DESIGN OF HEAVY METALS ADSORPTION COLUMN BASED ON BOHART-ADAMS EQUATION

Abstract

Removal of heavy metals from water and wastewater has received a great deal of attention recently. Adsorption technique is one of the technologies being used for the treatment of polluted water, but seeking for low cost adsorbent is the objective of this study. This study records laboratory scale experiments to test the efficiency of washed quarry dust (WQD) in the removal of heavy metals; zinc and copper from wastewater of electroplating industry. Wastewater which was found to have high levels of zinc and copper ions was passed up the adsorption column. The column had a circular cross section with a diameter of 80 millimeters and a height of 1.2 metres. Sampling points were located at 0.50, 0.75 and 1 metre height of the column. A holding (regulating tank), 30 cm diameter and 50 cm height was placed at a height of 1.5 m from the column inlet to enable the wastewater to flow upwards. A gate valve was fixed at the holding tank’s outlet to regulate the effluent the flow rate. Leachate samples collected at the outlets of the column were analyzed for concentration of zinc and copper ions using atomic absorption spectrophotometer (AAS). Flow rate and column depths were varied to study their effects on the removal efficiency of heavy metals. This method of heavy metals removal proved highly effective. The mean removal efficiency was 94% and 92% for zinc and copper respectively. Maximum adsorption occurred at a depth of 1 m when wastewater was passed up the column at linear flow rate of 2.4 l/min/m2 as compared to 0.5 m and 0.75 m column depth. The elemental analyses of quarry dusts were done using X-ray fluorescence (XRF). Bohart-Adams equation was applied in the design of the other adsorption columns using the laboratory results for three columns. The service time predicted using the equation for 0.5, 0.75 and 1 m columns at a linear flow rate of 1.8 l/min/m2 were similar to those found in the laboratory column experiment.