Characterisation of Oyster Shell for Neutralisation of Bio-leached Effluent

Abstract

Characterisation studies of Oyster Shell (Mercenera mercenera) collected from coastal towns of Ghana and its neutralising effect on bio-leached effluent has been studied using XRF, XRD, Zeta Meter, BET and SEM/EDX.     The study confirmed that OS contains high calcium equivalent to about 54% CaO. The OS consists mainly of aragonite (96.1%) and calcite (2.6%) which are carbonates hence OS can be used to neutralise any acid solution. OS is very hard to mill as it has high Bond work  index of 48.54 kWh/t. The Zeta Potential analysis indicates that OS will not be stable below pH of 3 and above pH of 10. Therefore   OS powder dissolved and   raised  the pH of bio-leached effluent from pH 1.85 to 6.0 in 30 minutes. The arsenic removal increased with increasing OS concentration. The morphological study revealed that the surfaces of the reacting particles were coated with precipitates like FeAsO₄ at pH of 4.5. Consequently,   surface area of reacting powder increased from 4.15 m²/g to 75.46 m²/g. In a similar manner, the D₅₀ decreased from 16.69 µm to 7.77 µm for the reacting particles at pH 4.5. Particle   size distribution at pH 7.0 showed that the D₅₀ of the OS material increased to 9.23 µm which can be due to coating of precipitates like CaSO₄ on the reacting particles during acid neutralisation. Mobile arsenic extracted from the precipitate averaged 6.42 mg/L as against the EPA maximum allowable concentration of 5.0 mg/L indicating that the precipitate formed is fairly stable. 

Keywords: Effluent, Neutralisation, Oyster Shells, Characterisation, Work Index