Activated Carbon Modification Method And Its Technical Study On Adsorption Performance Of Ammonia Nitrogen In Water

This study aimed to explore ways to improve the removal performance of ammonia nitrogen in water by activated carbon adsorption method and to explore the mechanism.The content of lactone,carboxyl and phenolic hydroxyl groups on the surface functional groups of the unmodified activated carbon was determined by Beohm titration to be 0.904 mmol/g,1.179 mmol/g and 0.466 mmol/g,respectively.The time for the adsorption of ammonia nitrogen in water to reach equilibrium was 10 min,and the equilibrium adsorption amount was 0.97 mg/g.The adsorption kinetics is consistent with the quasi-secondary kinetic model and there is chemisorption.The adsorption amount of ammonia nitrogen in water by unmodified activated carbon under alkaline condition is greater than acidic condition.The adsorption of NH₃molecules in ammonia nitrogen solution by unmodified activated carbon is obvious double-layer adsorption.The saturated adsorption amount of the first layer of the NH₃molecule on the unmodified activated carbon is about 2 mg/g.The modification of activated carbon by nitric acid oxidation method increases the total amount of surface acidic functional groups with the increase of modification temperature,and increases first and then decreases with the modification time.The modification conditions for maximizing the total amount of acidic functional groups on the surface of the activated carbon were:1 mol/L of nitric acid,65°C,and a time of 6h?this activated carbon is represented by AC?N1-65?-6h??.The adsorbed amount of activated carbon increases as the total amount of acidic functional groups on the surface increases.The time for AC?N1-65?-6h?to reach equilibrium in the adsorption of ammonia nitrogen in water was 30 min.The equilibrium adsorption amount is increased to 4.73mg/g compared with unmodified activated carbon.AC?N1-65?-6h?adsorption of ammonia nitrogen in water has both physical adsorption and chemical adsorption.In a certain concentration range,when the temperature is below 35°C,the main adsorption mode is physical adsorption;the main adsorption mode is chemical adsorption at a higher temperature of 35?and above.The adsorption isotherms at 15?,25?,35?,and 65?have peaks.The higher the temperature,the lower the equilibrium concentration of ammonia nitrogen corresponding to the peak of the adsorption amount.The adsorption amount of ammonia nitrogen in water by AC?N1-65?-6h?under alkaline condition is greater than that under acidic condition.However,When the pH is 10,the adsorption amount of AC?N1-65?-6h?is larger than that at pH 12.The reason may be that the amount of sodium ions introduced during pH adjustment is different,and the degree of competitive adsorption is different.NH₃ molecule is the dominant component of AC?N1-65?-6h?adsorption of ammonia nitrogen in water,and it is the main factor for the adsorption of AC?N1-65?-6h?compared with unmodified activated carbon.The first layer of saturated adsorption of NH₃ molecules on AC?N1-65?-6h?is about 7 mg/g,which is 5 mg/g higher than that of unmodified activated carbon.