煤矿排水沉淀物作为一种新的吸附剂对重金属吸附作用的动力学与热力学研究

1、Kinetic and thermodynamic studies of the adsorption Kinetic and thermodynamic studies of the adsorption of heavy metals on to a new adsorbent:of heavy metals on to a new adsorbent:coal mine drainage sludgecoal mine drainage sludge煤矿排水沉淀物作为一种新的吸附剂对煤矿排水沉淀物作为一种新的吸附剂对重金属吸附作用重金属吸附作用的动的动力学与热力学研究力学与热力学研究AB

2、STRACT摘要 In this study, we investigated the application of sludge waste obtained from a coal mine drainage treatment facility that treats acid mine drainage (designated as AMD) from metal-mine water. The coal mine drainage sludge (designated as CMDS), which contained 70% goethite and 30% calcite, wa

3、s utilized as a sorption material for Cu(II) and Zn(II) removal from an aqueous solution of metallic mine drainage.这本次研究中，我们研究了来自于煤矿处理厂的沉淀废物的应用，用这种沉淀废物处理来自于金属矿山排水中的酸性矿物废水（简称为AMD）。这种煤矿排水沉淀物（简称为CMDS），它包含了70%的针铁矿和30%的方解石，被利用作为一种吸附移除来自金属矿山废水中的Cu（II）和Zn（II）。 The equilibriums and kinetics were investigate

4、d during a series of batch adsorption experiments. The Langmuir model was used to fit the equilibrium data, resulting in the best fits. The removal efficiencies were controlled by solution pH, temperature, initial concentration of heavy metal, sorbent amount and contact time. The pseudo-second-order

5、 kinetic model was used to fit the kinetic data, providing a good correlation with the experimental data.在整个分批吸附实验中都用到了热力学和动力学平衡的研究。结果显示：Langumir模型能够很好的拟合热力学平衡数据。整个吸附过程中移除效率由溶液的pH值，温度，重金属溶液的初始浓度，吸附剂数量以及接触时间所控制。而拟二级动力学方程能够很好的拟合动力学数据，并且显示了与实验数据的一个很好的关联度。 The results of a thermodynamic study showed tha

6、t the activation energies (EA) were 3.75 and 1.75 kJ mol1for the adsorption of Cu(II) and Zn(II)on to CMDS at pH 5.5. These values of activation energy could correspond to physisorption. The positive values obtained for both the standard enthalpy change,0, and the standard entropy change,S0, suggest

7、 that the adsorption of Cu(II) and Zn(II) on to the CMDS was an endothermic reaction and that randomness increased at the solidliquid interface during the adsorption of Cu(II) and Zn(II) on to the CMDS. The adsorption process also followed a pseudo-second-order kinetic model.本次热力学研究表明：吸附剂CMDS在pH=5.5

8、时，对Cu（II）和Zn（II）的吸附的活化能（EA）为3.75和1.75 KJ mol-1。这些活化能量对于物理吸附式由价值的。而这各数据的得出对于标准焓变0 和标准熵变S0提供了一定的价值，表明：吸附剂CMDS对于Cu（II）和Zn（II）的吸附是一个吸热反应，并且表明：吸附剂CMDS对于Cu（II）和Zn（II）的吸附过程在固-液界面的随机性有所增加。这个吸附过程仍然符合拟二级动力学方程。INTRODUCTION介绍 Acid mine drainage (AMD) released from abandoned gold mines can not only pollute natur

9、al environments such as surrounding soils, surface and ground waters, but also has some sequential toxic effects on crops and humans through concentration through the food chain 1. Although the most widespread method to remove heavy metals in AMD is coagulation and flocculation through neutralizatio

10、n by increase of pH, it is not very economic or effective, and can also release secondary pollution.从金矿中随意排放 AMD不仅能污染环境例如周围的土壤环境，表明和地下水，而且能够通过食物链对农作物和人类产生连续的毒性效应。尽管去除重金属废水中的AMD的大多数方法是利用化学中和反应通过控制pH的增加来形成凝结物或者是絮凝产物，但是这种方法并不是很经济和有效，并且会产生二次污染。Accordingly, other treatment methods have been extensively s

11、tudied. Among them, adsorption techniques have been studied, using metal oxide, active carbon, fly ash, peat, activity sludge and waste sludge 25. In particular, research has been conducted on the adsorption of heavy metals by the use of iron compounds including ferric saltsand zero valent iron (ZVI

12、) 6,7. The adsorption of cationic heavy metal species on the hydroxyl group of sorbents has been found to be an endothermic reaction in an adsorption study of heavy metals using goethite (FeOOH). 因此，其他的处理方法被广泛的研究。其间，化学吸附技术也被研究，通过利用金属氧化物，活性碳粉尘灰，泥煤，活跃沉淀物和废物泥。特别是通过研究利用铁化合物包括铁盐和零化合价铁（ZVI）来吸附重金属。在用针铁矿（Fe

13、OOH）作为吸附剂吸附重金属离子的实验中，是将阳离子金属吸附在吸附剂的羟基上，并且该实验属于吸热反应。 Thus, the adsorption capacities and equilibrium constants increase as the temperature increases 815.The relationship between pH and adsorption and/or coprecipitation, using goethite for the removal of heavy metals, has also been actively studied 16

14、. The different ratios of each hydroxyl group (FeOH2+ , FeOH, FeO) may depend on the pH. In contrast, clay minerals such as bentonite show a clarification reaction, in which their equilibrium constants and adsorption capacities decrease with an increase in temperature as a result of the exothermic n

15、ature of metal adsorption 17.因此，当随着温度的增加，吸附能力和平衡常数也随着增加。在用铁针石对重金属进行移除期间，pH和吸附以及/或者共同沉淀的关系也有很多的研究。而每个羟基的不同配比可能取决于pH。与此相反，例如膨润土的黏土矿物却显示出了一种澄清反应，在反应中平衡常数和吸附容量随着温度的增加而减少是由于金属吸附的放热特性所导致的结果。 In this study, the adsorption characteristics of coal mine drainage sludge (CMDS) for heavy metals in AMD released

16、from a metal-mine area were investigated.The CMDS contains mainly Fe2O3(64.7%) and has been produced by drying the sludge cake produced from an electric purification facility in Korea. The Fe hydroxide/oxide of CMDS is usually amorphous and has amphiphilic adsorption characteristic for both cationic

17、 heavy metals and anionic metalloids. Thus, the application of sludge as a sorption material for treating AMD of metal mines could have an economic potential in terms of recycling waste material.在本次研究中，关于吸附剂CMDS对于从金属矿山区域中排放的AMD中的重金属吸附的吸附特性是研究过的。吸附剂CMDS主要包含了64.7%的Fe2O3和在位于韩国的一个电动净化厂产生的已经干燥的污泥饼。在CMDS中

18、的Fe的氢氧化物/氧化物通常是无定型的并且对于阳离子重金属和阴离子非金属有两亲性的吸附特性。因此，将沉淀物作为吸附材料对金属矿山的AMD进行处理在废物资源回收方面可能会有经济上的潜在性。 The objective in this study was to investigate the adsorption, in terms of reaction speed and thermodynamics, of the main heavy metals in the AMD releasedfrom metal mines-Cu(II) and Zn(II)-on to CMDS.本次实验的目

19、的是为了研究在吸附中的反应速度和利用吸附材料CMDS吸附在从金属矿山中排放的AMD中的Cu（II）和Zn（II）的热力学特性。EXPERIMENTAL实验EXPERIMENTALWATER AND SLUDGE SAMPLES水和沉淀物的样品 Water was sampled from the effluent of three settling tanks that were previously setup to remediate AMD of a metal mine located at 351823.2 longitude and1291339.1 latitude in Sou

20、th Korea. The CMDS was simply prepared by drying at 25 the sludge taken from an electric purification facility treating acidic mine drainage from a coal mine.水样是从三个不同的沉淀池提取的，这三个沉淀池提前建立去修复位于韩国的经度为351823.2和纬度1291339.1 的金属矿山中的AMD。CMDS是来自于一个通过电动净化厂处理来自煤矿中的酸性矿山排水，仅仅在25通过干燥制成的污泥饼。EXPERIMENTALANALYSES分析 Th

21、e surface area of CMDS was analysed by the Brunauer Emmett Teller (BET, ASAP 2010, Micromeritics Inc., USA) adsorption method using nitrogen gas (Sutosorb-1-C, Chemisorptions-Physisorption Analyser,Quantachrome Instruments, USA). The pH of water was measured with a Thermo Orion model 420A+, and heav

22、y metals were analysed by an inductively coupled plasma atomic emission spectrometer (ICP-AES, 5300DV, Perkin Elmer). X-ray diffraction (XRD,Xpert PRO/MRO, Philips) analyses were conducted for the selected freeze-dried powdered samples of CMDS by use of a PANalytical XPert Pro diffractometer (fitted

23、 with an XCelerator) with a CuK radiation source at a scan speed of 2.5min1.材料CMDS的曲面面积通过Brunauer Emmett Teller吸附方法利用氮气 进行了的分析。样品水的值通过型号为420A+热电奥利龙的仪器进行测试，并且通过ICP-AES分析了重金属离子的含量。XRD设备被用来测定经过冷冻干燥过的CMDS样品，所用的衍射仪为PANalytical XPert Pro，辐射源为Cu的Ka射线，转速为每分钟2.5。 The phase identification of CMDS was carried

24、out by the means of the XPert accompanying software program, High Score Plus, and the reference intensity ratio method (RIR method) ICDD PDF-4+ database (International Centre for Diffraction Database, USA, 1999). The X-rayfluorescence (XRF-1700/SHIM ADZUXRF) results showed that the CMDS was mainly c

25、omposed of SiO2(6.65%), Fe2O3(64.74%) and CaO(8.6%). These compounds exceeded 79.9%.对于CMDS的相位鉴别是通过XPert附带的软件High Score Plus和参考强度比率方法ICDD-PDF+数据库方法进行的。X射线荧光结果显示CMDS主要包含了6.65%二氧化硅，64.74%的三氧化二铁和8.6%的氧化钙。这些化合物超过了79.9%。 The buffer capacity of the sludge was measured as follows: 10 g of sludge and 25 mL o

26、f deionized water were added to a 50 mL centrifuge tube. Then different amounts of 0.1 M HCl were added to each sample and the suspensions were shaken at room temperature for 24 h prior to pH measurement 2,19. The sludge was reacted with 2 M HCl to dissolve the carbonate. The remaining acid was titr

27、ated using 0.1 M NaOH to measure the CaCO3 content of the CMDS 19. The easily extractable fractions of Fe and Mn from the CMDS could be analysed with the following methods. After extraction with 1 M hydroxylamine hydrochloride(NH2OHHCl), the Fe content of the CMDS was measured by ICP 20.沉淀物的缓冲容量通过测定

28、：10g沉淀物和25ml去离子水加入到50ml离心管中。然后将不同量的0.1mol HCl溶液加入到每个样品中，并且将悬浮液在pH测量前在室温下振荡24小时。沉淀物与2mol的 HCl反应使碳酸盐溶解。其余的酸用0.1mol的NaOH进行滴定去测量CMDS中含有的CaCO3含量。可很容易的从这个方法分析出CMDS中少量的Fe和Mn元素。之后提取1mol的羟胺盐酸盐，通过ICP测量出CMDS中的Fe元素。 The Mn ions in the CMDS were dissolved using 0.1 M hydroxylamine hydrochloride and analysed by I

29、CP 21. The organic carbon content and cation exchange capacity (CEC) of the CMDS were measured by the WalkleyBlack method and the ammonium acetate method, respectively. For the ammonium acetate method, the CMDS was treated with a salt of NH4+ ion and then NH4+ ions were substituted using a NaCl solu

30、tion. The replaced amount of NH4+ ions was analysed. Loss-on-ignition (LOI) of the CMDS was measured as follows: 1020 g of wet CMDS was dried at 105C for 18 h, and then heated at 450C for 6 h. During this procedure, the sample at each step was weighed 1.在CMDS中的Mn离子通过用0.1mol的羟胺盐酸盐去除并且用ICP进行分析。CMDS的有机

31、碳含量和阳离子交换能力（CEC）分别通过WalkleyBlack和醋酸铵方法进行测定。对于醋酸铵方法，CMDS用含NH4+的盐处理并且之后的NH4+用NaCl溶液进行替换。分析被替换的NH4+。CMDS的烧失量（LOI）用一下方法进行测定：在105下干燥10-20g的湿CMDS 18小时，然后在450下加热6小时。干燥过程中每一步都要称量。EXPERIMENTALADSORPTION STUDY吸附研究 The adsorption study was conducted in batch tests. A different mass of CMDS (5, 10, 20, 30 or 40

32、 g) was added to 500 mL of mine water; the bottles containing these slurries were shaken on a shaker (150 rpm) for24 h at 252C. After filtering the supernatant, the concentrations of copper, zinc and iron in the filtrates were measured. Copper, zinc and iron sorption data were analysed using the Lan

33、gmuir model to evaluate the parameters directly associated with the sorption process. The Langmuir model equation is by represented by: 吸附研究是批量试验。不同质量的CMDS（5,10,20,30或40g）被加到500ml的金属溶液中；包含这些泥浆的瓶子被放在振荡器（150r/min）中在252下振荡24小时。之后二次过滤悬浮液，测量在滤液中的Cu、Zn、Fe离子浓度。 铜、锌和铁吸附数据进行分析利用Langumir模型评价参数与吸附过程直接相关。Langum

34、ir模型表达式为：EXPERIMENTALKINETIC TESTS动力学实验 Adsorption kinetic tests were conducted to find out the adsorption behaviours such as maximum sorption capacity and energy of heavy metals for the sludge. A different mass of CMDS (5, 10, 20, 30 or 40 g) wasadded to 500 mL of mine water. Then, each of the susp

35、ensions was shaken at 150 rpm at different temperatures (278 K, 288 K, 298 K, or 308 K) without pH adjustment. After 24 h (more than the time required for equilibrium) of shaking, 5 mL of supernatant was withdrawn and centrifuged prior to analysis.吸附动力学实验旨在为了发现吸附行为例如：最大吸附容量和对于沉淀物吸附重金属的能量。不同质量的CMDS （

36、5,10,20,30或40g）被加到500ml的金属溶液中，然后，每一个悬浮液在不同温度（ 278 K, 288 K, 298 K, 或 308 K ）下以150r/min进行振荡吸附。24小时（超过这个时间后已经平衡）的振荡后，取出5ml悬浮液并且在分析前离心处理。 The pseudo-second-order kinetic equation has been extensively used to obtain more reliable kinetic constants for heterogeneous adsorption of heavy metals22. To inves

37、tigate the mechanism of sorption and the rate constants for the adsorption of Cu(II) and Zn(II) on to CMDS, the pseudo-second-order kinetic equation was used as shown below 23. The differential equation is as follows:Integrating Equation (2) for the boundary conditions t =0 to t, and qt= 0 to qt, gi

38、ves:拟二级动力学方程被广泛用于获得更可靠的异类重金属吸附的动力常数。为了研究吸附机理和CMDS对Cu（II）和Zn（II）的吸附速率常数，拟二级动力学方程在下面提到。它的不同形式为：综合化方程（2）的边界条件为t=0到t，qt=0到qt，给出：When Equation (3) is linearized, it gives:where v0(mg g1min1) is the initial sorption rate; therefore, the v0and qe values of the kinetic tests can be determined experimentally

39、 by plotting t versus t/qt; qe is the amount of Cu(II) and Zn(II) adsorbed at equilibrium(mg L1); qt is the amount of Cu(II) and Zn(II) adsorbed at time t (mg g1); and K2is the rate constant of the pseudo-second-order kinetic equation (g mg1min1).The pseudo-second-order kinetic rate constant (K2) is

40、 expressed as a function of temperature by the following Arrhenuius type relationship 24:当公式（3）被线性化，得到（4）和（5）。其中：v0为初始吸附速率；因此，v0和qe在动力学中可作为对实验中测量到的数据t/qt的验证。qe是Cu（II）和Zn（II）在时间t内被吸附的数量；K2为拟二级动力学方程的速率常数。拟二级动力学方程速率常数（K2）可以通过阿伦尼乌斯方程以温度为根据表达出来。EXPERIMENTALTHERMODYNAMIC PARAMETERS热力学参数 To explain the eff

41、ect of temperature on the adsorption thermodynamic parameters, standard free energyG0, standard enthalpyH0, and standard entropy S0 were determined. The thermodynamic parameters can be determined from the variation in the thermodynamic equilibrium constant K0, which can be defined as follows 25,26:

42、where Ce is the concentration of heavy metals in solution at equilibrium (mg L1), and qe is the surface concentration of heavy metals adsorbed in the sorbent (mg g1). The adsorption standard free energy changes (G0) can be calculated from:为了解释温度在吸附热力学参数、标准自由能G0，标准焓变H0以及标准熵变S0中的作用。热力学参数从热力学的变化中决定的平衡常

43、数K 0 ,而K0由（7）式给出。其中：Ce为反应平衡后重金属在溶液中的浓度。qe为吸附剂表面吸附的重金属的浓度。吸附标准自由能变由（8）式给出。 where R is the universal gas constant (8.314 J mol1K1) and T is the temperature in Kelvin. The average standard enthalpy change (H0) is determined from the vanHoof equation:其中：R为普遍气体参数，T为开尔文温度。平均自由焓变H0由范德霍夫方程给出。RESULTS AND DIS

44、CUSSION结果与讨论RESULTS AND DISCUSSIONCHARACTERIZATION OF THE AMD AND CMDSAMD 和CMDS 的特性 The physico-chemical properties of the AMD and CMDS are shown in Tables 1 to 4. The initial concentrations of Cu, Zn, and Fe were 10, 9.2 and 58 mgL1,respectively, and the pH (2.65) was acidic. Owing to the low pH an

45、d the high concentration of Fe, the acidity was high at 288 mg as CaCO3/L. The BET surface area and pH of the CMDS were 151 m2g1and 8.3, respectively. The buffer capacity of the CMDS was 82.3 mmol H+kg1pH1. X-ray diffraction (XRD) analyses and the RIR method ICDD PDF-4+ database showed that the CMDS

46、 mainly consisted of goethite and calcite. The composition ratio of goethite (reference code No: 010-81-0463) and calcite (reference code No: 010-81-02027) were 70% and 30% by weight, respectively.AMD和CMDS的物理-化学性能在表1到表4中给出。Cu, Zn,和Fe的初始浓度为10,9,2和58ppm，pH为2.65为酸性。由于Fe处于低pH和高浓度环境中，而CaCO3为288ppm。CMDS的比

47、表面积和pH分别为151m2/g和8.3。CMDS的缓冲容量为82.3 mmol H+/kg/pH。XRD分析和RIR方法的ICDD PDF-4+数据库表明：CMDS主要针铁矿和方解石构成。针铁矿和方解石的成分比例按质量算为70%和30%。 The most interesting aspect of this analysis is that the average pore sizes of the CMDS were in the range of mesopores. Porous materials can be classified by IUPAC as follows: mic

48、roporous (50.0 nm) 27. Macroporous materials are restricted for use as adsorbents because of their nonuniformity of pore size distribution and low surface area. Microporous materials have some limits regarding accessibility to the active surface area because of blocking problems. Regardless of seaso

49、n, the measured pore size (67.92 ) of the CMDS was in the mesopore range, which could have a low diffusion limit. Therefore, a sorption material that is well developed with mesopores could have a reduced adsorption equilibrium since adsorbate could easily adsorb on the sorption sites.这次分析中最为有趣的是CMDS

50、的孔隙尺寸是在中孔范围内。多孔材料由IUPAC分类为：微孔（50.0 nm）。大孔材料作为吸附材料是受限制的，因为它们的孔径分布的不均匀性和低表面积。微孔材料因为阻塞问题，活性表面积的可及性上有一些限制 。忽视季节问题，CMDS的孔径测量为67.92 为中孔材料，对此它有较低的扩散限制。因此，一个吸附材料, 中孔发达可以降低吸附平衡，因为被吸附物很容易吸附在吸附位上。RESULTS AND DISUSSIONADSORPTION KINETICS吸附动力学 Figure 1 shows the adsorption kinetics results for Cu(II), Zn(II), an

51、d Fe(III) in the AMD at different amounts of CMDS. When the concentration of CMDS was more than 5 g, about 100% of Cu(II), Zn(II), and Fe(III) were removed within 10 min, whereas, when 5 g of CMDS was applied, about 100% of Cu(II) and Zn(II) was removed within 100 min and 100% of Fe(III) was remved

52、within 20 min. But the copper, zinc and iron recovery decreased with increasing contact time. The Cu(II) and Zn(II) was completely removed by about 180 min of operation using 5g CMDS, while about 20 min was needed for Fe(III). Probably, the rapid removal of Fe(III) could be explained by the simultan

53、eous mechanism of hydrolysis and coagulation occurring at high pH. 图1描述了用不同质量的CMDS吸附AMD中的Cu(II), Zn(II)，和Fe(III)的吸附动力学结果。当CMDS的质量超过5g时，大约有100%的Cu(II), Zn(II)，和Fe(III)在10min内被移除，然而，当CMDS质量为5g时，约有100%的Cu(II), Zn(II)，在100min内移除，而100%的Fe(III)在20min内被移除。但是,铜、锌和铁恢复随接触时间增加而降低。 对于Cu(II) 和 Zn(II) ，5g的CMDS在18

54、0min时完全移除，而对于Fe(III)只需要20min。可能,在快速去除Fe(III)的时候，在高pH时可以用同时发生了水解反应和凝固反应来解释。 In general, the soluble Fe(III) transforms into insoluble forms by a polymerization reaction at higher pH, whereas Cu(II) and Zn(II) are predominantly removed by the adsorption mechanism. The Langmuirtreatment is based on the

55、 assumption that maximum adsorption corresponds to a saturated monolayer of adsorbate molecules on the adsorbent surface, that the energy of adsorption is constant, and that there is no transmigration of adsorbate molecules in the plane to the surface 25. 通常来说，可溶解的Fe(III)在高pH时通过聚合反应而变成了不溶解的一种形式。而对于C

56、u(II)和 Zn(II) 而言，很显著的因为吸附机理而被移除。Langumir模型是基于假设最大吸附对应于一个吸附分子的饱和单层的吸附剂表面,吸附的能量是恒定的，并且表面平面上没有其他的吸附物颗粒。 Figure 2 shows the adsorption amount vs. the maximum adsorption capacity rate when the CMDS weight reached the equilibrium state. When the CMDS weight was 5 g, the adsorption capacity rate of Cu and

57、Fe was 100% and when the CMDS weight was 10 g, the adsorption capacity rate of Zn showed 100%. These results are the same as in Figure 1 in that the maximum adsorption capacity rate was reached at the equilibrium state.图2描述了，当CMDS的重量达到平衡状态时，吸附量和最大吸附量的比值。当CMDS的重量为5g时，对Cu和Fe的吸附量的比值达到100%，当CDMS的重量达到10g

58、时，对Zn的吸附量的比值达到100%。这些结果与图1所示的达到平衡态的最大吸附容量速率是相同的。 Figure 3 shows the initial sorption rate vs. CMDS weight. The initial sorption rates of Cu and Zn corresponded to the pseudo-second-order kinetic model whereby the rates increased when CMDS weight increased. In the case of Fe, the sorption occurred ra

59、pidly. The initial sorption rate of Fe increased when the CMDS weight increased, but after the sorption reached 100% the initial sorption rate decreased. 图3描述了，初始吸附速率和CMDS质量的比值。当随着CMDS的质量增加而Cu和Zn的最初吸附速率也增加时，和拟二级速率方程模型有很好的拟合结果的。而对于Fe，吸附很迅速。当CMDS的质量增加时Fe的初始吸附速率也是增加的，但是之后吸附达到100%时初始吸附率开始降低。RESULTS AND

60、DISUSSIONEFFECT OF TEMPERATURE ON KINETICS温度对动力学的影响 Figure 4 shows adsorption kinetics and plots of the linearized form of the pseudo-second-order kinetic model for Cu(II) and Zn(II) at 5, 15, 25 and 35C. Table 5 shows the parameters obtained from fitting the pseudo-second-order kinetic model. These