外文原文-利用改良的粘土吸附剂去除废水中的镍、铜、锌.pdf

Applied Clay Science 18 2001 183 190 www elsevier nlrlocaterclay Nickel copper and zinc removal from waste water by a modified clay sorbent T Vengris R Binkiene A Sveikauskaite Institute of Chemistry A Gostauto 9 2600 Vilnius Lithuania Received 25 February 2000 received in revised form 11 August 2000 accepted 28 September 2000 Abstract The use of a sorbent produced by the chemical treatment of a locally available clay for the removal of some heavy metals from waste water has been investigated The modification of the natural clay was performed by treatment with hydrochloric acid and subsequent neutralisation of the resultant solution by sodium hydroxide The chemical and structural characteristics of the natural and modified clays were determined The amount of iron aluminium and magnesium compounds increased in the modified sorbent Acidic treatment led to the decomposition of the montmorillonite structure Sorption studies were carried out by both batch and column methods The uptake capacity of the modified clay for nickel copper and zinc did significantly increase Batch and column sorption methods enabled the removal of nickel copper and zinc ions till the permissible sewerage discharge concentration The sorption process is reflected by Langmuir type isotherm The release of presorbed metals by water at pH 5 was negligible q2001 Elsevier Science B V All rights reserved Keywords Modified clay Uptake capacity Nickel Copper Zinc 1 Introduction Some naturally occurring clay minerals may serve as cost effective sorbents for the removal of heavy metals While their sorption capacity is usually less than those of synthetic sorbents these materials could provide an inexpensive substitute for the treatment of heavy metal waste waters To enhance the sorption capacity the clays are modified in various ways such as treatment by inorganic and organic com pounds acids and bases For example montmoril lonite coated and intercalated by aluminium hydrox ides exhibits much higher adsorption capacity for Corresponding author Fax q 3702 61 70 18 E mail address tvengris takas lt T Vengris some heavy metal ions than that of natural montmo rilloniteLothenbach et al 1997 Treatment of zeolites by NaCl solution convert them into a near homoionic state in Na form and improves the ex change capacity for lead and zinc ions Curkovic et al 1997 Adsorption capacity of clayey minerals can also be enhanced by replacing the natural ex changeable cations with organic cations which makes the clay surface more hydrophobicCadena et al 1990 Malakul et al 1998 Modification of clay materials by alkaline solutions leads usually to zeoli tization and significantly increases their uptake ca pacity for heavy metal and ammonium ions Qi and Dingxue 1997 Ruiz et al 1997 The acidic treatment of clay materials has been well known for many years Ovcarenko 1961 Ko 0169 1317r01r see front matter q2001 Elsevier Science B V All rights reserved PII S0169 1317 00 00036 3 T Vengris et al rApplied Clay Science 18 2001 183 190184 marov 1970 This process leads to almost full removal of calcium magnesium and alkali metal oxides and partially diminishes the iron and alu minium content of clay minerals The changes in chemical composition and the mineralogical struc ture of clay resulting from hydrothermal reactions in acidic solutions are dependent upon the nature of the clay material and on the treatment conditions Acidic treatment is more effective on montmorillonitic clays and caused negligible change when the main compo nent is kaoliniteKomarov 1970 In some cases acidic modification causes the sorption capacity of bentonite to decrease Pradas et al 1994 Ahenach et al 1998 have shown that in highly acidic media the surface area and micropore volume of Al pillared montmorillonite significantly decreased Besides that the common shortcoming of acidic treatment is the heavy loss of clay material 25 30 Komarov has proposed an advanced method for clay treatment the main idea of which is that after acidic treatment the AmotherB solution should be neutralised by ammonium or sodium hydroxide thereby most of the dissolved components should form a reprecipitate Manufactured sorbents are usu ally treated thermally to improve their mechanical and sorption properties The primary aim of this work is to investigate the sorptive characteristics of several heavy metals onto modified locally available clay mineral 2 Experimental 2 1 Starting material A clay from Shaltishkiai deposit North Lithuania was used to prepare the modified sorbent The natu ral clay had a mineralogical composition wt of 50 55 hydromica 30 35 montmorillonite and 10 15 chlorite The total clay mineral content was esti mated to be 63 5 with the remainder taken up by quartz mica feldspar carbonate etc 2 2 Apparatus and methods The clay was treated as follows a mixture of dried 1058C pulverized clay and 20 HCl solution was boiled in a round bottom flask with a reflux condenser for 4 h The HCl contentas 100 amounted to 50 of the clay mass After an aging period of 20 h the mixture was diluted by tap water 1 1 then the liquid component was separated and 1r3 of the remaining solid remainder by volume was added This suspension was neutralised with 25 NaOH solution till pH 6 7 7 The sediment was filtered washed and dried at 608C Part of a resultant sorbent was heated at 3508C for 4 h The natural clay sorbents modified chemically and heated at 3508C are referred here as Sh Sh1 and Sh2 sorbents respectively The chemical compositions of the natural and modified clays were estimated by optical emission spectroscopyOESusing a direct current plasma emission spectroscopeBeckman SpectraSpan VI The samples for analysis were dissolved using HF HNOand HClOacids according to the method 34 described by Thompson and Walsh 1989 Calcina tion loss was established by weight difference after heating of samples at 10008C Mineralogical composition was determined by the analysis of X ray diffractograms which involved the identification and semiquantification of the charac teristic peaks of the minerals in the sample X ray diffractograms were recorded using a diffractometer DRON 2 Co Kradiation and a graphite monochro a mator The operation mode of the diffractometer tube was Us30 kV Is20 mA Sorption studies were carried out by both batch and column mode In batch experiments 1 g of sorbent0 5 0 75 mm fractionwere stirred with 100 ml solution in polyethylene bottles at a previ ously established metal concentration and pH rate Sorption samples were periodically taken from each bottle the solid separated by filtering and centrifuge and the metal ion concentration was analysed by an OES method Column tests were conducted in a glass column with an internal diameter of 13 mm The column was packed with successive layers of 2 cm glass beads 2 5 cm layer of sorbent0 5 1 mm fractionand 2 cm glass beads between synthetic mesh screens The test solution containing the target metal s flowed through the bed in up flow mode NaClO was used 4 as the inert electrolyte and was added to keep the ionic strength of the solution constant Effluent sam ples were collected at frequent intervals in poly T Vengris et al rApplied Clay Science 18 2001 183 190185 Table 1 Chemical composition wt of natural Sh and modified Sh2 sorbents Sorbents Fe OSiOAl OCaO MgO Calcination Sum 23223 loss Sh6 944 215 313 8 4 016 0100 2 Sh213 937 522 55 4 7 915 2102 4 ethylene tubes acidified and analysed for metals by OES method Sorption isotherm studies were conducted in well sealed 500 ml polyethylene bottles at room tempera ture20 18C Each bottle contained 100 ml of solution with various metal concentrations and 50 mg of sorbent The initial metal concentrations ranged from 10 to 200 mgrl Following a 24 h reaction period on a mini shaker the samples were taken out filtered and centrifuged to separate the solid Then pH was measured and acidified samples were anal ysed for equilibrium liquid phase concentration Solid phase loading of metal qmgrg was com e puted from the mass balance q s C yC rM e0e where C and C are total dissolved and equilibrium 0e liquid phase metal concentrationmgrl respec tively and M is the dose of sorbent grl Distilled water used in this experiment was pre pared by purging for at least 2 h by Ngas 2 Nickel copper and zinc were the metals exam ined in this study since they are most common heavy metals in the waste water of the electroplating industry Working solutions imitating waste water were prepared from the concentrated stock solutions of CuCl P2H O NiCl P6H O and ZnClsalts 22222 The pH was adjusted either with diluted HCl or NaOH solutions 3 Results and discussion The changes of the elemental composition of natural and modified clay are shown in Table 1 Acidic treatment causes the dissolution of calcium Fig 1 X ray diffractograms Sorbents aSh bSh2 C calcite Cl chlorite D dolomite F feldspar H hydromica M montmorillonite Q quartz K kaolinite T Vengris et al rApplied Clay Science 18 2001 183 190186 magnesium iron and aluminium oxides During the following neutralisation process most of the dis solved metals except calcium reprecipitate as hy droxides and their amounts in the produced sorbent did increase Calcination loss of the original clay is probably due to the decomposition of carbonates and organic matter and that of the Sh2 sorbent could be related to the partial dehydration of produced hydroxides Diffractograms of the samplesFig 1showed that after treatment only hydromica quartz and feldspar structures remain almost unchanged whereas montmorillonite dolomite and calcite were de stroyed The characteristic calcite peak at 34 2 2Q was reduced to about 34 One would expect that iron and aluminium hydroxide produced during chemical treatment should be due to the heavy metal removal process Fig 2 depicts the approach to equilibrium for the batch mode sorption of nickel copper and zinc onto natural and modified sorbents The most intensive metal uptake occurred within the first hour with further slow concentration decrease Sh1 and Sh2 acted more effectively than untreated clay Copper hydroxide precipitation must contribute to the re moval process taking into account the final pH val ues of solutionsTable 2 It covered a range of 6 2 6 8 in which copper hydroxide Cu OHbegins 2 to precipitateLurje 1989 Therefore calculated uptake capacity of used sorbents for copper ions should be taken as conventional In all cases pH increased probably due to the leachate of alkaline and earth alkaline metal ions from the sorbents After 6 h of batch reaction practically full metal removal occurred when the initial concentration was 380 mgrl Table 3 depicts metal uptake data using Sh2 sorbent in more concentrated solutions The uptake capacities of Sh2 sorbent significantly exceeded those of untreated clay These values were comparable with commercial ion exchange resin ca pacities that are typically in the range of 2 3 meqrg Helferrich 1962 The order of the removal capacity is Cu Ni Zn for both natural and treated sor bents All subsequent studies were performed with Sh2 as it was the most effective sorbent Batch removal tests in ternary systems have shown Fig 3 that Sh2 sorbent removes Ni Cu and Zn ions until the permissible sewerage discharges concentra Fig 2 Batch removal rate of 380 mgrl Ni a Cu b and Zn c ions in single component solutions onto sorbents 1 Sh 2 Sh1 3 Sh2 Initial pH s5 C C current and initial concentra i0 tions respectively tion Ni 0 5 Cu 1 Zn 1 mgrlWaste Water Standards 1996 Fig 4 depicts the column filtration curves of single component solutions The breakthrough point T Vengris et al rApplied Clay Science 18 2001 183 190187 Table 2 Final pH values after 6 h batch tests of metal ions solutions with various sorbents MetalsSorbents ShSh1Sh2 Ni6 56 26 1 Cu6 26 26 8 Zn6 05 65 3 pH s5 i at a flow rate of 2 mlrmin for copper ions occurred earlier than that for nickel and zinc Column uptake capacity at 40 breakthrough for nickel and zinc amounted to 1 15 and 0 92 meqrg respectively and 0 75 meqrg for copper at 50 breakthrough Cu breakthrough took place much earlier when the flow rate was 6 mlrmin resulting in only 0 17 meqrg uptake capacity at 50 breakthrough point At a flow rate of 2 mlrmin full copper removal has been obtained after a pass of 400 bed volumes full nickel and zinc removal after pass of 650 bed volumes The relative sorption affinity of the tested metals onto Sh2 is illustrated in the column test results Fig 5 In the initial stage of filtration when there was an excess of surface the solutes competed for available sites and metals with stronger binding affinities i e Cu competed more effectively with preferential re moval from solution As the run progressed and the available sites for binding zinc were saturated how ever copper and nickel not only reacted with the remaining sites but also displaced a portion of the weakly bound zinc resulting in a CrC value greater 0 than 1 Table 3 Batch mode metal uptake data using Sh2 sorbent Xe abcd MetalsCCpHUU iff Ni890935 72 750 5 Cu1000606 42 961 2 Zn9752905 92 090 35 Initial pHs5 a Initial metal concentrations mgrl b Final metal concentrations mgrl cFinal pH d Uptake capacity meqrg of Sh2 eUptake capacity of Sh sorbent Fig 3 Metal removal kinetics in ternary system on Sh2 sorbent Initial concentrations mgrl 85 Ni 1 90 Cu 2 98 Zn 3 pH s5 pH s6 2 if The metal uptake capacities in column tests were calculated at breakthrough point CrC const and 0 are given in Table 4 as well as the coefficients of the column uptake efficiencyKfor single compo nent solutions which means the ratio of column and batch uptake capacities The column uptake capacities for the ternary com ponent system at described conditions were less for nickel and zinc and some greater for copper than those for the single component solutions However the total capacity for these three metals exceeded the greatest capacity than that of a single metal The greater column efficiency coefficient of zinc in com Fig 4 Single component breakthrough curves for Sh2 column Initial concentrations mgrl 18 7 Ni 1 20 0 Cu 2 4 18 6 Zn 3 Flow rate 2 1 2 3 6 mlrmin 4 pH s5 fi Background electrolyte 0 01 M NaClO 4 T Vengris et al rApplied Clay Science 18 2001 183 190188 Fig 5 Ternary component breakthrough curves for Sh2 sorbent column Initial concentrationsmgrl 22 6 Ni1 30 2 Cu 2 25 6 Zn3 s2 mlrmin pH s5 Background elec fi trolyte 0 01 M NaClO 4 parison with that of nickel or copper Table 4 might show a more effective use of sorbent uptake capacity in column conditions It could be determined by zinc sorption on ion exchange sites located near the surface since they are most easily accessible Be sides that sorbed metal also can be more easily dislodged from surface sites rather than from sor bent pores when in the solution presents other metal ions with stronger binding affinity Fig 5 The uptake capacity of metals tested in column experiments could be arranged in the order Ni Zn Cu and differed from that established in batch uptake Probably part of the precipitated copper hydroxide penetrated through the column bed there fore copper uptake became smaller Desorption of metals was investigated using the metal laden sorbents in the same column by water Table 4 Metal uptake capacities meqrgand column efficiency coeffi cientsKin column tests for single and ternary component solutions a MetalsSingleTernaryK componentcomponent Ni1 150 440 42 Cu0 750 800 25 Zn0 920 460 44 aKsU rU where U and Uare uptake capacities for cbcb single component solutions in column and batch tests respec tively Fig 6 Zn 1 and Ni 2 ions column desorption kinetics for Sh2 sorbent and exit pH values3 Zn 4 Ni s2 mlrmin f pH s5 i with pH 5 The kinetics of nickel and zinc desorption is shown in Fig 6 After pass of 2 4 l of desorbing water the total zinc concentration in the exit volume was 0 04 mgrl thus 0 096 mg Zn was washed out Since 61 9 mg of zinc was presorbed the desorption degree amounted to 0 16 Nickel desorption began after several hours of water flow and in 12 h a constant desorption rate was established In 20 h of desorption test only 0 14 mg of nickel was released resulting in 0 19 of the Fig 7 Sorption isotherms 1 3 and equilibrium pH values 4 6 of single component Sh2 system Ni 1 4 Cu 2 5 Zn 3 6 pH s5 i T Vengris et al rApplied Clay Science 18 2001 183 190189 Fig 8 Sorption isotherms of ternary component Sh2 system 1 Ni 2 Cu 3 Zn pH s5 i presorbed amount 75 mg Thus water with pH 5 washed out negligible amounts of nickel and zinc A pH increase of exit solutions was probably related to the proton consumption in the regeneration process AfterpassingdesorbingwaterwithpHs5 through the copper laden column bed practically no copper ions were detected in the exit solution Figs 7 and 8 depict the sorption isotherms of single and ternary component solutions The shape of isotherm curves corresponded to an H type Ahigh affinityBcurve according to Giles classification systemGiles et al 1960 This was a case of a Langmuir isotherm when a solute had a high surface affinity and in dilute solutions it was completely Fig 9 Linearized form of Langmuir isotherms for the single component Sh2 system 1 Ni 2 Cu 3 Zn Fig 10 Linearized form of Langmuir isotherms for the ternary component Sh2 system 1 Ni 2 Cu 3 Zn sorbed causing the vertical initial part of the isotherm curve It could be due to ion exchange when a weakly bound ion for instance sodium was substi tuted Such a process would result in the increase of the pH value Langmuir isotherm constants were calculated from a linearized form of the Langmuir equation C11 e sqC e qa ba emm where aand b are Langmuir constants indicative m of maximum sorption capacity and the measure of sorption energy respectively Experimental data fit ted the linearized equation reasonably well Figs 9 and 10 testifying to a monolayer sorption process Langmuir constants and correlation coefficients are given in Table 5 Maximum sorption capacities for nic