Waste hemp and flax fibers and cotton and cotton/polyester yarns for removal of methylene blue from wastewater: Comparative study of adsorption properties

Waste hemp and flax fibers, and cotton and cotton/polyester yarns, available in large quantities from the textile industry, were used as cheap and effective sorbents for the removal of methylene blue from wastewater. Waste fibers and yarns were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, iodine sorption, water retention, and point of zero charge, as well as through the determination of crystallinity index and degree of surface crystallinity. Adsorption of methylene blue was optimized by examining the influence of contact time, initial concentration, temperature, and pH value. It was found that the more ordered structure of cotton and cotton/polyester yarns leads to lower adsorption capacities and better agreement with pseudo-second order kinetic and Langmuir isotherm model, while the more heterogeneous structure of flax and hemp fibers show higher capacities for methylene blue adsorption, better described by the pseudo-first order kinetic and Freundlich isotherm model. Based on the obtained results, waste lignocellulosic fibers and yarns can be utilized for the discoloration of wastewater, thereby solving the problem of waste generated in the textile industry.