The Synthesis Of Lignin Sulfonate Polymer And Study Of Its Adsorption To Malachite Green In Aqueous Solution

The usage of dyes in different industry, such as leather, pharmaceutical, paper mills, printing, textiles and dyeing, increase yearly because of their efficacy and easy to acquire. The effluents produced by these industries are full of dyes contents. The untreated discharge of these pollutants into different water body is extremely dangerous to aquatic organisms due to their high toxicity, high remains, poor degradability, high solubility in water with the carcinogenicity, teratogenicity. Lignin sulfonate, which derives from natural plants, is the by-product of the pulp process. There is a lot of lignin sulfonate in the effluent from paper mill. It possesses a relatively complex composition and a wide range of molecular weights, bonding with hydroxyl group at 4-position and methoxyl group at 3-position and being soluble in water, not suitable for adsorption materials. However, the reactive groups of lignin sulfonate are prone to condensation reaction, the condensation product in the presence of solid form has good adsorption to malachite green in aqueous solution. Based on the above characteristic of lignin sulfonate, the paper study the synthesis of modified lignin sulfonate polymer and its adsorption to malachite green in aqueous solutions.The first study of the paper describes the synthesis of lignin sulfonate polymer based on simply emulsion polymerization from lignin sulfonate derived from the facile by-products of paper pulp and the adsorption property of the lignin sulfonate polymer to dyes. Fourier transform infrared spectroscopy(FT-IR) was employed to characterize the successful synthesis of the lignin sulfonate polymer. The lignin sulfonate polymer presented selective adsorption to cationic dye in aqueous solution, with percentage adsorption(to malachite green) exceeding 95% in pH 7.0. The effects of pH, sorbent dosage, initial malachite green concentration and temperature on the adsorption have been discussed. 4 kinetic models and 3 isotherm models were employed to evaluate the experimental data. The results indicated that the adsorption kinetics data fitted the pseudo second-order kinetic model and Langmuir adsorption isotherm was applicable for the adsorption of malachite green onto the lignin silfonate polymer. Furthermore, the thermodynamic analysis(the values of ?G0 are negative and between-20 and 0 kJ mol-1, the values of ?H0 and ?S0 are positive) demonstrated that the process of adsorption of malachite green onto the lignin sulfonate polymer was endothermic, spontaneous and randomness. The results suggested that the lignin sulfonate polymer is a kind of low-cost, alternative sorbent and has the potential to adsorb refractory chemical oxygen demand(COD) in effluent.The second study of the paper shows Random copolymer of acrylic acid and acrylamide were grafted onto the lignin sulfonate molecule through radical reaction and lignin sulfonate-based grafted copolymer was prepared successfully by crosslinking of lignin sulfonate grafted random copolymer of acrylic acid and acrylamide in this work. Batch adsorption experiment of lignin sulfonate-based grafted copolymer to malachite green was performed on factors of pH, adsorbent dosage, initial dye concentration and temperature. The results indicated that the adsorption equilibrium can be achieved in 300 min with percentage adsorption exceeding 96 % and adsorption capacity 96 mg g-1 in pH 6.0-7.0, initial dye concentration 20 mg L-1, dosage 1g L-1. The adsorption kinetics and isotherm were analyzed by fitting experimental data with pseudo-second-order kinetic model, Weber-Morris model and Langmuir equation. Furthermore, the thermodynamic analysis demonstrated that the process of adsorption of malachite green onto the lignin sulfonate-based grafted copolymer was endothermic, spontaneous, randomness and physisorption is dominated. The results suggested that the lignin sulfonate, which is the by-production of pulp process, can be waste recycling, and the lignin sulfonate-based grafted copolymer is a low-cost adsorbent and has the potential to adsorb the resistant to be degraded organic dye in effluent.