The removal of copper in water using manganese activated saturated and unsaturated sand filters

Activated unsaturated sand filter (AUSF) is one among the few of the filtration technologies utilised to treat metal bearing waters. AUSF utilises activated sand as its filter media and operates under naturally flowing air to ensure unsaturated condition. In this study, manganese-activated sand was used for the removal of copper. Activation of the sand increased its BET surface area by 21% at 0.071 mg Mn/g sand and Mn leaching was significant only at pH < 4.5. SEM/EDS showed clusters of crystalline manganese oxides coating the sand surface and newborn copper hydroxides occupying sand surface after exposure to copper-bearing-water. A tracer study revealed that the gas voidage in the filter increased from 0.143 to 0.294 as the water flow rate reduced from 74.4 to 16.4 mL/min, which ensured better water aeration and increased copper removal. The ratio of manganese to sand was a key parameter as it increased almost exponentially the removal capacity of the AUSF. On the other hand, copper removal increased linearly with the inverse of the sand particle size, which indicates the importance of the surface area in the process. However, unexpectedly, when the inlet copper concentration increased from 3 to 20 mg/L, the filter capacity reduced by about 50% from 0.020 to 0.011 mg Cu/g sand. Based on the results obtained, mechanisms by which copper was removed in AUSF were proposed and they were found to vary as function of time [electrostatic attraction (t < 2 min); precipitation (t < 3.8 min), and adsorption/ion exchange (t < 60 min)].

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Copper is widely distributed in the environment and can have several health effects. ► Activated unsaturated sand filter was effective for Fe and Mn but not studied for Cu. ► AUSF was indeed found effective for removing copper from water. ► Removal mechanisms were suggested and supported by experiments.