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Wilolud Journals, 2012 http://www.wiloludjournal.com ` Printed in Nigeria doi:10.5707/cjwasp.2012.3.1.17.20

ADSORPTION OF CADMIUM AND CHROMIUM USING ACTIVATEDCARBON DERIVED FROM CARICA

PAPAYA SEED.

Ayeni K. E.

Department of SLT, Federal Polytechnic Offa, P.M. B 420 Offa, Kwara State, Nigeria.

Email: kikeyinka@yahoo.com

ABSTRACT

Heavy metals such as Cadmium and Chromium are toxic and may be found in both surface and

underground water. Carica papaya seed which is an agricultural wastes comprising mostly cellulose

materials was used for the removal of these toxic metals from aqueous solutions. Activated carbons were

prepared from Carica papaya seeds with particle sizes ranging from 355 835 um. 0.10M H3PO4 andZnCl2

were each used for chemical activation at 3 minutes residence time and at 7500C. This was after carbonizing

the source material at 5000C and also residence time of 5 minutes. The adsorption ofcadmium and

chromium from aqueous solution onto zncl2 and H3PO4activated carbons was studied and assessed for the

possibility of using thesource materials for the removal of heavy metals from aqueous solution. Theeffect of

varying the particle size of the activated carbons and the type ofactivating agents on the adsorption capacity

were well as for the carbonized or raw materials. Little adsorption took place when raw material was used

for theadsorption of the metals. The results indicated that the activity of 0.10M H3PO4and 0.10M ZnCl2

activated carbons with particle size of less than 355um gave the highest adsorption capacities; with ZnCl2

activatedcarbons exhibiting better adsorption capability than H3PO4 activated carbons. This work has shown

that Carica papaya seed can be used to remove these two metals from aqueous solution.

KEYWORDS: Activated carbon, H3PO4activated carbons, ZnCl2 activated carbons

INTRODUCTION

Since some heavy metals such as lead, cadmium,chromium, zinc, copper etc are toxic and may be found in both

surface andunderground water. A wide variety of Agricultural by product and agricultural wastes comprising mostly

cellulose materials were tried by different works forthe removal of toxic metals from aqueous solutions. This include

cassava fibre,(1) Biomass of fungi and yeast (2), Horse shoe sea crab shell (3) rice husk (4) saw dust (5) etc However, a

comprehensive list of naturally occurring adsorbents for removal ofdyes and heavy metals can be obtained from (6)

However factors such as physical and chemical characteristics of the adsorbate e.g. molecular size, molecular

polarity, chemical composition, residence time of the system, temperature and surface area of the adsorbent e.t.c.

affects adsorption ofcations from aqueous solution (7) The purpose of this work is to evaluate the adsorption capacity

of activated carbon from Carica papayaseed on some toxic metals, that is, activated carbon will be prepared from

Carica papaya seed and will be used to check the removal or adsorption of cadmiumand Chromium ions from

aqueous solution. It is also the intention of this work to compare and establish the ability of H3PO4 and ZnCl2as

activating agents for the purpose of producing activated carbon from Carica papaya seeds.

EXPERIMENTAL

Materials

Carica papaya seed were collected from different markets in Zariaand Kano, Nigeria. They were washed, air dried,

grinded and sieved into particle sizes of less than 355, 425 and 834m. All other reagents are of analytical grade were

used without further purification.

Ayeni K. E: Continental J. Water, Air and Soil Pollution 3 (1): 17 20, 2012

Procedure for Carbonization and Activation.

The sample were carbonized and activated by the two steps method (8). 2.00g of raw carica papaya seed sample was

weighed into reweighed crucibles and placed in a carbolite furnance at 5000Cfor 3 minutes to carbonize it.

Adsorption of Calcium and Chrominum using ActivatedCarbon Derived from Carica papaya Seed

500OC, 3 minutes

Raw Carica papaya seeds C(s)+ CO2 (CARBONIZATION)△AA, 750OC, 5 minutes

Carbonized- Carica papayaAC + CO2 (ACTIVATION)△Where AA represents Activating Agent and AC represents Activated Carbon. The above processes were repeated

until a substantial amount was obtained. It was allowed to cool in H 2O and allowed to dry at room temperature and

stored in dry polythene bags.

Preparation of 0.10M solution of H3P04.

0.10M of H3P04 was prepared by diluting 1.70cm3 of H3P04 in 250cm3volumetric flask with distilled water.

Preparation of 0.10M ZnCl2

0.10M of ZnCl2 was prepared by dissolving 3.40g of salt in 250cm3 volumetric flasks with distilled H2O.

Preparation of standard concentration of Cd2+and Cr6+.

1000ppm of Cr6+ was prepared by dissolving, 1.867g of K2Cr2O4 in 250cm3distilled water and it was later diluted to

500cm3 in a 500cm3volumetric flask. 000ppm Cd2+ was prepared by dissolving 1.0516g ofCd (NO3)2 in about

250cm3 distilled water andit was later diluted to 500cm3 in a volumetric flask.

Test for Cd2+ and Cr6+adsorption

1.00g each of the raw materials, the carbonized andthe activated samples was weighed into 250cm3 conical flask.

50cm3of the 1000ppm stock solution of Cd2+ and Cr6+ was added. Each mixture was shaken thoroughly with a

Griffin model electric shaker for an hour to attain equilibrium. Thereafter, the different supernatant were filteredand

the concentration remaining in the filtrate were determined using JENWAYS Atomic Absorption Spectrophotometer

RESULTS AND DISCUSSION

Table1: The percentage of Cd2+ adsorbed onto Carica papaya seeds activated with ZnCl2

Initial concentration of Cd2+ (ppm)Sss

Final concentration of Cd2+ (ppm)

Amount of Cd2+

adsorbed (ppm)% of Cd2+

adsorbed Particle size (um)

1000 80.00 920 92.00 < 3551000 390.00 610 61.00 4251000 548.40 451.60 45.16 835

Table 2: The percentage of Cd2+ adsorbed onto Carica papaya seeds activated with H3PO4

Initial concentration of Cd2+ (ppm)

Final concentration of Cd2+ (ppm)

Amount of Cd2+

adsorbed (ppm)% of Cd2+

adsorbed Particle size (um)

1000 147.10 852.90 85.29 < 3551000 358.40 641.60 64.16 425

1000 467.70 532.30 53.32 835Ayeni K. E: Continental J. Water, Air and Soil Pollution 3 (1): 17 20, 2012

Table 3: The percentage of Cd6+ adsorbed onto Carica papaya seeds activated with ZnCl2

Initial concentration of Cr6+ (ppm)

Final concentration of Cr6+ (ppm)

Amount of Cr6+

adsorbed (ppm)% of Cr6+ adsorbed Particle size (um)

1000 483.40 516.60 51.66 < 3551000 638.90 361.10 36.11 4251000 713.20 286.80 28.68 835

Table 4: The percentage of Cr6+ adsorbed onto Carica papaya seeds activated with H3PO4

Initial concentration of Cr6+ (ppm)

Final concentration of Cr6+ (ppm)

Amount of Cr6+

adsorbed (ppm)% of Cr6+

adsorbedParticle size (um)

1000 389.80 510.20 71.02 < 3551000 436.20 361.10 36.11 4251000 553.10 286.80 28.68 835

Table 1 and 2 show that the percentage of Cd2+adsorbed onto Carica papaya seeds carbon activated with ZnCl2and

H3PO4 respectively. The result shows that ZnCl2has better activating activity than H3PO4. The adsorbedof Cd2+ in the

aqueous solution increases with decreases in particle size. This may be explained as a result of increase in surface

area with decrease in particle size producing a large surface area for adsorbed ofcadmium in aqueous solution. This

is in agreement with studies by {8,9}.More so similar observation was also observed in the case of Cr6+adsorption from

aqueous solution using H3PO4 and ZnCl2activated Carica papaya seeds as shown on Table 3 and 6, but in this case

the result shows that H3PO4 has better activating activity than ZnCl2.

Table 5: The percentage of Cd2+ adsorbed onto carbonized Carica papaya seeds

Initial concentration of Cd2+ (ppm)

Final concentration of Cd2+ (ppm)

Amount of Cd2+

adsorbed (ppm)% of Cd2+ adsorbed Particle size (um)

1000 732,70 267.30 26.73 <3551000 848.90 151.10 15.11 4291000 887.40 112.60 11.26 835

Table 6: The percentage of Cd2+ adsorbed onto raw Carica papaya seeds

Initial concentration of Cd2+ (ppm)

Final concentration of Cd2+ (ppm)

Amount of Cd2+

adsorbed (ppm)% of Cd2+ adsorbed Particle size (um)

1000 917.70 82.30 8.32 <3551000 943.20 56.80 5.68 4251000 969.90 30.10 3.01 835

Table 7: The percentage of Cr6+ adsorbed onto carbonized Carica papaya seeds

Initial concentration of Cr6+ (ppm)

Final concentration of Cr6+ (ppm)

Amount of Cr6+

adsorbed (ppm)% of Cr6+ adsorbed Particle size (um)

1000 887.90 112.10 11.21 <3551000 936.20 638.00 6.38 4251000 967.80 32.20 3.22 835

Ayeni K. E: Continental J. Water, Air and Soil Pollution 3 (1): 17 20, 2012

Table 8: The percentage of Cr6+ adsorbed onto carbonized Carica papaya seed

Initial concentration of Cr6+ (ppm)

Final concentration of Cr6+ (ppm)

Amount of Cr6+

adsorbed (ppm)% of Cr6+ adsorbed Particle size (um)

1000 913.90 86.10 8.61 <3551000 956.70 43.30 4.33 4251000 972.40 27.60 2.76 835

Table 5,6,7,8 show control experiments. The carbonized samples and the raw forms of various particle sizes were

used for the adsorbed or raw samples with similar particle sizes could exhibit similar to theactivated samples. Table

5,6,7,8, show low affinities for metals uptakes in aqueous solution when compared to that of carbonized and

activated ones. Theraw sample has no sufficient exposed structure as compared to the carbonized ones because

molecular architecture of the surface has been altered during carbonization and subsequent activation.

CONCLUSION

Carbon prepared from Carica papaya seed can be a good source of raw material toward utilization as a cheap and

alternative source of commercial carbon that can be used for the recycling of heavy metals waste water. The

activated samples treated with H3PO4 andZnCl2 gave higher adsorption of Cd2+ and Cr6+when compared to the

carbonized and raw samples.

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Received for Publication: 04/02/2012

Accepted for Publication: 08/04/2012

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