عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Adsorption processes are widely used by various researchers for the removal of heavy metals from wastewaters and in this type of processes, activated carbon is frequently used as an adsorbent. Many conventional methods including oxidation, coagulation, membrane filtration, reverse osmosis, adsorption, ion exchange, and precipitation have been reported in the literature to be used for the removal of cadmium metals from wastewater. These methods may be ineffective or extremely expensive especially when the wastewaters contain the relatively low concentration of metal (1–100 mg/L) dissolved in a large volume of wastewater. However, adsorption can be considered as one of the most popular methods for the removal of heavy metals from the wastewater due to its low-cost, availability, simplicity of design, and high removal efficiency. Despite its extensive usage in water and wastewater treatment industries, activated carbon remains as an expensive material. In recent years, the need for safe and economic methods for elimination of Cu from contaminated water has directed researches' interest toward the production of other low-cost adsorbents. Therefore, there is an urgent need to find out all possible sources of agro-based inexpensive adsorbents and also for studying their feasibility for the removal of Cu. In this study, the possibility of the utilization of Phragmites australis and sugarcane straw for Cu adsorption was investigated.
The Phragmites australis plant and sugarcane straw were obtained from Khuzestan Province, southwest Iran. The collected materials were washed with double distilled water and then were used as dry Phragmites and sugarcane straw. The size of microparticles was examined by sieving with a 200 mesh-number sieve. Surface area and surface morphology of the Phragmites australis and sugarcane straw adsorbents were investigated by methylene blue method, scanning electron microscope (SEM), and Fourier-transform infrared spectra (FTIR). FTIR study was carried out to understand surface properties and available functional groups involved in adsorption mechanism.
All solutions for the adsorption and subsequent analysis were prepared by diluting the prepared stock solution. The initial pH of the Cd solution was changed by adding 0.1 N HCl or 0.1 N NaOH solutions as required. The adsorption experiments were conducted via batch process. The effects of experimental parameters such as initial pH, equilibrium contact time, adsorbent dosage, and initial Cu ion concentration on the adsorption process were investigated. Pseudo-first-order and second-order kinetic models were based on the assumption of physisorption and chemisorption process, respectively. Intraparticle diffusion in liquid-porous solid was explained by surface diffusion, pore volume diffusion, or both of the processes. Diffusion models were also employed to explain the Cd adsorption process. Three main steps are involved in the solid–liquid sorption process occurred between the metal ions and the adsorbent (a) the metal ions are transferred from the bulk solution to the external surface of the adsorbent; this is known as film diffusion, (b) the metal ions are transferred within the pores of the adsorbent; this is known as intraparticle diffusion, occurring either as pore diffusion or as a solid surface diffusion mechanism, (c) the active sites on the surface of the adsorbent capture the metal ions. The FTIR study of fresh adsorbent was carried out to identify the function groups effective in the adsorption process. The results of FTIR indicated the wave numbers for different functional groups present in adsorbents. Aliphatic C–H and C–O stretching may be responsible for Cd adsorption onto P. Australis and sugarcane straw as wave number shifts from 2,918.55 to 2,913.74 cm?1 and 1,058.08 to 1,035.36 cm?1, respectively.
The Aliphatic C–H and C–O can show cadmium adsorption ability by studied adsorbents.
Hence, considering the results of FTIR, it was expected that P. Australis and sugarcane straw play a major role in Cd absorption. The results showed that the optimum pH was equal to 7 as the equilibrium time were 30 and 60 min for Phragmites australis and sugarcane straw, respectively. For the two sorbents, as the adsorbent dose increased from 0.1g to 2g, the removal percentage became 93.55% at 0.1g for sugarcane straw and 87.34% at 0.3g for Phragmites australis; however, the other values remained almost constant with the changes in adsorbent dosage, ranging from 0.1g and 0.3 to 2g. With the increase in Cu concentrations (5, 10, 20, 30 and40 mg/L) in Phragmites australis and sugarcane straw adsorbents, percentage removal decreased from 88.9% to 42.5% and 93.34% to 89.8%, respectively. The adsorption kinetics of Cu ions onto Phragmites australis and sugarcane straw was described successfully by pseudo-first-order model. Also, the adsorption behavior of Cu ions fitted Langmuir isotherm. The results of the present study indicated that Phragmites australis and sugarcane straw can be used to remove Cu ions during water treatment process. Compared with Phragmites australis adsorbent, sugarcane straw showed greater capability of Cu adsorption.