INTRODUCTION:

Heavy metals such as copper, zinc, iron, cobalt etc. are required by our body in trace quantities, but they become harmful to body when present in high doses. The heavy metalslike mercury, lead, arsenic and cadmium cause serious illness and even can cause premature death. The industrialisation process of our world has dramatically increased the quantities of heavy metal toxicity. Nowadays heavy metals are abundant in air, soil and drinking water. They are present in almost every area of modern life, right from the construction materials to cosmetics, medicines, processed foods, fuels and in personal-care products. It is very difficult for the common man to avoid this exposure. But it is possible to take steps so as to understand and minimize the serious threat through acts of prevention and treatment which will surely help to lessen their negative impact on human health.

The main natural cause for metal content in water is due to chemical weathering of minerals and soil leaching. The anthropogenic activities are associated mainly with industrial and domestic effluents, urban storm, water run-off and landfill, mining of coal and ore, atmospheric sources and the inputs from rural areas. Unlike organic pollutants, heavy metal ions do not degrade into harmless end products¹.The task of removing pollutants from water and waste water is an essential process and is becoming more important with the present increasing impact of industrial activities.

Cadmium is introduced into water from smelting, metal plating, cadmium-nickel batteries, phosphate fertilizers, mining, pigments, stabilizers, alloy industries and sewage sludge². The harmful effects of cadmium include a number of acute and chronic disorders such as itai-itai disease, renal damage, emphysema, hypertension and testicular atrophy².Cadmium also causes intoxication of liver, kidneys, brain, lungs, heart and testicles. It is found to be a carcinogen.Therefore it is essential that potable water sources must be given propertreatment to remove the heavy metal content before being used for domestic supply. There are many methods for the treatment of water and waste water. Current methods for waste water treatment include precipitation, coagulation, sedimentation, floatation, filtration, membrane processes, electrochemical techniques, biological process, chemical treatment, adsorption and ion-exchange methods. But the selection of the waste water treatment method is normally based on the concentration of wastes and the cost of treatment.Adsorption with ion-exchange resin is one of the popular methods used for the removal of heavy metals from the water and waste water^3,4.

Adsorption is a surface phenomenon. Greater the surface area per unit mass of the adsorbent greater will be the capacity of adsorption under the given conditions of temperature and pressure. Sorption involves both physical and chemical process by which one substance becomes attached to another. In sorption, both adsorption and absorption takes place simultaneously. Therefore sorption refers to the surface and bulk phenomena on solids. This study emphasises on the use of biosorbents for adsorption process. Sorption done using a biosorbent is called biosorption.

The greater sorption capacities of biological materials are due to the presence of various functional groups on the surface of biosorbents. They can easily interact with the metal ions in the solution. FT-IR absorption spectral studies reveal the presence of different surface functional groups in biosorbents. Reactive functional groups act as ligands or as ion-exchangers or as binders tothe cations present more selectively. Cation-exchange capacity of natural materials is seen to be high and is based on the origin of the biosorbent.

An adsorption isotherm describes the equilibrium of adsorption on a surface at constant temperature. Adsorption isotherms are often used as empirical models which do not make statements about the underlying mechanisms and measured variables. The most frequently used adsorption isotherms are the Freundlich and Langmuir models.

MATERIAL AND METHODS:

Biosorbent used in this study is coffee powder. The biosorbent was powdered and sieved to a fine form for the analytical work.

Stock solution ofCd(II) ionswas prepared by dissolving the required quantity of Analytical Grade salt in double-distilled water. The stock solution was further diluted withdouble-distilled water to get the desired concentration of the test solution.

Batch mode adsorption experiments

Adsorption ofCd(II) ions on coffee powder was done by Batch sorption experiment. For all adsorption tests, blank experiments were performed to check the extent of adsorption in glass flasks and membrane filters.

A series of 50 mlCd(II) ion solutions of desired concentration(30 mg/L) were taken in reaction bottles of 100 mL capacity and then mixed in ashaker-cum-water bath for about 10 minutes to attain thermal equilibrium with the bath temperature. The pH of Cd(II) ion solutions were adjusted to 3.5 using diluted nitric acid or ammonia water. About 2 g of accurately weighed coffee powder was suspended in 50 ml Cd(II) ion solution. The solutions were agitated at 70°C in a shaking incubator for an equilibrium time (~1hour) which was pre-determined. The agitation speed of the shaker was fixed to 180 strokes per minute for all the batch experiments. At the end of the agitation process, the suspensions were centrifuged at3000 rpm for about 40 seconds and the clear supernatants were collected. Determination of Cd(II) ion content in the supernatant liquid was performed using atomic absorption spectrophotometer.

The effect of several parameters such as pH, biosorbent doses, initial Cd(II) ion concentration and contact time on the adsorption process were studied. The results of these studies were used to obtain the optimum conditions for the maximum removal of Cd(II) ionsfrom aqueous solution.

Adsorption isotherm studies

The quantity of Cd(II) ions that could be taken up by a biosorbent is a function of both the concentration of Cd(II) ions in solution and the temperature. This could be explained by adsorption isotherms. The sorption experiments were carried out at optimum conditions.

RESULTS:

1. Adsorption of Cd(II) ions on coffee powder

a. Effect of pH:

Batch sorption experiments were carried out with different pH values (1 to 7) for a fixed value of temperature(70^oC), initial concentration of Cd(II) ion (30 mg/L), contact time(1 hour), biosorbent dose (2 g) and particle size of biosorbent (75 microns). The results obtained are given in Figure 1

Fig. 1. Effect of pHon the adsorption of Cd(II) ions using coffee powder

Figure 1 shows the increasein adsorption of Cd(II) ions with increase of pH, attained maximum at a pHof 3.5 and then decreased.

b. Effect of Biosorbent doses:

Batch sorption experiments were carried out with different biosorbent doses (0.25 g to3.5 g) for a fixed value of pH (3.5), temperature (70°C), contact time (1 hour), initial concentration of Cd(II) ion (30 mg/L) and particle size of biosorbent (75 microns).The results obtained are shown in Figure 2.

Fig. 2. Effect of Biosorbent doses on the adsorption of Cd(II) ions using coffee powder

Figure 2 shows the increase in adsorption of Cd(II) ions with increase of biosorbent dose and remained almost constant for further dosage. Maximum adsorption of Cd(II) ions occurred with 2 g of the biosorbent.

c. Effect of Initial concentration of Cd(II) ions:

Batch sorption experiments were carried out with different initial concentration of Cd(II) ions (5 mg/L to 60 mg/L) at a fixed value of pH (3.5), temperature (70°C), contact time (1 hour), biosorbent dose (2 g) and particle size of biosorbent (75 microns).The results obtained are given in Figure 3

Fig. 3. Effect of Initial concentration of Cd(II) ions on the adsorption of Cd(II) ions using coffee powder

Figure 3 shows the increase of adsorption with the increase in initial concentration of Cd(II) ions. Maximum adsorption occurred with 30 mg/L and remained almost constant for further increase in ionic concentration.

d. Effect of Contact time:

Batch sorption experiments were carried out with different contact timings(0 minute to 130 minutes) for a fixed value of pH (3.5), temperature (70°C),initial concentration of Cd(II) ion (30 mg/L), biosorbent dose (2 g) and particle size of biosorbent (75 microns).The results obtained are shown in Figure 4.

Fig. 4. Effect of Contact time on the adsorption of Cd(II) ions using coffee powder

The figure 4 shows the rapid uptake of Cd(II) ions observed during the initial stage of contact and the maximum removal was observed within first 50 minutes. The equilibrium time noticed was 60 minutes (1hour).

2. Adsorption isotherm

a. Langmuir model using coffee powder as biosorbent

The sorption experiments were carried out at optimum conditions using coffee powder as biosorbent to determine the equilibrium distribution of Cd(II) ions at thesolid-liquid interface.The results obtained aregiven in figure 5.

Fig. 5. Langmuir adsorption isotherm for the biosorption of Cd(II) ions using coffee powder

b. Freundlich model using coffee powder as biosorbent

The sorption experiments were carried out at optimum conditions using coffee powder as biosorbent to determine the real heterogeneous nature of the surface sites involved in the Cd(II) ion uptake (Figure 6).

Fig. 6. Freundlich adsorption isotherm for the biosorption of Cd(II) ions using coffee powder

DISCUSSION:

The adsorption kinetics highlighted an ion-exchange mechanism responsible for the metal uptake. The extent of this mechanism depends on the nature of the metal ion. The overall metal adsorption efficiency depends on the total number of surface functional groups available in the biosorbents. The biosorption of Cd(II) ions from aqueous solution might be about 90% byion-exchange mechanism and 10% by complexation.

The present study shows that that adsorption ofCd(II) ions relied on the contact time, initial ionic concentration, biosorbent dose and pH of the solution^5,6. The maximum adsorption of Cd(II) ions occurred at 70°C⁷.Adsorption of Cd(II) ions from aqueous solution attained maximum value at a pHof 3.5 and then decreased. The solution pH affects the surface charge of the biosorbent, the degree of ionization and the speciation of the surface functional groups^6-9.

In the present analysis, it was seen that the adsorption of Cd(II) ions increased with increase of biosorbent dose and remained almost constant for further increase of dosage. Maximum adsorption occurred with 2 g of the biosorbent.Maximum adsorption occurred with an initial ionic concentration of 30 mg/L.Adsorption increases with increase of contact time. Rapid uptake of Cd(II) ions was observed during the initial stage of contact. Maximum removal was observed within the first 50 minutes when coffee powder was used as biosorbent. Equilibrium time for adsorption was about 60 minutes^8,10,11. In the present work, the sorption efficiency and the rate of sorption of Cd(II) ions on coffee powder was 99.5%^8,10-12.

In the present work, coffee powder had a large adsorptive capability for removingCd(II) ions from aqueous solution. The value obtained for adsorption capacity (Q_o) fromLangmuir adsorption isotherm model was 0.0591 mg/L for Cd(II) ions, when coffee powder was used as biosorbent^6,13. The value obtained for ‘b’ (Langmuir isotherm constant) was0.0202 L/mg and the value obtained for ‘R_L’ (the separation factor) was 0.6226.The Langmuir plots showed good agreement with the experimental data and suggests that the Cd(II) ions formed a monolayer coverage on the adsorbent surface. The values obtained for Q_o, b and R_L indicates that the sorption process was favourable^6,7,14.

In Freundlich model the value obtained for nwas 11.4678for Cd(II) ions on coffee powder.The value of 1/n was below 1 which showed that the adsorption process was favourable. From this it can be concluded that coffee powder takes up Cd(II) ions from aqueous solution onto a heterogeneous surface by multilayer adsorption^6,7. In the present work, the application of the Langmuir model seemed to be more appropriate than that of Freundlichmodel^9,15.

CONCLUSION:

In this study, batch adsorption experiments were performed to evaluate the use of coffee powder as biosorbent for Cd(II) ions. It was found that Cd(II) ions required a contact time of 50 minutes and an equilibrium time of 60 minutes. It was found that pHof the solution had a significant impact on the percentage removal of Cd(II) ions. At a pHof 3.5, the percent removal was99.5 % for Cd(II) ions. The adsorption isotherm studies reveal that the adsorptive behaviour of Cd(II) ions on coffee powder satisfies both the Langmuir and Freundlich assumptions. The results of this study prove that coffee powder serve as an effective adsorbentfor the removal of Cd(II) ions frompolluted water.

REFERENCES:

1. Gupta VK. Gupta M. and Sharma S. Process development for the removal of lead and chromium from aqueous solution using red mud- an aluminium industry waste. Wat. Res. 2001; 35(5): 1125-1134.

2. Kadirvelu K. Preparation and characterization of coir pith carbon and its utilisation in the treatment of metal-bearing waste waters. Ph.D. Thesis, Bharathiar University, Coimbatore, India. 2000.

3. Omer Y. Yalcin A. and Fuat G. Removal of copper, nickel, cobalt and manganese from aqueous solution by kaolinite. Wat. Res. 2003; 37(4): 948-952.

4. Rengaraj S. Kim Y. Joo, CK. and Yi J. Removal of copper from aqueous solution by aminated and protonated meso porous aluminas: kinetics and equilibrium. J. Colloid Interf. Sci. 2004; 73: 14-21.

5. Ajmal M. Rao RAK. Anwar S. Ahmad J. and Ahmad R. Adsorption studies on rice husk: removal and recovery of Cd(II) from waste water. Bioresour. Technol. 2003; 86(2): 147-149.

6. Taha A. Waly, Dakroury, A.M., El-Sayed, G.O. and El-Salam, S.A. (2010) Assessment on the removal of heavy metals ions from waste water by cement kiln dust (CKD). J. Am. Sci., 6(12), pp. 910-917. ISSN: 1545-1003.

7. Mohan, D. and Singh KP. Single and multi-component adsorption of cadmium and zinc using activated carbon derived from bagasse-an agricultural waste. Wat. Res. 2002; 36(9): 2304-2318.

8. Subramaniam P. Khan NA. and Ibrahim S. Rice-husk as an adsorbent for heavy metal. Proceedings of International Conference on water and waste water, (ASIAWATER 2004), Kuala Lumpur, Malaysia. 2004.

9. Heechan Cho, Dalyoung Oh and Kwanho Kim. A study on removal characteristics of heavy metals from aqueous solution by fly ash. J. Hazard. Mater. 2005; 127(1-3): pp. 187-195.

10. Guo Y. Qi S. Yang S. Yu K. Wang Z and Xu H. Adsorption of Cr(VI) on micro- and meso-porous rice husk-based active carbon. Mat. Chem. Physics. 2002; 78: 132-137.

11. Dalia Virbalyte, VidasPakotas, Remigijus Juokenas and Albinas Pigaga. Interaction of heavy metal ions with cement kiln dust. EKOLOGIJA. 2005: 1: 31-36.

12. Daifullah AAM. Girgis BS. and Gad HMH. Utilization of agro residues (rice husk) in small waste water treatment plants. Materials Letters, 2003; 57: 1723-1731.

13. Marshall WE. and Champagne ET. Agricultural by-product as adsorbents for metal ions in laboratory prepared solutions and in manufacturing waste water. J. Environ. Sci. Hlth A. 1995; 30(2): 241-261.

14. McKay G. Blair HS. and Gardener JR. Adsorption of dyes on chitin, equilibrium studies. J. Appl. Polym. Sci. 1982; 27; 3043-3057.

15. Ye H. Zhu Q. and Du D. Adsorptive removal of Cd(II) from aqueous solution using natural and modified rice husk. Bioresour. Technol., 2010; 101(14): 5175-5179.

Received on 21.11.2017 Modified on 28.12.2017

Asian J. Research Chem. 2018; 11(2):360-364.

DOI:10.5958/0974-4150.2018.00065.2