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磷酸铵镁的热分解行为及热分解产物的氨氮吸附性能

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Available online at www.sciencedirect.com 一 Transacfions of 舔 ELSl三VIER Press ScienceDirect Nonferrous Metals Society of China www.tnmsc.crl Trans.Nonferrous Met.Soc.China 25(2015)497—503 Thermal decomposition of magnesium ammonium phosphate and adsorption properties o士1ts pyrolysis products toward ammonia nitrogen 一 一 一 一一—— Yi.qing CHEN ,Jian-jun TANG ,Wen.1ong LI ,Zhen—hui ZHONG ,Juan YIN 1.Shenzhen Key Laboratory of Industrial Water Conservation&Municipal Wastewater Resources Technology, Shenzhen Polytechnic,Shenzhen 518055,China; 2.School of Civil Engineering,Guangzhou University,Guangzhou 5 1 0006,China Received 9 June 2014;accepted 29 July 2014 Abstract:High-purity magnesium ammonium phosphate(MAP)was precipitated by controlling pH value of the reaction system of 9.0-9.5.The thermal decomposition behavior of MAP and the adsorption properties of its pyrolysis products toward ammonia—nitrogen were also studied bv XRD,SEM,TGA.DTA and FT.IR methods.The results indicated that high—purity MAP was obtained at pH value of 9.0—9.5.Upon heating to 100—120。C for 120 min,MAP was thermally decomposed,losing water and ammonia concomitantly with a reduction in grain size and crystallinity.The capaciy of tpyrolysis products for ammonia nitrogen adsorption reached 72.5 mg/g,with a removal rate Of up to 95%from an 800 mg/L solution.The characteristic difraction peaks corresponding to MAP mainly appeared in their XRD pattems after adsorption of ammonia nitrogen.The pyrolysis products of MAP at 100-120。C could be recycling—used as the chemical treatment regents ofammonia nitrogen in the practical application. Key words:magnesium ammonium phosphate;magnesium hydrogen phosphate;thermaI decomposition;ammonia nirogen;t adsorption properties sedimentation of magnesium ammonium phosphate 1 IntrOductiOn Ammonia nitrogen is a common pollutant that causes eutrophication and environmental damage.In (MAP,MgNH4PO4‘6H20)is the expense of the precipitants(soluble phosphate and magnesium salts), which raises the processing cost.For example,the cost of applying the MAP method to the remediation of 1andfill nearly all Of China’s contaminated water,ammonia leachate was up to 22.9¥/r 『91. To solve the cost problems associated with the practical application of L chemical sedimentation nitrogen is one of the major pollutants at present.The effective and economical treatment of ammonia nitrogen in wastewater is an important objective of environmental research. Frequently used methods for treating methods,AHMAD and IDRIS『1 01 studied the acid regeneration ofMAP: MgNH4PO4・6H2O+H -- ̄MgHPO4・3H2O+NH4++3H20 ammoniated wastewater include air stripping[1], adsorption and ion exchange [2], biological treatment f31,and chemical sedimentation[4—6].The laRer method is typically simple,using various treatment reagents to produce sediments which are used as fertilizers.Some of these processes have already found (2) HE et al[1 1]developed a MAP regeneration method under alkaline conditions: MgNH4PO4’6H20+NaOH--- ̄MgNaPO4(s)+NH3+7H20 (3) MgNaPO4+NH4++6H20-- ̄MgNH4PO4’6H20(s)+Na+ application『7,81.Chemical sedimentation for the removal of ammonia nirogen from wastewater is based ton the following reaction: (4) which allowed recycling of the MAP and solved the problem of the precipitating agent cost.However,the acid regeneration method recovered ammonia nirogen itn HPO42-+Mg +NH4++6H2O-- ̄MgNH4PO4・6H2O+H (1) The major limitation for employing the chemical Foundation item:Project(ZDSY20120619093952884)supported by Shenzhen Strategic New Industry Development,China Corresponding author:Jian-jun TANG;Tel:+86—755-26731648;E—mail:tangjj7384@sina.corn DOI:10.1016/S1003—6326(15)6363O一5 498 Yi-qing CHEN,et al/Trans.Nonferrous Met.Soc.China 25(201 5)497—503 the form of an ammonium salt from the wastewater,and the recovered solution inevitably contains a small amount of Mg and HP0d which complicate its discharge. MAP regeneration under alkaline conditions consumes equimolar amount of NaOH,which is economically unsatisfactory,although ammonia nitrogen is recycled in the form of aqueous ammonia from the wastewater. The use of an ammonia neutralizer generally produces highly concentrated ammonia nitrogen wastewater in the chemical industry, metallurgy, electroplating and other industries.If the ammonia nirtogen pollutant is recovered in the form of aqueous ammonia,it can be directly reused,finally forming ammonia to close the circuit.This process should be regarded as the best solution for ammonia nitrogen wastewater仃eatment. The study of BHUIYAN et al『1 21 showed that MAP can be thermally decomposed into a mixture of MgHPO4.Mg3(PO4)2 and Mg2P207.SUGIY久MA et al f131 indicated that the thermal decomposition product of struvite had adsorption capabilities;the adsorption properties of MgHPO4 for NH4 were better than those of Mg3(PO4)2,whereas Mg2P207 hardly adsorbed NH4+. MAP could be employed as an advanced material for the removal/recovery of ammonium.ZHAO et al『141 investigated the formation of MAP from MHP and NHd by an exchange reaction under suitable PH conditions. Highly concentrated ammonia solutions could be recovered and the MHP adsorbent could be easily regenerated by heat decomposition of the M This process is an effective method that recycles not only the ammonia but also the MHE Theoretically,the steam released from the pyrolysis of MAP can generate 13.6% aqueous ammonia(mass fraction),which can fully meet the requirements of industrial processes.It is suggested that the thermal decomposition Of MAP under certain conditions can produce highly concentrated aqueous ammonia,but also pyrolysis products that may be used to treat ammonia nitrogen wastewater.This would allow recycling and reduce the costs of the ammonia nitrogen wastewater treatment agent. The therma1 decomposition of MAP can be conducted stepwise,and the temperature determines the composition of the pyrolysis products,thereby affecting their NH4 adsorption properties.In this work.the thermal decomposition process of MAP and the adsorption properties of its pyrolysis products toward ammonia nitrogen were investigated. 2 Experimental 2.1 Preparation of MAP Ammonia—containing simulated wastewater(2000 mg/L,200 mL)was prepared in a 250 mL conical flask. Sufncient Na2HP04・12HEO and MgC12’6H20 were added sequentially to achieve a N/P/Mg molar ratio of 1:1:1. The solution was stirred with a temperature.controlled magnetic stirrer,and the pH value was adjusted with 5 mol/L NaOH.The resulting precipitates were filtered after 20 min.The fi1trate was analyzed for the remaining ammonia nirtogen and total phosphorus content,and the Ⅳ【AP sediments after washing were dried in a thermostattedblast ovenat40。Cfor48 h. 2.2 Thermal decomposition of MAP The prepared MAP was placed in a tubular resistnace fumace and pyrolyzed at 1 00。C(unless otherwise stated)for 1 20 min.The pyrolysis products werefinelygroundandthen sealedforlateruse. 2.3 Adsorption of ammonia nitogen Ammonia.containing simulated wastewater(8oo mg/L,200 mL)was prepared with NH4C1(AR).The MAP pyrolysis product(4 was added,and hte mixture was magnetically stirred at room temperature for 40 min after adjusting the pH value to~10 wim 5 mol/L NaOH. Atier the reaction was completed,the mixture was separated using a Hitachi CR22G high-speed refrigerated centrifuge.The supematant was used to analyze the ammonia nitrogen concentration, and the solid precir)itate was treated as described in Section 2.1. 2.4 TestinR and characterization The ammonia nitrogen concentration was analyzed by Nessler’s reagent spectrophotometry.Phosphate concentration was determined by ammonium molybdate spectrophotometry. Atomic absorption spectro— photometry was used to analyze Mg concen仃ation (Shimadzu AA一6300F).Thermogravimetric.diferential thermal analysis rTGA.DTA1 studies were conducted by a TGA.DTA 6200 analyzer for a sample with mass of 27.5 mg,at a heating rate of 10。C/min,and a 1 00 mL/min of air flow.Infrared spectroscopy was analyzed by a Shimadzu FTIR一8400S Fourier transfcIrE infrared spectrophotometer,and KBr tablet method was used for measuring absorption spectrum.Powder morphology analysis was conducted by scanning electron microscopy(SEM.JE0L JSM一6700F).A Panalytica1 Pert Pro X.ray diffractometer was used to obtain X.ray diffraction(XRD)patterns at room temperature,using a Cu k source at 40 kV and 40 mA. Particle sizes were determined with a Microtrac¥3500 laser particle size analyzer(Microtrac USA1. 3 Resuits and discussion 3.1 Preparation and characterization of MAP The recovery of MAP by the chemical Yi—qing CHEN,et al/Trans.Nonferrous Met.Soc.China 25(2015)497—503 503 磷酸铵镁的热分解行为及 热分解产物的氨氮吸附性能 陈益清 ,唐建军 ,李文龙 ,钟振辉 ,尹娟 1.深圳职业技术学院深圳市工业节水与城市污水资源化技术重点实验室,深圳518055 2.广州大学土木工程学院,广州510006 摘要:通过控制反应体系的pH值为9.0~9.5,制得高纯度的磷酸铵镁(MAP);利用XRD、SEM、TGA.DTA及 FT-IR等技术,研究MAP的热分解行为及热解产物对氨氮的吸附性能。结果表明,在pH值为9.0~9.5的条件下 可制得高纯度的MAP。将MAP在100~120。C下热解120 min,可将氨及水脱除,热解固体产物粒径变小,结晶 度降低,对氨氮的吸附量达72.5 mg/g,对起始浓度为800 mg/L溶液的氨氮去除率达95%以上。吸附氨氮后,其 XRD谱中主要出现MAP的特征衍射峰。循环使用结果表明,将MAP在100~120。C条件下发生热解,热解固体 产物可循环用于氨氮的处理药剂。 关键词:磷酸铵镁;磷酸氢镁;热分解;氨氮;吸附性能 (Edited by Wei-ping CHEN) 

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