The efficiency of bivalve mollusk shell in removal of lead [Pb (II)] from aqueous solutions by central composite design model (CCD) and optimization of effective parameters

Background and

Lead (Pb) is an element that due to high solubility in aqueous solutions can cause poisoning in consumer. Therefore, removal or reduction of Pb (II) from industries wastewater and contaminated drinking water is inevitable. In recent years, particular attention to the variety of natural structures and cost-effective materials to remove pollutants from aqueous solutions has been made. Bivalve mollusk shell is one of the cheap-price natural adsorbents can remove these contaminants.

The requested adsorbent was derived from the shells of marine bivalve mollusk collected from the shores of the Caspian Sea, and then was powdered. After contacting the adsorbent with different concentrations of lead solution in laboratory conditions, readings of the secondary concentration by atomic absorption spectrophotometer were conducted. Experimental design of this study was central composite design (CCD), is one of the methods of response surface methodology (RSM). There were 31 standard samples.

The best pH for absorption by the adsorbent is 6. Increasing adsorbent dose to 0.55 mg/l and the contact-time to 45 minutes was optimal. The mechanism of adsorption followed the Langmuir isotherm and adsorption process was monolayer and homogeneous. Quadratic interaction for pH parameter was significant (P = 0.0001).

Bivalve mollusk shells have the ability to adsorp Pb (II). This ability is due to the mechanism of adsorption and ion exchange. Maximum efficiency is related to the interaction between pH and optimum adsorbent dose. As compared to other adsorbents such as epicarp etc. that their availability is follows their consumption, usage of absorbent due to its low cost and abundance can be economically justified.