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 (Co) 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 (Co) 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.
