The introduction of heavy metal ions into the environment from industrial, agricultural, and natural disposals has become a major environmental and health concern. Removal of heavy metals from industrial wastewaters can be conducted through various treatments such as coagulation, complexation, adsorption by activated carbon, ion exchange, solvent extraction, foam flotation, electro-deposition, cementation, and membrane operations. Among these sattracting more attentions due to their advantages of simplicity and low cost. In this research, the ability of nonwoven produced from milkweed fibers as a lignocellulose structure for adsorption of heavy metals of lead and nickel was investigated. Chitosan polymer was dissolved in Fluoroacetate acid/Dichloromethane (70/30) to make a 4% solution. The applied conditions during electrospinning technique such as voltage, the flow rate and the distances between needle tip and collector were 21 kV, 0.4 mL/h and 100 mm, respectively. Then the produced nano-fibers was cross-linked with Glutaraldehyde vapors in order to achieve a high structural stability. The impact of controllable factors such as pH, contact time, initial concentration and process temperature on the adsorption quantity of Pb (II) and Ni (II) by three adsorbents i.e milkweed nonwoven, Chitosan nano-fibers and Chitosan/milkweed structure was investigated. The findings revealed that increasing the solution pH causes to increase the absorption rate of both heavy metals and then decreased. Increasing the pH values enhance significantly the adsorption capacity so that maximum removal percent of both lead and copper ions was occurred at pH value of 6. At the beginning of adsorption process, removal of Pb +2 and Ni 2+ ions increase rapidly and then it continues slowly until the equilibrium state is reached. Also, increasing the solution concentration leads to decrease the percentage of adsorption. The results showed that adsorption capacity of three adsorbents for Pb 2+ and Ni 2+ ions decreased with increasing the temperature. For the milkweed/Chitosan structure, the equilibrium adsorption was reached within 60 min for both Pb 2+ and Ni 2+ ions. The findings also revealed that the removal percentage of Ni 2+ ions reaches the highest value of 85% and Pb 2+ ions removal was the highest, i.e. 93 %, at contact time of 60 min. The results of adsorption isotherms indicated that Langmuir was the best to modeling Ni 2+ ions adsorption by the milkweed fibers. Also, Freundlich model can describe the adsorption of Pb 2+ ions by all adsorbents and adsorption of Ni 2+ ions by Chitosan/milkweed adsorbent better than Langmuir isotherm model. Moreover, pseudo-second order model was the best model to describe the adsorption kinetic of both heavy metal ions investigated in this study. The Chitosan/milkweed adsorbent demonstrated superior performance for removal of Pb 2+ and Ni 2+ ions from wastewater.
