide is pH-dependent, decreasing with an increase in solution pH. However, ionic strength has little effect on phosphate adsorption. The effects of coexisting anions on phosphate adsorption decrease in the order of:SiO32->CO32->Cl->SO42-.4. As(Ⅴ) was removed by forming an inner-sphere complex on surface of the adsorbent. The removal mechanism of As(Ⅲ) is an oxidation coupled with sorption approach and is distinct from that of As(Ⅴ). During As(Ⅲ) oxidation, fresh adsorption sites for arsenic adsorption were created at the solid surface, due to the reductive dissolution of manganese dioxide. This was responsible for the higher As(Ⅲ) uptake. Specific adsorption occurs at the aqueous phosphate/Ce-Mn binary oxide interface and the replacement of surface hydroxyl groups by the phosphate species is the main removal mechanism.