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  Abstract The removal of heavy metals from wastewater by using activated alumina or chitosan as adsorbers wasevaluated. Cd(II) and Cr(III) were employed as models of the behaviour of divalent and trivalent metal ions. The ad-sorption of Cd(II) and Cr(III) onto the adsorbers evaluatedwas studied as a function of pH, time, amount of adsorber,concentration of metal ions and sample volume. A 0.4-gportion of activated alumina can retain 0.6mg Cr(III) and0.2mg Cd(II) from 20mL sample adjusted at pH4 andstirred for 30min. It is therefore possible to totally decon- taminate 500mL of a waste containing 5mgL  –1 Cd(II) and Cr(III) with 10g alumina. On the other hand, 0.4g chi-tosan can totally decontaminate 20mL of a pH5 solutioncontaining up to 50mgL  –1 Cd(II) and Cr(III). A 99.2±0.1% retention of Cd(II) and 83±1% retention of Cr(III)was obtained from 500mL of a laboratory waste. Theaforementioned strategies were applied for the minimiza-tion of analytical chemistry teaching laboratories andatomic spectrometry laboratory wastes. On comparingboth adsorbers it can be concluded that chitosan is morepreferable than alumina due to the reduced price of chi-tosan and the absence of side-pollution effects. Keywords Metal ion removal · Chitosan · Alumina ·Cadmium · Chromium Introduction Metal oxides can quantitatively adsorb heavy metals fromtheir aqueous solutions and are thus employed in metalpreconcentration [1, 2, 3] and metal removal [4].In order to facilitate wastewater remediation and to re-duce the amount of dangerous wastes containing metalions, different types of sorbents have been proposed [5],like clays [6], zeolites [7], seaweed [8], dead biomass [9]and solid wastes like coal fly ashes [10], bone charcoal[11] and chitosan.Chitosan is the deacylated product of chitin, a polysac-charide consisting predominantly of unbranched chains of  β  -(1 → 4)-2-acetamido-2-deoxy- D -glucose. Chitosan is found naturally in fungi and arthropods in which it is the maincomponent of the exoskeleton, it can be prepared fromfishery wastes and is obtained from shrimp, lobster, or crab shell and from cuttlebone [12].Previous studies have demonstrated the ability of chi-tosan to act as an adsorber of metal ions in aqueous solu-tions [13] with evidence that sorption occurs through theamine functional groups [14]. On the other hand, chitosanimpregnated with microemulsions [15], chitosan mem-branes [16], crosslinked chitosan beads [17], chitosan al-ginate encapsulated  Escherichia coli [18] and chitosanflakes [19, 20, 21] have been employed for metal ion re-moval.In the present study, we evaluate the use of chitosanflakes for the removal of heavy metal ions in terms of theeffect of time, nature and amount of chitosan, pH of sam-ples, concentration of metal ions and sample volume.Cd(II) and Cr(III) were employed as models of the behav-iour of divalent and trivalent ions and comparative studieson the use of activated alumina were developed. Finally,in the best conditions established, we evaluated the use of both alumina and chitosan for the reduction of laboratorywastes obtained from qualitative analysis and atomicspectrometry laboratories. Experimental ApparatusAtomic absorption measurements for Cd and Cr were made usinga Shimadzu, AA660 V-3 (Kumamoto, Japan) flame atomic ab-sorption spectrometer equipped with hollow cathode lamps of Cdand Cr Photron (Victoria, Australia) at conditions indicated inTable1.Laboratory wastes, both untreated and treated by alumina andchitosan, were analysed by ICP-MS using a Perkin–Elmer model M. LuisaCervera · M. CarmenArnal ·Miguel delaGuardia Removal of heavy metals by using adsorption on alumina or chitosan Anal Bioanal Chem (2003) 375:820–825DOI 10.1007/s00216-003-1796-2Received: 27 September 2002 / Revised: 19 December 2002 / Accepted: 20 December 2002 / Published online: 22 February 2003 ORIGINAL PAPER M. LuisaCervera ( ✉ ) · M. CarmenArnal · M. delaGuardiaDepartment of Analytical Chemistry, Research Building, University of Valencia, 50 Dr Moliner St. 46100 Burjassot, Valencia, Spaine-mail:©Springer-Verlag 2003  Elan5000 Spectrometer (Connecticut, USA) in the TotalQuantmode and an ICP-OES using a Perkin–Elmer model Optima 3200RL (Connecticut, USA).A Crison2000 pH meter (Barcelona, Spain), equipped with aglass electrode and an AgCl/Ag reference electrode, was used for measuring the pH of solutions.A Selecta (Barcelona, Spain) oscillant shaker Vibromatic, withoscillant regulation from 100 to 700oscillationsmin  –1 , a 8-mm os-cillation size and 60-min time programmer and a Jenway1000(Felsted, England) magnetic stirrer were employed for stirring thewaste samples in the presence of the solid sorbent. An HeraeusSepatech centrifuge was used for phase separations after sampletreatment.ReagentsLow (  M  r  ≈ 150,000), medium (  M  r  ≈ 400,000) and high molecular  weight (  M  r  ≈ 2,000,000) chitosan (2-amino-2-deoxy-(1 → 4)- β  - D -glu- copyranan; poly(1,4- β  - D -glucopyranosamine) were obtained fromFluka (Buchs, Swiss) and low-cost chitosan flakes from Guinama(Valencia, Spain). All these compounds were employed withoutany pre-treatment.Aluminium oxide, acid 504C type from Fluka was activated byheating at 500°C for 12h before being used.Standard solution of Cd(II) containing 1,000mgL  –1 was pre-pared by dissolving 1.000g of cadmium metal (reagent grade fromMerck, Darmstadt, Germany) in 20mL 5M HCl, adding 2drops of concentrated HNO 3 and diluting to 1L with deionized water. Stan-dard solution of Cr(III) was prepared by dissolving 7.6960gCr(NO 3 ) 3 ·9H 2 O (reagent grade from Merck, Darmstadt, Germany)in 250mL deionized water and diluting to 1L adding HNO 3 to ob-tain a final concentration of 2% (v/v); this was checked against atitrisol standard solution from Merck (Darmstadt, Germany).Analytical reagent-grade water with a resistivity of 18.2M Ω cmwas obtained with a Milli-Q water system from Millipore Inc.(Paris, France) and all additional reagents employed were of ana-lytical grade.Solutions were stored into polyethylene flasks and all polyeth-ylene and glassware material was soaked in 10% (v/v) HNO 3 for 12h and rinsed three times with deionized water before use.Experimental procedureWaste solution (500mL) was adjusted to pH4 and 5 with NH 4 OHand HNO 3 and then 10g activated alumina or chitosan was added,respectively. The system was shaken for 30min and then bothphases were separated by filtration. The metal content of the fil-trate was determined by atomic spectrometry. Results and discussion Cd and Cr sorption on activated alumina The effect of several experimental parameters on the metal retention capacity of alumina, such as pH, alumina activa-tion grade, alumina mass, the concentration of Cd(II) andCr(III), stirring system and the volume of sample were in-vestigated in order to establish the best conditions for metal removal. The initial conditions of this study were20mL of a solution containing 5mgL  –1 Cd(II) and Cr(III)at pH4 and 0.1g alumina. The mixture was shaken for 30min.  Effect of activation process Preliminary studies on the effect of activation of aluminawere carried out using alumina activated at 500°C over-night, untreated alumina and an alumina which was storedovernight with 2mL water; as can be seen in Table2 theactivation process drastically affects the sorption capacityof alumina and it is necessary to thermally treat the sor-bent before use and to remove water after operation in or-der to avoid deactivation processes. Additionally it can benoticed that alumina retains better Cr(III) than Cd(II).  Effect of pH  At mgL  –1 levels, Cd 2+ precipitates at around pH9 andCr  3+ precipitates at a pH near to 5; the latter species is pre-sent in low-acidity media as CrOH 2+ and Cr(OH) 2+ . 821 Table1 Instrumental parameters used in measures obtained withflame atomic absorption spectrometer AA 660 V-3 ShimadzuCdCr Wavelength (nm) 228.8 357.9Lamp current (mA) 8 10C 2 H 2 flow (Lmin  –1 ) 2 2.6Air flow (Lmin  –1 ) 8 8Bandpass (nm) 0.25 0.25Burner height (cm) 0.6 0.7Standard interval (mgL  –1 ) 0–2.0 0–2.5Background corrector D2 –  Table2 Effect of the activation of alumina on the retentionprocess of Cd(II) and Cr(III) a ActivatedUntreatedDeactivatedCd(II) 59±5 21±5 12±5Cr(III) 97.5±0.6 65±3 64±3 a Experimental conditions: 20mL solution of 5mgL  –1 Cd(II) andCr(III) treated at pH4 with 0.1g alumina during 30min. Data re-ported correspond to the retention percentage of consideredions±the standard deviation of 3independent assays Fig.1 Effect of pH on the retention of Cd(II) and Cr(III) on acti-vated alumina. Experimental conditions: 20mL 5mgl  –1 Cd(II) andCr(III) treated 30min with 0.1g alumina  In order to evaluate the effect of sample pH on the ad-sorption of Cd(II) and Cr(III) by alumina, a pH rangefrom 3 to 5 was assayed and the results are summarized inFig.1. As can be seen, the retention of metal ions in-creases on increasing the pH. However, in order to avoidthe influence of hydroxide precipitation and since non-quantitative removal data for Cd were found, pH4 was se-lected, at which Cr(III) was partially retained at a level of 80.3±0.8% and Cd(II) at 27±9%.  Effect of the alumina mass The increase of the alumina mass from 0.1g to 0.4g dra-matically increases the retention of Cd(II) from 40% up to100%; the affect on the retention of Cr(III) is less impres-sive (see Fig.2).  Effect of metal ion concentrations Figure3 depicts the effect of increasing concentrations of Cd(II) and Cr(III) on the retention of these elements on 0.4g activated alumina and, as can be seen, under the afore -mentioned conditions 0.6mg Cr(III) and 0.2mg Cd(II)can be retained quantitatively. Study of different shaking systems In order to provide a good contact between the metal ionpresent in aqueous wastes and the sorbent, we evaluated the use of different shaking systems: i) a vibrational shaker, ii) a magnetic stirrer, and iii) air bubbling. A 75-mLaliquot of a solution of 5mgL  –1 Cd(II) and Cr(III) wastreated with 1.5g activated alumina for 30min. Cr(III)was quantitatively retained by using all the stirring sys-tems and Cd(II) was retained at a level of 96.1±0.3%,96±1% and 99±1% by using vibrational, magnetic stir-ring, and air bubbling, respectively; thus, the shaking sys-tem is not at all a critical parameter for metal adsorptionon activated alumina, and it is thus being possible to adaptthe treatment procedure to the available facilities and con-venience of the laboratory.  Effect of the sample volume Waste samples (500mL) were treated with 10g activatedalumina in order to verify the possibility of using theaforementioned procedure for the reduction of waste vol-umes in an applications laboratory scale. For Cd(II) wefound a retention percentage of 95.1±0.1% using a mag-netic stirrer and 93±2% by using air bubbling; Cr(III) wasquantitatively retained in all cases. Treatment of laboratory wastes A 500-mL sample of qualitative analysis teaching labo- ratory waste, containing 16mgL  –1 Cr, 866mgL  –1 Cu, 1,152mg L  –1 Hg, 193mgL  –1 Mn and 208mgL  –1 Zn, wastreated with 10g alumina and, in this complex and highlyconcentrated medium an average recovery of 53±2% for Cr was found; the rest of elements were partially retainedat levels of 18±1% for Cu, 2±1% for Hg, 1±1% Mn and11±2% Zn, evidencing that 106mg of metal ions can beremoved with 10g alumina (10.6mgg  –1 alumina).On the other hand, the treatment of an atomic spec-trometry laboratory waste, containing several elements at µ gL  –1 concentration levels (see Table3) was decontami-nated to a large extent by alumina with only Ag and Babeing recovered at a low percentages.Cd and Cr sorption on chitosanA 20-mL aliquot of a solution containing 5mgL  –1 Cd(II)and Cr(III), adjusted to pH5 with HNO 3 and NH 4 OH, wastreated with 0.1g chitosan shaking mechanically for 5minbefore phase separation through filtration.The effect of pH, shaking time, molecular weight and particle size of chitosan, chitosan mass, shaking system and volume and metal concentration of treated wastes, wereevaluated in order to find the best decontamination condi-tions. Actual laboratory waste samples were treated anddata found are discussed critically. 822 Fig.2 Effect of alumina mass on the retention of Cd(II) andCr(III). Experimental conditions: 20mL 5mgL  –1 Cd(II) andCr(III) treated at pH4 for 30min with different activated mass of alumina Fig.3 Study of Cd(II) and Cr(III) retention capacity of 0.4g acti-vated alumina. Experimental conditions: 20mL aqueous waste ad- justed at pH4 and stirred for 30min with alumina   Effect of pH  Figure4 shows the influence of the waste pH, in the range3–9, on the retention of Cd(II) and Cr(III) by medium mo-lecular weight chitosan. As can be seen, the increase of pH also increases the retention percentage of both studiedelements. However, it must be mentioned that the use of pH values higher than 5 dramatically modifies the mecha-nism of metal removal from simple adsorption to hydrox-ide precipitation and because of that a pH of 5, for whichnon-quantitative removal data were found, was selectedfor the additional studies.  Effect of shaking time On increasing the contact time between metal wastes andchitosan we found an increase in the retention percentagesof both elements studied up to a maximum recovery of 77% for Cd(II) and 75% for Cr(III) at 30min; the use of ashaking times of 60 or 90min practically does not im-prove the metal retention by chitosan (see Fig.5).  Effect of molecular weight and particle size of chitosan In order to verify the influence of the nature and size of the sorbent on the retention of Cd(II) and Cr(III), threedifferent chitosan product, from Fluka (Buch, Swiss) bothpreviously crushed in a water-refrigerated mill and usedin flakes without further modification, were assayed.Table4 summarizes data found in these experimentsand it can be seen that medium molecular weight chitosanprovides the best adsorption capacity for both Cd(II) andCr(III) with the additional advantage of not requiring anysize reduction treatment before use. The maximum aver-age retentions of Cd(II), 66%, and Cr(III), 83%, corre-spond to the use of 400,000Da chitosan, employed inflakes without a further reduction of the particle size andare comparable with those found by using 2,000,000Da chitosan in a fine powder. Thus, medium molecular weight chitosan can be recommended for metal removal.Additional experiments, carried out using low-pricedchitosan obtained from the Spanish market, evidenced nodifferences with those found with 400,000Da chitosan. Itmust be noticed that this product is directly produced as afine powder and probably is a mixture of medium andhigh molecular weight chitosan. So, the product obtainedfrom Guinama can be recommended for application stud-ies.  Effect of chitosan mass The increase of the chitosan mass employed for treating20mL of a 5mgL  –1 solution of Cd(II) and Cr(III) also in-creases the retention efficiency; 0.4g Cd(II) is retained at 823 Table3 Metal removal from an atomic spectrometry laboratorywaste by using alumina and chitosan a ElementInitial Retention percentageconcentration ( µ gL  –1 )AluminaChitosanAg 32 32±2 97.0±0.2Ba 271.7 50±4 – Bi 1.5 91±3 88.3±0.7Ce 2.7 98.6±0.2 98.5±0.4Cd 107.9 99±1 99.75±0.04Co 77.65 97.1±1.5 84.8±0.5Cr 545 99.5±0.1 97.4±0.1Cu 206.3 98.4±0.3 95.3±0.3Fe 2092 100 100Hg 11,320 63.4±1.5 81±1In 89.5 99.6±0.3 99.4±0.2La 1.5 97.0±1.1 97.2±0.7Mn 110.6 84.5±1.8 87.2±0.4Ni 164.1 100 100Pb 232.2 99.3±0.1 93.4±0.1Sb 1.2 98.3±0.8 92±2Sn 13,320 96.4±0.9 95.8±0.4Te 0.6 100 98±4U 1.8 96.3±0.6 87±1Zn 755 100 100 a Experimental conditions: 500mL waste were treated with 10g ad-sorber at pH5 for chitosan and pH4 for alumina, following theprocedure described in the text Fig.5 Effect of the shaking time on the retention of Cd(II) andCr(III) by chitosan. Experimental conditions: 20mL 5mgL  –1 solu-tion with pH5 treated with 0.1g medium molecular weight chi-tosan Fig.4 Effect of pH on the retention percentage of Cd(II) andCr(III) using medium molecular weight chitosan. Experimentalconditions: 20mL 5mgL  –1 solutions treated for 5min with 0.1gchitosan
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