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  (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.