| Ammonia nitrogen is one of the most common water pollutants with a wide range of sources.It can lead to eutrophication and the deterioration of water environments and has serious impact on the ecological environment and human health.Therefore,the pollution control of ammonia nitrogen wastewater is crucial.Bentonite,a nonmetallic mineral material,is a rich resource with a low cost.It is commonly used as an environment-friendly adsorbent due to its good water absorption,expansibility,and adsorbability.In this study,sodium bentonite and porous agent Na HCO3were used as the primary raw materials to prepare granular bentonite via extrusion granulation.The structure,composition,and morphology of sodium bentonite powder and the formed granular bentonite were tested and analyzed via X-ray diffraction analysis,X-ray fluorescence analysis,and scanning electron microscopy.Second,an orthogonal experiment was conducted to explore the influence of granule formation conditions on the adsorption performance for ammonia nitrogen wastewater.Moreover,the effects of addition amount,granular bentonite adsorption time,p H,and concentration on the adsorption performance for ammonia nitrogen wastewater were studied.The optimum conditions for ammonia nitrogen wastewater treatment were determined.In addition,the kinetics,isotherm,and thermodynamics of ammonia nitrogen adsorption by granular bentonite were analyzed.Lastly,the practical application of granular bentonite as cat litter was examined.From the aforementioned investigations,this study draws the following major conclusions.?1?Sodium bentonite exhibits good adsorption property,and bentonite powder is formed into particles via extrusion and granulation,avoiding the disadvantage of powder of being easy to bond and separate while being used.The operation method is simple,and the formation of granules is easy to control.?2?Characterization test and analysis showed that the major components of the formed particles and the original soil powder were Al2O3and Si O2.The formed granular bentonite evidently differs from powder,which is lamellar and has clear holes inside.The pore structure of granular bentonite was effectively improved by the addition of the pore-forming agent Na HCO3.?3?The factors that influence the adsorption of ammonia nitrogen by the extruded pellets are shot speed,water amount,extrusion speed,and shot time.For reference,500 g of bentonite powder was used.The preparation of granular bentonite was good when water content was 150 m L,extrusion speed was 9 r/min,shotblasting time was 3 min,and shotblasting speed was 25 r/min.Under these granulation conditions,the prepared granular bentonite exhibited good adsorption performance when the mass ratio of the pore-forming agent?Na HCO3?and bentonite powder was1:25,the addition amount of granular bentonite was 60 g/L,adsorption time was 6 h,and solution p H was 8–9.?4?At room temperature,the adsorption of ammonia nitrogen wastewater by granular bentonite is consistent with the quasi-second-order kinetic adsorption model.At 298 K,313 K,and 328 K,the adsorption of ammonia nitrogen by granular bentonite fits close to the Freundlich equation,and all the correlation coefficients exceed 0.99.The thermodynamic study found that Gibbs free energy?G<0,standard enthalpy change?H>0,and standard entropy change?S>0.Results showed that the adsorption of ammonia nitrogen by granular bentonite is a spontaneous process dominated by physical adsorption.The results of thermodynamics and kinetics of adsorption of ammonia nitrogen by bentonite particles show that the adsorption of ammonia nitrogen by bentonite particles has both chemical adsorption and physical adsorption.?5?Bentonite raw materials are nontoxic,tasteless,and noncorrosive.The formed particles are dust-free.Cat litter can solve the problem of fecal and urine contamination caused by household pets;thus,it is good for indoor cleaning and the healthy growth of pets.Granular bentonite exhibit good water absorption,rapid agglomeration,and high strength.It can wrap and absorb pet waste and odor.This study provides a theoretical basis for the preparation of granular bentonite and the treatment of ammonia nitrogen wastewater.Moreover,results have a certain reference value for the application research of granular bentonite as cat litter. |
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