Wood sawdust and wood originate materials as adsorbents for heavy metal ions

Holz Roh Werkst (2004) 62:69–73DOI 10.1007/s00107-003-0449-7

O R I G I N A L A R B E I T E N · O R I G I N A L S

M. �ciban · M. KlaÐnja

Wood sawdust and wood originate materials as adsorbentsfor heavy metal ions

Published online: 24 January 2004� Springer-Verlag 2004

Abstract The abilities of different types of wood sawdustand wood originate materials for removing some toxicheavy metal ions from water were investigated. Sawdustof poplar, willow, fir, oak and black locust wood, pulpand Kraft lignin were used as adsorbents. The effects ofcontact time, pH, metal concentration and sawdust par-ticle size on the removal of Cu(II) ions by poplar sawdusthave been studied. Leaching from these adsorbents intowater during adsorption was also investigated.

S�gemehl, Zellstoff und Lignin als Absorbentienf�r SchwermetallionenZusammenfassung Das Potenzial von Holzmehl ausverschiedenen Holzarten zum Entfernen von toxischenSchwermetallionen aus w�ssrigen L�sungen wurde un-tersucht. Neben Holzmehl von Pappel, Weide, Tanne,Eiche und Robinie wurden auch Zellstoff und Kraft-Lignin als Adsorbentien eingesetzt. Untersucht wurde derEinfluss der Behandlungszeit, des pH, der Metallkonzen-tration und der Partikelgr�ße auf das Entfernen vonCu(II)-Ionen durch Pappel-S�gemehl. Das teilweise Auf-l�sen dieser Adsorbentien in Wasser w�hrend der Ad-sorption wurde ebenfalls untersucht.

1 Introduction

Heavy metals get into natural waters most frequently withdifferent industry wastewaters. Heavy metals are danger-ous for living organisms even in very small quantities. Forthis reason, it is necessary to remove them from waterand/or wastewater.

Adsorption is one of ways for removal of heavy metalsfrom water. When natural organic materials are used asadsorbents, the process is called biosorption. Complexorganic materials, organic macromolecules and decayingbiomass of microorganisms can be used as biosorbents.Biosorbents are, in most cases, waste organic materials.Lignocellulosic waste materials are suitable adsorbentsfor the removal of heavy metal ions from water orwastewater as they are cheap and the further treatment issimple and economic (for example incineration). Woodbark (Deshkar et al. 1990, Aoyama et al. 1993, Alves etal. 1993, Seki et al. 1997, Al-Asheh and Duvnjak 1997),tree leaves (Saito et al. 1992, Aoyama et al. 2000), walnutor nut wastes (Orhan and Bujukgungor 1993) and otherlignocellulosic materials were investigated as adsorbentsof heavy metal ions from water solutions. However, woodsawdust was rarely investigated for this purposes (Bryantet al. 1992, Zarraa 1995, Ajmal et al. 1998).

The aim of our work was to investigate the removal ofsome heavy metals (Cu, Zn, Cd, Ni) from aqueoussolutions using different kinds of wood sawdust (poplar,willow, oak, black locust and fir) and wood originatematerials (pulp and Kraft lignin). The effects of contacttime, pH and particle size have been studied.

2 Materials and methods

2.1 Materials

The stock solution of heavy metals was prepared byadding 0.25 mol/l of metal salt solution (CuSO4,Zn(CH3COO)2, NiCl2, Cd(CH3COO)2) to distillate water.

The sawdust of poplar, willow, oak, black locust andfir was sieved with sieves of 1.0 and 0.5 mm and the 0.5–1.0 mm fraction used for adsorption experiments, exceptwhen the effect of particle size on adsorption efficiencywas investigated. Pulp was obtained by pulping process ofpoplar (70%) and beech (30%). The middle fiber length ofpulp was 1 mm. Kraft lignin was obtained from blackliquor in the form of black-brown powder.

M. �ciban ()) · M. KlaÐnjaDepartment of Biotechnology and Pharmaceutical Engineering,Faculty of Technology,University of Novi Sad,Bul. Cara Lazara 1, 21000 Novi Sad, Yugoslaviae-mail: msciban@uns.ns.ac.yuTel.: +38-12-1350122/366Fax: +38-12-1450413

2.2 Batch adsorption studies

Batch adsorption experiments were carried out by shaking5 g/l of sawdust with model water of desired heavy metalions concentrations at certain pH. The pH was adjusted tothe desired value with 0.5 mol/l CH3COOH or 3 mol/lNH4OH solution. The suspension was shaken at roomtemperature for certain time. The adsorbent was thenfiltered off and residual heavy metal ions in the filtratewere determined. COD and tannins were also determinedin filtered water. Experiments were duplicated and resultsaveraged.

To quantify the adsorption capacity of investigatedadsorbents for the removal of heavy metal ions fromwater, the Langmuir (q=qm KL C/(1+KL C)) and Fre-undlich (q=KF C1/n) equations were used. A computersimulation technique has been applied to fit these equa-tions for the adsorption data.

2.3 Methods of analysis

Dry matter and wood extractives in cold water weredeterminated according to Stevanovic-Janezic and Bu-janovic (1998). Adsorbents surface area was analyzed bylow temperature nitrogen adsorption (Micrometrics,ASAP 2000).

The concentration of heavy metal ions in water wasdeterminated by potentiometric stripping analysis (Mar-janovic and Jankovits 1983) by ELU M1 analyser. CODwere determinated according to Standard methods (1998)and tannins according to Riberean-Gajon et al. (1972).

3 Results and discussion

Some characteristics of investigated materials, relevant toadsorption, were determined. The results obtained arepresented in Table 1. As shown in this table, with theexception of dry mater content, the investigated adsor-bents are mutually different. Their surface areas is smallerin comparison with usual activated carbons.

Previous to determination of ability of wood sawdust,pulp and Kraft lignin to adsorb different heavy metal ions,the appropriate conditions for the adsorption were inves-tigated. First, optimum contact time and pH value for

each heavy metal were determined. In this experiment thepoplar wood sawdust was applied as adsorbent.

The contact time of poplar sawdust and model waterwas varied to determine the optimal contact time for theexperiments. In this case, the initial pH in model waterwas 4 and initial concentration of heavy metal ions wereabout 0.8 mmol/l. The results are presented in Fig. 1.

On the basis of the obtained results, 2 h were chosenfor zinc and cadmium, and 3 h for copper and nickel ionsas the sufficient contact time for further trials. Similardinamic curve was also obtained for the adsorption of Hgions by Hardwickia binata bark (Deshkar et al. 1990), Cdions by Populus maximowiczii bark (Aoyama et al. 1993)or Picea jezoensis bark (Seki et al. 1997), and Cu ions bysawdust of mango tree (Ajmal et al. 1998).

The pH of the aqueous solution is an importantaffecting parameter in the adsorption process. Figure 2.shows the effect of water solution pH on the adsorptionefficiency of investigated heavy metals. In these exper-iments the initial concentration of heavy metals was about0.8 mmol/l.

It was observed that the adsorption efficiency increaseswith the increase of pH, since H+ ions compete with metalcations for adsorption sites in the system at lower pHvalue. To avoid heavy metal precipitation, as optimum forcopper pH 4 was chosen for further investigations, and forzinc, nickel and cadmium pH 6.

The influence of initial copper concentration andpoplar sawdust particle size on copper ions adsorptionefficiency was also investigated. Poplar sawdust wasscreened through sieves and the following fractions were

Table 1 The characteristics ofinvestigated materialsTabelle 1 Eigenschaften deruntersuchten Materialien

Material Dry matter Cold water extractives Bulk density Surface area

(%) (%) (kg/m3) (m2/g)

Poplar sawdust 93.5 3.50 83.8 1.05Willow sawdust 93.7 0.71 111 1.67Fir sawdust 92.5 0.50 105 3.85Oak sawdust 93.3 3.92 229 1.51B.locust sawdust 93.9 2.85 207 2.01Pulp 94.5 0.24 – 0.72Kraft lignin 96.8 10.7 – 0.77

Fig. 1 Time course of heavy metal ions adsorption by poplarsawdustAbb. 1 Zeitlicher Verlauf der Adsorption von Schwermetall-Ionendurch Pappel-S�gemehl

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used in further trials: 0.1–0.25, 0.25–0.5 and 0.5–1 mm.Each of these fractions was exposed to a series of coppersolutions in concentration range 0.08–3.15 mmol/l. Fig-ure 3. shows that the amount of adsorbed copper ions bythe adsorbent increased with the increase of initial copperconcentration in the solution, and decrease of particlesize.

The data presented in Fig. 3. were used to determinethe adsorption constants in Langmuir and Freundlichadsorption equations. The adsorption constants for eachparticle size are shown in Table 2.

It is evident from the results presented in Table 2. thatthe capacity increased with the decrease of particle size,

since the surface area was larger, however the adsorptionintensity decreased. AlAsheh and Duvnjak (1997), Ajmaland collaborators (1998) obtained similar results usingpine bark and Ho and McKay (1999) using peat. Asshown by the coefficient of determination, the Langmuirequation approaches somewhat better the copper ionsadsorption from water solution by poplar sawdust, indi-cating that this could be monolayer adsorption.

Finally, the abilitiy of sawdust of different woods, pulpand Kraft lignin to adsorb different heavy metal ions wasdetermined using 0.8 mmol/l solutions of heavy metalions at chosen pH value and contact time. The efficiencyof heavy metal ions adsorption by investigated adsorbentsis presented in Table 3.

Fig. 3 Relation of equilibrium copper concentration and its uptakeby various particle size poplar sawdustAbb. 3 Beziehung zwischen der Gleichgewichtskonzentration derKupferionen und der Aufnahmemenge f�r verschiedene Partikel-gr�ßen von Pappel-S�gemehl

Fig. 2 Effect of pH on the adsorption of heavy metal ions on poplarsawdustAbb. 2 Einfluss des pH-Wertes auf die Adsorption von Schwer-metall-Ionen durch Pappel-S�gemehl

Table 2 Adsorption constants for different particle size poplar sawdustTabelle 2 Adsorptionskonstanten von Pappel-S�gemehl f�r verschiedene Partikelgr�ßen

Particlesize (mm)

Langmuir constants Freundlich constants

KL(l/mmol) qm (mmol/g) r2 KF (l/g) 1/n r2

0.10–0.25 5.38 0.051 0.996 0.020 0.15 0.9390.25–0.50 4.83 0.045 0.995 0.019 0.17 0.9340.50–1.00 4.12 0.034 0.995 0.012 0.19 0.952

Table 3 Adsorption efficiency of heavy metal ions by differentkinds of sawdust, pulp and Kraft ligninTabelle 3 Effizienz der Adsorption von Schwermetallionen durchS�gemehl, Zellstoff und Lignin

Adsorbent Adsorption efficiency (%) of

Cu(II) Zn(II) Ni(II) Cd(II)

Poplar sawdust 22.0 5.1 14.0 2.8Willow sawdust 21.6 5.9 10.2 3.5Fir sawdust 23.6 6.1 6.5 3.0Oak sawdust 32.7 24.3 – –B.locust sawdust 28.2 16.5 – –Pulp 17.1 6.0 8.2 10.0Kraft lignin 27.1 8.4 12.6 21.0

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It is apparent that the materials were considerablydiffering in the adsorption ability to the metal ions. Highadsorption ability of copper and zinc ions was found inhardwood (oak and black locust) sawdust and Kraftlignin. Softwood sawdusts and pulp appeared to be theworst adsorbents. Generally, copper ions adsorption isbetter than adsorption of other investigated ions by alladsorbents.

Unfortunately, better adsorbents (hardwood and Kraftlignin) leach some organic matters into water duringadsorption resulting in discoloration of water. Leach oforganic matters from wood and other tannin-rich mate-rials is a well known phenomenon (Lens et al. 1994;Bousher et al. 1997; Bailey et al. 1999). This is confirmedby cold water extractives content presented in Table 1.

Leaching levels of investigated adsorbents were deter-mined in further experiments. The tests were performedusing the initial copper concentration of 0.8 mmol/l in a5 g/l adsorbent suspension at desired pH. After 3 hoursthe adsorbent was separated and COD and content oftannins were determined in the filtrate. The obtainedresults are presented in Table 4.

The wash out of soluble organics was more expressedduring adsorption from hardwood sawdust. In this casethe coloring (expressed as COD) arose from extractives.Also, Kraft lignin significantly colored the water, butCOD was not very high in this water. In this case thediscoloration of water probably arose only from verysmall particles of lignin powder, and not from extractives.

Due to leaching of organic matters, hardwood sawdustand Kraft lignin are acceptable adsorbents for adsorptionof heavy metal ions from wastewaters only.

The effect of leaching of organic matters from woodsawdust on adsorption efficiency was examined in thefollowing experiment. Adsorption of copper ions wascarried out as in previous trials, with the followingadsorbents:

– untreated poplar sawdust,– poplar sawdust soaked with distillate water overnight,

filtered and without drying applied in model water and– poplar sawdust washed twice with 100 ml/g distillate

water (1 h shaking), filtered, dried at 50�C and used forexperiments.

The obtained results are presented in Table 5. It isevident from these results that the previous soakingdecreased, and radical washing increased the quantity ofadsorbed copper ions, however the changes were rathersmall. Similar results were also obtained for the adsorp-tion of Cd, Cu and Zn ions by P. jezoensis bark extractedwith various solvents (Seki et al. 1997). In fact it meansthat wood sawdust leaching does not affect the heavymetal ions adsorption by such adsorbents.

4 Conclusions

All investigated materials can be used as adsorbents forsome heavy metal ions from water or wastewater. Theycan adsorb the following metals in the indicated order(mol basis): Cu>Ni>Zn>Cd, with some exceptions. Con-tact time and optimum initial pH for the adsorption ofthese metal ions from water solutions were determined.The uptake of copper ions was enhanced with decreasingpoplar sawdust particle size. Increase of copper ionsconcentration resulted in increase of copper uptake perunit weight of poplar sawdust. The Langmuir’s equationdescribes somewhat better the system than the Fre-undlich’s one, as indicated by surface homogeneity of thisadsorbent.

Leaching of organic matters from hardwood and Kraftlignin in water during adsorption, limits the application ofthis adsorbents to wastewaters treatment only. However,the leached organic matters do not prevent the adsorptionof heavy metal ions by investigated adsorbents.

Acknowledgements The results are the part of the project no. 1775“Development of methods for identification of toxic and cancero-genic pollutants in mass-cultures and procedures of their separa-tion”, which are financially supported by Ministry of Science,Technologies and Development of the Republic of Serbia.

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