Maize Stalk Obtained after Acid Treatment and Its Use for Simultaneous Removal of Cu(2+), Pb(2+), Ni(2+), Cd(2+), Cr(3+) and Fe(3+)

In this research, eco-friendly material represented by maize stalk (MS) obtained after acid treatment was employed for simultaneous removal of Cu(2+), Pb(2+), Ni(2+), Cd(2+), Cr(3+) and Fe(3+) (M(X+)) from simulated textile aqueous matrix and tannery wastewater produced by the leather industry. The acid treatment of MS was done with 4 M HCl. The influence of experimental parameters was evaluated in order to optimize the adsorption process for simulated textile matrix. The contact time 10–60 min and initial concentration of 0.5–1 mg/L M(X+) influence were studied by batch method. Additionally, the adsorption data of M(X+) onto MS was fitting by kinetic and isotherm models. The results obtained showed that the 60 min was necessary to reach adsorption equilibrium of the MS. The adsorption capacity of MS was 0.052 mg Cu(2+)/g of MS, 0.024 mg Pb(2+)/g of MS, 0.042 mg Ni(2+)/g of MS, 0.050 mg Cd(2+)/g of MS, 0.056 mg Fe(3+)/g of MS and 0.063 mg Cr(3+)/g of MS at pH = 4.2. The Langmuir model described the adsorption process very well. The MS showed huge selectivity for Cr(3+) and Fe(3+) in the presence of Cu(2+), Pb(2+), Ni(2+) and Cd(2+). The adsorption of M(X+) from liquid phases were analyzed by spectrometric adsorption method (AAS). The solid phases of MS before and after adsorption by TG and SEM analysis were characterized. When MS was used for removal of M(X+) from tannery wastewater, two major issues were investigated: First, the decrease of M(X+) content from highly polluted and difficult to treat tannery wastewaters by improve its quality and in the second part, specific recovery of M(X+) from MS mass increasing the economic efficiency of metals production based on green technology.