Biogenic derived binary metal oxide as a reactive material for remediation of pyrophosphate contaminated aqua system

Abstract

Owing to the recent discovery about the potentials of pyrophosphate (PP) as a contributor to eutrophication, the ability of a binary metal oxide (BMO) as an adsorbent for PP removal from aqua system was investigated. The choice of a BMO was based on the synergy of the constituent metal oxides in sequestrating ionic species. The binary metal oxide (BMO) of Ca and Fe, synthesized using a Gastropod shell, as precursor, exhibited high removal efficiency (>99%) for pyrophosphate (PP), irrespective of initial PP concentration studied (25–300mg/L). The pseudo second order kinetic model had the best (r2−1.00) fitting to the time-concentration profile data. The determination of the saturation index (SI) value of calcium pyrophosphate and application of the principle of constant solubility product affirmed the role of precipitation as a paramount factor in the PP removal process by BMO, in addition to the complex formation between any of the ionic species (i.e. Ca and Fe) in the system. The XRD analysis of the derived sludge revealed the formation of amorphous calcium pyrophosphate. Process variables optimization revealed that initial solution pH, organic load, and ionic strength had no negative impact on the PP removal efficiency. The results of the equilibrium isotherm analysis showed that the Freundlich isotherm equation gave the best description of the sorption process (r2=0.9109) and the Langmuir monolayer sorption capacity (qm, mg/g) value of 120.48 was obtained.