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    15 April 2005, Volume 26 Issue 4 Previous Issue    Next Issue

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    OriginalPaper
    Design of D-stable robust state observer for Delta operator systems
    Liu, Man (1); Jing, Yuan-Wei (1); Zhang, Si-Ying (1)
    2005, 26 (4):  205-208.  DOI: -
    Abstract ( 180 )   HTML   PDF (163KB) ( 477 )  
    The design of a state observer based on the pole assignment in a circular region is studied for uncertain Delta operator systems, which is defined as a D-stable robust state observer. Utilizing the algebraic Riccati equations of discrete Delta operators, a necessary and sufficient condition is given to the existence of the D-stable robust state observer for a class of Delta operator systems with uncertain parameters and its design method. It will be beneficial to theoretical derivation and, further, to the calculation to transform the outcome as above into linear matrix inequalities. The D-stable robust state observer thus designed has a good robustness and is able to unify the unsolved problems related to continuous and discrete time systems together within a Delta operator framework.
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    Design of delay-dependent observer for a class of neutral delay systems
    Sun, Xi-Ming (1); Chen, Bing (2); Sun, Wen-An (3); Zhao, Jun (1)
    2005, 26 (4):  209-212.  DOI: -
    Abstract ( 223 )   HTML   PDF (246KB) ( 671 )  
    The design of delay-dependent state observer for a class of linear neutral delay systems is concerned with. Based on the model transformation technique, a criterion of delay-dependent stability is therefore presented in form of linear matrix inequality (LMI), where the system stability depends on the size of time delay. Then, a conceptual design is given to the delay-dependent observer. Compared with the delay-independent results, the state of stability and conceptual design proposed here are both less conservative in case of not long time delays.
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    Guaranteed cost robust control for a class of uncertain switched linear systems
    Wang, Rui (1); Sun, Wen-An (2); Qi, Li (1); Zhao, Jun (1)
    2005, 26 (4):  213-215.  DOI: -
    Abstract ( 189 )   HTML   PDF (283KB) ( 690 )  
    The problem of guaranteed cost robust control is studied for a class of uncertain switched linear systems. Based on multiple-Lyapunov function method, a conceptual design is given to the hybrid state feedback controllers to guarantee cost such that the corresponding closed-loop system is globally asymptotically stable for all admissible uncertainties, to which a sufficient condition is given in terms of linear matrix inequalities (LMI). A simulation example is provided to illustrate the effectiveness of the approach proposed.
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    Matching problem of electronic brokerage in second-hand vehicle trade
    Zhang, Zhen-Hua (1); Wang, Ding-Wei (1)
    2005, 26 (4):  216-218.  DOI: -
    Abstract ( 206 )   HTML   PDF (710KB) ( 444 )  
    A bipartite matching problem of electronic brokerage is discussed in case each and every one of several buyers/sellers wants to buy/sell a second-hand vehicle. A multi-objective apportion model is therefore developed, of which the two objectives are to maximize the gross volume of trade and total trade surplus, supposing that the clearing price is just the mid-value of bid price and offering price. This multi-objective model is solved through weighted method. A simulation is made to compare broker's commission and change in trade surplus from two aspects: taking account of both the objectives simultaneously and one of them only, i.e., to maximize the gross volume of trade. A conclusion is reached through computation that taking account of the former is more gainful, i. e., the gross volume of trade will decrease by about 12%, while the total trade surplus will increase by about 88%. Moreover the brokerage rate will increase to 2.27% from 2% if broker's commission remains unchanged.
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    Modified genetic algorithm based on real-coding
    Dong, Ying (1); Liu, Huan-Jie (1); Xu, Bao-Dong (1); Tang, Jia-Fu (1)
    2005, 26 (4):  219-221.  DOI: -
    Abstract ( 306 )   HTML   PDF (205KB) ( 1601 )  
    Analyzing the advantages of real-coded genetic algorithm and disadvantages of its genetic mechanism, a modified genetic algorithm (MGA) is developed focusing on its linear crossover operator in real coding. The merits of this genetic operator lies in that after crossover a filial generation is in between the parents and the other one is in the vicinity of a better paternal generation so that they are feasible with an optimal solution available. Calculating some typical instances and comparing the results with other real-coded genetic algorithms, the proposed algorithm shows its superiority in convergence rate and precision for solving optimization problems.
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    Combined hierarchical mobility management protocol in mobile wireless Internet
    Wang, Xing-Wei (1); Sun, Xue-Bo (1); B., Song; M., Huang
    2005, 26 (4):  222-225.  DOI: -
    Abstract ( 175 )   HTML   PDF (176KB) ( 448 )  
    CHMMP (Combined Hierarchical Mobility Management Protocol), as a network layer protocol, is presented for handover registration. It utilizes the registration mechanism in IETF Mobile IP and a hierarchical registration mechanism alternatively according to different MH (Mobile Host) locations, with a new domain management mechanism added to them. Simulations results shows that CHMMP costs leas handover registration overhead and spends shorter average handover registration delay than IETF Mobile IP. It is very suitable for the frequent MH handovers within a domain.
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    Intelligent polling scheme of fault management in the MAN
    Zheng, Hong-Fang (1); Yuan, Zhen-Wei (1); G.-X., Wang; Y.-X., Wang
    2005, 26 (4):  226-229.  DOI: -
    Abstract ( 233 )   HTML   PDF (169KB) ( 573 )  
    In order to enhance the real-time operability and efficiency, which are both required for fault detection, the fault polling scheme based on SNMP is discussed and improved, thus presenting a new intelligent polling algorithm. This algorithm can dynamically adjust the intervals in accordance to the performance parameters of network equipment. Simulation results showed that the intelligent algorithm could display data in detail more accurately than the traditional equal-interval polling scheme such that the distortion in data collection can effectively be minimized with the network bandwidth used rationally. The above advantages have all been verified in practice.
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    New QoS model of IP network
    Xia, Li (1); Guan, Shao-Ying (1); Zhao, Juan (1); Wang, Guang-Xing (1)
    2005, 26 (4):  230-233.  DOI: -
    Abstract ( 260 )   HTML   PDF (122KB) ( 728 )  
    After a discussion on differentiated service (DiffServ), multi-protocol label switching (MPLS) and quality of service routing (QoSR) as well as the integrated approaches among them, a new QoS model of next generation IP network is introduced, which incorporates QoSR in MPLS + DiffServ. The structure of the model and the functions of units in its framework are described individually, and the processes in edge-router and core-router are discussed in detail with the mapping procedure between DiffServ and MPLS stated. Some simulations are carried out for the model, which the results show the traffic engineering capabilities of the model to balance network load and reroute around fault points.
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    Collaborative service model for multi-agent system
    Guan, Mo (1); Zhao, Hai (1); Wang, Jin-Dong (1); Zhang, Wen-Bo (1)
    2005, 26 (4):  234-237.  DOI: -
    Abstract ( 166 )   HTML   PDF (164KB) ( 498 )  
    A notion of grade field is presented and introduced into contract net to eliminate the disadvantages of the contract net model so as to solve the problems due to the collaboration among different service agents, thus minimizing the region to search collaborative service agents. Meanwhile, the time consumption for service agents in collaboration is considered to balance their loads, avoid the blindness of selection of anyone of them and increase the throughput of the multiple service agent system. Based on the fusion of grade field and the time consumption, a new model named grade-field-and-time-based contract net model or GT-CNM is developed, which will suppress occurrence of either overload or underload to a certain extent. Simulation results verified the effectiveness of this model.
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    Tumor image fusion based on wavelet multiresolution decomposition
    Wang, Hong (1); Yang, Chun-Mei (2); Yuan, Zhen-Hua (3); Zhao, Hai-Bin (3)
    2005, 26 (4):  238-241.  DOI: -
    Abstract ( 628 )   HTML   PDF (209KB) ( 6740 )  
    A new image fusion technique is put forward using wavelet transform to decompose the multi-resolution signals from each and every image so as to fuse differently the subimages within different bandwidths at every resolution levels. Template matching is used in high-frequency domain to calculate the statistical average and mean square deviation in image display area, thus determining the proportion of information provided by source images in image fusion process. In low-frequency domain the fusion is carried out using averaging operator so as to keep on the background of image. Then, image fusion can be completed by wavelet transform. The technique proposed has successfully been used in CT image fusion for tumor diagnosis, and experimental results revealed that it is an efficient way to provide fused image more adaptable to human vision.
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    Fast high-precision algorithm for ramification value of nonlinear algebraic mapping problems
    Hou, Xiang-Lin (1); Han, Xu (2)
    2005, 26 (4):  242-244.  DOI: -
    Abstract ( 224 )   HTML   PDF (160KB) ( 608 )  
    The ramification values of nonlinear algebraic mapping dynamic system are studied, and a novel high precision algorithm of dimidiate reducing ramification values is proposed. Thus, the longer computing time spent for the step redistribution in the step-increment algorithm can be shortened, and the relatively low computing accuracy of optimal algorithm for ramification values, which are due to the errors of the objective function itself, can be improved further. A logistic mapping problem is computed typically via the programming and a number of ramifications values are obtained within the accuracy of 10-10. Compared with other existing algorithms, the method proposed is faster in computing speed and higher in precision, and will provide a reference for nonlinear problem and chaos studying.
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    Effect of Mn addition on microstructures and properties of Al-Mg-Si-Cu system alloys for automotive body sheets
    Liu, Hong (1); Zhao, Gang (1); Liu, Chun-Ming (1); Zuo, Liang (1)
    2005, 26 (4):  245-248.  DOI: -
    Abstract ( 266 )   HTML   PDF (233KB) ( 747 )  
    By means of scan electron microscope (SEM), energy dispersive spectrum (EDS), transmission electron microscope (TEM), metallographic analysis, tensile and Ericsson tests, the effect of variation of the addition Mn content on the microstructures, tensile properties and formabilities of Al-Mg-Si-Cu system alloys for automotive body sheets was investigated. The results indicated that the numbers of insoluble constituents and dispersoids particles both increase with the increasing mass fraction of Mn in the alloys. The insoluble constituents of the distribution with continuous line in microstructures are unfavourable to the pressing formability of automotive body sheets, whereas the dispersoid particles will inhibit the growth of grains during recrystallization. Therefore, increasing the Mn mass fraction will improve the strength of the alloys but reduce their percentage elongation and pressing formability.
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    Kinetic simulation of strain induced precipitation in Nb microalloyed steels
    Xu, Yun-Bo (1); Yu, Yong-Hai (1); Liu, Xiang-Hua (1); Wang, Guo-Dong (1)
    2005, 26 (4):  249-252.  DOI: -
    Abstract ( 222 )   HTML   PDF (325KB) ( 667 )  
    The precipitation behavior of Fe-Nb-C-N system in austenite was simulated on the basis of thermodynamics and kinetics. Thus, the precipitation kinetics of carbonitride in isothermal and cooling process was predicted, and the influence of deformation process and cooling condition on kinetic parameters, such as volume fraction and starting/finishing time of precipitation was analyzed. The results indicate that the precipitation is obviously accelerated kinetically at about 900°C, because the deformation greatly enhances the carbonitride precipitation and shortens the starting time for precipitation. With increasing cooling rate, the starting/finishing temperatures of CCP both decrease with full precipitation more and more difficult to take place. The simulated results are in agreement with experimental results.
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    Secondarily precipitated phases of a Ni-based superalloy during durable thermal treatment
    Zhang, Xiao-Bin (1); Liu, Chang-Sheng (1); Lu, Jun-Ying (1); Yang, Hong-Cai (1)
    2005, 26 (4):  253-256.  DOI: -
    Abstract ( 437 )   HTML   PDF (218KB) ( 1202 )  
    A Ni-based superalloy was heated as durable ageing treatment at 800°C and 900°C for 100-1000 hr to observe its change in microstructures. Further, the samples of secondarily precipitated phases in the aging treatment process were analyzed by means of SEM, TEM and electro-probe. It was found that both the carbide and TCP-phase precipitates are easier to be precipitated at 800°C than at higher temperature and their particle sizes are bigger at 800°C than at 900 °C. The types of precipitated carbides are M23C6 and M7C3 phases, while those of TCP phases are μ and σ. The average radius of γ′-phase grains, as measured, provides such a conclusion that their precipitation behavior is coincident with Liftshitz-Wagner theory. As a result, the investigation as above offers a foundation on which the examination of tensile and duration properties are available.
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    Effect of silicon-barium compound inoculants on microstructure and properties of boron-bearing gray cast iron
    He, Jiang-Ai (1); Zhao, Pei-Lin (1); Xin, Qi-Bin (1); Liu, Su-Lan (1)
    2005, 26 (4):  257-260.  DOI: -
    Abstract ( 327 )   HTML   PDF (213KB) ( 1014 )  
    Investigates how the compound inoculants of which the mass fractions of Si-Ba is formulated differently, affect the burn-off rate of boron, microstructure and mechanical properties of the B-bearing gray cast iron. The results show that the burn-off rate of boron decreases from 25% to 8% with the increasing Si-Ba content, while the tensile strength and hardness increase gradually. When the Si-Ba mass fraction is 0.48%, the peak values of both tensile strength and hardness are found, i.e., 282 MPa and 228 HBS, respectively. At that moment, the graphite shows morphologically the A-type distribution and the eutectic cells become finer, of which the number increases from 390 to 780 per cm2. The boron-carbide is morphologically smaller than that without inoculants added to the cast iron and spreads over the pearlite evenly. Compared with the normal diagram, the volume fraction of pearlite is greater than 95%.
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    Application of fuzzy causal classification model for forecasting coke ratio in blast furnace
    Hao, Xiao-Jing (1); Du, Gang (2); Xie, Zhi (1); Shen, Feng-Man (2)
    2005, 26 (4):  261-264.  DOI: -
    Abstract ( 206 )   HTML   PDF (949KB) ( 696 )  
    By means of path analysis, the data collected in situ were processed. Among the variables given to describe blast furnace system, the main variable influencing factors on objective function were determined according to the minimum remaining path coefficient. The relation among those factors was simplified and classified into two groups, i.e., direct paths and indirect paths, then they were ranked to find out the influenced objective functions, i.e., the direct and indirect paths to coke ratio. Analyzing comprehensively the effects of the two paths, a conclusion is drawn that the furnace roof temperature, batch weight, ore weight, coke burden and [Si] are not only the direct influencing factors, but also the indirect influencing factors on coke ratio.
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    Preparation of SnO2 nanopowder by ultrasonic-chemical precipitation process
    Zhang, Xiao-Shun (1); Qiu, Zhu-Xian (1); Zhai, Xiu-Jing (1); Fu, Yan (1)
    2005, 26 (4):  265-267.  DOI: -
    Abstract ( 241 )   HTML   PDF (894KB) ( 744 )  
    The SnO2 nanopowder was prepared by the chemical precipitation reaction of SnCl2·2H2O and NH3·H2O under the action of ultrasonic wave, in which no inclusions were found with a yield approaching theoretical value if controlling pH = 5.0. The structure of SnO2 was transformed from amorphous to crystalline via calcination process, and the calcination temperature affected obviously its grain size which increased with increasing calcination temperature and in accordance to the equation d = 0.2027 t - 30.7750. However, the time for calcination exerts no significant influence on the grain size. It was found preferable that the structure transform of SnO2 nanopowder is calcined at 350°C for 15 min, thus obtaining the spherical crystals about 20 nm.
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    Development of sulphur sensor using MgS + TiS2 solid electrolyte
    Liu, Tao (1); Yu, Jing-Kun (1); Chen, Min (1)
    2005, 26 (4):  268-270.  DOI: -
    Abstract ( 202 )   HTML   PDF (235KB) ( 587 )  
    A sulphur sensor was developed using MgS + TiS2 solid electrolyte with Mo+ MoS2 taken as reference electrode, and it was applied to determining the sulphur content in liquid carbon-saturated iron at 1623 K in lab through EMF measurement. Further, the problems of gas leakage and burst of solid electrolyte tubes were solved by optimizing the construction of those tubes, and the hydration and oxidation of the sulphide were also avoided by special processes. The results showed that the sulphur sensor could be continuously used with stable EMF signals and good reproducibility provided.
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    Synthesis and electrochemical performance of cathode material LiFePO4 for lithium-ion battery
    Qu, Tao (1); Tian, Yan-Wen (1); Zhong, Can-Yun (1); Zhai, Yu-Chun (1)
    2005, 26 (4):  271-274.  DOI: -
    Abstract ( 226 )   HTML   PDF (234KB) ( 1096 )  
    The olivine LiFePO4 was studied as cathode material for lithium-ion battery. Carbon-doped LiFePO4 was synthesized through solid-state reaction at different temperatures, of which the structural parameters of samples were calculated and electrochemical tests were performed for samples. The calculated results showed that with the elevated synthesizing temperature, the samples show higher crystallinity and more compact and stable structure. The testing results showed that the samples synthesized at 700°C have good electrochemical performance. The initial specific capacity discharged at 0.1 C rate and room temperature is 140.4 mAh/g, with very little capacity fading after 10 cycles. The discharge capacity of LiFePO4 synthesized in such a way is equivalent to that of the present commercial LiCoO2 as cathode material. It has a promising future in application.
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    Synthesis and characterization of side-chain liquid crystalline polysiloxanes containing sulfonic acid ionic groups
    Sun, Qiu-Ju (1); Zang, Bao-Ling (1); Zhang, Bao-Yan (1); Wang, Ye-Xiang (1)
    2005, 26 (4):  275-278.  DOI: -
    Abstract ( 174 )   HTML   PDF (118KB) ( 572 )  
    A series of side-chain liquid crystalline polysiloxanes containing sulfonate acid ionic groups were synthesized via copolymerization reaction of liquid crystalline monomers M1(4-allyoxybenzoyloxy-4′-methyloxybenzoyloxy-p-bi phenyl), M2(4-allyoxybenzoyloxy-4′-buthylbenzoyloxy-p-phenyl) and ionic monomer M3(4-[4-(2-propenyloxy) phenyl] azo) benzenesulfonic acid) with polymethylhydrosiloxane, and their structures and properties were characterized by FTIR, DSC, POM and TG. The results showed that introducing ionic groups in the liquid crystal will weaken the mesomorphic properties of relevant polymer in which no ionic groups contained, but not change the type of liquid crystal phase.
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    Parameter optimization based on workspace for a parallel CNC machine tool
    Meng, Xiang-Zhi (1); Liu, Zhi-Feng (2); Cai, Guang-Qi (1)
    2005, 26 (4):  279-282.  DOI: -
    Abstract ( 214 )   HTML   PDF (250KB) ( 538 )  
    A general-purpose method of dimension integration and the objective functions of parameter optimization during dimension integration are introduced. A new dimension integration flow is given combining the structural characteristics of machine tool with requirements for its design. A method of structural optimization is therefore given with a prerequisite of fixed workspace, of which the optimization aims at minimizing the length of every driving subchain so as to allow all the hinge positions and swing angles of Hooke's joints to be in a rational range and providing the conditions under which the smartnesses of the machine and the maximum actuating velocity and acceleration of all driving subchains can be minimized through integration process. With this method used, the structural parameters of a 3-chain parallel CNC machine tool are designed optimally with 3 sets of optimal parameters.
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    Numerical simulation of crack development in reinforced concrete structures
    Zhang, Juan-Xia (1); Tang, Chun-An (1); Wang, Shu-Hong (1); Zhang, Hou-Quan (1)
    2005, 26 (4):  283-286.  DOI: -
    Abstract ( 231 )   HTML   PDF (146KB) ( 876 )  
    A numerical code MFPA (Material Failure Process Analysis) is used to model the crack initiation and propagation in reinforced concrete bridge pier, which are subjected to eccentric loading. Mathematically, the MFPA code is a linear finite element method (FEM) also a continuum mechanics method for numerically processing non-linear and discontinuum problems. Reinforced concrete structures are generally designed to allow cracking under service loading. Therefore, accurate modeling is important. The reinforced concrete here is expressed by a set of elements which are of the same size but different mechanically so as to reflect its heterogeneous mechanical properties. Load-displacement curve, elastic modulus and principal stress photos are provided to simulate the failure process, and an analysis is made for the failure process. The simulation results showed that tensile stress causes the failure, which is similar to the experimental result as showed by some literatures as references.
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    Modeling of strain localization in asphaltic concrete and numerical analysis
    Zhang, Wen-Xian (1); Liu, Xue-Yan (2); Wang, Shu-Hong (1)
    2005, 26 (4):  287-290.  DOI: -
    Abstract ( 211 )   HTML   PDF (179KB) ( 749 )  
    Finite element strain localization analyses of strain rate, history and temperature dependent material like asphaltic concrete were conducted. The theory of rate-dependent consistent plasticity was chosen as the most suitable material for constitutive framework in modeling the nonlinear response of rate-dependent material. With this model, mesh sensitivity issue for strain localization simulation was demonstrated by means of one-dimensional bar compression test. The asphaltic concrete, as a typical rate-dependent material, was chosen for the finite element analysis. A one-dimensional asphalt concrete bar subjected to dynamic compression load with different numbers of elements was examined. It was found that the independence due to the strain-rate-dependent characteristics within the model mesh can be ensured. The contribution of the model on the formation of localization within the semi-circular bending (SCB) test is presented in detail.
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    Load-bearing deformation of pre-stressed steel and high strength concrete composite beams
    Xu, Wei (1); Wang, Lian-Guang (1); Xu, Feng (2); Zhu, Fu-Sheng (1)
    2005, 26 (4):  291-294.  DOI: -
    Abstract ( 232 )   HTML   PDF (246KB) ( 530 )  
    A load-deformation curve was obtained through experiments for the pre-stressed steel and high strength concrete composite beams. The result showed that the elastic bearing capacity of such beams can increase by about 10%. Taking account of the relative slip in between two joint faces of those beams and its effect on the deformation of the simple supported beams, a differential equation of deformation is given on the basis of theory of elastic analysis. Then, the formulas to calculate the deformation of a beam span on which concentrated, distributed or symmetrically concentrated load is acting are proposed. A good agreement is obtained between the calculating results and experimental results.
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    New method of urban ecological footprint calculation based on national hectare
    Gu, Xiao-Wei (1); Wang, Qing (1); Liu, Jian-Xing (1); Li, Guang-Jun (1)
    2005, 26 (4):  295-298.  DOI: -
    Abstract ( 286 )   HTML   PDF (107KB) ( 1602 )  
    Based on the ecological footprint concept, national hectare or nha is proposed as a new area unit to calculate the urban ecological footprint. For comparison, the ecological footprint within Shenyang was calculated in nha and gha for the year of 2001, with both results compared and analyzed. The results showed that the ecological footprint within Shenyang in 2001 was 1.2372 hm2·cap-1 and the available ecologically productive area was 0.7496 hm2·cap-1, as a results, the ecological deficit was 0.4876 hm2·cap-1 if using gha as unit area. But, the three indices mentioned above were 0.7418 hm2·cap-1, 0.6219 hm2·cap-1 and 0.1199 hm2·cap-1, respectively, if using nha as unit area. The reasons of discrepancies arising from the different area units used are discussed in detail, and it is found that using nha to calculate ecological footprint is well worth studying in application.
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    Environmental treatment of anionic surfactants LAS wastewater by modified fly ash
    Yu, Xiao-Cai (1); Wang, En-De (1); Xu, Wei (2); Xin, Zhe (2)
    2005, 26 (4):  299-302.  DOI: -
    Abstract ( 240 )   HTML   PDF (196KB) ( 975 )  
    Utilizing the adsorption/coagulation effect of modified fly ash to treat the wastewater containing the anionic surfactant LAS was investigated. The results showed that fly ash modified by the modifier CaO was effective to adsorb the environmental harmful substance LAS when LAS concentration is 20-120 mg/L in the wastewater of which the pH value is 9-13 and the amount of modified fly ash with particle size 74-83 μm is 20-25 g per 200 ml wastewater. The fact conforms to Langmuir theory of adsorption. The LAS removal rate can be up to over 98% on the conditions mentioned above.
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    Magnetic field effect on As extraction in industrial wastewater
    Ling, Guo-Liang (1); Han, Tian-Fang (1); Liu, Dong-Sheng (1)
    2005, 26 (4):  303-306.  DOI: -
    Abstract ( 182 )   HTML   PDF (186KB) ( 739 )  
    The effect of magnetic field on extracting As in industrial wastewater was investigated experimentally through the change in exacting time/temperature and pH value, as well as whether the wastewater is magnetized or not. The (C2H5C6H13)2 PO4 was directly used as extractant with small amount of (C4H9)3PO4 and sulphurized kerosene added to it so as to extract As through vitrolization. After premagnetizing the As-containing wastewater, As extraction rate increases with extraction behavior effectively improved. At the same time, the distribution ratio of extracting other impurities in the wastewater is also changed. After extraction and enrichment, pure As in the wastewater could be deoxidized by electrolytic sediment or hydrated NH2NH2. The wastewater after As extraction and purification can be regarded as up to the state effluent standard. The As extraction process can also be applied to other industrial wastewater treatment if containing harmful/toxic impurities.
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