Modification Of Natural Zeolite And Its Removal Properties Of Ammonia Nitrogen In Water

The continuous accumulation of ammonia nitrogen content in the water environment is not only having a negative impact on the ecological environment,but also harms human health.The adsorption method is considered to be an economical and effective ammonia nitrogen removal technology.Zeolite,because of its rich porosity and special crystal structure,it has shown many excellent performances as an adsorbent,and the global market is reported to reach 1.8 million tons per year.However,in the process of natural zeolite mining,a large number of waste material——natural zeolite powder is produced,this fine powder cannot be used as the market product,has dust harm and also has an adverse impact on the processing efficiency,disposal cost,environment and other aspects.In addition,the adsorption capacity of natural zeolite is limited due to contaminating by impurities such as quartz or metal,therefore,this study proposes the synthesis of zeolite with higher cation exchange capacity-zeolite W using cheap natural zeolite powder as precursor.The conditions of shaping zeolite W powder are preliminarily explored.The removal efficiency of ammonia nitrogen in water is further studied by using zeolite W powder and beads to verify the feasibility of its application.The results are as follows:（1）Since the natural zeolite structure is stable,the efficiency of synthesis of zeolite W by direct method is relatively low.When the reaction temperature is T=150℃,K₂O/SiO₂=1.5,H₂O/SiO₂=20,SiO₂/Al₂O₃=5.88 and the reaction time is 8 h,the highest yield in this study is36.79%.When zeolite W is synthesized by two-step method,the activation efficiency of alkali fusion to natural zeolite is higher than that of heat treatment.Under the synthesis route of alkali fusion-hydrothermal reaction,the optimum synthesis conditions of zeolite W are as follows:SiO₂/Al₂O₃=5.88,K₂O/SiO₂=0.4,H₂O/SiO₂=35,reaction temperature T=150℃,reaction time t=16h,stirring,and the yield of zeolite W is 75.04%.The synthesized zeolite W are characterized by X ray diffraction（XRD）,scanning electron microscopy（SEM）,X ray fluorescence（XRF）and cation exchange capacity（CEC）.The results show that the zeolite W obtained by this method has high purity and typical tetragonal prismatic crystal morphology.The cation exchange capacity of it can up to 323.8 meq NH₄⁺/100g,and alumina and silica are still its main chemical composition（Si/Al=2.66）.（2）Shaping experiment of zeolite W powder shows that water volume and binder content have an important influence on powder shaping.The optimal water consumption of this study is 70%,when well-shaped zeolite bead can be formed and as the binder content increases from 15%to 35%,the mechanical strength of zeolite bead increases and the loss rate decreases significantly from 96%to 19%.（3）The optimum conditions for adsorption of ammonia nitrogen by zeolite W powder and zeolite W beads in 50 mL 120mg/L NH₄Cl solution are dosage of 16 g/L,the initial pH=6-7,and the reaction time t=360 mins.The adsorption kinetics and adsorption isotherm models show that zeolite W powder and zeolite W beads have similar adsorption process of ammonia nitrogen.The quasi-second-order model could better fit the adsorption data.The adsorption process of ammonia nitrogen on zeolite W is mainly chemisorption,and the adsorption process is in accordance with the intra-particle diffusion process.At room temperature,the adsorption data of the two materials are more in line with the Langmuir Vageler model.The maximum adsorption capacities of zeolite W powder and zeolite W beads are 34.374 mg/g and 25.430 mg/g respectively.（4）The adsorption capacity of zeolite W powder（34.374 mg/g）to ammonia nitrogen is greatly improved compared with that of natural zeolite powder（8.178 mg/g）,which indicates that zeolite W has better adsorption potential.After shaping,the number of active adsorption sites on the zeolite particles may decrease due to the decrease of the specific surface,which results in a certain loss of adsorption capacity（25.430 mg/g）,but zeolite W beads still have good adsorption capacity.