Removal of Heavy Metals from Electroplating Waste Water Industry Using Adsorption Techinque(Lignite Coal)

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Addis Ababa University


Wastewater from industry can lead to water pollution if untreated, especially due to its high concentration of heavy metals. Heavy metals are considered extremely harmful because they can cause illnesses, disorder and diseases to human. Therefore, industrial wastewater containing heavy metal should be treated before discharge to the water stream but its treatment is very costly. There are several techniques to remove heavy metals from wastewater such as biosorption, filtration and adsorption of heavy metal but there is some limitation such as long treatment time. The adsorption of copper and zinc from synthetic wastewater by lignite coal was investigated. The effect of different environmental conditions such as contact time, initial metal ion concentration adsorbent dosage and pH on metal ions removal has been studied by keeping stirring at 200rpm and solution temperature of 25oc. Experiment results showed that maximum removal of Cupper ion by lignite coal at optimum condition (6 pH, 120 min. contact time, 2g adsorbent dose and 200ppm concentration) is 82.32% and for Zinc ion are 77.54% at optimum condition (4 pH, 90 min. contact time and 1.5g adsorbent dose, 150ppm concentration). These experimental studies on adsorbents would be quite useful in developing an appropriate technology for the removal of heavy metal ions from contaminated industrial effluents.The adsorption data of metal ions at temperature of 25°C have been described by the Freundlich and Langmuir isotherm models. The sorption process conformed to both Langmuir and Freundlich isotherms with maximum sorption capacities of 16.468 and 13.45mg/g for copper and zinc, respectively. The equilibrium time was found to be of the order of 120 minute for copper and 90 minute for zinc sorption by lignite coal. Sorption kinetics was determined using pseudo first-order, second order and, hence adsorption rate constants were calculated. The results revealed that sorption kinetics of copper and zinc followed pseudo second order with regration coefficients of 0.9994 and 0.9988 respectively. Optimum results were applied to remove copper and zinc from real electroplating wastewater. Optimum parameters for copper sorption were pH=6, contact time =120 mins, and lignite dosage of 2gm and for zinc batch sorption were; pH=4, contact time =90 minute, and lignite dosage of 1.5gm. The results showed lignite coal reduced copper ions from its initial concentration of 187.67 mg/l to 38.37 mg/l while zinc was reduced from 147.45 mg/l to 88.73 mg/l. Their respective removal efficiency was 63.45% and 59.65%



Adsorption techinque