Extended Langmuir model fitting to the filter column adsorption data of copper and zinc

Abstract

This study involved laboratory scale experiments to test the efficiency of washed quarry dust (WQD) in the removal of heavy metals such as zinc and copper from wastewater of electroplating industry, before their safe disposal into public sewer. The washed quarry dust collected from Aristocrust quarries in Mlolongo was prepared and characterized for various physiochemical properties. The wastewater samples were collected from Master Platers Ltd, located in Nairobi’s industrial area. To determine the heavy metals’ removal efficiency of WQD, samples of wastewater were treated by column adsorption experiments. The concentration (C_o) of heavy metals in the industrial effluent were analyzed and compared to that treated with the adsorbent. The heavy metals analyzed were zinc, copper, cadmium, chromium, arsenic, lead and iron. It was established that zinc and copper concentrations were high in the industrial effluents while the concentrations of other metals were within the requirements of the Kenya Standard; KS1966‐2:2007. Wastewater samples of known heavy metal concentrations (C_o) were passed through the 0.5, 0.75 and 1 M columns at varying flow rates of 6, 9 and 12 ml/min. Leachate samples collected at different depths of WQD column were analyzed for concentrations of zinc and copper ions using atomic absorption spectrometer. The removal efficiency was around 94% and 92% for zinc and copper respectively using column depth of 1 M at a flow rate of 12 ml/min. The adsorption model adopted was described by extended Langmuir adsorption isotherm since the adsorption process involved competitive adsorption in the presence of more than one heavy metal in the wastewater. The model represented the data well when adsorption density curves were plotted for model and laboratory test results. From the column experimental results, washed quarry dust filtration has a high potential to be used in the removal of heavy metals from industrial wastewater. Unlike other adsorbents, WQD is readily available, efficient and cost effective.

Key words: adsorbent, copper, heavy metals, treatment, wastewater, washed quarry dust (WQD), zinc