Study On The Adsorption Of Heavy Metals In Water By The Modified Sodium Alginate Composite Hydrogels

With the continuous development of social economy,various industries in our country have sprung up across the country.From the perspective of politics,economy,and rural construction,the overall situation is satisfactory.However,it will bring regional and rapid impacts and pressures on the environment,ecology and health,and also put forward new requirements for environmental protection.Especially,heavy metal pollution in water has become an environmental problem that needs to be solved urgently.In recent years,scholars have put forward many different ideas on how to control water pollution quickly,efficiently and safely.Compared with the traditional heavy metal treatment technology,the adsorption method has shown the characteristics of energy saving,high efficiency,low cost and easy operation.Hence,the adsorption method is recognized as one of the most effective and economical methods to treat the heavy metal in water.In addition,the new adsorption materials such as natural minerals,chitosan,lignin and sodium alginate have gradually attracted the attention of scholars.These adsorption materials are widespread in nature and have the advantages of safety,environmental protection,easy recovery of activity and high adsorption performance.Hence,the use of natural hydrogels as adsorbent can achieve maximum utilization value of waste while controlling pollution.Using the natural hydrogels to adsorb heavy metals in water is currently one of the most ideal methods for wastewater treatment.In this paper,the sodium alginate（SA）was first modified to prepare the thiolated sodium alginate（TSA）by graft copolymerization.Then,graphene（GO）and thiolated graphene（TGO）were added respectively to TSA with Ca Cl₂ cross-linking agent to prepare two TSA-based composite gel bead adsorbents:TSA-GO and TSA-TGO.The effect of gel bead adsorbents on the removal of Pb²⁺and Cu²⁺in simulated wastewater was studied by single factor experiment.The influence of solution p H,initial concentration of metal ions and adsorption time on the adsorption of heavy metal ions was discussed.The Langmuir and Freudlich adsorption isotherm models and adsorption kinetic models were used to study and analyze the adsorption performance of the gel beads for Pb²⁺and Cu²⁺.Furthermore,the adsorption regeneration and the structure of the gel beads were studied.The adsorption mechanism of the gel beads on heavy metal ions was explored.The results show that:（1）The optimal adsorption conditions for Cu²⁺removal by TSA-GO gel beads are:p H of the solution is 4.0 and the initial concentration of metal ions is 200 mg/L;the optimal adsorption conditions for Pb²⁺removal are:p H of the solution is 5.5 and the initial concentration of metal ions is 500 mg/L.The adsorption of heavy metals by TSA-GO is a relatively fast process,and the adsorption equilibrium can be reached in about 40-50 min.In terms of isotherm,the adsorption data of Pb²⁺and Cu²⁺are more in line with the Langmuir model,indicating that the adsorption of heavy metals on the gel beads is monolayer.In terms of kinetics,the adsorption data are more in line with the quasi-second-order kinetic model,indicating that the adsorption is dominated by chemical adsorption.The adsorption and regeneration tests shows that the TSA-GO gel beads still retain high adsorption capacity for Pb²⁺and Cu²⁺after 5 times of adsorption analysis.（2）The introduction of modified thiolated graphene gives TSA-TGO better adsorption performance than TSA-GO gel beads.The maximum adsorption capacity of TSA-TGO gel beads for Cu²⁺and Pb²⁺were higher than the maximum adsorption capacity of TSA-GO for Cu²⁺and Pb²⁺.furthermore,the adsorption of Cu²⁺and Pb²⁺by TSA-TGO gel beads could reach equilibrium about within 40 and 30 min,indicating that the adsorption speed of TSA-TGO for heavy metal ion wasfaster than TSA-GO.In addition,the adsorption isotherms of Pb²⁺and Cu²⁺by TSA-TGO gel beads conform to the Langmuir model,and the adsorption process follows the quasi-second-order kinetic model.After 5 times of adsorption and desorption,the adsorption capacity of TSA-TGO gel beads for Pb²⁺and Cu²⁺only are reduced by less than 8%,indicating that TSA-TGO gel beads possess excellent regeneration performance.