Adsorption Of Modified Walnut Shells On Simulated NH₃-N And Cd（Ⅱ）-containing Wastewater

This paper first discusses the sources and hazards of ammonia-containing wastewater and cadmium-containing wastewater,as well as the commonly used treatment methods.For the treatment of these two types of wastewater,the waste walnut shell is used as a raw material,and it is crushed to a specific particle size and washed.After drying,an ordinary walnut shell adsorbent is obtained;a common walnut shell is impregnated with a certain mass fraction of KMnO4 solution to obtain a potassium permanganate modified adsorbent;and a common walnut shell is impregnated with a certain mass fraction of an ethanol solution to obtain an ethanol modified adsorbent.The three adsorbents were studied for the treatment of low-concentration ammonia nitrogen and low-concentration cadmium-containing wastewater.Static adsorption experiments were conducted and the effect of initial pH,adsorption time,adsorbent dosage,adsorbent particle size,and initial concentration of water sample on the adsorption effect was investigated through experiments.The repeated utilization was studied by repeated adsorption experiments..The surface structures of the three adsorbents were characterized by scanning electron microscopy（SEM）,specific surface area（BET）,and infrared spectroscopy（FTIR）in modern analytical techniques.At the same time,adsorption thermodynamics and adsorption kinetics were used for the three adsorptions.The adsorption mechanism of the agent was preliminary discussed.Adsorption experiments show:（1）Under the limited experimental conditions,the ammonia nitrogen wastewater adsorption experiments were conducted using ordinary walnut shells,FeCl₃ modified walnut shells,ZnCl₂ modified walnut shells,and NaOH modified walnut shells.The experimental conditions were pH 7.0 and initial concentration of ammonia nitrogen.Take 10mg/L,the oscillation intensity is 220r/min,reaction time is 120min.Adsorption treatment results are not obvious.（2）In order to further expand the application range of the above-mentioned adsorbents,three types of adsorbents were used to adsorb 100 mL of cadmium-containing simulated wastewater with an initial concentration of 10 mg/L.The dosage of common walnut shell was20 g/L,the initial pH of the water sample was 7.0,and the oscillating intensity was 171 r/min.The adsorption reaction was performed at room temperature.The adsorption equilibrium time was 150 min,and the removal rate of Cd（II）was obtained.Achieves 79.81%%,the maximum adsorption capacity is 0.399 mg/g;（3）The ethanol modified walnut shell dosage was 20 g/L,the initial pH of the water sample was also 7.0,the reaction temperature was room temperature,and the shaking strength was 171 r/min.After 150 min,the adsorption equilibrium was observed for Cd（II）.The removal rate can reach 93.90%,and its maximum adsorption is 0.723 mg/g.This shows that the modified walnut shell adsorbent has greatly improved the removal rate of Cd（II）.The fitting results show that the adsorption behavior of Cd（II）on ordinary walnut shell and ethanol modified walnut shell can be better described by the Freundlich adsorption isotherm equation,and Langmuir adsorption isotherm equation can properly describe the modification of Cd（II）in KMnO₄.Adsorption behaviors on walnut shells were fitted with maximum adsorption capacities of 0.399 mg/g,1.644 mg/g,and 0.723 mg/g,respectively,which were close to experimental values.The pseudo-second-order kinetic equation agrees well with the adsorption behavior of ordinary walnut shells and ethanol modified walnut shells,while the adsorption behavior on KMnO₄ modified walnut shells fits better with the intragranular diffusion equation.The correlation coefficients are 0.9037,0.9607 and 0.9721have good fitting effect,which indicates that the adsorption process of adsorbent on Cd（II）is based on chemical adsorption as the main control step.The characterization results showed that the pore size distribution of the three walnut shell adsorbents were wide and the pore structure was well developed.However,after KMnO4 modification and ethanol modification,the specific surface area has been greatly improved.In the infrared spectrum analysis,the typical functional groups that the common walnut shell,the KMnO₄ modified walnut shell and the ethanol modified walnut shell can exhibit are C=O,CH,OH,CO,NH,and COC.These functional groups participate in the adsorption reaction process.get on.Analytical experiments show that the modified walnut shells can be analyzed and regenerated by using suitable analyzers.The reusability of the modified walnut shells is better.It is verified that both modified walnut shells can be used as ideal new adsorption materials.In order to make full use of the two types of modified walnut shells,the number of analytical rejuvenation should be controlled within their respective specified number of times.In this paper,when the adsorption mechanism of three kinds of walnut shell adsorbents on Cd（II）was explored,the characterization of the materials was combined with the adsorption isotherm model and the adsorption kinetics model to jointly analyze,and it was presumed that the adsorption process of Cd（II）was not a single one.The adsorption mechanism,but the result of a variety of adsorption mechanisms,is a complex process controlled by both physical adsorption and chemical adsorption,and is dominated by chemical adsorption.