ADSORPTION OF LEAD (II) IONS FROM INDUSTRIAL EFFLUENT BY USE OF EGGSHELL

Abstract

Heavy metals are major toxicants found in industrial effluent and have been known to contaminate the water resources. They include metals such as lead, cadmium, arsenic and chromium which pose a significant threat to the environment and public health because of their toxicity, accumulation along the food chain and their recalcitrance in nature. The aim of the study was to investigate the removal of lead (II) ions from raw industrial effluent using low cost sorbent; eggshell. Industrial effluent samples were collected through purposive sampling at the point of discharge before treatment, from the Associated Battery Manufacturing Company in Nairobi. The lead concentration in the effluent samples collected was analyzed by use of the Atomic Absorption Spectrophotometer (AAS) (Spectra AA50). Crushed eggshell of different particle size were added to the sample stirred using magnetic stirrer for 30 minutes to attain equilibrium. After contact time, equilibrium uptake of lead (II) ions by the eggshell was achieved. Filter paper grade 54 was used to filter the eggshell so as to obtain the filtrate. The exact concentration of the filtrate was then determined using the AAS. The experimental research design used was the Randomized block design. This entailed the varying of process parameters like effects of pH, sorbent size, sorbent amount, and contact time in the sampled effluent. Results obtained were analyzed to compare the lead (II) ions removal efficiency between raw and boiled eggshells. All the data represents the mean of three independent experiments. Data analysis was performed using statistical function of the Microsoft excel 2007. Maximum adsorption of Pb2+ on eggshell was observed at pH = 5. Adsorption equilibrium was established in about 120 minutes and the mass of eggshell used was 10 g/L of particle size using sieve No. 355μm. The data generated were fitted on three adsorption models, Langmuir, Freundlich and Temkin models to determine the best fit model. Langmuir model was the best fitted model on the raw eggshell with a correlation coefficient R2 = 0.994 and adsorption capacity of 11.63 mg/g, this was followed by Freundlich R2 =0.926 and then the Temkin Isotherm R2 = 0.875. The results showed that the egg shell removed the lead (II) ions from the industrial effluent from 19.2 mg/L to 0.2023 mg/L which is below the recommended water quality standards for effluent discharge to public sewers within optimum conditions.