Preparation Of Composite Adsorbents Based On Sodium Alginate And Their Adsorption Properties On Methylene Blue

With the rapid development of economy,the environmental problems have become the constraints of sustainable development.The treatment of dye wastewater has become the top priority in the field of wastewater treatment,while the traditional treatment technology of dye wastewater has many problems.In recent years,adsorption began to emerge in the field of dye wastewater treatment and become the research focus of water treatment technology due to its significant advantages.The research focus of adsorption is the development and utilization of new adsorbents.Sodium alginate（SA）is a kind of natural polysaccharide.There are many active groups in SA molecular structure chain,which can interact with dye molecules,thus SA has a good prospect in the treatment of dye wastewater.However,SA has some drawbacks such as high cost and low utilization ratio,which limits its practical application.In order to solve the above problems,this paper introduces other materials to prepare SA-based composites to improve the utilization ratio of SA.In this paper,SA was used as matrix material and Ca²⁺as crosslinking agent.Attapulgite（APT）,loofah（LS）and agar（AG）were mixed with SA respectively.Three kinds of SA based composite adsorbents were prepared by blending and crosslinking method:SA-APT composites,LS@SA,and AG-SA-APT aerogels.The influence of pH,initial concentration,contact time and the amount of adsorbent on the adsorption capacity of three kinds of adsorbents were studied.The experimental data were fitted by pseudo-first order kinetic and pseudo-second order models,Langmuir and freudlich adsorption isotherm models.The adsorption mechanism of methylene blue on the adsorbent was investigated.The main results are as follows:（1）For SA-APT composite spheres,it is found that the combination between APT and SA matrix is good,and APT rod crystal can be evenly dispersed in SA matrix.The introduction of APT can increase the surface coarseness of SA matrix,increase its contact with dye molecules,improve the utilization of SA and reduce the cost of composite adsorbent.By studying the adsorption behavior of methylene blue on the adsorbents,the optimal pH of methylene blue solution is between 6 and 10,and the maximum adsorption capacity appears at pH 8.The data of methylene blue adsorption conforms to Langmuir adsorption isotherm model.The pseudo-second order kinetic model is more suitable in the kinetic study,so the adsorption of methylene blue by this kind of adsorbent belongs to single molecular layer chemisorption.（2）As for the LS@SA composite adsorbent,SA is attached to the LS three-dimensional network structure by the way of immersed-crosslinking,and a series of composite adsorbents with different SA loading rate are prepared.The composite adsorbent has a connection structure.The adsorption speed is faster and the utilization rate of SA adsorbent is improved to a large extent.The results of adsorption experiments show that the adsorbent with the highest loading rate has the best adsorption effect toward methylene blue,and the maximum adsorption capacity is 199.66 mg/g.The LS@SA composite adsorbent showed better adsorption at pH 4-10.The adsorption rate changed rapidly in the first 50 min,then the adsorption capacity increased slowly,and the adsorption equilibrium time was 100 min.The adsorption equilibrium data of methylene blue on the adsorbent accorded with the Langmuir isotherm model,indicating that the adsorption of methylene blue on the adsorbent is uniform monolayer adsorption.The pseudo-second order kinetic model can well describe the adsorption process,which shows that the chemical adsorption is the main rate control step.（3）The composite hydrogels were prepared by blending method with SA,AG and APT as raw materials.The prepared hydrogels were crosslinked and freeze-dried to prepare composite aerogels.Through the study of methylene blue adsorption,it was found that the acid condition was not ideal,and the optimal pH value was 8.The adsorption rate of methylene blue by aerogels is faster.The introduction of APT endowed SA-AG aerogel with better adsorption efficiency in the adsorption of low concentration methylene blue wastewater.The pseudo-second order kinetic model can well describe the adsorption process,indicating that the adsorption process is mainly chemical adsorption.Aerogels have high specific surface area and rough surface,which are highly efficient dye adsorbent.