Phosphate uptake behavior of ZnAlZr ternary layered double hydroxides through surface precipitation

Abstract

Tetravalent Zr 4+ ion incorporated ZnAl hydrotalcite-like material with varying Zn/(Al + Zr) atomic ratio (2–4) and Al/Zr atomic ratio 0.7:0.3 with CO 3 2 - as interlayer anion were successfully synthesized and characterized by various physicochemical methods. The phosphate uptake studies were carried out over these materials by batch method with the objective of enhancing the uptake through creation of higher positive charge on brucite-like layers by the incorporation of Zr 4+. The studies revealed that ternary ZnAlZr hydrotalcites show good uptake capacity for phosphate, among which ZnAlZr4-HT depicts a maximum uptake of around 91 mgP/g. We observed that phosphate uptake results in the formation of layered hopeite mineral (Zn 3(PO 4) 3·4H 2O) on the surface of material by the surface precipitation of dissolved zinc ion through the outer-sphere complex formation of phosphate. The phosphate uptake increases with a decrease in Zn/Al and Zn/(Al + Zr) atomic ratios. Effects of initial phosphate concentration, contact time, adsorbent amount and temperature variation on phosphate uptake were studied. Co-presence of competitive anion like nitrate enhances the uptake of phosphate to 148 mgP/g. Recycle studies of the material shows a decrease in the uptake of phosphate with the number of cycles due to an increase in the crystallinity. Very high uptake of phosphate by these materials even in the presence of other anions/cations suggests their potential role in waste water remediation.