Removal of the Cd2+ and Pb2+ from the Wastewater by the use of Grafted Poly ) Ethylene Terephthalate (Fibers with 2-Hydroxypropyl Methacrylate as Monomer

Abstract

Wastewater containing pollutants such as heavy metals must be purified before use for irrigation. The objectives of this study were to investigate the sorption-desorption properties of poly (ethylene terephthalate) (PET) grafted with 2-hydroxy propyl methacrylate for the removal of cadmium (Cd) and lead (Pb) from wastewater. Polymers with different levels of grafting (0-20, 20-40, and higher than 40%). were synthesized. In order to confirm the grafting process, the scanning electron microscopes (SEM) of the fiber samples were also taken from raw and grafted PET. Thermo-gravimetric analyses (TGA) as well as Fourier transform infrared (FTIR) test of the samples were also conducted. The specific surface area of the sorbent was measured with BET (Branuer–Emmet-Teller) method using a Quanto-chrome Autosorb Instrument and found to be equal to 0.40 and 0.42 square meters per gram for raw and grafted pet, respectively. Cation exchange capacity (CEC) was calculated to be 7.80 and 45.50 Cmol of charge per Kg of sorbent for raw PET and higher than 40 percent for grafted PET, respectively. The point of zero charge (ZPC) was determined to be 5.80. In order to achieve optimal sorption conditions, factors such as solution pH, contact time, sorbent quantity, grafting yield and sorbate concentrations were determined for Cd2+ and Pb2+ sorption. The best conditions for Cd sorptin on PET were pH=6.7, contact time= 60 min, and 2.5 grams sorbent per liter, for 40% grafted PET and 120 mg Cd2+ per liter. And for Pb the conditions were pH= 6, contact time = 30 minutes and other conditions were the same as Cd2+. Adsorption isotherms of Cd2+ and Pb2+ were studied at different concentrations of sorbent and 3 temperatures of 15ºC, 25ºC, and 40ºC. Four isotherms isotherms including Langmuir, Freundlich, Temkin-Pyozhev and Dubinin-Redushkevich were tested. Freundlich and Langmuir models were the most appropriate to explain the experimental data. Kinetics studies were conducted at 15 and 25ºC. Five models including: Lagergren's pseudo-first order, Ho's pseudo-second order, Intra-particle diffusion, Bangham and modified Freundlich were examined. The best model for Cd2+ sorption was pseudo-second order equation. The best model for Pb2+ at 15ºC and 25ºC were modified Freundlich and pseudo-second order equations, respectively. Physiochemical properties (thermodynamic) were calculated using the Gibbs equation. To determine the initial and ease of desorption, activation energy of the Arrhenius equation was used. The negative value of ΔG showed that the sorption was spontaneous. The activation energy was very low indicating that sorption and desorption could proceed without energy .Desorption of Cd2+ and Pb2+ were studied with the fiber samples initially treated with the metal loadings of 25, 50 ,75 and 100% maximum sorption capacity during the sorption study .Removal of sorbed Cd and Pb from filter were examined using 0.01M Ca(NO3)2, 1M HNO3 and 1M NaOH. Amount of 93 to 95 and 3 to 8 percent of the sorbed ions by the filter were removed by HNO3 and NaOH, respectively. While Ca (NO3)2 was able to desorb 40 percent of sorbed ions. Sorption-desorption experiments were repeated 5 times and after 5Th steps, sorbed amount of Cd2+ and Pb2+ were determined. Isfehan Zob Ahan factory’s wastewater was used to study the filter heavy metals sorption properties of wastewater. The filter could sorb about 61 to 66 percent of Cd2+ and 50 percent of Pb2+ from wastewater.